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dl |
1.2 |
/* |
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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. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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tim |
1.1 |
package java.util.concurrent; |
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dl |
1.2 |
import java.util.concurrent.atomic.*; |
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import java.util.Date; |
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tim |
1.1 |
|
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dl |
1.3 |
|
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tim |
1.1 |
/** |
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dl |
1.8 |
* A reentrant mutual exclusion {@link Lock} with the same basic |
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* behavior and semantics as the implicit monitor lock accessed by the |
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* use of <tt>synchronized</tt> methods and statements, but without |
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* the forced block-structured locking and unlocking that occurs with |
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* <tt>synchronized</tt> methods and statements. |
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tim |
1.1 |
* |
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* <p>The order in which blocked threads are granted the lock is not |
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dl |
1.2 |
* specified. |
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tim |
1.1 |
* |
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* <p>If you want a non-reentrant mutual exclusion lock then it is a simple |
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* matter to use a reentrant lock in a non-reentrant way by ensuring that |
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* the lock is not held by the current thread prior to locking. |
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* See {@link #getHoldCount} for a way to check this. |
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* |
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* |
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dl |
1.5 |
* <p><tt>ReentrantLock</tt> instances are intended to be used primarily |
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tim |
1.1 |
* in before/after constructions such as: |
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* |
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* <pre> |
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* class X { |
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* ReentrantLock lock; |
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* // ... |
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* |
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* public void m() { |
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* lock.lock(); // block until condition holds |
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* try { |
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* // ... method body |
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* } finally { |
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* lock.unlock() |
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* } |
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* } |
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* } |
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* </pre> |
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* |
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* <p>This class supports the interruption of lock acquisition and provides a |
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* {@link #newCondition Condition} implementation that supports the |
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* interruption of thread suspension. |
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* |
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* <p>Except where noted, passing a <tt>null</tt> value for any parameter |
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* will result in a {@link NullPointerException} being thrown. |
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* |
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* @since 1.5 |
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* @spec JSR-166 |
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dholmes |
1.13 |
* @revised $Date: 2003/06/11 13:17:20 $ |
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* @editor $Author: dl $ |
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dl |
1.2 |
* @author Doug Lea |
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tim |
1.1 |
* |
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**/ |
61 |
dholmes |
1.13 |
public class ReentrantLock extends ReentrantLockQueueNode |
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implements Lock, java.io.Serializable { |
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dl |
1.2 |
/* |
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dl |
1.8 |
The basic fastpath/slowpath algorithm looks like this, ignoring |
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reentrance, cancellation, timeouts, error checking etc: |
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dl |
1.2 |
Lock: |
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if (!fair && casOwner(null, currentThread)) // fastpath |
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return; |
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node = create and enq a wait node; |
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for (;;) { |
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if (node is first on queue) { |
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if (casOwner(null, currentThread)) { |
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deq(node); |
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return; |
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} |
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} |
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park(currentThread); |
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} |
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Unlock: |
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owner = null; // volatile assignment |
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h = first node on queue; |
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if (h != null) unpark(h's successor's thread); |
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|
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* The fast path uses one atomic CAS operation, plus one |
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dl |
1.6 |
StoreLoad barrier (i.e., volatile-write-barrier) per |
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lock/unlock pair. The "owner" field is handled as a simple |
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spinlock. To lock, the owner field is set to current thread |
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using conditional atomic update. To unlock, the owner field |
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is set to null, checking if anyone needs waking up, if so |
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doing so. Recursive locks/unlocks instead increment/decrement |
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recursion field. |
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dl |
1.2 |
|
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* By default, contended locks use a kind of "greedy" / |
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"renouncement" / barging / convoy-avoidance strategy: When a |
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lock is released, a waiting thread is signalled so that it can |
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(re)contend for the lock. It might lose and thus need to |
