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
 * @author Doug Lea
 *
 */
public class FairSemaphore extends Semaphore {
    private static final long serialVersionUID = -3222578661600680210L;

    /*
     * 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 */
        ReentrantLock.ConditionObject 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 transient Node head;

    /** Pointer to last node of the wait queue */
    private transient 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 is next to be assigned a 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 is next to be assigned a 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 is next to be assigned a 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.
     * 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 permits that were to be assigned to this thread, are instead 
     * assigned to the next waiting thread(s), 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 permits that were to be assigned to this thread, are instead 
     * assigned to the next waiting thread(s), 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.
     * If the time is
     * less than or equal to zero, the method will not wait at all.
     * Any permits that were to be assigned to this thread, are instead 
     * assigned to the next waiting thread(s), 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:	1.13
Committed:	Mon Nov 3 13:49:56 2003 UTC (20 years, 6 months ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.12:	+0 -0 lines
State:	*FILE REMOVED*
Log Message:	Merged FairSemaphore into Semaphore
#	Content
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	import java.util.concurrent.locks.*;
9
10	/**
11	* 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	*
20	* <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	*
24	* @since 1.5
25	* @author Doug Lea
26	*
27	*/
28	public class FairSemaphore extends Semaphore {
29	private static final long serialVersionUID = -3222578661600680210L;
30
31	/*
32	* Basic algorithm is a variant of the one described
33	* in CPJ book 2nd edition, section 3.7.3
34	*/
35
36	/**
37	* Nodes of the wait queue. Opportunistically subclasses ReentrantLock.
38	*/
39	private static class Node extends ReentrantLock {
40	/** The condition to wait on */
41	ReentrantLock.ConditionObject done = newCondition();
42	/** True if interrupted before released */
43	boolean cancelled;
44	/** Number of permits remaining until can release */
45	long permitsNeeded;
46	/** Next node of queue */
47	Node next;
48
49	Node(long n) { permitsNeeded = n; }
50	}
51
52	/** Head of the wait queue */
53	private transient Node head;
54
55	/** Pointer to last node of the wait queue */
56	private transient Node last;
57
58	/** Add a new node to wait queue with given number of permits needed */
59	private Node enq(long n) {
60	Node p = new Node(n);
61	if (last == null)
62	last = head = p;
63	else
64	last = last.next = p;
65	return p;
66	}
67
68	/** Remove first node from wait queue */
69	private void removeFirst() {
70	Node p = head;
71	assert p != null;
72	if (p != null && (head = p.next) == null)
73	last = null;
74	}
75
76	/**
77	* Construct a <tt>FairSemaphore</tt> with the given number of
78	* permits.
79	* @param permits the initial number of permits available
80	*/
81	public FairSemaphore(long permits) {
82	super(permits, new ReentrantLock(true));
83	}
84
85	/**
86	* Acquires a permit from this semaphore, blocking until one is
87	* available, or the thread is {@link Thread#interrupt interrupted}.
88	*
89	* <p>Acquires a permit, if one is available and returns immediately,
90	* reducing the number of available permits by one.
91	* <p>If no permit is available then the current thread becomes
92	* disabled for thread scheduling purposes and lies dormant until
93	* one of two things happens:
94	* <ul>
95	* <li>Some other thread invokes the {@link #release} method for this
96	* semaphore and the current thread is next to be assigned a permit; or
97	* <li>Some other thread {@link Thread#interrupt interrupts} the current
98	* thread.
99	* </ul>
100	*
101	* <p>If the current thread:
102	* <ul>
103	* <li>has its interrupted status set on entry to this method; or
104	* <li>is {@link Thread#interrupt interrupted} while waiting
105	* for a permit,
106	* </ul>
107	* then {@link InterruptedException} is thrown and the current thread's
108	* interrupted status is cleared.
109	*
110	* @throws InterruptedException if the current thread is interrupted
111	*
112	* @see Thread#interrupt
113	*/
114	public void acquire() throws InterruptedException {
115	acquire(1L);
116	}
117
118	/**
119	* Acquires a permit from this semaphore, blocking until one is
120	* available.
121	*
122	* <p>Acquires a permit, if one is available and returns immediately,
123	* reducing the number of available permits by one.
124	* <p>If no permit is available then the current thread becomes
125	* disabled for thread scheduling purposes and lies dormant until
126	* some other thread invokes the {@link #release} method for this
127	* semaphore and the current thread is next to be assigned a permit.
