1/* Single thread optimization, Linux version.
2 Copyright (C) 2019-2021 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 <https://www.gnu.org/licenses/>. */
18
19#ifndef _SINGLE_THREAD_H
20#define _SINGLE_THREAD_H
21
22/* The default way to check if the process is single thread is by using the
23 pthread_t 'multiple_threads' field. However, for some architectures it is
24 faster to either use an extra field on TCB or global variables (the TCB
25 field is also used on x86 for some single-thread atomic optimizations).
26
27 The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
28 check to use global variables instead of the pthread_t field. */
29
30#ifdef SINGLE_THREAD_BY_GLOBAL
31# if IS_IN (libc)
32extern int __libc_multiple_threads;
33# define SINGLE_THREAD_P \
34 __glibc_likely (__libc_multiple_threads == 0)
35# elif IS_IN (libpthread)
36extern int __pthread_multiple_threads;
37# define SINGLE_THREAD_P \
38 __glibc_likely (__pthread_multiple_threads == 0)
39# elif IS_IN (librt)
40# define SINGLE_THREAD_P \
41 __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
42 header.multiple_threads) == 0)
43# else
44/* For rtld, et cetera. */
45# define SINGLE_THREAD_P (1)
46# endif
47#else /* SINGLE_THREAD_BY_GLOBAL */
48# if IS_IN (libc) || IS_IN (libpthread) || IS_IN (librt)
49# define SINGLE_THREAD_P \
50 __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
51 header.multiple_threads) == 0)
52# else
53/* For rtld, et cetera. */
54# define SINGLE_THREAD_P (1)
55# endif
56#endif /* SINGLE_THREAD_BY_GLOBAL */
57
58#define RTLD_SINGLE_THREAD_P \
59 __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
60 header.multiple_threads) == 0)
61
62#endif /* _SINGLE_THREAD_H */
63