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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent.locks; |
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|
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import java.util.concurrent.TimeUnit; |
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import java.util.ArrayList; |
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import java.util.Collection; |
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import java.util.Date; |
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import sun.misc.Unsafe; |
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|
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/** |
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* A version of {@link AbstractQueuedSynchronizer} in |
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* which synchronization state is maintained as a {@code long}. |
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* This class has exactly the same structure, properties, and methods |
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* as {@code AbstractQueuedSynchronizer} with the exception |
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* that all state-related parameters and results are defined |
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* as {@code long} rather than {@code int}. This class |
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* may be useful when creating synchronizers such as |
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* multilevel locks and barriers that require |
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* 64 bits of state. |
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* |
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* <p>See {@link AbstractQueuedSynchronizer} for usage |
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* notes and examples. |
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* |
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* @since 1.6 |
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* @author Doug Lea |
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*/ |
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public abstract class AbstractQueuedLongSynchronizer |
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extends AbstractOwnableSynchronizer |
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implements java.io.Serializable { |
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|
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private static final long serialVersionUID = 7373984972572414692L; |
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|
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/* |
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To keep sources in sync, the remainder of this source file is |
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exactly cloned from AbstractQueuedSynchronizer, replacing class |
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name and changing ints related with sync state to longs. Please |
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keep it that way. |
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*/ |
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|
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/** |
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* Creates a new {@code AbstractQueuedLongSynchronizer} instance |
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* with initial synchronization state of zero. |
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*/ |
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protected AbstractQueuedLongSynchronizer() { } |
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|
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/** |
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* Wait queue node class. |
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* |
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* <p>The wait queue is a variant of a "CLH" (Craig, Landin, and |
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* Hagersten) lock queue. CLH locks are normally used for |
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* spinlocks. We instead use them for blocking synchronizers, but |
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* use the same basic tactic of holding some of the control |
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* information about a thread in the predecessor of its node. A |
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* "status" field in each node keeps track of whether a thread |
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* should block. A node is signalled when its predecessor |
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* releases. Each node of the queue otherwise serves as a |
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* specific-notification-style monitor holding a single waiting |
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* thread. The status field does NOT control whether threads are |
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* granted locks etc though. A thread may try to acquire if it is |
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* first in the queue. But being first does not guarantee success; |
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* it only gives the right to contend. So the currently released |
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* contender thread may need to rewait. |
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* |
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* <p>To enqueue into a CLH lock, you atomically splice it in as new |
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* tail. To dequeue, you just set the head field. |
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* <pre> |
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* +------+ prev +-----+ +-----+ |
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* head | | <---- | | <---- | | tail |
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* +------+ +-----+ +-----+ |
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* </pre> |
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* |
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* <p>Insertion into a CLH queue requires only a single atomic |
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* operation on "tail", so there is a simple atomic point of |
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* demarcation from unqueued to queued. Similarly, dequeuing |
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* involves only updating the "head". However, it takes a bit |
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* more work for nodes to determine who their successors are, |
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* in part to deal with possible cancellation due to timeouts |
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* and interrupts. |
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* |
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* <p>The "prev" links (not used in original CLH locks), are mainly |
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* needed to handle cancellation. If a node is cancelled, its |
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* successor is (normally) relinked to a non-cancelled |
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* predecessor. For explanation of similar mechanics in the case |
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* of spin locks, see the papers by Scott and Scherer at |
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* http://www.cs.rochester.edu/u/scott/synchronization/ |
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* |
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* <p>We also use "next" links to implement blocking mechanics. |
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* The thread id for each node is kept in its own node, so a |
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* predecessor signals the next node to wake up by traversing |
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* next link to determine which thread it is. Determination of |
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* successor must avoid races with newly queued nodes to set |
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* the "next" fields of their predecessors. This is solved |
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* when necessary by checking backwards from the atomically |
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* updated "tail" when a node's successor appears to be null. |
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* (Or, said differently, the next-links are an optimization |
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* so that we don't usually need a backward scan.) |
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* |
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* <p>Cancellation introduces some conservatism to the basic |
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* algorithms. Since we must poll for cancellation of other |
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* nodes, we can miss noticing whether a cancelled node is |
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* ahead or behind us. This is dealt with by always unparking |
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* successors upon cancellation, allowing them to stabilize on |
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* a new predecessor, unless we can identify an uncancelled |
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* predecessor who will carry this responsibility. |
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* |
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* <p>CLH queues need a dummy header node to get started. But |
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* we don't create them on construction, because it would be wasted |
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* effort if there is never contention. Instead, the node |
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* is constructed and head and tail pointers are set upon first |
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* contention. |
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* |
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* <p>Threads waiting on Conditions use the same nodes, but |
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* use an additional link. Conditions only need to link nodes |
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* in simple (non-concurrent) linked queues because they are |
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* only accessed when exclusively held. Upon await, a node is |
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* inserted into a condition queue. Upon signal, the node is |
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* transferred to the main queue. A special value of status |
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* field is used to mark which queue a node is on. |
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* |
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* <p>Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill |
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* Scherer and Michael Scott, along with members of JSR-166 |
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* expert group, for helpful ideas, discussions, and critiques |
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* on the design of this class. |
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*/ |
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static final class Node { |
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/** Marker to indicate a node is waiting in shared mode */ |
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static final Node SHARED = new Node(); |
