1/* Single thread optimization, Linux version.
 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   <https://www.gnu.org/licenses/>.  */
18
19#ifndef _SINGLE_THREAD_H
20#define _SINGLE_THREAD_H
21
22#ifndef __ASSEMBLER__
23# include <sys/single_threaded.h>
24#endif
25
26/* The default way to check if the process is single thread is by using the
27   pthread_t 'multiple_threads' field.  However, for some architectures it is
28   faster to either use an extra field on TCB or global variables (the TCB
29   field is also used on x86 for some single-thread atomic optimizations).
30
31   The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
32   check to use global variables instead of the pthread_t field.  */
33
34#if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld)
35# define SINGLE_THREAD_P \
36  (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0)
37#else
38# define SINGLE_THREAD_P (__libc_single_threaded_internal != 0)
39#endif
40
41#define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P
42
43#endif /* _SINGLE_THREAD_H  */