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Editing: struct_mutex.h
/* Default mutex implementation struct definitions. Copyright (C) 2019-2022 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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