diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/s390/elision-trylock.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/s390/elision-trylock.c | 97 |
1 files changed, 0 insertions, 97 deletions
diff --git a/sysdeps/unix/sysv/linux/s390/elision-trylock.c b/sysdeps/unix/sysv/linux/s390/elision-trylock.c deleted file mode 100644 index aa09073324..0000000000 --- a/sysdeps/unix/sysv/linux/s390/elision-trylock.c +++ /dev/null @@ -1,97 +0,0 @@ -/* Elided pthread mutex trylock. - Copyright (C) 2014-2017 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - <http://www.gnu.org/licenses/>. */ - -#include <pthread.h> -#include <pthreadP.h> -#include <lowlevellock.h> -#include <htm.h> -#include <elision-conf.h> - -#define aconf __elision_aconf - -/* Try to elide a futex trylock. FUTEX is the futex variable. ADAPT_COUNT is - the adaptation counter in the mutex. */ - -int -__lll_trylock_elision (int *futex, short *adapt_count) -{ - /* Implement POSIX semantics by forbiding nesting elided trylocks. - Sorry. After the abort the code is re-executed - non transactional and if the lock was already locked - return an error. */ - if (__libc_tx_nesting_depth () > 0) - { - /* Note that this abort may terminate an outermost transaction that - was created outside glibc. - This persistently aborts the current transactions to force - them to use the default lock instead of retrying transactions - until their try_tbegin is zero. - */ - __libc_tabort (_HTM_FIRST_USER_ABORT_CODE | 1); - __builtin_unreachable (); - } - - /* adapt_count can be accessed concurrently; these accesses can be both - inside of transactions (if critical sections are nested and the outer - 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. */ - if (atomic_load_relaxed (adapt_count) <= 0 && aconf.try_tbegin > 0) - { - int status = __libc_tbegin ((void *) 0); - 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 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. - 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 - 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) - atomic_store_relaxed (adapt_count, aconf.skip_lock_busy); - } - else if (status != _HTM_TBEGIN_TRANSIENT) - { - /* A persistent abort (cc 1 or 3) indicates that a retry is - probably futile. Use the normal locking now and for the - next couple of calls. - Be careful to avoid writing to the lock. */ - if (aconf.skip_trylock_internal_abort > 0) - *adapt_count = aconf.skip_trylock_internal_abort; - } - /* Could do some retries here. */ - } - - /* Use normal locking as fallback path if the transaction does not - succeed. */ - return lll_trylock (*futex); -} |