about summary refs log tree commit diff
diff options
context:
space:
mode:
authorH.J. Lu <hjl.tools@gmail.com>2021-11-12 11:47:42 -0800
committerH.J. Lu <hjl.tools@gmail.com>2021-11-15 05:50:56 -0800
commit120ac6d238825452e8024e2f627da33b2508dfd3 (patch)
tree4215cb357a961543c55aa8bbe5ef754d212be1e8
parentcbcd65c8b526555d9b98628338973f91f74002ad (diff)
downloadglibc-120ac6d238825452e8024e2f627da33b2508dfd3.tar.gz
glibc-120ac6d238825452e8024e2f627da33b2508dfd3.tar.xz
glibc-120ac6d238825452e8024e2f627da33b2508dfd3.zip
Move assignment out of the CAS condition
Update

commit 49302b8fdf9103b6fc0a398678668a22fa19574c
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:54:01 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

and

commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:31:51 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

by moving assignment out of the CAS condition.
-rw-r--r--nptl/pthread_mutex_lock.c7
-rw-r--r--nptl/pthread_mutex_timedlock.c7
2 files changed, 6 insertions, 8 deletions
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 762059b230..47b88a6b5b 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -304,10 +304,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index f763cfc7fa..791a2b54b1 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -233,10 +233,9 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;