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/** Marker to indicate a node is waiting in exclusive mode */ |
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static final Node EXCLUSIVE = null; |
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|
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/** waitStatus value to indicate thread has cancelled */ |
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static final int CANCELLED = 1; |
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/** waitStatus value to indicate successor's thread needs unparking */ |
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static final int SIGNAL = -1; |
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/** waitStatus value to indicate thread is waiting on condition */ |
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static final int CONDITION = -2; |
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/** |
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* waitStatus value to indicate the next acquireShared should |
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* unconditionally propagate |
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*/ |
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static final int PROPAGATE = -3; |
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|
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/** |
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* Status field, taking on only the values: |
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* SIGNAL: The successor of this node is (or will soon be) |
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* blocked (via park), so the current node must |
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* unpark its successor when it releases or |
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* cancels. To avoid races, acquire methods must |
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* first indicate they need a signal, |
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* then retry the atomic acquire, and then, |
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* on failure, block. |
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* CANCELLED: This node is cancelled due to timeout or interrupt. |
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* Nodes never leave this state. In particular, |
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* a thread with cancelled node never again blocks. |
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* CONDITION: This node is currently on a condition queue. |
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* It will not be used as a sync queue node |
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* until transferred, at which time the status |
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* will be set to 0. (Use of this value here has |
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* nothing to do with the other uses of the |
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* field, but simplifies mechanics.) |
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* PROPAGATE: A releaseShared should be propagated to other |
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* nodes. This is set (for head node only) in |
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* doReleaseShared to ensure propagation |
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* continues, even if other operations have |
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* since intervened. |
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* 0: None of the above |
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* |
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* The values are arranged numerically to simplify use. |
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* Non-negative values mean that a node doesn't need to |
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* signal. So, most code doesn't need to check for particular |
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* values, just for sign. |
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* |
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* The field is initialized to 0 for normal sync nodes, and |
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* CONDITION for condition nodes. It is modified using CAS |
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* (or when possible, unconditional volatile writes). |
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*/ |
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volatile int waitStatus; |
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|
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/** |
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* Link to predecessor node that current node/thread relies on |
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* for checking waitStatus. Assigned during enqueuing, and nulled |
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* out (for sake of GC) only upon dequeuing. Also, upon |
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* cancellation of a predecessor, we short-circuit while |
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* finding a non-cancelled one, which will always exist |
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* because the head node is never cancelled: A node becomes |
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* head only as a result of successful acquire. A |
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* cancelled thread never succeeds in acquiring, and a thread only |
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* cancels itself, not any other node. |
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*/ |
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volatile Node prev; |
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|
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/** |
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* Link to the successor node that the current node/thread |
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* unparks upon release. Assigned during enqueuing, adjusted |
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* when bypassing cancelled predecessors, and nulled out (for |
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* sake of GC) when dequeued. The enq operation does not |
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* assign next field of a predecessor until after attachment, |
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* so seeing a null next field does not necessarily mean that |
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* node is at end of queue. However, if a next field appears |
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* to be null, we can scan prev's from the tail to |
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* double-check. The next field of cancelled nodes is set to |
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* point to the node itself instead of null, to make life |
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* easier for isOnSyncQueue. |
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*/ |
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volatile Node next; |
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|
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/** |
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* The thread that enqueued this node. Initialized on |
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* construction and nulled out after use. |
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*/ |
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volatile Thread thread; |
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|
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/** |
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* Link to next node waiting on condition, or the special |
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* value SHARED. Because condition queues are accessed only |
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* when holding in exclusive mode, we just need a simple |
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* linked queue to hold nodes while they are waiting on |
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* conditions. They are then transferred to the queue to |
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* re-acquire. And because conditions can only be exclusive, |
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* we save a field by using special value to indicate shared |
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* mode. |
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*/ |
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Node nextWaiter; |
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|
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/** |
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* Returns true if node is waiting in shared mode. |
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*/ |
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final boolean isShared() { |
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return nextWaiter == SHARED; |
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} |
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|
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/** |
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* Returns previous node, or throws NullPointerException if null. |
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* Use when predecessor cannot be null. The null check could |
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* be elided, but is present to help the VM. |
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* |
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* @return the predecessor of this node |
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*/ |
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final Node predecessor() throws NullPointerException { |
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Node p = prev; |
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if (p == null) |
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throw new NullPointerException(); |
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else |
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return p; |
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} |
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|
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Node() { // Used to establish initial head or SHARED marker |
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} |
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|
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Node(Thread thread, Node mode) { // Used by addWaiter |
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this.nextWaiter = mode; |
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this.thread = thread; |
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} |
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|
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Node(Thread thread, int waitStatus) { // Used by Condition |
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this.waitStatus = waitStatus; |
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this.thread = thread; |
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} |
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} |
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|
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/** |
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* Head of the wait queue, lazily initialized. Except for |
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* initialization, it is modified only via method setHead. Note: |
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* If head exists, its waitStatus is guaranteed not to be |
