Source Code Cross Referenced for ReentrantLock.java in  » Rule-Engine » drolls-Rule-Engine » org » drools » util » concurrent » locks » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Rule Engine » drolls Rule Engine » org.drools.util.concurrent.locks 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Written by Doug Lea with assistance from members of JCP JSR-166
003:         * Expert Group and released to the public domain, as explained at
004:         * http://creativecommons.org/licenses/publicdomain
005:         */
006:
007:        package org.drools.util.concurrent.locks;
008:
009:        import java.io.Serializable;
010:        import java.util.Collection;
011:
012:        /**
013:         *  This is a stripped down version of jdk1.5 ReentrantLock. 
014:         *  All the condition and wait stuff has been removed
015:         *
016:         * @since 1.5
017:         * @author Doug Lea
018:         * @author Dawid Kurzyniec
019:         */
020:        public class ReentrantLock implements  Lock, java.io.Serializable {
021:            private static final long serialVersionUID = 400L;
022:
023:            private final NonfairSync sync;
024:
025:            final static class NonfairSync implements  Serializable {
026:                private static final long serialVersionUID = 400L;
027:
028:                protected transient Thread owner_ = null;
029:                protected transient int holds_ = 0;
030:
031:                final void incHolds() {
032:                    final int nextHolds = ++this .holds_;
033:                    if (nextHolds < 0) {
034:                        throw new Error("Maximum lock count exceeded");
035:                    }
036:                    this .holds_ = nextHolds;
037:                }
038:
039:                public boolean tryLock() {
040:                    final Thread caller = Thread.currentThread();
041:                    synchronized (this ) {
042:                        if (this .owner_ == null) {
043:                            this .owner_ = caller;
044:                            this .holds_ = 1;
045:                            return true;
046:                        } else if (caller == this .owner_) {
047:                            incHolds();
048:                            return true;
049:                        }
050:                    }
051:                    return false;
052:                }
053:
054:                public synchronized int getHoldCount() {
055:                    return isHeldByCurrentThread() ? this .holds_ : 0;
056:                }
057:
058:                public synchronized boolean isHeldByCurrentThread() {
059:                    return this .holds_ > 0
060:                            && Thread.currentThread() == this .owner_;
061:                }
062:
063:                public synchronized boolean isLocked() {
064:                    return this .owner_ != null;
065:                }
066:
067:                protected synchronized Thread getOwner() {
068:                    return this .owner_;
069:                }
070:
071:                public boolean hasQueuedThreads() {
072:                    throw new UnsupportedOperationException("Use FAIR version");
073:                }
074:
075:                public int getQueueLength() {
076:                    throw new UnsupportedOperationException("Use FAIR version");
077:                }
078:
079:                public Collection getQueuedThreads() {
080:                    throw new UnsupportedOperationException("Use FAIR version");
081:                }
082:
083:                public boolean isQueued(final Thread thread) {
084:                    throw new UnsupportedOperationException("Use FAIR version");
085:                }
086:
087:                public void lock() {
088:                    final Thread caller = Thread.currentThread();
089:                    synchronized (this ) {
090:                        if (this .owner_ == null) {
091:                            this .owner_ = caller;
092:                            this .holds_ = 1;
093:                            return;
094:                        } else if (caller == this .owner_) {
095:                            incHolds();
096:                            return;
097:                        } else {
098:                            boolean wasInterrupted = Thread.interrupted();
099:                            try {
100:                                while (true) {
101:                                    try {
102:                                        wait();
103:                                    } catch (final InterruptedException e) {
104:                                        wasInterrupted = true;
105:                                        // no need to notify; if we were signalled, we
106:                                        // will act as signalled, ignoring the
107:                                        // interruption
108:                                    }
109:                                    if (this .owner_ == null) {
110:                                        this .owner_ = caller;
111:                                        this .holds_ = 1;
112:                                        return;
113:                                    }
114:                                }
115:                            } finally {
116:                                if (wasInterrupted) {
117:                                    Thread.currentThread().interrupt();
118:                                }
119:                            }
