diff options
Diffstat (limited to 'contrib/libc++/src/mutex.cpp')
| -rw-r--r-- | contrib/libc++/src/mutex.cpp | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/contrib/libc++/src/mutex.cpp b/contrib/libc++/src/mutex.cpp index e56271d..5f8ba0a 100644 --- a/contrib/libc++/src/mutex.cpp +++ b/contrib/libc++/src/mutex.cpp @@ -12,6 +12,7 @@ #include "limits" #include "system_error" #include "cassert" +#include "support/atomic_support.h" _LIBCPP_BEGIN_NAMESPACE_STD #ifndef _LIBCPP_HAS_NO_THREADS @@ -220,6 +221,9 @@ static pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER; static pthread_cond_t cv = PTHREAD_COND_INITIALIZER; #endif +/// NOTE: Changes to flag are done via relaxed atomic stores +/// even though the accesses are protected by a mutex because threads +/// just entering 'call_once` concurrently read from flag. void __call_once(volatile unsigned long& flag, void* arg, void(*func)(void*)) { @@ -252,11 +256,11 @@ __call_once(volatile unsigned long& flag, void* arg, void(*func)(void*)) try { #endif // _LIBCPP_NO_EXCEPTIONS - flag = 1; + __libcpp_relaxed_store(&flag, 1ul); pthread_mutex_unlock(&mut); func(arg); pthread_mutex_lock(&mut); - flag = ~0ul; + __libcpp_relaxed_store(&flag, ~0ul); pthread_mutex_unlock(&mut); pthread_cond_broadcast(&cv); #ifndef _LIBCPP_NO_EXCEPTIONS @@ -264,7 +268,7 @@ __call_once(volatile unsigned long& flag, void* arg, void(*func)(void*)) catch (...) { pthread_mutex_lock(&mut); - flag = 0ul; + __libcpp_relaxed_store(&flag, 0ul); pthread_mutex_unlock(&mut); pthread_cond_broadcast(&cv); throw; |