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* CANCELLED. |
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*/ |
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private transient volatile Node head; |
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|
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/** |
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* Tail of the wait queue, lazily initialized. Modified only via |
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* method enq to add new wait node. |
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*/ |
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private transient volatile Node tail; |
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|
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/** |
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* The synchronization state. |
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*/ |
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private volatile long state; |
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|
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/** |
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* Returns the current value of synchronization state. |
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* This operation has memory semantics of a {@code volatile} read. |
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* @return current state value |
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*/ |
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protected final long getState() { |
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return state; |
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} |
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|
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/** |
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* Sets the value of synchronization state. |
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* This operation has memory semantics of a {@code volatile} write. |
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* @param newState the new state value |
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*/ |
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protected final void setState(long newState) { |
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state = newState; |
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} |
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|
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/** |
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* Atomically sets synchronization state to the given updated |
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* value if the current state value equals the expected value. |
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* This operation has memory semantics of a {@code volatile} read |
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* and write. |
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* |
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* @param expect the expected value |
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* @param update the new value |
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* @return true if successful. False return indicates that the actual |
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* value was not equal to the expected value. |
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*/ |
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protected final boolean compareAndSetState(long expect, long update) { |
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// See below for intrinsics setup to support this |
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return unsafe.compareAndSwapLong(this, stateOffset, expect, update); |
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} |
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|
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// Queuing utilities |
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|
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/** |
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* The number of nanoseconds for which it is faster to spin |
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* rather than to use timed park. A rough estimate suffices |
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* to improve responsiveness with very short timeouts. |
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*/ |
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static final long spinForTimeoutThreshold = 1000L; |
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|
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/** |
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* Inserts node into queue, initializing if necessary. See picture above. |
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* @param node the node to insert |
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* @return node's predecessor |
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*/ |
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private Node enq(final Node node) { |
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for (;;) { |
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Node t = tail; |
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if (t == null) { // Must initialize |
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if (compareAndSetHead(new Node())) |
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tail = head; |
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} else { |
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node.prev = t; |
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if (compareAndSetTail(t, node)) { |
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t.next = node; |
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return t; |
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} |
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} |
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} |
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} |
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|
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/** |
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* Creates and enqueues node for current thread and given mode. |
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* |
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* @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared |
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* @return the new node |
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*/ |
355 |
private Node addWaiter(Node mode) { |
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Node node = new Node(Thread.currentThread(), mode); |
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// Try the fast path of enq; backup to full enq on failure |
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Node pred = tail; |
359 |
if (pred != null) { |
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node.prev = pred; |
361 |
if (compareAndSetTail(pred, node)) { |
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pred.next = node; |
363 |
return node; |
364 |
} |
365 |
} |
366 |
enq(node); |
367 |
return node; |
368 |
} |
369 |
|
370 |
/** |
371 |
* Sets head of queue to be node, thus dequeuing. Called only by |
372 |
* acquire methods. Also nulls out unused fields for sake of GC |
373 |
* and to suppress unnecessary signals and traversals. |
374 |
* |
375 |
* @param node the node |
376 |
*/ |
377 |
private void setHead(Node node) { |
378 |
head = node; |
379 |
node.thread = null; |
380 |
node.prev = null; |
381 |
} |
382 |
|
383 |
/** |
384 |
* Wakes up node's successor, if one exists. |
385 |
* |
386 |
* @param node the node |
387 |
*/ |
388 |
private void unparkSuccessor(Node node) { |
389 |
/* |
390 |
* If status is negative (i.e., possibly needing signal) try |
391 |
* to clear in anticipation of signalling. It is OK if this |
392 |
* fails or if status is changed by waiting thread. |
393 |
*/ |
394 |
int ws = node.waitStatus; |
395 |
if (ws < 0) |
396 |
compareAndSetWaitStatus(node, ws, 0); |
397 |
|
398 |
/* |
399 |
* Thread to unpark is held in successor, which is normally |
400 |
* just the next node. But if cancelled or apparently null, |
401 |
* traverse backwards from tail to find the actual |
402 |
* non-cancelled successor. |
403 |
*/ |
404 |
Node s = node.next; |
405 |
if (s == null || s.waitStatus > 0) { |
406 |
s = null; |
407 |
for (Node p = tail; p != null && p != node; p = p.prev) |
408 |
if (p.waitStatus <= 0) |
409 |
s = p; |
410 |
} |
411 |
if (s != null) |
412 |
LockSupport.unpark(s.thread); |
413 |
} |
414 |
|
415 |
/** |
416 |
* Release action for shared mode -- signals successor and ensures |
417 |
* propagation. (Note: For exclusive mode, release just amounts |
418 |
* to calling unparkSuccessor of head if it needs signal.) |
419 |
*/ |
420 |
private void doReleaseShared() { |
421 |
/* |
422 |
* Ensure that a release propagates, even if there are other |
423 |
* in-progress acquires/releases. This proceeds in the usual |
424 |
* way of trying to unparkSuccessor of head if it needs |
425 |
* signal. But if it does not, status is set to PROPAGATE to |
426 |
* ensure that upon release, propagation continues. |
427 |
* Additionally, we must loop in case a new node is added |
428 |
* while we are doing this. Also, unlike other uses of |
429 |
* unparkSuccessor, we need to know if CAS to reset status |
430 |
* fails, if so rechecking. |
431 |
*/ |
432 |
for (;;) { |
433 |
Node h = head; |
434 |
if (h != null && h != tail) { |
435 |
int ws = h.waitStatus; |
436 |
if (ws == Node.SIGNAL) { |
437 |
if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0)) |
438 |
continue; // loop to recheck cases |
439 |
unparkSuccessor(h); |
440 |
} |
441 |
else if (ws == 0 && |
442 |
!compareAndSetWaitStatus(h, 0, Node.PROPAGATE)) |
443 |
continue; // loop on failed CAS |
444 |
} |
445 |
if (h == head) // loop if head changed |
446 |
break; |
447 |
} |
448 |
} |
449 |
|
450 |
/** |
451 |
* Sets head of queue, and checks if successor may be waiting |
452 |
* in shared mode, if so propagating if either propagate > 0 or |
453 |
* PROPAGATE status was set. |
454 |
* |
455 |
* @param node the node |
456 |
* @param propagate the return value from a tryAcquireShared |
457 |
*/ |
458 |
private void setHeadAndPropagate(Node node, long propagate) { |
459 |
Node h = head; // Record old head for check below |
460 |
setHead(node); |
461 |
/* |
462 |
* Try to signal next queued node if: |
463 |
* Propagation was indicated by caller, |
464 |
* or was recorded (as h.waitStatus) by a previous operation |
465 |
* (note: this uses sign-check of waitStatus because |
466 |
* PROPAGATE status may transition to SIGNAL.) |
467 |
* and |
468 |
* The next node is waiting in shared mode, |
469 |
* or we don't know, because it appears null |
470 |
* |
471 |
* The conservatism in both of these checks may cause |
472 |
* unnecessary wake-ups, but only when there are multiple |
473 |
* racing acquires/releases, so most need signals now or soon |
474 |
* anyway. |
475 |
*/ |
476 |
if (propagate > 0 || h == null || h.waitStatus < 0) { |
477 |
Node s = node.next; |
478 |
if (s == null || s.isShared()) |
479 |
doReleaseShared(); |
480 |
} |
481 |
} |
482 |
|
483 |
// Utilities for various versions of acquire |
484 |
|
485 |
/** |
486 |
* Cancels an ongoing attempt to acquire. |
487 |
* |
488 |
* @param node the node |
489 |
*/ |
490 |
private void cancelAcquire(Node node) { |
491 |
// Ignore if node doesn't exist |
492 |
if (node == null) |
493 |
return; |
494 |
|
495 |
node.thread = null; |
496 |
|
497 |
// Skip cancelled predecessors |
498 |
Node pred = node.prev; |
499 |
while (pred.waitStatus > 0) |
500 |
node.prev = pred = pred.prev; |
501 |
|
502 |
// predNext is the apparent node to unsplice. CASes below will |
503 |
// fail if not, in which case, we lost race vs another cancel |
504 |
// or signal, so no further action is necessary. |
