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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.ArrayList; |
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import java.util.Collection; |
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import java.util.Date; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.ForkJoinPool; |
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import java.util.concurrent.RejectedExecutionException; |
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import jdk.internal.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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* Constructor for subclasses to call. |
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*/ |
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public AbstractQueuedLongSynchronizer() {} |
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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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// Node status bits, also used as argument and return values |
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static final int WAITING = 1; // must be 1 |
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static final int CANCELLED = 0x80000000; // must be negative |
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static final int COND = 2; // in a condition wait |
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|
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/** CLH Nodes */ |
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abstract static class Node { |
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volatile Node prev; // initially attached via casTail |
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volatile Node next; // visibly nonnull when signallable |
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Thread waiter; // visibly nonnull when enqueued |
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volatile int status; // written by owner, atomic bit ops by others |
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|
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// methods for atomic operations |
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final boolean casPrev(Node c, Node v) { // for cleanQueue |
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return U.weakCompareAndSetReference(this, PREV, c, v); |
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} |
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final boolean casNext(Node c, Node v) { // for cleanQueue |
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return U.weakCompareAndSetReference(this, NEXT, c, v); |
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} |
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final int getAndUnsetStatus(int v) { // for signalling |
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return U.getAndBitwiseAndInt(this, STATUS, ~v); |
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} |
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final void setPrevRelaxed(Node p) { // for off-queue assignment |
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U.putReference(this, PREV, p); |
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} |
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final void setStatusRelaxed(int s) { // for off-queue assignment |
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U.putInt(this, STATUS, s); |
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} |
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final void clearStatus() { // for reducing unneeded signals |
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U.putIntOpaque(this, STATUS, 0); |
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} |
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|
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private static final long STATUS |
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= U.objectFieldOffset(Node.class, "status"); |
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private static final long NEXT |
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= U.objectFieldOffset(Node.class, "next"); |
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private static final long PREV |
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= U.objectFieldOffset(Node.class, "prev"); |
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} |
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|
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// Concrete classes tagged by type |
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static final class ExclusiveNode extends Node { } |
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static final class SharedNode extends Node { } |
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|
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static final class ConditionNode extends Node |
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implements ForkJoinPool.ManagedBlocker { |
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ConditionNode nextWaiter; // link to next waiting node |
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|
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/** |
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* Allows Conditions to be used in ForkJoinPools without |
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* risking fixed pool exhaustion. This is usable only for |
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* untimed Condition waits, not timed versions. |
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*/ |
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public final boolean isReleasable() { |
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return status <= 1 || Thread.currentThread().isInterrupted(); |
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} |
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|
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public final boolean block() { |
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while (!isReleasable()) LockSupport.park(); |
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return true; |
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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. |
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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. After initialization, modified only via casTail. |
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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 {@code 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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return U.compareAndSetLong(this, STATE, expect, update); |
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} |
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|
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// Queuing utilities |
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|
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private boolean casTail(Node c, Node v) { |
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return U.compareAndSetReference(this, TAIL, c, v); |
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} |
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|
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/** tries once to CAS a new dummy node for head */ |
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private void tryInitializeHead() { |
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Node h = new ExclusiveNode(); |
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if (U.compareAndSetReference(this, HEAD, null, h)) |
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tail = h; |
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} |
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|
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/** |
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* Enqueues the node unless null. (Currently used only for |
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* ConditionNodes; other cases are interleaved with acquires.) |
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*/ |
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final void enqueue(Node node) { |
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if (node != null) { |
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for (;;) { |
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Node t = tail; |
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node.setPrevRelaxed(t); // avoid unnecessary fence |
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if (t == null) // initialize |
