| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/licenses/publicdomain |
| */ |
| |
| package java.util.concurrent.locks; |
| |
| import java.util.Date; |
| import java.util.concurrent.TimeUnit; |
| |
| /** |
| * {@code Condition} factors out the {@code Object} monitor |
| * methods ({@link Object#wait() wait}, {@link Object#notify notify} |
| * and {@link Object#notifyAll notifyAll}) into distinct objects to |
| * give the effect of having multiple wait-sets per object, by |
| * combining them with the use of arbitrary {@link Lock} implementations. |
| * Where a {@code Lock} replaces the use of {@code synchronized} methods |
| * and statements, a {@code Condition} replaces the use of the Object |
| * monitor methods. |
| * |
| * <p>Conditions (also known as <em>condition queues</em> or |
| * <em>condition variables</em>) provide a means for one thread to |
| * suspend execution (to "wait") until notified by another |
| * thread that some state condition may now be true. Because access |
| * to this shared state information occurs in different threads, it |
| * must be protected, so a lock of some form is associated with the |
| * condition. The key property that waiting for a condition provides |
| * is that it <em>atomically</em> releases the associated lock and |
| * suspends the current thread, just like {@code Object.wait}. |
| * |
| * <p>A {@code Condition} instance is intrinsically bound to a lock. |
| * To obtain a {@code Condition} instance for a particular {@link Lock} |
| * instance use its {@link Lock#newCondition newCondition()} method. |
| * |
| * <p>As an example, suppose we have a bounded buffer which supports |
| * {@code put} and {@code take} methods. If a |
| * {@code take} is attempted on an empty buffer, then the thread will block |
| * until an item becomes available; if a {@code put} is attempted on a |
| * full buffer, then the thread will block until a space becomes available. |
| * We would like to keep waiting {@code put} threads and {@code take} |
| * threads in separate wait-sets so that we can use the optimization of |
| * only notifying a single thread at a time when items or spaces become |
| * available in the buffer. This can be achieved using two |
| * {@link Condition} instances. |
| * <pre> |
| * class BoundedBuffer { |
| * <b>final Lock lock = new ReentrantLock();</b> |
| * final Condition notFull = <b>lock.newCondition(); </b> |
| * final Condition notEmpty = <b>lock.newCondition(); </b> |
| * |
| * final Object[] items = new Object[100]; |
| * int putptr, takeptr, count; |
| * |
| * public void put(Object x) throws InterruptedException { |
| * <b>lock.lock(); |
| * try {</b> |
| * while (count == items.length) |
| * <b>notFull.await();</b> |
| * items[putptr] = x; |
| * if (++putptr == items.length) putptr = 0; |
| * ++count; |
| * <b>notEmpty.signal();</b> |
| * <b>} finally { |
| * lock.unlock(); |
| * }</b> |
| * } |
| * |
| * public Object take() throws InterruptedException { |
| * <b>lock.lock(); |
| * try {</b> |
| * while (count == 0) |
| * <b>notEmpty.await();</b> |
| * Object x = items[takeptr]; |
| * if (++takeptr == items.length) takeptr = 0; |
| * --count; |
| * <b>notFull.signal();</b> |
| * return x; |
| * <b>} finally { |
| * lock.unlock(); |
| * }</b> |
| * } |
| * } |
| * </pre> |
| * |
| * (The {@link java.util.concurrent.ArrayBlockingQueue} class provides |
| * this functionality, so there is no reason to implement this |
| * sample usage class.) |
| * |
| * <p>A {@code Condition} implementation can provide behavior and semantics |
| * that is |
| * different from that of the {@code Object} monitor methods, such as |
| * guaranteed ordering for notifications, or not requiring a lock to be held |
| * when performing notifications. |
| * If an implementation provides such specialized semantics then the |
| * implementation must document those semantics. |
| * |
| * <p>Note that {@code Condition} instances are just normal objects and can |
| * themselves be used as the target in a {@code synchronized} statement, |
| * and can have their own monitor {@link Object#wait wait} and |
| * {@link Object#notify notification} methods invoked. |
| * Acquiring the monitor lock of a {@code Condition} instance, or using its |
| * monitor methods, has no specified relationship with acquiring the |
| * {@link Lock} associated with that {@code Condition} or the use of its |
| * {@linkplain #await waiting} and {@linkplain #signal signalling} methods. |
| * It is recommended that to avoid confusion you never use {@code Condition} |
| * instances in this way, except perhaps within their own implementation. |
| * |
| * <p>Except where noted, passing a {@code null} value for any parameter |
| * will result in a {@link NullPointerException} being thrown. |
| * |
| * <h3>Implementation Considerations</h3> |
| * |
| * <p>When waiting upon a {@code Condition}, a "<em>spurious |
| * wakeup</em>" is permitted to occur, in |
