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85 lines
3.0 KiB
C
85 lines
3.0 KiB
C
/* Default mutex implementation struct definitions.
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Copyright (C) 2019-2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _THREAD_MUTEX_INTERNAL_H
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#define _THREAD_MUTEX_INTERNAL_H 1
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/* Generic struct for both POSIX and C11 mutexes. New ports are expected
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to use the default layout, however architecture can redefine it to
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add arch-specific extension (such as lock-elision). The struct have
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a size of 32 bytes on LP32 and 40 bytes on LP64 architectures. */
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struct __pthread_mutex_s
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{
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int __lock __LOCK_ALIGNMENT;
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unsigned int __count;
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int __owner;
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#if __WORDSIZE == 64
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unsigned int __nusers;
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#endif
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/* KIND must stay at this position in the structure to maintain
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binary compatibility with static initializers.
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Concurrency notes:
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The __kind of a mutex is initialized either by the static
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PTHREAD_MUTEX_INITIALIZER or by a call to pthread_mutex_init.
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After a mutex has been initialized, the __kind of a mutex is usually not
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changed. BUT it can be set to -1 in pthread_mutex_destroy or elision can
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be enabled. This is done concurrently in the pthread_mutex_*lock
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functions by using the macro FORCE_ELISION. This macro is only defined
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for architectures which supports lock elision.
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For elision, there are the flags PTHREAD_MUTEX_ELISION_NP and
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PTHREAD_MUTEX_NO_ELISION_NP which can be set in addition to the already
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set type of a mutex. Before a mutex is initialized, only
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PTHREAD_MUTEX_NO_ELISION_NP can be set with pthread_mutexattr_settype.
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After a mutex has been initialized, the functions pthread_mutex_*lock can
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enable elision - if the mutex-type and the machine supports it - by
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setting the flag PTHREAD_MUTEX_ELISION_NP. This is done concurrently.
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Afterwards the lock / unlock functions are using specific elision
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code-paths. */
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int __kind;
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#if __WORDSIZE != 64
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unsigned int __nusers;
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#endif
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#if __WORDSIZE == 64
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int __spins;
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__pthread_list_t __list;
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# define __PTHREAD_MUTEX_HAVE_PREV 1
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#else
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__extension__ union
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{
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int __spins;
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__pthread_slist_t __list;
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};
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# define __PTHREAD_MUTEX_HAVE_PREV 0
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#endif
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};
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#if __PTHREAD_MUTEX_HAVE_PREV == 1
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# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
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0, 0, 0, 0, __kind, 0, { 0, 0 }
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#else
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# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
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0, 0, 0, __kind, 0, { 0 }
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#endif
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#endif
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