reentrantlock.java

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                    holds_ = 1;
                    return true;
                }
                else if (caller == owner_) {
                    ++holds_;
                    return true;
                }
            }
            WaitQueue.WaitNode n = new WaitQueue.WaitNode();
            return n.doTimedWait(this, nanos);
        }

        protected synchronized WaitQueue.WaitNode getSignallee(Thread caller) {
            if (caller != owner_)
                throw new IllegalMonitorStateException("Not owner");
            // assert (holds_ > 0)
            if (holds_ >= 2) { // current thread will keep the lock
                --holds_;
                return null;
            }
            // assert (holds_ == 1)
            WaitQueue.WaitNode w = wq_.extract();
            if (w == null) { // if none, clear for new arrivals
                owner_ = null;
                holds_ = 0;
            }
            return w;
        }

        public void unlock() {
            Thread caller = Thread.currentThread();
            for (;;) {
                WaitQueue.WaitNode w = getSignallee(caller);
                if (w == null) return;  // no one to signal
                if (w.signal(this)) return; // notify if still waiting, else skip
            }
        }

        public final boolean isFair() {
            return true;
        }

        public synchronized boolean hasQueuedThreads() {
            return wq_.hasNodes();
        }

        public synchronized int getQueueLength() {
            return wq_.getLength();
        }

        public synchronized Collection getQueuedThreads() {
            return wq_.getWaitingThreads();
        }

        public synchronized boolean isQueued(Thread thread) {
            return wq_.isWaiting(thread);
        }
    }

    /**
     * Creates an instance of <tt>ReentrantLock</tt>.
     * This is equivalent to using <tt>ReentrantLock(false)</tt>.
     */
    public ReentrantLock() {
        impl = new NonfairImpl();
    }

    /**
     * Creates an instance of <tt>ReentrantLock</tt> with the
     * given fairness policy.
     * @param fair true if this lock will be fair; else false
     */
    public ReentrantLock(boolean fair) {
        impl = (fair)? (Impl)new FairImpl() : new NonfairImpl();
    }


    /**
     * Acquires the lock.
     *
     * <p>Acquires the lock if it is not held by another thread and returns
     * immediately, setting the lock hold count to one.
     *
     * <p>If the current thread
     * already holds the 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 lock has been acquired,
     * at which time the lock hold count is set to one.
     */
    public void lock() {
        boolean wasInterrupted = false;
        while (true) {
            try {
                impl.lockInterruptibly();
                if (wasInterrupted) {
                    Thread.currentThread().interrupt();
                }
                return;
            }
            catch (InterruptedException e) {
                wasInterrupted = true;
            }
        }
    }

    /**
     * Acquires the lock unless the current thread is
     * {@link Thread#interrupt interrupted}.
     *
     * <p>Acquires the lock if it is not held by another thread and returns
     * immediately, setting the 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 lock is acquired by the current thread; or
     *
     * <li>Some other thread {@link Thread#interrupt interrupts} the current
     * thread.
     *
     * </ul>
     *
     * <p>If the 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 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 {
        impl.lockInterruptibly();
    }

    /**
     * Acquires the lock only if it is not held by another thread at the time
     * of invocation.
     *
     * <p>Acquires the lock if it is not held by another thread and
     * returns immediately with the value <tt>true</tt>, setting the
     * 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 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 lock was already held by the current thread; and
     * <tt>false</tt> otherwise.
     */
    public boolean tryLock() {
        return impl.tryLock();
    }

    /**
     * Acquires the 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 lock if it is not held by another thread and returns
     * immediately with the value <tt>true</tt>, setting the 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 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>.
     *
     * <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 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 lock is acquired then the value <tt>true</tt> is returned and
     * 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 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 lock
     * @param unit the time unit of the timeout argument
     *
     * @return <tt>true</tt> if the lock was free and was acquired by the
     * current thread, or the lock was already held by the current thread; and
     * <tt>false</tt> if the waiting time elapsed before the lock could be
     * 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 impl.tryLock(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() {
        impl.unlock();
    }

    /**
     * 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.