1/* Default mutex implementation struct definitions.
 2   Copyright (C) 2019-2025 Free Software Foundation, Inc.
 3   This file is part of the GNU C Library.
 4
 5   The GNU C Library is free software; you can redistribute it and/or
 6   modify it under the terms of the GNU Lesser General Public
 7   License as published by the Free Software Foundation; either
 8   version 2.1 of the License, or (at your option) any later version.
 9
10   The GNU C Library is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public
16   License along with the GNU C Library; if not, see
17   <http://www.gnu.org/licenses/>.  */
18
19#ifndef _THREAD_MUTEX_INTERNAL_H
20#define _THREAD_MUTEX_INTERNAL_H 1
21
22/* Generic struct for both POSIX and C11 mutexes.  New ports are expected
23   to use the default layout, however architecture can redefine it to
24   add arch-specific extension (such as lock-elision).  The struct have
25   a size of 32 bytes on LP32 and 40 bytes on LP64 architectures.  */
26
27struct __pthread_mutex_s
28{
29  int __lock __LOCK_ALIGNMENT;
30  unsigned int __count;
31  int __owner;
32#if __WORDSIZE == 64
33  unsigned int __nusers;
34#endif
35  /* KIND must stay at this position in the structure to maintain
36     binary compatibility with static initializers.
37
38     Concurrency notes:
39     The __kind of a mutex is initialized either by the static
40     PTHREAD_MUTEX_INITIALIZER or by a call to pthread_mutex_init.
41
42     After a mutex has been initialized, the __kind of a mutex is usually not
43     changed.  BUT it can be set to -1 in pthread_mutex_destroy or elision can
44     be enabled.  This is done concurrently in the pthread_mutex_*lock
45     functions by using the macro FORCE_ELISION. This macro is only defined
46     for architectures which supports lock elision.
47
48     For elision, there are the flags PTHREAD_MUTEX_ELISION_NP and
49     PTHREAD_MUTEX_NO_ELISION_NP which can be set in addition to the already
50     set type of a mutex.  Before a mutex is initialized, only
51     PTHREAD_MUTEX_NO_ELISION_NP can be set with pthread_mutexattr_settype.
52
53     After a mutex has been initialized, the functions pthread_mutex_*lock can
54     enable elision - if the mutex-type and the machine supports it - by
55     setting the flag PTHREAD_MUTEX_ELISION_NP. This is done concurrently.
56     Afterwards the lock / unlock functions are using specific elision
57     code-paths.  */
58  int __kind;
59#if __WORDSIZE != 64
60  unsigned int __nusers;
61#endif
62#if __WORDSIZE == 64
63  int __spins;
64  __pthread_list_t __list;
65# define __PTHREAD_MUTEX_HAVE_PREV      1
66#else
67  __extension__ union
68  {
69    int __spins;
70    __pthread_slist_t __list;
71  };
72# define __PTHREAD_MUTEX_HAVE_PREV      0
73#endif
74};
75
76#if __PTHREAD_MUTEX_HAVE_PREV == 1
77# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
78  0, 0, 0, 0, __kind, 0, { 0, 0 }
79#else
80# define __PTHREAD_MUTEX_INITIALIZER(__kind) \
81  0, 0, 0, __kind, 0, { 0 }
82#endif
83
84#endif