mirror of
https://https.git.savannah.gnu.org/git/gnulib.git
synced 2026-06-15 15:25:49 +00:00
Bruno Haible
86488a20ea
* lib/thread-optim.h: Include <stdbool.h>. (gl_multithreaded): Define differently on ELF platforms. (_GL_MULTITHREADED_ALWAYS_TRUE, _GL_MULTITHREADED_VIA_ELF): New macros. (gl_set_multithreaded): New declaration. * lib/thread-optim.c: New file. * lib/thread-creators.gperf: New file. * lib/thread-optim-proto.c: New file. * modules/thread-optim (Files): Add these files. (Depends-on): Add gperf, bool, stdint-h. (configure.ac): Test for <link.h>, dl_iterate_phdr. (Makefile.am): Compile thread-optim.c. Create thread-creators.h through gperf. tweak
110 lines
3.5 KiB
C
110 lines
3.5 KiB
C
/* Optimization of multithreaded code.
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Copyright (C) 2020-2026 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Bruno Haible <bruno@clisp.org>, 2020. */
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#ifndef _THREAD_OPTIM_H
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#define _THREAD_OPTIM_H
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/* This file defines a way to optimize multithreaded code for the
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single-threaded case, based on the variable '__libc_single_threaded',
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defined in glibc >= 2.32. */
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/* Typical use: In a block or function, use
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bool mt = gl_multithreaded ();
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...
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if (mt)
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if (pthread_mutex_lock (&lock)) abort ();
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...
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if (mt)
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if (pthread_mutex_unlock (&lock)) abort ();
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gl_multithreaded () returns true if the process might be multithreaded,
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and false if the process is definitely single-threaded.
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if (mt) STATEMENT executes STATEMENT in the possibly-multithreaded case,
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and skips it in the single-threaded case.
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The code between the gl_multithreaded () invocation and any use of the
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variable 'mt' must not create threads or invoke functions that may
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indirectly create threads (e.g. 'dlopen' may, indirectly through C++
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initializers of global variables in the shared library being opened,
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create threads).
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The lock here is meant to synchronize threads in the same process. The
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same optimization cannot be applied to locks that synchronize different
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processes (e.g. through shared memory mappings). */
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/* This file uses HAVE_SYS_SINGLE_THREADED_H. */
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#if !_GL_CONFIG_H_INCLUDED
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#error "Please include config.h first."
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#endif
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#include <stdbool.h>
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#if HAVE_SYS_SINGLE_THREADED_H /* glibc >= 2.32 */
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# include <sys/single_threaded.h>
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# define gl_multithreaded() (!__libc_single_threaded)
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#elif defined __APPLE__ && defined __MACH__ /* macOS */
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/* One of the most basic libraries on macOS, CoreFoundation,
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creates new threads without being asked for. Therefore,
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assume that the process might be multithreaded. */
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# define gl_multithreaded() 1
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# define _GL_MULTITHREADED_ALWAYS_TRUE
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#elif defined __ELF__ /* Linux, Hurd, FreeBSD, NetBSD, OpenBSD, Solaris, ... */\
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&& HAVE_LINK_H \
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&& HAVE_DL_ITERATE_PHDR /* not Solaris 10, not Haiku */
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/* We can detect whether pthread_create() can be invoked, by looking
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at the contents of the PLT of the executable and of each shared object. */
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# ifdef __cplusplus
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extern "C" {
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# endif
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extern bool gl_multithreaded (void);
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# define _GL_MULTITHREADED_VIA_ELF
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# ifdef __cplusplus
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}
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# endif
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#else
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/* On other platforms, such as Windows, threads are created for relatively
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simple tasks, such as events, alarms, or interruptible sleep. Therefore,
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assume that the process might be multithreaded. */
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# define gl_multithreaded() 1
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# define _GL_MULTITHREADED_ALWAYS_TRUE
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#endif
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Allows programs to override the result of gl_multithreaded(). */
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extern void gl_set_multithreaded (bool mt);
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#ifdef __cplusplus
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}
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#endif
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#endif /* _THREAD_OPTIM_H */
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