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authorTorvald Riegel <triegel@redhat.com>2013-10-11 18:58:04 +0300
committerTorvald Riegel <triegel@redhat.com>2014-10-20 18:22:30 +0200
commit63668b7084ac26865136e59fdf17781f9f49bd99 (patch)
tree25f39623e3ce1562a1330e2119ae5a3173cd2d7e /nptl
parent42b7f5d48549b85386a9b28a1a90e66fd81ba273 (diff)
downloadglibc-63668b7084ac26865136e59fdf17781f9f49bd99.tar.gz
pthread_once: Clean up constants.
[BZ #15215] This just gives a name to the integer constants being used.
Diffstat (limited to 'nptl')
-rw-r--r--nptl/pthreadP.h6
-rw-r--r--nptl/pthread_once.c21
2 files changed, 18 insertions, 9 deletions
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index d4415ba933..3aa24c283b 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -161,6 +161,12 @@ enum
#define FUTEX_TID_MASK 0x3fffffff
+/* pthread_once definitions. See __pthread_once for how these are used. */
+#define __PTHREAD_ONCE_INPROGRESS 1
+#define __PTHREAD_ONCE_DONE 2
+#define __PTHREAD_ONCE_FORK_GEN_INCR 4
+
+
/* Internal variables. */
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);