reentrantreadwritelock.java

java1.6众多例子参考

         * <p>Acquires the read lock if the write lock is not held by
         * another thread and returns immediately with the value
         * {@code true}. If this lock has been set to use a fair
         * ordering policy then an available lock <em>will not</em> be
         * acquired if any other threads are waiting for the
         * lock. This is in contrast to the {@link #tryLock()}
         * method. If you want a timed {@code tryLock} that does
         * permit barging on a fair lock then combine the timed and
         * un-timed forms together:
         *
         * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
         * </pre>
         *
         * <p>If the write lock is held by another thread then the
         * current thread becomes disabled for thread scheduling
         * purposes and lies dormant until one of three things happens:
         *
         * <ul>
         *
         * <li>The read lock is acquired by the current thread; or
         *
         * <li>Some other thread {@linkplain Thread#interrupt interrupts}
         * the current thread; or
         *
         * <li>The specified waiting time elapses.
         *
         * </ul>
         *
         * <p>If the read lock is acquired then the value {@code true} is
         * returned.
         *
         * <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
         * acquiring the read lock,
         *
         * </ul> then {@link InterruptedException} is thrown and the
         * current thread's interrupted status is cleared.
         *
         * <p>If the specified waiting time elapses then the value
         * {@code false} is returned.  If the time is less than or
         * equal to zero, the method will not wait at all.
         *
         * <p>In this implementation, as this method is an explicit
         * interruption point, preference is given to responding to
         * the interrupt over normal or reentrant acquisition of the
         * lock, and over reporting the elapse of the waiting time.
         *
         * @param timeout the time to wait for the read lock
         * @param unit the time unit of the timeout argument
         * @return {@code true} if the read lock was acquired
         * @throws InterruptedException if the current thread is interrupted
         * @throws NullPointerException if the time unit is null
         *
         */
        public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
            return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
        }

        /**
         * Attempts to release this lock.
         *
         * <p> If the number of readers is now zero then the lock
         * is made available for write lock attempts.
         */
        public  void unlock() {
            sync.releaseShared(1);
        }

        /**
         * Throws {@code UnsupportedOperationException} because
	 * {@code ReadLocks} do not support conditions.
         *
         * @throws UnsupportedOperationException always
         */
        public Condition newCondition() {
            throw new UnsupportedOperationException();
        }

        /**
         * Returns a string identifying this lock, as well as its lock state.
         * The state, in brackets, includes the String {@code "Read locks ="}
         * followed by the number of held read locks.
         *
         * @return a string identifying this lock, as well as its lock state
         */
        public String toString() {
            int r = sync.getReadLockCount();
            return super.toString() +
                "[Read locks = " + r + "]";
        }
    }

    /**
     * The lock returned by method {@link ReentrantReadWriteLock#writeLock}.
     */
    public static class WriteLock implements Lock, java.io.Serializable  {
        private static final long serialVersionUID = -4992448646407690164L;
	private final Sync sync;

        /**
         * Constructor for use by subclasses
         *
         * @param lock the outer lock object
         * @throws NullPointerException if the lock is null
         */
        protected WriteLock(ReentrantReadWriteLock lock) {
            sync = lock.sync;
        }

        /**
         * Acquires the write lock.
         *
         * <p>Acquires the write lock if neither the read nor write lock
	 * are held by another thread
         * and returns immediately, setting the write lock hold count to
         * one.
         *
         * <p>If the current thread already holds the write lock then the
         * hold count is incremented by one and the method returns
         * immediately.
         *
         * <p>If the lock is held by another thread then the current
         * thread becomes disabled for thread scheduling purposes and
         * lies dormant until the write lock has been acquired, at which
         * time the write lock hold count is set to one.
         */
        public void lock() {
            sync.acquire(1);
        }

        /**
         * Acquires the write lock unless the current thread is
         * {@linkplain Thread#interrupt interrupted}.
         *
         * <p>Acquires the write lock if neither the read nor write lock
	 * are held by another thread
         * and returns immediately, setting the write lock hold count to
         * one.
         *
         * <p>If the current thread already holds this lock then the
         * hold count is incremented by one and the method returns
         * immediately.
         *
         * <p>If the lock is held by another thread then the current
         * thread becomes disabled for thread scheduling purposes and
         * lies dormant until one of two things happens:
         *
         * <ul>
         *
         * <li>The write lock is acquired by the current thread; or
         *
         * <li>Some other thread {@linkplain Thread#interrupt interrupts}
         * the current thread.
         *
         * </ul>
         *
         * <p>If the write lock is acquired by the current thread then the
         * lock hold count is set to one.
         *
         * <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
         * acquiring the write lock,
         *
         * </ul>
         *
         * then {@link InterruptedException} is thrown and the current
         * thread's interrupted status is cleared.
         *
         * <p>In this implementation, as this method is an explicit
         * interruption point, preference is given to responding to
         * the interrupt over normal or reentrant acquisition of the
         * lock.
         *
         * @throws InterruptedException if the current thread is interrupted
         */
        public void lockInterruptibly() throws InterruptedException {
            sync.acquireInterruptibly(1);
        }

