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87fb310b69
In documentation and comments, be more like POSIX in terminology involving multithreading. Explain the distinction between multithreaded process vs multithreaded program. Change “program” to “process” when the latter wording is more accurate or informative. Simplify the wording for the constraints on processes that use unlocked I/O. Change “multithread-safe” to “thread-safe”. Change “thread-safety” to “thread safety”. However, do not change “multithreaded” to “multi-threaded” even though there are some uses of both spellinga, as there are a whole bunch of uses of “multithreaded”, also in identifier names; perhaps Gnulib should even standardize on “multithreaded” (not “multi-threaded”), contra POSIX.
66 lines
2.3 KiB
C
66 lines
2.3 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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#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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