I am practicing the IPC message Queue, I have written Below program to send and fetch message from the queue. Program is working fine on Linux Platform.
But when I run the Program on WSL in windows, I see multiple entries ipcs -q with same key and msgqid, Looks like some kind of bug in WSL.
-> uname -a
Linux kumars-pc 5.4.72-microsoft-standard-WSL2 #1 SMP Wed Oct 28 23:40:43 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Below is my program:
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#define MAX_PATHNAME_SIZE 100
#define MAX_MESSAGE_SIZE 100
static struct mymsg {
int msg_type;
char text[MAX_MESSAGE_SIZE];
} msg;
int open_msg_queue(key_t key) {
int id;
if ((id = msgget(key, IPC_CREAT | 0660)) == -1) {
printf("Error while creating msg Queue\n");
return -1;
}
return id;
}
int msg_snd(int id, struct mymsg *buf) {
int status;
size_t msg_size;
msg_size = sizeof(struct mymsg);
if((status = msgsnd(id, buf, msg_size, 0)) == -1) {
printf("Error in appending msg to queue %i\n, %d\n", id, EXIT_FAILURE);
return status;
}
return status;
}
size_t msg_rcv(int id, struct mymsg *buf) {
size_t msg_size;
int length;
length = sizeof(struct mymsg);
if ((msg_size = msgrcv(id, buf, length, 0, 0)) == -1) {
printf("Error in fetching the msg from the queue: %i\n", id);
}
return msg_size;
}
int main(int argc, char *argv[]) {
key_t msg_queue_key;
int msg_queue_id;
int status;
char filepath[MAX_PATHNAME_SIZE];
size_t msg_size;
char mode[2];
if(argc < 3) {
printf("Usage: binary <path> <s/r>");
exit(1);
}
// exit if filename is larger than MAX_PATHNAME_SIZE
if(strlen(argv[1]) > MAX_PATHNAME_SIZE) {
printf("File path too long\n");
exit(1);
}
strcpy(filepath, *++argv);
printf("filepath: %s\n", filepath);
// Create IPC identier key
if ((msg_queue_key = ftok(filepath, 'a')) == -1) {
printf("Error in creating key for message queue\n");
exit(1);
}
printf("key: %x\n", msg_queue_key);
msg_queue_id = open_msg_queue(msg_queue_key);
if (msg_queue_id == -1) {
exit(1);
}
printf("msg_queue_id: %i\n", msg_queue_id);
strcpy(mode, *++argv);
if (strcmp(mode, "s") == 0) {
msg.msg_type = 1;
strcpy(msg.text, "Hello World");
status = msg_snd(msg_queue_id, &msg);
}
if (strcmp(mode, "r") == 0) {
msg_size = msg_rcv(msg_queue_id, &msg);
printf("msg: %s\n", msg.text);
}
}
Before sending the message:
-> ipcs
------ Message Queues --------
key msqid owner perms used-bytes messages
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
------ Semaphore Arrays --------
key semid owner perms nsems
Lets run my program
-> cc basic/IPC/msg_queue.c
-> ./a.out /tmp/test.txt s # s indicates send the message
filepath: /tmp/test.txt
key: 6110e08b
msg_queue_id: 19
Msg is sent, check the ipcs -q entry
-> ipcs -q
------ Message Queues --------
key msqid owner perms used-bytes messages
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
0x6110e08b 19 kumars 660 104 1
As we can see multiple entries with same key and msgqid, I dont know whey it is happening like that.
Lets Consume the Message and again list msg queue entry
-> ./a.out /tmp/test.txt r # r is to fetch msg from the queue
filepath: /tmp/test.txt
key: 6110e08b
msg_queue_id: 19
msg: Hello World
AS you can see msg is fetched properly "Hellow World"
-> ipcs -q
------ Message Queues --------
key msqid owner perms used-bytes messages
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
0x6110e08b 19 kumars 660 0 0
We can see msg is consumed from the Queue, I am just wondering why so many entries
