/* Test of once-only execution in multithreaded situations.
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/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2005. */
#include <config.h>
#if USE_ISOC_THREADS || USE_POSIX_THREADS || USE_ISOC_AND_POSIX_THREADS || USE_WINDOWS_THREADS
/* Whether to enable locking.
Uncomment this to get a test program without locking, to verify that
it crashes. */
#define ENABLE_LOCKING 1
/* Whether to help the scheduler through explicit sched_yield().
Uncomment this to see if the operating system has a fair scheduler. */
#define EXPLICIT_YIELD 1
/* Whether to print debugging messages. */
#define ENABLE_DEBUGGING 0
/* Number of simultaneous threads. */
#define THREAD_COUNT 10
/* Number of operations performed in each thread.
This is quite high, because with a smaller count, say 5000, we often get
an "OK" result even without ENABLE_LOCKING (on Linux/x86). */
#define REPEAT_COUNT 50000
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if EXPLICIT_YIELD
# include <sched.h>
#endif
#if HAVE_DECL_ALARM
# include <signal.h>
# include <unistd.h>
#endif
#include "macros.h"
#if ENABLE_DEBUGGING
# define dbgprintf printf
#else
# define dbgprintf if (0) printf
#endif
#if EXPLICIT_YIELD
# define yield() sched_yield ()
#else
# define yield()
#endif
/* Returns a reference to the current thread as a pointer, for debugging. */
#if defined __MVS__
/* On IBM z/OS, pthread_t is a struct with an 8-byte '__' field.
The first three bytes of this field appear to uniquely identify a
pthread_t, though not necessarily representing a pointer. */
# define pthread_self_pointer() (*((void **) pthread_self ().__))
#else
# define pthread_self_pointer() ((void *) (uintptr_t) pthread_self ())
#endif
/* ------------------------ Test once-only execution ------------------------ */
/* Test once-only execution by having several threads attempt to grab a
once-only task simultaneously (triggered by releasing a read-write lock). */
static pthread_once_t fresh_once = PTHREAD_ONCE_INIT;
static int ready[THREAD_COUNT];
static pthread_mutex_t ready_lock[THREAD_COUNT];
#if ENABLE_LOCKING
static pthread_rwlock_t fire_signal[REPEAT_COUNT];
#else
static volatile int fire_signal_state;
#endif
static pthread_once_t once_control;
static int performed;
static pthread_mutex_t performed_lock;
static void
once_execute (void)
{
ASSERT (pthread_mutex_lock (&performed_lock) == 0);
performed++;
ASSERT (pthread_mutex_unlock (&performed_lock) == 0);
}
static void *
once_contender_thread (void *arg)
{
int id = (int) (intptr_t) arg;
int repeat;
for (repeat = 0; repeat <= REPEAT_COUNT; repeat++)
{
/* Tell the main thread that we're ready. */
ASSERT (pthread_mutex_lock (&ready_lock[id]) == 0);
ready[id] = 1;
ASSERT (pthread_mutex_unlock (&ready_lock[id]) == 0);
if (repeat == REPEAT_COUNT)
break;
dbgprintf ("Contender %p waiting for signal for round %d\n",
pthread_self_pointer (), repeat);
#if ENABLE_LOCKING
/* Wait for the signal to go. */
ASSERT (pthread_rwlock_rdlock (&fire_signal[repeat]) == 0);
/* And don't hinder the others (if the scheduler is unfair). */
ASSERT (pthread_rwlock_unlock (&fire_signal[repeat]) == 0);
#else
/* Wait for the signal to go. */
while (fire_signal_state <= repeat)
yield ();
#endif
dbgprintf ("Contender %p got the signal for round %d\n",
