diff options
Diffstat (limited to 'nptl/pthread_once.c')
| -rw-r--r-- | nptl/pthread_once.c | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c index 10c01d6023..595bd7e298 100644 --- a/nptl/pthread_once.c +++ b/nptl/pthread_once.c @@ -40,8 +40,11 @@ clear_once_control (void *arg) /* This is similar to a lock implementation, but we distinguish between three - states: not yet initialized (0), initialization finished (2), and - initialization in progress (__fork_generation | 1). If in the first state, + states: not yet initialized (0), initialization in progress + (__fork_generation | __PTHREAD_ONCE_INPROGRESS), and initialization + finished (__PTHREAD_ONCE_DONE); __fork_generation does not use the bits + that are used for __PTHREAD_ONCE_INPROGRESS and __PTHREAD_ONCE_DONE (which + is what __PTHREAD_ONCE_FORK_GEN_INCR is used for). If in the first state, threads will try to run the initialization by moving to the second state; the first thread to do so via a CAS on once_control runs init_routine, other threads block. @@ -66,14 +69,14 @@ __pthread_once (once_control, init_routine) int oldval, val, newval; /* We need acquire memory order for this load because if the value - signals that initialization has finished, we need to be see any + signals that initialization has finished, we need to see any data modifications done during initialization. */ val = *once_control; atomic_read_barrier(); do { /* Check if the initialization has already been done. */ - if (__glibc_likely ((val & 2) != 0)) + if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0)) return 0; oldval = val; @@ -82,7 +85,7 @@ __pthread_once (once_control, init_routine) generation because it's immutable in a particular process, and forked child processes start with a single thread that modified the generation. */ - newval = __fork_generation | 1; + newval = __fork_generation | __PTHREAD_ONCE_INPROGRESS; /* We need acquire memory order here for the same reason as for the load from once_control above. */ val = atomic_compare_and_exchange_val_acq (once_control, newval, @@ -91,11 +94,11 @@ __pthread_once (once_control, init_routine) while (__glibc_unlikely (val != oldval)); /* Check if another thread already runs the initializer. */ - if ((oldval & 1) != 0) + if ((oldval & __PTHREAD_ONCE_INPROGRESS) != 0) { /* Check whether the initializer execution was interrupted by a - fork. We know that for both values, bit 0 is set and bit 1 is - not. */ + fork. We know that for both values, __PTHREAD_ONCE_INPROGRESS + is set and __PTHREAD_ONCE_DONE is not. */ if (oldval == newval) { /* Same generation, some other thread was faster. Wait. */ @@ -118,7 +121,7 @@ __pthread_once (once_control, init_routine) release memory order here because we need to synchronize with other threads that want to use the initialized data. */ atomic_write_barrier(); - *once_control = 2; + *once_control = __PTHREAD_ONCE_DONE; /* Wake up all other threads. */ lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); |