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1.1 |
/* |
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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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package jsr166e; |
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import java.util.concurrent.TimeUnit; |
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1.6 |
import java.util.concurrent.TimeoutException; |
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1.1 |
import java.util.concurrent.locks.Lock; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.AbstractQueuedLongSynchronizer; |
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import java.util.Collection; |
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import java.io.ObjectOutputStream; |
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import java.io.ObjectInputStream; |
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import java.io.IOException; |
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/** |
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* A reentrant mutual exclusion {@link Lock} in which each lock |
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* acquisition or release advances a sequence number. When the |
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* sequence number (accessible using {@link #getSequence()}) is odd, |
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1.2 |
* the lock is held. When it is even (i.e., ({@code lock.getSequence() |
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1.1 |
* & 1L) == 0L}), the lock is released. Method {@link |
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* #awaitAvailability} can be used to await availability of the lock, |
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* returning its current sequence number. Sequence numbers are of type |
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* {@code long} to ensure that they will not wrap around until |
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* hundreds of years of use under current processor rates. A |
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* SequenceLock can be created with a specified number of |
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dl |
1.6 |
* spins. Attempts to lock or await release will retry at least the |
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* given number of times before blocking. If not specified, a default, |
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1.1 |
* possibly platform-specific, value is used. |
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* |
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* <p>Except for the lack of support for specified fairness policies, |
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1.6 |
* or {@link Condition} objects, a SequenceLock can be used in the |
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* same way as {@link ReentrantLock}. It provides similar status and |
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* monitoring methods such as {@link #isHeldByCurrentThread}. |
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* SequenceLocks may be preferable in contexts in which multiple |
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* threads invoke short read-only methods much more frequently than |
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* fully locked methods. |
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1.3 |
* |
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1.1 |
* <p> Methods {@code awaitAvailability} and {@code getSequence} can |
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* be used together to define (partially) optimistic read-only methods |
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* that are usually more efficient than ReadWriteLocks when they |
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* apply. These read-only methods typically read multiple field |
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* values into local variables when the lock is not held, retrying if |
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* the sequence number changed while doing so. Alternatively, because |
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* {@code awaitAvailability} accommodates reentrancy, a method can |
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* retry a bounded number of times before switching to locking mode. |
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* While conceptually straightforward, expressing these ideas can be |
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* verbose. For example: |
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* |
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* <pre> {@code |
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* class Point { |
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* private float x, y; |
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* private final SequenceLock sl = new SequenceLock(); |
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* |
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jsr166 |
1.5 |
* void move(float deltaX, float deltaY) { // an exclusively locked method |
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1.1 |
* sl.lock(); |
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* try { |
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* x += deltaX; |
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* y += deltaY; |
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* } finally { |
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* sl.unlock(); |
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* } |
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* } |
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* |
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* float distanceFromOriginV1() { // A read-only method |
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* float currentX, currentY; |
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* long seq; |
