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Re: [RFC 2/2] Add steady_clock support to condition_variable


On 06/07/15 13:55 +0100, Mike Crowe wrote:
If __gthread_cond_timedwaitonclock is available it can be used it to fix
part of https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41861 by supporting
std::chrono::steady_clock properly with std::condition_variable.

This means that code using std::condition_variable::wait_for or
std::condition_variable::wait_until with std::chrono::steady_clock is no
longer subject to timing out early or potentially waiting for much
longer if the system clock is changed at an inopportune moment.

If __gthread_cond_timedwaitonclock is available then
std::chrono::steady_clock is deemed to be the "best" clock available
which means that it is used for the relative wait_for calls and absolute
wait_until calls that aren't choosing to use std::chrono::system_clock.
Calls explicitly using std::chrono::system_clock continue to use
CLOCK_REALTIME.

If __gthread_cond_timedwaitonclock is not available then
std::chrono::system_clock is deemed to be the "best" clock available
which means that the previous suboptimal behaviour remains.

From a quick glance this looks like a good change. As I said in my
other mail about the gthr-posix.h changes, it might be better to keep
this change to libstdc++ rather than splitting it across libstdc++ and
libgcc's gthr-posix.h

Do you have a copyright assignment in place for GCC contributions?



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