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rewait. This strategy has much higher throughput than |
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"directed handoff" because it reduces blocking of running |
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threads, but poorer fairness. The wait queue is FIFO, but |
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newly entering threads can barge ahead and grab lock before |
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woken waiters, so acquires are not strictly FIFO, and transfer |
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is not deterministically fair. It is probablistically fair |
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though. Earlier queued threads are allowed to recontend before |
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later queued threads, and each recontention has an unbiased |
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chance to succeed. |
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* The base class also sets up support for FairReentrantLock |
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subclass, that differs only in that barging is disabled when |
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there is contention, so locks proceed FIFO. There can be |
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some races in detecting contention, but it is still FIFO from |
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a definable (although complicated to describe) single point, |
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so qualifies as a FIFO lock. |
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|
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* The wait queue is a variant of a "CLH" (Craig, Landin, and |
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Hagersten) lock. CLH locks are normally used for spinlocks. |
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We instead use them for blocking locks, but use the same basic |
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tactic of holding the information about whether a thread is |
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released (i.e, eligible to contend for ownership lock) in the |
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predecessor of each node. A node waits until its predecessor |
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says it is released. It is signalled when its predecessor |
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releases the lock. Each node of the queue otherwise serves as |
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a specific-notification-style monitor holding a single waiting |
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thread. |
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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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+------+ prev +-----+ +-----+ |
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head | | <---- | | <---- | | tail |
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+------+ +-----+ +-----+ |
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The great thing about CLH Locks is that insertion into a CLH |
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queue requires only a single atomic operation on "tail", so |
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there is a simple atomic point of demarcation from unqueued to |
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queued. Similarly, dequeing involves only updating the |
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"head". However, it takes a bit more work for nodes to |
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determine who their successors are, in part to deal with |
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possible cancellation due to timeouts and interrupts. |
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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 must be relinked to a non-cancelled predecessor. For |
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explanation in the case of spin locks, see the papers by Scott |
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& Scherer at |
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http://www.cs.rochester.edu/u/scott/synchronization/ |
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148 |
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Being first in the queue does not mean that you have the lock, |
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only that you may contend for it (by CAS'ing owner field). So |
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the currently released contender thread may need to rewait. |
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We also use "next" links to implement blocking mechanics. The |
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thread id for each node is kept in its node, so a predecessor |
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signals the next node to wake up by traversing next link to |
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determine which thread it is. Determination of successor must |
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avoid races with newly queued nodes to set the "next" fields |
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of their predecessors. This is solved by checking backwards |
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from the atomically updated "tail" when a node's successor |
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appears to be null. |
160 |
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Cancellation introduces some conservatism to the basic |
162 |
dl |
1.6 |
algorithms. Since we must poll for cancellation of other |
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nodes, we can miss noticing whether a cancelled node is ahead |
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or behind us. This is dealt with by always unparking |
165 |
dl |
1.2 |
successors upon cancellation, and not letting them park again |
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(by saturating release counts) until they stabilize on a new |
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predecessor. |
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* Threads waiting on Conditions use the same kind of nodes, but |
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only need to link them in simple (non-concurrent) linked |
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queues because they are only accessed when lock is held. To |
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wait, a thread makes a node inserted into a condition queue. |
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Upon signal, the node is transferred to the lock queue. |
174 |
dl |
1.6 |
Special values of releaseStatus fields are used to mark which |
175 |
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queue a node is on. |
176 |
dl |
1.2 |
|
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dl |
1.6 |
* All suspension and resumption of threads uses the internal |
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JSR166 native park/unpark API. These are safe versions of |
179 |
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suspend/resume (plus timeout support) that avoid the intrinsic |
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race problems with suspend/resume: Park suspends if not |
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preceded by an unpark. Unpark resumes if waiting, else causes |
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next park not to suspend. While safe and efficient, these are |
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not general-purpose public operations because we cannot allow |
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code outside this package to randomly call these methods -- |
185 |
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parks and unparks should be matched up. (It is OK to have more |
