272 lines
8.8 KiB
C
272 lines
8.8 KiB
C
/* Once-only initialization in multithreaded situations.
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Copyright (C) 2005-2025 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>, 2005.
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Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-win32.h. */
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/* This file contains once-only initialization primitives for use with a given
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thread library.
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It does not contain primitives for creating threads or for other
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synchronization primitives.
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Once-only execution:
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Type: gl_once_t
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Initializer: gl_once_define(extern, name)
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Execution: gl_once (name, initfunction);
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Equivalent functions with control of error handling:
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Execution: err = glthread_once (&name, initfunction);
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*/
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#ifndef _ONCE_H
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#define _ONCE_H
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/* This file uses HAVE_THREADS_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 <errno.h>
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#include <stdlib.h>
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#if !defined c11_threads_in_use
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# if HAVE_THREADS_H && USE_POSIX_THREADS_FROM_LIBC
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# define c11_threads_in_use() 1
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# elif HAVE_THREADS_H && USE_POSIX_THREADS_WEAK
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# include <threads.h>
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# pragma weak thrd_exit
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# define c11_threads_in_use() (thrd_exit != NULL)
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# else
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# define c11_threads_in_use() 0
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# endif
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#endif
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/* ========================================================================= */
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#if USE_ISOC_THREADS || USE_ISOC_AND_POSIX_THREADS
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/* Use the ISO C threads library. */
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# include <threads.h>
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# ifdef __cplusplus
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extern "C" {
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# endif
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/* -------------------------- gl_once_t datatype -------------------------- */
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typedef once_flag gl_once_t;
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# define gl_once_define(STORAGECLASS, NAME) \
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STORAGECLASS once_flag NAME = ONCE_FLAG_INIT;
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# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
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(call_once (ONCE_CONTROL, INITFUNCTION), 0)
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# ifdef __cplusplus
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}
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# endif
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#endif
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/* ========================================================================= */
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#if USE_POSIX_THREADS
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/* Use the POSIX threads library. */
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# include <pthread.h>
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# ifdef __cplusplus
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extern "C" {
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# endif
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# if PTHREAD_IN_USE_DETECTION_HARD
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/* The pthread_in_use() detection needs to be done at runtime. */
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# define pthread_in_use() \
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glthread_in_use ()
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extern int glthread_in_use (void);
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# endif
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# if USE_POSIX_THREADS_WEAK
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/* Use weak references to the POSIX threads library. */
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/* Weak references avoid dragging in external libraries if the other parts
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of the program don't use them. Here we use them, because we don't want
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every program that uses libintl to depend on libpthread. This assumes
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that libpthread would not be loaded after libintl; i.e. if libintl is
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loaded first, by an executable that does not depend on libpthread, and
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then a module is dynamically loaded that depends on libpthread, libintl
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will not be multithread-safe. */
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/* The way to test at runtime whether libpthread is present is to test
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whether a function pointer's value, such as &pthread_mutex_init, is
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non-NULL. However, some versions of GCC have a bug through which, in
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PIC mode, &foo != NULL always evaluates to true if there is a direct
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call to foo(...) in the same function. To avoid this, we test the
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address of a function in libpthread that we don't use. */
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# pragma weak pthread_mutex_init
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# pragma weak pthread_mutex_lock
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# pragma weak pthread_mutex_unlock
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# pragma weak pthread_mutex_destroy
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/* Work around clang bug <https://github.com/llvm/llvm-project/issues/104670> */
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# ifndef pthread_rwlock_init
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# pragma weak pthread_rwlock_init
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# endif
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# pragma weak pthread_rwlock_rdlock
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# pragma weak pthread_rwlock_wrlock
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# pragma weak pthread_rwlock_unlock
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# pragma weak pthread_rwlock_destroy
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# pragma weak pthread_once
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# pragma weak pthread_cond_init
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# pragma weak pthread_cond_wait
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# pragma weak pthread_cond_signal
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# pragma weak pthread_cond_broadcast
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# pragma weak pthread_cond_destroy
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# pragma weak pthread_mutexattr_init
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# pragma weak pthread_mutexattr_settype
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# pragma weak pthread_mutexattr_destroy
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/* Work around clang bug <https://github.com/llvm/llvm-project/issues/104670> */
