From be8efac78d067c138ad8dda03df4336e73f94887 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Sat, 8 Jan 2022 11:51:07 +0100 Subject: New upstream version 1.0 --- lib/thread-optim.h | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) create mode 100644 lib/thread-optim.h (limited to 'lib/thread-optim.h') diff --git a/lib/thread-optim.h b/lib/thread-optim.h new file mode 100644 index 0000000..daf887f --- /dev/null +++ b/lib/thread-optim.h @@ -0,0 +1,60 @@ +/* Optimization of multithreaded code. + + Copyright (C) 2020-2022 Free Software Foundation, Inc. + + This file is free software: you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + This file is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see . */ + +/* Written by Bruno Haible , 2020. */ + +#ifndef _THREAD_OPTIM_H +#define _THREAD_OPTIM_H + +/* This file defines a way to optimize multithreaded code for the single-thread + case, based on the variable '__libc_single_threaded', defined in + glibc >= 2.32. */ + +/* Typical use: In a block or function, use + + bool mt = gl_multithreaded (); + ... + if (mt) + if (pthread_mutex_lock (&lock)) abort (); + ... + if (mt) + if (pthread_mutex_unlock (&lock)) abort (); + + The gl_multithreaded () invocation determines whether the program currently + is multithreaded. + + if (mt) STATEMENT executes STATEMENT in the multithreaded case, and skips + it in the single-threaded case. + + The code between the gl_multithreaded () invocation and any use of the + variable 'mt' must not create threads or invoke functions that may + indirectly create threads (e.g. 'dlopen' may, indirectly through C++ + initializers of global variables in the shared library being opened, + create threads). + + The lock here is meant to synchronize threads in the same process. The + same optimization cannot be applied to locks that synchronize different + processes (e.g. through shared memory mappings). */ + +#if HAVE_SYS_SINGLE_THREADED_H /* glibc >= 2.32 */ +# include +# define gl_multithreaded() !__libc_single_threaded +#else +# define gl_multithreaded() 1 +#endif + +#endif /* _THREAD_OPTIM_H */ -- cgit v1.2.3