120:                        }
121:                    }
122:                }
123:
124:                public void lockInterruptibly() throws InterruptedException {
125:                    if (Thread.interrupted()) {
126:                        throw new InterruptedException();
127:                    }
128:                    final Thread caller = Thread.currentThread();
129:                    synchronized (this ) {
130:                        if (this .owner_ == null) {
131:                            this .owner_ = caller;
132:                            this .holds_ = 1;
133:                            return;
134:                        } else if (caller == this .owner_) {
135:                            incHolds();
136:                            return;
137:                        } else {
138:                            try {
139:                                do {
140:                                    wait();
141:                                } while (this .owner_ != null);
142:                                this .owner_ = caller;
143:                                this .holds_ = 1;
144:                                return;
145:                            } catch (final InterruptedException ex) {
146:                                if (this .owner_ == null) {
147:                                    notify();
148:                                }
149:                                throw ex;
150:                            }
151:                        }
152:                    }
153:                }
154:
155:                public synchronized void unlock() {
156:                    if (Thread.currentThread() != this .owner_) {
157:                        throw new IllegalMonitorStateException("Not owner");
158:                    }
159:
160:                    if (--this .holds_ == 0) {
161:                        this .owner_ = null;
162:                        notify();
163:                    }
164:                }
165:            }
166:
167:            /**
168:             * Creates an instance of <tt>ReentrantLock</tt>.
169:             * This is equivalent to using <tt>ReentrantLock(false)</tt>.
170:             */
171:            public ReentrantLock() {
172:                this .sync = new NonfairSync();
173:            }
174:
175:            /**
176:             * Acquires the lock.
177:             *
178:             * <p>Acquires the lock if it is not held by another thread and returns
179:             * immediately, setting the lock hold count to one.
180:             *
181:             * <p>If the current thread
182:             * already holds the lock then the hold count is incremented by one and
183:             * the method returns immediately.
184:             *
185:             * <p>If the lock is held by another thread then the
186:             * current thread becomes disabled for thread scheduling
187:             * purposes and lies dormant until the lock has been acquired,
188:             * at which time the lock hold count is set to one.
189:             */
190:            public void lock() {
191:                this .sync.lock();
192:            }
193:
194:            /**
195:             * Acquires the lock unless the current thread is
196:             * {@link Thread#interrupt interrupted}.
197:             *
198:             * <p>Acquires the lock if it is not held by another thread and returns
199:             * immediately, setting the lock hold count to one.
200:             *
201:             * <p>If the current thread already holds this lock then the hold count
202:             * is incremented by one and the method returns immediately.
203:             *
204:             * <p>If the lock is held by another thread then the
205:             * current thread becomes disabled for thread scheduling
206:             * purposes and lies dormant until one of two things happens:
207:             *
208:             * <ul>
209:             *
210:             * <li>The lock is acquired by the current thread; or
211:             *
212:             * <li>Some other thread {@link Thread#interrupt interrupts} the current
213:             * thread.
214:             *
215:             * </ul>
216:             *
217:             * <p>If the lock is acquired by the current thread then the lock hold
218:             * count is set to one.
219:             *
220:             * <p>If the current thread:
221:             *
222:             * <ul>
223:             *
224:             * <li>has its interrupted status set on entry to this method; or
225:             *
226:             * <li>is {@link Thread#interrupt interrupted} while acquiring
227:             * the lock,
228:             *
229:             * </ul>
230:             *
231:             * then {@link InterruptedException} is thrown and the current thread's
232:             * interrupted status is cleared.
233:             *
234:             * <p>In this implementation, as this method is an explicit interruption
235:             * point, preference is
236:             * given to responding to the interrupt over normal or reentrant
237:             * acquisition of the lock.
238:             *
239:             * @throws InterruptedException if the current thread is interrupted
240:             */
241:            public void lockInterruptibly() throws InterruptedException {
242:                this .sync.lockInterruptibly();
243:            }
244:
245:            /**
246:             * Acquires the lock only if it is not held by another thread at the time
247:             * of invocation.
