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| author | Mike Crowe <mac@mcrowe.com> | 2019-12-02 16:23:10 +0000 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2019-12-02 16:23:10 +0000 |
| commit | ab40695a46c6649bac40f4251e37993d73fa7a13 (patch) | |
| tree | 1bdab64d9d7ca9afe4f3b1d7c4affbcb4be178f3 /libstdc++-v3/config.h.in | |
| parent | a7334019b11798a9e791edef62a690b521e78a5b (diff) | |
| download | gcc-ab40695a46c6649bac40f4251e37993d73fa7a13.zip gcc-ab40695a46c6649bac40f4251e37993d73fa7a13.tar.gz gcc-ab40695a46c6649bac40f4251e37993d73fa7a13.tar.bz2 | |
libstdc++: Add full steady_clock support to shared_timed_mutex
The pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock functions
were added to glibc in v2.30. They have also been added to Android
Bionic. If these functions are available in the C library then they can
be used to implement shared_timed_mutex::try_lock_until,
shared_timed_mutex::try_lock_for,
shared_timed_mutex::try_lock_shared_until and
shared_timed_mutex::try_lock_shared_for so that they are no longer
unaffected by the system clock being warped. (This is the shared_mutex
equivalent of PR libstdc++/78237 for mutex.)
If the new functions are available then steady_clock is deemed to be the
"best" clock available which means that it is used for the relative
try_lock_for calls and absolute try_lock_until calls using steady_clock
and user-defined clocks. It's not possible to have
_GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK defined without
_GLIBCXX_USE_PTHREAD_RWLOCK_T, so the requirement that the clock be the
same as condition_variable is maintained. Calls explicitly using
system_clock (aka high_resolution_clock) continue to use CLOCK_REALTIME
via the old pthread_rwlock_timedrdlock and pthread_rwlock_timedwrlock
functions.
If the new functions are not available then system_clock is deemed to be
the "best" clock available which means that the previous suboptimal
behaviour remains.
Additionally, the user-defined clock used with
shared_timed_mutex::try_lock_for and shared_mutex::try_lock_shared_for
may have higher precision than __clock_t. We may need to round the
duration up to ensure that the timeout is long enough. (See
__timed_mutex_impl::_M_try_lock_for)
2019-12-02 Mike Crowe <mac@mcrowe.com>
Add full steady_clock support to shared_timed_mutex
* acinclude.m4 (GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK): Define
to check for the presence of both pthread_rwlock_clockrdlock and
pthread_rwlock_clockwrlock.
* config.h.in: Regenerate.
* configure.ac: Call GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK.
* configure: Regenerate.
* include/std/shared_mutex (shared_timed_mutex): Define __clock_t as
the best clock to use for relative waits.
(shared_timed_mutex::try_lock_for) Round up wait duration if necessary.
(shared_timed_mutex::try_lock_shared_for): Likewise.
(shared_timed_mutex::try_lock_until): Use existing try_lock_until
implementation for system_clock (which matches __clock_t when
_GLIBCCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK is not defined). Add new
overload for steady_clock that uses pthread_rwlock_clockwrlock if it
is available. Simplify overload for non-standard clock to just call
try_lock_for with a relative timeout.
(shared_timed_mutex::try_lock_shared_until): Likewise.
From-SVN: r278903
Diffstat (limited to 'libstdc++-v3/config.h.in')
| -rw-r--r-- | libstdc++-v3/config.h.in | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in index 3d51534..8940e0c 100644 --- a/libstdc++-v3/config.h.in +++ b/libstdc++-v3/config.h.in @@ -1005,6 +1005,10 @@ /* Define if pthread_mutex_clocklock is available in <pthread.h>. */ #undef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK +/* Define if pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock are + available in <pthread.h>. */ +#undef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK + /* Define if POSIX read/write locks are available in <gthr.h>. */ #undef _GLIBCXX_USE_PTHREAD_RWLOCK_T |