util/concurrent/FairSemaphore.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.concurrent.locks.*;

/**
 * A semaphore guaranteeing that threads invoking any of the {@link
 * #acquire() acquire} methods are allocated permits in the order in
 * which their invocation of those methods was processed
 * (first-in-first-out; FIFO). Note that FIFO ordering necessarily
 * applies to specific internal points of execution within these
 * methods.  So, it is possible for one thread to invoke
 * <tt>acquire</tt> before another, but reach the ordering point after
 * the other, and similarly upon return from the method.
 *
 * <p>Because permits are allocated in-order, this class also provides
 * convenience methods to {@link #acquire(long) acquire} and {@link
 * #release(long) release} multiple permits at a time. 
 *
 * @since 1.5
 * @spec JSR-166
 * @revised $Date: 2003/07/09 23:23:17 $
 * @editor $Author: dl $
 * @author Doug Lea
 *
 */
public class FairSemaphore extends Semaphore {

    /*
     * Basic algorithm is a variant of the one described
     * in CPJ book 2nd edition, section 3.7.3
     */

    /**
     * Nodes of the wait queue. Opportunistically subclasses ReentrantLock.
     */
    private static class Node extends ReentrantLock {
        /** The condition to wait on */
        Condition done = newCondition();
        /** True if interrupted before released */
        boolean cancelled;
        /** Number of permits remaining until can release */
        long permitsNeeded;
        /** Next node of queue */
        Node next;

        Node(long n) { permitsNeeded = n; }
    }

    /** Head of the wait queue */
    private Node head;

    /** Pointer to last node of the wait queue */
    private Node last;

    /** Add a new node to wait queue with given number of permits needed */
    private Node enq(long n) { 
        Node p = new Node(n);
        if (last == null) 
            last = head = p;
        else 
            last = last.next = p;
        return p;
    }

    /** Remove first node from wait queue */
    private void removeFirst() {
        Node p = head;
        assert p != null;
        if (p != null && (head = p.next) == null) 
            last = null;
    }

    /**
     * Construct a <tt>FairSemaphore</tt> with the given number of
     * permits.
     * @param permits the initial number of permits available
     */
    public FairSemaphore(long permits) { 
        super(permits, new ReentrantLock(true)); 
    }

    /**
     * Acquires a permit from this semaphore, blocking until one is
     * available, or the thread is {@link Thread#interrupt interrupted}.
     *
     * <p>Acquires a permit, if one is available and returns immediately,
     * reducing the number of available permits by one.
     * <p>If no permit is available then the current thread becomes
     * disabled for thread scheduling purposes and lies dormant until
     * one of two things happens:
     * <ul>
     * <li>Some other thread invokes the {@link #release} method for this
     * semaphore and the current thread happens to be chosen as the
     * thread to receive the permit; 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 waiting
     * for a permit,
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared.
     *
     * @throws InterruptedException if the current thread is interrupted
     *
     * @see Thread#interrupt
     */
    public void acquire() throws InterruptedException {
        acquire(1L);
    }

    /**
     * Acquires a permit from this semaphore, blocking until one is
     * available.
     *
     * <p>Acquires a permit, if one is available and returns immediately,
     * reducing the number of available permits by one.
     * <p>If no permit is available then the current thread becomes
     * disabled for thread scheduling purposes and lies dormant until
     * some other thread invokes the {@link #release} method for this
     * semaphore and the current thread happens to be chosen as the
     * thread to receive the permit.
     *
     * <p>If the current thread
     * is {@link Thread#interrupt interrupted} while waiting
     * for a permit then it will continue to wait, but the time at which
     * the thread is assigned a permit may change compared to the time it
     * would have received the permit had no interruption occurred. When the
     * thread does return from this method its interrupt status will be set.
     *
     */
    public void acquireUninterruptibly() {
        acquireUninterruptibly(1L);
    }

    /**
     * Acquires a permit from this semaphore, only if one is available at the 
     * time of invocation.
     * <p>Acquires a permit, if one is available and returns immediately,
     * with the value <tt>true</tt>,
     * reducing the number of available permits by one.
     *
     * <p>If no permit is available then this method will return
     * immediately with the value <tt>false</tt>.
     *
     * @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
     * otherwise.
     */
    public boolean tryAcquire() {
        return tryAcquire(1L);
    }