505 |
Node predNext = pred.next; |
506 |
|
507 |
// Can use unconditional write instead of CAS here. |
508 |
// After this atomic step, other Nodes can skip past us. |
509 |
// Before, we are free of interference from other threads. |
510 |
node.waitStatus = Node.CANCELLED; |
511 |
|
512 |
// If we are the tail, remove ourselves. |
513 |
if (node == tail && compareAndSetTail(node, pred)) { |
514 |
compareAndSetNext(pred, predNext, null); |
515 |
} else { |
516 |
// If successor needs signal, try to set pred's next-link |
517 |
// so it will get one. Otherwise wake it up to propagate. |
518 |
int ws; |
519 |
if (pred != head && |
520 |
((ws = pred.waitStatus) == Node.SIGNAL || |
521 |
(ws <= 0 && compareAndSetWaitStatus(pred, ws, Node.SIGNAL))) && |
522 |
pred.thread != null) { |
523 |
Node next = node.next; |
524 |
if (next != null && next.waitStatus <= 0) |
525 |
compareAndSetNext(pred, predNext, next); |
526 |
} else { |
527 |
unparkSuccessor(node); |
528 |
} |
529 |
|
530 |
node.next = node; // help GC |
531 |
} |
532 |
} |
533 |
|
534 |
/** |
535 |
* Checks and updates status for a node that failed to acquire. |
536 |
* Returns true if thread should block. This is the main signal |
537 |
* control in all acquire loops. Requires that pred == node.prev. |
538 |
* |
539 |
* @param pred node's predecessor holding status |
540 |
* @param node the node |
541 |
* @return {@code true} if thread should block |
542 |
*/ |
543 |
private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) { |
544 |
int ws = pred.waitStatus; |
545 |
if (ws == Node.SIGNAL) |
546 |
/* |
547 |
* This node has already set status asking a release |
548 |
* to signal it, so it can safely park. |
549 |
*/ |
550 |
return true; |
551 |
if (ws > 0) { |
552 |
/* |
553 |
* Predecessor was cancelled. Skip over predecessors and |
554 |
* indicate retry. |
555 |
*/ |
556 |
do { |
557 |
node.prev = pred = pred.prev; |
558 |
} while (pred.waitStatus > 0); |
559 |
pred.next = node; |
560 |
} else { |
561 |
/* |
562 |
* waitStatus must be 0 or PROPAGATE. Indicate that we |
563 |
* need a signal, but don't park yet. Caller will need to |
564 |
* retry to make sure it cannot acquire before parking. |
565 |
*/ |
566 |
compareAndSetWaitStatus(pred, ws, Node.SIGNAL); |
567 |
} |
568 |
return false; |
569 |
} |
570 |
|
571 |
/** |
572 |
* Convenience method to interrupt current thread. |
573 |
*/ |
574 |
static void selfInterrupt() { |
575 |
Thread.currentThread().interrupt(); |
576 |
} |
577 |
|
578 |
/** |
579 |
* Convenience method to park and then check if interrupted |
580 |
* |
581 |
* @return {@code true} if interrupted |
582 |
*/ |
583 |
private final boolean parkAndCheckInterrupt() { |
584 |
LockSupport.park(this); |
585 |
return Thread.interrupted(); |
586 |
} |
587 |
|
588 |
/* |
589 |
* Various flavors of acquire, varying in exclusive/shared and |
590 |
* control modes. Each is mostly the same, but annoyingly |
591 |
* different. Only a little bit of factoring is possible due to |
592 |
* interactions of exception mechanics (including ensuring that we |
593 |
* cancel if tryAcquire throws exception) and other control, at |
594 |
* least not without hurting performance too much. |
595 |
*/ |
596 |
|
597 |
/** |
598 |
* Acquires in exclusive uninterruptible mode for thread already in |
599 |
* queue. Used by condition wait methods as well as acquire. |
600 |
* |
601 |
* @param node the node |
602 |
* @param arg the acquire argument |
603 |
* @return {@code true} if interrupted while waiting |
604 |
*/ |
605 |
final boolean acquireQueued(final Node node, long arg) { |
606 |
boolean failed = true; |
607 |
try { |
608 |
boolean interrupted = false; |
609 |
for (;;) { |
610 |
final Node p = node.predecessor(); |
611 |
if (p == head && tryAcquire(arg)) { |
612 |
setHead(node); |
613 |
p.next = null; // help GC |
614 |
failed = false; |
615 |
return interrupted; |
616 |
} |
617 |
if (shouldParkAfterFailedAcquire(p, node) && |
618 |
parkAndCheckInterrupt()) |
619 |
interrupted = true; |
620 |
} |
621 |
} finally { |
622 |
if (failed) |
623 |
cancelAcquire(node); |
624 |
} |
625 |
} |
626 |
|
627 |
/** |
628 |
* Acquires in exclusive interruptible mode. |
629 |
* @param arg the acquire argument |
630 |
*/ |
631 |
private void doAcquireInterruptibly(long arg) |
632 |
throws InterruptedException { |
633 |
final Node node = addWaiter(Node.EXCLUSIVE); |
634 |
boolean failed = true; |
635 |
try { |
636 |
for (;;) { |
637 |
final Node p = node.predecessor(); |
638 |
if (p == head && tryAcquire(arg)) { |
639 |
setHead(node); |
640 |
p.next = null; // help GC |
641 |
failed = false; |
642 |
return; |
643 |
} |
644 |
if (shouldParkAfterFailedAcquire(p, node) && |
645 |
parkAndCheckInterrupt()) |
646 |
throw new InterruptedException(); |
647 |
} |
648 |
} finally { |
649 |
if (failed) |
650 |
cancelAcquire(node); |
651 |
} |
652 |
} |
653 |
|
654 |
/** |
655 |
* Acquires in exclusive timed mode. |
656 |
* |
657 |
* @param arg the acquire argument |
658 |
* @param nanosTimeout max wait time |
659 |
* @return {@code true} if acquired |
660 |
*/ |
661 |
private boolean doAcquireNanos(long arg, long nanosTimeout) |
662 |
throws InterruptedException { |
663 |
if (nanosTimeout <= 0L) |
664 |
return false; |
665 |
final long deadline = System.nanoTime() + nanosTimeout; |
666 |
final Node node = addWaiter(Node.EXCLUSIVE); |
667 |
boolean failed = true; |
668 |
try { |
669 |
for (;;) { |
670 |
final Node p = node.predecessor(); |
671 |
if (p == head && tryAcquire(arg)) { |
672 |
setHead(node); |
673 |
p.next = null; // help GC |
674 |
failed = false; |
675 |
return true; |
676 |
} |
677 |
nanosTimeout = deadline - System.nanoTime(); |
678 |
if (nanosTimeout <= 0L) |
679 |
return false; |
680 |
if (shouldParkAfterFailedAcquire(p, node) && |
681 |
nanosTimeout > spinForTimeoutThreshold) |
682 |
LockSupport.parkNanos(this, nanosTimeout); |
683 |
if (Thread.interrupted()) |
684 |
throw new InterruptedException(); |
685 |
} |
686 |
} finally { |
687 |
if (failed) |
688 |
cancelAcquire(node); |
689 |
} |
690 |
} |
691 |
|
692 |
/** |
693 |
* Acquires in shared uninterruptible mode. |
694 |
* @param arg the acquire argument |
695 |
*/ |
696 |
private void doAcquireShared(long arg) { |
697 |
final Node node = addWaiter(Node.SHARED); |
698 |
boolean failed = true; |
699 |
try { |
700 |
boolean interrupted = false; |
701 |
for (;;) { |
702 |
final Node p = node.predecessor(); |
703 |
if (p == head) { |
704 |
long r = tryAcquireShared(arg); |
705 |
if (r >= 0) { |
706 |
setHeadAndPropagate(node, r); |
707 |
p.next = null; // help GC |
708 |
if (interrupted) |
709 |
selfInterrupt(); |
710 |
failed = false; |
711 |
return; |
712 |
} |
713 |
} |
714 |
if (shouldParkAfterFailedAcquire(p, node) && |
715 |
parkAndCheckInterrupt()) |
716 |
interrupted = true; |
717 |
} |
718 |
} finally { |
719 |
if (failed) |
720 |
cancelAcquire(node); |
721 |
} |
722 |
} |
723 |
|
724 |
/** |
725 |
* Acquires in shared interruptible mode. |
726 |
* @param arg the acquire argument |
727 |
*/ |
728 |
private void doAcquireSharedInterruptibly(long arg) |
729 |
throws InterruptedException { |
730 |
final Node node = addWaiter(Node.SHARED); |
731 |
boolean failed = true; |
732 |
try { |
733 |
for (;;) { |
734 |
final Node p = node.predecessor(); |
735 |
if (p == head) { |
736 |
long r = tryAcquireShared(arg); |
737 |
if (r >= 0) { |
738 |
setHeadAndPropagate(node, r); |
739 |
p.next = null; // help GC |
740 |
failed = false; |
741 |
return; |
742 |
} |
743 |
} |
744 |
if (shouldParkAfterFailedAcquire(p, node) && |
745 |
parkAndCheckInterrupt()) |
746 |
throw new InterruptedException(); |
747 |
} |
748 |
} finally { |
749 |
if (failed) |
750 |
cancelAcquire(node); |
751 |
} |
752 |
} |
753 |
|
754 |
/** |
755 |
* Acquires in shared timed mode. |
756 |
* |
757 |
* @param arg the acquire argument |
758 |
* @param nanosTimeout max wait time |
759 |
* @return {@code true} if acquired |
760 |
*/ |
761 |
private boolean doAcquireSharedNanos(long arg, long nanosTimeout) |
762 |
throws InterruptedException { |
763 |
if (nanosTimeout <= 0L) |
764 |
return false; |
765 |
final long deadline = System.nanoTime() + nanosTimeout; |
766 |
final Node node = addWaiter(Node.SHARED); |
767 |
boolean failed = true; |
768 |
try { |
769 |
for (;;) { |
770 |
final Node p = node.predecessor(); |
771 |
if (p == head) { |
772 |
long r = tryAcquireShared(arg); |
773 |
if (r >= 0) { |
774 |
setHeadAndPropagate(node, r); |
775 |
p.next = null; // help GC |
776 |
failed = false; |
777 |
return true; |
778 |
} |
779 |
} |
780 |
nanosTimeout = deadline - System.nanoTime(); |
781 |
if (nanosTimeout <= 0L) |
782 |
return false; |
783 |
if (shouldParkAfterFailedAcquire(p, node) && |
784 |
nanosTimeout > spinForTimeoutThreshold) |
785 |
LockSupport.parkNanos(this, nanosTimeout); |
786 |
if (Thread.interrupted()) |
787 |
throw new InterruptedException(); |
788 |
} |
789 |
} finally { |
790 |
if (failed) |
791 |
cancelAcquire(node); |
792 |
} |
793 |
} |
794 |
|
795 |
// Main exported methods |
796 |
|
797 |
/** |
798 |
* Attempts to acquire in exclusive mode. This method should query |
799 |
* if the state of the object permits it to be acquired in the |
800 |
* exclusive mode, and if so to acquire it. |
801 |
* |
802 |
* <p>This method is always invoked by the thread performing |
803 |
* acquire. If this method reports failure, the acquire method |
804 |
* may queue the thread, if it is not already queued, until it is |
805 |
* signalled by a release from some other thread. This can be used |
806 |
* to implement method {@link Lock#tryLock()}. |
807 |
* |
808 |
* <p>The default |
809 |
* implementation throws {@link UnsupportedOperationException}. |
810 |
* |
811 |
* @param arg the acquire argument. This value is always the one |
812 |
* passed to an acquire method, or is the value saved on entry |
813 |
* to a condition wait. The value is otherwise uninterpreted |
814 |
* and can represent anything you like. |
815 |
* @return {@code true} if successful. Upon success, this object has |
816 |
* been acquired. |
817 |
* @throws IllegalMonitorStateException if acquiring would place this |
818 |
* synchronizer in an illegal state. This exception must be |
819 |
* thrown in a consistent fashion for synchronization to work |
820 |
* correctly. |
821 |
* @throws UnsupportedOperationException if exclusive mode is not supported |
822 |
*/ |
823 |
protected boolean tryAcquire(long arg) { |
824 |
throw new UnsupportedOperationException(); |
825 |
} |
826 |
|
827 |
/** |
828 |
* Attempts to set the state to reflect a release in exclusive |
829 |
* mode. |
830 |
* |
831 |
* <p>This method is always invoked by the thread performing release. |
832 |
* |
833 |
* <p>The default implementation throws |
834 |
* {@link UnsupportedOperationException}. |
835 |
* |
836 |
* @param arg the release argument. This value is always the one |
837 |
* passed to a release method, or the current state value upon |
838 |
* entry to a condition wait. The value is otherwise |
839 |
* uninterpreted and can represent anything you like. |
840 |
* @return {@code true} if this object is now in a fully released |
841 |
* state, so that any waiting threads may attempt to acquire; |
842 |
* and {@code false} otherwise. |
843 |
* @throws IllegalMonitorStateException if releasing would place this |
844 |
* synchronizer in an illegal state. This exception must be |
845 |
* thrown in a consistent fashion for synchronization to work |
846 |
* correctly. |
847 |
* @throws UnsupportedOperationException if exclusive mode is not supported |
848 |
*/ |
849 |
protected boolean tryRelease(long arg) { |
850 |
throw new UnsupportedOperationException(); |
851 |
} |
852 |
|
853 |
/** |
854 |
* Attempts to acquire in shared mode. This method should query if |
855 |
* the state of the object permits it to be acquired in the shared |
856 |
* mode, and if so to acquire it. |
857 |
* |
858 |
* <p>This method is always invoked by the thread performing |
859 |
* acquire. If this method reports failure, the acquire method |
860 |
* may queue the thread, if it is not already queued, until it is |