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unparks than unparks, but it causes threads to spuriously wake |
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up. So minimizing excessive unparks is a performance concern.) |
188 |
dl |
1.3 |
|
189 |
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* The ReentrantLock class extends package-private |
190 |
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ReentrantLockQueueNode class as an expedient and efficient |
191 |
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(although slightly sleazy) solution to serialization and |
192 |
dl |
1.6 |
initialization problems -- we need head and tail nodes to be |
193 |
dl |
1.8 |
initialized to an otherwise useless dummy node, so use the |
194 |
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ReeantrantLock itself as that node. |
195 |
dl |
1.2 |
*/ |
196 |
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197 |
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/* |
198 |
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Note that all fields are transient and defined in a way that |
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deserialized locks are in initial unlocked state. |
200 |
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*/ |
201 |
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202 |
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/** |
203 |
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* Creates an instance of <tt>ReentrantLock</tt>. |
204 |
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*/ |
205 |
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public ReentrantLock() { } |
206 |
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207 |
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/** |
208 |
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* Current owner of lock, or null iff the lock is free. Acquired |
209 |
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* only using CAS. |
210 |
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*/ |
211 |
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private transient volatile Thread owner; |
212 |
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213 |
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/** Number of recursive acquires. Note: total holds = recursions+1 */ |
214 |
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private transient int recursions; |
215 |
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216 |
dl |
1.3 |
/** Head of the wait queue, initialized to point to self as dummy node */ |
217 |
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private transient volatile ReentrantLockQueueNode head = this; |
218 |
dl |
1.2 |
|
219 |
dl |
1.3 |
/** Tail of the wait queue, initialized to point to self as dummy node */ |
220 |
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private transient volatile ReentrantLockQueueNode tail = this; |
221 |
dl |
1.2 |
|
222 |
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// Atomics support |
223 |
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224 |
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private final static AtomicReferenceFieldUpdater<ReentrantLock, Thread> ownerUpdater = new AtomicReferenceFieldUpdater<ReentrantLock, Thread>(new ReentrantLock[0], new Thread[0], "owner"); |
225 |
dl |
1.3 |
private final static AtomicReferenceFieldUpdater<ReentrantLock, ReentrantLockQueueNode> tailUpdater = new AtomicReferenceFieldUpdater<ReentrantLock, ReentrantLockQueueNode>(new ReentrantLock[0], new ReentrantLockQueueNode[0], "tail"); |
226 |
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private final static AtomicReferenceFieldUpdater<ReentrantLock, ReentrantLockQueueNode> headUpdater = new AtomicReferenceFieldUpdater<ReentrantLock, ReentrantLockQueueNode>(new ReentrantLock[0], new ReentrantLockQueueNode[0], "head"); |
227 |
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private final static AtomicIntegerFieldUpdater<ReentrantLockQueueNode> releaseStatusUpdater = |
228 |
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new AtomicIntegerFieldUpdater<ReentrantLockQueueNode>(new ReentrantLockQueueNode[0], "releaseStatus"); |
229 |
dl |
1.2 |
|
230 |
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private boolean acquireOwner(Thread current) { |
231 |
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return ownerUpdater.compareAndSet(this, null, current); |
232 |
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} |
233 |
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234 |
dl |
1.3 |
private boolean casTail(ReentrantLockQueueNode cmp, ReentrantLockQueueNode val) { |
235 |
dl |
1.2 |
return tailUpdater.compareAndSet(this, cmp, val); |
236 |
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} |
237 |
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238 |
dl |
1.3 |
private boolean casHead(ReentrantLockQueueNode cmp, ReentrantLockQueueNode val) { |
239 |
dl |
1.2 |
return headUpdater.compareAndSet(this, cmp, val); |
240 |
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} |
241 |
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242 |
dl |
1.3 |
// casReleaseStatus non-private because also accessed by Conditions |
243 |
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final boolean casReleaseStatus(ReentrantLockQueueNode node, int cmp, int val) { |
244 |
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return releaseStatusUpdater.compareAndSet(node, cmp, val); |
245 |
dl |
1.2 |
} |
246 |
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247 |
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/** |
248 |
dl |
1.3 |
* Special value for releaseStatus indicating that node is cancelled. |
249 |
dl |
1.2 |
* Must be a large positive number. |
250 |
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*/ |
251 |
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static private final int CANCELLED = Integer.MAX_VALUE; |
252 |
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253 |
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/** |
254 |
dl |
1.3 |
* Special value for node releaseStatus indicating that node is on a |
255 |
dl |
1.2 |
* condition queue. Must be large negative number. |
256 |
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*/ |
257 |
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static private final int ON_CONDITION_QUEUE = Integer.MIN_VALUE; |
258 |
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259 |
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/** |
260 |
dl |
1.3 |
* Special value for node releaseStatus indicating that node is in |
261 |
dl |
1.2 |
* process of transfer. Must be negative and greater than |
262 |
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* ON_CONDITION_QUEUE. |
263 |
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*/ |
264 |
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static private final int TRANSFERRING = ON_CONDITION_QUEUE+1; |
265 |
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266 |
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267 |
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/** |
268 |
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* Utility to throw an exception if lock not held by given thread. |
269 |
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*/ |
270 |
|
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final void checkOwner(Thread current) { |
271 |
|
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if (current != owner) |
272 |
|
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throw new IllegalMonitorStateException(); |
273 |
|
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} |
274 |
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275 |
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/** |
276 |
dl |
1.5 |
* Return whether lock wait queue is empty |
277 |
dl |
1.2 |
*/ |
278 |
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final boolean queueEmpty() { |
279 |
dl |
1.3 |
ReentrantLockQueueNode h = head; // force order of the volatile reads |
