Question

I am reading the 7th chapter of Java Concurrency in Practice.

In a section which speaks about methods that do not have a cancellation policy of its own but calls methods that can be interruped, the book has the following thing to say.

Activities that do not support cancellation but still call interruptible
blocking methods will have to call them in a loop, retrying when
interruption is detected.In this case, they should save the
interruption status locally and restore it just before returning,
rather than immediately upon catching InterruptedException.

I haven’t understood this fully.

Does it mean, if I call Thread.sleep in my method, I will have to call it in a loop or something?

Can anyone explain why it should be done so?

Answer 1

I call Thread.sleep in my method, I will have to call it in a loop or something ?

Thread.sleep() will throw an InterruptedException when the current thread is interrupted (by another thread). It’s your choice how to react to that. If you want to sleep, regardless of if someone is trying to interrupt you, then yes, you have to build some kind of loop around the try-catch block. Probably you should use a clock (e.g. System.nanoTime()) to check how long you had slept before the exception was thrown, and then continue sleeping for the remaining time etc.

Note that InterruptedException is thrown only if another thread has interrupted the current thread, by calling (current)Thread.interrupt(). It doesn’t happen by itself, so in general you don’t need to build any loops around sleeps or anything like that. Usually threads are interrupted only for a good reason (e.g. application shutting down), so you probably want to support cancellation / interruption unless there’s no special reason not to. A “special reason” could be, for instance, writing to an I/O device and trying to guarantee that all data will be written, regardless of cancellation attempts.