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# ifndef pthread_rwlockattr_init
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# pragma weak pthread_rwlockattr_init
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# endif
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# if __GNU_LIBRARY__ > 1
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# pragma weak pthread_rwlockattr_setkind_np
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# endif
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# pragma weak pthread_rwlockattr_destroy
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# ifndef pthread_self
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# pragma weak pthread_self
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# endif
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# if !PTHREAD_IN_USE_DETECTION_HARD
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/* Considering all platforms with USE_POSIX_THREADS_WEAK, only few symbols
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can be used to determine whether libpthread is in use. These are:
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pthread_mutexattr_gettype
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pthread_rwlockattr_destroy
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pthread_rwlockattr_init
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*/
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# pragma weak pthread_mutexattr_gettype
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# define pthread_in_use() \
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(pthread_mutexattr_gettype != NULL || c11_threads_in_use ())
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# endif
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# else
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# if !PTHREAD_IN_USE_DETECTION_HARD
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# define pthread_in_use() 1
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# endif
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# endif
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/* -------------------------- gl_once_t datatype -------------------------- */
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typedef pthread_once_t gl_once_t;
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# define gl_once_define(STORAGECLASS, NAME) \
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STORAGECLASS pthread_once_t NAME = PTHREAD_ONCE_INIT;
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# if PTHREAD_IN_USE_DETECTION_HARD || USE_POSIX_THREADS_WEAK
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# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
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(pthread_in_use () \
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? pthread_once (ONCE_CONTROL, INITFUNCTION) \
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: (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
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# else
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# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
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(pthread_in_use () \
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? glthread_once_multithreaded (ONCE_CONTROL, INITFUNCTION) \
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: (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
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extern int glthread_once_multithreaded (pthread_once_t *once_control,
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void (*init_function) (void));
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# endif
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extern int glthread_once_singlethreaded (pthread_once_t *once_control);
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# ifdef __cplusplus
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}
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# endif
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#endif
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/* ========================================================================= */
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#if USE_WINDOWS_THREADS
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# define WIN32_LEAN_AND_MEAN /* avoid including junk */
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# include <windows.h>
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# include "windows-once.h"
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# ifdef __cplusplus
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extern "C" {
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# endif
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/* We can use CRITICAL_SECTION directly, rather than the native Windows Event,
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Mutex, Semaphore types, because
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- we need only to synchronize inside a single process (address space),
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not inter-process locking,
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- we don't need to support trylock operations. (TryEnterCriticalSection
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does not work on Windows 95/98/ME. Packages that need trylock usually
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define their own mutex type.) */
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/* There is no way to statically initialize a CRITICAL_SECTION. It needs
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to be done lazily, once only. For this we need spinlocks. */
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/* -------------------------- gl_once_t datatype -------------------------- */
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typedef glwthread_once_t gl_once_t;
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# define gl_once_define(STORAGECLASS, NAME) \
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STORAGECLASS gl_once_t NAME = GLWTHREAD_ONCE_INIT;
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# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
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(glwthread_once (ONCE_CONTROL, INITFUNCTION), 0)
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# ifdef __cplusplus
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}
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# endif
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#endif
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/* ========================================================================= */
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#if !(USE_ISOC_THREADS || USE_POSIX_THREADS || USE_ISOC_AND_POSIX_THREADS || USE_WINDOWS_THREADS)
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/* Provide dummy implementation if threads are not supported. */
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/* -------------------------- gl_once_t datatype -------------------------- */
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typedef int gl_once_t;
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# define gl_once_define(STORAGECLASS, NAME) \
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STORAGECLASS gl_once_t NAME = 0;
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# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
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(*(ONCE_CONTROL) == 0 ? (*(ONCE_CONTROL) = ~ 0, INITFUNCTION (), 0) : 0)
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#endif
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/* ========================================================================= */
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/* Macros with built-in error handling. */
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/* -------------------------- gl_once_t datatype -------------------------- */
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#define gl_once(NAME, INITFUNCTION) \
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do \
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{ \
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if (glthread_once (&NAME, INITFUNCTION)) \
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abort (); \
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} \
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while (0)
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/* ========================================================================= */
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#endif /* _ONCE_H */
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