#include <assert.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <string.h>

static pthread_mutex_t mutex;
static const int use_dead_thread = 1;

static void
lock_attempt(char *tag)
{
	int error;

	printf("%s: calling pthread_mutex_lock()...\n", tag);
	error = pthread_mutex_lock(&mutex);
	printf("%s: pthread_mutex_lock() finished, returned %d.\n", tag,
	    error);
}

static void
unlock_attempt(char *tag)
{
	int error;

	printf("%s: calling pthread_mutex_unlock()...\n", tag);
	error = pthread_mutex_unlock(&mutex);
	printf("%s: pthread_mutex_unlock() finished, returned %d.\n", tag,
	    error);
}

void *
locker_thread(void *arg)
{
	lock_attempt("Thread (L)");
	return (NULL);
}
void *

unlocker_thread(void *arg)
{
	unlock_attempt("Thread (U)");
	return (NULL);
}

int
main(int argc, char *argv[])
{

	pthread_mutexattr_t mattr;
	pthread_t tid;

        assert(pthread_mutexattr_init(&mattr) == 0);
	assert(pthread_mutexattr_settype(&mattr, PTHREAD_MUTEX_NORMAL) == 0);
	assert(pthread_mutex_init(&mutex, &mattr) == 0);

	printf("\n");
	printf("Checking unlock on mutex owned by non-dead thread.\n");
	printf("--------------------------------------------------\n");
	lock_attempt("Main");
	pthread_create(&tid, NULL, unlocker_thread, (void *)NULL);
	pthread_join(tid, NULL);
	printf("\n");

	pthread_mutex_trylock(&mutex);
	assert(pthread_mutex_unlock(&mutex) == 0);

	printf("Checking unlock on mutex owned by dead thread.\n");
	printf("----------------------------------------------\n");
	pthread_create(&tid, NULL, locker_thread, (void *)NULL);
	pthread_join(tid, NULL);
	unlock_attempt("Main");

	return (0);
}