diff options
Diffstat (limited to 'mysys/my_winthread.c')
| -rw-r--r-- | mysys/my_winthread.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/mysys/my_winthread.c b/mysys/my_winthread.c index aecb2f7cc78..49534370a2f 100644 --- a/mysys/my_winthread.c +++ b/mysys/my_winthread.c @@ -155,8 +155,19 @@ int pthread_cancel(pthread_t thread) int my_pthread_once(my_pthread_once_t *once_control, void (*init_routine)(void)) { - LONG state= InterlockedCompareExchange(once_control, MY_PTHREAD_ONCE_INPROGRESS, - MY_PTHREAD_ONCE_INIT); + LONG state; + + /* + Do "dirty" read to find out if initialization is already done, to + save an interlocked operation in common case. Memory barriers are ensured by + Visual C++ volatile implementation. + */ + if (*once_control == MY_PTHREAD_ONCE_DONE) + return 0; + + state= InterlockedCompareExchange(once_control, MY_PTHREAD_ONCE_INPROGRESS, + MY_PTHREAD_ONCE_INIT); + switch(state) { case MY_PTHREAD_ONCE_INIT: |