280 |
dl |
1.2 |
return h == tail; |
281 |
|
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} |
282 |
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283 |
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/** |
284 |
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* Insert node into queue. Return predecessor. |
285 |
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*/ |
286 |
dl |
1.3 |
private ReentrantLockQueueNode enq(ReentrantLockQueueNode node) { |
287 |
dl |
1.2 |
for (;;) { |
288 |
dl |
1.3 |
ReentrantLockQueueNode p = tail; |
289 |
dl |
1.2 |
node.prev = p; // prev must be valid before/upon CAS |
290 |
|
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if (casTail(p, node)) { |
291 |
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p.next = node; // Note: next field assignment lags CAS |
292 |
|
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return p; |
293 |
|
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} |
294 |
|
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} |
295 |
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} |
296 |
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297 |
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/** |
298 |
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* Return true if it is OK to take fast path to lock. |
299 |
|
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* Overridden in FairReentrantLock. |
300 |
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*/ |
301 |
|
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boolean canBarge() { |
302 |
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return true; |
303 |
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} |
304 |
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305 |
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/** |
306 |
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* Main locking code, parameterized across different policies. |
307 |
|
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* @param current current thread |
308 |
dl |
1.7 |
* @param node its wait-node, if it already exists; else null in |
309 |
dl |
1.2 |
* which case it is created, |
310 |
dl |
1.7 |
* @param interruptible - true if can abort for interrupt or timeout |
311 |
dl |
1.2 |
* @param nanos time to wait, or zero if untimed |
312 |
dl |
1.6 |
* @return true if lock acquired (can be false only if interruptible) |
313 |
dl |
1.2 |
*/ |
314 |
dl |
1.6 |
final boolean doLock(Thread current, |
315 |
|
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ReentrantLockQueueNode node, |
316 |
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boolean interruptible, |
317 |
|
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long nanos) { |
318 |
dl |
1.2 |
/* |
319 |
|
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* Bypass queueing if a recursive lock |
320 |
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*/ |
321 |
|
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if (owner == current) { |
322 |
|
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++recursions; |
323 |
dl |
1.6 |
return true; |
324 |
dl |
1.2 |
} |
325 |
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|
326 |
dl |
1.7 |
long lastTime = 0; // for adjusting timeouts, below |
327 |
|
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boolean interrupted = false; // for restoring interrupt status on exit |
328 |
dl |
1.2 |
|
329 |
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/* |
330 |
dl |
1.3 |
* p is our predecessor node, that holds releaseStatus giving |
331 |
dl |
1.2 |
* permission to try to obtain lock if we are first in queue. |
332 |
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*/ |
333 |
dl |
1.3 |
ReentrantLockQueueNode p; |
334 |
dl |
1.2 |
|
335 |
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/* |
336 |
|
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* Create and enqueue node if not already created. Nodes |
337 |
|
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* transferred from condition queues will already be created |
338 |
|
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* and queued. |
339 |
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*/ |
340 |
|
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if (node == null) { |
341 |
dl |
1.3 |
node = new ReentrantLockQueueNode(current); |
342 |
dl |
1.2 |
p = enq(node); |
343 |
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} |
344 |
|
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else |
345 |
|
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p = node.prev; |
346 |
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|
347 |
|
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/* |
348 |
|
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* Repeatedly try to get ownership if first in queue, else |
349 |
|
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* block. |
350 |
|
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*/ |
351 |
|
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for (;;) { |
352 |
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/* |
353 |
|
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* If we are the first thread in queue, try to get the |
354 |
|
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* lock. (We must not try to get lock if we are not |
355 |
|
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* first.) Note that if we become first after p == head |
356 |
|
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* check, all is well -- we can be sure an unlocking |
357 |
|
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* thread will signal us. |
358 |
|
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*/ |
359 |
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|
360 |
|
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if (p == head && acquireOwner(current)) { |
361 |
dl |
1.6 |
if (interrupted) // re-interrupt on exit |
362 |
dl |
1.2 |
current.interrupt(); |
363 |
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|
364 |
|
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p.next = null; // clear for GC and to suppress signals |
365 |
|
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node.thread = null; |
366 |
|
|
node.prev = null; |
367 |
|
|
head = node; |
368 |
dl |
1.6 |
return true; |
369 |
dl |
1.2 |
} |
370 |
|
|
|
371 |
dl |
1.3 |
int releaseStatus = p.releaseStatus; |
372 |
dl |
1.2 |
|
373 |
|
|
/* |
374 |
|
|
* If our predecessor was cancelled, use its predecessor. |
375 |
|
|
* There will always be a non-cancelled one somewhere |
376 |
|
|
* because head node is never cancelled, so at worst we |
377 |
|
|
* will hit it. (Note that because head is never |
378 |
|
|
* cancelled, we can perform this check after trying to |
379 |
|
|
* acquire ownership). |
380 |
|
|
*/ |
381 |
dl |
1.3 |
if (releaseStatus == CANCELLED) { |
382 |
dl |
1.2 |
node.prev = p = p.prev; |
383 |
|
|
} |
384 |
|
|
|
385 |
|
|
/* |
386 |
|
|
* Wait if we are not not first in queue, or if we are |
387 |
|
|
* first, we have tried to acquire owner and failed since |
388 |
dl |
1.3 |
* either entry or last release. (Note that releaseStatus can |
389 |
dl |
1.2 |
* already be less than zero if we spuriously returned |
390 |
|
|
* from a previous park or got new a predecessor due to |
391 |
|
|
* cancellation.) |
392 |
|
|
* |
393 |
dl |
1.3 |
* We also don't wait if atomic decrement of releaseStatus |
394 |
dl |
1.2 |
* fails. We just continue main loop on failure to |
395 |
dl |
1.3 |
* atomically update releaseStatus because interference |
396 |
dl |
1.2 |
* causing failure is almost surely due to someone |
397 |
|
|
* releasing us anyway. |
398 |
|
|
* |
399 |
|
|
* Each wait consumes all available releases. Normally |
400 |
|
|
* there is only one anyway because release doesn't bother |
401 |
|
|
* incrementing if already positive. |
402 |
|
|
* |
403 |
|
|
*/ |
404 |
dl |
1.6 |
else if (casReleaseStatus(p, releaseStatus, |
405 |
|
|
(releaseStatus > 0)? 0 : -1) && |
406 |
|
|
releaseStatus <= 0) { |
