65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
/* Optimization of multithreaded code.
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Copyright (C) 2020-2025 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 single-thread
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case, based on the variable '__libc_single_threaded', defined in
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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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The gl_multithreaded () invocation determines whether the program currently
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is multithreaded.
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if (mt) STATEMENT executes STATEMENT in the multithreaded case, and skips
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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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#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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#else
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# define gl_multithreaded() 1
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#endif
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#endif /* _THREAD_OPTIM_H */
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