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Merge branch 'chrishantha:master' into master
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‎.travis.yml‎

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language: java
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jdk:
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- oraclejdk8
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- openjdk8

‎allocations/README.md‎

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Sample to show allocations in Java Flight Recording
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===================================================
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Sample to show allocations in a Java Flight Recording
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=====================================================
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This program checks whether a number is prime.
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Run the program and also make a profiling recording.
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### How to run
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`java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Allocations,filename=allocations.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/allocations.jar`
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```bash
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java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Allocations,filename=allocations.jfr -Xlog:jfr=info -jar target/allocations.jar
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```
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### Analyzing Java Flight Recording
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In Memory -> Allocation tab, you should see a high allocation rate.
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Also see Memory -> Garbage Collections tab and check the frequency of GC events.
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Also, see Memory -> Garbage Collections tab and check the frequency of GC events.
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### Improving Performance
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Try the program again after changing `Long` types to primitive `long`
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Try the program again after changing `Long` types to primitive `long`.

‎base/src/main/java/com/github/chrishantha/sample/base/Utils.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.base;
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import java.util.Timer;

‎highcpu/README.md‎

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A java program consuming high CPU usage. This program was inspired by a sample found in the article "[Identifying which Java Thread is consuming most CPU](http://code.nomad-labs.com/2010/11/18/identifying-which-java-thread-is-consuming-most-cpu/)"
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### How to run
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`java -Xms128m -Xmx128m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=HighCPU,filename=highcpu.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/highcpu.jar`
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```bash
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java -Xms128m -Xmx128m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=HighCPU,filename=highcpu.jfr -Xlog:jfr=info -jar target/highcpu.jar
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```

‎hotmethods/README.md‎

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Sample to show hot methods in Java Flight Recording
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Sample to show hot methods in a Java Flight Recording
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=====================================================
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This program checks whether a given random number is primitive or not.
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Run the program and also make a profiling recording.
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### How to run
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`java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=60s,name=Hotmethods,filename=hotmethods.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/hotmethods.jar`
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```bash
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java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=60s,name=Hotmethods,filename=hotmethods.jfr -Xlog:jfr=info -jar target/hotmethods.jar
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```
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### Analyzing Java Flight Recording
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‎latencies/README.md‎

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Sample to show latencies in Java Flight Recording
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=================================================
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Sample to show latencies in a Java Flight Recording
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===================================================
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This program has two threads: Even and Odd to print Even and Odd numbers.
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Run the program and also make a profiling recording.
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### How to run
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`java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Latencies,filename=latencies.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/latencies.jar`
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```bash
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java -Xms64m -Xmx64m -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Latencies,filename=latencies.jfr -Xlog:jfr=info -jar target/latencies.jar
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```
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### Analyzing Java Flight Recording
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‎memoryleak/README.md‎

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Sample to a memory leak in Java Application
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Sample to show a memory leak in Java Application
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This sample application implements a simple caching solution using a `HashMap`.
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‎memoryref/README.md‎

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Sample to a show memory references in a Java Application
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========================================================
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This sample application creates objects from classes `A`, `B`, `C`, `D`, `E`, `F`, and `G`.
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Each of the previously mentioned classes extend to `Base` class, which creates a significantly
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large byte array in the constructor.
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Following is the class diagram.
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![Class Diagram](classes.png "Class Diagram")
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The application is created to demonstrate the references among objects.
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The sample application creates an object from class `A` in the main thread and another object from
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class `G` in a daemon thread.
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The instance created from class `A` references the instances created from other classes as shown below.
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![References](references.png "References")
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Following is the object diagram showing the object references after the application is started.
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![Object Diagram](objects.png "Object Diagram")
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### How to run
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Use the following command to run the application. The application creates an object from class `A` in
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the main thread and another object from class `G` in a daemon thread. After that the application will
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wait for a keyboard input.
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```bash
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java -Xmn1g -Xmx2g -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCDateStamps -javaagent:target/memoryref.jar -jar target/memoryref.jar
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```
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### Looking at object references using a Heap Dump.
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A heap dump can be obtained from following command to look at the object references in heap memory.
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```bash
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jmap -dump:file=target/heap.hprof $(pgrep -f memoryref)
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```
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Use [Eclipse Memory Analyzer Tool (MAT)](https://www.eclipse.org/mat/) to analyze the heap dump.
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For more information, read following story based on this sample application.
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[Basic concepts of Java heap dump analysis with Eclipse Memory Analyzer Tool (MAT)](https://medium.com/@chrishantha/basic-concepts-of-java-heap-dump-analysis-with-mat-e3615fd79eb)
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Note: Images were created using [draw.io](https://www.draw.io/).

‎memoryref/classes.png‎

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‎memoryref/objects.png‎

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