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/* Locking in multithreaded situations.
Copyright (C) 2005-2008, 2015-2016 Free Software Foundation, Inc.
This program 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 program 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 <http://www.gnu.org/licenses/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2005.
Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-solaris.h,
gthr-win32.h. */
#include <config.h>
#include "lock.h"
/* ========================================================================= */
#if USE_POSIX_THREADS
/* -------------------------- gl_lock_t datatype -------------------------- */
/* ------------------------- gl_rwlock_t datatype ------------------------- */
# if HAVE_PTHREAD_RWLOCK
# if !defined PTHREAD_RWLOCK_INITIALIZER
int
glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_rwlock_init (&lock->rwlock, NULL);
if (err != 0)
return err;
lock->initialized = 1;
return 0;
}
int
glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
{
if (!lock->initialized)
{
int err;
err = pthread_mutex_lock (&lock->guard);
if (err != 0)
return err;
if (!lock->initialized)
{
err = glthread_rwlock_init_multithreaded (lock);
if (err != 0)
{
pthread_mutex_unlock (&lock->guard);
return err;
}
}
err = pthread_mutex_unlock (&lock->guard);
if (err != 0)
return err;
}
return pthread_rwlock_rdlock (&lock->rwlock);
}
int
glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
{
if (!lock->initialized)
{
int err;
err = pthread_mutex_lock (&lock->guard);
if (err != 0)
return err;
if (!lock->initialized)
{
err = glthread_rwlock_init_multithreaded (lock);
if (err != 0)
{
pthread_mutex_unlock (&lock->guard);
return err;
}
}
err = pthread_mutex_unlock (&lock->guard);
if (err != 0)
return err;
}
return pthread_rwlock_wrlock (&lock->rwlock);
}
int
glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
{
if (!lock->initialized)
return EINVAL;
return pthread_rwlock_unlock (&lock->rwlock);
}
int
glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
{
int err;
if (!lock->initialized)
return EINVAL;
err = pthread_rwlock_destroy (&lock->rwlock);
if (err != 0)
return err;
lock->initialized = 0;
return 0;
}
# endif
# else
int
glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_mutex_init (&lock->lock, NULL);
if (err != 0)
return err;
err = pthread_cond_init (&lock->waiting_readers, NULL);
if (err != 0)
return err;
err = pthread_cond_init (&lock->waiting_writers, NULL);
if (err != 0)
return err;
lock->waiting_writers_count = 0;
lock->runcount = 0;
return 0;
}
int
glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_mutex_lock (&lock->lock);
if (err != 0)
return err;
/* Test whether only readers are currently running, and whether the runcount
field will not overflow. */
/* POSIX says: "It is implementation-defined whether the calling thread
acquires the lock when a writer does not hold the lock and there are
writers blocked on the lock." Let's say, no: give the writers a higher
priority. */
while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
{
/* This thread has to wait for a while. Enqueue it among the
waiting_readers. */
err = pthread_cond_wait (&lock->waiting_readers, &lock->lock);
if (err != 0)
{
pthread_mutex_unlock (&lock->lock);
return err;
}
}
lock->runcount++;
return pthread_mutex_unlock (&lock->lock);
}
int
glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_mutex_lock (&lock->lock);
if (err != 0)
return err;
/* Test whether no readers or writers are currently running. */
while (!(lock->runcount == 0))
{
/* This thread has to wait for a while. Enqueue it among the
waiting_writers. */
lock->waiting_writers_count++;
