1/* Default mutex implementation struct definitions.
2 Copyright (C) 2019-2022 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
85