128	*
129	* <p>If the current thread
130	* is {@link Thread#interrupt interrupted} while waiting
131	* for a permit then it will continue to wait, but the time at which
132	* the thread is assigned a permit may change compared to the time it
133	* would have received the permit had no interruption occurred. When the
134	* thread does return from this method its interrupt status will be set.
135	*
136	*/
137	public void acquireUninterruptibly() {
138	acquireUninterruptibly(1L);
139	}
140
141	/**
142	* Acquires a permit from this semaphore, only if one is available at the
143	* time of invocation.
144	* <p>Acquires a permit, if one is available and returns immediately,
145	* with the value <tt>true</tt>,
146	* reducing the number of available permits by one.
147	*
148	* <p>If no permit is available then this method will return
149	* immediately with the value <tt>false</tt>.
150	*
151	* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
152	* otherwise.
153	*/
154	public boolean tryAcquire() {
155	return tryAcquire(1L);
156	}
157
158	/**
159	* Acquires a permit from this semaphore, if one becomes available
160	* within the given waiting time and the
161	* current thread has not been {@link Thread#interrupt interrupted}.
162	* <p>Acquires a permit, if one is available and returns immediately,
163	* with the value <tt>true</tt>,
164	* reducing the number of available permits by one.
165	* <p>If no permit is available then
166	* the current thread becomes disabled for thread scheduling
167	* purposes and lies dormant until one of three things happens:
168	* <ul>
169	* <li>Some other thread invokes the {@link #release} method for this
170	* semaphore and the current thread is next to be assigned a permit; or
171	* <li>Some other thread {@link Thread#interrupt interrupts} the current
172	* thread; or
173	* <li>The specified waiting time elapses.
174	* </ul>
175	* <p>If a permit is acquired then the value <tt>true</tt> is returned.
176	* <p>If the current thread:
177	* <ul>
178	* <li>has its interrupted status set on entry to this method; or
179	* <li>is {@link Thread#interrupt interrupted} while waiting to acquire
180	* a permit,
181	* </ul>
182	* then {@link InterruptedException} is thrown and the current thread's
183	* interrupted status is cleared.
184	* <p>If the specified waiting time elapses then the value <tt>false</tt>
185	* is returned.
186	* If the time is less than or equal to zero, the method will not wait
187	* at all.
188	*
189	* @param timeout the maximum time to wait for a permit
190	* @param unit the time unit of the <tt>timeout</tt> argument.
191	* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
192	* if the waiting time elapsed before a permit was acquired.
193	*
194	* @throws InterruptedException if the current thread is interrupted
195	*
196	* @see Thread#interrupt
197	*
198	*/
199	public boolean tryAcquire(long timeout, TimeUnit unit)
200	throws InterruptedException {
201	return tryAcquire(1L, timeout, unit);
202	}
203
204	/**
205	* Releases a permit, returning it to the semaphore.
206	* <p>Releases a permit, increasing the number of available permits
207	* by one.
208	* If any threads are blocking trying to acquire a permit, then one
209	* is selected and given the permit that was just released.
210	* That thread is re-enabled for thread scheduling purposes.
211	* <p>There is no requirement that a thread that releases a permit must
212	* have acquired that permit by calling {@link #acquire}.
213	* Correct usage of a semaphore is established by programming convention
214	* in the application.
215	*/
216	public void release() {
217	release(1L);
218	}
219
220
221	/**
222	* Acquires the given number of permits from this semaphore,
223	* blocking until all are available,
224	* or the thread is {@link Thread#interrupt interrupted}.
225	*
226	* <p>Acquires the given number of permits, if they are available,
227	* and returns immediately,
228	* reducing the number of available permits by the given amount.
229	*
230	* <p>If insufficient permits are available then the current thread becomes
231	* disabled for thread scheduling purposes and lies dormant until
232	* one of two things happens:
233	* <ul>
234	* <li>Some other thread invokes one of the {@link #release() release}
235	* methods for this semaphore, the current thread is next to be assigned
236	* permits and the number of available permits satisfies this request; or
237	* <li>Some other thread {@link Thread#interrupt interrupts} the current
238	* thread.
239	* </ul>
240	*
241	* <p>If the current thread:
242	* <ul>
243	* <li>has its interrupted status set on entry to this method; or
244	* <li>is {@link Thread#interrupt interrupted} while waiting
245	* for a permit,
246	* </ul>
247	* then {@link InterruptedException} is thrown and the current thread's
248	* interrupted status is cleared.
249	* Any permits that were to be assigned to this thread, are instead
250	* assigned to the next waiting thread(s), as if
251	* they had been made available by a call to {@link #release()}.