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tryInitializeHead(); |
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else if (casTail(t, node)) { |
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t.next = node; |
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if (t.status < 0) // wake up to clean link |
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LockSupport.unpark(node.waiter); |
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break; |
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} |
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} |
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} |
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} |
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|
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/** Returns true if node is found in traversal from tail */ |
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final boolean isEnqueued(Node node) { |
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for (Node t = tail; t != null; t = t.prev) |
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if (t == node) |
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return true; |
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return false; |
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} |
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|
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/** |
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* Wakes up the successor of given node, if one exists, and unsets its |
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* WAITING status to avoid park race. This may fail to wake up an |
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* eligible thread when one or more have been cancelled, but |
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* cancelAcquire ensures liveness. |
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*/ |
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private static void signalNext(Node h) { |
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Node s; |
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if (h != null && (s = h.next) != null && s.status != 0) { |
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s.getAndUnsetStatus(WAITING); |
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LockSupport.unpark(s.waiter); |
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} |
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} |
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|
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/** Wakes up the given node if in shared mode */ |
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private static void signalNextIfShared(Node h) { |
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Node s; |
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if (h != null && (s = h.next) != null && |
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(s instanceof SharedNode) && s.status != 0) { |
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s.getAndUnsetStatus(WAITING); |
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LockSupport.unpark(s.waiter); |
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} |
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} |
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|
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/** |
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* Main acquire method, invoked by all exported acquire methods. |
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* |
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* @param node null unless a reacquiring Condition |
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* @param arg the acquire argument |
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* @param shared true if shared mode else exclusive |
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* @param interruptible if abort and return negative on interrupt |
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* @param timed if true use timed waits |
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* @param time if timed, the System.nanoTime value to timeout |
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* @return positive if acquired, 0 if timed out, negative if interrupted |
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*/ |
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final int acquire(Node node, long arg, boolean shared, |
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boolean interruptible, boolean timed, long time) { |
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Thread current = Thread.currentThread(); |
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byte spins = 0, postSpins = 0; // retries upon unpark of first thread |
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boolean interrupted = false, first = false; |
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Node pred = null; // predecessor of node when enqueued |
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|
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/* |
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* Repeatedly: |
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* Check if node now first |
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* if so, ensure head stable, else ensure valid predecessor |
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* if node is first or not yet enqueued, try acquiring |
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* else if node not yet created, create it |
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* else if not yet enqueued, try once to enqueue |
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* else if woken from park, retry (up to postSpins times) |
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* else if WAITING status not set, set and retry |
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* else park and clear WAITING status, and check cancellation |
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*/ |
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|
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for (;;) { |
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if (!first && (pred = (node == null) ? null : node.prev) != null && |
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!(first = (head == pred))) { |
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if (pred.status < 0) { |
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cleanQueue(); // predecessor cancelled |
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continue; |
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} else if (pred.prev == null) { |
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Thread.onSpinWait(); // ensure serialization |
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continue; |
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} |
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} |
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if (first || pred == null) { |
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boolean acquired; |
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try { |
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if (shared) |
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acquired = (tryAcquireShared(arg) >= 0); |
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else |
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acquired = tryAcquire(arg); |
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} catch (Throwable ex) { |
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cancelAcquire(node, interrupted, false); |
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throw ex; |
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} |
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if (acquired) { |
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if (first) { |
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node.prev = null; |
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head = node; |
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pred.next = null; |
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node.waiter = null; |
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if (shared) |
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signalNextIfShared(node); |
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if (interrupted) |
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current.interrupt(); |
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} |
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return 1; |
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} |
