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/* Default mutex implementation struct definitions.
Copyright (C) 2019-2023 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/>. */
#ifndef _THREAD_MUTEX_INTERNAL_H
#define _THREAD_MUTEX_INTERNAL_H 1
/* Generic struct for both POSIX and C11 mutexes. New ports are expected
to use the default layout, however architecture can redefine it to
add arch-specific extension (such as lock-elision). The struct have
a size of 32 bytes on LP32 and 40 bytes on LP64 architectures. */
struct __pthread_mutex_s
{
int __lock __LOCK_ALIGNMENT;
unsigned int __count;
int __owner;
#if __WORDSIZE == 64
unsigned int __nusers;
#endif
/* KIND must stay at this position in the structure to maintain
binary compatibility with static initializers.
Concurrency notes:
The __kind of a mutex is initialized either by the static
PTHREAD_MUTEX_INITIALIZER or by a call to pthread_mutex_init.
After a mutex has been initialized, the __kind of a mutex is usually not
changed. BUT it can be set to -1 in pthread_mutex_destroy or elision can
be enabled. This is done concurrently in the pthread_mutex_*lock
functions by using the macro FORCE_ELISION. This macro is only defined
for architectures which supports lock elision.
For elision, there are the flags PTHREAD_MUTEX_ELISION_NP and
PTHREAD_MUTEX_NO_ELISION_NP which can be set in addition to the already
set type of a mutex. Before a mutex is initialized, only
PTHREAD_MUTEX_NO_ELISION_NP can be set with pthread_mutexattr_settype.
After a mutex has been initialized, the functions pthread_mutex_*lock can
enable elision - if the mutex-type and the machine supports it - by
setting the flag PTHREAD_MUTEX_ELISION_NP. This is done concurrently.
Afterwards the lock / unlock functions are using specific elision
code-paths. */
int __kind;
#if __WORDSIZE != 64
unsigned int __nusers;
#endif
#if __WORDSIZE == 64
int __spins;
__pthread_list_t __list;
# define __PTHREAD_MUTEX_HAVE_PREV 1
#else
__extension__ union
{
int __spins;
__pthread_slist_t __list;
};
# define __PTHREAD_MUTEX_HAVE_PREV 0
#endif
};
#if __PTHREAD_MUTEX_HAVE_PREV == 1
# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
0, 0, 0, 0, __kind, 0, { 0, 0 }
#else
# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
0, 0, 0, __kind, 0, { 0 }
#endif
#endif
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