407 |
dl |
1.2 |
|
408 |
|
|
// Update and check timeout value |
409 |
|
|
if (nanos > 0) { |
410 |
|
|
long now = TimeUnit.nanoTime(); |
411 |
|
|
if (lastTime != 0) { |
412 |
|
|
nanos -= now - lastTime; |
413 |
dl |
1.6 |
if (nanos == 0) // avoid zero |
414 |
|
|
nanos = -1; |
415 |
dl |
1.2 |
} |
416 |
|
|
lastTime = now; |
417 |
|
|
} |
418 |
|
|
|
419 |
dl |
1.6 |
if (nanos >= 0) |
420 |
dl |
1.2 |
JSR166Support.park(false, nanos); |
421 |
|
|
|
422 |
dl |
1.6 |
if (!interruptible) { |
423 |
|
|
if (Thread.interrupted()) // consume interrupt for now |
424 |
|
|
interrupted = true; |
425 |
|
|
} |
426 |
|
|
else if (nanos < 0 || current.isInterrupted()) { |
427 |
dl |
1.2 |
node.thread = null; // disable signals |
428 |
dl |
1.3 |
releaseStatusUpdater.set(node, CANCELLED); // don't need CAS here |
429 |
dl |
1.2 |
signalSuccessor(node); |
430 |
dl |
1.6 |
return false; |
431 |
dl |
1.2 |
} |
432 |
|
|
} |
433 |
|
|
} |
434 |
|
|
} |
435 |
tim |
1.1 |
|
436 |
|
|
/** |
437 |
dl |
1.2 |
* Wake up node's successor, if one exists |
438 |
tim |
1.1 |
*/ |
439 |
dl |
1.3 |
private void signalSuccessor(ReentrantLockQueueNode node) { |
440 |
dl |
1.2 |
/* |
441 |
|
|
* Find successor -- normally just node.next. |
442 |
|
|
*/ |
443 |
dl |
1.3 |
ReentrantLockQueueNode s = node.next; |
444 |
dl |
1.2 |
|
445 |
|
|
/* |
446 |
|
|
* if s is cancelled, traverse through next's. |
447 |
|
|
*/ |
448 |
|
|
|
449 |
dl |
1.3 |
while (s != null && s.releaseStatus == CANCELLED) { |
450 |
dl |
1.2 |
node = s; |
451 |
|
|
s = s.next; |
452 |
|
|
} |
453 |
|
|
|
454 |
|
|
/* |
455 |
|
|
* If successor appears to be null, check to see if a newly |
456 |
|
|
* queued node is successor by starting at tail and working |
457 |
|
|
* backwards. If so, help out the enqueing thread by setting |
458 |
|
|
* next field. We don't expect this loop to trigger often, |
459 |
|
|
* and hardly ever to iterate. |
460 |
|
|
*/ |
461 |
|
|
|
462 |
|
|
if (s == null) { |
463 |
dl |
1.3 |
ReentrantLockQueueNode t = tail; |
464 |
dl |
1.2 |
for (;;) { |
465 |
|
|
/* |
466 |
|
|
* If t == node, there is no successor. |
467 |
|
|
*/ |
468 |
|
|
if (t == node) |
469 |
|
|
return; |
470 |
|
|
|
471 |
dl |
1.3 |
ReentrantLockQueueNode tp = t.prev; |
472 |
dl |
1.2 |
|
473 |
|
|
/* |
474 |
|
|
* t's predecessor is null if we are lagging so far |
475 |
|
|
* behind the actions of other nodes/threads that an |
476 |
|
|
* intervening head.prev was nulled by some |
477 |
|
|
* non-cancelled successor of node. In which case, |
478 |
|
|
* there's no live successor. |
479 |
|
|
*/ |
480 |
|
|
|
481 |
|
|
if (tp == null) |
482 |
|
|
return; |
483 |
|
|
|
484 |
|
|
/* |
485 |
|
|
* If we find successor, we can do the assignment to |
486 |
|
|
* next (don't even need CAS) on behalf of enqueuing |
487 |
|
|
* thread. At worst we will stall now and lag behind |
488 |
|
|
* both the setting and the later clearing of next |
489 |
|
|
* field. But if so, we will reattach an internal link |
490 |
|
|
* in soon-to-be unreachable set of nodes, so no harm |
491 |
|
|
* done. |
492 |
|
|
*/ |
493 |
|
|
|
494 |
|
|
if (tp == node) { |
495 |
|
|
node.next = s = t; |
496 |
|
|
break; |
497 |
|
|
} |
498 |
|
|
|
499 |
|
|
t = tp; |
500 |
|
|
|
501 |
|
|
/* |
502 |
|
|
* Before iterating, check to see if link has |
503 |
|
|
* appeared. |
504 |
|
|
*/ |
505 |
dl |
1.3 |
ReentrantLockQueueNode n = node.next; |
506 |
dl |
1.2 |
if (n != null) { |
507 |
|
|
s = n; |
508 |
|
|
break; |
509 |
|
|
} |
510 |
|
|
} |
511 |
|
|
} |
512 |
|
|
|
513 |
|
|
Thread thr = s.thread; |
514 |
|
|
if (thr != null && thr != owner) // don't bother signalling if has lock |
515 |
|
|
JSR166Support.unpark(thr); |
516 |
|
|
} |
517 |
|
|
|
518 |
|
|
|
519 |
|
|
/** |
520 |
dl |
1.3 |
* Increment releaseStatus and signal next thread in queue if one |
521 |
dl |
1.2 |
* exists and is waiting. Called only by unlock. This code is split |
522 |
|
|
* out from unlock to encourage inlining of non-contended cases. |
523 |
|
|
*/ |
524 |
dl |
1.4 |
private void releaseFirst() { |
525 |
dl |
1.2 |
for (;;) { |
526 |
dl |
1.4 |
ReentrantLockQueueNode h = head; |
527 |
|
|
if (h == tail) // No successor |
528 |
|
|
return; |
529 |
|
|
|
530 |
dl |
1.3 |
int c = h.releaseStatus; |
531 |
dl |
1.2 |
if (c > 0) // Don't need signal if already positive |
532 |
|
|
return; |
533 |
|
|
if (owner != null) // Don't bother if some thread got lock |
534 |
|
|
return; |
535 |
dl |
1.6 |
|
536 |
dl |
1.3 |
if (casReleaseStatus(h, c, (c < 0)? 0 : 1)) { // saturate at 1 |
537 |
dl |
1.2 |
if (c < 0) |
538 |
|
|
signalSuccessor(h); |
539 |
|
|
return; |
540 |
|
|
} |
541 |
dl |
1.6 |
// else retry if CAS fails |
542 |
dl |
1.2 |
} |
543 |
|
|
} |
544 |
tim |
1.1 |
|
545 |
|
|
/** |
546 |
dholmes |
1.9 |
* Attempts to release this lock. |
547 |
|
|
* <p>If the current thread is the |
548 |
dl |
1.2 |
* holder of this lock then the hold count is decremented. If the |
549 |
dholmes |
1.9 |
* hold count is now zero then the lock is released. If the |
550 |
dl |
1.2 |
* current thread is not the holder of this lock then {@link |
551 |
|
|
* IllegalMonitorStateException} is thrown. |
552 |
|
|
* @throws IllegalMonitorStateException if the current thread does not |
553 |
|
|
* hold this lock. |
554 |
|
|
*/ |
555 |
|
|
public void unlock() { |
556 |
|
|
checkOwner(Thread.currentThread()); |
557 |
dl |
1.6 |
if (recursions > 0) |
558 |
dl |
1.2 |
--recursions; |
559 |
dl |
1.6 |
else { |
560 |
|
|
ownerUpdater.set(this, null); |
561 |
|
|
if (tail != this) // don't bother if never contended |
562 |
|
|
releaseFirst(); |
563 |
dl |
1.2 |
} |
564 |
|
|
} |
565 |
|
|
|
566 |
|
|
/** |
567 |
|
|
* Acquire the lock. |
568 |
dholmes |
1.9 |
* <p>Acquires the lock if it is not held by another thread and returns |
569 |
tim |
1.1 |
* immediately, setting the lock hold count to one. |
570 |
|
|
* <p>If the current thread |
571 |
|
|
* already holds the lock then the hold count is incremented by one and |
572 |
|
|
* the method returns immediately. |
573 |
|
|
* <p>If the lock is held by another thread then the |
574 |
dholmes |
1.9 |
* current thread becomes disabled for thread scheduling |
575 |
|
|
* purposes and lies dormant until the lock has been acquired, |
576 |
tim |
1.1 |
* at which time the lock hold count is set to one. |
577 |
|
|
*/ |
578 |
dl |
1.2 |
public void lock() { |
579 |
|
|
Thread current = Thread.currentThread(); |
580 |
dl |
1.6 |
if (!canBarge() || !acquireOwner(current)) |
581 |
|
|
doLock(current, null, false, 0); |
582 |
dl |
1.7 |
|
583 |
dl |
1.2 |
} |
584 |
tim |
1.1 |
|
585 |
|
|
/** |
586 |
|
|
* Acquires the lock unless the current thread is |
587 |
|
|
* {@link Thread#interrupt interrupted}. |
588 |
|
|
* <p>Acquires the lock if it is not held by another thread and returns |
589 |
|
|
* immediately, setting the lock hold count to one. |
590 |
|
|
* <p>If the current thread already holds this lock then the hold count |
591 |
|
|
* is incremented by one and the method returns immediately. |
592 |
|
|
* <p>If the lock is held by another thread then the |
593 |
dholmes |
1.9 |
* current thread becomes disabled for thread scheduling |
594 |
tim |
1.1 |
* purposes and lies dormant until one of two things happens: |
595 |
|
|
* <ul> |
596 |
|
|
* <li> The lock is acquired by the current thread; or |
597 |
|
|
* <li> Some other thread {@link Thread#interrupt interrupts} the current |
598 |
|
|
* thread. |
599 |
|
|
* </ul> |
600 |
|
|
* <p>If the lock is acquired by the current thread then the lock hold |
601 |
|
|
* count is set to one. |
602 |
|
|
* <p>If the current thread: |
603 |
|
|
* <ul> |
604 |
|
|
* <li>has its interrupted status set on entry to this method; or |
605 |
dholmes |
1.13 |
* <li>is {@link Thread#interrupt interrupted} while acquiring |
606 |
tim |
1.1 |
* the lock, |
607 |
|
|
* </ul> |
608 |
|
|
* then {@link InterruptedException} is thrown and the current thread's |
609 |
dholmes |
1.13 |
* interrupted status is cleared. |
610 |
|
|
* <p>As this method is an explicit interruption point, preference is |
611 |
|
|
* given to responding to the interrupt over normal or reentrant |
612 |
|
|