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} |
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if (node == null) { // allocate; retry before enqueue |
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if (shared) |
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node = new SharedNode(); |
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else |
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node = new ExclusiveNode(); |
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} else if (pred == null) { // try to enqueue |
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node.waiter = current; |
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Node t = tail; |
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node.setPrevRelaxed(t); // avoid unnecessary fence |
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if (t == null) |
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tryInitializeHead(); |
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else if (!casTail(t, node)) |
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node.setPrevRelaxed(null); // back out |
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else |
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t.next = node; |
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} else if (first && spins != 0) { |
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--spins; // reduce unfairness on rewaits |
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Thread.onSpinWait(); |
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} else if (node.status == 0) { |
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node.status = WAITING; // enable signal and recheck |
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} else { |
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long nanos; |
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spins = postSpins = (byte)((postSpins << 1) | 1); |
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if (!timed) |
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LockSupport.park(this); |
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else if ((nanos = time - System.nanoTime()) > 0L) |
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LockSupport.parkNanos(this, nanos); |
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else |
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break; |
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node.clearStatus(); |
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if ((interrupted |= Thread.interrupted()) && interruptible) |
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break; |
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} |
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} |
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return cancelAcquire(node, interrupted, interruptible); |
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} |
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|
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/** |
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* Possibly repeatedly traverses from tail, unsplicing cancelled |
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* nodes until none are found. |
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*/ |
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private void cleanQueue() { |
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for (;;) { // restart point |
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for (Node q = tail, s = null, p, n;;) { // (p, q, s) triples |
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if (q == null || (p = q.prev) == null) |
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return; // end of list |
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if (s == null ? tail != q : (s.prev != q || s.status < 0)) |
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break; // inconsistent |
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if (q.status < 0) { // cancelled |
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if ((s == null ? casTail(q, p) : s.casPrev(q, p)) && |
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q.prev == p) { |
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p.casNext(q, s); // OK if fails |
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if (p.prev == null) |
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signalNext(p); |
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} |
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break; |
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} |
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if ((n = p.next) != q) { // help finish |
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if (n != null && q.prev == p) { |
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p.casNext(n, q); |
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if (p.prev == null) |
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signalNext(p); |
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} |
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break; |
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} |
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s = q; |
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q = q.prev; |
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} |
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} |
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} |
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|
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/** |
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* Cancels an ongoing attempt to acquire. |
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* |
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* @param node the node (may be null if cancelled before enqueuing) |
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* @param interrupted true if thread interrupted |
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* @param interruptible if should report interruption vs reset |
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*/ |
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private int cancelAcquire(Node node, boolean interrupted, |
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boolean interruptible) { |
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if (node != null) { |
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node.waiter = null; |
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node.status = CANCELLED; |
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if (node.prev != null) |
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cleanQueue(); |
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} |
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if (interrupted) { |
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if (interruptible) |
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return CANCELLED; |
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else |
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Thread.currentThread().interrupt(); |
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} |
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return 0; |
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} |
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|
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// Main exported methods |
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|
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/** |
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* Attempts to acquire in exclusive mode. This method should query |
394 |
* if the state of the object permits it to be acquired in the |
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* exclusive mode, and if so to acquire it. |
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* |
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* <p>This method is always invoked by the thread performing |
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* acquire. If this method reports failure, the acquire method |
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* may queue the thread, if it is not already queued, until it is |
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* signalled by a release from some other thread. This can be used |
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* to implement method {@link Lock#tryLock()}. |
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* |
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* <p>The default |
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* implementation throws {@link UnsupportedOperationException}. |