252	*
253	* @param permits the number of permits to acquire
254	*
255	* @throws InterruptedException if the current thread is interrupted
256	* @throws IllegalArgumentException if permits less than zero.
257	*
258	* @see Thread#interrupt
259	*/
260	public void acquire(long permits) throws InterruptedException {
261	if (permits < 0) throw new IllegalArgumentException();
262	Node node = null;
263	lock.lockInterruptibly();
264	try {
265	long remaining = count - permits;
266	if (remaining >= 0) {
267	count = remaining;
268	return;
269	}
270	count = 0;
271	node = enq(-remaining);
272	} finally {
273	lock.unlock();
274	}
275
276	node.lock();
277	try {
278	while (node.permitsNeeded > 0)
279	node.done.await();
280	} catch(InterruptedException ie) {
281	if (node.permitsNeeded > 0) {
282	node.cancelled = true;
283	release(permits - node.permitsNeeded);
284	throw ie;
285	} else { // ignore interrupt
286	Thread.currentThread().interrupt();
287	}
288	} finally {
289	node.unlock();
290	}
291	}
292
293	/**
294	* Acquires the given number of permits from this semaphore,
295	* blocking until all are available.
296	*
297	* <p>Acquires the given number of permits, if they are available,
298	* and returns immediately,
299	* reducing the number of available permits by the given amount.
300	*
301	* <p>If insufficient permits are available then the current thread becomes
302	* disabled for thread scheduling purposes and lies dormant until
303	* some other thread invokes one of the {@link #release() release}
304	* methods for this semaphore, the current thread is next to be assigned
305	* permits and the number of available permits satisfies this request.
306	*
307	* <p>If the current thread
308	* is {@link Thread#interrupt interrupted} while waiting
309	* for permits then it will continue to wait and its position in the
310	* queue is not affected. When the
311	* thread does return from this method its interrupt status will be set.
312	*
313	* @param permits the number of permits to acquire
314	* @throws IllegalArgumentException if permits less than zero.
315	*
316	*/
317	public void acquireUninterruptibly(long permits) {
318	if (permits < 0) throw new IllegalArgumentException();
319	Node node = null;
320	lock.lock();
321	try {
322	long remaining = count - permits;
323	if (remaining >= 0) {
324	count = remaining;
325	return;
326	}
327	count = 0;
328	node = enq(-remaining);
329	} finally {
330	lock.unlock();
331	}
332
333	node.lock();
334	try {
335	while (node.permitsNeeded > 0)
336	node.done.awaitUninterruptibly();
337	} finally {
338	node.unlock();
339	}
340	}
341
342	/**
343	* Acquires the given number of permits from this semaphore, only if
344	* all are available at the time of invocation.
345	* <p>Acquires the given number of permits, if they are available, and
346	* returns immediately, with the value <tt>true</tt>,
347	* reducing the number of available permits by the given amount.
348	*
349	* <p>If insufficient permits are available then this method will return
350	* immediately with the value <tt>false</tt> and the number of available
351	* permits is unchanged.
352	*
353	* @param permits the number of permits to acquire
354	*
355	* @return <tt>true</tt> if the permits were acquired and <tt>false</tt>
356	* otherwise.
357	* @throws IllegalArgumentException if permits less than zero.
358	*/
359	public boolean tryAcquire(long permits) {
360	if (permits < 0) throw new IllegalArgumentException();
361	lock.lock();
362	try {
363	long remaining = count - permits;
364	if (remaining >= 0) {
365	count = remaining;
366	return true;
367	}
368	return false;
369	} finally {
370	lock.unlock();
371	}
372	}
373
374	/**
375	* Acquires the given number of permits from this semaphore, if all
376	* become available within the given waiting time and the
377	* current thread has not been {@link Thread#interrupt interrupted}.
378	* <p>Acquires the given number of permits, if they are available and
379	* returns immediately, with the value <tt>true</tt>,
380	* reducing the number of available permits by the given amount.
381	* <p>If insufficient permits are available then
382	* the current thread becomes disabled for thread scheduling
383	* purposes and lies dormant until one of three things happens:
384	* <ul>
385	* <li>Some other thread invokes one of the {@link #release() release}
386	* methods for this semaphore, the current thread is next to be assigned
387	* permits and the number of available permits satisfies this request; or
388	* <li>Some other thread {@link Thread#interrupt interrupts} the current
389	* thread; or
390	* <li>The specified waiting time elapses.
391	* </ul>
392	* <p>If the permits are acquired then the value <tt>true</tt> is returned.
