How to Ensure the Termination of Tasks When Shutting Down a Java ExecutorService?

ExecutorService Shutdown Termination Strategy

Question:

How do you ensure the termination of running tasks when shutting down a Java ExecutorService?

Answer:

The Oracle API documentation for ExecutorService recommends the following approach:

<code class="java">void shutdownAndAwaitTermination(ExecutorService pool) {
   pool.shutdown(); // Disable new tasks
   try {
     // Wait for existing tasks
     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
       pool.shutdownNow(); // Cancel executing tasks
       if (!pool.awaitTermination(60, TimeUnit.SECONDS))
           System.err.println("Pool did not terminate");
     }
   } catch (InterruptedException ie) {
     pool.shutdownNow();
     Thread.currentThread().interrupt();
   }
}</code>

Shutdown Related Methods:

• shutdown: Initiates orderly shutdown, executing previously submitted tasks and rejecting new tasks.
• shutdownNow: Attempts to stop all running tasks and return a list of tasks awaiting execution.
• awaitTermination: Blocks until all tasks complete or until a timeout or interruption occurs.

Enhanced Termination Waiting:

If the pool takes more time to shut down, you can change:

<code class="java">if (!pool.awaitTermination(60, TimeUnit.SECONDS))</code>

to:

<code class="java">while (!pool.awaitTermination(60, TimeUnit.SECONDS))</code>

This will continue waiting indefinitely until termination is achieved.

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