405 |
* |
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* @param arg the acquire argument. This value is always the one |
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* passed to an acquire method, or is the value saved on entry |
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* to a condition wait. The value is otherwise uninterpreted |
409 |
* and can represent anything you like. |
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* @return {@code true} if successful. Upon success, this object has |
411 |
* been acquired. |
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* @throws IllegalMonitorStateException if acquiring would place this |
413 |
* synchronizer in an illegal state. This exception must be |
414 |
* thrown in a consistent fashion for synchronization to work |
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* correctly. |
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* @throws UnsupportedOperationException if exclusive mode is not supported |
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*/ |
418 |
protected boolean tryAcquire(long arg) { |
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throw new UnsupportedOperationException(); |
420 |
} |
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|
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/** |
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* Attempts to set the state to reflect a release in exclusive |
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* mode. |
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* |
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* <p>This method is always invoked by the thread performing release. |
427 |
* |
428 |
* <p>The default implementation throws |
429 |
* {@link UnsupportedOperationException}. |
430 |
* |
431 |
* @param arg the release argument. This value is always the one |
432 |
* passed to a release method, or the current state value upon |
433 |
* entry to a condition wait. The value is otherwise |
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* uninterpreted and can represent anything you like. |
435 |
* @return {@code true} if this object is now in a fully released |
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* state, so that any waiting threads may attempt to acquire; |
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* and {@code false} otherwise. |
438 |
* @throws IllegalMonitorStateException if releasing would place this |
439 |
* synchronizer in an illegal state. This exception must be |
440 |
* thrown in a consistent fashion for synchronization to work |
441 |
* correctly. |
442 |
* @throws UnsupportedOperationException if exclusive mode is not supported |
443 |
*/ |
444 |
protected boolean tryRelease(long arg) { |
445 |
throw new UnsupportedOperationException(); |
446 |
} |
447 |
|
448 |
/** |
449 |
* Attempts to acquire in shared mode. This method should query if |
450 |
* the state of the object permits it to be acquired in the shared |
451 |
* mode, and if so to acquire it. |
452 |
* |
453 |
* <p>This method is always invoked by the thread performing |
454 |
* acquire. If this method reports failure, the acquire method |
455 |
* may queue the thread, if it is not already queued, until it is |
456 |
* signalled by a release from some other thread. |
457 |
* |
458 |
* <p>The default implementation throws {@link |
459 |
* UnsupportedOperationException}. |
460 |
* |
461 |
* @param arg the acquire argument. This value is always the one |
462 |
* passed to an acquire method, or is the value saved on entry |
463 |
* to a condition wait. The value is otherwise uninterpreted |
464 |
* and can represent anything you like. |
465 |
* @return a negative value on failure; zero if acquisition in shared |
466 |
* mode succeeded but no subsequent shared-mode acquire can |
467 |
* succeed; and a positive value if acquisition in shared |
468 |
* mode succeeded and subsequent shared-mode acquires might |
469 |
* also succeed, in which case a subsequent waiting thread |
470 |
* must check availability. (Support for three different |
471 |
* return values enables this method to be used in contexts |
472 |
* where acquires only sometimes act exclusively.) Upon |
473 |
* success, this object has been acquired. |
474 |
* @throws IllegalMonitorStateException if acquiring would place this |
475 |
* synchronizer in an illegal state. This exception must be |
476 |
* thrown in a consistent fashion for synchronization to work |
477 |
* correctly. |
478 |
* @throws UnsupportedOperationException if shared mode is not supported |
479 |
*/ |
480 |
protected long tryAcquireShared(long arg) { |
481 |
throw new UnsupportedOperationException(); |
482 |
} |
483 |
|
484 |
/** |
485 |
* Attempts to set the state to reflect a release in shared mode. |
486 |
* |
487 |
* <p>This method is always invoked by the thread performing release. |
488 |
* |
489 |
* <p>The default implementation throws |
490 |
* {@link UnsupportedOperationException}. |
491 |
* |
492 |
* @param arg the release argument. This value is always the one |
493 |
* passed to a release method, or the current state value upon |
494 |
* entry to a condition wait. The value is otherwise |
495 |
* uninterpreted and can represent anything you like. |
496 |
* @return {@code true} if this release of shared mode may permit a |
497 |
* waiting acquire (shared or exclusive) to succeed; and |
498 |
* {@code false} otherwise |
499 |
* @throws IllegalMonitorStateException if releasing would place this |
500 |
* synchronizer in an illegal state. This exception must be |
501 |
* thrown in a consistent fashion for synchronization to work |
502 |
* correctly. |
503 |
* @throws UnsupportedOperationException if shared mode is not supported |
504 |
*/ |
505 |
protected boolean tryReleaseShared(long arg) { |
506 |
throw new UnsupportedOperationException(); |
507 |
} |
508 |
|
509 |
/** |
510 |
* Returns {@code true} if synchronization is held exclusively with |
511 |
* respect to the current (calling) thread. This method is invoked |
512 |
* upon each call to a {@link ConditionObject} method. |
513 |
* |
514 |
* <p>The default implementation throws {@link |
515 |
* UnsupportedOperationException}. This method is invoked |
516 |
* internally only within {@link ConditionObject} methods, so need |
517 |
* not be defined if conditions are not used. |
518 |
* |
519 |
* @return {@code true} if synchronization is held exclusively; |
520 |
* {@code false} otherwise |
521 |
* @throws UnsupportedOperationException if conditions are not supported |
522 |
*/ |
523 |
protected boolean isHeldExclusively() { |
524 |
throw new UnsupportedOperationException(); |
525 |
} |
526 |
|
527 |
/** |
528 |
* Acquires in exclusive mode, ignoring interrupts. Implemented |
529 |
* by invoking at least once {@link #tryAcquire}, |
530 |
* returning on success. Otherwise the thread is queued, possibly |
531 |
* repeatedly blocking and unblocking, invoking {@link |
532 |
* #tryAcquire} until success. This method can be used |
533 |
* to implement method {@link Lock#lock}. |
534 |
* |
535 |
* @param arg the acquire argument. This value is conveyed to |
536 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
537 |
* can represent anything you like. |
538 |
*/ |
539 |
public final void acquire(long arg) { |
540 |
if (!tryAcquire(arg)) |
541 |
acquire(null, arg, false, false, false, 0L); |
542 |
} |
543 |
|
544 |
/** |
545 |
* Acquires in exclusive mode, aborting if interrupted. |
546 |
* Implemented by first checking interrupt status, then invoking |
547 |
* at least once {@link #tryAcquire}, returning on |
548 |
* success. Otherwise the thread is queued, possibly repeatedly |
549 |
* blocking and unblocking, invoking {@link #tryAcquire} |
550 |
* until success or the thread is interrupted. This method can be |
551 |
* used to implement method {@link Lock#lockInterruptibly}. |
552 |
* |
553 |
* @param arg the acquire argument. This value is conveyed to |
554 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
555 |
* can represent anything you like. |
556 |
* @throws InterruptedException if the current thread is interrupted |
557 |
*/ |
558 |
public final void acquireInterruptibly(long arg) |
559 |
throws InterruptedException { |
560 |
if (Thread.interrupted() || |
561 |
(!tryAcquire(arg) && acquire(null, arg, false, true, false, 0L) < 0)) |
562 |
throw new InterruptedException(); |
563 |
} |
564 |
|
565 |
/** |
566 |
* Attempts to acquire in exclusive mode, aborting if interrupted, |
567 |
* and failing if the given timeout elapses. Implemented by first |
568 |
* checking interrupt status, then invoking at least once {@link |
569 |
* #tryAcquire}, returning on success. Otherwise, the thread is |