    /**
     * Acquires a permit from this semaphore, if one becomes available 
     * within the given waiting time and the
     * current thread has not been {@link Thread#interrupt interrupted}.
     * <p>Acquires a permit, if one is available and returns immediately,
     * with the value <tt>true</tt>,
     * reducing the number of available permits by one.
     * <p>If no permit is available then
     * the current thread becomes disabled for thread scheduling
     * purposes and lies dormant until one of three things happens:
     * <ul>
     * <li>Some other thread invokes the {@link #release} method for this
     * semaphore and the current thread happens to be chosen as the
     * thread to receive the permit; or
     * <li>Some other thread {@link Thread#interrupt interrupts} the current
     * thread; or
     * <li>The specified waiting time elapses.
     * </ul>
     * <p>If a permit 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 waiting to acquire
     * a permit,
     * </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.
     * The given waiting time is a best-effort lower bound. If the time is
     * less than or equal to zero, the method will not wait at all.
     *
     * @param timeout the maximum time to wait for a permit
     * @param unit the time unit of the <tt>timeout</tt> argument.
     * @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
     * if the waiting time elapsed before a permit was acquired.
     *
     * @throws InterruptedException if the current thread is interrupted
     *
     * @see Thread#interrupt
     *
     */
    public boolean tryAcquire(long timeout, TimeUnit unit) 
        throws InterruptedException {
        return tryAcquire(1L, timeout, unit);
    }

    /**
     * Releases a permit, returning it to the semaphore.
     * <p>Releases a permit, increasing the number of available permits
     * by one.
     * If any threads are blocking trying to acquire a permit, then one
     * is selected and given the permit that was just released.
     * That thread is re-enabled for thread scheduling purposes.
     * <p>There is no requirement that a thread that releases a permit must
     * have acquired that permit by calling {@link #acquire}.
     * Correct usage of a semaphore is established by programming convention
     * in the application.
     */
    public void release() {
        release(1L);
    }

       
    /**
     * Acquires the given number of permits from this semaphore, 
     * blocking until all are available, 
     * or the thread is {@link Thread#interrupt interrupted}.
     *
     * <p>Acquires the given number of permits, if they are available,
     * and returns immediately,
     * reducing the number of available permits by the given amount.
     *
     * <p>If insufficient permits are available then the current thread becomes
     * disabled for thread scheduling purposes and lies dormant until
     * one of two things happens:
     * <ul>
     * <li>Some other thread invokes one of the {@link #release() release} 
     * methods for this semaphore, the current thread is next to be assigned
     * permits and the number of available permits satisfies this request; 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 waiting
     * for a permit,
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared. 
     * Any available permits are assigned to the next waiting thread as if
     * they had been made available by a call to {@link #release()}.
     *
     * @param permits the number of permits to acquire
     *
     * @throws InterruptedException if the current thread is interrupted
     * @throws IllegalArgumentException if permits less than zero.
     *
     * @see Thread#interrupt
     */
    public void acquire(long permits) throws InterruptedException {
        if (permits < 0) throw new IllegalArgumentException();
        Node node = null;
        lock.lockInterruptibly();
        try {
            long remaining = count - permits;
            if (remaining >= 0) {
                count = remaining;
                return;
            }
            count = 0;
            node = enq(-remaining);
        }
        finally {
            lock.unlock();
        }

        node.lock();
        try {
            while (node.permitsNeeded > 0) 
                node.done.await();
        }
        catch(InterruptedException ie) {
            if (node.permitsNeeded > 0) {
                node.cancelled = true;
                release(permits - node.permitsNeeded);
                throw ie;
            }
            else { // ignore interrupt
                Thread.currentThread().interrupt();
            }
        }
        finally {
            node.unlock();
        }
    }

