util/concurrent/FifoSemaphore.java

package java.util.concurrent;

/**
 * A semaphore that guarantees 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).
 *
 * <p>This class introduces a fairness guarantee that can be useful
 * in some contexts.
 * However, it needs to be realized that the order in which invocations are
 * processed can be different from the order in which an application perceives
 * those invocations to be processed. Effectively, when no permit is available
 * each thread is stored in a FIFO queue. As permits are released, they
 * are allocated to the thread at the head of the queue, and so the order
 * in which threads enter the queue, is the order in which they come out.  
 * This order need not have any relationship to the order in which requests 
 * were made, nor the order in which requests actually return to the caller as 
 * these depend on the underlying thread scheduling, which is not guaranteed 
 * to be predictable or fair.
 *
 * <p>As 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: 2003/05/14 21:30:46 $
 * @editor $Author: tim $
 *
 */
public class FifoSemaphore extends Semaphore {

    /**
     * Construct a <tt>FiFoSemaphore</tt> with the given number of
     * permits.
     * @param permits the initial number of permits available
     */
    public FifoSemaphore(long permits) { 
        super(permits); 
    }

    /**
     * Acquires a permit from this semaphore, blocking until one is
     * available, or the thread is {@link Thread#interrupt interrupted}.
     *
     * <p>This is equivalent to invoking {@link #acquire(long) acquire(1)}.
     *
     * @throws InterruptedException if the current thread is interrupted
     *
     * @see Thread#interrupt
     */
    public void acquire() throws InterruptedException {
        acquire(1);
    }

    /**
     * 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
     *
     * @see Thread#interrupt
     */
    public void acquire(long permits) throws InterruptedException {}

    /**
     * Acquires a permit from this semaphore, blocking until one is
     * available.
     *
     * <p>This is equivalent to invoking 
     * {@link #acquireUninterruptibly(long) acquireUninterruptibly(1)}.
     *
     */
    public void acquireUninterruptibly() {
        acquireUninterruptibly(1);
    }

    /**
     * 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
     *
     */
    public void acquireUninterruptibly(long permits) {}

    /**
     * Acquires a permit from this semaphore, only if one is available at 
     * the time of invocation.
     *
     * <p>This is equivalent to invoking 
     * {@link #tryAcquire(long) tryAcquire(1)}.
     *
     * @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
     * otherwise.
     */
    public boolean tryAcquire() {
        return tryAcquire(1);
    }

    /**
     * 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.
     */
    public boolean tryAcquire(long permits) {
        return false;
    }

    /**
     * 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>This is equivalent to invoking 
     * {@link #tryAcquire(long, long, TimeUnit) 
     * tryAcquire(1, timeout, granularity)}.
     *
     * @param timeout the maximum time to wait for a permit
     * @param granularity 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 granularity)
        throws InterruptedException {
        return tryAcquire(1, timeout, granularity);
    }

    /**
     * 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 granularity 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
     *
     * @see Thread#interrupt
     *
     */
    public boolean tryAcquire(long permits, long timeout, TimeUnit granularity)
        throws InterruptedException {
        return false;
    }


    /**
     * Releases a permit, returning it to the semaphore.
     * <p>This is equivalent to invoking {@link #release(long) release(1)}.
     */
    public void release() {
        release(1);
    }

    /**
     * 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
     */
    public void release(long permits) {}

