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Add Memory Leak Sample Application
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‎memoryleak/README.md‎

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Sample to a memory leak in Java Application
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===========================================
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This sample application implements a simple caching solution using a `HashMap`.
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For example, see following code.
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Map<Key, String> map = new HashMap<>();
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while (true) {
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for (int i = 0; i < max; i++) {
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Key key = new Key(i);
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if (!map.containsKey(key)) {
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map.put(key, "Number:" + i);
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}
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}
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}
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The map is not expected to grow beyond `max` value as all keys will be there in the map after the first `while` loop.
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However, if the `Key` class does not contain a proper `equals()` implementation along with the `hashCode()`
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implementation, the key elements will be keep getting added as the `!map.containsKey(key)` will always return `false`.
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This is a good example of a memory leak and this sample was inspired by the blog post:
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"[How to create a memory leak](https://plumbr.io/blog/memory-leaks/how-to-create-a-memory-leak)"
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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 -XX:+PrintGCDetails -XX:+PrintGC -XX:+PrintGCDateStamps -Xloggc:gc.log
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-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath="/tmp/heap-dump.hprof"
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-XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints
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-XX:+UnlockCommercialFeatures -XX:+FlightRecorder
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-XX:StartFlightRecording=settings=profile,duration=5m,name=MemoryLeak,filename=memoryleak.jfr
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-XX:FlightRecorderOptions=loglevel=info
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-jar target/memoryleak.jar`
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### Analyzing Java Flight Recording
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In Memory -> Memory tab, you should see a high memory growth rate.
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Also see Memory -> Garbage Collections tab and check the frequency of GC events.
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### Analyzing Garbage Collection Logs (GC)
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You can analyze the GC logs using [GCViewer](https://github.com/chewiebug/GCViewer)
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### How to fix the Memory Leak
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Run the application with `--key-type GOOD` parameter, which will use a Key object with proper `equals()` implementation.

‎memoryleak/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>memoryleak</artifactId>
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<packaging>jar</packaging>
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<name>memoryleak</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>

‎memoryleak/src/main/java/com/github/chrishantha/sample/memoryleak/BadKey.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.memoryleak;
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public class BadKey extends Key {
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public BadKey(long NUMBER, long LENGTH) {
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super(NUMBER, LENGTH);
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}
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@Override
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public boolean equals(Object o) {
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return super.equals(o);
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}
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}

‎memoryleak/src/main/java/com/github/chrishantha/sample/memoryleak/GoodKey.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.memoryleak;
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import java.util.Objects;
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public class GoodKey extends Key {
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public GoodKey(long NUMBER, long LENGTH) {
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super(NUMBER, LENGTH);
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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Key key = (Key) o;
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return Objects.equals(KEY, key.KEY);
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}
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}

‎memoryleak/src/main/java/com/github/chrishantha/sample/memoryleak/Key.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.memoryleak;
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import java.util.Objects;
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public abstract class Key {
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protected final String KEY;
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public Key(final long NUMBER, final long LENGTH) {
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String binaryString = Long.toBinaryString(NUMBER);
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StringBuilder keyBuilder = new StringBuilder();
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long limit = LENGTH - binaryString.length();
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for (long i = 0; i < limit; i++) {
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keyBuilder.append('0');
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}
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keyBuilder.append(binaryString);
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KEY = keyBuilder.toString();
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}
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@Override
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public final int hashCode() {
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return Objects.hash(KEY);
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}
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@Override
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public final String toString() {
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StringBuilder builder = new StringBuilder();
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builder.append(this.getClass().getSimpleName());
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builder.append(" [key=");
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builder.append(KEY);
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builder.append("]");
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return builder.toString();
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}
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}

‎memoryleak/src/main/java/com/github/chrishantha/sample/memoryleak/MemoryLeakApplication.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.memoryleak;
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import com.beust.jcommander.Parameter;
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import com.github.chrishantha.sample.base.SampleApplication;
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import java.util.HashMap;
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import java.util.Map;
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public class MemoryLeakApplication implements SampleApplication {
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private enum KeyType {
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BAD,
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GOOD
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}
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@Parameter(names = "--length", description = "Length of the Key")
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private long length = 1024 * 1024;
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@Parameter(names = "--max", description = "Maximum limit to generate keys")
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private int max = 100;
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@Parameter(names = "--key-type", description = "Key Type: Good or Bad")
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private KeyType keyType = KeyType.BAD;
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@Override
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public void start() {
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Map<Key, String> map = new HashMap<>();
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while (true) {
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for (int i = 0; i < max; i++) {
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Key key = KeyType.GOOD.equals(keyType) ? new GoodKey(i, length) : new BadKey(i, length);
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if (!map.containsKey(key)) {
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map.put(key, "Number:" + i);
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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("MemoryLeakApplication [length=");
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builder.append(length);
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builder.append(", max=");
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builder.append(max);
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builder.append(", keyType=");
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builder.append(keyType);
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builder.append("]");
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return builder.toString();
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}
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}

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

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com.github.chrishantha.sample.memoryleak.MemoryLeakApplication

‎pom.xml‎

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<module>hotmethods</module>
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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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</modules>
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<dependencyManagement>

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