248:             *
249:             * <p>Acquires the lock if it is not held by another thread and
250:             * returns immediately with the value <tt>true</tt>, setting the
251:             * lock hold count to one. Even when this lock has been set to use a
252:             * fair ordering policy, a call to <tt>tryLock()</tt> <em>will</em>
253:             * immediately acquire the lock if it is available, whether or not
254:             * other threads are currently waiting for the lock.
255:             * This &quot;barging&quot; behavior can be useful in certain
256:             * circumstances, even though it breaks fairness. If you want to honor
257:             * the fairness setting for this lock, then use
258:             * {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
259:             * which is almost equivalent (it also detects interruption).
260:             *
261:             * <p> If the current thread
262:             * already holds this lock then the hold count is incremented by one and
263:             * the method returns <tt>true</tt>.
264:             *
265:             * <p>If the lock is held by another thread then this method will return
266:             * immediately with the value <tt>false</tt>.
267:             *
268:             * @return <tt>true</tt> if the lock was free and was acquired by the
269:             * current thread, or the lock was already held by the current thread; and
270:             * <tt>false</tt> otherwise.
271:             */
272:            public boolean tryLock() {
273:                return this .sync.tryLock();
274:            }
275:
276:            /**
277:             * Attempts to release this lock.
278:             *
279:             * <p>If the current thread is the
280:             * holder of this lock then the hold count is decremented. If the
281:             * hold count is now zero then the lock is released.  If the
282:             * current thread is not the holder of this lock then {@link
283:             * IllegalMonitorStateException} is thrown.
284:             * @throws IllegalMonitorStateException if the current thread does not
285:             * hold this lock.
286:             */
287:            public void unlock() {
288:                this .sync.unlock();
289:            }
290:
291:            /**
292:             * Queries the number of holds on this lock by the current thread.
293:             *
294:             * <p>A thread has a hold on a lock for each lock action that is not
295:             * matched by an unlock action.
296:             *
297:             * <p>The hold count information is typically only used for testing and
298:             * debugging purposes. For example, if a certain section of code should
299:             * not be entered with the lock already held then we can assert that
300:             * fact:
301:             *
302:             * <pre>
303:             * class X {
304:             *   ReentrantLock lock = new ReentrantLock();
305:             *   // ...
306:             *   public void m() {
307:             *     assert lock.getHoldCount() == 0;
308:             *     lock.lock();
309:             *     try {
310:             *       // ... method body
311:             *     } finally {
312:             *       lock.unlock();
313:             *     }
314:             *   }
315:             * }
316:             * </pre>
317:             *
318:             * @return the number of holds on this lock by the current thread,
319:             * or zero if this lock is not held by the current thread.
320:             */
321:            public int getHoldCount() {
322:                return this .sync.getHoldCount();
323:            }
324:
325:            /**
326:             * Queries if this lock is held by the current thread.
327:             *
328:             * <p>Analogous to the {@link Thread#holdsLock} method for built-in
329:             * monitor locks, this method is typically used for debugging and
330:             * testing. For example, a method that should only be called while
331:             * a lock is held can assert that this is the case:
332:             *
333:             * <pre>
334:             * class X {
335:             *   ReentrantLock lock = new ReentrantLock();
336:             *   // ...
337:             *
338:             *   public void m() {
339:             *       assert lock.isHeldByCurrentThread();
340:             *       // ... method body
341:             *   }
342:             * }
343:             * </pre>
344:             *
345:             * <p>It can also be used to ensure that a reentrant lock is used
346:             * in a non-reentrant manner, for example:
347:             *
348:             * <pre>
349:             * class X {
350:             *   ReentrantLock lock = new ReentrantLock();
351:             *   // ...
352:             *
353:             *   public void m() {
354:             *       assert !lock.isHeldByCurrentThread();
355:             *       lock.lock();
356:             *       try {
357:             *           // ... method body
358:             *       } finally {
359:             *           lock.unlock();
360:             *       }
361:             *   }
362:             * }
363:             * </pre>
364:             * @return <tt>true</tt> if current thread holds this lock and
365:             * <tt>false</tt> otherwise.
