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Merge pull request #1012 from mogronalol/master 

BAEL-613 CountDownLatch
This commit is contained in:
pedja4 2017-01-25 11:46:22 +01:00 committed by GitHub
parent dd2772a387 21649ab375
commit 3793b32dee
4 changed files with 178 additions and 0 deletions
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23
core-java/src/main/java/com/baeldung/concurrent/countdownlatch/BrokenWorker.java Normal file
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package com.baeldung.concurrent.countdownlatch;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class BrokenWorker implements Runnable {
private final List<String> outputScraper;
private final CountDownLatch countDownLatch;
public BrokenWorker(final List<String> outputScraper, final CountDownLatch countDownLatch) {
this.outputScraper = outputScraper;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
if (true) {
throw new RuntimeException("Oh dear");
}
countDownLatch.countDown();
outputScraper.add("Counted down");
}
}

37
core-java/src/main/java/com/baeldung/concurrent/countdownlatch/WaitingWorker.java Normal file
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package com.baeldung.concurrent.countdownlatch;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class WaitingWorker implements Runnable {
private final List<String> outputScraper;
private final CountDownLatch readyThreadCounter;
private final CountDownLatch callingThreadBlocker;
private final CountDownLatch completedThreadCounter;
public WaitingWorker(final List<String> outputScraper,
final CountDownLatch readyThreadCounter,
final CountDownLatch callingThreadBlocker,
CountDownLatch completedThreadCounter) {
this.outputScraper = outputScraper;
this.readyThreadCounter = readyThreadCounter;
this.callingThreadBlocker = callingThreadBlocker;
this.completedThreadCounter = completedThreadCounter;
}
@Override
public void run() {
// Mark this thread as read / started
readyThreadCounter.countDown();
try {
callingThreadBlocker.await();
outputScraper.add("Counted down");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
completedThreadCounter.countDown();
}
}
}

22
core-java/src/main/java/com/baeldung/concurrent/countdownlatch/Worker.java Normal file
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package com.baeldung.concurrent.countdownlatch;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class Worker implements Runnable {
private final List<String> outputScraper;
private final CountDownLatch countDownLatch;
public Worker(final List<String> outputScraper, final CountDownLatch countDownLatch) {
this.outputScraper = outputScraper;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
// Do some work
System.out.println("Doing some logic");
countDownLatch.countDown();
outputScraper.add("Counted down");
}
}

96
core-java/src/test/java/com/baeldung/concurrent/countdownlatch/CountdownLatchExampleTest.java Normal file
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package com.baeldung.concurrent.countdownlatch;
import org.junit.Test;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
import static org.assertj.core.api.Assertions.assertThat;
public class CountdownLatchExampleTest {
@Test
public void whenParallelProcessing_thenMainThreadWillBlockUntilCompletion() throws InterruptedException {
// Given
List<String> outputScraper = Collections.synchronizedList(new ArrayList<>());
CountDownLatch countDownLatch = new CountDownLatch(5);
List<Thread> workers = Stream
.generate(() -> new Thread(new Worker(outputScraper, countDownLatch)))
.limit(5)
.collect(toList());
// When
workers.forEach(Thread::start);
countDownLatch.await(); // Block until workers finish
outputScraper.add("Latch released");
// Then
outputScraper.forEach(Object::toString);
assertThat(outputScraper)
.containsExactly(
"Counted down",
"Counted down",
"Counted down",
"Counted down",
"Counted down",
"Latch released"
);
}
@Test
public void whenFailingToParallelProcess_thenMainThreadShouldTimeout() throws InterruptedException {
// Given
List<String> outputScraper = Collections.synchronizedList(new ArrayList<>());
CountDownLatch countDownLatch = new CountDownLatch(5);
List<Thread> workers = Stream
.generate(() -> new Thread(new BrokenWorker(outputScraper, countDownLatch)))
.limit(5)
.collect(toList());
// When
workers.forEach(Thread::start);
final boolean result = countDownLatch.await(3L, TimeUnit.SECONDS);
// Then
assertThat(result).isFalse();
}
@Test
public void whenDoingLotsOfThreadsInParallel_thenStartThemAtTheSameTime() throws InterruptedException {
// Given
List<String> outputScraper = Collections.synchronizedList(new ArrayList<>());
CountDownLatch readyThreadCounter = new CountDownLatch(5);
CountDownLatch callingThreadBlocker = new CountDownLatch(1);
CountDownLatch completedThreadCounter = new CountDownLatch(5);
List<Thread> workers = Stream
.generate(() -> new Thread(new WaitingWorker(outputScraper, readyThreadCounter, callingThreadBlocker, completedThreadCounter)))
.limit(5)
.collect(toList());
// When
workers.forEach(Thread::start);
readyThreadCounter.await(); // Block until workers start
outputScraper.add("Workers ready");
callingThreadBlocker.countDown(); // Start workers
completedThreadCounter.await(); // Block until workers finish
outputScraper.add("Workers complete");
// Then
outputScraper.forEach(Object::toString);
assertThat(outputScraper)
.containsExactly(
"Workers ready",
"Counted down",
"Counted down",
"Counted down",
"Counted down",
"Counted down",
"Workers complete"
);
}
}