861 |
* signalled by a release from some other thread. |
862 |
* |
863 |
* <p>The default implementation throws {@link |
864 |
* UnsupportedOperationException}. |
865 |
* |
866 |
* @param arg the acquire argument. This value is always the one |
867 |
* passed to an acquire method, or is the value saved on entry |
868 |
* to a condition wait. The value is otherwise uninterpreted |
869 |
* and can represent anything you like. |
870 |
* @return a negative value on failure; zero if acquisition in shared |
871 |
* mode succeeded but no subsequent shared-mode acquire can |
872 |
* succeed; and a positive value if acquisition in shared |
873 |
* mode succeeded and subsequent shared-mode acquires might |
874 |
* also succeed, in which case a subsequent waiting thread |
875 |
* must check availability. (Support for three different |
876 |
* return values enables this method to be used in contexts |
877 |
* where acquires only sometimes act exclusively.) Upon |
878 |
* success, this object has been acquired. |
879 |
* @throws IllegalMonitorStateException if acquiring would place this |
880 |
* synchronizer in an illegal state. This exception must be |
881 |
* thrown in a consistent fashion for synchronization to work |
882 |
* correctly. |
883 |
* @throws UnsupportedOperationException if shared mode is not supported |
884 |
*/ |
885 |
protected long tryAcquireShared(long arg) { |
886 |
throw new UnsupportedOperationException(); |
887 |
} |
888 |
|
889 |
/** |
890 |
* Attempts to set the state to reflect a release in shared mode. |
891 |
* |
892 |
* <p>This method is always invoked by the thread performing release. |
893 |
* |
894 |
* <p>The default implementation throws |
895 |
* {@link UnsupportedOperationException}. |
896 |
* |
897 |
* @param arg the release argument. This value is always the one |
898 |
* passed to a release method, or the current state value upon |
899 |
* entry to a condition wait. The value is otherwise |
900 |
* uninterpreted and can represent anything you like. |
901 |
* @return {@code true} if this release of shared mode may permit a |
902 |
* waiting acquire (shared or exclusive) to succeed; and |
903 |
* {@code false} otherwise |
904 |
* @throws IllegalMonitorStateException if releasing would place this |
905 |
* synchronizer in an illegal state. This exception must be |
906 |
* thrown in a consistent fashion for synchronization to work |
907 |
* correctly. |
908 |
* @throws UnsupportedOperationException if shared mode is not supported |
909 |
*/ |
910 |
protected boolean tryReleaseShared(long arg) { |
911 |
throw new UnsupportedOperationException(); |
912 |
} |
913 |
|
914 |
/** |
915 |
* Returns {@code true} if synchronization is held exclusively with |
916 |
* respect to the current (calling) thread. This method is invoked |
917 |
* upon each call to a non-waiting {@link ConditionObject} method. |
918 |
* (Waiting methods instead invoke {@link #release}.) |
919 |
* |
920 |
* <p>The default implementation throws {@link |
921 |
* UnsupportedOperationException}. This method is invoked |
922 |
* internally only within {@link ConditionObject} methods, so need |
923 |
* not be defined if conditions are not used. |
924 |
* |
925 |
* @return {@code true} if synchronization is held exclusively; |
926 |
* {@code false} otherwise |
927 |
* @throws UnsupportedOperationException if conditions are not supported |
928 |
*/ |
929 |
protected boolean isHeldExclusively() { |
930 |
throw new UnsupportedOperationException(); |
931 |
} |
932 |
|
933 |
/** |
934 |
* Acquires in exclusive mode, ignoring interrupts. Implemented |
935 |
* by invoking at least once {@link #tryAcquire}, |
936 |
* returning on success. Otherwise the thread is queued, possibly |
937 |
* repeatedly blocking and unblocking, invoking {@link |
938 |
* #tryAcquire} until success. This method can be used |
939 |
* to implement method {@link Lock#lock}. |
940 |
* |
941 |
* @param arg the acquire argument. This value is conveyed to |
942 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
943 |
* can represent anything you like. |
944 |
*/ |
945 |
public final void acquire(long arg) { |
946 |
if (!tryAcquire(arg) && |
947 |
acquireQueued(addWaiter(Node.EXCLUSIVE), arg)) |
948 |
selfInterrupt(); |
949 |
} |
950 |
|
951 |
/** |
952 |
* Acquires in exclusive mode, aborting if interrupted. |
953 |
* Implemented by first checking interrupt status, then invoking |
954 |
* at least once {@link #tryAcquire}, returning on |
955 |
* success. Otherwise the thread is queued, possibly repeatedly |
956 |
* blocking and unblocking, invoking {@link #tryAcquire} |
957 |
* until success or the thread is interrupted. This method can be |
958 |
* used to implement method {@link Lock#lockInterruptibly}. |
959 |
* |
960 |
* @param arg the acquire argument. This value is conveyed to |
961 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
962 |
* can represent anything you like. |
963 |
* @throws InterruptedException if the current thread is interrupted |
964 |
*/ |
965 |
public final void acquireInterruptibly(long arg) |
966 |
throws InterruptedException { |
967 |
if (Thread.interrupted()) |
968 |
throw new InterruptedException(); |
969 |
if (!tryAcquire(arg)) |
970 |
doAcquireInterruptibly(arg); |
971 |
} |
972 |
|
973 |
/** |
974 |
* Attempts to acquire in exclusive mode, aborting if interrupted, |
975 |
* and failing if the given timeout elapses. Implemented by first |
976 |
* checking interrupt status, then invoking at least once {@link |
977 |
* #tryAcquire}, returning on success. Otherwise, the thread is |
978 |
* queued, possibly repeatedly blocking and unblocking, invoking |
979 |
* {@link #tryAcquire} until success or the thread is interrupted |
980 |
* or the timeout elapses. This method can be used to implement |
981 |
* method {@link Lock#tryLock(long, TimeUnit)}. |
982 |
* |
983 |
* @param arg the acquire argument. This value is conveyed to |
984 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
985 |
* can represent anything you like. |
986 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
987 |
* @return {@code true} if acquired; {@code false} if timed out |
988 |
* @throws InterruptedException if the current thread is interrupted |
989 |
*/ |
990 |
public final boolean tryAcquireNanos(long arg, long nanosTimeout) |
991 |
throws InterruptedException { |
992 |
if (Thread.interrupted()) |
993 |
throw new InterruptedException(); |
994 |
return tryAcquire(arg) || |
995 |
doAcquireNanos(arg, nanosTimeout); |
996 |
} |
997 |
|
998 |
/** |
999 |
* Releases in exclusive mode. Implemented by unblocking one or |
1000 |
* more threads if {@link #tryRelease} returns true. |
1001 |
* This method can be used to implement method {@link Lock#unlock}. |
1002 |
* |
1003 |
* @param arg the release argument. This value is conveyed to |
1004 |
* {@link #tryRelease} but is otherwise uninterpreted and |
1005 |
* can represent anything you like. |
1006 |
* @return the value returned from {@link #tryRelease} |
1007 |
*/ |
1008 |
public final boolean release(long arg) { |
1009 |
if (tryRelease(arg)) { |
1010 |
Node h = head; |
1011 |
if (h != null && h.waitStatus != 0) |
1012 |
unparkSuccessor(h); |
1013 |
return true; |
1014 |
} |
1015 |
return false; |
1016 |
} |
1017 |
|
1018 |
/** |
1019 |
* Acquires in shared mode, ignoring interrupts. Implemented by |
1020 |
* first invoking at least once {@link #tryAcquireShared}, |
1021 |
* returning on success. Otherwise the thread is queued, possibly |
1022 |
* repeatedly blocking and unblocking, invoking {@link |
1023 |
* #tryAcquireShared} until success. |
1024 |
* |
1025 |
* @param arg the acquire argument. This value is conveyed to |
1026 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
1027 |
* and can represent anything you like. |
1028 |
*/ |
1029 |
public final void acquireShared(long arg) { |
1030 |
if (tryAcquireShared(arg) < 0) |
1031 |
doAcquireShared(arg); |
1032 |
} |
1033 |
|
1034 |
/** |
1035 |
* Acquires in shared mode, aborting if interrupted. Implemented |
1036 |
* by first checking interrupt status, then invoking at least once |
1037 |
* {@link #tryAcquireShared}, returning on success. Otherwise the |
1038 |
* thread is queued, possibly repeatedly blocking and unblocking, |
1039 |
* invoking {@link #tryAcquireShared} until success or the thread |
1040 |
* is interrupted. |
1041 |
* @param arg the acquire argument. |
1042 |
* This value is conveyed to {@link #tryAcquireShared} but is |
1043 |
* otherwise uninterpreted and can represent anything |
1044 |
* you like. |
1045 |
* @throws InterruptedException if the current thread is interrupted |
1046 |
*/ |
1047 |
public final void acquireSharedInterruptibly(long arg) |
1048 |
throws InterruptedException { |
1049 |
if (Thread.interrupted()) |
1050 |
throw new InterruptedException(); |
1051 |
if (tryAcquireShared(arg) < 0) |
1052 |
doAcquireSharedInterruptibly(arg); |
1053 |
} |
1054 |
|
1055 |
/** |
1056 |
* Attempts to acquire in shared mode, aborting if interrupted, and |
1057 |
* failing if the given timeout elapses. Implemented by first |
1058 |
* checking interrupt status, then invoking at least once {@link |
1059 |
* #tryAcquireShared}, returning on success. Otherwise, the |
1060 |
* thread is queued, possibly repeatedly blocking and unblocking, |
1061 |
* invoking {@link #tryAcquireShared} until success or the thread |
1062 |
* is interrupted or the timeout elapses. |
1063 |
* |
1064 |
* @param arg the acquire argument. This value is conveyed to |
1065 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
1066 |
* and can represent anything you like. |
1067 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
1068 |
* @return {@code true} if acquired; {@code false} if timed out |
1069 |
* @throws InterruptedException if the current thread is interrupted |
1070 |
*/ |
1071 |
public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout) |
1072 |
throws InterruptedException { |
1073 |
if (Thread.interrupted()) |
1074 |
throw new InterruptedException(); |
1075 |
return tryAcquireShared(arg) >= 0 || |
1076 |
doAcquireSharedNanos(arg, nanosTimeout); |
1077 |
} |
1078 |
|
1079 |
/** |
1080 |
* Releases in shared mode. Implemented by unblocking one or more |
1081 |
* threads if {@link #tryReleaseShared} returns true. |
1082 |
* |
1083 |
* @param arg the release argument. This value is conveyed to |
1084 |
* {@link #tryReleaseShared} but is otherwise uninterpreted |
1085 |
* and can represent anything you like. |
1086 |
* @return the value returned from {@link #tryReleaseShared} |
1087 |
*/ |
1088 |
public final boolean releaseShared(long arg) { |
1089 |
if (tryReleaseShared(arg)) { |
1090 |
doReleaseShared(); |
1091 |
return true; |
1092 |
} |
1093 |
return false; |
1094 |
} |
1095 |
|
1096 |
// Queue inspection methods |
1097 |
|
1098 |
/** |
1099 |
* Queries whether any threads are waiting to acquire. Note that |
1100 |
* because cancellations due to interrupts and timeouts may occur |
1101 |
* at any time, a {@code true} return does not guarantee that any |
1102 |
* other thread will ever acquire. |
1103 |
* |
1104 |
* <p>In this implementation, this operation returns in |
1105 |
* constant time. |
1106 |
* |
1107 |
* @return {@code true} if there may be other threads waiting to acquire |
1108 |
*/ |
1109 |
public final boolean hasQueuedThreads() { |
1110 |
return head != tail; |
1111 |
} |
1112 |
|
1113 |
/** |
1114 |
* Queries whether any threads have ever contended to acquire this |
1115 |
* synchronizer; that is, if an acquire method has ever blocked. |
1116 |
* |
1117 |
* <p>In this implementation, this operation returns in |
1118 |
* constant time. |
1119 |
* |
1120 |
* @return {@code true} if there has ever been contention |
1121 |
*/ |
1122 |
public final boolean hasContended() { |
1123 |
return head != null; |
1124 |
} |
1125 |
|
1126 |
/** |
1127 |
* Returns the first (longest-waiting) thread in the queue, or |
1128 |
* {@code null} if no threads are currently queued. |
1129 |
* |
1130 |
* <p>In this implementation, this operation normally returns in |
1131 |
* constant time, but may iterate upon contention if other threads are |
1132 |