    /**
     * Acquires the given number of permits from this semaphore, 
     * blocking until all are available.
     *
     * <p>Acquires the given number of permits, if they are available,
     * and returns immediately,
     * reducing the number of available permits by the given amount.
     *
     * <p>If insufficient permits are available then the current thread becomes
     * disabled for thread scheduling purposes and lies dormant until
     * some other thread invokes one of the {@link #release() release} 
     * methods for this semaphore, the current thread is next to be assigned
     * permits and the number of available permits satisfies this request.
     *
     * <p>If the current thread
     * is {@link Thread#interrupt interrupted} while waiting
     * for permits then it will continue to wait and its position in the
     * queue is not affected. When the
     * thread does return from this method its interrupt status will be set.
     *
     * @param permits the number of permits to acquire
     * @throws IllegalArgumentException if permits less than zero.
     *
     */
    public void acquireUninterruptibly(long permits) {
        if (permits < 0) throw new IllegalArgumentException();
        Node node = null;
        lock.lock();
        try {
            long remaining = count - permits;
            if (remaining >= 0) {
                count = remaining;
                return;
            }
            count = 0;
            node = enq(-remaining);
        }
        finally {
            lock.unlock();
        }

        node.lock();
        try {
            while (node.permitsNeeded > 0) 
                node.done.awaitUninterruptibly();
        }
        finally {
            node.unlock();
        }
    }

    /**
     * Acquires the given number of permits from this semaphore, only if 
     * all are available at the  time of invocation.
     * <p>Acquires the given number of permits, if they are available, and 
     * returns immediately, with the value <tt>true</tt>,
     * reducing the number of available permits by the given amount.
     *
     * <p>If insufficient permits are available then this method will return
     * immediately with the value <tt>false</tt> and the number of available
     * permits is unchanged.
     *
     * @param permits the number of permits to acquire
     *
     * @return <tt>true</tt> if the permits were acquired and <tt>false</tt>
     * otherwise.
     * @throws IllegalArgumentException if permits less than zero.
     */
    public boolean tryAcquire(long permits) {
        if (permits < 0) throw new IllegalArgumentException();
        lock.lock();
        try {
            long remaining = count - permits;
            if (remaining >= 0) {
                count = remaining;
                return true;
            }
            return false;
        }
        finally {
            lock.unlock();
        }
    }

    /**
     * Acquires the given number of permits from this semaphore, if all 
     * become available within the given waiting time and the
     * current thread has not been {@link Thread#interrupt interrupted}.
     * <p>Acquires the given number of permits, if they are available and 
     * returns immediately, with the value <tt>true</tt>,
     * reducing the number of available permits by the given amount.
     * <p>If insufficient permits are available then
     * the current thread becomes disabled for thread scheduling
     * purposes and lies dormant until one of three things happens:
     * <ul>
     * <li>Some other thread invokes one of the {@link #release() release} 
     * methods for this semaphore, the current thread is next to be assigned
     * permits and the number of available permits satisfies this request; or
     * <li>Some other thread {@link Thread#interrupt interrupts} the current
     * thread; or
     * <li>The specified waiting time elapses.
     * </ul>
     * <p>If the permits are 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 waiting to acquire
     * the permits,
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared.
     * Any available permits are assigned to the next waiting thread as if
     * they had been made available by a call to {@link #release()}.
     *
     * <p>If the specified waiting time elapses then the value <tt>false</tt>
     * is returned.
     * The given waiting time is a best-effort lower bound. If the time is
     * less than or equal to zero, the method will not wait at all.
     * Any available permits are assigned to the next waiting thread as if
     * they had been made available by a call to {@link #release()}.
     *
     * @param permits the number of permits to acquire
     * @param timeout the maximum time to wait for the permits
     * @param unit the time unit of the <tt>timeout</tt> argument.
     * @return <tt>true</tt> if all permits were acquired and <tt>false</tt>
     * if the waiting time elapsed before all permits were acquired.
     *
     * @throws InterruptedException if the current thread is interrupted
     * @throws IllegalArgumentException if permits less than zero.
     *
     * @see Thread#interrupt
     *
     */
    public boolean tryAcquire(long permits, long timeout, TimeUnit unit)
        throws InterruptedException {
        if (permits < 0) throw new IllegalArgumentException();
        Node node = null;
        long nanos = unit.toNanos(timeout);
        lock.lockInterruptibly();
        try {
            long remaining = count - permits;
            if (remaining >= 0) {
                count = remaining;
                return true;
            }
            if (nanos <= 0)
                return false;
            count = 0;
            node = enq(-remaining);
        }
        finally {
            lock.unlock();
        }
        
        node.lock();
        try {
            while (node.permitsNeeded > 0) {
                nanos = node.done.awaitNanos(nanos);
                if (nanos <= 0) {
                    release(permits - node.permitsNeeded);
                    return false;
                }
            }
            return true;
        }
        catch(InterruptedException ie) {
            if (node.permitsNeeded > 0) {
                node.cancelled = true;
                release(permits - node.permitsNeeded);
                throw ie;
            }
            else { // ignore interrupt
                Thread.currentThread().interrupt();
                return true;
            }
        }
        finally {
            node.unlock();
        }
    }


