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My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

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1+/*
2+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3+ *
4+ * This code is free software; you can redistribute it and/or modify it
5+ * under the terms of the GNU General Public License version 2 only, as
6+ * published by the Free Software Foundation. Oracle designates this
7+ * particular file as subject to the "Classpath" exception as provided
8+ * by Oracle in the LICENSE file that accompanied this code.
9+ *
10+ * This code is distributed in the hope that it will be useful, but WITHOUT
11+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13+ * version 2 for more details (a copy is included in the LICENSE file that
14+ * accompanied this code).
15+ *
16+ * You should have received a copy of the GNU General Public License version
17+ * 2 along with this work; if not, write to the Free Software Foundation,
18+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19+ *
20+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21+ * or visit www.oracle.com if you need additional information or have any
22+ * questions.
23+ */
24+
25+/*
26+ * This file is available under and governed by the GNU General Public
27+ * License version 2 only, as published by the Free Software Foundation.
28+ * However, the following notice accompanied the original version of this
29+ * file:
30+ *
31+ * Written by Doug Lea with assistance from members of JCP JSR-166
32+ * Expert Group and released to the public domain, as explained at
33+ * http://creativecommons.org/publicdomain/zero/1.0/
34+ */
35+
36+package java.util.concurrent;
37+import java.util.concurrent.locks.*;
38+import java.util.concurrent.atomic.*;
39+
40+/**
41+ * A synchronization aid that allows one or more threads to wait until
42+ * a set of operations being performed in other threads completes.
43+ *
44+ * <p>A {@code CountDownLatch} is initialized with a given <em>count</em>.
45+ * The {@link #await await} methods block until the current count reaches
46+ * zero due to invocations of the {@link #countDown} method, after which
47+ * all waiting threads are released and any subsequent invocations of
48+ * {@link #await await} return immediately. This is a one-shot phenomenon
49+ * -- the count cannot be reset. If you need a version that resets the
50+ * count, consider using a {@link CyclicBarrier}.
51+ *
52+ * <p>A {@code CountDownLatch} is a versatile synchronization tool
53+ * and can be used for a number of purposes. A
54+ * {@code CountDownLatch} initialized with a count of one serves as a
55+ * simple on/off latch, or gate: all threads invoking {@link #await await}
56+ * wait at the gate until it is opened by a thread invoking {@link
57+ * #countDown}. A {@code CountDownLatch} initialized to <em>N</em>
58+ * can be used to make one thread wait until <em>N</em> threads have
59+ * completed some action, or some action has been completed N times.
60+ *
61+ * <p>A useful property of a {@code CountDownLatch} is that it
62+ * doesn't require that threads calling {@code countDown} wait for
63+ * the count to reach zero before proceeding, it simply prevents any
64+ * thread from proceeding past an {@link #await await} until all
65+ * threads could pass.
66+ *
67+ * <p><b>Sample usage:</b> Here is a pair of classes in which a group
68+ * of worker threads use two countdown latches:
69+ * <ul>
70+ * <li>The first is a start signal that prevents any worker from proceeding
71+ * until the driver is ready for them to proceed;
72+ * <li>The second is a completion signal that allows the driver to wait
73+ * until all workers have completed.
74+ * </ul>
75+ *
76+ * <pre>
77+ * class Driver { // ...