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* do { |
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* seq = sl.awaitAvailability(); |
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* currentX = x; |
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* currentY = y; |
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* } while (sl.getSequence() != seq); // retry if sequence changed |
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* return (float)Math.sqrt(currentX * currentX + currentY * currentY); |
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* } |
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* |
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* float distanceFromOriginV2() { // Uses bounded retries before locking |
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* float currentX, currentY; |
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* long seq; |
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* int retries = RETRIES_BEFORE_LOCKING; // for example 8 |
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* try { |
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* do { |
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* if (--retries < 0) |
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* sl.lock(); |
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* seq = sl.awaitAvailability(); |
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* currentX = x; |
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* currentY = y; |
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* } while (sl.getSequence() != seq); |
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* } finally { |
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* if (retries < 0) |
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* sl.unlock(); |
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* } |
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* return (float)Math.sqrt(currentX * currentX + currentY * currentY); |
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* } |
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*}}</pre> |
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* |
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* @since 1.8 |
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* @author Doug Lea |
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*/ |
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public class SequenceLock implements Lock, java.io.Serializable { |
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private static final long serialVersionUID = 7373984872572414699L; |
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static final class Sync extends AbstractQueuedLongSynchronizer { |
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/** |
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* The number of times to spin in lock() and awaitAvailability(). |
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*/ |
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final int spins; |
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/** |
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* The number of reentrant holds on this lock. Uses a long for |
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* compatibility with other AbstractQueuedLongSynchronizer |
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* operations. |
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*/ |
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long holds; |
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Sync(int spins) { this.spins = spins; } |
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// overrides of AQLS methods |
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public final boolean isHeldExclusively() { |
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return (getState() & 1L) != 0L && |
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getExclusiveOwnerThread() == Thread.currentThread(); |
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} |
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dl |
1.3 |
|
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jsr166 |
1.4 |
public final boolean tryAcquire(long acquires) { |
128 |
dl |
1.1 |
Thread current = Thread.currentThread(); |
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long c = getState(); |
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if ((c & 1L) == 0L) { |
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if (compareAndSetState(c, c + 1L)) { |
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holds = acquires; |
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setExclusiveOwnerThread(current); |
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return true; |
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} |
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} |
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else if (current == getExclusiveOwnerThread()) { |
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holds += acquires; |
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return true; |
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} |
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return false; |
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} |
143 |
dl |
1.3 |
|
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dl |
1.1 |
public final boolean tryRelease(long releases) { |
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if (Thread.currentThread() != getExclusiveOwnerThread()) |
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throw new IllegalMonitorStateException(); |
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if ((holds -= releases) == 0L) { |
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setExclusiveOwnerThread(null); |
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setState(getState() + 1L); |
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return true; |
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} |