393	* <p>If the current thread:
394	* <ul>
395	* <li>has its interrupted status set on entry to this method; or
396	* <li>is {@link Thread#interrupt interrupted} while waiting to acquire
397	* the permits,
398	* </ul>
399	* then {@link InterruptedException} is thrown and the current thread's
400	* interrupted status is cleared.
401	* Any permits that were to be assigned to this thread, are instead
402	* assigned to the next waiting thread(s), as if
403	* they had been made available by a call to {@link #release()}.
404	*
405	* <p>If the specified waiting time elapses then the value <tt>false</tt>
406	* is returned.
407	* If the time is
408	* less than or equal to zero, the method will not wait at all.
409	* Any permits that were to be assigned to this thread, are instead
410	* assigned to the next waiting thread(s), as if
411	* they had been made available by a call to {@link #release()}.
412	*
413	* @param permits the number of permits to acquire
414	* @param timeout the maximum time to wait for the permits
415	* @param unit the time unit of the <tt>timeout</tt> argument.
416	* @return <tt>true</tt> if all permits were acquired and <tt>false</tt>
417	* if the waiting time elapsed before all permits were acquired.
418	*
419	* @throws InterruptedException if the current thread is interrupted
420	* @throws IllegalArgumentException if permits less than zero.
421	*
422	* @see Thread#interrupt
423	*
424	*/
425	public boolean tryAcquire(long permits, long timeout, TimeUnit unit)
426	throws InterruptedException {
427	if (permits < 0) throw new IllegalArgumentException();
428	Node node = null;
429	long nanos = unit.toNanos(timeout);
430	lock.lockInterruptibly();
431	try {
432	long remaining = count - permits;
433	if (remaining >= 0) {
434	count = remaining;
435	return true;
436	}
437	if (nanos <= 0)
438	return false;
439	count = 0;
440	node = enq(-remaining);
441	} finally {
442	lock.unlock();
443	}
444
445	node.lock();
446	try {
447	while (node.permitsNeeded > 0) {
448	nanos = node.done.awaitNanos(nanos);
449	if (nanos <= 0) {
450	release(permits - node.permitsNeeded);
451	return false;
452	}
453	}
454	return true;
455	} catch(InterruptedException ie) {
456	if (node.permitsNeeded > 0) {
457	node.cancelled = true;
458	release(permits - node.permitsNeeded);
459	throw ie;
460	} else { // ignore interrupt
461	Thread.currentThread().interrupt();
462	return true;
463	}
464	} finally {
465	node.unlock();
466	}
467	}
468
469
470	/**
471	* Releases the given number of permits, returning them to the semaphore.
472	* <p>Releases the given number of permits, increasing the number of
473	* available permits by that amount.
474	* If any threads are blocking trying to acquire permits, then the
475	* one that has been waiting the longest
476	* is selected and given the permits that were just released.
477	* If the number of available permits satisfies that thread's request
478	* then that thread is re-enabled for thread scheduling purposes; otherwise
479	* the thread continues to wait. If there are still permits available
480	* after the first thread's request has been satisfied, then those permits
481	* are assigned to the next waiting thread. If it is satisfied then it is
482	* re-enabled for thread scheduling purposes. This continues until there
483	* are insufficient permits to satisfy the next waiting thread, or there
484	* are no more waiting threads.
485	*
486	* <p>There is no requirement that a thread that releases a permit must
487	* have acquired that permit by calling {@link Semaphore#acquire acquire}.
488	* Correct usage of a semaphore is established by programming convention
489	* in the application.
490	*
491	* @param permits the number of permits to release
492	* @throws IllegalArgumentException if permits less than zero.
493	*/
494	public void release(long permits) {
495	if (permits < 0) throw new IllegalArgumentException();
496	if (permits == 0)
497	return;
498	// Even when using fair locks, releases should try to barge in.
499	if (!lock.tryLock())
500	lock.lock();
501	try {
502	long p = permits;
503	while (p > 0) {
504	Node node = head;
505	if (node == null) {
506	count += p;
507	p = 0;
508	} else {
509	node.lock();
510	try {
511	if (node.cancelled)
512	removeFirst();
513	else if (node.permitsNeeded > p) {
514	node.permitsNeeded -= p;
515	p = 0;
516	} else {
517	p -= node.permitsNeeded;
518	node.permitsNeeded = 0;
519	node.done.signal();
520	removeFirst();
521	}
522	} finally {
523	node.unlock();
524	}
525	}
526	}
527	} finally {
528	lock.unlock();
529	}
530	}
531	}