err = pthread_cond_wait (&lock->waiting_writers, &lock->lock);
if (err != 0)
{
lock->waiting_writers_count--;
pthread_mutex_unlock (&lock->lock);
return err;
}
lock->waiting_writers_count--;
}
lock->runcount--; /* runcount becomes -1 */
return pthread_mutex_unlock (&lock->lock);
}
int
glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_mutex_lock (&lock->lock);
if (err != 0)
return err;
if (lock->runcount < 0)
{
/* Drop a writer lock. */
if (!(lock->runcount == -1))
{
pthread_mutex_unlock (&lock->lock);
return EINVAL;
}
lock->runcount = 0;
}
else
{
/* Drop a reader lock. */
if (!(lock->runcount > 0))
{
pthread_mutex_unlock (&lock->lock);
return EINVAL;
}
lock->runcount--;
}
if (lock->runcount == 0)
{
/* POSIX recommends that "write locks shall take precedence over read
locks", to avoid "writer starvation". */
if (lock->waiting_writers_count > 0)
{
/* Wake up one of the waiting writers. */
err = pthread_cond_signal (&lock->waiting_writers);
if (err != 0)
{
pthread_mutex_unlock (&lock->lock);
return err;
}
}
else
{
/* Wake up all waiting readers. */
err = pthread_cond_broadcast (&lock->waiting_readers);
if (err != 0)
{
pthread_mutex_unlock (&lock->lock);
return err;
}
}
}
return pthread_mutex_unlock (&lock->lock);
}
int
glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
{
int err;
err = pthread_mutex_destroy (&lock->lock);
if (err != 0)
return err;
err = pthread_cond_destroy (&lock->waiting_readers);
if (err != 0)
return err;
err = pthread_cond_destroy (&lock->waiting_writers);
if (err != 0)
return err;
return 0;
}
# endif
/* --------------------- gl_recursive_lock_t datatype --------------------- */
# if HAVE_PTHREAD_MUTEX_RECURSIVE
# if defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER || defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
int
glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
{
pthread_mutexattr_t attributes;
int err;
err = pthread_mutexattr_init (&attributes);
if (err != 0)
return err;
err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
if (err != 0)
{
pthread_mutexattr_destroy (&attributes);
return err;
}
err = pthread_mutex_init (lock, &attributes);
if (err != 0)
{
pthread_mutexattr_destroy (&attributes);
return err;
}
err = pthread_mutexattr_destroy (&attributes);
if (err != 0)
return err;
return 0;
}
# else
int
glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
{
pthread_mutexattr_t attributes;
int err;
err = pthread_mutexattr_init (&attributes);
if (err != 0)
return err;
err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
if (err != 0)
{
pthread_mutexattr_destroy (&attributes);
return err;
}
err = pthread_mutex_init (&lock->recmutex, &attributes);
if (err != 0)
{
pthread_mutexattr_destroy (&attributes);
return err;
}
err = pthread_mutexattr_destroy (&attributes);
if (err != 0)
return err;
lock->initialized = 1;
return 0;
}
int
glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
{
if (!lock->initialized)
{
int err;
err = pthread_mutex_lock (&lock->guard);
if (err != 0)
return err;
if (!lock->initialized)
{
err = glthread_recursive_lock_init_multithreaded (lock);
if (err != 0)
{
pthread_mutex_unlock (&lock->guard);
return err;
}
}
err = pthread_mutex_unlock (&lock->guard);
if (err != 0)
return err;
}
return pthread_mutex_lock (&lock->recmutex);
}
int
glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
{
if (!lock->initialized)
return EINVAL;
return pthread_mutex_unlock (&lock->recmutex);
}
int
glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
{
int err;
if (!lock->initialized)
return EINVAL;
err = pthread_mutex_destroy (&lock->recmutex);
if (err != 0)
return err;
lock->initialized = 0;
return 0;
}
# endif
# else
int
glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
{
int err;
err = pthread_mutex_init (&lock->mutex, NULL);
if (err != 0)
return err;
lock->owner = (pthread_t) 0;
lock->depth = 0;
return 0;
}
int
glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
{
pthread_t self = pthread_self ();
if (lock->owner != self)
{
int err;
err = pthread_mutex_lock (&lock->mutex);
if (err != 0)
return err;
lock->owner = self;
}
if (++(lock->depth) == 0) /* wraparound? */
{
lock->depth--;
return EAGAIN;
}
return 0;
}
int
glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
{
if (lock->owner != pthread_self ())
return EPERM;
if (lock->depth == 0)
return EINVAL;
if (--(lock->depth) == 0)
{
lock->owner = (pthread_t) 0;
return pthread_mutex_unlock (&lock->mutex);
}
else
return 0;
}
int
glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
{
if (lock->owner != (pthread_t) 0)
return EBUSY;
return pthread_mutex_destroy (&lock->mutex);
}
# endif
/* -------------------------- gl_once_t datatype -------------------------- */
static const pthread_once_t fresh_once = PTHREAD_ONCE_INIT;
int
glthread_once_singlethreaded (pthread_once_t *once_control)
{
/* We don't know whether pthread_once_t is an integer type, a floating-point
type, a pointer type, or a structure type. */
char *firstbyte = (char *)once_control;
if (*firstbyte == *(const char *)&fresh_once)
{
/* First time use of once_control. Invert the first byte. */
*firstbyte = ~ *(const char *)&fresh_once;
return 1;
}
else
return 0;
}
#endif
/* ========================================================================= */
#if USE_PTH_THREADS
/* Use the GNU Pth threads library. */
/* -------------------------- gl_lock_t datatype -------------------------- */
/* ------------------------- gl_rwlock_t datatype ------------------------- */
/* --------------------- gl_recursive_lock_t datatype --------------------- */
/* -------------------------- gl_once_t datatype -------------------------- */
static void
glthread_once_call (void *arg)
{
void (**gl_once_temp_addr) (void) = (void (**) (void)) arg;
void (*initfunction) (void) = *gl_once_temp_addr;
initfunction ();
}
int
glthread_once_multithreaded (pth_once_t *once_control, void (*initfunction) (void))
{
void (*temp) (void) = initfunction;
return (!pth_once (once_control, glthread_once_call, &temp) ? errno : 0);
}
int
glthread_once_singlethreaded (pth_once_t *once_control)
{
/* We know that pth_once_t is an integer type. */
if (*once_control == PTH_ONCE_INIT)
{
/* First time use of once_control. Invert the marker. */
*once_control = ~ PTH_ONCE_INIT;
return 1;
}
else
return 0;
}
#endif
/* ========================================================================= */
#if USE_SOLARIS_THREADS
/* Use the old Solaris threads library. */
/* -------------------------- gl_lock_t datatype -------------------------- */
/* ------------------------- gl_rwlock_t datatype ------------------------- */
/* --------------------- gl_recursive_lock_t datatype --------------------- */
int
glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
{
int err;
err = mutex_init (&lock->mutex, USYNC_THREAD, NULL);
if (err != 0)
return err;
lock->owner = (thread_t) 0;
lock->depth = 0;
return 0;
}
int
glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
{
thread_t self = thr_self ();
if (lock->owner != self)
{
int err;
err = mutex_lock (&lock->mutex);
if (err != 0)
return err;
lock->owner = self;
}
if (++(lock->depth) == 0) /* wraparound? */
{
lock->depth--;
return EAGAIN;
}
return 0;
}
int
glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
{
if (lock->owner != thr_self ())
return EPERM;
if (lock->depth == 0)
return EINVAL;
if (--(lock->depth) == 0)
{