570 |
* queued, possibly repeatedly blocking and unblocking, invoking |
571 |
* {@link #tryAcquire} until success or the thread is interrupted |
572 |
* or the timeout elapses. This method can be used to implement |
573 |
* method {@link Lock#tryLock(long, TimeUnit)}. |
574 |
* |
575 |
* @param arg the acquire argument. This value is conveyed to |
576 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
577 |
* can represent anything you like. |
578 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
579 |
* @return {@code true} if acquired; {@code false} if timed out |
580 |
* @throws InterruptedException if the current thread is interrupted |
581 |
*/ |
582 |
public final boolean tryAcquireNanos(long arg, long nanosTimeout) |
583 |
throws InterruptedException { |
584 |
if (!Thread.interrupted()) { |
585 |
if (tryAcquire(arg)) |
586 |
return true; |
587 |
if (nanosTimeout <= 0L) |
588 |
return false; |
589 |
int stat = acquire(null, arg, false, true, true, |
590 |
System.nanoTime() + nanosTimeout); |
591 |
if (stat > 0) |
592 |
return true; |
593 |
if (stat == 0) |
594 |
return false; |
595 |
} |
596 |
throw new InterruptedException(); |
597 |
} |
598 |
|
599 |
/** |
600 |
* Releases in exclusive mode. Implemented by unblocking one or |
601 |
* more threads if {@link #tryRelease} returns true. |
602 |
* This method can be used to implement method {@link Lock#unlock}. |
603 |
* |
604 |
* @param arg the release argument. This value is conveyed to |
605 |
* {@link #tryRelease} but is otherwise uninterpreted and |
606 |
* can represent anything you like. |
607 |
* @return the value returned from {@link #tryRelease} |
608 |
*/ |
609 |
public final boolean release(long arg) { |
610 |
if (tryRelease(arg)) { |
611 |
signalNext(head); |
612 |
return true; |
613 |
} |
614 |
return false; |
615 |
} |
616 |
|
617 |
/** |
618 |
* Acquires in shared mode, ignoring interrupts. Implemented by |
619 |
* first invoking at least once {@link #tryAcquireShared}, |
620 |
* returning on success. Otherwise the thread is queued, possibly |
621 |
* repeatedly blocking and unblocking, invoking {@link |
622 |
* #tryAcquireShared} until success. |
623 |
* |
624 |
* @param arg the acquire argument. This value is conveyed to |
625 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
626 |
* and can represent anything you like. |
627 |
*/ |
628 |
public final void acquireShared(long arg) { |
629 |
if (tryAcquireShared(arg) < 0) |
630 |
acquire(null, arg, true, false, false, 0L); |
631 |
} |
632 |
|
633 |
/** |
634 |
* Acquires in shared mode, aborting if interrupted. Implemented |
635 |
* by first checking interrupt status, then invoking at least once |
636 |
* {@link #tryAcquireShared}, returning on success. Otherwise the |
637 |
* thread is queued, possibly repeatedly blocking and unblocking, |
638 |
* invoking {@link #tryAcquireShared} until success or the thread |
639 |
* is interrupted. |
640 |
* @param arg the acquire argument. |
641 |
* This value is conveyed to {@link #tryAcquireShared} but is |
642 |
* otherwise uninterpreted and can represent anything |
643 |
* you like. |
644 |
* @throws InterruptedException if the current thread is interrupted |
645 |
*/ |
646 |
public final void acquireSharedInterruptibly(long arg) |
647 |
throws InterruptedException { |
648 |
if (Thread.interrupted() || |
649 |
(tryAcquireShared(arg) < 0 && |
650 |
acquire(null, arg, true, true, false, 0L) < 0)) |
651 |
throw new InterruptedException(); |
652 |
} |
653 |
|
654 |
/** |
655 |
* Attempts to acquire in shared mode, aborting if interrupted, and |
656 |
* failing if the given timeout elapses. Implemented by first |
657 |
* checking interrupt status, then invoking at least once {@link |
658 |
* #tryAcquireShared}, returning on success. Otherwise, the |
659 |
* thread is queued, possibly repeatedly blocking and unblocking, |
660 |
* invoking {@link #tryAcquireShared} until success or the thread |
661 |
* is interrupted or the timeout elapses. |
662 |
* |
663 |
* @param arg the acquire argument. This value is conveyed to |
664 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
665 |
* and can represent anything you like. |
666 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
667 |
* @return {@code true} if acquired; {@code false} if timed out |
668 |
* @throws InterruptedException if the current thread is interrupted |
669 |
*/ |
670 |
public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout) |
671 |
throws InterruptedException { |
672 |
if (!Thread.interrupted()) { |
673 |
if (tryAcquireShared(arg) >= 0) |
674 |
return true; |
675 |
if (nanosTimeout <= 0L) |
676 |
return false; |
677 |
int stat = acquire(null, arg, true, true, true, |
678 |
System.nanoTime() + nanosTimeout); |
679 |
if (stat > 0) |
680 |
return true; |
681 |
if (stat == 0) |
682 |
return false; |
683 |
} |
684 |
throw new InterruptedException(); |
685 |
} |
686 |
|
687 |
/** |
688 |
* Releases in shared mode. Implemented by unblocking one or more |
689 |
* threads if {@link #tryReleaseShared} returns true. |
690 |
* |
691 |
* @param arg the release argument. This value is conveyed to |
692 |
* {@link #tryReleaseShared} but is otherwise uninterpreted |
693 |
* and can represent anything you like. |
694 |
* @return the value returned from {@link #tryReleaseShared} |
695 |
*/ |
696 |
public final boolean releaseShared(long arg) { |
697 |
if (tryReleaseShared(arg)) { |
698 |
signalNext(head); |
699 |
return true; |
700 |
} |
701 |
return false; |
702 |
} |
703 |
|
704 |
// Queue inspection methods |
705 |
|
706 |
/** |
707 |
* Queries whether any threads are waiting to acquire. Note that |
708 |
* because cancellations due to interrupts and timeouts may occur |
709 |
* at any time, a {@code true} return does not guarantee that any |
710 |
* other thread will ever acquire. |
711 |
* |
712 |
* @return {@code true} if there may be other threads waiting to acquire |
713 |
*/ |
714 |
public final boolean hasQueuedThreads() { |
715 |
for (Node p = tail, h = head; p != h && p != null; p = p.prev) |
716 |
if (p.status >= 0) |
717 |
return true; |
718 |
return false; |
719 |
} |
720 |
|
721 |
/** |
722 |
* Queries whether any threads have ever contended to acquire this |
723 |
* synchronizer; that is, if an acquire method has ever blocked. |
724 |
* |
725 |
* <p>In this implementation, this operation returns in |
726 |
* constant time. |
727 |
* |
728 |
* @return {@code true} if there has ever been contention |
729 |
*/ |
730 |
public final boolean hasContended() { |
731 |
return head != null; |
732 |
} |
733 |
|
734 |
/** |
735 |
* Returns the first (longest-waiting) thread in the queue, or |
736 |
* {@code null} if no threads are currently queued. |
737 |
* |
738 |
* <p>In this implementation, this operation normally returns in |
739 |
* constant time, but may iterate upon contention if other threads are |
740 |
* concurrently modifying the queue. |
741 |
* |
742 |
* @return the first (longest-waiting) thread in the queue, or |
743 |
* {@code null} if no threads are currently queued |
744 |
*/ |
745 |
public final Thread getFirstQueuedThread() { |
746 |
Thread first = null, w; Node h, s; |
747 |
if ((h = head) != null && ((s = h.next) == null || |
748 |
(first = s.waiter) == null || |
749 |
s.prev == null)) { |
750 |
// traverse from tail on stale reads |
751 |
for (Node p = tail, q; p != null && (q = p.prev) != null; p = q) |
752 |
if ((w = p.waiter) != null) |
753 |
first = w; |
754 |
} |
755 |
return first; |
756 |
} |
757 |
|
758 |
/** |
759 |
* Returns true if the given thread is currently queued. |
760 |
* |
761 |
* <p>This implementation traverses the queue to determine |
762 |
* presence of the given thread. |
763 |
* |
764 |
* @param thread the thread |
765 |
* @return {@code true} if the given thread is on the queue |
766 |
* @throws NullPointerException if the thread is null |
767 |
*/ |
768 |
public final boolean isQueued(Thread thread) { |
769 |
if (thread == null) |
770 |
throw new NullPointerException(); |
771 |
for (Node p = tail; p != null; p = p.prev) |
772 |
if (p.waiter == thread) |
773 |
return true; |
774 |
return false; |
775 |
} |
776 |
|
777 |
/** |
778 |
* Returns {@code true} if the apparent first queued thread, if one |
779 |
* exists, is waiting in exclusive mode. If this method returns |
780 |
* {@code true}, and the current thread is attempting to acquire in |
781 |
* shared mode (that is, this method is invoked from {@link |
782 |
* #tryAcquireShared}) then it is guaranteed that the current thread |
783 |
* is not the first queued thread. Used only as a heuristic in |
784 |
* ReentrantReadWriteLock. |
785 |
*/ |
786 |
final boolean apparentlyFirstQueuedIsExclusive() { |
787 |
Node h, s; |
788 |
return (h = head) != null && (s = h.next) != null && |