* acquisition of the lock. |
613 |
tim |
1.1 |
* |
614 |
dholmes |
1.9 |
* @throws InterruptedException if the current thread is interrupted |
615 |
tim |
1.1 |
*/ |
616 |
dl |
1.2 |
public void lockInterruptibly() throws InterruptedException { |
617 |
|
|
Thread current = Thread.currentThread(); |
618 |
dl |
1.10 |
if (!Thread.interrupted()) { |
619 |
dl |
1.12 |
if ((canBarge() && acquireOwner(current)) || |
620 |
|
|
doLock(current, null, true, 0)) |
621 |
dl |
1.10 |
return; |
622 |
dl |
1.12 |
Thread.interrupted(); // clear interrupt status on failure |
623 |
dl |
1.10 |
} |
624 |
|
|
throw new InterruptedException(); |
625 |
dl |
1.2 |
} |
626 |
tim |
1.1 |
|
627 |
|
|
/** |
628 |
|
|
* Acquires the lock only if it is not held by another thread at the time |
629 |
|
|
* of invocation. |
630 |
|
|
* <p>Acquires the lock if it is not held by another thread and returns |
631 |
|
|
* immediately with the value <tt>true</tt>, setting the lock hold count |
632 |
|
|
* to one. |
633 |
|
|
* <p> If the current thread |
634 |
|
|
* already holds this lock then the hold count is incremented by one and |
635 |
dl |
1.5 |
* the method returns <tt>true</tt>. |
636 |
tim |
1.1 |
* <p>If the lock is held by another thread then this method will return |
637 |
|
|
* immediately with the value <tt>false</tt>. |
638 |
|
|
* |
639 |
|
|
* @return <tt>true</tt>if the lock was free and was acquired by the |
640 |
|
|
* current thread, or the lock was already held by the current thread; and |
641 |
|
|
* <tt>false</tt> otherwise. |
642 |
|
|
*/ |
643 |
|
|
public boolean tryLock() { |
644 |
dl |
1.2 |
Thread current = Thread.currentThread(); |
645 |
|
|
if (acquireOwner(current)) |
646 |
|
|
return true; |
647 |
|
|
if (owner == current) { |
648 |
|
|
++recursions; |
649 |
|
|
return true; |
650 |
|
|
} |
651 |
tim |
1.1 |
return false; |
652 |
|
|
} |
653 |
|
|
|
654 |
|
|
/** |
655 |
|
|
* |
656 |
dholmes |
1.13 |
* Acquires the lock if it is not held by another thread within the given |
657 |
|
|
* waiting time and the current thread has not been |
658 |
|
|
* {@link Thread#interrupt interrupted}. |
659 |
tim |
1.1 |
* <p>Acquires the lock if it is not held by another thread and returns |
660 |
|
|
* immediately with the value <tt>true</tt>, setting the lock hold count |
661 |
|
|
* to one. |
662 |
|
|
* <p> If the current thread |
663 |
|
|
* already holds this lock then the hold count is incremented by one and |
664 |
dl |
1.5 |
* the method returns <tt>true</tt>. |
665 |
tim |
1.1 |
* <p>If the lock is held by another thread then the |
666 |
dholmes |
1.9 |
* current thread becomes disabled for thread scheduling |
667 |
tim |
1.1 |
* purposes and lies dormant until one of three things happens: |
668 |
|
|
* <ul> |
669 |
|
|
* <li> The lock is acquired by the current thread; or |
670 |
|
|
* <li> Some other thread {@link Thread#interrupt interrupts} the current |
671 |
|
|
* thread; or |
672 |
|
|
* <li> The specified waiting time elapses |
673 |
|
|
* </ul> |
674 |
|
|
* <p>If the lock is acquired then the value <tt>true</tt> is returned and |
675 |
|
|
* the lock hold count is set to one. |
676 |
|
|
* <p>If the current thread: |
677 |
|
|
* <ul> |
678 |
|
|
* <li>has its interrupted status set on entry to this method; or |
679 |
dholmes |
1.13 |
* <li>is {@link Thread#interrupt interrupted} while acquiring |
680 |
tim |
1.1 |
* the lock, |
681 |
|
|
* </ul> |
682 |
|
|
* then {@link InterruptedException} is thrown and the current thread's |
683 |
dholmes |
1.13 |
* interrupted status is cleared. |
684 |
|
|
* <p>As this method is an explicit interruption point, preference is |
685 |
|
|
* given to responding to the interrupt over normal or reentrant |
686 |
|
|
* acquisition of the lock, and over reporting the elapse of the waiting |
687 |
|
|
* time. |
688 |
tim |
1.1 |
* <p>If the specified waiting time elapses then the value <tt>false</tt> |
689 |
|
|
* is returned. |
690 |
dholmes |
1.13 |
* The given waiting time is a best-effort lower bound. If the time is |
691 |
tim |
1.1 |
* less than or equal to zero, the method will not wait at all. |
692 |
|
|
* |
693 |
|
|
* |
694 |
|
|
* @return <tt>true</tt> if the lock was free and was acquired by the |
695 |
|
|
* current thread, or the lock was already held by the current thread; and |
696 |
|
|
* <tt>false</tt> if the waiting time elapsed before the lock could be |
697 |
|
|
* acquired. |
698 |
|
|
* |
699 |
|
|
* @throws InterruptedException if the current thread is interrupted |
700 |
dholmes |
1.9 |
* |
701 |
tim |
1.1 |
*/ |
702 |
dl |
1.2 |
public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException { |
703 |
|
|
if (unit == null) |
704 |
|
|
throw new NullPointerException(); |
705 |
|
|
if (Thread.interrupted()) |
706 |
|
|
throw new InterruptedException(); |
707 |
|
|
Thread current = Thread.currentThread(); |
708 |
|
|
if (canBarge() && acquireOwner(current)) |
709 |
|
|
return true; |
710 |
dl |
1.6 |
if (owner == current) { // check recursions before timeout |
711 |
dl |
1.2 |
++recursions; |
712 |
|
|
return true; |
713 |
|
|
} |
714 |
|
|
if (timeout <= 0) |
715 |
|
|
return false; |
716 |
dl |
1.6 |
if (doLock(current, null, true, unit.toNanos(timeout))) |
717 |
dl |
1.2 |
return true; |
718 |
dl |
1.6 |
if (Thread.interrupted()) |
719 |
dl |
1.2 |
throw new InterruptedException(); |
720 |
dl |
1.6 |
return false; // timed out |
721 |
tim |
1.1 |
} |
722 |
|
|
|
723 |
|
|
|
724 |
|
|
/** |
725 |
|
|
* Queries the number of holds on this lock by the current thread. |
726 |
|
|
* <p>A thread has a hold on a lock for each lock action that is not |
727 |
|
|
* matched by an unlock action. |
728 |
|
|
* <p>The hold count information is typically only used for testing and |
729 |
|
|
* debugging purposes. For example, if a certain section of code should |
730 |
|
|
* not be entered with the lock already held then we can assert that |
731 |
|
|
* fact: |
732 |
|
|
* <pre> |
733 |
|
|
* class X { |
734 |
|
|
* ReentrantLock lock = new ReentrantLock(); |
735 |
|
|
* // ... |
736 |
|
|
* |
737 |
|
|
* public void m() { |
738 |
|
|
* assert lock.getHoldCount() == 0; |
739 |
|
|
* lock.lock(); |
740 |
|
|
* try { |
741 |
|
|
* // ... method body |
742 |
|
|
* } finally { |
743 |
|
|
* lock.unlock() |
744 |
|
|
* } |
745 |
|
|
* } |
746 |
|
|
* } |
747 |
|
|
* </pre> |
748 |
|
|
* |
749 |
dholmes |
1.13 |
* @return the number of holds on this lock by the current thread, |
750 |
|
|
* or zero if this lock is not held by the current thread. |
751 |
tim |
1.1 |
**/ |
752 |
|
|
public int getHoldCount() { |
753 |
dl |
1.2 |
return (owner == Thread.currentThread()) ? recursions + 1 : 0; |
754 |
tim |
1.1 |
} |
755 |
|
|
|
756 |
|
|
/** |
757 |
|
|
* Queries if this lock is held by the current thread. |
758 |
|
|
* <p>Analogous to the {@link Thread#holdsLock} method for built-in |
759 |
|
|
* monitor locks, this method is typically used for debugging and |
760 |
|
|
* testing. For example, a method that should only be called while |
761 |
|
|
* a lock is held can assert that this is the case: |
762 |
|
|
* <pre> |
763 |
|
|
* class X { |
764 |
|
|
* ReentrantLock lock = new ReentrantLock(); |
765 |
|
|
* // ... |
766 |
|
|
* |
767 |
|
|
* public void m() { |
768 |
|
|
* assert lock.isHeldByCurrentThread(); |
769 |
|
|
* // ... method body |
770 |
|
|
* } |
771 |
|
|
* } |
772 |
|
|
* </pre> |
773 |
|
|
* |
774 |
|
|
* @return <tt>true</tt> if current thread holds this lock and |
775 |
|
|
* <tt>false</tt> otherwise. |
776 |
|
|
**/ |
777 |
|
|
public boolean isHeldByCurrentThread() { |
778 |
dl |
1.2 |
return (owner == Thread.currentThread()); |
779 |
|
|
} |
780 |
|
|
|
781 |
|
|
|
782 |
|
|
/** |
783 |
dholmes |
1.9 |
* Queries if this lock is held by any thread. This method is |
784 |
dl |
1.2 |
* designed for use in monitoring, not for synchronization control. |
785 |
|
|
* @return <tt>true</tt> if any thread holds this lock and |
786 |
|
|
* <tt>false</tt> otherwise. |
787 |
|
|
**/ |
788 |
|
|
public boolean isLocked() { |
789 |
|
|
return owner != null; |
790 |
tim |
1.1 |
} |
791 |
|
|
|
792 |
dl |
1.3 |
/** |
793 |
|
|
