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.
