reentrantreadwritelock.java

JAVA的一些源码 JAVA2 STANDARD EDITION DEVELOPMENT KIT 5.0

                        return -1;
                } else {
		    Thread first = getFirstQueuedThread();
		    if (first != null && first != current)
			return -1;
		}
                int nextc = c + (acquires << SHARED_SHIFT);
                if (nextc < c)
                    throw new Error("Maximum lock count exceeded");
                if (compareAndSetState(c, nextc))
                    return 1;
                // Recheck count if lost CAS
            }
        }

        final void wlock() { // no fast path
            acquire(1);
        }
    }

    /**
     * The lock returned by method {@link ReentrantReadWriteLock#readLock}.
     */
    public static class ReadLock implements Lock, java.io.Serializable  {
        private static final long serialVersionUID = -5992448646407690164L;
        private final Sync sync;

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

        /**
         * Acquires the read lock. 
         *
         * <p>Acquires the read lock if the write lock is not held by
         * another thread and returns immediately.
         *
         * <p>If the write lock is held by another thread then
         * the current thread becomes disabled for thread scheduling
         * purposes and lies dormant until the read lock has been acquired.
         */
        public void lock() { 
            sync.acquireShared(1);
        }

        /**
         * Acquires the read lock unless the current thread is 
         * {@link Thread#interrupt interrupted}.
         *
         * <p>Acquires the read lock if the write lock is not held
         * by another thread and returns immediately.
         *
         * <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 two things happens:
         *
         * <ul>
         *
         * <li>The read lock is acquired by the current thread; or
         *
         * <li>Some other thread {@link Thread#interrupt interrupts}
         * the current thread.
         *
         * </ul>
         *
         * <p>If the current thread:
         *
         * <ul>
         *
         * <li>has its interrupted status set on entry to this method; or 
         *
         * <li>is {@link Thread#interrupt interrupted} while acquiring 
         * the read 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.acquireSharedInterruptibly(1);
        }

        /**
         * Acquires the read lock only if the write lock is not held by
         * another thread at the time of invocation.
         *
         * <p>Acquires the read lock if the write lock is not held by
         * another thread and returns immediately with the value
         * <tt>true</tt>. Even when this lock has been set to use a
         * fair ordering policy, a call to <tt>tryLock()</tt>
         * <em>will</em> immediately acquire the read lock if it is
         * available, whether or not other threads are currently
         * waiting for the read 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 write lock is held by another thread then
         * this method will return immediately with the value
         * <tt>false</tt>.
         *
         * @return <tt>true</tt> if the read lock was acquired.
         */
        public  boolean tryLock() {
            return sync.nonfairTryAcquireShared(1) >= 0;
        }

        /**
         * Acquires the read lock if the write lock is not held by
         * another thread within the given waiting time and the
         * current thread has not been {@link Thread#interrupt
         * interrupted}.
         *
         * <p>Acquires the read lock if the write lock is not held by
         * another thread and returns immediately with the value
         * <tt>true</tt>. 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 <tt>tryLock</tt> 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 {@link Thread#interrupt interrupts} the current
         * thread; or
         *
         * <li>The specified waiting time elapses
         *
         * </ul>
         *
         * <p>If the read lock is acquired then the value <tt>true</tt> is
         * returned.
         *
         * <p>If the current thread:
         *
         * <ul>
         *
         * <li>has its interrupted status set on entry to this method; or 
         *
         * <li>is {@link 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
         * <tt>false</tt> 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 <tt>true</tt> if the read lock was acquired.
         *
         * @throws InterruptedException if the current thread is interrupted
         * @throws NullPointerException if 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 <tt>UnsupportedOperationException</tt> because
	 * <tt>ReadLocks</tt> 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 
         * &quot;Read locks =&quot; 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 lock null
         */
        protected WriteLock(ReentrantReadWriteLock lock) {
            sync = lock.sync;
        }

        /**
         * Acquire 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.wlock();
        }

        /**
         * Acquires the write lock unless the current thread is {@link
         * 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 {@link 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 {@link 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 <tt>true</tt>,
         * setting the write lock hold count to one. Even when this lock has
         * been set to use a fair ordering policy, a call to
         * <tt>tryLock()</tt> <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
         * <tt>true</tt>.
         *
         * <p>If the lock is held by another thread then this method
         * will return immediately with the value <tt>false</tt>.
         *
         * @return <tt>true</tt> if the lock was free and was acquired
         * by the current thread, or the write lock was already held
         * by the current thread; and <tt>false</tt> otherwise.
         */
        public boolean tryLock( ) {
            return sync.nonfairTryAcquire(1);
        }

        /**
         * Acquires the write lock if it is not held by another thread
         * within the given waiting time and the current thread has
         * not been {@link 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 <tt>true</tt>,
         * 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 <tt>tryLock</tt>
         * 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
         * <tt>true</tt>.
         *