| * general, as a concession to the underlying platform semantics. |
| * This has little practical impact on most application programs as a |
| * {@code Condition} should always be waited upon in a loop, testing |
| * the state predicate that is being waited for. An implementation is |
| * free to remove the possibility of spurious wakeups but it is |
| * recommended that applications programmers always assume that they can |
| * occur and so always wait in a loop. |
| * |
| * <p>The three forms of condition waiting |
| * (interruptible, non-interruptible, and timed) may differ in their ease of |
| * implementation on some platforms and in their performance characteristics. |
| * In particular, it may be difficult to provide these features and maintain |
| * specific semantics such as ordering guarantees. |
| * Further, the ability to interrupt the actual suspension of the thread may |
| * not always be feasible to implement on all platforms. |
| * |
| * <p>Consequently, an implementation is not required to define exactly the |
| * same guarantees or semantics for all three forms of waiting, nor is it |
| * required to support interruption of the actual suspension of the thread. |
| * |
| * <p>An implementation is required to |
| * clearly document the semantics and guarantees provided by each of the |
| * waiting methods, and when an implementation does support interruption of |
| * thread suspension then it must obey the interruption semantics as defined |
| * in this interface. |
| * |
| * <p>As interruption generally implies cancellation, and checks for |
| * interruption are often infrequent, an implementation can favor responding |
| * to an interrupt over normal method return. This is true even if it can be |
| * shown that the interrupt occurred after another action that may have |
| * unblocked the thread. An implementation should document this behavior. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| */ |
| public interface Condition { |
| |
| /** |
| * Causes the current thread to wait until it is signalled or |
| * {@linkplain Thread#interrupt interrupted}. |
| * |
| * <p>The lock associated with this {@code Condition} is atomically |
| * released and the current thread becomes disabled for thread scheduling |
| * purposes and lies dormant until <em>one</em> of four things happens: |
| * <ul> |
| * <li>Some other thread invokes the {@link #signal} method for this |
| * {@code Condition} and the current thread happens to be chosen as the |
| * thread to be awakened; or |
| * <li>Some other thread invokes the {@link #signalAll} method for this |
| * {@code Condition}; or |
| * <li>Some other thread {@linkplain Thread#interrupt interrupts} the |
| * current thread, and interruption of thread suspension is supported; or |
| * <li>A "<em>spurious wakeup</em>" occurs. |
| * </ul> |
| * |
| * <p>In all cases, before this method can return the current thread must |
| * re-acquire the lock associated with this condition. When the |
| * thread returns it is <em>guaranteed</em> to hold this lock. |
| * |
| * <p>If the current thread: |
| * <ul> |
| * <li>has its interrupted status set on entry to this method; or |
| * <li>is {@linkplain Thread#interrupt interrupted} while waiting |
| * and interruption of thread suspension is supported, |
| * </ul> |
| * then {@link InterruptedException} is thrown and the current thread's |
| * interrupted status is cleared. It is not specified, in the first |
| * case, whether or not the test for interruption occurs before the lock |
| * is released. |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated with this |
| * {@code Condition} when this method is called. |
| * It is up to the implementation to determine if this is |
| * the case and if not, how to respond. Typically, an exception will be |
| * thrown (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| * |
| * <p>An implementation can favor responding to an interrupt over normal |
| * method return in response to a signal. In that case the implementation |
| * must ensure that the signal is redirected to another waiting thread, if |
| * there is one. |
| * |
| * @throws InterruptedException if the current thread is interrupted |
| * (and interruption of thread suspension is supported) |
| */ |
| void await() throws InterruptedException; |
| |
| /** |
| * Causes the current thread to wait until it is signalled. |
| * |
| * <p>The lock associated with this condition is atomically |
| * released and the current thread becomes disabled for thread scheduling |
| * purposes and lies dormant until <em>one</em> of three things happens: |
| * <ul> |
| * <li>Some other thread invokes the {@link #signal} method for this |
| * {@code Condition} and the current thread happens to be chosen as the |
| * thread to be awakened; or |
| * <li>Some other thread invokes the {@link #signalAll} method for this |
| * {@code Condition}; or |
| * <li>A "<em>spurious wakeup</em>" occurs. |
