Question

I am new to Java concurrecny and I am reading this at the moment: Java Tutorial-Interrupts But I can’t really understand where and why I should use an Interrupt. Can someone give me an example (code) so I better understand it? thx

Answer 1

Interrupts are used when you want to (cough) interrupt the thread — typically meaning stop it from operating. Thread.stop() has been deprecated because of various issues so Thread.interrupt() is the way that you tell the thread that it should cease running — it should cleanup what it is doing and quit. In reality, the programmer can use the interrupt signal on a thread in any way that they want.

Some examples:

• Your thread might be sleeping for a minute and then spidering a web-page. You want it to stop this behavior.
• Maybe you have a thread which is consuming from a queue of jobs and you want to tell it that no more jobs are coming its way.
• Maybe you have a number of background threads that you want to interrupt because the process is shutting down and you want to do so cleanly.

There are certainly many ways to accomplish the above signaling but interrupt can be used.

One of the more powerful ways that Thread.interrupt() affects a running thread is by throwing InterruptedException from a couple different methods including Thread.sleep(), Object.wait(), and others.

try {
   Thread.sleep(1000);
} catch (InterruptedException e) {
   // i've been interrupted
   // catching InterruptedException clears the interrupt status on the thread
   // so a good pattern is to re-interrupt the thread
   Thread.currentThread().interrupt();
   // but maybe we want to just kill the thread
   return;
}

Also, often in a thread we are looping doing some task and so we check for interrupt status:

while (!Thread.currentThread().isInterrupted()) {
    // keep doing our task until we are interrupted
}