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/* Atomic integers. Useful for testing multithreaded locking primitives.
Copyright (C) 2005, 2008-2024 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Whether to use 'volatile' on some variables that communicate information
between threads. If set to 0, a semaphore or a lock is used to protect
these variables. If set to 1, 'volatile' is used; this is theoretically
equivalent but can lead to much slower execution (e.g. 30x slower total
run time on a 40-core machine), because 'volatile' does not imply any
synchronization/communication between different CPUs. */
#define USE_VOLATILE 0
#if USE_POSIX_THREADS && HAVE_SEMAPHORE_H
/* Whether to use a semaphore to communicate information between threads.
If set to 0, a lock is used. If set to 1, a semaphore is used.
Uncomment this to reduce the dependencies of this test. */
# define USE_SEMAPHORE 1
/* Mac OS X provides only named semaphores (sem_open); its facility for
unnamed semaphores (sem_init) does not work. */
# if defined __APPLE__ && defined __MACH__
# define USE_NAMED_SEMAPHORE 1
# else
# define USE_UNNAMED_SEMAPHORE 1
# endif
#endif
#if USE_SEMAPHORE
# include <errno.h>
# include <fcntl.h>
# include <semaphore.h>
# include <unistd.h>
#endif
#if USE_VOLATILE
struct atomic_int {
volatile int value;
};
static void
init_atomic_int (struct atomic_int *ai)
{
}
static int
get_atomic_int_value (struct atomic_int *ai)
{
return ai->value;
}
static void
set_atomic_int_value (struct atomic_int *ai, int new_value)
{
ai->value = new_value;
}
#elif USE_SEMAPHORE
/* This atomic_int implementation can only support the values 0 and 1.
It is initially 0 and can be set to 1 only once. */
# if USE_UNNAMED_SEMAPHORE
struct atomic_int {
sem_t semaphore;
};
#define atomic_int_semaphore(ai) (&(ai)->semaphore)
static void
init_atomic_int (struct atomic_int *ai)
{
sem_init (&ai->semaphore, 0, 0);
}
# endif
# if USE_NAMED_SEMAPHORE
struct atomic_int {
sem_t *semaphore;
};
#define atomic_int_semaphore(ai) ((ai)->semaphore)
static void
init_atomic_int (struct atomic_int *ai)
{
sem_t *s;
unsigned int count;
for (count = 0; ; count++)
{
char name[80];
/* Use getpid() in the name, so that different processes running at the
same time will not interfere. Use ai in the name, so that different
atomic_int in the same process will not interfere. Use a count in
the name, so that even in the (unlikely) case that a semaphore with
the specified name already exists, we can try a different name. */
sprintf (name, "test-lock-%lu-%p-%u",
(unsigned long) getpid (), ai, count);
s = sem_open (name, O_CREAT | O_EXCL, 0600, 0);
if (s == SEM_FAILED)
{
if (errno == EEXIST)
/* Retry with a different name. */
continue;
else
{
perror ("sem_open failed");
fflush (stderr);
abort ();
}
}
else
{
/* Try not to leave a semaphore hanging around on the file system
eternally, if we can avoid it. */
sem_unlink (name);
break;
}
}
ai->semaphore = s;
}
# endif
static int
get_atomic_int_value (struct atomic_int *ai)
{
if (sem_trywait (atomic_int_semaphore (ai)) == 0)
{
if (sem_post (atomic_int_semaphore (ai)))
abort ();
return 1;
}
else if (errno == EAGAIN)
return 0;
else
abort ();
}
static void
set_atomic_int_value (struct atomic_int *ai, int new_value)
{
if (new_value == 0)
/* It's already initialized with 0. */
return;
/* To set the value 1: */
if (sem_post (atomic_int_semaphore (ai)))
abort ();
}
#else
struct atomic_int {
pthread_mutex_t lock;
int value;
};
static void
init_atomic_int (struct atomic_int *ai)
{
pthread_mutexattr_t attr;
ASSERT (pthread_mutexattr_init (&attr) == 0);
ASSERT (pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_NORMAL) == 0);
ASSERT (pthread_mutex_init (&ai->lock, &attr) == 0);
ASSERT (pthread_mutexattr_destroy (&attr) == 0);
}
static int
get_atomic_int_value (struct atomic_int *ai)
{
ASSERT (pthread_mutex_lock (&ai->lock) == 0);
int ret = ai->value;
ASSERT (pthread_mutex_unlock (&ai->lock) == 0);
return ret;
}
static void
set_atomic_int_value (struct atomic_int *ai, int new_value)
{
ASSERT (pthread_mutex_lock (&ai->lock) == 0);
ai->value = new_value;
ASSERT (pthread_mutex_unlock (&ai->lock) == 0);
}
#endif
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