Posix mqueue bad file descriptor.

Hi, I trying to make a program with one thread sending a message to a message queue and the other receiving and printing it. This is what I've written so far:

Code:

#include <stdlib.h>
#include <stdio.h>
#include <sched.h>
#include <time.h>
#include <mqueue.h>
#include <pthread.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#define MQUEUE_NAME "/mqueue"

pthread_t send_thread, receive_thread;

pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

struct timespec start_time, end_time, thread_sleep_time;

mqd_t message_queue;
struct mq_attr mqueue_attr;

char msg = 'a';
char msg_received;

unsigned int TimespecToNanosec(struct timespec tspec) {
	unsigned int nanosec = tspec.tv_sec * 1000000000 + tspec.tv_nsec;
	return(nanosec);
}

void* send_task() {
	pthread_mutex_lock(&mtx);
	mqueue_attr.mq_flags = 0;
	mqueue_attr.mq_maxmsg = 2;
	mqueue_attr.mq_msgsize = sizeof(msg);
	mqueue_attr.mq_curmsgs = 0;
	int flags = O_RDWR | O_CREAT;
	mode_t mode  = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
	printf("Opening mqueue \n");	
	if(mq_open(MQUEUE_NAME, flags, mode, &mqueue_attr) == -1) {
		perror("In mq_open ");
		exit(-1);
	}
	printf("Sending message \n");
	if(mq_send(message_queue, (char *) &msg, sizeof(msg), 0) == -1) {
		perror("In mq_send()");
		exit(-1);
	}
	pthread_mutex_unlock(&mtx);
}

void* receive_task() {
	pthread_mutex_lock(&mtx);
	printf("Receiving message \n");
	if(mq_receive(message_queue, (char* ) &msg_received, mqueue_attr.mq_msgsize, 0) == -1) {
		perror("In mq_receive()");
	}
	else printf("Message is: %c \n", msg_received);
	pthread_mutex_unlock(&mtx);
}

int main() {


	pthread_attr_t attr;
	struct sched_param thread_param, main_param;

	thread_param.sched_priority = 90;
	main_param.sched_priority = 80;

	if(sched_setscheduler(0, SCHED_FIFO, &main_param) == -1) {
		perror("sched_setscheduler failed");
		exit(-1);
	}

	pthread_attr_init(&attr);
	pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
	pthread_attr_setschedparam(&attr, &thread_param);

	pthread_create(&send_thread, &attr, send_task, NULL);
	pthread_create(&receive_thread, &attr, receive_task, NULL);
	pthread_join(send_thread, NULL);
	pthread_join(receive_thread, NULL);
	return(0);
}

When I run the program I get a bad file descriptor error in mq_send. Can anyone check the code and tell me what I'm doing wrong? Thanks.

Code:

mq_open(MQUEUE_NAME, flags, mode, &mqueue_attr)

You open a message queue, and then throw it away. How do you intend to send to that message queue later, when you no longer know where it is?