789 |
!(s instanceof SharedNode) && s.waiter != null; |
790 |
} |
791 |
|
792 |
/** |
793 |
* Queries whether any threads have been waiting to acquire longer |
794 |
* than the current thread. |
795 |
* |
796 |
* <p>An invocation of this method is equivalent to (but may be |
797 |
* more efficient than): |
798 |
* <pre> {@code |
799 |
* getFirstQueuedThread() != Thread.currentThread() |
800 |
* && hasQueuedThreads()}</pre> |
801 |
* |
802 |
* <p>Note that because cancellations due to interrupts and |
803 |
* timeouts may occur at any time, a {@code true} return does not |
804 |
* guarantee that some other thread will acquire before the current |
805 |
* thread. Likewise, it is possible for another thread to win a |
806 |
* race to enqueue after this method has returned {@code false}, |
807 |
* due to the queue being empty. |
808 |
* |
809 |
* <p>This method is designed to be used by a fair synchronizer to |
810 |
* avoid <a href="AbstractQueuedSynchronizer.html#barging">barging</a>. |
811 |
* Such a synchronizer's {@link #tryAcquire} method should return |
812 |
* {@code false}, and its {@link #tryAcquireShared} method should |
813 |
* return a negative value, if this method returns {@code true} |
814 |
* (unless this is a reentrant acquire). For example, the {@code |
815 |
* tryAcquire} method for a fair, reentrant, exclusive mode |
816 |
* synchronizer might look like this: |
817 |
* |
818 |
* <pre> {@code |
819 |
* protected boolean tryAcquire(long arg) { |
820 |
* if (isHeldExclusively()) { |
821 |
* // A reentrant acquire; increment hold count |
822 |
* return true; |
823 |
* } else if (hasQueuedPredecessors()) { |
824 |
* return false; |
825 |
* } else { |
826 |
* // try to acquire normally |
827 |
* } |
828 |
* }}</pre> |
829 |
* |
830 |
* @return {@code true} if there is a queued thread preceding the |
831 |
* current thread, and {@code false} if the current thread |
832 |
* is at the head of the queue or the queue is empty |
833 |
* @since 1.7 |
834 |
*/ |
835 |
public final boolean hasQueuedPredecessors() { |
836 |
Thread first = null; Node h, s; |
837 |
if ((h = head) != null && ((s = h.next) == null || |
838 |
(first = s.waiter) == null || |
839 |
s.prev == null)) |
840 |
first = getFirstQueuedThread(); // retry via getFirstQueuedThread |
841 |
return first != null && first != Thread.currentThread(); |
842 |
} |
843 |
|
844 |
// Instrumentation and monitoring methods |
845 |
|
846 |
/** |
847 |
* Returns an estimate of the number of threads waiting to |
848 |
* acquire. The value is only an estimate because the number of |
849 |
* threads may change dynamically while this method traverses |
850 |
* internal data structures. This method is designed for use in |
851 |
* monitoring system state, not for synchronization control. |
852 |
* |
853 |
* @return the estimated number of threads waiting to acquire |
854 |
*/ |
855 |
public final int getQueueLength() { |
856 |
int n = 0; |
857 |
for (Node p = tail; p != null; p = p.prev) { |
858 |
if (p.waiter != null) |
859 |
++n; |
860 |
} |
861 |
return n; |
862 |
} |
863 |
|
864 |
/** |
865 |
* Returns a collection containing threads that may be waiting to |
866 |
* acquire. Because the actual set of threads may change |
867 |
* dynamically while constructing this result, the returned |
868 |
* collection is only a best-effort estimate. The elements of the |
869 |
* returned collection are in no particular order. This method is |
870 |
* designed to facilitate construction of subclasses that provide |
871 |
* more extensive monitoring facilities. |
872 |
* |
873 |
* @return the collection of threads |
874 |
*/ |
875 |
public final Collection<Thread> getQueuedThreads() { |
876 |
ArrayList<Thread> list = new ArrayList<>(); |
877 |
for (Node p = tail; p != null; p = p.prev) { |
878 |
Thread t = p.waiter; |
879 |
if (t != null) |
880 |
list.add(t); |
881 |
} |
882 |
return list; |
883 |
} |
884 |
|
885 |
/** |
886 |
* Returns a collection containing threads that may be waiting to |
887 |
* acquire in exclusive mode. This has the same properties |
888 |
* as {@link #getQueuedThreads} except that it only returns |
889 |
* those threads waiting due to an exclusive acquire. |
890 |
* |
891 |
* @return the collection of threads |
892 |
*/ |
893 |
public final Collection<Thread> getExclusiveQueuedThreads() { |
894 |
ArrayList<Thread> list = new ArrayList<>(); |
895 |
for (Node p = tail; p != null; p = p.prev) { |
896 |
if (!(p instanceof SharedNode)) { |
897 |
Thread t = p.waiter; |
898 |
if (t != null) |
899 |
list.add(t); |
900 |
} |
901 |
} |
902 |
return list; |
903 |
} |
904 |
|
905 |
/** |
906 |
* Returns a collection containing threads that may be waiting to |
907 |
* acquire in shared mode. This has the same properties |
908 |
* as {@link #getQueuedThreads} except that it only returns |
909 |
* those threads waiting due to a shared acquire. |
910 |
* |
911 |
* @return the collection of threads |
912 |
*/ |
913 |
public final Collection<Thread> getSharedQueuedThreads() { |
914 |
ArrayList<Thread> list = new ArrayList<>(); |
915 |
for (Node p = tail; p != null; p = p.prev) { |
916 |
if (p instanceof SharedNode) { |
917 |
Thread t = p.waiter; |
918 |
if (t != null) |
919 |
list.add(t); |
920 |
} |
921 |
} |
922 |
return list; |
923 |
} |
924 |
|
925 |
/** |
926 |
* Returns a string identifying this synchronizer, as well as its state. |
927 |
* The state, in brackets, includes the String {@code "State ="} |
928 |
* followed by the current value of {@link #getState}, and either |
929 |
* {@code "nonempty"} or {@code "empty"} depending on whether the |
930 |
* queue is empty. |
931 |
* |
932 |
* @return a string identifying this synchronizer, as well as its state |
933 |
*/ |
934 |
public String toString() { |
935 |
return super.toString() |
936 |
+ "[State = " + getState() + ", " |
937 |
+ (hasQueuedThreads() ? "non" : "") + "empty queue]"; |
938 |
} |
939 |
|
940 |
// Instrumentation methods for conditions |
941 |
|
942 |
/** |
943 |
* Queries whether the given ConditionObject |
944 |
* uses this synchronizer as its lock. |
945 |
* |
946 |
* @param condition the condition |
947 |
* @return {@code true} if owned |
948 |
* @throws NullPointerException if the condition is null |
949 |
*/ |
950 |
public final boolean owns(ConditionObject condition) { |
951 |
return condition.isOwnedBy(this); |
952 |
} |
953 |
|
954 |
/** |
955 |
* Queries whether any threads are waiting on the given condition |
956 |
* associated with this synchronizer. Note that because timeouts |
957 |
* and interrupts may occur at any time, a {@code true} return |
958 |
* does not guarantee that a future {@code signal} will awaken |
959 |
* any threads. This method is designed primarily for use in |
960 |
* monitoring of the system state. |
961 |
* |
962 |
* @param condition the condition |
963 |
* @return {@code true} if there are any waiting threads |
964 |
* @throws IllegalMonitorStateException if exclusive synchronization |
965 |
* is not held |
966 |
* @throws IllegalArgumentException if the given condition is |
967 |
* not associated with this synchronizer |
968 |
* @throws NullPointerException if the condition is null |
969 |
*/ |
970 |
public final boolean hasWaiters(ConditionObject condition) { |
971 |
if (!owns(condition)) |
972 |
throw new IllegalArgumentException("Not owner"); |
973 |
return condition.hasWaiters(); |
974 |
} |
975 |
|
976 |
/** |
977 |
* Returns an estimate of the number of threads waiting on the |
978 |
* given condition associated with this synchronizer. Note that |
979 |
* because timeouts and interrupts may occur at any time, the |
980 |
* estimate serves only as an upper bound on the actual number of |
981 |
* waiters. This method is designed for use in monitoring system |
982 |
* state, not for synchronization control. |
983 |
* |
984 |
* @param condition the condition |
985 |
* @return the estimated number of waiting threads |
986 |
* @throws IllegalMonitorStateException if exclusive synchronization |
987 |
* is not held |
988 |
* @throws IllegalArgumentException if the given condition is |
989 |
* not associated with this synchronizer |
990 |
* @throws NullPointerException if the condition is null |
991 |
*/ |
992 |
public final int getWaitQueueLength(ConditionObject condition) { |
993 |
if (!owns(condition)) |
994 |
throw new IllegalArgumentException("Not owner"); |
995 |
return condition.getWaitQueueLength(); |
996 |
} |
997 |
|
998 |
/** |
999 |
* Returns a collection containing those threads that may be |
1000 |
* waiting on the given condition associated with this |
1001 |
* synchronizer. Because the actual set of threads may change |
1002 |
* dynamically while constructing this result, the returned |
1003 |