366:             */
367:            public boolean isHeldByCurrentThread() {
368:                return this .sync.isHeldByCurrentThread();
369:            }
370:
371:            /**
372:             * Queries if this lock is held by any thread. This method is
373:             * designed for use in monitoring of the system state,
374:             * not for synchronization control.
375:             * @return <tt>true</tt> if any thread holds this lock and
376:             * <tt>false</tt> otherwise.
377:             */
378:            public boolean isLocked() {
379:                return this .sync.isLocked();
380:            }
381:
382:            /**
383:             * <tt>null</tt> if not owned. When this method is called by a
384:             * thread that is not the owner, the return value reflects a
385:             * best-effort approximation of current lock status. For example,
386:             * the owner may be momentarily <tt>null</tt> even if there are
387:             * threads trying to acquire the lock but have not yet done so.
388:             * This method is designed to facilitate construction of
389:             * subclasses that provide more extensive lock monitoring
390:             * facilities.
391:             *
392:             * @return the owner, or <tt>null</tt> if not owned
393:             */
394:            protected Thread getOwner() {
395:                return this .sync.getOwner();
396:            }
397:
398:            /**
399:             * Queries whether any threads are waiting to acquire this lock. Note that
400:             * because cancellations may occur at any time, a <tt>true</tt>
401:             * return does not guarantee that any other thread will ever
402:             * acquire this lock.  This method is designed primarily for use in
403:             * monitoring of the system state.
404:             *
405:             * @return true if there may be other threads waiting to acquire
406:             * the lock.
407:             */
408:            public final boolean hasQueuedThreads() {
409:                return this .sync.hasQueuedThreads();
410:            }
411:
412:            /**
413:             * Queries whether the given thread is waiting to acquire this
414:             * lock. Note that because cancellations may occur at any time, a
415:             * <tt>true</tt> return does not guarantee that this thread
416:             * will ever acquire this lock.  This method is designed primarily for use
417:             * in monitoring of the system state.
418:             *
419:             * @param thread the thread
420:             * @return true if the given thread is queued waiting for this lock.
421:             * @throws NullPointerException if thread is null
422:             */
423:            public final boolean hasQueuedThread(final Thread thread) {
424:                return this .sync.isQueued(thread);
425:            }
426:
427:            /**
428:             * Returns an estimate of the number of threads waiting to
429:             * acquire this lock.  The value is only an estimate because the number of
430:             * threads may change dynamically while this method traverses
431:             * internal data structures.  This method is designed for use in
432:             * monitoring of the system state, not for synchronization
433:             * control.
434:             * @return the estimated number of threads waiting for this lock
435:             */
436:            public final int getQueueLength() {
437:                return this .sync.getQueueLength();
438:            }
439:
440:            /**
441:             * Returns a collection containing threads that may be waiting to
442:             * acquire this lock.  Because the actual set of threads may change
443:             * dynamically while constructing this result, the returned
444:             * collection is only a best-effort estimate.  The elements of the
445:             * returned collection are in no particular order.  This method is
446:             * designed to facilitate construction of subclasses that provide
447:             * more extensive monitoring facilities.
448:             * @return the collection of threads
449:             */
450:            protected Collection getQueuedThreads() {
451:                return this .sync.getQueuedThreads();
452:            }
453:
454:            /**
455:             * Returns a string identifying this lock, as well as its lock
456:             * state.  The state, in brackets, includes either the String
457:             * &quot;Unlocked&quot; or the String &quot;Locked by&quot;
458:             * followed by the {@link Thread#getName} of the owning thread.
459:             * @return a string identifying this lock, as well as its lock state.
460:             */
461:            public String toString() {
462:                final Thread o = getOwner();
463:                return super .toString()
464:                        + ((o == null) ? "[Unlocked]" : "[Locked by thread "
465:                                + o.getName() + "]");
466:            }
467:        }
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