        /**
         * Acquires the write lock only if it is not held by another thread
         * at the time of invocation.
         *
         * <p>Acquires the write lock if neither the read nor write lock
	 * are held by another thread
         * and returns immediately with the value {@code true},
         * setting the write lock hold count to one. Even when this lock has
         * been set to use a fair ordering policy, a call to
         * {@code tryLock()} <em>will</em> immediately acquire the
         * lock if it is available, whether or not other threads are
         * currently waiting for the write lock.  This &quot;barging&quot;
         * behavior can be useful in certain circumstances, even
         * though it breaks fairness. If you want to honor the
         * fairness setting for this lock, then use {@link
         * #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
         * which is almost equivalent (it also detects interruption).
         *
         * <p> If the current thread already holds this lock then the
         * hold count is incremented by one and the method returns
         * {@code true}.
         *
         * <p>If the lock is held by another thread then this method
         * will return immediately with the value {@code false}.
         *
         * @return {@code true} if the lock was free and was acquired
         * by the current thread, or the write lock was already held
         * by the current thread; and {@code false} otherwise.
         */
        public boolean tryLock( ) {
            return sync.tryWriteLock();
        }

        /**
         * Acquires the write lock if it is not held by another thread
         * within the given waiting time and the current thread has
         * not been {@linkplain Thread#interrupt interrupted}.
         *
         * <p>Acquires the write lock if neither the read nor write lock
	 * are held by another thread
         * and returns immediately with the value {@code true},
         * setting the write lock hold count to one. If this lock has been
         * set to use a fair ordering policy then an available lock
         * <em>will not</em> be acquired if any other threads are
         * waiting for the write lock. This is in contrast to the {@link
         * #tryLock()} method. If you want a timed {@code tryLock}
         * that does permit barging on a fair lock then combine the
         * timed and un-timed forms together:
         *
         * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
         * </pre>
         *
         * <p>If the current thread already holds this lock then the
         * hold count is incremented by one and the method returns
         * {@code true}.
         *
         * <p>If the lock is held by another thread then the current
         * thread becomes disabled for thread scheduling purposes and
         * lies dormant until one of three things happens:
         *
         * <ul>
         *
         * <li>The write lock is acquired by the current thread; or
         *
         * <li>Some other thread {@linkplain Thread#interrupt interrupts}
         * the current thread; or
         *
         * <li>The specified waiting time elapses
         *
         * </ul>
         *
         * <p>If the write lock is acquired then the value {@code true} is
         * returned and the write lock hold count is set to one.
         *
         * <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
         * acquiring the write lock,
         *
         * </ul>
         *
         * then {@link InterruptedException} is thrown and the current
         * thread's interrupted status is cleared.
         *
         * <p>If the specified waiting time elapses then the value
         * {@code false} is returned.  If the time is less than or
         * equal to zero, the method will not wait at all.
         *
         * <p>In this implementation, as this method is an explicit
         * interruption point, preference is given to responding to
         * the interrupt over normal or reentrant acquisition of the
         * lock, and over reporting the elapse of the waiting time.
         *
         * @param timeout the time to wait for the write lock
         * @param unit the time unit of the timeout argument
         *
         * @return {@code true} if the lock was free and was acquired
         * by the current thread, or the write lock was already held by the
         * current thread; and {@code false} if the waiting time
         * elapsed before the lock could be acquired.
         *
         * @throws InterruptedException if the current thread is interrupted
         * @throws NullPointerException if the time unit is null
         *
         */
        public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
            return sync.tryAcquireNanos(1, unit.toNanos(timeout));
        }

        /**
         * Attempts to release this lock.
         *
         * <p>If the current thread is the holder of this lock then
         * the hold count is decremented. If the hold count is now
         * zero then the lock is released.  If the current thread is
         * not the holder of this lock then {@link
         * IllegalMonitorStateException} is thrown.
         *
         * @throws IllegalMonitorStateException if the current thread does not
         * hold this lock.
         */
        public void unlock() {
            sync.release(1);
        }

        /**
         * Returns a {@link Condition} instance for use with this
         * {@link Lock} instance.
         * <p>The returned {@link Condition} instance supports the same
         * usages as do the {@link Object} monitor methods ({@link
         * Object#wait() wait}, {@link Object#notify notify}, and {@link
         * Object#notifyAll notifyAll}) when used with the built-in
         * monitor lock.
         *
         * <ul>
         *
         * <li>If this write lock is not held when any {@link
         * Condition} method is called then an {@link
         * IllegalMonitorStateException} is thrown.  (Read locks are
         * held independently of write locks, so are not checked or
         * affected. However it is essentially always an error to
         * invoke a condition waiting method when the current thread