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return false; |
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} |
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public final long tryAcquireShared(long unused) { |
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dl |
1.3 |
return ((getState() & 1L) == 0L || |
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jsr166 |
1.4 |
getExclusiveOwnerThread() == Thread.currentThread()) ? |
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1.1 |
1L : -1L; // must return long |
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} |
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public final boolean tryReleaseShared(long unused) { |
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return true; |
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} |
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dl |
1.3 |
public final Condition newCondition() { |
166 |
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1.2 |
throw new UnsupportedOperationException(); |
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} |
168 |
dl |
1.1 |
|
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// Other methods in support of SequenceLock |
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final long getSequence() { |
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return getState(); |
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} |
174 |
dl |
1.3 |
|
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dl |
1.1 |
final void lock() { |
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int k = spins; |
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dl |
1.6 |
while (!tryAcquire(1L)) { |
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dl |
1.1 |
if (k == 0) { |
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dl |
1.6 |
acquire(1L); |
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dl |
1.1 |
break; |
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} |
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--k; |
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} |
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} |
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dl |
1.3 |
|
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dl |
1.1 |
final long awaitAvailability() { |
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long s; |
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int k = spins; |
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while (((s = getState()) & 1L) != 0L && |
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getExclusiveOwnerThread() != Thread.currentThread()) { |
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if (k > 0) |
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--k; |
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else { |
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dl |
1.6 |
acquireShared(1L); |
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releaseShared(1L); |
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dl |
1.1 |
} |
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} |
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return s; |
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} |
200 |
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dl |
1.6 |
final long tryAwaitAvailability(long nanos) |
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throws InterruptedException, TimeoutException { |
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Thread current = Thread.currentThread(); |
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for (;;) { |
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long s = getState(); |
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if ((s & 1L) == 0L || getExclusiveOwnerThread() == current) { |
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releaseShared(1L); |
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return s; |
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} |
210 |
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if (!tryAcquireSharedNanos(1L, nanos)) |
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throw new TimeoutException(); |
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// since tryAcquireSharedNanos doesn't return seq |
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// retry with minimal wait time. |
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nanos = 1L; |
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} |
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} |
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218 |
dl |
1.1 |
final boolean isLocked() { |
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return (getState() & 1L) != 0L; |
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} |
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final Thread getOwner() { |
223 |
dl |
1.2 |
return (getState() & 1L) == 0L ? null : getExclusiveOwnerThread(); |
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dl |
1.1 |
} |
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final long getHoldCount() { |
227 |
jsr166 |
1.4 |
return isHeldExclusively() ? holds : 0; |
228 |
dl |
1.1 |
} |
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private void readObject(ObjectInputStream s) |
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throws IOException, ClassNotFoundException { |
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s.defaultReadObject(); |
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holds = 0L; |
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setState(0L); // reset to unlocked state |
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} |
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} |
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private final Sync sync; |
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dl |
1.3 |
/** |
241 |
dl |
1.1 |
* The default spin value for constructor. Future versions of this |
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* class might choose platform-specific values. Currently, except |
