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 #ifndef __ASSEMBLER__ 31 extern int __libc_multiple_threads; 32 libc_hidden_proto (__libc_multiple_threads) 33 #endif 34 35 #if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld) 36 # define SINGLE_THREAD_P \ 37 (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0) 38 #else 39 # define SINGLE_THREAD_P (__libc_multiple_threads == 0) 40 #endif 41 42 #define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P 43 44 #endif /* _SINGLE_THREAD_H */ 45