* collection is only a best-effort estimate. The elements of the |
1004 |
* returned collection are in no particular order. |
1005 |
* |
1006 |
* @param condition the condition |
1007 |
* @return the collection of threads |
1008 |
* @throws IllegalMonitorStateException if exclusive synchronization |
1009 |
* is not held |
1010 |
* @throws IllegalArgumentException if the given condition is |
1011 |
* not associated with this synchronizer |
1012 |
* @throws NullPointerException if the condition is null |
1013 |
*/ |
1014 |
public final Collection<Thread> getWaitingThreads(ConditionObject condition) { |
1015 |
if (!owns(condition)) |
1016 |
throw new IllegalArgumentException("Not owner"); |
1017 |
return condition.getWaitingThreads(); |
1018 |
} |
1019 |
|
1020 |
/** |
1021 |
* Condition implementation for a {@link AbstractQueuedLongSynchronizer} |
1022 |
* serving as the basis of a {@link Lock} implementation. |
1023 |
* |
1024 |
* <p>Method documentation for this class describes mechanics, |
1025 |
* not behavioral specifications from the point of view of Lock |
1026 |
* and Condition users. Exported versions of this class will in |
1027 |
* general need to be accompanied by documentation describing |
1028 |
* condition semantics that rely on those of the associated |
1029 |
* {@code AbstractQueuedLongSynchronizer}. |
1030 |
* |
1031 |
* <p>This class is Serializable, but all fields are transient, |
1032 |
* so deserialized conditions have no waiters. |
1033 |
*/ |
1034 |
public class ConditionObject implements Condition, java.io.Serializable { |
1035 |
private static final long serialVersionUID = 1173984872572414699L; |
1036 |
/** First node of condition queue. */ |
1037 |
private transient ConditionNode firstWaiter; |
1038 |
/** Last node of condition queue. */ |
1039 |
private transient ConditionNode lastWaiter; |
1040 |
|
1041 |
/** |
1042 |
* Creates a new {@code ConditionObject} instance. |
1043 |
*/ |
1044 |
public ConditionObject() { } |
1045 |
|
1046 |
// Signalling methods |
1047 |
|
1048 |
/** |
1049 |
* Removes and transfers one or all waiters to sync queue. |
1050 |
*/ |
1051 |
private void doSignal(ConditionNode first, boolean all) { |
1052 |
while (first != null) { |
1053 |
ConditionNode next = first.nextWaiter; |
1054 |
if ((firstWaiter = next) == null) |
1055 |
lastWaiter = null; |
1056 |
if ((first.getAndUnsetStatus(COND) & COND) != 0) { |
1057 |
enqueue(first); |
1058 |
if (!all) |
1059 |
break; |
1060 |
} |
1061 |
first = next; |
1062 |
} |
1063 |
} |
1064 |
|
1065 |
/** |
1066 |
* Moves the longest-waiting thread, if one exists, from the |
1067 |
* wait queue for this condition to the wait queue for the |
1068 |
* owning lock. |
1069 |
* |
1070 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1071 |
* returns {@code false} |
1072 |
*/ |
1073 |
public final void signal() { |
1074 |
ConditionNode first = firstWaiter; |
1075 |
if (!isHeldExclusively()) |
1076 |
throw new IllegalMonitorStateException(); |
1077 |
if (first != null) |
1078 |
doSignal(first, false); |
1079 |
} |
1080 |
|
1081 |
/** |
1082 |
* Moves all threads from the wait queue for this condition to |
1083 |
* the wait queue for the owning lock. |
1084 |
* |
1085 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1086 |
* returns {@code false} |
1087 |
*/ |
1088 |
public final void signalAll() { |
1089 |
ConditionNode first = firstWaiter; |
1090 |
if (!isHeldExclusively()) |
1091 |
throw new IllegalMonitorStateException(); |
1092 |
if (first != null) |
1093 |
doSignal(first, true); |
1094 |
} |
1095 |
|
1096 |
// Waiting methods |
1097 |
|
1098 |
/** |
1099 |
* Adds node to condition list and releases lock. |
1100 |
* |
1101 |
* @param node the node |
1102 |
* @return savedState to reacquire after wait |
1103 |
*/ |
1104 |
private long enableWait(ConditionNode node) { |
1105 |
if (isHeldExclusively()) { |
1106 |
node.waiter = Thread.currentThread(); |
1107 |
node.setStatusRelaxed(COND | WAITING); |
1108 |
ConditionNode last = lastWaiter; |
1109 |
if (last == null) |
1110 |
firstWaiter = node; |
1111 |
else |
1112 |
last.nextWaiter = node; |
1113 |
lastWaiter = node; |
1114 |
long savedState = getState(); |
1115 |
if (release(savedState)) |
1116 |
return savedState; |
1117 |
} |
1118 |
node.status = CANCELLED; // lock not held or inconsistent |
1119 |
throw new IllegalMonitorStateException(); |
1120 |
} |
1121 |
|
1122 |
/** |
1123 |
* Returns true if a node that was initially placed on a condition |
1124 |
* queue is now ready to reacquire on sync queue. |
1125 |
* @param node the node |
1126 |
* @return true if is reacquiring |
1127 |
*/ |
1128 |
private boolean canReacquire(ConditionNode node) { |
1129 |
// check links, not status to avoid enqueue race |
1130 |
Node p; // traverse unless known to be bidirectionally linked |
1131 |
return node != null && (p = node.prev) != null && |
1132 |
(p.next == node || isEnqueued(node)); |
1133 |
} |
1134 |
|
1135 |
/** |
1136 |
* Unlinks the given node and other non-waiting nodes from |
1137 |
* condition queue unless already unlinked. |
1138 |
*/ |
1139 |
private void unlinkCancelledWaiters(ConditionNode node) { |
1140 |
if (node == null || node.nextWaiter != null || node == lastWaiter) { |
1141 |
ConditionNode w = firstWaiter, trail = null; |
1142 |
while (w != null) { |
1143 |
ConditionNode next = w.nextWaiter; |
1144 |
if ((w.status & COND) == 0) { |
1145 |
w.nextWaiter = null; |
1146 |
if (trail == null) |
1147 |
firstWaiter = next; |
1148 |
else |
1149 |
trail.nextWaiter = next; |
1150 |
if (next == null) |
1151 |
lastWaiter = trail; |
1152 |
} else |
1153 |
trail = w; |
1154 |
w = next; |
1155 |
} |
1156 |
} |
1157 |
} |
1158 |
|
1159 |
/** |
1160 |
* Implements uninterruptible condition wait. |
1161 |
* <ol> |
1162 |
* <li>Save lock state returned by {@link #getState}. |
1163 |
* <li>Invoke {@link #release} with saved state as argument, |
1164 |
* throwing IllegalMonitorStateException if it fails. |
1165 |
* <li>Block until signalled. |
1166 |
* <li>Reacquire by invoking specialized version of |
1167 |
* {@link #acquire} with saved state as argument. |
1168 |
* </ol> |
1169 |
*/ |
1170 |
public final void awaitUninterruptibly() { |
1171 |
ConditionNode node = new ConditionNode(); |
1172 |
long savedState = enableWait(node); |
1173 |
LockSupport.setCurrentBlocker(this); // for back-compatibility |
1174 |
boolean interrupted = false, rejected = false; |
1175 |
while (!canReacquire(node)) { |
1176 |
if (Thread.interrupted()) |
1177 |
interrupted = true; |
1178 |
else if ((node.status & COND) != 0) { |
1179 |
try { |
1180 |
if (rejected) |
1181 |
node.block(); |
1182 |
else |
1183 |
ForkJoinPool.managedBlock(node); |
1184 |
} catch (RejectedExecutionException ex) { |
1185 |
rejected = true; |
1186 |
} catch (InterruptedException ie) { |
1187 |
interrupted = true; |
1188 |
} |
1189 |
} else |
1190 |
Thread.onSpinWait(); // awoke while enqueuing |
1191 |
} |
1192 |
LockSupport.setCurrentBlocker(null); |
1193 |
node.clearStatus(); |
1194 |
acquire(node, savedState, false, false, false, 0L); |
1195 |
if (interrupted) |
1196 |
Thread.currentThread().interrupt(); |
1197 |
} |
1198 |
|
1199 |
/** |
1200 |
* Implements interruptible condition wait. |
1201 |
* <ol> |
1202 |
* <li>If current thread is interrupted, throw InterruptedException. |
1203 |
* <li>Save lock state returned by {@link #getState}. |
1204 |
* <li>Invoke {@link #release} with saved state as argument, |
1205 |
* throwing IllegalMonitorStateException if it fails. |
1206 |
* <li>Block until signalled or interrupted. |
1207 |
* <li>Reacquire by invoking specialized version of |
1208 |
* {@link #acquire} with saved state as argument. |
1209 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1210 |
* </ol> |
1211 |
*/ |
1212 |
public final void await() throws InterruptedException { |
1213 |
if (Thread.interrupted()) |
1214 |
throw new InterruptedException(); |
1215 |
ConditionNode node = new ConditionNode(); |
1216 |
long savedState = enableWait(node); |
1217 |
LockSupport.setCurrentBlocker(this); // for back-compatibility |
1218 |
boolean interrupted = false, cancelled = false, rejected = false; |
1219 |
while (!canReacquire(node)) { |
1220 |
if (interrupted |= Thread.interrupted()) { |
1221 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
1222 |
break; // else interrupted after signal |
1223 |
} else if ((node.status & COND) != 0) { |
1224 |
try { |
1225 |
if (rejected) |
1226 |
node.block(); |
1227 |
else |
1228 |
ForkJoinPool.managedBlock(node); |
1229 |
} catch (RejectedExecutionException ex) { |
1230 |
rejected = true; |
1231 |
} catch (InterruptedException ie) { |
1232 |
interrupted = true; |
1233 |
} |
1234 |
} else |
1235 |
Thread.onSpinWait(); // awoke while enqueuing |
1236 |
} |
1237 |
LockSupport.setCurrentBlocker(null); |