    /**
     * Releases the given number of permits, returning them to the semaphore.
     * <p>Releases the given number of permits, increasing the number of 
     * available permits by that amount.
     * If any threads are blocking trying to acquire permits, then the
     * one that has been waiting the longest
     * is selected and given the permits that were just released.
     * If the number of available permits satisfies that thread's request
     * then that thread is re-enabled for thread scheduling purposes; otherwise
     * the thread continues to wait. If there are still permits available
     * after the first thread's request has been satisfied, then those permits
     * are assigned to the next waiting thread. If it is satisfied then it is
     * re-enabled for thread scheduling purposes. This continues until there
     * are insufficient permits to satisfy the next waiting thread, or there
     * are no more waiting threads.
     *
     * <p>There is no requirement that a thread that releases a permit must
     * have acquired that permit by calling {@link Semaphore#acquire acquire}.
     * Correct usage of a semaphore is established by programming convention
     * in the application.
     *
     * @param permits the number of permits to release
     * @throws IllegalArgumentException if permits less than zero.
     */
    public void release(long permits) {
        if (permits < 0) throw new IllegalArgumentException();
        if (permits == 0)
            return;
        // Even when using fair locks, releases should try to barge in.
        if (!lock.tryLock())
            lock.lock();
        try {
            long p = permits;
            while (p > 0) {
                Node node = head;
                if (node == null) {
                    count += p;
                    p = 0;
                }
                else {
                    node.lock();
                    try {
                        if (node.cancelled)
                            removeFirst();
                        else if (node.permitsNeeded > p) {
                            node.permitsNeeded -= p;
                            p = 0;
                        }
                        else {
                            p -= node.permitsNeeded;
                            node.permitsNeeded = 0;
                            node.done.signal();
                            removeFirst();
                        }
                    }
                    finally {
                        node.unlock();
                    }
                }
            }
        }
        finally {
            lock.unlock();
        }
    }
}
Revision:	1.6
Committed:	Fri Jul 11 13:12:06 2003 UTC (20 years, 10 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRELIMINARY_TEST_RELEASE_2, JSR166_CR1
Changes since 1.5:	+298 -46 lines
Log Message:	Fair semaphores actually fair now.
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7			package java.util.concurrent;
8	dl	1.4	import java.util.concurrent.locks.*;
9	dl	1.1
10			/**
11	dl	1.2	* A semaphore guaranteeing that threads invoking any of the {@link
12			* #acquire() acquire} methods are allocated permits in the order in
13			* which their invocation of those methods was processed
14			* (first-in-first-out; FIFO). Note that FIFO ordering necessarily
15			* applies to specific internal points of execution within these
16			* methods. So, it is possible for one thread to invoke
17			* <tt>acquire</tt> before another, but reach the ordering point after
18			* the other, and similarly upon return from the method.
19	dl	1.1	*
20	dl	1.2	* <p>Because permits are allocated in-order, this class also provides
21			* convenience methods to {@link #acquire(long) acquire} and {@link
22			* #release(long) release} multiple permits at a time.
23	dl	1.1	*
24			* @since 1.5
25			* @spec JSR-166
26	dl	1.6	* @revised $Date: 2003/07/09 23:23:17 $
27	dl	1.2	* @editor $Author: dl $
28	dl	1.3	* @author Doug Lea
29	dl	1.1	*
30			*/
31			public class FairSemaphore extends Semaphore {
32
33			/*
34	dl	1.6	* Basic algorithm is a variant of the one described
35			* in CPJ book 2nd edition, section 3.7.3
36	dl	1.1	*/
37
38			/**
39	dl	1.6	* Nodes of the wait queue. Opportunistically subclasses ReentrantLock.
40			*/
41			private static class Node extends ReentrantLock {
42			/** The condition to wait on */
43			Condition done = newCondition();
44			/** True if interrupted before released */
45			boolean cancelled;
46			/** Number of permits remaining until can release */
