From: Ben Hutchings (ben.hutchings_at_[hidden])
Date: 2005-03-21 16:29:32
Thorsten Froehlich wrote:
> Ben Hutchings wrote:
>
>> I'm not sure whether you mean that the thread has exited or that it
>> has also been joined.
>
> The thread ended normally as the thread's function returned. There does
> not appear to be any way to detect this in boost::thread.
Right.
>>> EINVAL, thus triggering the assertion res == 0. Is this intentional
>>> or a bug?
>>
>> Which part of this behaviour are you questioning?
>
> That when I try to join a thread that is no longer running, which cannot
> be reliably determined by the given thread class interface (well, it
> cannot at all in fact), then getting an assertion upon try to join that
> thread is a bug.
If the thread is supposed to be joinable, then of course this is a bug, yes.
>> The reasons why pthread_join may fail all represent bugs rather than
>> unpredictable errors, hence the assertion.
>
>
> Sorry, this is incorrect, see below.
I think you misunderstand me. I don't mean that a failure of
pthread_join necessarily indicates a bug in your program, but that it
indicates a bug at some level. The specification doesn't provide for
any error conditions like lack of resources.
> > Joining a thread makes the
>
>> thread object an empty shell which has no further use. Detaching a
>> thread also makes it non-joinable and makes the thread object almost
>> useless. If your program attempts to join a non-joinable thread,
>> that's the bug. Otherwise, it is conceivable that you have found a
>> bug in MacOS X or in Boost.Threads, but I'd be surprised.
>
>
> I am perfectly aware what happens in the code. My code is certainly
> correct and doing nothing invalid at all - the problem is with boost
> thread behavior or interface (well, lack of it) to prevent the
> assertion, which would only be possible by checking if a thread
> terminated already, and checking for this in a reliable manner. Boost
> threads does not provide that facility. Thus, an assertion is incorrect
> at that point in the boost thread join code.
If a thread is joinable then pthread_join must succeed whether it is
called before or after the thread exits. Similarly for
boost::thread::join. Since you apparently don't understand the
semantics of joining, perhaps you have in fact made an error. Why don't
you post an example that shows the behaviour you're reporting?
Ben.