Java Concurrency - Executor (Thread manager)

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1 - About

An executor is a thread management module (thread creation and management).

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3 - Java.util.concurrent

java.util.concurrent provides two executor interfaces:

3.1 - Executor

Executor is a simple standardized interface for defining custom thread-like subsystems, including:

  • thread pools,
  • asynchronous I/O,
  • and lightweight task frameworks.

Depending on which concrete Executor class is being used, tasks may:

  • execute in:
    • a newly created thread,
    • an existing task-execution thread,
    • or the thread calling execute,
  • and may execute
    • sequentially
    • or concurrently.

An object that executes submitted Runnable tasks.

An Executor is normally used instead of explicitly creating threads.

Executor executor = anExecutor;
 executor.execute(new RunnableTask1());
 executor.execute(new RunnableTask2());
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3.2 - ExecutorService

ExecutorService is more extensive interface Executor by providing a more complete asynchronous task execution framework.

An ExecutorService manages:

  • queuing
  • scheduling of tasks,
  • and controlled shutdown.

ExecutorServices provide methods arranging asynchronous execution of any function expressed as Callable, the result-bearing analog of Runnable.

The ScheduledExecutorService subinterface and associated interfaces add support for:

  • delayed
  • and periodic

task execution.

4 - Example

In a producer-consumer context:

// Start the threads
ExecutorService targetWorkExecutor = Executors.newFixedThreadPool(targetWorkerCount);
targetWorkExecutor.execute(resultSetLoaderConsumer);
 
// Wait the producer
producer.join();
producerWorkIsDone.set(true);
 
// Shut down the targetWorkExecutor
targetWorkExecutor.shutdown();
// And wait the termination of the threads
targetWorkExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.MICROSECONDS);
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