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javamultithreadingperformancejvmexecutor
hoffmax91
hoffmax91

Reputation: 131

Java Multithread Application uses only one Core

I have a problem with my JVM Running on a CentOS 6.0 with openJDK 1.7.0_51 64Bit. My System is a 4-Core System with 8GB Ram.

I'm running a Java multithread application that I wrote myself. It's supposed to insert tons of Data into a NoSQL Database. For that, I'm spawning 4 threads, using a "CachedThreadPoolExecutor" from java.concurrent.Executors.

I instantiate 4 Workers that implement the "Runnable" Interface. Afterwards I execute the Thread using the threadpool. Here's my code:

 public void startDataPump(int numberOfWorkers){
   //class "DataPump" implements runnable
   for (int i = 0; i < numberOfWorkers; i++){
      DataPump pump = new DataPump();
      //"workerList" contains all workers and is a simple arrayList to keep track of the workers
      workerList.add(pump);
      //"workers" is the thradpool that has been 
      //initialized earlier with "Executors.newCachedThreadPool()
      workers.execute(pump);
   }
 }

When running this, using a parameter of 4, it will spawn 4 Threads in the Threadpool. I assumed that the JVM or my OS would be smart enough to schedule these threads on all of my cores. HOWEVER, only one core of my cpu is working at 100%,the others remain almost idle.

Am I doing anything wrong in my code or is this a JVM/OS problem. If so, is there anything I can do about that? Running this application on only 1 core is extremeley slowing down the whole app.

Help is greatly appreciated :)

Upvotes: 7

Views: 9427

Answers (3)

Mojtaba Talebi
Mojtaba Talebi

Reputation: 21

If your environment are virtual or in other hand special cpu scheduling like docker, there is no way to get Java to automatically use find out many cores are available and use them all. You have to specify how many cores you want to use via

On JDK >= 10, use the following JDK options:

-XX:ActiveProcessorCount=2

On JDK >= 8, use the following JDK options:

-XX:+UnlockExperimentalVMOptions > -XX:ActiveProcessorCount=2

Upvotes: 1

Nachiket Kate
Nachiket Kate

Reputation: 8571

Scheduling thread is not JVM activity but it is OS activity.if OS finds threads are independent of each other and can be executed seperately then it schedules it on another core.

I am not sure about schedutils but I think it works at application level (it allows you to set cpu affinity but last decision is taken by OS)

one thing about using cores is OS scheduler schedules new processes on new cores as every process has its own process area independent of other processes (thus they can be executed parallely without any obstruction)

Try creating new process for each thread that will help improve your cpu utilization(use of more cores) but there is disadvantage of it also, Every process creates its own process area so extra memory is required for each process (for each thread in your case) if you have good amount of memory available then you can try this one.

if it just a linux OS then "sar" command is enough for monitoring per core cpu utilization (sar is base package in linux almost all utilities use 'sar' so overhead on system will be less).

Upvotes: 0

ali haider
ali haider

Reputation: 20202

Please bear in mind that its the OS and not the JVM responsible for CPU affinity - which is why I suggested that you first figure out how many CPU's you have and then perhaps use schedutils to configure processor affinity for a certain process.

cpu info - use one of the three below

/proc/cpuinfo
lscpu
nproc

install schedutils to confgure processor affinity

yum install schedutils

You can assign cpu affinity via schedutils as follows (2 is second proceccor and 23564 is process id):

taskset -c 2 -p 23564

Upvotes: 3

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