Java Thread Pool – ExecutorService

Java Thread Pool is a performance solution for scaling system, so JavaSampleApproach will guide you how to work with Java Thread Pool by ExecutorService and Executors.

I. Concepts
1. ExecutorService & Executors

java.util.concurrent.ExecutorService provides methods to manage termination and methods to produce a Future for tracking progress of tasks.

java.util.concurrent.Executors class provides factory methods for the executor services.

2. Methods

public static ExecutorService newFixedThreadPool(int nThreads): creates a thread pool for reusing a fixed number of threads . At any point if having any tasked are submitted when all threads are active, they will wait until a thread is available.

public static ExecutorService newSingleThreadExecutor(): creates an Executor that uses a single worker thread. Tasks are guaranteed to execute sequentially, and no more than one task will be active at a specific time.

– Difference between newFixedThreadPool(1) & newSingleThreadExecutor(): Executor of newSingleThreadExecutor() factory method guaranteed not to be reconfigurable at runtime.

– If a thread terminates(both: newFixedThreadPool() & newSingleThreadExecutor()) due to a failure during execution prior to shutdown, a new one will created for executing subsequent tasks.

void java.util.concurrent.Executor.execute(Runnable command): executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the Executor implementation.

void java.util.concurrent.ExecutorService.shutdown(): setup a shutdown right after all submitted tasks are executed, and not accepted any new task.

boolean java.util.concurrent.ExecutorService.isTerminated(): returns true if all tasks have completed after shut down.
Note: isTerminated is always false unless either shutdown or shutdownNow was called first.

II. Practice
1. Create WorkerThread

2. Sample with newFixedThreadPool



3. Sample with newSingleThreadExecutor



4. Source code

Java ThreadPool

By JavaSampleApproach | December 21, 2016.

Last updated on June 4, 2017.

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