* concurrently modifying the queue. |
1133 |
* |
1134 |
* @return the first (longest-waiting) thread in the queue, or |
1135 |
* {@code null} if no threads are currently queued |
1136 |
*/ |
1137 |
public final Thread getFirstQueuedThread() { |
1138 |
// handle only fast path, else relay |
1139 |
return (head == tail) ? null : fullGetFirstQueuedThread(); |
1140 |
} |
1141 |
|
1142 |
/** |
1143 |
* Version of getFirstQueuedThread called when fastpath fails |
1144 |
*/ |
1145 |
private Thread fullGetFirstQueuedThread() { |
1146 |
/* |
1147 |
* The first node is normally head.next. Try to get its |
1148 |
* thread field, ensuring consistent reads: If thread |
1149 |
* field is nulled out or s.prev is no longer head, then |
1150 |
* some other thread(s) concurrently performed setHead in |
1151 |
* between some of our reads. We try this twice before |
1152 |
* resorting to traversal. |
1153 |
*/ |
1154 |
Node h, s; |
1155 |
Thread st; |
1156 |
if (((h = head) != null && (s = h.next) != null && |
1157 |
s.prev == head && (st = s.thread) != null) || |
1158 |
((h = head) != null && (s = h.next) != null && |
1159 |
s.prev == head && (st = s.thread) != null)) |
1160 |
return st; |
1161 |
|
1162 |
/* |
1163 |
* Head's next field might not have been set yet, or may have |
1164 |
* been unset after setHead. So we must check to see if tail |
1165 |
* is actually first node. If not, we continue on, safely |
1166 |
* traversing from tail back to head to find first, |
1167 |
* guaranteeing termination. |
1168 |
*/ |
1169 |
|
1170 |
Node t = tail; |
1171 |
Thread firstThread = null; |
1172 |
while (t != null && t != head) { |
1173 |
Thread tt = t.thread; |
1174 |
if (tt != null) |
1175 |
firstThread = tt; |
1176 |
t = t.prev; |
1177 |
} |
1178 |
return firstThread; |
1179 |
} |
1180 |
|
1181 |
/** |
1182 |
* Returns true if the given thread is currently queued. |
1183 |
* |
1184 |
* <p>This implementation traverses the queue to determine |
1185 |
* presence of the given thread. |
1186 |
* |
1187 |
* @param thread the thread |
1188 |
* @return {@code true} if the given thread is on the queue |
1189 |
* @throws NullPointerException if the thread is null |
1190 |
*/ |
1191 |
public final boolean isQueued(Thread thread) { |
1192 |
if (thread == null) |
1193 |
throw new NullPointerException(); |
1194 |
for (Node p = tail; p != null; p = p.prev) |
1195 |
if (p.thread == thread) |
1196 |
return true; |
1197 |
return false; |
1198 |
} |
1199 |
|
1200 |
/** |
1201 |
* Returns {@code true} if the apparent first queued thread, if one |
1202 |
* exists, is waiting in exclusive mode. If this method returns |
1203 |
* {@code true}, and the current thread is attempting to acquire in |
1204 |
* shared mode (that is, this method is invoked from {@link |
1205 |
* #tryAcquireShared}) then it is guaranteed that the current thread |
1206 |
* is not the first queued thread. Used only as a heuristic in |
1207 |
* ReentrantReadWriteLock. |
1208 |
*/ |
1209 |
final boolean apparentlyFirstQueuedIsExclusive() { |
1210 |
Node h, s; |
1211 |
return (h = head) != null && |
1212 |
(s = h.next) != null && |
1213 |
!s.isShared() && |
1214 |
s.thread != null; |
1215 |
} |
1216 |
|
1217 |
/** |
1218 |
* Queries whether any threads have been waiting to acquire longer |
1219 |
* than the current thread. |
1220 |
* |
1221 |
* <p>An invocation of this method is equivalent to (but may be |
1222 |
* more efficient than): |
1223 |
* <pre> {@code |
1224 |
* getFirstQueuedThread() != Thread.currentThread() && |
1225 |
* hasQueuedThreads()}</pre> |
1226 |
* |
1227 |
* <p>Note that because cancellations due to interrupts and |
1228 |
* timeouts may occur at any time, a {@code true} return does not |
1229 |
* guarantee that some other thread will acquire before the current |
1230 |
* thread. Likewise, it is possible for another thread to win a |
1231 |
* race to enqueue after this method has returned {@code false}, |
1232 |
* due to the queue being empty. |
1233 |
* |
1234 |
* <p>This method is designed to be used by a fair synchronizer to |
1235 |
* avoid <a href="AbstractQueuedSynchronizer.html#barging">barging</a>. |
1236 |
* Such a synchronizer's {@link #tryAcquire} method should return |
1237 |
* {@code false}, and its {@link #tryAcquireShared} method should |
1238 |
* return a negative value, if this method returns {@code true} |
1239 |
* (unless this is a reentrant acquire). For example, the {@code |
1240 |
* tryAcquire} method for a fair, reentrant, exclusive mode |
1241 |
* synchronizer might look like this: |
1242 |
* |
1243 |
* <pre> {@code |
1244 |
* protected boolean tryAcquire(int arg) { |
1245 |
* if (isHeldExclusively()) { |
1246 |
* // A reentrant acquire; increment hold count |
1247 |
* return true; |
1248 |
* } else if (hasQueuedPredecessors()) { |
1249 |
* return false; |
1250 |
* } else { |
1251 |
* // try to acquire normally |
1252 |
* } |
1253 |
* }}</pre> |
1254 |
* |
1255 |
* @return {@code true} if there is a queued thread preceding the |
1256 |
* current thread, and {@code false} if the current thread |
1257 |
* is at the head of the queue or the queue is empty |
1258 |
* @since 1.7 |
1259 |
*/ |
1260 |
public final boolean hasQueuedPredecessors() { |
1261 |
// The correctness of this depends on head being initialized |
1262 |
// before tail and on head.next being accurate if the current |
1263 |
// thread is first in queue. |
1264 |
Node t = tail; // Read fields in reverse initialization order |
1265 |
Node h = head; |
1266 |
Node s; |
1267 |
return h != t && |
1268 |
((s = h.next) == null || s.thread != Thread.currentThread()); |
1269 |
} |
1270 |
|
1271 |
|
1272 |
// Instrumentation and monitoring methods |
1273 |
|
1274 |
/** |
1275 |
* Returns an estimate of the number of threads waiting to |
1276 |
* acquire. The value is only an estimate because the number of |
1277 |
* threads may change dynamically while this method traverses |
1278 |
* internal data structures. This method is designed for use in |
1279 |
* monitoring system state, not for synchronization |
1280 |
* control. |
1281 |
* |
1282 |
* @return the estimated number of threads waiting to acquire |
1283 |
*/ |
1284 |
public final int getQueueLength() { |
1285 |
int n = 0; |
1286 |
for (Node p = tail; p != null; p = p.prev) { |
1287 |
if (p.thread != null) |
1288 |
++n; |
1289 |
} |
1290 |
return n; |
1291 |
} |
1292 |
|
1293 |
/** |
1294 |
* Returns a collection containing threads that may be waiting to |
1295 |
* acquire. Because the actual set of threads may change |
1296 |
* dynamically while constructing this result, the returned |
1297 |
* collection is only a best-effort estimate. The elements of the |
1298 |
* returned collection are in no particular order. This method is |
1299 |
* designed to facilitate construction of subclasses that provide |
1300 |
* more extensive monitoring facilities. |
1301 |
* |
1302 |
* @return the collection of threads |
1303 |
*/ |
1304 |
public final Collection<Thread> getQueuedThreads() { |
1305 |
ArrayList<Thread> list = new ArrayList<Thread>(); |
1306 |
for (Node p = tail; p != null; p = p.prev) { |
1307 |
Thread t = p.thread; |
1308 |
if (t != null) |
1309 |
list.add(t); |
1310 |
} |
1311 |
return list; |
1312 |
} |
1313 |
|
1314 |
/** |
1315 |
* Returns a collection containing threads that may be waiting to |
1316 |
* acquire in exclusive mode. This has the same properties |
1317 |
* as {@link #getQueuedThreads} except that it only returns |
1318 |
* those threads waiting due to an exclusive acquire. |
1319 |
* |
1320 |
* @return the collection of threads |
1321 |
*/ |
1322 |
public final Collection<Thread> getExclusiveQueuedThreads() { |
1323 |
ArrayList<Thread> list = new ArrayList<Thread>(); |
1324 |
for (Node p = tail; p != null; p = p.prev) { |
1325 |
if (!p.isShared()) { |
1326 |
Thread t = p.thread; |
1327 |
if (t != null) |
1328 |
list.add(t); |
1329 |
} |
1330 |
} |
1331 |
return list; |
1332 |
} |
1333 |
|
1334 |
/** |
1335 |
* Returns a collection containing threads that may be waiting to |
1336 |
* acquire in shared mode. This has the same properties |
1337 |
* as {@link #getQueuedThreads} except that it only returns |
1338 |
* those threads waiting due to a shared acquire. |
1339 |
* |
1340 |
* @return the collection of threads |
1341 |
*/ |
1342 |
public final Collection<Thread> getSharedQueuedThreads() { |
1343 |
ArrayList<Thread> list = new ArrayList<Thread>(); |
1344 |
for (Node p = tail; p != null; p = p.prev) { |
1345 |
if (p.isShared()) { |
1346 |
Thread t = p.thread; |
1347 |
if (t != null) |
1348 |
list.add(t); |
1349 |
} |
1350 |
} |
1351 |
return list; |
1352 |
} |
1353 |
|
1354 |
/** |
1355 |
* Returns a string identifying this synchronizer, as well as its state. |
1356 |
* The state, in brackets, includes the String {@code "State ="} |
1357 |
* followed by the current value of {@link #getState}, and either |
1358 |
* {@code "nonempty"} or {@code "empty"} depending on whether the |
1359 |
* queue is empty. |
1360 |
* |
1361 |
* @return a string identifying this synchronizer, as well as its state |
1362 |
*/ |
1363 |
public String toString() { |
1364 |
return super.toString() |
1365 |
+ "[State = " + getState() + ", " |
1366 |
+ (hasQueuedThreads() ? "non" : "") + "empty queue]"; |
1367 |
} |
1368 |
|
1369 |
|
1370 |
// Internal support methods for Conditions |
1371 |
|
1372 |
/** |
1373 |
* Returns true if a node, always one that was initially placed on |
1374 |
* a condition queue, is now waiting to reacquire on sync queue. |
1375 |
* @param node the node |
1376 |
* @return true if is reacquiring |
1377 |
*/ |
1378 |
final boolean isOnSyncQueue(Node node) { |
1379 |
if (node.waitStatus == Node.CONDITION || node.prev == null) |
1380 |
return false; |
1381 |
if (node.next != null) // If has successor, it must be on queue |
1382 |
return true; |
1383 |
/* |
1384 |
* node.prev can be non-null, but not yet on queue because |
1385 |
* the CAS to place it on queue can fail. So we have to |
1386 |
* traverse from tail to make sure it actually made it. It |
1387 |
* will always be near the tail in calls to this method, and |
1388 |
* unless the CAS failed (which is unlikely), it will be |
1389 |
* there, so we hardly ever traverse much. |
1390 |
*/ |
1391 |
return findNodeFromTail(node); |
1392 |
} |
1393 |
|
1394 |
/** |
1395 |
* Returns true if node is on sync queue by searching backwards from tail. |
1396 |
* Called only when needed by isOnSyncQueue. |
1397 |
* @return true if present |
1398 |
*/ |
1399 |
private boolean findNodeFromTail(Node node) { |
1400 |
Node p = tail; |
1401 |
for (;;) { |
1402 |
if (p == node) |
1403 |
return true; |
1404 |
if (p == null) |
1405 |
return false; |
1406 |
p = p.prev; |
1407 |
} |
1408 |
} |
1409 |
|
1410 |
/** |
1411 |
* Transfers a node from a condition queue onto sync queue. |
1412 |
* Returns true if successful. |
1413 |
* @param node the node |
1414 |
* @return true if successfully transferred (else the node was |
1415 |
* cancelled before signal) |
1416 |
*/ |
1417 |
final boolean transferForSignal(Node node) { |
1418 |
/* |
1419 |
* If cannot change waitStatus, the node has been cancelled. |
1420 |
*/ |
1421 |
if (!compareAndSetWaitStatus(node, Node.CONDITION, 0)) |
1422 |
return false; |
1423 |
|
1424 |
/* |
1425 |
* Splice onto queue and try to set waitStatus of predecessor to |
1426 |
* indicate that thread is (probably) waiting. If cancelled or |
1427 |
* attempt to set waitStatus fails, wake up to resync (in which |
1428 |
* case the waitStatus can be transiently and harmlessly wrong). |
1429 |
*/ |
1430 |
Node p = enq(node); |
1431 |
int ws = p.waitStatus; |
1432 |
if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL)) |
1433 |
LockSupport.unpark(node.thread); |
1434 |
return true; |
1435 |
} |
1436 |
|
1437 |
/** |
1438 |
* Transfers node, if necessary, to sync queue after a cancelled wait. |
1439 |
* Returns true if thread was cancelled before being signalled. |
1440 |
* |
1441 |
* @param node the node |
1442 |
* @return true if cancelled before the node was signalled |
1443 |
*/ |
1444 |
final boolean transferAfterCancelledWait(Node node) { |
1445 |