* Reconstitute by resetting head and tail to point back to the lock. |
794 |
|
|
*/ |
795 |
|
|
private void readObject(java.io.ObjectInputStream s) |
796 |
|
|
throws java.io.IOException, ClassNotFoundException { |
797 |
|
|
s.defaultReadObject(); |
798 |
|
|
head = tail = this; |
799 |
|
|
} |
800 |
dl |
1.2 |
|
801 |
tim |
1.1 |
/** |
802 |
|
|
* Returns a {@link Condition} instance for use with this |
803 |
|
|
* {@link Lock} instance. |
804 |
|
|
* |
805 |
|
|
* <p>The returned {@link Condition} instance has the same behavior and |
806 |
|
|
* usage |
807 |
|
|
* restrictions with this lock as the {@link Object} monitor methods |
808 |
|
|
* ({@link Object#wait() wait}, {@link Object#notify notify}, and |
809 |
|
|
* {@link Object#notifyAll notifyAll}) have with the built-in monitor |
810 |
|
|
* lock: |
811 |
|
|
* <ul> |
812 |
|
|
* <li>If this lock is not held when any of the {@link Condition} |
813 |
|
|
* {@link Condition#await() waiting} or {@link Condition#signal signalling} |
814 |
|
|
* methods are called, then an {@link IllegalMonitorStateException} is |
815 |
|
|
* thrown. |
816 |
|
|
* <li>When the condition {@link Condition#await() waiting} methods are |
817 |
|
|
* called the lock is released and before they return the lock is |
818 |
|
|
* reacquired and the lock hold count restored to what it was when the |
819 |
|
|
* method was called. |
820 |
|
|
* <li>If a thread is {@link Thread#interrupt interrupted} while waiting |
821 |
|
|
* then the wait will terminate, an {@link InterruptedException} will be |
822 |
|
|
* thrown, and the thread's interrupted status will be cleared. |
823 |
|
|
* <li>The order in which waiting threads are signalled is not specified. |
824 |
|
|
* <li>The order in which threads returning from a wait, and threads trying |
825 |
|
|
* to acquire the lock, are granted the lock, is not specified. |
826 |
|
|
* </ul> |
827 |
|
|
*/ |
828 |
|
|
public Condition newCondition() { |
829 |
dl |
1.2 |
return new ReentrantLockConditionObject(); |
830 |
|
|
} |
831 |
|
|
|
832 |
|
|
// Helper methods for Conditions |
833 |
|
|
|
834 |
|
|
/** |
835 |
|
|
* Return true if a node, always one that was initially placed on |
836 |
|
|
* a condition queue, is off the condition queue (and thus, |
837 |
|
|
* normally is now on lock queue.) |
838 |
|
|
*/ |
839 |
dl |
1.3 |
boolean isOffConditionQueue(ReentrantLockQueueNode w) { |
840 |
|
|
return w.releaseStatus > TRANSFERRING; |
841 |
dl |
1.2 |
} |
842 |
|
|
|
843 |
|
|
/** |
844 |
dl |
1.6 |
* Transfer a node from a condition queue onto lock queue. |
845 |
dl |
1.2 |
* Return true if successful (i.e., node not cancelled) |
846 |
|
|
*/ |
847 |
dl |
1.3 |
final boolean transferToLockQueue(ReentrantLockQueueNode node) { |
848 |
dl |
1.2 |
/* |
849 |
|
|
* Atomically change status to TRANSFERRING to avoid races |
850 |
|
|
* with cancelling waiters. We use a special value that causes |
851 |
|
|
* any waiters spuriously waking up to re-park until the node |
852 |
|
|
* has been placed on lock queue. |
853 |
|
|
*/ |
854 |
dl |
1.3 |
if (!casReleaseStatus(node, ON_CONDITION_QUEUE, TRANSFERRING)) |
855 |
dl |
1.2 |
return false; |
856 |
|
|
|
857 |
|
|
/* |
858 |
|
|
* Splice onto queue |
859 |
|
|
*/ |
860 |
dl |
1.3 |
ReentrantLockQueueNode p = enq(node); |
861 |
dl |
1.2 |
|
862 |
|
|
/* |
863 |
dl |
1.3 |
* Establish normal lock-queue releaseStatus for node. The |
864 |
dl |
1.2 |
* CAS can fail if node already was involved in a cancellation |
865 |
|
|
* on lock-queue, in which case we signal to be sure. |
866 |
|
|
*/ |
867 |
dl |
1.3 |
if (!casReleaseStatus(node, TRANSFERRING, 0)) |
868 |
dl |
1.2 |
signalSuccessor(node); |
869 |
|
|
|
870 |
|
|
/* |
871 |
dl |
1.3 |
* Ensure releaseStatus of predecessor is negative to indicate |
872 |
|
|
* that thread is (probably) waiting. If attempt to set releaseStatus |
873 |
dl |
1.2 |
* fails or is pred is/becomes cancelled, wake up successor |
874 |
|
|
* (which will ordinarily be "node") to resynch. |
875 |
|
|
*/ |
876 |
|
|
|
877 |
|
|
for (;;) { |
878 |
dl |
1.3 |
int c = p.releaseStatus; |
879 |
|
|
if (c < 0 || (c != CANCELLED && casReleaseStatus(p, c, -1))) |
880 |
dl |
1.2 |
break; |
881 |
|
|
signalSuccessor(p); |
882 |
|
|
if (c == CANCELLED) |
883 |
|
|
break; |
884 |
|
|
} |
885 |
|
|
|
886 |
|
|
return true; |
887 |
tim |
1.1 |
} |
888 |
|
|
|
889 |
dl |
1.2 |
/** |
890 |
|
|
* Hook method used by ReentrantReadWriteLock. Called |
891 |
|
|
* before unlocking lock to enter wait. |
892 |
|
|
*/ |
893 |
|
|
void beforeWait() { } |
894 |
|
|
|
895 |
|
|
|
896 |
|
|
/** |
897 |
|
|
* Hook method used by ReentrantReadWriteLock. Called |
898 |
|
|
* after locking lock after exiting wait. |
899 |
|
|
*/ |
900 |
|
|
void afterWait() { } |
901 |
|
|
|
902 |
|
|
private class ReentrantLockConditionObject implements Condition, java.io.Serializable { |
903 |
|
|
/* |
904 |
|
|
* Because condition queues are accessed only when locks are |
905 |
|
|
* already held, we just need a simple linked queue to hold |
906 |
|
|
* nodes while they are waiting on conditions. They are then |
907 |
|
|
* transferred to the lock queue to re-acquire locks. |
908 |
|
|
*/ |
909 |
|
|
|
910 |
|
|
/** |
911 |
|
|
* First node of condition queue. |
912 |
|
|
*/ |
913 |
dl |
1.3 |
private transient ReentrantLockQueueNode firstWaiter; |
914 |
dl |
1.2 |
|
915 |
|
|
/** |
916 |
|
|
* Last node of condition queue. |
917 |
|
|
*/ |
918 |
dl |
1.3 |
private transient ReentrantLockQueueNode lastWaiter; |
919 |
dl |
1.2 |
|
920 |
|
|
/** |
921 |
|
|
* Basic linked queue insertion. |
922 |
|
|
*/ |
923 |
dl |
1.3 |
private ReentrantLockQueueNode addWaiter(Thread current) { |
924 |
|
|
ReentrantLockQueueNode w = new ReentrantLockQueueNode(current); |
925 |
|
|
w.releaseStatus = ON_CONDITION_QUEUE; |
926 |
dl |
1.2 |
if (lastWaiter == null) |
927 |
|
|
firstWaiter = lastWaiter = w; |
928 |
|
|
else { |
929 |
dl |
1.3 |
ReentrantLockQueueNode t = lastWaiter; |
930 |
dl |
1.2 |
lastWaiter = w; |
931 |
|
|
t.next = w; |
932 |
|
|
} |
933 |
|
|
return w; |
934 |
|
|
} |
935 |
|
|
|
936 |
|
|
/** |
937 |
|
|
* Main code for signal. Dequeue and transfer nodes until hit |
938 |
|
|
* non-cancelled one or null. Split out from signal to |
939 |
|
|
* encourage compilers to inline the case of no waiters. |
940 |
|
|
*/ |
941 |
dl |
1.3 |
private void doSignal(ReentrantLockQueueNode first) { |
942 |
dl |
1.2 |
do { |
943 |
|
|
if ( (firstWaiter = first.next) == null) |
944 |
|
|
lastWaiter = null; |
945 |
|
|
first.next = null; |
946 |
|
|
if (transferToLockQueue(first)) |
947 |
|
|
return; |
948 |
|
|
first = firstWaiter; |
949 |
|
|
} while (first != null); |
950 |
|
|
} |
951 |
|
|
|
952 |
|
|
public void signal() { |
953 |
|
|
checkOwner(Thread.currentThread()); |
954 |
dl |
1.3 |
ReentrantLockQueueNode w = firstWaiter; |
955 |
dl |
1.2 |
if (w != null) |
956 |
|
|
doSignal(w); |
957 |
|
|
} |
958 |
|
|
|
959 |
|
|
public void signalAll() { |
960 |
|
|
checkOwner(Thread.currentThread()); |
961 |
|
|
// Pull off list all at once and traverse. |
962 |
dl |
1.3 |
ReentrantLockQueueNode w = firstWaiter; |
963 |
dl |
1.2 |
if (w != null) { |
964 |
|
|
lastWaiter = firstWaiter = null; |
965 |
|
|
do { |
966 |
dl |
1.3 |
ReentrantLockQueueNode n = w.next; |
967 |
dl |
1.2 |
w.next = null; |
968 |
|
|
transferToLockQueue(w); |
969 |
|
|
w = n; |
970 |
|
|
} while (w != null); |
971 |
|
|
} |
972 |
|
|
} |
973 |
|
|
|
974 |
|
|
/* |
975 |
|
|
* Various flavors of wait. Each almost the same, but |
976 |
|
|
* annoyingly different and no nice way to factor common code. |
977 |
|
|
*/ |
978 |
|
|
|
979 |
|
|
public void await() throws InterruptedException { |
980 |
|
|
Thread current = Thread.currentThread(); |
981 |
|
|
checkOwner(current); |
982 |
|
|
|
983 |
dl |
1.3 |
ReentrantLockQueueNode w = addWaiter(current); |
984 |
dl |
1.2 |
beforeWait(); |
985 |
|
|
int recs = recursions; |
986 |
|
|
unlock(); |
987 |
|
|
|
988 |
|
|
boolean wasInterrupted = false; |
989 |
|
|
|
990 |
|
|
while (!isOffConditionQueue(w)) { |
991 |
|
|
JSR166Support.park(false, 0); |
992 |
|
|
if (Thread.interrupted()) { |
993 |
|
|
wasInterrupted = true; |
994 |
dl |
1.3 |
