diff options
Diffstat (limited to 'REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-trylock.c')
| -rw-r--r-- | REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-trylock.c | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-trylock.c b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-trylock.c new file mode 100644 index 0000000000..aa09073324 --- /dev/null +++ b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-trylock.c @@ -0,0 +1,97 @@ +/* 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); +} |