Hi!!
This code works if I don't remove the message queue.
In A.c I create 3 processes that send a message in a message queue.
in B.c other 3 processes receive 1 message for each (the messages sent from A), change the value of "dato" and put again the message in the queue.
The processes in A.c receive the modified message and then I should remove the queue.
The answer is: How can I remove the queue after ALL the processes have received the message? I tried with 3 wait(0) but the queue is removed after the first process has received the message and I can't understand why
Code here:
A.c
Code:
#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<unistd.h>
#include<sys/msg.h>
#define key 121121
#define max 20
typedef struct {
long type;
char data[max];
}message;
message mex;
int main(){
int i,n;
int father;
char stringaint[max];
mex.type=357;
int idqueue=msgget(key,IPC_CREAT |0600);
for(i=0;i<3;i++){
father=fork();
if(!father){
sprintf(stringaint,"%d",getpid());
strcpy(mex.dato,stringaint);
printf("The son will send the data with his PID: %s\n",mex.data);
if(msgsnd(idqueue,&mex,sizeof(message),0)==-1)
printf("It's not working!");
if(msgrcv(idqueue,&mex,sizeof(message),getpid(),0)==-1)
printf("\nMessage not received\n");
else
printf("\nMessage received");
i=3;
}
}
for (i=0; i<3; i++)
wait(0);
//Without this part the program works (but I need to remove the queue!)
msgctl(idcoda,IPC_RMID,0);
//
}
B.c
Code:
#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<unistd.h>
#include<sys/msg.h>
#define key 121121
#define max 20
typedef struct {
long type;
char data[max];
}message;
int main(){
int i;
int father;
char str[80];
messaggio temp;
int idqueue=msgget(key,IPC_CREAT |0600);
for(i=0;i<3;i++){
father=fork();
if(!father){
if(msgrcv(idqueue,&temp,sizeof(message),0,0)==-1)
printf("\nB hasn't received the message from A\n");
else
printf("\nB has received the message from A");
temp.type=atoi(temp.data);
printf("\n%d\n", temp.type);
strcat(temp.dato," ADD");
printf("%s\n",temp.data);
if(msgsnd(idqueue,&(temp),sizeof(message),0)==-1)
printf("\nNot working!!");
i=3;
}
}
}
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LEARN ABOUT NETBSD
msgget
MSGGET(2) BSD System Calls Manual MSGGET(2)NAME
msgget -- get message queue identifier
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/msg.h>
int
msgget(key_t key, int msgflg);
DESCRIPTION
The msgget() system call returns the message queue identifier associated with key. A message queue identifier is a unique integer greater
than zero.
A message queue is created if either key is equal to IPC_PRIVATE, or key does not have a message queue identifier associated with it and the
IPC_CREAT bit is set in msgflg. If both the IPC_CREAT bit and the IPC_EXCL bit are set in msgflg, and key has a message queue identifier
associated with it already, the operation will fail.
If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows:
o msg_perm.cuid and msg_perm.uid are set to the effective uid of the calling process.
o msg_perm.gid and msg_perm.cgid are set to the effective gid of the calling process.
o msg_perm.mode is set to the lower 9 bits of msgflg.
o msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.
o msg_qbytes is set to the system wide maximum value for the number of bytes in a queue (MSGMNB).
o msg_ctime is set to the current time.
RETURN VALUES
Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set
to indicate the error.
ERRORS
[EACCES] A message queue is already associated with key and the caller has no permission to access it.
[EEXIST] Both IPC_CREAT and IPC_EXCL are set in msgflg, and a message queue is already associated with key.
[ENOSPC] A new message queue could not be created because the system limit for the number of message queues has been reached.
[ENOENT] IPC_CREAT is not set in msgflg and no message queue associated with key was found.
SEE ALSO msgctl(2), msgrcv(2), msgsnd(2), ftok(3)STANDARDS
The msgget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
HISTORY
Message queues appeared in the first release of AT&T System V UNIX.
BSD May 13, 2004 BSD
06-09-2008
[C]Problem removing a message queue