if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) { |
1446 |
enq(node); |
1447 |
return true; |
1448 |
} |
1449 |
/* |
1450 |
* If we lost out to a signal(), then we can't proceed |
1451 |
* until it finishes its enq(). Cancelling during an |
1452 |
* incomplete transfer is both rare and transient, so just |
1453 |
* spin. |
1454 |
*/ |
1455 |
while (!isOnSyncQueue(node)) |
1456 |
Thread.yield(); |
1457 |
return false; |
1458 |
} |
1459 |
|
1460 |
/** |
1461 |
* Invokes release with current state value; returns saved state. |
1462 |
* Cancels node and throws exception on failure. |
1463 |
* @param node the condition node for this wait |
1464 |
* @return previous sync state |
1465 |
*/ |
1466 |
final long fullyRelease(Node node) { |
1467 |
boolean failed = true; |
1468 |
try { |
1469 |
long savedState = getState(); |
1470 |
if (release(savedState)) { |
1471 |
failed = false; |
1472 |
return savedState; |
1473 |
} else { |
1474 |
throw new IllegalMonitorStateException(); |
1475 |
} |
1476 |
} finally { |
1477 |
if (failed) |
1478 |
node.waitStatus = Node.CANCELLED; |
1479 |
} |
1480 |
} |
1481 |
|
1482 |
// Instrumentation methods for conditions |
1483 |
|
1484 |
/** |
1485 |
* Queries whether the given ConditionObject |
1486 |
* uses this synchronizer as its lock. |
1487 |
* |
1488 |
* @param condition the condition |
1489 |
* @return {@code true} if owned |
1490 |
* @throws NullPointerException if the condition is null |
1491 |
*/ |
1492 |
public final boolean owns(ConditionObject condition) { |
1493 |
return condition.isOwnedBy(this); |
1494 |
} |
1495 |
|
1496 |
/** |
1497 |
* Queries whether any threads are waiting on the given condition |
1498 |
* associated with this synchronizer. Note that because timeouts |
1499 |
* and interrupts may occur at any time, a {@code true} return |
1500 |
* does not guarantee that a future {@code signal} will awaken |
1501 |
* any threads. This method is designed primarily for use in |
1502 |
* monitoring of the system state. |
1503 |
* |
1504 |
* @param condition the condition |
1505 |
* @return {@code true} if there are any waiting threads |
1506 |
* @throws IllegalMonitorStateException if exclusive synchronization |
1507 |
* is not held |
1508 |
* @throws IllegalArgumentException if the given condition is |
1509 |
* not associated with this synchronizer |
1510 |
* @throws NullPointerException if the condition is null |
1511 |
*/ |
1512 |
public final boolean hasWaiters(ConditionObject condition) { |
1513 |
if (!owns(condition)) |
1514 |
throw new IllegalArgumentException("Not owner"); |
1515 |
return condition.hasWaiters(); |
1516 |
} |
1517 |
|
1518 |
/** |
1519 |
* Returns an estimate of the number of threads waiting on the |
1520 |
* given condition associated with this synchronizer. Note that |
1521 |
* because timeouts and interrupts may occur at any time, the |
1522 |
* estimate serves only as an upper bound on the actual number of |
1523 |
* waiters. This method is designed for use in monitoring of the |
1524 |
* system state, not for synchronization control. |
1525 |
* |
1526 |
* @param condition the condition |
1527 |
* @return the estimated number of waiting threads |
1528 |
* @throws IllegalMonitorStateException if exclusive synchronization |
1529 |
* is not held |
1530 |
* @throws IllegalArgumentException if the given condition is |
1531 |
* not associated with this synchronizer |
1532 |
* @throws NullPointerException if the condition is null |
1533 |
*/ |
1534 |
public final int getWaitQueueLength(ConditionObject condition) { |
1535 |
if (!owns(condition)) |
1536 |
throw new IllegalArgumentException("Not owner"); |
1537 |
return condition.getWaitQueueLength(); |
1538 |
} |
1539 |
|
1540 |
/** |
1541 |
* Returns a collection containing those threads that may be |
1542 |
* waiting on the given condition associated with this |
1543 |
* synchronizer. Because the actual set of threads may change |
1544 |
* dynamically while constructing this result, the returned |
1545 |
* collection is only a best-effort estimate. The elements of the |
1546 |
* returned collection are in no particular order. |
1547 |
* |
1548 |
* @param condition the condition |
1549 |
* @return the collection of threads |
1550 |
* @throws IllegalMonitorStateException if exclusive synchronization |
1551 |
* is not held |
1552 |
* @throws IllegalArgumentException if the given condition is |
1553 |
* not associated with this synchronizer |
1554 |
* @throws NullPointerException if the condition is null |
1555 |
*/ |
1556 |
public final Collection<Thread> getWaitingThreads(ConditionObject condition) { |
1557 |
if (!owns(condition)) |
1558 |
throw new IllegalArgumentException("Not owner"); |
1559 |
return condition.getWaitingThreads(); |
1560 |
} |
1561 |
|
1562 |
/** |
1563 |
* Condition implementation for a {@link |
1564 |
* AbstractQueuedLongSynchronizer} serving as the basis of a {@link |
1565 |
* Lock} implementation. |
1566 |
* |
1567 |
* <p>Method documentation for this class describes mechanics, |
1568 |
* not behavioral specifications from the point of view of Lock |
1569 |
* and Condition users. Exported versions of this class will in |
1570 |
* general need to be accompanied by documentation describing |
1571 |
* condition semantics that rely on those of the associated |
1572 |
* {@code AbstractQueuedLongSynchronizer}. |
1573 |
* |
1574 |
* <p>This class is Serializable, but all fields are transient, |
1575 |
* so deserialized conditions have no waiters. |
1576 |
* |
1577 |
* @since 1.6 |
1578 |
*/ |
1579 |
public class ConditionObject implements Condition, java.io.Serializable { |
1580 |
private static final long serialVersionUID = 1173984872572414699L; |
1581 |
/** First node of condition queue. */ |
1582 |
private transient Node firstWaiter; |
1583 |
/** Last node of condition queue. */ |
1584 |
private transient Node lastWaiter; |
1585 |
|
1586 |
/** |
1587 |
* Creates a new {@code ConditionObject} instance. |
1588 |
*/ |
1589 |
public ConditionObject() { } |
1590 |
|
1591 |
// Internal methods |
1592 |
|
1593 |
/** |
1594 |
* Adds a new waiter to wait queue. |
1595 |
* @return its new wait node |
1596 |
*/ |
1597 |
private Node addConditionWaiter() { |
1598 |
Node t = lastWaiter; |
1599 |
// If lastWaiter is cancelled, clean out. |
1600 |
if (t != null && t.waitStatus != Node.CONDITION) { |
1601 |
unlinkCancelledWaiters(); |
1602 |
t = lastWaiter; |
1603 |
} |
1604 |
Node node = new Node(Thread.currentThread(), Node.CONDITION); |
1605 |
if (t == null) |
1606 |
firstWaiter = node; |
1607 |
else |
1608 |
t.nextWaiter = node; |
1609 |
lastWaiter = node; |
1610 |
return node; |
1611 |
} |
1612 |
|
1613 |
/** |
1614 |
* Removes and transfers nodes until hit non-cancelled one or |
1615 |
* null. Split out from signal in part to encourage compilers |
1616 |
* to inline the case of no waiters. |
1617 |
* @param first (non-null) the first node on condition queue |
1618 |
*/ |
1619 |
private void doSignal(Node first) { |
1620 |
do { |
1621 |
if ( (firstWaiter = first.nextWaiter) == null) |
1622 |
lastWaiter = null; |
1623 |
first.nextWaiter = null; |
1624 |
} while (!transferForSignal(first) && |
1625 |
(first = firstWaiter) != null); |
1626 |
} |
1627 |
|
1628 |
/** |
1629 |
* Removes and transfers all nodes. |
1630 |
* @param first (non-null) the first node on condition queue |
1631 |
*/ |
1632 |
private void doSignalAll(Node first) { |
1633 |
lastWaiter = firstWaiter = null; |
1634 |
do { |
1635 |
Node next = first.nextWaiter; |
1636 |
first.nextWaiter = null; |
1637 |
transferForSignal(first); |
1638 |
first = next; |
1639 |
} while (first != null); |
1640 |
} |
1641 |
|
1642 |
/** |
1643 |
* Unlinks cancelled waiter nodes from condition queue. |
1644 |
* Called only while holding lock. This is called when |
1645 |
* cancellation occurred during condition wait, and upon |
1646 |
* insertion of a new waiter when lastWaiter is seen to have |
1647 |
* been cancelled. This method is needed to avoid garbage |
1648 |
* retention in the absence of signals. So even though it may |
1649 |
* require a full traversal, it comes into play only when |
1650 |
* timeouts or cancellations occur in the absence of |
1651 |
* signals. It traverses all nodes rather than stopping at a |
1652 |
* particular target to unlink all pointers to garbage nodes |
1653 |
* without requiring many re-traversals during cancellation |
1654 |
* storms. |
1655 |
*/ |
1656 |
private void unlinkCancelledWaiters() { |
1657 |
Node t = firstWaiter; |
1658 |
Node trail = null; |
1659 |
while (t != null) { |
1660 |
Node next = t.nextWaiter; |
1661 |
if (t.waitStatus != Node.CONDITION) { |
1662 |
t.nextWaiter = null; |
1663 |
if (trail == null) |
1664 |
firstWaiter = next; |
1665 |
else |
1666 |
trail.nextWaiter = next; |
1667 |
if (next == null) |
1668 |
lastWaiter = trail; |
1669 |
} |
1670 |
else |
1671 |
trail = t; |
1672 |
t = next; |
1673 |
} |
1674 |
} |
1675 |
|
1676 |
// public methods |
1677 |
|
1678 |
/** |
1679 |
* Moves the longest-waiting thread, if one exists, from the |
1680 |
* wait queue for this condition to the wait queue for the |
1681 |
* owning lock. |
1682 |
* |
1683 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1684 |
* returns {@code false} |
1685 |
*/ |
1686 |
public final void signal() { |
1687 |
if (!isHeldExclusively()) |
1688 |
throw new IllegalMonitorStateException(); |
1689 |
Node first = firstWaiter; |
1690 |
if (first != null) |
1691 |
doSignal(first); |
1692 |
} |
1693 |
|
1694 |
/** |
1695 |
* Moves all threads from the wait queue for this condition to |
1696 |
* the wait queue for the owning lock. |
1697 |
* |
1698 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1699 |
* returns {@code false} |
1700 |
*/ |
1701 |
public final void signalAll() { |
1702 |
if (!isHeldExclusively()) |
1703 |
throw new IllegalMonitorStateException(); |
1704 |
Node first = firstWaiter; |
1705 |
if (first != null) |
1706 |
doSignalAll(first); |
1707 |
} |
1708 |
|
1709 |
/** |
1710 |
* Implements uninterruptible condition wait. |
1711 |
* <ol> |
1712 |
* <li>Save lock state returned by {@link #getState}. |
1713 |
* <li>Invoke {@link #release} with saved state as argument, |
1714 |
* throwing IllegalMonitorStateException if it fails. |
1715 |
* <li>Block until signalled. |
1716 |
* <li>Reacquire by invoking specialized version of |
1717 |
* {@link #acquire} with saved state as argument. |
1718 |
* </ol> |
1719 |
*/ |
1720 |
public final void awaitUninterruptibly() { |
1721 |
Node node = addConditionWaiter(); |
1722 |
long savedState = fullyRelease(node); |
1723 |
boolean interrupted = false; |
1724 |
while (!isOnSyncQueue(node)) { |
1725 |
LockSupport.park(this); |
1726 |
if (Thread.interrupted()) |
1727 |
interrupted = true; |
1728 |
} |
1729 |
if (acquireQueued(node, savedState) || interrupted) |
1730 |
selfInterrupt(); |
1731 |
} |
1732 |
|
1733 |
/* |
1734 |
* For interruptible waits, we need to track whether to throw |
1735 |
* InterruptedException, if interrupted while blocked on |
1736 |
* condition, versus reinterrupt current thread, if |
1737 |
* interrupted while blocked waiting to re-acquire. |
1738 |
*/ |
1739 |
|
1740 |
/** Mode meaning to reinterrupt on exit from wait */ |
1741 |
private static final int REINTERRUPT = 1; |
1742 |
/** Mode meaning to throw InterruptedException on exit from wait */ |
1743 |
private static final int THROW_IE = -1; |
1744 |
|
1745 |
/** |
1746 |
* Checks for interrupt, returning THROW_IE if interrupted |
1747 |
* before signalled, REINTERRUPT if after signalled, or |
1748 |
* 0 if not interrupted. |
1749 |
*/ |
1750 |
private int checkInterruptWhileWaiting(Node node) { |
1751 |
return Thread.interrupted() ? |
1752 |
(transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) : |
1753 |
0; |
1754 |
} |
1755 |
|
1756 |
/** |
1757 |
* Throws InterruptedException, reinterrupts current thread, or |
1758 |
* does nothing, depending on mode. |
1759 |
*/ |
1760 |
private void reportInterruptAfterWait(int interruptMode) |
1761 |
throws InterruptedException { |
1762 |
if (interruptMode == THROW_IE) |
1763 |
throw new InterruptedException(); |
1764 |
else if (interruptMode == REINTERRUPT) |