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jsr166 |
1.5 |
* on uniprocessors, it is set to a small value that overcomes near |
244 |
dl |
1.1 |
* misses between releases and acquires. |
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*/ |
246 |
dl |
1.3 |
static final int DEFAULT_SPINS = |
247 |
dl |
1.1 |
Runtime.getRuntime().availableProcessors() > 1 ? 64 : 0; |
248 |
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249 |
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/** |
250 |
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* Creates an instance of {@code SequenceLock} with the default |
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* number of retry attempts to lock or await release before |
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* blocking. |
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*/ |
254 |
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public SequenceLock() { sync = new Sync(DEFAULT_SPINS); } |
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/** |
257 |
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* Creates an instance of {@code SequenceLock} that |
258 |
dl |
1.3 |
* will retry attempts to lock or await release |
259 |
dl |
1.1 |
* at least the given number times before blocking. |
260 |
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*/ |
261 |
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public SequenceLock(int spins) { sync = new Sync(spins); } |
262 |
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/** |
264 |
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* Returns the current sequence number of this lock. The sequence |
265 |
dl |
1.6 |
* number is advanced upon each acquire or release action. When |
266 |
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* this value is odd, the lock is held; when even, it is released. |
267 |
dl |
1.1 |
* |
268 |
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* @return the current sequence number |
269 |
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*/ |
270 |
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public long getSequence() { return sync.getSequence(); } |
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272 |
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/** |
273 |
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* Returns the current sequence number when the lock is, or |
274 |
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* becomes, available. A lock is available if it is either |
275 |
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* released, or is held by the current thread. If the lock is not |
276 |
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* available, the current thread becomes disabled for thread |
277 |
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* scheduling purposes and lies dormant until the lock has been |
278 |
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* released by some other thread. |
279 |
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* |
280 |
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* @return the current sequence number |
281 |
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*/ |
282 |
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public long awaitAvailability() { return sync.awaitAvailability(); } |
283 |
dl |
1.3 |
|
284 |
dl |
1.1 |
/** |
285 |
dl |
1.6 |
* Returns the current sequence number if the lock is, or |
286 |
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* becomes, available within the specified waiting time. |
287 |
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* |
288 |
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* <p>If the lock is not available, the current thread becomes |
289 |
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* disabled for thread scheduling purposes and lies dormant until |
290 |
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* one of three things happens: |
291 |
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* |
292 |
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* <ul> |
293 |
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* |
294 |
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* <li>The lock becomes available, in which case the current |
295 |
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* sequence number is returned. |
296 |
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* |
297 |
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* <li>Some other thread {@linkplain Thread#interrupt interrupts} |
298 |
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* the current thread, in which case this method throws |
299 |
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* {@link InterruptedException}. |
300 |
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* |
301 |
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* <li>The specified waiting time elapses, in which case |
302 |
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* this method throws {@link TimeoutException}. |
303 |
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* |
304 |
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* </ul> |
305 |
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* |
306 |
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* @param timeout the time to wait for availability |
307 |
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* @param unit the time unit of the timeout argument |
308 |
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* @return the current sequence number if the lock is available |
309 |
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* upon return from this method. |
310 |
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* @throws InterruptedException if the current thread is interrupted |
311 |
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* @throws TimeoutException if the lock was not available within |
312 |
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* the specified waiting time. |
313 |