47			long permitsNeeded;
48			/** Next node of queue */
49			Node next;
50
51			Node(long n) { permitsNeeded = n; }
52			}
53
54			/** Head of the wait queue */
55			private Node head;
56
57			/** Pointer to last node of the wait queue */
58			private Node last;
59
60			/** Add a new node to wait queue with given number of permits needed */
61			private Node enq(long n) {
62			Node p = new Node(n);
63			if (last == null)
64			last = head = p;
65			else
66			last = last.next = p;
67			return p;
68			}
69
70			/** Remove first node from wait queue */
71			private void removeFirst() {
72			Node p = head;
73			assert p != null;
74			if (p != null && (head = p.next) == null)
75			last = null;
76			}
77
78			/**
79			* Construct a <tt>FairSemaphore</tt> with the given number of
80	dl	1.1	* permits.
81			* @param permits the initial number of permits available
82			*/
83			public FairSemaphore(long permits) {
84	dl	1.4	super(permits, new ReentrantLock(true));
85	dl	1.1	}
86
87			/**
88	dl	1.6	* Acquires a permit from this semaphore, blocking until one is
89			* available, or the thread is {@link Thread#interrupt interrupted}.
90			*
91			* <p>Acquires a permit, if one is available and returns immediately,
92			* reducing the number of available permits by one.
93			* <p>If no permit is available then the current thread becomes
94			* disabled for thread scheduling purposes and lies dormant until
95			* one of two things happens:
96			* <ul>
97			* <li>Some other thread invokes the {@link #release} method for this
98			* semaphore and the current thread happens to be chosen as the
99			* thread to receive the permit; or
100			* <li>Some other thread {@link Thread#interrupt interrupts} the current
101			* thread.
102			* </ul>
103			*
104			* <p>If the current thread:
105			* <ul>
106			* <li>has its interrupted status set on entry to this method; or
107			* <li>is {@link Thread#interrupt interrupted} while waiting
108			* for a permit,
109			* </ul>
110			* then {@link InterruptedException} is thrown and the current thread's
111			* interrupted status is cleared.
112			*
113			* @throws InterruptedException if the current thread is interrupted
114			*
115			* @see Thread#interrupt
116			*/
117			public void acquire() throws InterruptedException {
118			acquire(1L);
119			}
120
121			/**
122			* Acquires a permit from this semaphore, blocking until one is
123			* available.
124			*
125			* <p>Acquires a permit, if one is available and returns immediately,
126			* reducing the number of available permits by one.
127			* <p>If no permit is available then the current thread becomes
128			* disabled for thread scheduling purposes and lies dormant until
129			* some other thread invokes the {@link #release} method for this
130			* semaphore and the current thread happens to be chosen as the
131			* thread to receive the permit.
132			*
133			* <p>If the current thread
134			* is {@link Thread#interrupt interrupted} while waiting
135			* for a permit then it will continue to wait, but the time at which
136			* the thread is assigned a permit may change compared to the time it
137			* would have received the permit had no interruption occurred. When the
138			* thread does return from this method its interrupt status will be set.
139			*
140			*/
141			public void acquireUninterruptibly() {
142			acquireUninterruptibly(1L);
143			}
144
145			/**
146			* Acquires a permit from this semaphore, only if one is available at the
147			* time of invocation.
148			* <p>Acquires a permit, if one is available and returns immediately,
149			* with the value <tt>true</tt>,
150			* reducing the number of available permits by one.
151			*
152			* <p>If no permit is available then this method will return
153			* immediately with the value <tt>false</tt>.
154			*
155			* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
156			* otherwise.
157			*/
158			public boolean tryAcquire() {
159			return tryAcquire(1L);
160			}
161
162			/**
163			* Acquires a permit from this semaphore, if one becomes available
164			* within the given waiting time and the
165			* current thread has not been {@link Thread#interrupt interrupted}.
166			* <p>Acquires a permit, if one is available and returns immediately,
167			* with the value <tt>true</tt>,
168			* reducing the number of available permits by one.
169			* <p>If no permit is available then
170			* the current thread becomes disabled for thread scheduling
171			* purposes and lies dormant until one of three things happens:
172			* <ul>
