Add _monotonic_np versions of timed wait functions
As a follow up to Ibba98f5d88be1c306d14e9b9366302ecbef6d534, where we
added a work around to convert the CLOCK_REALTIME timeouts to
CLOCK_MONOTONIC for pthread and semaphore timed wait functions, we're
introducing a set of _monotonic_np versions of each of these functions
that wait on CLOCK_MONOTONIC directly.
The primary motivation here is that while the above work around helps
for 3rd party code, it creates a dilemma when implementing new code
that would use these functions: either one implements code with these
functions knowing there is a race condition possible or one avoids
these functions and reinvent their own waiting/signaling mechanisms.
Neither are satisfactory, so we create a third option to use these
Android specific _monotonic_np functions that completely remove the
race condition while keeping the rest of the interface.
Specifically this adds the below functions:
pthread_mutex_timedlock_monotonic_np()
pthread_cond_timedwait_monotonic_np()
pthread_rwlock_timedrdlock_monotonic_np()
pthread_rwlock_timedwrlock_monotonic_np()
sem_timedwait_monotonic_np()
Note that pthread_cond_timedwait_monotonic_np() previously existed and
was removed since it's possible to initialize a condition variable to
use CLOCK_MONOTONIC. It is added back for a mix of reasons,
1) Symmetry with the rest of the functions we're adding
2) libc++ cannot easily take advantage of the new initializer, but
will be able to use this function in order to wait on
std::steady_clock
3) Frankly, it's a better API to specify the clock in the waiter function
than to specify the clock when the condition variable is
initialized.
Bug: 73951740
Test: new unit tests
Change-Id: I23aa5c204e36a194237d41e064c5c8ccaa4204e3
diff --git a/libc/bionic/pthread_cond.cpp b/libc/bionic/pthread_cond.cpp
index cbe67f9..a42506a 100644
--- a/libc/bionic/pthread_cond.cpp
+++ b/libc/bionic/pthread_cond.cpp
@@ -209,19 +209,18 @@
return __pthread_cond_timedwait(cond, mutex, cond->use_realtime_clock(), abstime);
}
+extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond_interface,
+ pthread_mutex_t* mutex,
+ const timespec* abs_timeout) {
+ return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, false, abs_timeout);
+}
+
#if !defined(__LP64__)
// TODO: this exists only for backward binary compatibility on 32 bit platforms.
extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond_interface,
pthread_mutex_t* mutex,
const timespec* abs_timeout) {
-
- return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, false, abs_timeout);
-}
-
-extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond_interface,
- pthread_mutex_t* mutex,
- const timespec* abs_timeout) {
- return pthread_cond_timedwait_monotonic(cond_interface, mutex, abs_timeout);
+ return pthread_cond_timedwait_monotonic_np(cond_interface, mutex, abs_timeout);
}
// Force this function using CLOCK_MONOTONIC because it was always using