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/include/pthread.h b/libc/include/pthread.h
index 8d95a3b..5b0c3a2 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -122,6 +122,16 @@
int pthread_cond_init(pthread_cond_t* __cond, const pthread_condattr_t* __attr);
int pthread_cond_signal(pthread_cond_t* __cond);
int pthread_cond_timedwait(pthread_cond_t* __cond, pthread_mutex_t* __mutex, const struct timespec* __timeout);
+/*
+ * Condition variables use CLOCK_REALTIME by default for their timeouts, however that is
+ * typically inappropriate, since that clock can change dramatically, causing the timeout to
+ * either expire earlier or much later than intended.
+ * Condition variables have an initialization option to use CLOCK_MONOTONIC, and in addition,
+ * Android provides this API to use CLOCK_MONOTONIC on a condition variable for this single wait
+ * no matter how it was initialized.
+ */
+int pthread_cond_timedwait_monotonic_np(pthread_cond_t* __cond, pthread_mutex_t* __mutex,
+ const struct timespec* __timeout) __INTRODUCED_IN_64(28);
int pthread_cond_wait(pthread_cond_t* __cond, pthread_mutex_t* __mutex);
int pthread_create(pthread_t* __pthread_ptr, pthread_attr_t const* __attr, void* (*__start_routine)(void*), void*);
@@ -159,6 +169,16 @@
int pthread_mutex_lock(pthread_mutex_t* __mutex);
int pthread_mutex_timedlock(pthread_mutex_t* __mutex, const struct timespec* __timeout)
__INTRODUCED_IN(21);
+
+/*
+ * POSIX only supports using pthread_mutex_timedlock() with CLOCK_REALTIME, however that is
+ * typically inappropriate, since that clock can change dramatically, causing the timeout to
+ * either expire earlier or much later than intended.
+ * This function is added to use a timespec based on CLOCK_MONOTONIC that does not suffer
+ * from this issue.
+ */
+int pthread_mutex_timedlock_monotonic_np(pthread_mutex_t* __mutex, const struct timespec* __timeout)
+ __INTRODUCED_IN(28);
int pthread_mutex_trylock(pthread_mutex_t* __mutex);
int pthread_mutex_unlock(pthread_mutex_t* __mutex);
@@ -176,7 +196,6 @@
*/
int pthread_mutex_lock_timeout_np(pthread_mutex_t* __mutex, unsigned __timeout_ms);
int pthread_cond_timeout_np(pthread_cond_t* __cond, pthread_mutex_t* __mutex, unsigned __timeout_ms);
-int pthread_cond_timedwait_monotonic_np(pthread_cond_t* __cond, pthread_mutex_t* __mutex, const struct timespec* __timeout);
int pthread_cond_timedwait_relative_np(pthread_cond_t* __cond, pthread_mutex_t* __mutex, const struct timespec* __relative_timeout);
#endif
@@ -194,7 +213,13 @@
int pthread_rwlock_init(pthread_rwlock_t* __rwlock, const pthread_rwlockattr_t* __attr);
int pthread_rwlock_rdlock(pthread_rwlock_t* __rwlock);
int pthread_rwlock_timedrdlock(pthread_rwlock_t* __rwlock, const struct timespec* __timeout);
+/* See the comment on pthread_mutex_timedlock_monotonic_np for usage of this function. */
+int pthread_rwlock_timedrdlock_monotonic_np(pthread_rwlock_t* __rwlock,
+ const struct timespec* __timeout) __INTRODUCED_IN(28);
int pthread_rwlock_timedwrlock(pthread_rwlock_t* __rwlock, const struct timespec* __timeout);
+/* See the comment on pthread_mutex_timedlock_monotonic_np for usage of this function. */
+int pthread_rwlock_timedwrlock_monotonic_np(pthread_rwlock_t* __rwlock,
+ const struct timespec* __timeout) __INTRODUCED_IN(28);
int pthread_rwlock_tryrdlock(pthread_rwlock_t* __rwlock);
int pthread_rwlock_trywrlock(pthread_rwlock_t* __rwlock);
int pthread_rwlock_unlock(pthread_rwlock_t* __rwlock);
diff --git a/libc/include/semaphore.h b/libc/include/semaphore.h
index 7e3dc1c..01d685b 100644
--- a/libc/include/semaphore.h
+++ b/libc/include/semaphore.h
@@ -49,6 +49,13 @@
int sem_init(sem_t* __sem, int __shared, unsigned int __value);
int sem_post(sem_t* __sem);
int sem_timedwait(sem_t* __sem, const struct timespec* __ts);
+/*
+ * POSIX only supports using sem_timedwait() with CLOCK_REALTIME, however that is typically
+ * inappropriate, since that clock can change dramatically, causing the timeout to either
+ * expire earlier or much later than intended. This function is added to use a timespec based
+ * on CLOCK_MONOTONIC that does not suffer from this issue.
+ */
+int sem_timedwait_monotonic_np(sem_t* __sem, const struct timespec* __ts) __INTRODUCED_IN(28);
int sem_trywait(sem_t* __sem);
int sem_wait(sem_t* __sem);