| * </ul> |
| * |
| * <p>In all cases, before this method can return the current thread must |
| * re-acquire the lock associated with this condition. When the |
| * thread returns it is <em>guaranteed</em> to hold this lock. |
| * |
| * <p>If the current thread's interrupted status is set when it enters |
| * this method, or it is {@linkplain Thread#interrupt interrupted} |
| * while waiting, it will continue to wait until signalled. When it finally |
| * returns from this method its interrupted status will still |
| * be set. |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated with this |
| * {@code Condition} when this method is called. |
| * It is up to the implementation to determine if this is |
| * the case and if not, how to respond. Typically, an exception will be |
| * thrown (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| */ |
| void awaitUninterruptibly(); |
| |
| /** |
| * Causes the current thread to wait until it is signalled or interrupted, |
| * or the specified waiting time elapses. |
| * |
| * <p>The lock associated with this condition is atomically |
| * released and the current thread becomes disabled for thread scheduling |
| * purposes and lies dormant until <em>one</em> of five things happens: |
| * <ul> |
| * <li>Some other thread invokes the {@link #signal} method for this |
| * {@code Condition} and the current thread happens to be chosen as the |
| * thread to be awakened; or |
| * <li>Some other thread invokes the {@link #signalAll} method for this |
| * {@code Condition}; or |
| * <li>Some other thread {@linkplain Thread#interrupt interrupts} the |
| * current thread, and interruption of thread suspension is supported; or |
| * <li>The specified waiting time elapses; or |
| * <li>A "<em>spurious wakeup</em>" occurs. |
| * </ul> |
| * |
| * <p>In all cases, before this method can return the current thread must |
| * re-acquire the lock associated with this condition. When the |
| * thread returns it is <em>guaranteed</em> to hold this lock. |
| * |
| * <p>If the current thread: |
| * <ul> |
| * <li>has its interrupted status set on entry to this method; or |
| * <li>is {@linkplain Thread#interrupt interrupted} while waiting |
| * and interruption of thread suspension is supported, |
| * </ul> |
| * then {@link InterruptedException} is thrown and the current thread's |
| * interrupted status is cleared. It is not specified, in the first |
| * case, whether or not the test for interruption occurs before the lock |
| * is released. |
| * |
| * <p>The method returns an estimate of the number of nanoseconds |
| * remaining to wait given the supplied {@code nanosTimeout} |
| * value upon return, or a value less than or equal to zero if it |
| * timed out. This value can be used to determine whether and how |
| * long to re-wait in cases where the wait returns but an awaited |
| * condition still does not hold. Typical uses of this method take |
| * the following form: |
| * |
| * <pre> |
| * synchronized boolean aMethod(long timeout, TimeUnit unit) { |
| * long nanosTimeout = unit.toNanos(timeout); |
| * while (!conditionBeingWaitedFor) { |
| * if (nanosTimeout > 0) |
| * nanosTimeout = theCondition.awaitNanos(nanosTimeout); |
| * else |
| * return false; |
| * } |
| * // ... |
| * } |
| * </pre> |
| * |
| * <p> Design note: This method requires a nanosecond argument so |
| * as to avoid truncation errors in reporting remaining times. |
| * Such precision loss would make it difficult for programmers to |
| * ensure that total waiting times are not systematically shorter |
| * than specified when re-waits occur. |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated with this |
| * {@code Condition} when this method is called. |
| * It is up to the implementation to determine if this is |
| * the case and if not, how to respond. Typically, an exception will be |
| * thrown (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| * |
| * <p>An implementation can favor responding to an interrupt over normal |
| * method return in response to a signal, or over indicating the elapse |
| * of the specified waiting time. In either case the implementation |
| * must ensure that the signal is redirected to another waiting thread, if |
| * there is one. |
| * |
| * @param nanosTimeout the maximum time to wait, in nanoseconds |
| * @return an estimate of the {@code nanosTimeout} value minus |
| * the time spent waiting upon return from this method. |
| * A positive value may be used as the argument to a |
| * subsequent call to this method to finish waiting out |
| * the desired time. A value less than or equal to zero |
| * indicates that no time remains. |
| * @throws InterruptedException if the current thread is interrupted |
| * (and interruption of thread suspension is supported) |
| */ |
| long awaitNanos(long nanosTimeout) throws InterruptedException; |
| |
| /** |
| * Causes the current thread to wait until it is signalled or interrupted, |
