pi_mutex.c

#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <errno.h>

static int stop;

static void sighandler(int sig) {
	fprintf(stdout, "receive signal, set flag.\n");
	stop = 1;
}

static void *thread_start(void *arg) {
	pthread_mutex_t *mutex = arg;

	if (pthread_mutex_lock(mutex) < 0) {
		perror("%s: pthread_mutex_lock");
		return NULL;
	}

	while (stop != -1) {
		fprintf(stdout, "thread %lx is holding the lock...\n", pthread_self());
		sleep(1);
	}

	return NULL;
}

static int mutex_init(pthread_mutex_t *mutex) {
	pthread_mutexattr_t attr;

	pthread_mutexattr_init(&attr);
	pthread_mutexattr_setprotocol(&attr, PTHREAD_PRIO_INHERIT);
	pthread_mutex_init(mutex, &attr);

	return 0;
}

int main(int argc, char *argv[]) {
	pthread_mutex_t mutex;
	pthread_t thread_info;
	int retval;

	if (signal(SIGINT, sighandler) != 0) {
		perror("signal");
		return -1;
	}

	mutex_init(&mutex);

	retval = pthread_create(&thread_info, NULL, thread_start, &mutex);
	if (retval != 0) {
		perror("pthread_create");
		return -1;
	}

	// should failed, return EINTR
	retval = pthread_mutex_trylock(&mutex);
	fprintf(stdout, "pthread_mutex_trylock retval %d: %s\n", retval, strerror(retval));

	while (stop != 1)
		sleep(1);

	stop = -1;

	if (pthread_join(thread_info, NULL) < 0) {
		perror("pthread_join");
		return -1;
	}

	// should success
	retval = pthread_mutex_trylock(&mutex);
	fprintf(stdout, "pthread_mutex_trylock retval %d: %s\n", retval, strerror(retval));

	exit(0);
	return 0;
}