}


Revision:	1.2
Committed:	Fri Jun 6 18:42:17 2003 UTC (20 years, 11 months ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.1:	+2 -2 lines
State:	*FILE REMOVED*
Log Message:	Added to emulation Fixed some javadoc format errors
#	Content
1	package java.util.concurrent;
2
3	/**
4	* A semaphore that guarantees that threads invoking
5	* any of the {@link #acquire() acquire} methods
6	* are allocated permits in the order in
7	* which their invocation of those methods was processed (first-in-first-out).
8	*
9	* <p>This class introduces a fairness guarantee that can be useful
10	* in some contexts.
11	* However, it needs to be realized that the order in which invocations are
12	* processed can be different from the order in which an application perceives
13	* those invocations to be processed. Effectively, when no permit is available
14	* each thread is stored in a FIFO queue. As permits are released, they
15	* are allocated to the thread at the head of the queue, and so the order
16	* in which threads enter the queue, is the order in which they come out.
17	* This order need not have any relationship to the order in which requests
18	* were made, nor the order in which requests actually return to the caller as
19	* these depend on the underlying thread scheduling, which is not guaranteed
20	* to be predictable or fair.
21	*
22	* <p>As permits are allocated in-order, this class also provides convenience
23	* methods to {@link #acquire(long) acquire} and
24	* {@link #release(long) release} multiple permits at a time.
25	*
26	* @since 1.5
27	* @spec JSR-166
28	* @revised $Date: 2003/05/14 21:30:46 $
29	* @editor $Author: tim $
30	*
31	*/
32	public class FifoSemaphore extends Semaphore {
33
34	/**
35	* Construct a <tt>FiFoSemaphore</tt> with the given number of
36	* permits.
37	* @param permits the initial number of permits available
38	*/
39	public FifoSemaphore(long permits) {
40	super(permits);
41	}
42
43	/**
44	* Acquires a permit from this semaphore, blocking until one is
45	* available, or the thread is {@link Thread#interrupt interrupted}.
46	*
47	* <p>This is equivalent to invoking {@link #acquire(long) acquire(1)}.
48	*
49	* @throws InterruptedException if the current thread is interrupted
50	*
51	* @see Thread#interrupt
52	*/
53	public void acquire() throws InterruptedException {
54	acquire(1);
55	}
56
57	/**
58	* Acquires the given number of permits from this semaphore,
59	* blocking until all are available,
60	* or the thread is {@link Thread#interrupt interrupted}.
61	*
62	* <p>Acquires the given number of permits, if they are available,
63	* and returns immediately,
64	* reducing the number of available permits by the given amount.
65	*
66	* <p>If insufficient permits are available then the current thread becomes
67	* disabled for thread scheduling purposes and lies dormant until
68	* one of two things happens:
69	* <ul>
70	* <li>Some other thread invokes one of the {@link #release() release}
71	* methods for this semaphore, the current thread is next to be assigned
72	* permits and the number of available permits satisfies this request; or
73	* <li>Some other thread {@link Thread#interrupt interrupts} the current
74	* thread.
75	* </ul>
76	*
77	* <p>If the current thread:
78	* <ul>
79	* <li>has its interrupted status set on entry to this method; or
80	* <li>is {@link Thread#interrupt interrupted} while waiting
81	* for a permit,
82	* </ul>
83	* then {@link InterruptedException} is thrown and the current thread's
84	* interrupted status is cleared.
85	* Any available permits are assigned to the next waiting thread as if
86	* they had been made available by a call to {@link #release()}.
87	*
88	* @param permits the number of permits to acquire
89	*
90	* @throws InterruptedException if the current thread is interrupted
91	*
92	* @see Thread#interrupt
93	*/
94	public void acquire(long permits) throws InterruptedException {}
95
96	/**
97	* Acquires a permit from this semaphore, blocking until one is
98	* available.
99	*
100	* <p>This is equivalent to invoking
101	* {@link #acquireUninterruptibly(long) acquireUninterruptibly(1)}.
102	*
103	*/
104	public void acquireUninterruptibly() {
105	acquireUninterruptibly(1);
106	}
107
108	/**
109	* Acquires the given number of permits from this semaphore,
110	* blocking until all are available.
111	*
112	* <p>Acquires the given number of permits, if they are available,
113	* and returns immediately,
114	* reducing the number of available permits by the given amount.
115	*
116	* <p>If insufficient permits are available then the current thread becomes
117	* disabled for thread scheduling purposes and lies dormant until
118	* some other thread invokes one of the {@link #release() release}
119	* methods for this semaphore, the current thread is next to be assigned
120	* permits and the number of available permits satisfies this request.
121	*
122	* <p>If the current thread
123	* is {@link Thread#interrupt interrupted} while waiting
124	* for permits then it will continue to wait and its position in the
125	* queue is not affected. When the
126	* thread does return from this method its interrupt status will be set.
127	*
128	* @param permits the number of permits to acquire
129	*
130	*/
131	public void acquireUninterruptibly(long permits) {}
132
133	/**
134	* Acquires a permit from this semaphore, only if one is available at
135	* the time of invocation.
136	*
137	* <p>This is equivalent to invoking
138	* {@link #tryAcquire(long) tryAcquire(1)}.
139	*
140	* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
141	* otherwise.
142	*/
143	public boolean tryAcquire() {
144	return tryAcquire(1);
145	}
146
147	/**