173			* <li>Some other thread invokes the {@link #release} method for this
174			* semaphore and the current thread happens to be chosen as the
175			* thread to receive the permit; or
176			* <li>Some other thread {@link Thread#interrupt interrupts} the current
177			* thread; or
178			* <li>The specified waiting time elapses.
179			* </ul>
180			* <p>If a permit is acquired then the value <tt>true</tt> is returned.
181			* <p>If the current thread:
182			* <ul>
183			* <li>has its interrupted status set on entry to this method; or
184			* <li>is {@link Thread#interrupt interrupted} while waiting to acquire
185			* a permit,
186			* </ul>
187			* then {@link InterruptedException} is thrown and the current thread's
188			* interrupted status is cleared.
189			* <p>If the specified waiting time elapses then the value <tt>false</tt>
190			* is returned.
191			* The given waiting time is a best-effort lower bound. If the time is
192			* less than or equal to zero, the method will not wait at all.
193			*
194			* @param timeout the maximum time to wait for a permit
195			* @param unit the time unit of the <tt>timeout</tt> argument.
196			* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
197			* if the waiting time elapsed before a permit was acquired.
198			*
199			* @throws InterruptedException if the current thread is interrupted
200			*
201			* @see Thread#interrupt
202			*
203			*/
204			public boolean tryAcquire(long timeout, TimeUnit unit)
205			throws InterruptedException {
206			return tryAcquire(1L, timeout, unit);
207			}
208
209			/**
210			* Releases a permit, returning it to the semaphore.
211			* <p>Releases a permit, increasing the number of available permits
212			* by one.
213			* If any threads are blocking trying to acquire a permit, then one
214			* is selected and given the permit that was just released.
215			* That thread is re-enabled for thread scheduling purposes.
216			* <p>There is no requirement that a thread that releases a permit must
217			* have acquired that permit by calling {@link #acquire}.
218			* Correct usage of a semaphore is established by programming convention
219			* in the application.
220			*/
221			public void release() {
222			release(1L);
223			}
224
225
226			/**
227	dl	1.1	* Acquires the given number of permits from this semaphore,
228			* blocking until all are available,
229			* or the thread is {@link Thread#interrupt interrupted}.
230			*
231			* <p>Acquires the given number of permits, if they are available,
232			* and returns immediately,
233			* reducing the number of available permits by the given amount.
234			*
235			* <p>If insufficient permits are available then the current thread becomes
236			* disabled for thread scheduling purposes and lies dormant until
237			* one of two things happens:
238			* <ul>
239			* <li>Some other thread invokes one of the {@link #release() release}
240			* methods for this semaphore, the current thread is next to be assigned
241			* permits and the number of available permits satisfies this request; or
242			* <li>Some other thread {@link Thread#interrupt interrupts} the current
243			* thread.
244			* </ul>
245			*
246			* <p>If the current thread:
247			* <ul>
248			* <li>has its interrupted status set on entry to this method; or
249			* <li>is {@link Thread#interrupt interrupted} while waiting
250			* for a permit,
251			* </ul>
252			* then {@link InterruptedException} is thrown and the current thread's
253			* interrupted status is cleared.
254			* Any available permits are assigned to the next waiting thread as if
255			* they had been made available by a call to {@link #release()}.
256			*
257			* @param permits the number of permits to acquire
258			*
259			* @throws InterruptedException if the current thread is interrupted
260			* @throws IllegalArgumentException if permits less than zero.
261			*
262			* @see Thread#interrupt
263			*/
264			public void acquire(long permits) throws InterruptedException {
265			if (permits < 0) throw new IllegalArgumentException();
266	dl	1.6	Node node = null;
267	dl	1.1	lock.lockInterruptibly();
268			try {
269	dl	1.6	long remaining = count - permits;
270			if (remaining >= 0) {
271			count = remaining;
272			return;
273			}
274			count = 0;
275			node = enq(-remaining);
276	dl	1.1	}
277			finally {
278			lock.unlock();
279			}
280	dl	1.6
281			node.lock();
282			try {
283			while (node.permitsNeeded > 0)
284			node.done.await();
285			}
286			catch(InterruptedException ie) {
287			if (node.permitsNeeded > 0) {
288			node.cancelled = true;