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* @throws NullPointerException if the time unit is null |
314 |
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*/ |
315 |
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public long tryAwaitAvailability(long timeout, TimeUnit unit) |
316 |
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throws InterruptedException, TimeoutException { |
317 |
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return sync.tryAwaitAvailability(unit.toNanos(timeout)); |
318 |
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} |
319 |
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320 |
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/** |
321 |
dl |
1.1 |
* Acquires the lock. |
322 |
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* |
323 |
dl |
1.6 |
* <p>If the current thread already holds this lock then the hold count |
324 |
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* is incremented by one and the method returns immediately without |
325 |
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* incrementing the sequence number. |
326 |
dl |
1.1 |
* |
327 |
dl |
1.6 |
* <p>If this lock not held by another thread, this method |
328 |
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* increments the sequence number (which thus becomes an odd |
329 |
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* number), sets the lock hold count to one, and returns |
330 |
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* immediately. |
331 |
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* |
332 |
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* <p>If the lock is held by another thread then the current |
333 |
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* thread may retry acquiring this lock, depending on the {@code |
334 |
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* spin} count established in constructor. If the lock is still |
335 |
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* not acquired, the current thread becomes disabled for thread |
336 |
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* scheduling purposes and lies dormant until enabled by |
337 |
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* some other thread releasing the lock. |
338 |
dl |
1.1 |
*/ |
339 |
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public void lock() { sync.lock(); } |
340 |
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|
341 |
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/** |
342 |
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* Acquires the lock unless the current thread is |
343 |
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* {@linkplain Thread#interrupt interrupted}. |
344 |
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* |
345 |
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* <p>If the current thread already holds this lock then the hold count |
346 |
dl |
1.6 |
* is incremented by one and the method returns immediately without |
347 |
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* incrementing the sequence number. |
348 |
dl |
1.1 |
* |
349 |
dl |
1.6 |
* <p>If this lock not held by another thread, this method |
350 |
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* increments the sequence number (which thus becomes an odd |
351 |
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* number), sets the lock hold count to one, and returns |
352 |
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* immediately. |
353 |
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* |
354 |
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* <p>If the lock is held by another thread then the current |
355 |
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* thread may retry acquiring this lock, depending on the {@code |
356 |
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* spin} count established in constructor. If the lock is still |
357 |
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* not acquired, the current thread becomes disabled for thread |
358 |
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* scheduling purposes and lies dormant until one of two things |
359 |
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* happens: |
360 |
dl |
1.1 |
* |
361 |
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* <ul> |
362 |
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* |
363 |
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* <li>The lock is acquired by the current thread; or |
364 |
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* |
365 |
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* <li>Some other thread {@linkplain Thread#interrupt interrupts} the |
366 |
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* current thread. |
367 |
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* |
368 |
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* </ul> |
369 |
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* |
370 |
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* <p>If the lock is acquired by the current thread then the lock hold |
371 |
dl |
1.6 |
* count is set to one and the sequence number is incremented. |
372 |
dl |
1.1 |
* |
373 |
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* <p>If the current thread: |
374 |
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* |
375 |
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* <ul> |
376 |
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* |
377 |
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* <li>has its interrupted status set on entry to this method; or |
378 |
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* |
379 |
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* <li>is {@linkplain Thread#interrupt interrupted} while acquiring |
380 |
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* the lock, |
381 |
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* |
382 |
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* </ul> |
383 |
