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/semaphore.cpp b/libc/bionic/semaphore.cpp
index 610a1b2..d401b66 100644
--- a/libc/bionic/semaphore.cpp
+++ b/libc/bionic/semaphore.cpp
@@ -231,7 +231,7 @@
}
}
-int sem_timedwait(sem_t* sem, const timespec* abs_timeout) {
+static int __sem_timedwait(sem_t* sem, const timespec* abs_timeout, bool use_realtime_clock) {
atomic_uint* sem_count_ptr = SEM_TO_ATOMIC_POINTER(sem);
// POSIX says we need to try to decrement the semaphore
@@ -257,7 +257,8 @@
}
// Contention detected. Wait for a wakeup event.
- int result = __futex_wait_ex(sem_count_ptr, shared, shared | SEMCOUNT_MINUS_ONE, true, abs_timeout);
+ int result = __futex_wait_ex(sem_count_ptr, shared, shared | SEMCOUNT_MINUS_ONE,
+ use_realtime_clock, abs_timeout);
// Return in case of timeout or interrupt.
if (result == -ETIMEDOUT || result == -EINTR) {
@@ -267,6 +268,14 @@
}
}
+int sem_timedwait(sem_t* sem, const timespec* abs_timeout) {
+ return __sem_timedwait(sem, abs_timeout, true);
+}
+
+int sem_timedwait_monotonic_np(sem_t* sem, const timespec* abs_timeout) {
+ return __sem_timedwait(sem, abs_timeout, false);
+}
+
int sem_post(sem_t* sem) {
atomic_uint* sem_count_ptr = SEM_TO_ATOMIC_POINTER(sem);
unsigned int shared = SEM_GET_SHARED(sem_count_ptr);