When does Java's Thread.sleep throw InterruptedException?

You should generally NOT ignore the exception. Take a look at the following paper:

Don't swallow interrupts

Sometimes throwing InterruptedException is not an option, such as when a task defined by Runnable calls an interruptible method. In this case, you can't rethrow InterruptedException, but you also do not want to do nothing. When a blocking method detects interruption and throws InterruptedException, it clears the interrupted status. If you catch InterruptedException but cannot rethrow it, you should preserve evidence that the interruption occurred so that code higher up on the call stack can learn of the interruption and respond to it if it wants to. This task is accomplished by calling interrupt() to "reinterrupt" the current thread, as shown in Listing 3. At the very least, whenever you catch InterruptedException and don't rethrow it, reinterrupt the current thread before returning.

public class TaskRunner implements Runnable {
    private BlockingQueue<Task> queue;
 
    public TaskRunner(BlockingQueue<Task> queue) { 
        this.queue = queue; 
    }
 
    public void run() { 
        try {
             while (true) {
                 Task task = queue.take(10, TimeUnit.SECONDS);
                 task.execute();
             }
         }
         catch (InterruptedException e) { 
             // Restore the interrupted status
             Thread.currentThread().interrupt();
         }
    }
}

• From Don't swallow interrupts

See the entire paper here:

http://www.ibm.com/developerworks/java/library/j-jtp05236/index.html?ca=drs-

The Java Specialists newsletter (which I can unreservedly recommend) had an interesting article on this, and how to handle the InterruptedException. It's well worth reading and digesting.

A solid and easy way to handle it in single threaded code would be to catch it and retrow it in a RuntimeException, to avoid the need to declare it for every method.

From the docs:

An InterruptedException is thrown when a thread is waiting, sleeping, or otherwise occupied, and the thread is interrupted, either before or during the activity.

In other words, InterruptedException occurs when some code has called the interrupt() method on a specific thread. It's a checked exception, and many blocking operations in Java can throw it.

The purpose of the interrupt system is to provide a alternative workflow for allowing threads to interrupt tasks in other threads. An interruption necessarily may not interrupt a running thread but it can also request that the thread interrupt itself at the next convenient opportunity.

Threads may get blocked for several reasons:

• waiting to wake up from a Thread.sleep()
• waiting to acquire a lock, waiting for I/O completion
• waiting for the result of a computation in another thread, etc.

The InterruptedException is usually thrown by all blocking methods so that it can be handled and the corrective action can be performed.

However, in majority of the cases as our code is a part of a Runnable, in this situation, we must catch it and restore the status.

There are a handfull of methods in Java that throws InterruptedException. Some examples are:

• Object class:

  • Thread.sleep()
  • Thread.join()
  • wait()

• BlockingQueue:

  • put()
  • take()

From personal experience, I simply changed thread.sleep() into this.sleep()