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* |
384 |
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* then {@link InterruptedException} is thrown and the current thread's |
385 |
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* interrupted status is cleared. |
386 |
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* |
387 |
|
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* <p>In this implementation, as this method is an explicit |
388 |
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* interruption point, preference is given to responding to the |
389 |
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* interrupt over normal or reentrant acquisition of the lock. |
390 |
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* |
391 |
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* @throws InterruptedException if the current thread is interrupted |
392 |
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*/ |
393 |
|
|
public void lockInterruptibly() throws InterruptedException { |
394 |
dl |
1.6 |
sync.acquireInterruptibly(1L); |
395 |
dl |
1.1 |
} |
396 |
|
|
|
397 |
|
|
/** |
398 |
|
|
* Acquires the lock only if it is not held by another thread at the time |
399 |
|
|
* of invocation. |
400 |
|
|
* |
401 |
dl |
1.6 |
* <p>If the current thread already holds this lock then the hold |
402 |
|
|
* count is incremented by one and the method returns {@code true} |
403 |
|
|
* without incrementing the sequence number. |
404 |
|
|
* |
405 |
|
|
* <p>If this lock not held by another thread, this method |
406 |
|
|
* increments the sequence number (which thus becomes an odd |
407 |
|
|
* number), sets the lock hold count to one, and returns {@code |
408 |
|
|
* true}. |
409 |
dl |
1.1 |
* |
410 |
dl |
1.6 |
* <p>If the lock is held by another thread then this method |
411 |
|
|
* returns {@code false}. |
412 |
dl |
1.1 |
* |
413 |
|
|
* @return {@code true} if the lock was free and was acquired by the |
414 |
|
|
* current thread, or the lock was already held by the current |
415 |
|
|
* thread; and {@code false} otherwise |
416 |
|
|
*/ |
417 |
dl |
1.6 |
public boolean tryLock() { return sync.tryAcquire(1L); } |
418 |
dl |
1.1 |
|
419 |
|
|
/** |
420 |
|
|
* Acquires the lock if it is not held by another thread within the given |
421 |
|
|
* waiting time and the current thread has not been |
422 |
|
|
* {@linkplain Thread#interrupt interrupted}. |
423 |
|
|
* |
424 |
dl |
1.6 |
* <p>If the current thread already holds this lock then the hold count |
425 |
|
|
* is incremented by one and the method returns immediately without |
426 |
|
|
* incrementing the sequence number. |
427 |
|
|
* |
428 |
|
|
* <p>If this lock not held by another thread, this method |
429 |
|
|
* increments the sequence number (which thus becomes an odd |
430 |
|
|
* number), sets the lock hold count to one, and returns |
431 |
|
|
* immediately. |
432 |
|
|
* |
433 |
|
|
* <p>If the lock is held by another thread then the current |
434 |
|
|
* thread may retry acquiring this lock, depending on the {@code |
435 |
|
|
* spin} count established in constructor. If the lock is still |
436 |
|
|
* not acquired, the current thread becomes disabled for thread |
437 |
|
|
* scheduling purposes and lies dormant until one of three things |
438 |
|
|
* happens: |
439 |
dl |
1.1 |
* |
440 |
|
|
* <ul> |
441 |
|
|
* |
442 |
|
|
* <li>The lock is acquired by the current thread; or |
443 |
|
|
* |
444 |
|
|
* <li>Some other thread {@linkplain Thread#interrupt interrupts} |
445 |
|
|
* the current thread; or |
446 |
|
|
* |
447 |
|
|
* <li>The specified waiting time elapses |
448 |
|
|
* |
449 |
|
|
* </ul> |
450 |
|
|
* |
451 |
|
|
* <p>If the lock is acquired then the value {@code true} is returned and |
452 |
|
|
* the lock hold count is set to one. |
453 |
|
|
* |
454 |
|
|
* <p>If the current thread: |
455 |
|
|
* |
456 |
|
|
* <ul> |
457 |
|
|
* |
458 |
|
|
* <li>has its interrupted status set on entry to this method; or |
459 |
|
|
* |
460 |
|
|
* <li>is {@linkplain Thread#interrupt interrupted} while |
461 |
|
|
* acquiring the lock, |
462 |
|
|
* |
463 |
|
|
* </ul> |
464 |
|
|
* then {@link InterruptedException} is thrown and the current thread's |
465 |
|
|
* interrupted status is cleared. |
466 |
|
|
* |
467 |
|
|
* <p>If the specified waiting time elapses then the value {@code false} |
468 |
|
|
* is returned. If the time is less than or equal to zero, the method |
469 |
|
|
* will not wait at all. |
470 |
|
|
* |
471 |
|
|
* <p>In this implementation, as this method is an explicit |
472 |
|
|
* interruption point, preference is given to responding to the |
473 |
|
|
* interrupt over normal or reentrant acquisition of the lock, and |
474 |
|
|
* over reporting the elapse of the waiting time. |
475 |
|
|
* |
476 |
|
|
* @param timeout the time to wait for the lock |
477 |
|
|
* @param unit the time unit of the timeout argument |
478 |
|
|
* @return {@code true} if the lock was free and was acquired by the |
479 |
|
|
* current thread, or the lock was already held by the current |
480 |
|
|
* thread; and {@code false} if the waiting time elapsed before |
481 |
|
|
* the lock could be acquired |
482 |
|
|
* @throws InterruptedException if the current thread is interrupted |
483 |
|
|
* @throws NullPointerException if the time unit is null |
484 |
|
|
* |
485 |
|
|
*/ |
486 |
|
|
public boolean tryLock(long timeout, TimeUnit unit) |
487 |
|
|
throws InterruptedException { |
488 |
dl |
1.6 |
return sync.tryAcquireNanos(1L, unit.toNanos(timeout)); |
489 |
dl |
1.1 |
} |
490 |
|
|
|
491 |
|
|
/** |
492 |
|
|
* Attempts to release this lock. |
493 |
|
|
* |
494 |
dl |
1.6 |
* <p>If the current thread is the holder of this lock then the |
495 |
|
|
* hold count is decremented. If the hold count is now zero then |
496 |
|
|
* the sequence number is incremented (thus becoming an even |
497 |
|
|
* number) and the lock is released. If the current thread is not |
498 |
|
|
* the holder of this lock then {@link |
499 |
|
|
* IllegalMonitorStateException} is thrown. |
500 |
dl |
1.1 |
* |
501 |
|
|
