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From: Sunil Pandey <skpgkp2@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.33/master] Move assignment out of the CAS condition Date: Thu, 29 Sep 2022 00:48:09 +0000 (GMT) [thread overview] Message-ID: <20220929004809.433423858437@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=60b8295333a076ff853c1093c502c7bf5197ab2e commit 60b8295333a076ff853c1093c502c7bf5197ab2e Author: H.J. Lu <hjl.tools@gmail.com> Date: Fri Nov 12 11:47:42 2021 -0800 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. (cherry picked from commit 120ac6d238825452e8024e2f627da33b2508dfd3) Diff: --- nptl/pthread_mutex_lock.c | 7 +++---- nptl/pthread_mutex_timedlock.c | 7 +++---- 2 files changed, 6 insertions(+), 8 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index ac8a472c08..2895926953 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -296,10 +296,9 @@ __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 541ec18938..22174f74c9 100644 --- a/nptl/pthread_mutex_timedlock.c +++ b/nptl/pthread_mutex_timedlock.c @@ -247,10 +247,9 @@ __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;
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