In Mutex.aquire why do we need to throw InterruptedException

[puzzlecracker]

It is a copy and paste from Doug Lea's Mutex implementation. I dont
understand the point of this line:
if (Thread.interrupted()) throw new InterruptedException();


public void acquire() throws InterruptedException {
if (Thread.interrupted()) throw new InterruptedException();
synchronized(this) {
try {
while (inuse_) wait();
inuse_ = true;
}
catch (InterruptedException ex) {
notify();
throw ex;
}
}
}


Thx

 

[Arne Vajhøj]

It is a copy and paste from Doug Lea's Mutex implementation. I dont
understand the point of this line:
if (Thread.interrupted()) throw new InterruptedException();

If interrupt has been called on the thread, then you do not
want to start waiting !?!?

Arne

 

[Arne Vajhøj]

Is that simply a performance optimization? If not, it looks like
there's a race condition, because the thread can get interrupted
after that 'if'-statement completes but before entering the
'synchronized' block.

Or to put it a different way, if the thread is interrupted, this
code doesn't seem to guarantee that you won't start waiting.

Correct.

But 99% early detect interrupt and 1% have wait throw
InterruptedException can still be considered an advantage.

I would assume Dough Lea to know what he is doing.

Arne

 

[Szabolcs Ferenczi]

Is that simply a performance optimization?  If not, it looks like
there's a race condition, because the thread can get interrupted
after that 'if'-statement completes but before entering the
'synchronized' block.

Or to put it a different way, if the thread is interrupted, this
code doesn't seem to guarantee that you won't start waiting.

I agree with you that it is an optimisation. However, since it is only
an optimisation, a race condition does not harm.

On the other hand, the check (Thread.interrupted()) is always added to
the call so it is also optimised for the interrupt rather than for the
normal case.

Best Regards,
Szabolcs