* @throws IllegalMonitorStateException if the current thread does not |
502 |
|
|
* hold this lock |
503 |
|
|
*/ |
504 |
|
|
public void unlock() { sync.release(1); } |
505 |
|
|
|
506 |
|
|
/** |
507 |
dl |
1.2 |
* Throws UnsupportedOperationException. SequenceLocks |
508 |
|
|
* do not support Condition objects. |
509 |
dl |
1.1 |
* |
510 |
dl |
1.2 |
* @throws UnsupportedOperationException |
511 |
dl |
1.1 |
*/ |
512 |
dl |
1.3 |
public Condition newCondition() { |
513 |
dl |
1.2 |
throw new UnsupportedOperationException(); |
514 |
|
|
} |
515 |
dl |
1.1 |
|
516 |
|
|
/** |
517 |
|
|
* Queries the number of holds on this lock by the current thread. |
518 |
|
|
* |
519 |
|
|
* <p>A thread has a hold on a lock for each lock action that is not |
520 |
|
|
* matched by an unlock action. |
521 |
|
|
* |
522 |
|
|
* <p>The hold count information is typically only used for testing and |
523 |
dl |
1.3 |
* debugging purposes. |
524 |
dl |
1.1 |
* |
525 |
|
|
* @return the number of holds on this lock by the current thread, |
526 |
|
|
* or zero if this lock is not held by the current thread |
527 |
|
|
*/ |
528 |
|
|
public long getHoldCount() { return sync.getHoldCount(); } |
529 |
|
|
|
530 |
|
|
/** |
531 |
|
|
* Queries if this lock is held by the current thread. |
532 |
|
|
* |
533 |
|
|
* @return {@code true} if current thread holds this lock and |
534 |
|
|
* {@code false} otherwise |
535 |
|
|
*/ |
536 |
|
|
public boolean isHeldByCurrentThread() { return sync.isHeldExclusively(); } |
537 |
|
|
|
538 |
|
|
/** |
539 |
|
|
* Queries if this lock is held by any thread. This method is |
540 |
|
|
* designed for use in monitoring of the system state, |
541 |
|
|
* not for synchronization control. |
542 |
|
|
* |
543 |
|
|
* @return {@code true} if any thread holds this lock and |
544 |
|
|
* {@code false} otherwise |
545 |
|
|
*/ |
546 |
|
|
public boolean isLocked() { return sync.isLocked(); } |
547 |
|
|
|
548 |
|
|
/** |
549 |
|
|
* Returns the thread that currently owns this lock, or |
550 |
|
|
* {@code null} if not owned. When this method is called by a |
551 |
|
|
* thread that is not the owner, the return value reflects a |
552 |
|
|
* best-effort approximation of current lock status. For example, |
553 |
|
|
* the owner may be momentarily {@code null} even if there are |
554 |
|
|
* threads trying to acquire the lock but have not yet done so. |
555 |
|
|
* This method is designed to facilitate construction of |
556 |
|
|
* subclasses that provide more extensive lock monitoring |
557 |
|
|
* facilities. |
558 |
|
|
* |
559 |
|
|
* @return the owner, or {@code null} if not owned |
560 |
|
|
*/ |
561 |
|
|
protected Thread getOwner() { return sync.getOwner(); } |
562 |
|
|
|
563 |
|
|
/** |
564 |
|
|
* Queries whether any threads are waiting to acquire this lock. Note that |
565 |
|
|
* because cancellations may occur at any time, a {@code true} |
566 |
|
|
* return does not guarantee that any other thread will ever |
567 |
|
|
* acquire this lock. This method is designed primarily for use in |
568 |
|
|
* monitoring of the system state. |
569 |
|
|
* |
570 |
|
|
* @return {@code true} if there may be other threads waiting to |
571 |
|
|
* acquire the lock |
572 |
|
|
*/ |
573 |
|
|
public final boolean hasQueuedThreads() { |
574 |
|
|
return sync.hasQueuedThreads(); |
575 |
|
|
} |
576 |
|
|
|
577 |
|
|
/** |
578 |
|
|
* Queries whether the given thread is waiting to acquire this |
579 |
|
|
* lock. Note that because cancellations may occur at any time, a |
580 |
|
|
* {@code true} return does not guarantee that this thread |
581 |
|
|
* will ever acquire this lock. This method is designed primarily for use |
582 |
|
|
* in monitoring of the system state. |
583 |
|
|
* |
584 |
|
|
* @param thread the thread |
585 |
|
|
* @return {@code true} if the given thread is queued waiting for this lock |
586 |
|
|
* @throws NullPointerException if the thread is null |
587 |
|
|
*/ |
588 |
|
|
public final boolean hasQueuedThread(Thread thread) { |
589 |
|
|
return sync.isQueued(thread); |
590 |
|
|
} |
591 |
|
|
|
592 |
|
|
/** |
593 |
|
|
* Returns an estimate of the number of threads waiting to |
594 |
|
|
* acquire this lock. The value is only an estimate because the number of |
595 |
|
|
* threads may change dynamically while this method traverses |
596 |
|
|
* internal data structures. This method is designed for use in |
597 |
|
|
* monitoring of the system state, not for synchronization |
598 |
|
|
* control. |
599 |
|
|
* |
600 |
|
|
* @return the estimated number of threads waiting for this lock |
601 |
|
|
*/ |
602 |
|
|
public final int getQueueLength() { |
603 |
|
|
return sync.getQueueLength(); |
604 |
|
|
} |
605 |
|
|
|
606 |
|
|
/** |
607 |
|
|
* Returns a collection containing threads that may be waiting to |
608 |
|
|
* acquire this lock. Because the actual set of threads may change |
609 |
|
|
* dynamically while constructing this result, the returned |
610 |
|
|
* collection is only a best-effort estimate. The elements of the |
611 |
|
|
* returned collection are in no particular order. This method is |
612 |
|
|
* designed to facilitate construction of subclasses that provide |
613 |
|
|
* more extensive monitoring facilities. |
614 |
|
|
* |
615 |
|
|
* @return the collection of threads |
616 |
|
|
*/ |
617 |
|
|
protected Collection<Thread> getQueuedThreads() { |
618 |
|
|
return sync.getQueuedThreads(); |
619 |
|
|
} |
620 |
|
|
|
621 |
|
|
/** |
622 |
|
|
* Returns a string identifying this lock, as well as its lock state. |
623 |
|
|
* The state, in brackets, includes either the String {@code "Unlocked"} |
624 |
|
|
* or the String {@code "Locked by"} followed by the |
625 |
|
|
* {@linkplain Thread#getName name} of the owning thread. |
626 |
|
|
* |
627 |
|
|
* @return a string identifying this lock, as well as its lock state |
628 |
|
|
*/ |
629 |
|
|
public String toString() { |
630 |
|
|
Thread o = sync.getOwner(); |
631 |
|
|
return super.toString() + ((o == null) ? |
632 |
|
|
"[Unlocked]" : |
633 |
|
|
"[Locked by thread " + o.getName() + "]"); |
634 |
|
|
} |
635 |
|
|
|
636 |
|
|
} |
637 |
dl |
1.3 |
|