lock->owner = (thread_t) 0;
return mutex_unlock (&lock->mutex);
}
else
return 0;
}
int
glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
{
if (lock->owner != (thread_t) 0)
return EBUSY;
return mutex_destroy (&lock->mutex);
}
/* -------------------------- gl_once_t datatype -------------------------- */
int
glthread_once_multithreaded (gl_once_t *once_control, void (*initfunction) (void))
{
if (!once_control->inited)
{
int err;
/* Use the mutex to guarantee that if another thread is already calling
the initfunction, this thread waits until it's finished. */
err = mutex_lock (&once_control->mutex);
if (err != 0)
return err;
if (!once_control->inited)
{
once_control->inited = 1;
initfunction ();
}
return mutex_unlock (&once_control->mutex);
}
else
return 0;
}
int
glthread_once_singlethreaded (gl_once_t *once_control)
{
/* We know that gl_once_t contains an integer type. */
if (!once_control->inited)
{
/* First time use of once_control. Invert the marker. */
once_control->inited = ~ 0;
return 1;
}
else
return 0;
}
#endif
/* ========================================================================= */
#if USE_WINDOWS_THREADS
/* -------------------------- gl_lock_t datatype -------------------------- */
void
glthread_lock_init_func (gl_lock_t *lock)
{
InitializeCriticalSection (&lock->lock);
lock->guard.done = 1;
}
int
glthread_lock_lock_func (gl_lock_t *lock)
{
if (!lock->guard.done)
{
if (InterlockedIncrement (&lock->guard.started) == 0)
/* This thread is the first one to need this lock. Initialize it. */
glthread_lock_init (lock);
else
/* Yield the CPU while waiting for another thread to finish
initializing this lock. */
while (!lock->guard.done)
Sleep (0);
}
EnterCriticalSection (&lock->lock);
return 0;
}
int
glthread_lock_unlock_func (gl_lock_t *lock)
{
if (!lock->guard.done)
return EINVAL;
LeaveCriticalSection (&lock->lock);
return 0;
}
int
glthread_lock_destroy_func (gl_lock_t *lock)
{
if (!lock->guard.done)
return EINVAL;
DeleteCriticalSection (&lock->lock);
lock->guard.done = 0;
return 0;
}
/* ------------------------- gl_rwlock_t datatype ------------------------- */
/* In this file, the waitqueues are implemented as circular arrays. */
#define gl_waitqueue_t gl_carray_waitqueue_t
static void
gl_waitqueue_init (gl_waitqueue_t *wq)
{
wq->array = NULL;
wq->count = 0;
wq->alloc = 0;
wq->offset = 0;
}
/* Enqueues the current thread, represented by an event, in a wait queue.
Returns INVALID_HANDLE_VALUE if an allocation failure occurs. */
static HANDLE
gl_waitqueue_add (gl_waitqueue_t *wq)
{
HANDLE event;
unsigned int index;
if (wq->count == wq->alloc)
{
unsigned int new_alloc = 2 * wq->alloc + 1;
HANDLE *new_array =
(HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE));
if (new_array == NULL)
/* No more memory. */
return INVALID_HANDLE_VALUE;
/* Now is a good opportunity to rotate the array so that its contents
starts at offset 0. */
if (wq->offset > 0)
{
unsigned int old_count = wq->count;
unsigned int old_alloc = wq->alloc;
unsigned int old_offset = wq->offset;
unsigned int i;
if (old_offset + old_count > old_alloc)
{
unsigned int limit = old_offset + old_count - old_alloc;
for (i = 0; i < limit; i++)
new_array[old_alloc + i] = new_array[i];
}
for (i = 0; i < old_count; i++)
new_array[i] = new_array[old_offset + i];
wq->offset = 0;
}
wq->array = new_array;
wq->alloc = new_alloc;
}
/* Whether the created event is a manual-reset one or an auto-reset one,
does not matter, since we will wait on it only once. */
event = CreateEvent (NULL, TRUE, FALSE, NULL);
if (event == INVALID_HANDLE_VALUE)
/* No way to allocate an event. */
return INVALID_HANDLE_VALUE;
index = wq->offset + wq->count;
