mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-04 19:00:09 +00:00
63 lines
2.8 KiB
C
63 lines
2.8 KiB
C
/* force-elision.h: Automatic enabling of elision for mutexes
|
|
Copyright (C) 2013-2020 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
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
/* Automatically enable elision for existing user lock kinds. */
|
|
#define FORCE_ELISION(m, s) \
|
|
if (__pthread_force_elision) \
|
|
{ \
|
|
/* See concurrency notes regarding __kind in \
|
|
struct __pthread_mutex_s in \
|
|
sysdeps/nptl/bits/thread-shared-types.h. \
|
|
\
|
|
There are the following cases for the kind of a mutex \
|
|
(The mask PTHREAD_MUTEX_ELISION_FLAGS_NP covers the flags \
|
|
PTHREAD_MUTEX_ELISION_NP and PTHREAD_MUTEX_NO_ELISION_NP where \
|
|
only one of both flags can be set): \
|
|
- both flags are not set: \
|
|
This is the first lock operation for this mutex. Enable \
|
|
elision as it is not enabled so far. \
|
|
Note: It can happen that multiple threads are calling e.g. \
|
|
pthread_mutex_lock at the same time as the first lock \
|
|
operation for this mutex. Then elision is enabled for this \
|
|
mutex by multiple threads. Storing with relaxed MO is enough \
|
|
as all threads will store the same new value for the kind of \
|
|
the mutex. But we have to ensure that we always use the \
|
|
elision path regardless if this thread has enabled elision or \
|
|
another one. \
|
|
\
|
|
- PTHREAD_MUTEX_ELISION_NP flag is set: \
|
|
Elision was already enabled for this mutex by a previous lock \
|
|
operation. See case above. Just use the elision path. \
|
|
\
|
|
- PTHREAD_MUTEX_NO_ELISION_NP flag is set: \
|
|
Elision was explicitly disabled by pthread_mutexattr_settype. \
|
|
Do not use the elision path. \
|
|
Note: The flag PTHREAD_MUTEX_NO_ELISION_NP will never be \
|
|
changed after mutex initialization. */ \
|
|
int mutex_kind = atomic_load_relaxed (&((m)->__data.__kind)); \
|
|
if ((mutex_kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0) \
|
|
{ \
|
|
mutex_kind |= PTHREAD_MUTEX_ELISION_NP; \
|
|
atomic_store_relaxed (&((m)->__data.__kind), mutex_kind); \
|
|
} \
|
|
if ((mutex_kind & PTHREAD_MUTEX_ELISION_NP) != 0) \
|
|
{ \
|
|
s; \
|
|
} \
|
|
}
|