diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/s390/elision-trylock.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/s390/elision-trylock.c | 31 |
1 files changed, 15 insertions, 16 deletions
diff --git a/sysdeps/unix/sysv/linux/s390/elision-trylock.c b/sysdeps/unix/sysv/linux/s390/elision-trylock.c index 3c1d00953b..aa09073324 100644 --- a/sysdeps/unix/sysv/linux/s390/elision-trylock.c +++ b/sysdeps/unix/sysv/linux/s390/elision-trylock.c @@ -51,31 +51,29 @@ __lll_trylock_elision (int *futex, short *adapt_count) critical section uses lock elision) and outside of transactions. Thus, we need to use atomic accesses to avoid data races. However, the value of adapt_count is just a hint, so relaxed MO accesses are - sufficient. - Do not begin a transaction if another cpu has locked the - futex with normal locking. If adapt_count is zero, it remains and the - next pthread_mutex_lock call will try to start a transaction again. */ - if (atomic_load_relaxed (futex) == 0 - && atomic_load_relaxed (adapt_count) <= 0 && aconf.try_tbegin > 0) + sufficient. */ + if (atomic_load_relaxed (adapt_count) <= 0 && aconf.try_tbegin > 0) { int status = __libc_tbegin ((void *) 0); - if (__builtin_expect (status == _HTM_TBEGIN_STARTED, - _HTM_TBEGIN_STARTED)) + if (__glibc_likely (status == _HTM_TBEGIN_STARTED)) { /* Check the futex to make sure nobody has touched it in the mean time. This forces the futex into the cache and makes - sure the transaction aborts if some other cpu uses the - lock (writes the futex). */ - if (__builtin_expect (atomic_load_relaxed (futex) == 0, 1)) + sure the transaction aborts if another thread acquires the lock + concurrently. */ + if (__glibc_likely (atomic_load_relaxed (futex) == 0)) /* Lock was free. Return to user code in a transaction. */ return 0; - /* Lock was busy. Fall back to normal locking. Since we are in - a non-nested transaction there is no need to abort, which is - expensive. Simply end the started transaction. */ + /* Lock was busy. Fall back to normal locking. + This can be the case if e.g. adapt_count was decremented to zero + by a former release and another thread has been waken up and + acquired it. + Since we are in a non-nested transaction there is no need to abort, + which is expensive. Simply end the started transaction. */ __libc_tend (); /* Note: Changing the adapt_count here might abort a transaction on a - different cpu, but that could happen anyway when the futex is + different CPU, but that could happen anyway when the futex is acquired, so there's no need to check the nesting depth here. See above for why relaxed MO is sufficient. */ if (aconf.skip_lock_busy > 0) @@ -93,6 +91,7 @@ __lll_trylock_elision (int *futex, short *adapt_count) /* Could do some retries here. */ } - /* Use normal locking as fallback path if transaction does not succeed. */ + /* Use normal locking as fallback path if the transaction does not + succeed. */ return lll_trylock (*futex); } |