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Updated README instructions · deezeesms/sample-java-programs@149a704 · GitHub

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Updated README instructions
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‎allocations/README.md‎

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Sample to show allocations in Java Flight Recording
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This program checks whether a number is prime.
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Run the program without any arguments and also make a profiling recording.
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Run the program and also make a profiling recording.
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For example:
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`java -Xms64m -Xmx64m -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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### 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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### 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
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Also see Memory -> Garbage Collections tab and check the frequency of GC events.
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Try the program again after changing `Long` types to primitive `long`
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### Improving Performance
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Run the program without locks.
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`java -Xms64m -Xmx64m -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Allocations,filename=allocations-fixed.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/allocations.jar`
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Try the program again after changing `Long` types to primitive `long`

‎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`

‎hotmethods/README.md‎

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This program checks whether a given random number is primitive or not.
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Run the program without any arguments and also make a profiling recording.
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Run the program and also make a profiling recording.
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For example:
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`java -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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### 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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### Analyzing Java Flight Recording
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In Code -> Hot Methods tab, you should see that the program has spent a lot of time in the LinkedList.indexOf(Object) method, which is called from contains method.
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### Improving Performance
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By changing LinkedList to a HashSet, you can make the program run a lot faster.
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The contains methods in Linked List checks all the items. Algorithm run time is O(n). However the HashSet contains algorithm's run time is O(1).
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In the program, change `Collection<Integer> primeNumbers = new LinkedList<>()` to `Collection<Integer> primeNumbers = new HashSet<>()` to use a HashSet for Prime Numbers
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Check the runtime using HashSet.
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`java -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=60s,name=Hotmethods,filename=hotmethods-fixed.jfr -XX:FlightRecorderOptions=loglevel=info -jar target/hotmethods.jar`
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Use `time` command in Linux to measure the time.
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Use `time` command in Linux to measure the time.

‎latencies/README.md‎

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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 without any arguments and also make a profiling recording.
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Run the program and also make a profiling recording.
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For example:
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`java -jar -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Latencies,filename=latencies.jfr -XX:FlightRecorderOptions=loglevel=info target/latencies.jar`
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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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### Analyzing Java Flight Recording
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In Threads -> Latencies tab, you should see that the program has many blocked events.
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You should also see red blocks in Events -> Graph tab. Red blocks are not good as the thread is just waiting to acquire a lock.
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See Threads -> Contention tab to see the Locks and also see Threads -> Lock Instances to check whether both threads share the same lock instances.
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Since there is no shared resource, you can avoid the lock and improve the performance.
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### Improving Performance
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Remove the `synchronized` keyword in `isEven` method.
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Since there is no shared resource to protect, you can avoid the synchronized keyword and improve the performance.
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Run the program without locks.
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`java -jar -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=settings=profile,duration=30s,name=Latencies,filename=latencies-fixed.jfr -XX:FlightRecorderOptions=loglevel=info target/latencies.jar`
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Try the program again after removing the `synchronized` keyword in `isEven` method.

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