176 lines
7.4 KiB
HTML
176 lines
7.4 KiB
HTML
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<meta name="DC.Title" content="Example: Use condition variables in Java programs" />
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<meta name="abstract" content="This example shows a Java program using condition variables in the form of the wait and notify methods on a Java object. Note the locking protocol used." />
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<title>Example: Use condition variables in Java programs</title>
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<body id="rzahwex5-ex5rx"><a name="rzahwex5-ex5rx"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Example: Use condition variables in Java programs</h1>
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<div><p>This example shows a Java™ program using condition variables in
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the form of the wait and notify methods on a Java object. Note the locking protocol used.</p>
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<div class="section"><div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
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</div>
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<div class="example"> <pre>/*
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FileName: ATEST18.java
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The output of this example is as follows:
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Entered the testcase
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Create/start the thread
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Consumer Thread-1: Entered
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Consumer Thread-1: Wait for the data to be produced
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Producer: 'Finding data
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Consumer Thread-2: Entered
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Consumer Thread-2: Wait for the data to be produced
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Consumer Thread-2: Found data or notified, CONSUME IT while holding inside the monitor
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Consumer Thread-2: Wait for the data to be produced
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Producer: 'Finding data
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Producer: 'Finding data
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Consumer Thread-2: Found data or notified, CONSUME IT while holding inside the monitor
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Consumer Thread-2: All done
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Producer: 'Finding data
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Consumer Thread-1: Found data or notified, CONSUME IT while holding inside the monitor
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Consumer Thread-1: Wait for the data to be produced
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Producer: Make data shared and notify consumer
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Producer: Unlock shared data and flag
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Wait for the threads to complete
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Consumer Thread-1: Found data or notified, CONSUME IT while holding inside the monitor
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Consumer Thread-1: All done
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Testcase completed
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*/
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import java.lang.*;
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/* This class is an encapsulation of the condition variable plus */
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/* mutex locking logic that can be seen in the Pthread example */
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class theSharedData extends Object {
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int dataPresent;
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int sharedData;
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public theSharedData() {
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dataPresent=0;
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sharedData=0;
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}
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public synchronized void get() {
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while (dataPresent == 0) {
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try {
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System.out.print("Consumer " +
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Thread.currentThread().getName() +
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": Wait for the data to be produced\n");
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wait();
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}
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catch (InterruptedException e) {
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System.out.print("Consumer " +
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Thread.currentThread().getName() +
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": wait interrupted\n");
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}
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}
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System.out.print("Consumer " +
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Thread.currentThread().getName() +
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": Found data or notified, CONSUME IT " +
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"while holding inside the monitor\n");
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--sharedData;
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if (sharedData == 0) {dataPresent=0;}
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/* in a real world application, the actual data would be returned */
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/* here */
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}
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public synchronized void put() {
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System.out.print("Producer: Make data shared and notify consumer\n");
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++sharedData;
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dataPresent=1;
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notify();
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System.out.print("Producer: Unlock shared data and flag\n");
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/* unlock occurs when leaving the synchronized method */
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}
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}
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public class ATEST18 {
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public final static int NUMTHREADS = 2;
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public static theSharedData dataConditionEncapsulation = new theSharedData();
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static class theThread extends Thread {
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public void run() {
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int retries=2;
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System.out.print("Consumer " + getName() + ": Entered\n");
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while (retries-- != 0) {
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dataConditionEncapsulation.get();
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/* Typically an application would process the data outside */
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/* the monitor (synchronized get method here) */
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}
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System.out.print("Consumer " + getName() + ": All done\n");
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}
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}
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public static void main(String argv[]) {
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int amountOfData = 4;
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theThread threads[] = new theThread[NUMTHREADS];
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System.out.print("Entered the testcase\n");
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System.out.print("Create/start the thread\n");
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for (int i=0; i <NUMTHREADS; ++i) {
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threads[i] = new theThread();
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threads[i].start();
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}
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while (amountOfData-- != 0) {
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System.out.print("Producer: 'Finding data\n");
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try {
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Thread.sleep(3000);
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}
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catch (InterruptedException e) {
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System.out.print("sleep interrupted\n");
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}
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dataConditionEncapsulation.put();
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}
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System.out.print("Wait for the threads to complete\n");
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for(int i=0; i <NUMTHREADS; ++i) {
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try {
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threads[i].join();
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}
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catch (InterruptedException e) {
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System.out.print("Join interrupted\n");
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}
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}
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System.out.print("Testcase completed\n");
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System.exit(0);
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}
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}
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</pre>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwvarco.htm" title="Condition variables allow threads to wait for certain events or conditions to occur and they notify other threads that are also waiting for the same events or conditions.">Condition variables and threads</a></div>
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</div>
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</div>
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</body>
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