if (casReleaseStatus(w, ON_CONDITION_QUEUE, CANCELLED)) { |
995 |
dl |
1.2 |
w.thread = null; |
996 |
|
|
w = null; |
997 |
|
|
} |
998 |
|
|
break; |
999 |
|
|
} |
1000 |
|
|
} |
1001 |
|
|
|
1002 |
|
|
/* |
1003 |
|
|
* If we exited above loop due to cancellation, then w is |
1004 |
|
|
* null, and doLock will make a new lock node for |
1005 |
|
|
* us. Otherwise, upon exit, our node is already in the |
1006 |
|
|
* lock queue when doLock is called. |
1007 |
|
|
*/ |
1008 |
dl |
1.6 |
doLock(current, w, false, 0); |
1009 |
dl |
1.2 |
|
1010 |
|
|
recursions = recs; |
1011 |
|
|
afterWait(); |
1012 |
|
|
|
1013 |
dl |
1.6 |
if (wasInterrupted || Thread.interrupted()) |
1014 |
dl |
1.2 |
throw new InterruptedException(); |
1015 |
|
|
} |
1016 |
|
|
|
1017 |
|
|
public void awaitUninterruptibly() { |
1018 |
|
|
Thread current = Thread.currentThread(); |
1019 |
|
|
checkOwner(current); |
1020 |
|
|
|
1021 |
dl |
1.3 |
ReentrantLockQueueNode w = addWaiter(current); |
1022 |
dl |
1.2 |
beforeWait(); |
1023 |
|
|
int recs = recursions; |
1024 |
|
|
unlock(); |
1025 |
|
|
|
1026 |
|
|
boolean wasInterrupted = false; |
1027 |
|
|
while (!isOffConditionQueue(w)) { |
1028 |
|
|
JSR166Support.park(false, 0); |
1029 |
|
|
if (Thread.interrupted()) |
1030 |
|
|
wasInterrupted = true; |
1031 |
|
|
} |
1032 |
|
|
|
1033 |
dl |
1.6 |
doLock(current, w, false, 0); |
1034 |
dl |
1.2 |
recursions = recs; |
1035 |
|
|
afterWait(); |
1036 |
|
|
// avoid re-interrupts on exit |
1037 |
|
|
if (wasInterrupted && !current.isInterrupted()) |
1038 |
|
|
current.interrupt(); |
1039 |
|
|
} |
1040 |
|
|
|
1041 |
|
|
|
1042 |
|
|
public long awaitNanos(long nanos) throws InterruptedException { |
1043 |
|
|
Thread current = Thread.currentThread(); |
1044 |
|
|
checkOwner(current); |
1045 |
|
|
|
1046 |
dl |
1.3 |
ReentrantLockQueueNode w = addWaiter(current); |
1047 |
dl |
1.2 |
beforeWait(); |
1048 |
|
|
int recs = recursions; |
1049 |
|
|
unlock(); |
1050 |
|
|
|
1051 |
|
|
if (nanos <= 0) nanos = 1; // park arg must be positive |
1052 |
|
|
long timeLeft = nanos; |
1053 |
|
|
long startTime = TimeUnit.nanoTime(); |
1054 |
|
|
boolean wasInterrupted = false; |
1055 |
|
|
boolean cancelled = false; |
1056 |
|
|
|
1057 |
|
|
if (!isOffConditionQueue(w)) { |
1058 |
|
|
for (;;) { |
1059 |
|
|
JSR166Support.park(false, timeLeft); |
1060 |
|
|
if (Thread.interrupted()) |
1061 |
|
|
wasInterrupted = true; |
1062 |
|
|
else if (isOffConditionQueue(w)) |
1063 |
|
|
break; |
1064 |
|
|
else |
1065 |
|
|
timeLeft = nanos - (TimeUnit.nanoTime() - startTime); |
1066 |
|
|
|
1067 |
|
|
if (wasInterrupted || timeLeft <= 0) { |
1068 |
dl |
1.3 |
if (casReleaseStatus(w, ON_CONDITION_QUEUE, CANCELLED)) { |
1069 |
dl |
1.2 |
w.thread = null; |
1070 |
|
|
w = null; |
1071 |
|
|
} |
1072 |
|
|
break; |
1073 |
|
|
} |
1074 |
|
|
} |
1075 |
|
|
} |
1076 |
|
|
|
1077 |
dl |
1.6 |
doLock(current, w, false, 0); |
1078 |
dl |
1.2 |
recursions = recs; |
1079 |
|
|
afterWait(); |
1080 |
|
|
|
1081 |
dl |
1.6 |
if (wasInterrupted || Thread.interrupted()) |
1082 |
dl |
1.2 |
throw new InterruptedException(); |
1083 |
|
|
else if (timeLeft <= 0) |
1084 |
|
|
return timeLeft; |
1085 |
|
|
else |
1086 |
|
|
return nanos - (TimeUnit.nanoTime() - startTime); |
1087 |
|
|
} |
1088 |
|
|
|
1089 |
|
|
public boolean awaitUntil(Date deadline) throws InterruptedException { |
1090 |
|
|
Thread current = Thread.currentThread(); |
1091 |
|
|
checkOwner(current); |
1092 |
|
|
|
1093 |
dl |
1.3 |
ReentrantLockQueueNode w = addWaiter(current); |
1094 |
dl |
1.2 |
beforeWait(); |
1095 |
|
|
int recs = recursions; |
1096 |
|
|
unlock(); |
1097 |
|
|
|
1098 |
|
|
boolean wasInterrupted = false; |
1099 |
|
|
boolean cancelled = false; |
1100 |
|
|
long abstime = deadline.getTime(); |
1101 |
|
|
|
1102 |
|
|
if (!isOffConditionQueue(w)) { |
1103 |
|
|
for (;;) { |
1104 |
|
|
JSR166Support.park(true, abstime); |
1105 |
|
|
|
1106 |
|
|
boolean timedOut = false; |
1107 |
|
|
if (Thread.interrupted()) |
1108 |
|
|
wasInterrupted = true; |
1109 |
|
|
else if (isOffConditionQueue(w)) |
1110 |
|
|
break; |
1111 |
|
|
else if (System.currentTimeMillis() <= abstime) |
1112 |
|
|
timedOut = true; |
1113 |
|
|
|
1114 |
|
|
if (wasInterrupted || timedOut) { |
1115 |
dl |
1.3 |
if (casReleaseStatus(w, ON_CONDITION_QUEUE, CANCELLED)) { |
1116 |
dl |
1.2 |
w.thread = null; |
1117 |
|
|
w = null; |
1118 |
|
|
} |
1119 |
|
|
break; |
1120 |
|
|
} |
1121 |
|
|
} |
1122 |
|
|
} |
1123 |
tim |
1.1 |
|
1124 |
dl |
1.6 |
doLock(current, w, false, 0); |
1125 |
dl |
1.2 |
recursions = recs; |
1126 |
|
|
afterWait(); |
1127 |
tim |
1.1 |
|
1128 |
dl |
1.6 |
if (wasInterrupted || Thread.interrupted()) |
1129 |
dl |
1.2 |
throw new InterruptedException(); |
1130 |
|
|
return !cancelled; |
1131 |
|
|
} |
1132 |
tim |
1.1 |
|
1133 |
dl |
1.2 |
public boolean await(long time, TimeUnit unit) throws InterruptedException { |
1134 |
|
|
return awaitNanos(unit.toNanos(time)) > 0; |
1135 |
|
|
} |
1136 |
tim |
1.1 |
|
1137 |
dl |
1.2 |
} |
1138 |
|
|
|
1139 |
dl |
1.3 |
} |
1140 |
|
|
|
1141 |
|
|
/** |
1142 |
|
|
* Node class for threads waiting for locks. This cannot be nested |
1143 |
|
|
* inside ReentrantLock because of Java inheritance circularity rules. |
1144 |
|
|
*/ |
1145 |
|
|
class ReentrantLockQueueNode { |
1146 |
|
|
/** |
1147 |
|
|
* Controls whether successor node is allowed to try to obtain |
1148 |
|
|
* ownership. Acts as a saturating (in both directions) counting |
1149 |
|
|
* semaphore: Upon each wait, the releaseStatus is reduced to zero |
1150 |
|
|
* if positive, else reduced to negative, in which case the thread |
1151 |
|
|
* will park. The releaseStatus is incremented on each unlock that |
1152 |
|
|
* would enable successor thread to obtain lock (succeeding if |
1153 |
|
|
* there is no contention). The special value of CANCELLED is used |
1154 |
|
|
* to mean that the releaseStatus cannot be either incremented or |
1155 |
|
|
* decremented. The special value of ON_CONDITION_QUEUE is used |
1156 |
|
|
* when nodes are on conditions queues instead of lock queue, and |
1157 |
|
|
* the special value TRANSFERRING is used while signals are in |
1158 |
|
|
* progress. |
1159 |
|
|
*/ |
1160 |
|
|
transient volatile int releaseStatus; |
1161 |
|
|
|
1162 |
|
|
/** |
1163 |
|
|
* Link to predecessor node that current node/thread relies on |
1164 |
|
|
* for checking releaseStatus. Assigned once during enqueing, |
1165 |
|
|
* and nulled out (for sake of GC) only upon dequeuing. Upon |
1166 |
|
|
* cancellation, we do NOT adjust this field, but simply |
1167 |
|
|
* traverse through prev's until we hit a non-cancelled node. |
1168 |
|
|
* A valid predecessor will always exist because the head node |
1169 |
|
|
* is never cancelled. |
1170 |
|
|
*/ |
1171 |
|
|
transient volatile ReentrantLockQueueNode prev; |
1172 |
|
|
|
1173 |
|
|
/** |
1174 |
|
|
* Link to the successor node that the current node/thread |
1175 |
|
|
* unparks upon lock release. Assigned once during enquing. |
1176 |
|
|
* Upon cancellation, we do NOT adjust this field, but simply |
1177 |
|
|
* traverse through next's until we hit a non-cancelled node, |
1178 |
|
|
* (or null if at end of queue). The enqueue operation does |
1179 |
|
|
* not assign next field of a predecessor until after |
1180 |
|
|
* attachment, so seeing a null next field not necessarily |
1181 |
|
|
* mean that node is at end of queue. However, if a next field |
1182 |
|
|
* appears to be null, we can scan prev's from the tail to |
1183 |
|
|
* double-check. |
1184 |
|
|
*/ |
1185 |
|
|
transient volatile ReentrantLockQueueNode next; |
1186 |
|
|
|
1187 |
|
|
/** |
1188 |
|
|
* The thread that enqueued this node. Initialized on |
1189 |
|
|
* construction and nulled out after use. Note that this need |
1190 |
|
|
* not be declared volatile since it is always accessed after |
1191 |
|
|
* traversing volatile links, and written before writing |
1192 |
|
|
* links. |
1193 |
|
|
*/ |
1194 |
|
|
transient Thread thread; |
1195 |
|
|
|
1196 |
|
|
ReentrantLockQueueNode() { } |
1197 |
|
|
ReentrantLockQueueNode(Thread t) { thread = t; } |
1198 |
dl |
1.2 |
} |