Similar threads exist but none of them helped. I am getting bad file descriptor error while reading with below code under linux. I also specify queue attributes when cerating with O_CREAT flag. Any idea? Thanks.
#include <stdio.h>
#include <mqueue.h>
#include <pthread.h>
#include <errno.h>
#include <string.h>
#define Log(...) printf(__VA_ARGS__); fflush(stdout)
int error;
void* producer(void* arg) {
Log("producer\n");
mqd_t q = mq_open("/ytm", O_RDWR);
mq_send(q, "kardeshians", sizeof("kardeshians"), 1);
}
void* consumer(void* arg) {
Log("consumer\n");
char buff[32];
mqd_t q = mq_open("/ytm", O_RDONLY);
int prio;
while(1) {
error = mq_receive(q,buff,sizeof(buff), NULL);
if(error) {
printf("read error %d %s\n", errno, strerror(errno));
}
}
}
int main() {
struct mq_attr attr;
attr.mq_maxmsg = 10;
attr.mq_msgsize = 32;
mqd_t queue = mq_open("/ytm", O_CREAT | O_RDWR, 0, &attr);
pthread_t tid;
pthread_create(&tid, 0 , producer, 0);
pthread_create(&tid, 0 , consumer, 0);
while(1);
}
Problem was both with the execute permission and message size. After running as a root and making read buffer size bigger than the mq_msgsize it worked. Thanks for error checking suggestions. Here is the working code:
#include <stdio.h>
#include <mqueue.h>
#include <pthread.h>
#include <errno.h>
#include <string.h>
#define Log(...) printf(__VA_ARGS__); fflush(stdout)
int error;
void* producer(void* arg) {
Log("producer\n");
mqd_t q = mq_open("/ytm", O_RDWR);
if(q == -1) {
printf("mq_open error %d %s\n", errno, strerror(errno));
exit(0);
}
while(1) {
int retval = mq_send(q, "kardeshians\n", sizeof("kardeshians\n"), 1);
if(retval == -1) {
printf("mq_open error %d %s\n", errno, strerror(errno));
exit(0);
}
}
}
void* consumer(void* arg) {
Log("consumer\n");
char buff[64];
mqd_t q = mq_open("/ytm", O_RDONLY);
int prio;
while(1) {
int retval = mq_receive(q,buff,sizeof(buff), NULL);
if(retval == -1) {
printf("read error %d %s\n", errno, strerror(errno));
} else {
printf("got message : %s", buff);
}
}
}
int main() {
struct mq_attr attr;
attr.mq_maxmsg = 10;
attr.mq_msgsize = 32;
mq_unlink ("/ytm");
mqd_t queue = mq_open("/ytm", O_CREAT | O_RDWR, 0, &attr);
pthread_t tid;
pthread_create(&tid, 0 , producer, 0);
pthread_create(&tid, 0 , consumer, 0);
while(1);
}
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