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 PHP
msg_stat_queue
MSG_STAT_QUEUE(3) 1 MSG_STAT_QUEUE(3)msg_stat_queue - Returns information from the message queue data structureSYNOPSIS
array msg_stat_queue (resource $queue)
DESCRIPTION msg_stat_queue(3) returns the message queue meta data for the message queue specified by the $queue. This is useful, for example, to deter-
mine which process sent the message that was just received.
PARAMETERS
o $queue
- Message queue resource handle
RETURN VALUES
The return value is an array whose keys and values have the following meanings:
Array structure for msg_stat_queue
+--------------+---------------------------------------------------+
| | |
|msg_perm.uid | |
| | |
| | The uid of the owner of the queue. |
| | |
| | |
|msg_perm.gid | |
| | |
| | The gid of the owner of the queue. |
| | |
| | |
|msg_perm.mode | |
| | |
| | The file access mode of the queue. |
| | |
| | |
| msg_stime | |
| | |
| | The time that the last message was sent to the |
| | queue. |
| | |
| | |
| msg_rtime | |
| | |
| | The time that the last message was received from |
| | the queue. |
| | |
| | |
| msg_ctime | |
| | |
| | The time that the queue was last changed. |
| | |
| | |
| msg_qnum | |
| | |
| | The number of messages waiting to be read from |
| | the queue. |
| | |
| | |
| msg_qbytes | |
| | |
| | The maximum number of bytes allowed in one mes- |
| | sage queue. On Linux, this value may be read and |
| | modified via /proc/sys/kernel/msgmnb. |
| | |
| | |
| msg_lspid | |
| | |
| | The pid of the process that sent the last mes- |
| | sage to the queue. |
| | |
| | |
| msg_lrpid | |
| | |
| | The pid of the process that received the last |
| | message from the queue. |
| | |
+--------------+---------------------------------------------------+
SEE ALSO msg_remove_queue(3), msg_receive(3), msg_get_queue(3), msg_set_queue(3).
PHP Documentation Group MSG_STAT_QUEUE(3)
06-09-2008
[C]Problem removing a message queue
