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From: "lhyatt at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/54185] [4.7/4.8 Regression] condition_variable not
 properly destructed
Date: Thu, 13 Aug 2020 21:37:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D54185

Lewis Hyatt <lhyatt at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lhyatt at gmail dot com

--- Comment #14 from Lewis Hyatt <lhyatt at gmail dot com> ---
Created attachment 49061
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D49061&action=3Dedit
Fix for random pthread_create() failures

Hello-

I have problems with the test case for this bug
(libstdc++-v3/testsuite/30_threads/condition_variable/54185.cc) failing
randomly. It happens more often with parallel make, and especially if runni=
ng
the testsuite as a whole more than once in parallel. On my system at least
(x86-64, Ubuntu 18), it seems that pthread_create() will return EAGAIN
sometimes in any loop like the one this testcase uses:

for(int i =3D 0; i !=3D 1000; ++i) {pthread_create(...); pthread_join(...);}

If such a loop is running in 3 or more processes in parallel it happens more
than 50% of the time. I am not sure what global resource gets used up, it
happens even if ulimit -a shows nothing being limited like processes or mem=
ory.

The attached patch fixes the failures for me; if thread creation fails, it =
just
gives up and moves on to the next iteration instead. I had to convert the
cond->wait() to the predicate form since it becomes possible for the notify=
 to
take place prior to all threads calling wait.

I can submit this to gcc-patches if it makes sense to you? Thanks...

-Lewis=