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Add deadlock sample application
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‎deadlock/README.md‎

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Sample to a deadlock in Java Application
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===========================================
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This sample application shows an example of a deadlock. Following is the definition of "deadlock" according to
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[Java Tutorial](https://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.html)
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> Deadlock describes a situation where two or more threads are blocked forever, waiting for each other.
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In this application, there are two threads trying to acquire two locks.
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### How to run
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The application will throw Out of Memory error after some time when you run following command
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`java -Xms1g -Xmx1g -jar target/deadlock.jar`
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### How to detect a deadlock
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Take a thread dump (using `jstack <pid>` command or `jcmd <pid> Thread.print`).
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The thread dump should show the Java level deadlock details as follows.
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```
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Found one Java-level deadlock:
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=============================
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"Thread Group 1-2":
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waiting to lock monitor 0x00007f8ab4003a78 (object 0x00000000eaca1488, a java.lang.Object),
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which is held by "Thread Group 1-1"
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"Thread Group 1-1":
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waiting to lock monitor 0x00007f8ab4006518 (object 0x00000000eaca1498, a java.lang.Object),
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which is held by "Thread Group 1-2"
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Java stack information for the threads listed above:
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===================================================
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"Thread Group 1-2":
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at com.github.chrishantha.sample.deadlock.DeadlockApplication$SampleLockThread.run(DeadlockApplication.java:54)
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- waiting to lock <0x00000000eaca1488> (a java.lang.Object)
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- locked <0x00000000eaca1498> (a java.lang.Object)
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"Thread Group 1-1":
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at com.github.chrishantha.sample.deadlock.DeadlockApplication$SampleLockThread.run(DeadlockApplication.java:54)
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- waiting to lock <0x00000000eaca1498> (a java.lang.Object)
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- locked <0x00000000eaca1488> (a java.lang.Object)
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Found 1 deadlock.
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```

‎deadlock/pom.xml‎

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<?xml version="1.0" encoding="utf-8"?>
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<!--
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# Copyright 2018 M. Isuru Tharanga Chrishantha Perera
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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-->
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<groupId>com.github.chrishantha.sample</groupId>
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<artifactId>java-samples</artifactId>
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<version>0.0.2-SNAPSHOT</version>
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<relativePath>../pom.xml</relativePath>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>deadlock</artifactId>
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<packaging>jar</packaging>
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<name>deadlock</name>
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<dependencies>
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<dependency>
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<groupId>com.github.chrishantha.sample</groupId>
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<artifactId>base</artifactId>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-shade-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>

‎deadlock/src/main/java/com/github/chrishantha/sample/deadlock/DeadlockApplication.java‎

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/*
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* Copyright 2018 M. Isuru Tharanga Chrishantha Perera
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.github.chrishantha.sample.deadlock;
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import com.beust.jcommander.Parameter;
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import com.github.chrishantha.sample.base.SampleApplication;
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public class DeadlockApplication implements SampleApplication {
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@Parameter(names = "--count", description = "Number of deadlocks")
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private int count = 1;
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@Parameter(names = "--delay", description = "Delay in milliseconds to start a new thread group")
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private int delay = 0;
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private static class SampleLockThread extends Thread {
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private final Object lock1;
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private final Object lock2;
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public SampleLockThread(final String name, final Object lock1, final Object lock2) {
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super(name);
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this.lock1 = lock1;
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this.lock2 = lock2;
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}
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@Override
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public void run() {
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System.out.format("%s: Acquiring lock : %s%n", getName(), lock1);
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synchronized (lock1) {
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System.out.format("%s: Acquired lock : %s%n", getName(), lock1);
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try {
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Thread.sleep(100);
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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System.out.format("%s: Acquiring lock : %s%n", getName(), lock2);
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synchronized (lock2) {
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System.out.format("%s: Acquired lock : %s%n", getName(), lock2);
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}
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}
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}
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}
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@Override
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public void start() {
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final String nameFormat = "Thread Group %2d-%d";
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for (int i = 1; i <= count; i++) {
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final Object lock1 = new Object();
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final Object lock2 = new Object();
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SampleLockThread t1 = new SampleLockThread(String.format(nameFormat, i, 1), lock1, lock2);
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SampleLockThread t2 = new SampleLockThread(String.format(nameFormat, i, 2), lock2, lock1);
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t1.start();
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t2.start();
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if (delay > 0) {
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try {
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Thread.sleep(delay);
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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}
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}
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@Override
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public String toString() {
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StringBuilder builder = new StringBuilder();
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builder.append("DeadlockApplication [count=");
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builder.append(count);
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builder.append(", delay=");
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builder.append(delay);
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builder.append("]");
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return builder.toString();
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}
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}

‎deadlock/src/main/resources/META-INF/services/com.github.chrishantha.sample.base.SampleApplication‎

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com.github.chrishantha.sample.deadlock.DeadlockApplication

‎pom.xml‎

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<module>latencies</module>
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<module>allocations</module>
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<module>memoryleak</module>
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<module>deadlock</module>
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</modules>
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<dependencyManagement>

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