1238 |
node.clearStatus(); |
1239 |
acquire(node, savedState, false, false, false, 0L); |
1240 |
if (interrupted) { |
1241 |
if (cancelled) { |
1242 |
unlinkCancelledWaiters(node); |
1243 |
throw new InterruptedException(); |
1244 |
} |
1245 |
Thread.currentThread().interrupt(); |
1246 |
} |
1247 |
} |
1248 |
|
1249 |
/** |
1250 |
* Implements timed condition wait. |
1251 |
* <ol> |
1252 |
* <li>If current thread is interrupted, throw InterruptedException. |
1253 |
* <li>Save lock state returned by {@link #getState}. |
1254 |
* <li>Invoke {@link #release} with saved state as argument, |
1255 |
* throwing IllegalMonitorStateException if it fails. |
1256 |
* <li>Block until signalled, interrupted, or timed out. |
1257 |
* <li>Reacquire by invoking specialized version of |
1258 |
* {@link #acquire} with saved state as argument. |
1259 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1260 |
* </ol> |
1261 |
*/ |
1262 |
public final long awaitNanos(long nanosTimeout) |
1263 |
throws InterruptedException { |
1264 |
if (Thread.interrupted()) |
1265 |
throw new InterruptedException(); |
1266 |
ConditionNode node = new ConditionNode(); |
1267 |
long savedState = enableWait(node); |
1268 |
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout; |
1269 |
long deadline = System.nanoTime() + nanos; |
1270 |
boolean cancelled = false, interrupted = false; |
1271 |
while (!canReacquire(node)) { |
1272 |
if ((interrupted |= Thread.interrupted()) || |
1273 |
(nanos = deadline - System.nanoTime()) <= 0L) { |
1274 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
1275 |
break; |
1276 |
} else |
1277 |
LockSupport.parkNanos(this, nanos); |
1278 |
} |
1279 |
node.clearStatus(); |
1280 |
acquire(node, savedState, false, false, false, 0L); |
1281 |
if (cancelled) { |
1282 |
unlinkCancelledWaiters(node); |
1283 |
if (interrupted) |
1284 |
throw new InterruptedException(); |
1285 |
} else if (interrupted) |
1286 |
Thread.currentThread().interrupt(); |
1287 |
long remaining = deadline - System.nanoTime(); // avoid overflow |
1288 |
return (remaining <= nanosTimeout) ? remaining : Long.MIN_VALUE; |
1289 |
} |
1290 |
|
1291 |
/** |
1292 |
* Implements absolute timed condition wait. |
1293 |
* <ol> |
1294 |
* <li>If current thread is interrupted, throw InterruptedException. |
1295 |
* <li>Save lock state returned by {@link #getState}. |
1296 |
* <li>Invoke {@link #release} with saved state as argument, |
1297 |
* throwing IllegalMonitorStateException if it fails. |
1298 |
* <li>Block until signalled, interrupted, or timed out. |
1299 |
* <li>Reacquire by invoking specialized version of |
1300 |
* {@link #acquire} with saved state as argument. |
1301 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1302 |
* <li>If timed out while blocked in step 4, return false, else true. |
1303 |
* </ol> |
1304 |
*/ |
1305 |
public final boolean awaitUntil(Date deadline) |
1306 |
throws InterruptedException { |
1307 |
long abstime = deadline.getTime(); |
1308 |
if (Thread.interrupted()) |
1309 |
throw new InterruptedException(); |
1310 |
ConditionNode node = new ConditionNode(); |
1311 |
long savedState = enableWait(node); |
1312 |
boolean cancelled = false, interrupted = false; |
1313 |
while (!canReacquire(node)) { |
1314 |
if ((interrupted |= Thread.interrupted()) || |
1315 |
System.currentTimeMillis() >= abstime) { |
1316 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
1317 |
break; |
1318 |
} else |
1319 |
LockSupport.parkUntil(this, abstime); |
1320 |
} |
1321 |
node.clearStatus(); |
1322 |
acquire(node, savedState, false, false, false, 0L); |
1323 |
if (cancelled) { |
1324 |
unlinkCancelledWaiters(node); |
1325 |
if (interrupted) |
1326 |
throw new InterruptedException(); |
1327 |
} else if (interrupted) |
1328 |
Thread.currentThread().interrupt(); |
1329 |
return !cancelled; |
1330 |
} |
1331 |
|
1332 |
/** |
1333 |
* Implements timed condition wait. |
1334 |
* <ol> |
1335 |
* <li>If current thread is interrupted, throw InterruptedException. |
1336 |
* <li>Save lock state returned by {@link #getState}. |
1337 |
* <li>Invoke {@link #release} with saved state as argument, |
1338 |
* throwing IllegalMonitorStateException if it fails. |
1339 |
* <li>Block until signalled, interrupted, or timed out. |
1340 |
* <li>Reacquire by invoking specialized version of |
1341 |
* {@link #acquire} with saved state as argument. |
1342 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
1343 |
* <li>If timed out while blocked in step 4, return false, else true. |
1344 |
* </ol> |
1345 |
*/ |
1346 |
public final boolean await(long time, TimeUnit unit) |
1347 |
throws InterruptedException { |
1348 |
long nanosTimeout = unit.toNanos(time); |
1349 |
if (Thread.interrupted()) |
1350 |
throw new InterruptedException(); |
1351 |
ConditionNode node = new ConditionNode(); |
1352 |
long savedState = enableWait(node); |
1353 |
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout; |
1354 |
long deadline = System.nanoTime() + nanos; |
1355 |
boolean cancelled = false, interrupted = false; |
1356 |
while (!canReacquire(node)) { |
1357 |
if ((interrupted |= Thread.interrupted()) || |
1358 |
(nanos = deadline - System.nanoTime()) <= 0L) { |
1359 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
1360 |
break; |
1361 |
} else |
1362 |
LockSupport.parkNanos(this, nanos); |
1363 |
} |
1364 |
node.clearStatus(); |
1365 |
acquire(node, savedState, false, false, false, 0L); |
1366 |
if (cancelled) { |
1367 |
unlinkCancelledWaiters(node); |
1368 |
if (interrupted) |
1369 |
throw new InterruptedException(); |
1370 |
} else if (interrupted) |
1371 |
Thread.currentThread().interrupt(); |
1372 |
return !cancelled; |
1373 |
} |
1374 |
|
1375 |
// support for instrumentation |
1376 |
|
1377 |
/** |
1378 |
* Returns true if this condition was created by the given |
1379 |
* synchronization object. |
1380 |
* |
1381 |
* @return {@code true} if owned |
1382 |
*/ |
1383 |
final boolean isOwnedBy(AbstractQueuedLongSynchronizer sync) { |
1384 |
return sync == AbstractQueuedLongSynchronizer.this; |
1385 |
} |
1386 |
|
1387 |
/** |
1388 |
* Queries whether any threads are waiting on this condition. |
1389 |
* Implements {@link AbstractQueuedLongSynchronizer#hasWaiters(ConditionObject)}. |
1390 |
* |
1391 |
* @return {@code true} if there are any waiting threads |
1392 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1393 |
* returns {@code false} |
1394 |
*/ |
1395 |
protected final boolean hasWaiters() { |
1396 |
if (!isHeldExclusively()) |
1397 |
throw new IllegalMonitorStateException(); |
1398 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1399 |
if ((w.status & COND) != 0) |
1400 |
return true; |
1401 |
} |
1402 |
return false; |
1403 |
} |
1404 |
|
1405 |
/** |
1406 |
* Returns an estimate of the number of threads waiting on |
1407 |
* this condition. |
1408 |
* Implements {@link AbstractQueuedLongSynchronizer#getWaitQueueLength(ConditionObject)}. |
1409 |
* |
1410 |
* @return the estimated number of waiting threads |
1411 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1412 |
* returns {@code false} |
1413 |
*/ |
1414 |
protected final int getWaitQueueLength() { |
1415 |
if (!isHeldExclusively()) |
1416 |
throw new IllegalMonitorStateException(); |
1417 |
int n = 0; |
1418 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1419 |
if ((w.status & COND) != 0) |
1420 |
++n; |
1421 |
} |
1422 |
return n; |
1423 |
} |
1424 |
|
1425 |
/** |
1426 |
* Returns a collection containing those threads that may be |
1427 |
* waiting on this Condition. |
1428 |
* Implements {@link AbstractQueuedLongSynchronizer#getWaitingThreads(ConditionObject)}. |
1429 |
* |
1430 |
* @return the collection of threads |
1431 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
1432 |
* returns {@code false} |
1433 |
*/ |
1434 |
protected final Collection<Thread> getWaitingThreads() { |
1435 |
if (!isHeldExclusively()) |
1436 |
throw new IllegalMonitorStateException(); |
1437 |
ArrayList<Thread> list = new ArrayList<>(); |
1438 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1439 |
if ((w.status & COND) != 0) { |
1440 |
Thread t = w.waiter; |
1441 |
if (t != null) |
1442 |
list.add(t); |
1443 |
} |
1444 |
} |
1445 |
return list; |
1446 |
} |
1447 |
} |
1448 |
|
1449 |
// Unsafe |
1450 |
private static final Unsafe U = Unsafe.getUnsafe(); |
1451 |
private static final long STATE |
1452 |
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "state"); |
1453 |
private static final long HEAD |
1454 |
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "head"); |
1455 |
private static final long TAIL |
1456 |
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "tail"); |
1457 |
|
1458 |
static { |
1459 |
Class<?> ensureLoaded = LockSupport.class; |
1460 |
} |
1461 |
} |