Thread.interrupt() and blocking operations

[Christopher Benson-Manica]

In general, if a thread's interrupt status has been set, will a call
to a blocking method produce the same behavior as would occur if the
thread were interrupted during the blocking call? The JavaDocs seem
to indicate that this is not true - for example, wait() is documented
to throw an InterruptedException if the thread is interrupted before
or during the call, but Thread.sleep()'s documentation is silent on
what, if anything, occurs if the thread has been interrupted prior to
the call to sleep(). The same also seems to be true of the select()
methods of Selector. Assuming that select() does, in fact, block even
if the current thread's interrupt status is set, is there any
alternative to simply checking Thread.interrupted() prior to calling
select() and taking appropriate action (i.e., throwing an
InterruptedException manually)?

 

[Knute Johnson]

In general, if a thread's interrupt status has been set, will a call
to a blocking method produce the same behavior as would occur if the
thread were interrupted during the blocking call? The JavaDocs seem
to indicate that this is not true - for example, wait() is documented
to throw an InterruptedException if the thread is interrupted before
or during the call, but Thread.sleep()'s documentation is silent on
what, if anything, occurs if the thread has been interrupted prior to
the call to sleep().

Thread.sleep() with throw an InterruptedException if the interrupt
method has been called prior or during a sleep.

The same also seems to be true of the select()

methods of Selector. Assuming that select() does, in fact, block even
if the current thread's interrupt status is set, is there any
alternative to simply checking Thread.interrupted() prior to calling
select() and taking appropriate action (i.e., throwing an
InterruptedException manually)?

I don't know about Selectors as I have not used them but here is what
the docs say about Selectors:

"If this thread is blocked in a Selector then the thread's interrupt
status will be set and it will return immediately from the selection
operation, possibly with a non-zero value, just as if the selector's
wakeup method were invoked."

Thread.sleep(), Thread.join() and Object.wait() will all throw
InterruptedExceptions if their threads are interrupted.

In all other cases the interrupt status of the thread is set so that you
can detect it with Thread.isInterrupted() or Thread.interrupted(). Note
the difference between the two, interrupted() clears the interrupt
status while isInterrupted() doesn't.

 

[Christopher Benson-Manica]

"If this thread is blocked in a Selector then the thread's interrupt
status will be set and it will return immediately from the selection
operation, possibly with a non-zero value, just as if the selector's
wakeup method were invoked."

Yes, I've read that, but it only incompletely answers my question.

Thread.sleep(), Thread.join() and Object.wait() will all throw
InterruptedExceptions if their threads are interrupted.

I know about Object.wait(), because the docs say so. Can you point me
to a a reference (possibly in the documentation) that says the same
thing about Thread.sleep()? Also of immediate interest to me is how
blocking operations on Channels respond when the current thread has
already been interrrupted; sadly, again I have no evidence from the
documentation that they handle the situation intelligently.

In all other cases the interrupt status of the thread is set so that you
can detect it with Thread.isInterrupted() or Thread.interrupted(). Note
the difference between the two, interrupted() clears the interrupt
status while isInterrupted() doesn't.

Yes, that's what I'm doing, but it seems silly to have to do so in
light of the fact that Object.wait() is smart enough to handle the
situation.

 

[Knute Johnson]

Yes, I've read that, but it only incompletely answers my question.

I've really not played with Selectors so I can't help you with those.

I know about Object.wait(), because the docs say so. Can you point me
to a a reference (possibly in the documentation) that says the same
thing about Thread.sleep()? Also of immediate interest to me is how
blocking operations on Channels respond when the current thread has
already been interrrupted; sadly, again I have no evidence from the
documentation that they handle the situation intelligently.

Look at Thread.interrupt(). The last line is really the most important
one "If none of the previous conditions hold then this thread's
interrupt status will be set." If it is not blocked on sleep(), wait()
or join() it will set the interrupt status. When it encounters a
sleep(), wait() or join() it will then throw an InterruptedException.

Yes, that's what I'm doing, but it seems silly to have to do so in
light of the fact that Object.wait() is smart enough to handle the
situation.

If you need to detect it before it reaches one of the interruptible
methods you will have to test for it. I don't see where this is silly.
You call interrupt, it sets a flag, you test for it, I don't know how
else you would do it.