Java newFixedThreadPool example

Executor’s newFixedThreadPool factory method :

This method returns thread pool executor whose maximum size(let’s say n threads) is fixed.If all n threads are busy performing the task and additional tasks are submitted, then they will have to be in the queue until a thread is available.

Syntax:

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ExecutorService executorService=Executors.newFixedThreadPool(noOfThreads);

Java newFixedThreadPool example:

Let’s create a very simple example.

Step 1: Create a Runnable task named “LoopTask.java”.

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package org.arpit.java2blog;   public class LoopTask implements Runnable {   private String loopTaskName; public LoopTask(String loopTaskName) { super(); this.loopTaskName = loopTaskName; }   @Override public void run() { System.out.println("Starting "+loopTaskName); for (int i = 1; i <= 10; i++) { System.out.println("Executing "+loopTaskName+" with "+Thread.currentThread().getName()+"===="+i); } System.out.println("Ending "+loopTaskName); } }

Step 2: Create a class named “FixedThreadPoolMain”. This will be our main class.

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package org.arpit.java2blog;   import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;   public class FixedThreadPoolMain {   public static void main(String args[]) { ExecutorService es=Executors.newFixedThreadPool(3); for (int i = 1; i <= 6; i++) { LoopTask loopTask=new LoopTask("LoopTask "+i); es.submit(loopTask); } es.shutdown(); } }

Let’s run above program to check the output:

Starting LoopTask 1
Starting LoopTask 3
Starting LoopTask 2
Executing LoopTask 3 with pool-1-thread-3====1
Executing LoopTask 1 with pool-1-thread-1====1
Executing LoopTask 3 with pool-1-thread-3====2
Executing LoopTask 2 with pool-1-thread-2====1
Executing LoopTask 3 with pool-1-thread-3====3
Executing LoopTask 1 with pool-1-thread-1====2
Executing LoopTask 3 with pool-1-thread-3====4
Executing LoopTask 2 with pool-1-thread-2====2
Executing LoopTask 3 with pool-1-thread-3====5
Executing LoopTask 3 with pool-1-thread-3====6
Executing LoopTask 1 with pool-1-thread-1====3
Executing LoopTask 3 with pool-1-thread-3====7
Executing LoopTask 2 with pool-1-thread-2====3
Executing LoopTask 3 with pool-1-thread-3====8
Executing LoopTask 1 with pool-1-thread-1====4
Executing LoopTask 3 with pool-1-thread-3====9
Executing LoopTask 2 with pool-1-thread-2====4
Executing LoopTask 3 with pool-1-thread-3====10
Executing LoopTask 1 with pool-1-thread-1====5
Executing LoopTask 1 with pool-1-thread-1====6
Ending LoopTask 3
Executing LoopTask 2 with pool-1-thread-2====5
Executing LoopTask 2 with pool-1-thread-2====6
Executing LoopTask 2 with pool-1-thread-2====7
Executing LoopTask 2 with pool-1-thread-2====8
Executing LoopTask 2 with pool-1-thread-2====9
Executing LoopTask 1 with pool-1-thread-1====7
Executing LoopTask 2 with pool-1-thread-2====10
Starting LoopTask 4
Ending LoopTask 2
Executing LoopTask 1 with pool-1-thread-1====8
Starting LoopTask 5
Executing LoopTask 4 with pool-1-thread-3====1
Executing LoopTask 5 with pool-1-thread-2====1
Executing LoopTask 1 with pool-1-thread-1====9
Executing LoopTask 1 with pool-1-thread-1====10
Ending LoopTask 1
Executing LoopTask 5 with pool-1-thread-2====2
Executing LoopTask 4 with pool-1-thread-3====2
Executing LoopTask 4 with pool-1-thread-3====3
Executing LoopTask 5 with pool-1-thread-2====3
Starting LoopTask 6
Executing LoopTask 5 with pool-1-thread-2====4
Executing LoopTask 4 with pool-1-thread-3====4
Executing LoopTask 5 with pool-1-thread-2====5
Executing LoopTask 5 with pool-1-thread-2====6
Executing LoopTask 6 with pool-1-thread-1====1
Executing LoopTask 6 with pool-1-thread-1====2
Executing LoopTask 6 with pool-1-thread-1====3
Executing LoopTask 6 with pool-1-thread-1====4
Executing LoopTask 5 with pool-1-thread-2====7
Executing LoopTask 4 with pool-1-thread-3====5
Executing LoopTask 4 with pool-1-thread-3====6
Executing LoopTask 4 with pool-1-thread-3====7
Executing LoopTask 4 with pool-1-thread-3====8
Executing LoopTask 5 with pool-1-thread-2====8
Executing LoopTask 6 with pool-1-thread-1====5
Executing LoopTask 5 with pool-1-thread-2====9
Executing LoopTask 4 with pool-1-thread-3====9
Executing LoopTask 4 with pool-1-thread-3====10
Executing LoopTask 5 with pool-1-thread-2====10
Ending LoopTask 5
Executing LoopTask 6 with pool-1-thread-1====6
Ending LoopTask 4
Executing LoopTask 6 with pool-1-thread-1====7
Executing LoopTask 6 with pool-1-thread-1====8
Executing LoopTask 6 with pool-1-thread-1====9
Executing LoopTask 6 with pool-1-thread-1====10
Ending LoopTask 6

We have used new newFixedThreadPool, so when we have submitted 6 task, 3 new threads will be created and will execute 3 tasks. Other 3 tasks will wait in wait queue. As soon as any task will be completed by thread, another task will be picked by this thread and will execute it.