78+ * void main() throws InterruptedException {
79+ * CountDownLatch startSignal = new CountDownLatch(1);
80+ * CountDownLatch doneSignal = new CountDownLatch(N);
81+ *
82+ * for (int i = 0; i < N; ++i) // create and start threads
83+ * new Thread(new Worker(startSignal, doneSignal)).start();
84+ *
85+ * doSomethingElse(); // don't let run yet
86+ * startSignal.countDown(); // let all threads proceed
87+ * doSomethingElse();
88+ * doneSignal.await(); // wait for all to finish
89+ * }
90+ * }
91+ *
92+ * class Worker implements Runnable {
93+ * private final CountDownLatch startSignal;
94+ * private final CountDownLatch doneSignal;
95+ * Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
96+ * this.startSignal = startSignal;
97+ * this.doneSignal = doneSignal;
98+ * }
99+ * public void run() {
100+ * try {
101+ * startSignal.await();
102+ * doWork();
103+ * doneSignal.countDown();
104+ * } catch (InterruptedException ex) {} // return;
105+ * }
106+ *
107+ * void doWork() { ... }
108+ * }
109+ *
110+ * </pre>
111+ *
112+ * <p>Another typical usage would be to divide a problem into N parts,
113+ * describe each part with a Runnable that executes that portion and
114+ * counts down on the latch, and queue all the Runnables to an
115+ * Executor. When all sub-parts are complete, the coordinating thread
116+ * will be able to pass through await. (When threads must repeatedly
117+ * count down in this way, instead use a {@link CyclicBarrier}.)
118+ *
119+ * <pre>
120+ * class Driver2 { // ...
121+ * void main() throws InterruptedException {
122+ * CountDownLatch doneSignal = new CountDownLatch(N);
123+ * Executor e = ...
124+ *
125+ * for (int i = 0; i < N; ++i) // create and start threads
126+ * e.execute(new WorkerRunnable(doneSignal, i));
127+ *
128+ * doneSignal.await(); // wait for all to finish
129+ * }
130+ * }
131+ *
132+ * class WorkerRunnable implements Runnable {
133+ * private final CountDownLatch doneSignal;
134+ * private final int i;
135+ * WorkerRunnable(CountDownLatch doneSignal, int i) {
136+ * this.doneSignal = doneSignal;
137+ * this.i = i;
138+ * }
139+ * public void run() {
140+ * try {
141+ * doWork(i);
142+ * doneSignal.countDown();
143+ * } catch (InterruptedException ex) {} // return;
144+ * }
145+ *
146+ * void doWork() { ... }
147+ * }
148+ *
149+ * </pre>
150+ *
151+ * <p>Memory consistency effects: Until the count reaches
152+ * zero, actions in a thread prior to calling
153+ * {@code countDown()}
154+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
155+ * actions following a successful return from a corresponding
156+ * {@code await()} in another thread.
157+ *
158+ * @since 1.5
159+ * @author Doug Lea
160+ */
161+public class CountDownLatch {
162+ /**
163+ * Synchronization control For CountDownLatch.
164+ * Uses AQS state to represent count.
165+ */
166+ private static final class Sync extends AbstractQueuedSynchronizer {
167+ private static final long serialVersionUID = 4982264981922014374L;
168+
169+ Sync(int count) {
170+ setState(count);
171+ }
172+
173+ int getCount() {
174+ return getState();
175+ }
176+
177+ protected int tryAcquireShared(int acquires) {
178+ return (getState() == 0) ? 1 : -1;
179+ }
180+
181+ protected boolean tryReleaseShared(int releases) {
182+ // Decrement count; signal when transition to zero
183+ for (;;) {
184+ int c = getState();
185+ if (c == 0)
186+ return false;
187+ int nextc = c-1;
188+ if (compareAndSetState(c, nextc))
189+ return nextc == 0;
190+ }
191+ }
192+ }
193+
194+ private final Sync sync;
195+
196+ /**
197+ * Constructs a {@code CountDownLatch} initialized with the given count.
198+ *
199+ * @param count the number of times {@link #countDown} must be invoked
200+ * before threads can pass through {@link #await}
201+ * @throws IllegalArgumentException if {@code count} is negative
202+ */
203+ public CountDownLatch(int count) {
204+ if (count < 0) throw new IllegalArgumentException("count < 0");
205+ this.sync = new Sync(count);
206+ }
207+
208+ /**
209+ * Causes the current thread to wait until the latch has counted down to
210+ * zero, unless the thread is {@linkplain Thread#interrupt interrupted}.