if (index >= wq->alloc)
index -= wq->alloc;
wq->array[index] = event;
wq->count++;
return event;
}
/* Notifies the first thread from a wait queue and dequeues it. */
static void
gl_waitqueue_notify_first (gl_waitqueue_t *wq)
{
SetEvent (wq->array[wq->offset + 0]);
wq->offset++;
wq->count--;
if (wq->count == 0 || wq->offset == wq->alloc)
wq->offset = 0;
}
/* Notifies all threads from a wait queue and dequeues them all. */
static void
gl_waitqueue_notify_all (gl_waitqueue_t *wq)
{
unsigned int i;
for (i = 0; i < wq->count; i++)
{
unsigned int index = wq->offset + i;
if (index >= wq->alloc)
index -= wq->alloc;
SetEvent (wq->array[index]);
}
wq->count = 0;
wq->offset = 0;
}
void
glthread_rwlock_init_func (gl_rwlock_t *lock)
{
InitializeCriticalSection (&lock->lock);
gl_waitqueue_init (&lock->waiting_readers);
gl_waitqueue_init (&lock->waiting_writers);
lock->runcount = 0;
lock->guard.done = 1;
}
int
glthread_rwlock_rdlock_func (gl_rwlock_t *lock)
{
if (!lock->guard.done)
{
if (InterlockedIncrement (&lock->guard.started) == 0)
/* This thread is the first one to need this lock. Initialize it. */
glthread_rwlock_init (lock);
else
/* Yield the CPU while waiting for another thread to finish
initializing this lock. */
while (!lock->guard.done)
Sleep (0);
}
EnterCriticalSection (&lock->lock);
/* Test whether only readers are currently running, and whether the runcount
field will not overflow. */
if (!(lock->runcount + 1 > 0))
{
/* This thread has to wait for a while. Enqueue it among the
waiting_readers. */
HANDLE event = gl_waitqueue_add (&lock->waiting_readers);
if (event != INVALID_HANDLE_VALUE)
{
DWORD result;
LeaveCriticalSection (&lock->lock);
/* Wait until another thread signals this event. */
result = WaitForSingleObject (event, INFINITE);
if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
abort ();
CloseHandle (event);
/* The thread which signalled the event already did the bookkeeping:
removed us from the waiting_readers, incremented lock->runcount. */
if (!(lock->runcount > 0))
abort ();
return 0;
}
else
{
/* Allocation failure. Weird. */
do
{
LeaveCriticalSection (&lock->lock);
Sleep (1);
EnterCriticalSection (&lock->lock);
}
while (!(lock->runcount + 1 > 0));
}
}
lock->runcount++;
LeaveCriticalSection (&lock->lock);
return 0;
}
int
glthread_rwlock_wrlock_func (gl_rwlock_t *lock)
{
if (!lock->guard.done)
{
if (InterlockedIncrement (&lock->guard.started) == 0)
/* This thread is the first one to need this lock. Initialize it. */
glthread_rwlock_init (lock);
else
/* Yield the CPU while waiting for another thread to finish
initializing this lock. */
while (!lock->guard.done)
Sleep (0);
}
EnterCriticalSection (&lock->lock);
/* Test whether no readers or writers are currently running. */
if (!(lock->runcount == 0))
{
/* This thread has to wait for a while. Enqueue it among the
waiting_writers. */
HANDLE event = gl_waitqueue_add (&lock->waiting_writers);
if (event != INVALID_HANDLE_VALUE)
{
DWORD result;
LeaveCriticalSection (&lock->lock);
/* Wait until another thread signals this event. */
result = WaitForSingleObject (event, INFINITE);
if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
abort ();
CloseHandle (event);
/* The thread which signalled the event already did the bookkeeping:
removed us from the waiting_writers, set lock->runcount = -1. */
if (!(lock->runcount == -1))
abort ();
return 0;
}
else
{
/* Allocation failure. Weird. */
do
{
LeaveCriticalSection (&lock->lock);
Sleep (1);
EnterCriticalSection (&lock->lock);
}
while (!(lock->runcount == 0));
}
}
lock->runcount--; /* runcount becomes -1 */
LeaveCriticalSection (&lock->lock);
return 0;
}
int
glthread_rwlock_unlock_func (gl_rwlock_t *lock)