| * or the specified waiting time elapses. This method is behaviorally |
| * equivalent to:<br> |
| * <pre> |
| * awaitNanos(unit.toNanos(time)) > 0 |
| * </pre> |
| * @param time the maximum time to wait |
| * @param unit the time unit of the {@code time} argument |
| * @return {@code false} if the waiting time detectably elapsed |
| * before return from the method, else {@code true} |
| * @throws InterruptedException if the current thread is interrupted |
| * (and interruption of thread suspension is supported) |
| */ |
| boolean await(long time, TimeUnit unit) throws InterruptedException; |
| |
| /** |
| * Causes the current thread to wait until it is signalled or interrupted, |
| * or the specified deadline elapses. |
| * |
| * <p>The lock associated with this condition is atomically |
| * released and the current thread becomes disabled for thread scheduling |
| * purposes and lies dormant until <em>one</em> of five things happens: |
| * <ul> |
| * <li>Some other thread invokes the {@link #signal} method for this |
| * {@code Condition} and the current thread happens to be chosen as the |
| * thread to be awakened; or |
| * <li>Some other thread invokes the {@link #signalAll} method for this |
| * {@code Condition}; or |
| * <li>Some other thread {@linkplain Thread#interrupt interrupts} the |
| * current thread, and interruption of thread suspension is supported; or |
| * <li>The specified deadline elapses; or |
| * <li>A "<em>spurious wakeup</em>" occurs. |
| * </ul> |
| * |
| * <p>In all cases, before this method can return the current thread must |
| * re-acquire the lock associated with this condition. When the |
| * thread returns it is <em>guaranteed</em> to hold this lock. |
| * |
| * |
| * <p>If the current thread: |
| * <ul> |
| * <li>has its interrupted status set on entry to this method; or |
| * <li>is {@linkplain Thread#interrupt interrupted} while waiting |
| * and interruption of thread suspension is supported, |
| * </ul> |
| * then {@link InterruptedException} is thrown and the current thread's |
| * interrupted status is cleared. It is not specified, in the first |
| * case, whether or not the test for interruption occurs before the lock |
| * is released. |
| * |
| * |
| * <p>The return value indicates whether the deadline has elapsed, |
| * which can be used as follows: |
| * <pre> |
| * synchronized boolean aMethod(Date deadline) { |
| * boolean stillWaiting = true; |
| * while (!conditionBeingWaitedFor) { |
| * if (stillWaiting) |
| * stillWaiting = theCondition.awaitUntil(deadline); |
| * else |
| * return false; |
| * } |
| * // ... |
| * } |
| * </pre> |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated with this |
| * {@code Condition} when this method is called. |
| * It is up to the implementation to determine if this is |
| * the case and if not, how to respond. Typically, an exception will be |
| * thrown (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| * |
| * <p>An implementation can favor responding to an interrupt over normal |
| * method return in response to a signal, or over indicating the passing |
| * of the specified deadline. In either case the implementation |
| * must ensure that the signal is redirected to another waiting thread, if |
| * there is one. |
| * |
| * @param deadline the absolute time to wait until |
| * @return {@code false} if the deadline has elapsed upon return, else |
| * {@code true} |
| * @throws InterruptedException if the current thread is interrupted |
| * (and interruption of thread suspension is supported) |
| */ |
| boolean awaitUntil(Date deadline) throws InterruptedException; |
| |
| /** |
| * Wakes up one waiting thread. |
| * |
| * <p>If any threads are waiting on this condition then one |
| * is selected for waking up. That thread must then re-acquire the |
| * lock before returning from {@code await}. |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated |
| * with this {@code Condition} when this method is called. It is |
| * up to the implementation to determine if this is the case and |
| * if not, how to respond. Typically, an exception will be thrown |
| * (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| */ |
| void signal(); |
| |
| /** |
| * Wakes up all waiting threads. |
| * |
| * <p>If any threads are waiting on this condition then they are |
| * all woken up. Each thread must re-acquire the lock before it can |
| * return from {@code await}. |
| * |
| * <p><b>Implementation Considerations</b> |
| * |
| * <p>The current thread is assumed to hold the lock associated |
| * with this {@code Condition} when this method is called. It is |
| * up to the implementation to determine if this is the case and |
| * if not, how to respond. Typically, an exception will be thrown |
| * (such as {@link IllegalMonitorStateException}) and the |
| * implementation must document that fact. |
| */ |
| void signalAll(); |
| } |
