Boost C++ Libraries: Ticket #9654: try_join_for(0) returns false when thread has exited

ernest.galbrun@… — Thu, 13 Feb 2014 08:59:03 GMT

Apparently it is caused by a previous bug fix: https://svn.boost.org/trac/boost/ticket/8323

Now try_join_for returns false immediatly if the current time is >= to the finish time.

It should, I think, check at least once if the thread has completed before returning false. I'm not sure how to do that, that's the point of calling try_join_for(0).

Is there a reason why there is no try_join() function ?

viboes — Thu, 13 Feb 2014 18:31:44 GMT

Replying to ernest.galbrun@…:

Apparently it is caused by a previous bug fix: https://svn.boost.org/trac/boost/ticket/8323

Now try_join_for returns false immediately if the current time is >= to the finish time.

Right.

It should, I think, check at least once if the thread has completed before returning false.

Well, this is not what the documentation says :(

I'm not sure how to do that, that's the point of calling try_join_for(0).

Have you tried try_join_for(nanoseconds(1))?

Is there a reason why there is no try_join() function ?

I don't know of a portable way to implement it.

Please see #9618 and if you are on Windows, please could you check if the proposed patch works for you.

ernest.galbrun@… — Fri, 14 Feb 2014 09:18:31 GMT

Hi viboes, thanks for your reply I had not seen the previous issue.

The patch works fine, thank you.

I think the documentation should be more explicit wether this is allowed or not, since this is the prefered way of checking if a thread has finished when searching on stackoverflow: http://stackoverflow.com/questions/1667420/how-can-i-tell-reliably-if-a-boost-thread-has-exited-its-run-method

Maybe we should change the SO answer, what is your stance about this issue ? What is the correct way of checking wether a thread has finished?

status changed; resolution set; milestone deleted

viboes — Sun, 16 Feb 2014 09:45:12 GMT

status new → closed
resolution → duplicate
milestone To Be Determined

Replying to ernest.galbrun@…:

Hi viboes, thanks for your reply I had not seen the previous issue.

The patch works fine, thank you.

I think the documentation should be more explicit wether this is allowed or not, since this is the prefered way of checking if a thread has finished when searching on stackoverflow: http://stackoverflow.com/questions/1667420/how-can-i-tell-reliably-if-a-boost-thread-has-exited-its-run-method

Maybe we should change the SO answer, what is your stance about this issue ? What is the correct way of checking whether a thread has finished?

The answer of MSalters is the correct one.

You fundamentally can't do this. The reason is that the two possible answers are "Yes" and "Not when I last looked but perhaps now". There is no reliable way to determine that a thread is still inside its run method, even if there was a reliable way to determine the opposite.

You can just join the thread if not already detached.

viboes — Sun, 16 Feb 2014 09:45:36 GMT

Duplicate #9618

attachment set

ernest.galbrun@… — Tue, 01 Jul 2014 14:29:36 GMT

attachment → 0001-changed-the-copy-from-rvalue-reference-to-copy-m_taa.patch

patch proposing fix