211+ *
212+ * <p>If the current count is zero then this method returns immediately.
213+ *
214+ * <p>If the current count is greater than zero then the current
215+ * thread becomes disabled for thread scheduling purposes and lies
216+ * dormant until one of two things happen:
217+ * <ul>
218+ * <li>The count reaches zero due to invocations of the
219+ * {@link #countDown} method; or
220+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
221+ * the current thread.
222+ * </ul>
223+ *
224+ * <p>If the current thread:
225+ * <ul>
226+ * <li>has its interrupted status set on entry to this method; or
227+ * <li>is {@linkplain Thread#interrupt interrupted} while waiting,
228+ * </ul>
229+ * then {@link InterruptedException} is thrown and the current thread's
230+ * interrupted status is cleared.
231+ *
232+ * @throws InterruptedException if the current thread is interrupted
233+ * while waiting
234+ */
235+ public void await() throws InterruptedException {
236+ sync.acquireSharedInterruptibly(1);
237+ }
238+
239+ /**
240+ * Causes the current thread to wait until the latch has counted down to
241+ * zero, unless the thread is {@linkplain Thread#interrupt interrupted},
242+ * or the specified waiting time elapses.
243+ *
244+ * <p>If the current count is zero then this method returns immediately
245+ * with the value {@code true}.
246+ *
247+ * <p>If the current count is greater than zero then the current
248+ * thread becomes disabled for thread scheduling purposes and lies
249+ * dormant until one of three things happen:
250+ * <ul>
251+ * <li>The count reaches zero due to invocations of the
252+ * {@link #countDown} method; or
253+ * <li>Some other thread {@linkplain Thread#interrupt interrupts}
254+ * the current thread; or
255+ * <li>The specified waiting time elapses.
256+ * </ul>
257+ *
258+ * <p>If the count reaches zero then the method returns with the
259+ * value {@code true}.
260+ *
261+ * <p>If the current thread:
262+ * <ul>
263+ * <li>has its interrupted status set on entry to this method; or
264+ * <li>is {@linkplain Thread#interrupt interrupted} while waiting,
265+ * </ul>
266+ * then {@link InterruptedException} is thrown and the current thread's
267+ * interrupted status is cleared.
268+ *
269+ * <p>If the specified waiting time elapses then the value {@code false}
270+ * is returned. If the time is less than or equal to zero, the method
271+ * will not wait at all.
272+ *
273+ * @param timeout the maximum time to wait
274+ * @param unit the time unit of the {@code timeout} argument
275+ * @return {@code true} if the count reached zero and {@code false}
276+ * if the waiting time elapsed before the count reached zero
277+ * @throws InterruptedException if the current thread is interrupted
278+ * while waiting
279+ */
280+ public boolean await(long timeout, TimeUnit unit)
281+ throws InterruptedException {
282+ return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
283+ }
284+
285+ /**
286+ * Decrements the count of the latch, releasing all waiting threads if
287+ * the count reaches zero.
288+ *
289+ * <p>If the current count is greater than zero then it is decremented.
290+ * If the new count is zero then all waiting threads are re-enabled for
291+ * thread scheduling purposes.
292+ *
293+ * <p>If the current count equals zero then nothing happens.
294+ */
295+ public void countDown() {
296+ sync.releaseShared(1);
297+ }
298+
299+ /**
300+ * Returns the current count.
301+ *
302+ * <p>This method is typically used for debugging and testing purposes.
303+ *
304+ * @return the current count
305+ */
306+ public long getCount() {
307+ return sync.getCount();
308+ }
309+
310+ /**
311+ * Returns a string identifying this latch, as well as its state.
312+ * The state, in brackets, includes the String {@code "Count ="}
313+ * followed by the current count.
314+ *
315+ * @return a string identifying this latch, as well as its state
316+ */
317+ public String toString() {
318+ return super.toString() + "[Count = " + sync.getCount() + "]";
319+ }
320+}