148	* Acquires the given number of permits from this semaphore, only if
149	* all are available at the time of invocation.
150	* <p>Acquires the given number of permits, if they are available, and
151	* returns immediately, with the value <tt>true</tt>,
152	* reducing the number of available permits by the given amount.
153	*
154	* <p>If insufficient permits are available then this method will return
155	* immediately with the value <tt>false</tt> and the number of available
156	* permits is unchanged.
157	*
158	* @param permits the number of permits to acquire
159	*
160	* @return <tt>true</tt> if the permits were acquired and <tt>false</tt>
161	* otherwise.
162	*/
163	public boolean tryAcquire(long permits) {
164	return false;
165	}
166
167	/**
168	* Acquires a permit from this semaphore, if one becomes available
169	* within the given waiting time and the
170	* current thread has not been {@link Thread#interrupt interrupted}.
171	*
172	* <p>This is equivalent to invoking
173	* {@link #tryAcquire(long, long, TimeUnit)
174	* tryAcquire(1, timeout, granularity)}.
175	*
176	* @param timeout the maximum time to wait for a permit
177	* @param granularity the time unit of the <tt>timeout</tt> argument.
178	* @return <tt>true</tt> if a permit was acquired and <tt>false</tt>
179	* if the waiting time elapsed before a permit was acquired.
180	*
181	* @throws InterruptedException if the current thread is interrupted
182	*
183	* @see Thread#interrupt
184	*
185	*/
186	public boolean tryAcquire(long timeout, TimeUnit granularity)
187	throws InterruptedException {
188	return tryAcquire(1, timeout, granularity);
189	}
190
191	/**
192	* Acquires the given number of permits from this semaphore, if all
193	* become available within the given waiting time and the
194	* current thread has not been {@link Thread#interrupt interrupted}.
195	* <p>Acquires the given number of permits, if they are available and
196	* returns immediately, with the value <tt>true</tt>,
197	* reducing the number of available permits by the given amount.
198	* <p>If insufficient permits are available then
199	* the current thread becomes disabled for thread scheduling
200	* purposes and lies dormant until one of three things happens:
201	* <ul>
202	* <li>Some other thread invokes one of the {@link #release() release}
203	* methods for this semaphore, the current thread is next to be assigned
204	* permits and the number of available permits satisfies this request; or
205	* <li>Some other thread {@link Thread#interrupt interrupts} the current
206	* thread; or
207	* <li>The specified waiting time elapses.
208	* </ul>
209	* <p>If the permits are acquired then the value <tt>true</tt> is returned.
210	* <p>If the current thread:
211	* <ul>
212	* <li>has its interrupted status set on entry to this method; or
213	* <li>is {@link Thread#interrupt interrupted} while waiting to acquire
214	* the permits,
215	* </ul>
216	* then {@link InterruptedException} is thrown and the current thread's
217	* interrupted status is cleared.
218	* Any available permits are assigned to the next waiting thread as if
219	* they had been made available by a call to {@link #release()}.
220	*
221	* <p>If the specified waiting time elapses then the value <tt>false</tt>
222	* is returned.
223	* The given waiting time is a best-effort lower bound. If the time is
224	* less than or equal to zero, the method will not wait at all.
225	* Any available permits are assigned to the next waiting thread as if
226	* they had been made available by a call to {@link #release()}.
227	*
228	* @param permits the number of permits to acquire
229	* @param timeout the maximum time to wait for the permits
230	* @param granularity the time unit of the <tt>timeout</tt> argument.
231	* @return <tt>true</tt> if all permits were acquired and <tt>false</tt>
232	* if the waiting time elapsed before all permits were acquired.
233	*
234	* @throws InterruptedException if the current thread is interrupted
235	*
236	* @see Thread#interrupt
237	*
238	*/
239	public boolean tryAcquire(long permits, long timeout, TimeUnit granularity)
240	throws InterruptedException {
241	return false;
242	}
243
244
245
246	/**
247	* Releases a permit, returning it to the semaphore.
248	* <p>This is equivalent to invoking {@link #release(long) release(1)}.
249	*/
250	public void release() {
251	release(1);
252	}
253
254	/**
255	* Releases the given number of permits, returning them to the semaphore.
256	* <p>Releases the given number of permits, increasing the number of
257	* available permits by that amount.
258	* If any threads are blocking trying to acquire permits, then the
259	* one that has been waiting the longest
260	* is selected and given the permits that were just released.
261	* If the number of available permits satisfies that thread's request
262	* then that thread is re-enabled for thread scheduling purposes; otherwise
263	* the thread continues to wait. If there are still permits available
264	* after the first thread's request has been satisfied, then those permits
265	* are assigned to the next waiting thread. If it is satisfied then it is
266	* re-enabled for thread scheduling purposes. This continues until there
267	* are insufficient permits to satisfy the next waiting thread, or there
268	* are no more waiting threads.
269	*
270	* <p>There is no requirement that a thread that releases a permit must
271	* have acquired that permit by calling {@link Semaphore#acquire acquire}.
272	* Correct usage of a semaphore is established by programming convention
273	* in the application.
274	*
275	* @param permits the number of permits to release
276	*/
277	public void release(long permits) {}
278
279	}
280
281
282
283
284