{
if (!lock->guard.done)
return EINVAL;
EnterCriticalSection (&lock->lock);
if (lock->runcount < 0)
{
/* Drop a writer lock. */
if (!(lock->runcount == -1))
abort ();
lock->runcount = 0;
}
else
{
/* Drop a reader lock. */
if (!(lock->runcount > 0))
{
LeaveCriticalSection (&lock->lock);
return EPERM;
}
lock->runcount--;
}
if (lock->runcount == 0)
{
/* POSIX recommends that "write locks shall take precedence over read
locks", to avoid "writer starvation". */
if (lock->waiting_writers.count > 0)
{
/* Wake up one of the waiting writers. */
lock->runcount--;
gl_waitqueue_notify_first (&lock->waiting_writers);
}
else
{
/* Wake up all waiting readers. */
lock->runcount += lock->waiting_readers.count;
gl_waitqueue_notify_all (&lock->waiting_readers);
}
}
LeaveCriticalSection (&lock->lock);
return 0;
}
int
glthread_rwlock_destroy_func (gl_rwlock_t *lock)
{
if (!lock->guard.done)
return EINVAL;
if (lock->runcount != 0)
return EBUSY;
DeleteCriticalSection (&lock->lock);
if (lock->waiting_readers.array != NULL)
free (lock->waiting_readers.array);
if (lock->waiting_writers.array != NULL)
free (lock->waiting_writers.array);
lock->guard.done = 0;
return 0;
}
/* --------------------- gl_recursive_lock_t datatype --------------------- */
void
glthread_recursive_lock_init_func (gl_recursive_lock_t *lock)
{
lock->owner = 0;
lock->depth = 0;
InitializeCriticalSection (&lock->lock);
lock->guard.done = 1;
}
int
glthread_recursive_lock_lock_func (gl_recursive_lock_t *lock)
{
if (!lock->guard.done)
{
if (InterlockedIncrement (&lock->guard.started) == 0)
/* This thread is the first one to need this lock. Initialize it. */
glthread_recursive_lock_init (lock);
else
/* Yield the CPU while waiting for another thread to finish
initializing this lock. */
while (!lock->guard.done)
Sleep (0);
}
{
DWORD self = GetCurrentThreadId ();
if (lock->owner != self)
{
EnterCriticalSection (&lock->lock);
lock->owner = self;
}
if (++(lock->depth) == 0) /* wraparound? */
{
lock->depth--;
return EAGAIN;
}
}
return 0;
}
int
glthread_recursive_lock_unlock_func (gl_recursive_lock_t *lock)
{
if (lock->owner != GetCurrentThreadId ())
return EPERM;
if (lock->depth == 0)
return EINVAL;
if (--(lock->depth) == 0)
{
lock->owner = 0;
LeaveCriticalSection (&lock->lock);
}
return 0;
}
int
glthread_recursive_lock_destroy_func (gl_recursive_lock_t *lock)
{
if (lock->owner != 0)
return EBUSY;
DeleteCriticalSection (&lock->lock);
lock->guard.done = 0;
return 0;
}
/* -------------------------- gl_once_t datatype -------------------------- */
void
glthread_once_func (gl_once_t *once_control, void (*initfunction) (void))
{
if (once_control->inited <= 0)
{
if (InterlockedIncrement (&once_control->started) == 0)
{
/* This thread is the first one to come to this once_control. */
InitializeCriticalSection (&once_control->lock);
EnterCriticalSection (&once_control->lock);
once_control->inited = 0;
initfunction ();
once_control->inited = 1;
LeaveCriticalSection (&once_control->lock);
}
else
{
/* Undo last operation. */
InterlockedDecrement (&once_control->started);
/* Some other thread has already started the initialization.
Yield the CPU while waiting for the other thread to finish
initializing and taking the lock. */
while (once_control->inited < 0)
Sleep (0);
if (once_control->inited <= 0)
{
/* Take the lock. This blocks until the other thread has
finished calling the initfunction. */
EnterCriticalSection (&once_control->lock);
LeaveCriticalSection (&once_control->lock);
if (!(once_control->inited > 0))
abort ();
}
}
}
}
#endif
/* ========================================================================= */
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