pthread_self_pointer (), repeat);
/* Contend for execution. */
ASSERT (pthread_once (&once_control, once_execute) == 0);
}
return NULL;
}
static void
test_once (void)
{
int i, repeat;
pthread_t threads[THREAD_COUNT];
/* Initialize all variables. */
for (i = 0; i < THREAD_COUNT; i++)
{
pthread_mutexattr_t attr;
ready[i] = 0;
ASSERT (pthread_mutexattr_init (&attr) == 0);
ASSERT (pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_NORMAL) == 0);
ASSERT (pthread_mutex_init (&ready_lock[i], &attr) == 0);
ASSERT (pthread_mutexattr_destroy (&attr) == 0);
}
#if ENABLE_LOCKING
for (i = 0; i < REPEAT_COUNT; i++)
ASSERT (pthread_rwlock_init (&fire_signal[i], NULL) == 0);
#else
fire_signal_state = 0;
#endif
#if ENABLE_LOCKING
/* Block all fire_signals. */
for (i = REPEAT_COUNT-1; i >= 0; i--)
ASSERT (pthread_rwlock_wrlock (&fire_signal[i]) == 0);
#endif
/* Spawn the threads. */
for (i = 0; i < THREAD_COUNT; i++)
ASSERT (pthread_create (&threads[i], NULL,
once_contender_thread, (void *) (intptr_t) i)
== 0);
for (repeat = 0; repeat <= REPEAT_COUNT; repeat++)
{
/* Wait until every thread is ready. */
dbgprintf ("Main thread before synchronizing for round %d\n", repeat);
for (;;)
{
int ready_count = 0;
for (i = 0; i < THREAD_COUNT; i++)
{
ASSERT (pthread_mutex_lock (&ready_lock[i]) == 0);
ready_count += ready[i];
ASSERT (pthread_mutex_unlock (&ready_lock[i]) == 0);
}
if (ready_count == THREAD_COUNT)
break;
yield ();
}
dbgprintf ("Main thread after synchronizing for round %d\n", repeat);
if (repeat > 0)
{
/* Check that exactly one thread executed the once_execute()
function. */
if (performed != 1)
abort ();
}
if (repeat == REPEAT_COUNT)
break;
/* Preparation for the next round: Initialize once_control. */
memcpy (&once_control, &fresh_once, sizeof (pthread_once_t));
/* Preparation for the next round: Reset the performed counter. */
performed = 0;
/* Preparation for the next round: Reset the ready flags. */
for (i = 0; i < THREAD_COUNT; i++)
{
ASSERT (pthread_mutex_lock (&ready_lock[i]) == 0);
ready[i] = 0;
ASSERT (pthread_mutex_unlock (&ready_lock[i]) == 0);
}
/* Signal all threads simultaneously. */
dbgprintf ("Main thread giving signal for round %d\n", repeat);
#if ENABLE_LOCKING
ASSERT (pthread_rwlock_unlock (&fire_signal[repeat]) == 0);
#else
fire_signal_state = repeat + 1;
#endif
}
/* Wait for the threads to terminate. */
for (i = 0; i < THREAD_COUNT; i++)
ASSERT (pthread_join (threads[i], NULL) == 0);
}
/* -------------------------------------------------------------------------- */
int
main ()
{
#if HAVE_DECL_ALARM
/* Declare failure if test takes too long, by using default abort
caused by SIGALRM. */
int alarm_value = 600;
signal (SIGALRM, SIG_DFL);
alarm (alarm_value);
#endif
{
pthread_mutexattr_t attr;
ASSERT (pthread_mutexattr_init (&attr) == 0);
ASSERT (pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_NORMAL) == 0);
ASSERT (pthread_mutex_init (&performed_lock, &attr) == 0);
ASSERT (pthread_mutexattr_destroy (&attr) == 0);
}
printf ("Starting test_once ..."); fflush (stdout);
test_once ();
printf (" OK\n"); fflush (stdout);
return test_exit_status;
}
#else
/* No multithreading available. */
#include <stdio.h>
int
main ()
{
fputs ("Skipping test: multithreading not enabled\n", stderr);
return 77;
}
#endif