1 /* Optimization of multithreaded code. 2 3 Copyright (C) 2020-2021 Free Software Foundation, Inc. 4 5 This file is free software: you can redistribute it and/or modify 6 it under the terms of the GNU Lesser General Public License as 7 published by the Free Software Foundation; either version 2.1 of the 8 License, or (at your option) any later version. 9 10 This file 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 13 GNU Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public License 16 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 17 18 /* Written by Bruno Haible <bruno@clisp.org>, 2020. */ 19 20 #ifndef _THREAD_OPTIM_H 21 #define _THREAD_OPTIM_H 22 23 /* This file defines a way to optimize multithreaded code for the single-thread 24 case, based on the variable '__libc_single_threaded', defined in 25 glibc >= 2.32. */ 26 27 /* Typical use: In a block or function, use 28 29 bool mt = gl_multithreaded (); 30 ... 31 if (mt) 32 if (pthread_mutex_lock (&lock)) abort (); 33 ... 34 if (mt) 35 if (pthread_mutex_unlock (&lock)) abort (); 36 37 The gl_multithreaded () invocation determines whether the program currently 38 is multithreaded. 39 40 if (mt) STATEMENT executes STATEMENT in the multithreaded case, and skips 41 it in the single-threaded case. 42 43 The code between the gl_multithreaded () invocation and any use of the 44 variable 'mt' must not create threads or invoke functions that may 45 indirectly create threads (e.g. 'dlopen' may, indirectly through C++ 46 initializers of global variables in the shared library being opened, 47 create threads). 48 49 The lock here is meant to synchronize threads in the same process. The 50 same optimization cannot be applied to locks that synchronize different 51 processes (e.g. through shared memory mappings). */ 52 53 #if HAVE_SYS_SINGLE_THREADED_H /* glibc >= 2.32 */ 54 # include <sys/single_threaded.h> 55 # define gl_multithreaded() !__libc_single_threaded 56 #else 57 # define gl_multithreaded() 1 58 #endif 59 60 #endif /* _THREAD_OPTIM_H */