How to Efficiently Wait for ExecutorService Task Completion?

ExecutorService Waiting for Task Completion

In multi-threaded applications, it is often necessary to wait for all tasks submitted to an ExecutorService to complete before proceeding. While crude techniques like polling or constantly checking a global task counter exist, more efficient and elegant solutions are available.

awaitTermination() and shutdown()

The recommended approach involves using the awaitTermination() method of ExecutorService. It allows you to specify a timeout or wait indefinitely for the threads to finish. Here's how it works:

// Create an ExecutorService instance
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);

// Submit tasks as needed
while(...) {
  taskExecutor.execute(new MyTask());
}

// Shutdown the ExecutorService to prevent new tasks from being submitted
taskExecutor.shutdown();

// Wait for threads to complete
try {
  taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
  // Handle any interruptions
}

This method blocks until the threads have completed or the timeout has been reached. You can also specify a finite timeout if you want the application to continue after a specific amount of time, even if some tasks have not finished.

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