289			release(permits - node.permitsNeeded);
290			throw ie;
291			}
292			else { // ignore interrupt
293			Thread.currentThread().interrupt();
294			}
295			}
296			finally {
297			node.unlock();
298			}
299	dl	1.1	}
300
301			/**
302			* Acquires the given number of permits from this semaphore,
303			* blocking until all are available.
304			*
305			* <p>Acquires the given number of permits, if they are available,
306			* and returns immediately,
307			* reducing the number of available permits by the given amount.
308			*
309			* <p>If insufficient permits are available then the current thread becomes
310			* disabled for thread scheduling purposes and lies dormant until
311			* some other thread invokes one of the {@link #release() release}
312			* methods for this semaphore, the current thread is next to be assigned
313			* permits and the number of available permits satisfies this request.
314			*
315			* <p>If the current thread
316			* is {@link Thread#interrupt interrupted} while waiting
317			* for permits then it will continue to wait and its position in the
318			* queue is not affected. When the
319			* thread does return from this method its interrupt status will be set.
320			*
321			* @param permits the number of permits to acquire
322			* @throws IllegalArgumentException if permits less than zero.
323			*
324			*/
325			public void acquireUninterruptibly(long permits) {
326			if (permits < 0) throw new IllegalArgumentException();
327	dl	1.6	Node node = null;
328	dl	1.1	lock.lock();
329			try {
330	dl	1.6	long remaining = count - permits;
331			if (remaining >= 0) {
332			count = remaining;
333			return;
334			}
335			count = 0;
336			node = enq(-remaining);
337	dl	1.1	}
338			finally {
339			lock.unlock();
340			}
341	dl	1.6
342			node.lock();
343			try {
344			while (node.permitsNeeded > 0)
345			node.done.awaitUninterruptibly();
346			}
347			finally {
348			node.unlock();
349			}
350	dl	1.1	}
351
352			/**
353			* Acquires the given number of permits from this semaphore, only if
354			* all are available at the time of invocation.
355			* <p>Acquires the given number of permits, if they are available, and
356			* returns immediately, with the value <tt>true</tt>,
357			* reducing the number of available permits by the given amount.
358			*
359			* <p>If insufficient permits are available then this method will return
360			* immediately with the value <tt>false</tt> and the number of available
361			* permits is unchanged.
362			*
363			* @param permits the number of permits to acquire
364			*
365			* @return <tt>true</tt> if the permits were acquired and <tt>false</tt>
366			* otherwise.
367			* @throws IllegalArgumentException if permits less than zero.
368			*/
369			public boolean tryAcquire(long permits) {
370			if (permits < 0) throw new IllegalArgumentException();
371			lock.lock();
372			try {
373	dl	1.6	long remaining = count - permits;
374			if (remaining >= 0) {
375			count = remaining;
376	dl	1.1	return true;
377			}
378			return false;
379			}
380			finally {
381			lock.unlock();
382			}
383			}
384
385			/**
386			* Acquires the given number of permits from this semaphore, if all
387			* become available within the given waiting time and the
388			* current thread has not been {@link Thread#interrupt interrupted}.
389			* <p>Acquires the given number of permits, if they are available and
390			* returns immediately, with the value <tt>true</tt>,
391			* reducing the number of available permits by the given amount.
392			* <p>If insufficient permits are available then
393			* the current thread becomes disabled for thread scheduling
394			* purposes and lies dormant until one of three things happens:
395			* <ul>
396			* <li>Some other thread invokes one of the {@link #release() release}
397			* methods for this semaphore, the current thread is next to be assigned
398			* permits and the number of available permits satisfies this request; or
399			* <li>Some other thread {@link Thread#interrupt interrupts} the current
400			* thread; or
401			* <li>The specified waiting time elapses.
402			* </ul>
403			* <p>If the permits are acquired then the value <tt>true</tt> is returned.
404			* <p>If the current thread:
405			* <ul>
406			* <li>has its interrupted status set on entry to this method; or
407			* <li>is {@link Thread#interrupt interrupted} while waiting to acquire
408			* the permits,
409			* </ul>
410			* then {@link InterruptedException} is thrown and the current thread's
411			* interrupted status is cleared.