1765 |
selfInterrupt(); |
1766 |
} |
1767 |
|
1768 |
/** |
1769 |
* Implements interruptible condition wait. |
1770 |
* <ol> |
1771 |
* <li>If current thread is interrupted, throw InterruptedException. |
1772 |
* <li>Save lock state returned by {@link #getState}. |
1773 |
* <li>Invoke {@link #release} with saved state as argument, |
1774 |
* throwing IllegalMonitorStateException if it fails. |
1775 |
* <li>Block until signalled or interrupted. |
1776 |
* <li>Reacquire by invoking specialized version of |
1777 |
* {@link #acquire} with saved state as argument. |
1778 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1779 |
* </ol> |
1780 |
*/ |
1781 |
public final void await() throws InterruptedException { |
1782 |
if (Thread.interrupted()) |
1783 |
throw new InterruptedException(); |
1784 |
Node node = addConditionWaiter(); |
1785 |
long savedState = fullyRelease(node); |
1786 |
int interruptMode = 0; |
1787 |
while (!isOnSyncQueue(node)) { |
1788 |
LockSupport.park(this); |
1789 |
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) |
1790 |
break; |
1791 |
} |
1792 |
if (acquireQueued(node, savedState) && interruptMode != THROW_IE) |
1793 |
interruptMode = REINTERRUPT; |
1794 |
if (node.nextWaiter != null) // clean up if cancelled |
1795 |
unlinkCancelledWaiters(); |
1796 |
if (interruptMode != 0) |
1797 |
reportInterruptAfterWait(interruptMode); |
1798 |
} |
1799 |
|
1800 |
/** |
1801 |
* Implements timed condition wait. |
1802 |
* <ol> |
1803 |
* <li>If current thread is interrupted, throw InterruptedException. |
1804 |
* <li>Save lock state returned by {@link #getState}. |
1805 |
* <li>Invoke {@link #release} with saved state as argument, |
1806 |
* throwing IllegalMonitorStateException if it fails. |
1807 |
* <li>Block until signalled, interrupted, or timed out. |
1808 |
* <li>Reacquire by invoking specialized version of |
1809 |
* {@link #acquire} with saved state as argument. |
1810 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1811 |
* </ol> |
1812 |
*/ |
1813 |
public final long awaitNanos(long nanosTimeout) |
1814 |
throws InterruptedException { |
1815 |
if (Thread.interrupted()) |
1816 |
throw new InterruptedException(); |
1817 |
long initialNanos = nanosTimeout; |
1818 |
Node node = addConditionWaiter(); |
1819 |
long savedState = fullyRelease(node); |
1820 |
final long deadline = System.nanoTime() + nanosTimeout; |
1821 |
int interruptMode = 0; |
1822 |
while (!isOnSyncQueue(node)) { |
1823 |
if (nanosTimeout <= 0L) { |
1824 |
transferAfterCancelledWait(node); |
1825 |
break; |
1826 |
} |
1827 |
if (nanosTimeout > spinForTimeoutThreshold) |
1828 |
LockSupport.parkNanos(this, nanosTimeout); |
1829 |
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) |
1830 |
break; |
1831 |
nanosTimeout = deadline - System.nanoTime(); |
1832 |
} |
1833 |
if (acquireQueued(node, savedState) && interruptMode != THROW_IE) |
1834 |
interruptMode = REINTERRUPT; |
1835 |
if (node.nextWaiter != null) |
1836 |
unlinkCancelledWaiters(); |
1837 |
if (interruptMode != 0) |
1838 |
reportInterruptAfterWait(interruptMode); |
1839 |
long remaining = deadline - System.nanoTime(); // avoid overflow |
1840 |
return (remaining < initialNanos) ? remaining : Long.MIN_VALUE; |
1841 |
} |
1842 |
|
1843 |
/** |
1844 |
* Implements absolute timed condition wait. |
1845 |
* <ol> |
1846 |
* <li>If current thread is interrupted, throw InterruptedException. |
1847 |
* <li>Save lock state returned by {@link #getState}. |
1848 |
* <li>Invoke {@link #release} with saved state as argument, |
1849 |
* throwing IllegalMonitorStateException if it fails. |
1850 |
* <li>Block until signalled, interrupted, or timed out. |
1851 |
* <li>Reacquire by invoking specialized version of |
1852 |
* {@link #acquire} with saved state as argument. |
1853 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1854 |
* <li>If timed out while blocked in step 4, return false, else true. |
1855 |
* </ol> |
1856 |
*/ |
1857 |
public final boolean awaitUntil(Date deadline) |
1858 |
throws InterruptedException { |
1859 |
long abstime = deadline.getTime(); |
1860 |
if (Thread.interrupted()) |
1861 |
throw new InterruptedException(); |
1862 |
Node node = addConditionWaiter(); |
1863 |
long savedState = fullyRelease(node); |
1864 |
boolean timedout = false; |
1865 |
int interruptMode = 0; |
1866 |
while (!isOnSyncQueue(node)) { |
1867 |
if (System.currentTimeMillis() >= abstime) { |
1868 |
timedout = transferAfterCancelledWait(node); |
1869 |
break; |
1870 |
} |
1871 |
LockSupport.parkUntil(this, abstime); |
1872 |
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) |
1873 |
break; |
1874 |
} |
1875 |
if (acquireQueued(node, savedState) && interruptMode != THROW_IE) |
1876 |
interruptMode = REINTERRUPT; |
1877 |
if (node.nextWaiter != null) |
1878 |
unlinkCancelledWaiters(); |
1879 |
if (interruptMode != 0) |
1880 |
reportInterruptAfterWait(interruptMode); |
1881 |
return !timedout; |
1882 |
} |
1883 |
|
1884 |
/** |
1885 |
* Implements timed condition wait. |
1886 |
* <ol> |
1887 |
* <li>If current thread is interrupted, throw InterruptedException. |
1888 |
* <li>Save lock state returned by {@link #getState}. |
1889 |
* <li>Invoke {@link #release} with saved state as argument, |
1890 |
* throwing IllegalMonitorStateException if it fails. |
1891 |
* <li>Block until signalled, interrupted, or timed out. |
1892 |
* <li>Reacquire by invoking specialized version of |
1893 |
* {@link #acquire} with saved state as argument. |
1894 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1895 |
* <li>If timed out while blocked in step 4, return false, else true. |
1896 |
* </ol> |
1897 |
*/ |
1898 |
public final boolean await(long time, TimeUnit unit) |
1899 |
throws InterruptedException { |
1900 |
long nanosTimeout = unit.toNanos(time); |
1901 |
if (Thread.interrupted()) |
1902 |
throw new InterruptedException(); |
1903 |
Node node = addConditionWaiter(); |
1904 |
long savedState = fullyRelease(node); |
1905 |
final long deadline = System.nanoTime() + nanosTimeout; |
1906 |
boolean timedout = false; |
1907 |
int interruptMode = 0; |
1908 |
while (!isOnSyncQueue(node)) { |
1909 |
if (nanosTimeout <= 0L) { |
1910 |
timedout = transferAfterCancelledWait(node); |
1911 |
break; |
1912 |
} |
1913 |
if (nanosTimeout > spinForTimeoutThreshold) |
1914 |
LockSupport.parkNanos(this, nanosTimeout); |
1915 |
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) |
1916 |
break; |
1917 |
nanosTimeout = deadline - System.nanoTime(); |
1918 |
} |
1919 |
if (acquireQueued(node, savedState) && interruptMode != THROW_IE) |
1920 |
interruptMode = REINTERRUPT; |
1921 |
if (node.nextWaiter != null) |
1922 |
unlinkCancelledWaiters(); |
1923 |
if (interruptMode != 0) |
1924 |
reportInterruptAfterWait(interruptMode); |
1925 |
return !timedout; |
1926 |
} |
1927 |
|
1928 |
// support for instrumentation |
1929 |
|
1930 |
/** |
1931 |
* Returns true if this condition was created by the given |
1932 |
* synchronization object. |
1933 |
* |
1934 |
* @return {@code true} if owned |
1935 |
*/ |
1936 |
final boolean isOwnedBy(AbstractQueuedLongSynchronizer sync) { |
1937 |
return sync == AbstractQueuedLongSynchronizer.this; |
1938 |
} |
1939 |
|
1940 |
/** |
1941 |
* Queries whether any threads are waiting on this condition. |
1942 |
* Implements {@link AbstractQueuedLongSynchronizer#hasWaiters}. |
1943 |
* |
1944 |
* @return {@code true} if there are any waiting threads |
1945 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1946 |
* returns {@code false} |
1947 |
*/ |
1948 |
protected final boolean hasWaiters() { |
1949 |
if (!isHeldExclusively()) |
1950 |
throw new IllegalMonitorStateException(); |
1951 |
for (Node w = firstWaiter; w != null; w = w.nextWaiter) { |
1952 |
if (w.waitStatus == Node.CONDITION) |
1953 |
return true; |
1954 |
} |
1955 |
return false; |
1956 |
} |
1957 |
|
1958 |
/** |
1959 |
* Returns an estimate of the number of threads waiting on |
1960 |
* this condition. |
1961 |
* Implements {@link AbstractQueuedLongSynchronizer#getWaitQueueLength}. |
1962 |
* |
1963 |
* @return the estimated number of waiting threads |
1964 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1965 |
* returns {@code false} |
1966 |
*/ |
1967 |
protected final int getWaitQueueLength() { |
1968 |
if (!isHeldExclusively()) |
1969 |
throw new IllegalMonitorStateException(); |
1970 |
int n = 0; |
1971 |
for (Node w = firstWaiter; w != null; w = w.nextWaiter) { |
1972 |
if (w.waitStatus == Node.CONDITION) |
1973 |
++n; |
1974 |
} |
1975 |
return n; |
1976 |
} |
1977 |
|
1978 |
/** |
1979 |
* Returns a collection containing those threads that may be |
1980 |
* waiting on this Condition. |
1981 |
* Implements {@link AbstractQueuedLongSynchronizer#getWaitingThreads}. |
1982 |
* |
1983 |
* @return the collection of threads |
1984 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1985 |
* returns {@code false} |
1986 |
*/ |
1987 |
protected final Collection<Thread> getWaitingThreads() { |
1988 |
if (!isHeldExclusively()) |
1989 |
throw new IllegalMonitorStateException(); |
1990 |
ArrayList<Thread> list = new ArrayList<Thread>(); |
1991 |
for (Node w = firstWaiter; w != null; w = w.nextWaiter) { |
1992 |
if (w.waitStatus == Node.CONDITION) { |
1993 |
Thread t = w.thread; |
1994 |
if (t != null) |
1995 |
list.add(t); |
1996 |
} |
1997 |
} |
1998 |
return list; |
1999 |
} |
2000 |
} |
2001 |
|
2002 |
/** |
2003 |
* Setup to support compareAndSet. We need to natively implement |
2004 |
* this here: For the sake of permitting future enhancements, we |
2005 |
* cannot explicitly subclass AtomicLong, which would be |
2006 |
* efficient and useful otherwise. So, as the lesser of evils, we |
2007 |
* natively implement using hotspot intrinsics API. And while we |
2008 |
* are at it, we do the same for other CASable fields (which could |
2009 |
* otherwise be done with atomic field updaters). |
2010 |
*/ |
2011 |
private static final Unsafe unsafe = Unsafe.getUnsafe(); |
2012 |
private static final long stateOffset; |
2013 |
private static final long headOffset; |
2014 |
private static final long tailOffset; |
2015 |
private static final long waitStatusOffset; |
2016 |
private static final long nextOffset; |
2017 |
|
2018 |
static { |
2019 |
try { |
2020 |
stateOffset = unsafe.objectFieldOffset |
2021 |
(AbstractQueuedLongSynchronizer.class.getDeclaredField("state")); |
2022 |
headOffset = unsafe.objectFieldOffset |
2023 |
(AbstractQueuedLongSynchronizer.class.getDeclaredField("head")); |
2024 |
tailOffset = unsafe.objectFieldOffset |
2025 |
(AbstractQueuedLongSynchronizer.class.getDeclaredField("tail")); |
2026 |
waitStatusOffset = unsafe.objectFieldOffset |
2027 |
(Node.class.getDeclaredField("waitStatus")); |
2028 |
nextOffset = unsafe.objectFieldOffset |
2029 |
(Node.class.getDeclaredField("next")); |
2030 |
|
2031 |
} catch (Exception ex) { throw new Error(ex); } |
2032 |
|
2033 |
// Reduce the risk of rare disastrous classloading in first call to |
2034 |
// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
2035 |
Class<?> ensureLoaded = LockSupport.class; |
2036 |
} |
2037 |
|
2038 |
/** |
2039 |
* CAS head field. Used only by enq. |
2040 |
*/ |
2041 |
private final boolean compareAndSetHead(Node update) { |
2042 |
return unsafe.compareAndSwapObject(this, headOffset, null, update); |
2043 |
} |
2044 |
|
2045 |
/** |
2046 |
* CAS tail field. Used only by enq. |
2047 |
*/ |
2048 |
private final boolean compareAndSetTail(Node expect, Node update) { |
2049 |
return unsafe.compareAndSwapObject(this, tailOffset, expect, update); |
2050 |
} |
2051 |
|
2052 |
/** |
2053 |
* CAS waitStatus field of a node. |
2054 |
*/ |
2055 |
private static final boolean compareAndSetWaitStatus(Node node, |
2056 |
int expect, |
2057 |
int update) { |
2058 |
return unsafe.compareAndSwapInt(node, waitStatusOffset, |
2059 |
expect, update); |
2060 |
} |
2061 |
|
2062 |
/** |
2063 |
* CAS next field of a node. |
2064 |
*/ |
2065 |
private static final boolean compareAndSetNext(Node node, |
2066 |
Node expect, |
2067 |
Node update) { |
2068 |
return unsafe.compareAndSwapObject(node, nextOffset, expect, update); |
2069 |
} |
2070 |
} |