Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 3 Aug 2016 13:27:52 +0200
From: Szabolcs Nagy <>
Subject: Re: std::condition_variable::wait_for() breakage when
 system_clock changes C++11 MIPS

* Ward Willats <> [2016-08-02 16:33:29 -0700]:
> We are running a C++ 11 app on a MIPS-based Linux/OpenWRT platform and linking against MUSCL 1.1.12 and libstdc++ v3. On cold boot, our system clock is often some random time in the future until ntpd or other software corrects it. This led to odd behavior and this experiment:
> If I use the busybox "date --set" to move our system's clock 24 hours into the future, and then call:
> std::condition_variable::wait_for() with the pre-canned std::chrono::duration, std::chrono::milliseconds( 120000 ), as a 2 minute wait timeout AND then...
> ...set the clock BACK 24 hours to the correct/current time with ntpd, wait_for() doesn't return after 2 minutes (assuming no notify() of course). (Presumably, wait_for() is using system_clock, and not steady_clock, and will fire in 24 hours + 2 minutes -- but I haven't waited to find out.)
> However, if I repeat this experiment and call std::condition_variable::wait_until() with a timeout time_point calculated as std::chrono::steady_clock::now() + std::chrono::milliseconds( 120000 ), which neatly binds a steady_clock ref into the time_point, it does indeed fire in 2 minutes after the clock is set back, as expected.
> In short, the std::condition_variable API that takes a std::chrono:duration does not work, but the one that takes a std::chrono::time_point does.

this is a libstdc++ issue so the gcc version matters.
(i can see condvar related issues fixed in gcc bugzilla)

there are several issues with the c++11 condvar timeout api e.g.
so i'd avoid using c++, it's just a broken abstraction layer
on top of the pthreads api with poor specification.. meanwhile
pthreads works fine and is portable.

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.