412			* Any available permits are assigned to the next waiting thread as if
413			* they had been made available by a call to {@link #release()}.
414			*
415			* <p>If the specified waiting time elapses then the value <tt>false</tt>
416			* is returned.
417			* The given waiting time is a best-effort lower bound. If the time is
418			* less than or equal to zero, the method will not wait at all.
419			* Any available permits are assigned to the next waiting thread as if
420			* they had been made available by a call to {@link #release()}.
421			*
422			* @param permits the number of permits to acquire
423			* @param timeout the maximum time to wait for the permits
424	dl	1.6	* @param unit the time unit of the <tt>timeout</tt> argument.
425	dl	1.1	* @return <tt>true</tt> if all permits were acquired and <tt>false</tt>
426			* if the waiting time elapsed before all permits were acquired.
427			*
428			* @throws InterruptedException if the current thread is interrupted
429			* @throws IllegalArgumentException if permits less than zero.
430			*
431			* @see Thread#interrupt
432			*
433			*/
434	dl	1.6	public boolean tryAcquire(long permits, long timeout, TimeUnit unit)
435	dl	1.1	throws InterruptedException {
436			if (permits < 0) throw new IllegalArgumentException();
437	dl	1.6	Node node = null;
438			long nanos = unit.toNanos(timeout);
439	dl	1.1	lock.lockInterruptibly();
440			try {
441	dl	1.6	long remaining = count - permits;
442			if (remaining >= 0) {
443			count = remaining;
444			return true;
445			}
446			if (nanos <= 0)
447			return false;
448			count = 0;
449			node = enq(-remaining);
450			}
451			finally {
452			lock.unlock();
453			}
454
455			node.lock();
456			try {
457			while (node.permitsNeeded > 0) {
458			nanos = node.done.awaitNanos(nanos);
459			if (nanos <= 0) {
460			release(permits - node.permitsNeeded);
461			return false;
462	dl	1.1	}
463			}
464	dl	1.6	return true;
465	dl	1.1	}
466	dl	1.6	catch(InterruptedException ie) {
467			if (node.permitsNeeded > 0) {
468			node.cancelled = true;
469			release(permits - node.permitsNeeded);
470			throw ie;
471			}
472			else { // ignore interrupt
473			Thread.currentThread().interrupt();
474			return true;
475			}
476	dl	1.1	}
477			finally {
478	dl	1.6	node.unlock();
479	dl	1.1	}
480			}
481
482
483			/**
484			* Releases the given number of permits, returning them to the semaphore.
485			* <p>Releases the given number of permits, increasing the number of
486			* available permits by that amount.
487			* If any threads are blocking trying to acquire permits, then the
488			* one that has been waiting the longest
489			* is selected and given the permits that were just released.
490			* If the number of available permits satisfies that thread's request
491			* then that thread is re-enabled for thread scheduling purposes; otherwise
492			* the thread continues to wait. If there are still permits available
493			* after the first thread's request has been satisfied, then those permits
494			* are assigned to the next waiting thread. If it is satisfied then it is
495			* re-enabled for thread scheduling purposes. This continues until there
496			* are insufficient permits to satisfy the next waiting thread, or there
497			* are no more waiting threads.
498			*
499			* <p>There is no requirement that a thread that releases a permit must
500			* have acquired that permit by calling {@link Semaphore#acquire acquire}.
501			* Correct usage of a semaphore is established by programming convention
502			* in the application.
503			*
504			* @param permits the number of permits to release
505			* @throws IllegalArgumentException if permits less than zero.
506			*/
507			public void release(long permits) {
508			if (permits < 0) throw new IllegalArgumentException();
509	dl	1.6	if (permits == 0)
510			return;
511			// Even when using fair locks, releases should try to barge in.
512	dl	1.5	if (!lock.tryLock())
513			lock.lock();
514	dl	1.1	try {
515	dl	1.6	long p = permits;
516			while (p > 0) {
517			Node node = head;
518			if (node == null) {
519			count += p;
520			p = 0;
521			}
522			else {
523			node.lock();
524			try {
525			if (node.cancelled)
526			removeFirst();
527			else if (node.permitsNeeded > p) {
528			node.permitsNeeded -= p;
529			p = 0;
530			}
531			else {
532			p -= node.permitsNeeded;
533			node.permitsNeeded = 0;
534			node.done.signal();
535			removeFirst();
536			}
537			}
538			finally {
539			node.unlock();
540			}
541			}
542			}
543	dl	1.1	}
544			finally {
545			lock.unlock();
546			}
547			}
548			}