Source Code Cross Referenced for Latch.java in  » Database-DBMS » Quadcap-Embeddable-Database » javax » concurrent » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Database DBMS » Quadcap Embeddable Database » javax.concurrent 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:          File: Latch.java
003:
004:          Originally written by Doug Lea and released into the public domain.
005:          This may be used for any purposes whatsoever without acknowledgment.
006:          Thanks for the assistance and support of Sun Microsystems Labs,
007:          and everyone contributing, testing, and using this code.
008:
009:          History:
010:          Date       Who                What
011:          11Jun1998  dl               Create public version
012:         */
013:
014:        package javax.concurrent;
015:
016:        /**
017:         * A latch is a boolean condition that is set at most once, ever.
018:         * Once a single release is issued, all acquires will pass.
019:         * <p>
020:         * <b>Sample usage.</b> Here are a set of classes that use
021:         * a latch as a start signal for a group of worker threads that
022:         * are created and started beforehand, and then later enabled.
023:         * <pre>
024:         * class Worker implements Runnable {
025:         *   private final Latch startSignal;
026:         *   Worker(Latch l) { startSignal = l; }
027:         *    public void run() {
028:         *      startSignal.acquire();
029:         *      doWork();
030:         *   }
031:         *   void doWork() { ... }
032:         * }
033:         *
034:         * class Driver { // ...
035:         *   void main() {
036:         *     Latch go = new Latch();
037:         *     for (int i = 0; i < N; ++i) // make threads
038:         *       new Thread(new Worker(go)).start();
039:         *     doSomethingElse();         // don't let run yet 
040:         *     go.release();              // let all threads proceed
041:         *   } 
042:         * }
043:         *</pre>
044:         * [<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p>
045:         **/
046:
047:        public class Latch implements  Sync {
048:            protected boolean latched_ = false;
049:
050:            /*
051:              This could use double-check, but doesn't.
052:              If the latch is being used as an indicator of
053:              the presence or state of an object, the user would
054:              not necessarily get the memory barrier that comes with synch
055:              that would be needed to correctly use that object. This
056:              would lead to errors that users would be very hard to track down. So, to
057:              be conservative, we always use synch.
058:             */
059:
060:            public void acquire() throws InterruptedException {
061:                if (Thread.interrupted())
062:                    throw new InterruptedException();
063:                synchronized (this ) {
064:                    while (!latched_)
065:                        wait();
066:                }
067:            }
068:
069:            public boolean attempt(long msecs) throws InterruptedException {
070:                if (Thread.interrupted())
071:                    throw new InterruptedException();
072:                synchronized (this ) {
073:                    if (latched_)
074:                        return true;
075:                    else if (msecs <= 0)
076:                        return false;
077:                    else {
078:                        long waitTime = msecs;
079:                        long start = System.currentTimeMillis();
080:                        for (;;) {
081:                            wait(waitTime);
082:                            if (latched_)
083:                                return true;
084:                            else {
085:                                waitTime = msecs
086:                                        - (System.currentTimeMillis() - start);
087:                                if (waitTime <= 0)
088:                                    return false;
089:                            }
090:                        }
091:                    }
092:                }
093:            }
094:
095:            /** Enable all current and future acquires to pass **/
096:            public synchronized void release() {
097:                latched_ = true;
098:                notifyAll();
099:            }
100:
101:        }
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