I am having difficulty in understanding IPC in multiprocess system. I have this system where there are three child
processes that send two types of signals to their process group. There are four types of signal handling
processes responsible for a particular type of signal.
There is this monitoring process which waits for both the signals and then
processes accordingly. When I run this program for a while, the monitoring process doesn't seem to pick up the signal as well as the signal handling process. I could see in the log that the signal is only being generated but not handled at all.
My code is given below
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <signal.h>
#include <unistd.h>
#include <fcntl.h>
#include <cstdio>
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
using namespace std;
double timestamp() {
struct timeval tp;
gettimeofday(&tp, NULL);
return (double)tp.tv_sec + tp.tv_usec / 1000000.;
}
double getinterval() {
srand(time(NULL));
int r = rand()%10 + 1;
double s = (double)r/100;
}
int count;
int count_1;
int count_2;
double time_1[10];
double time_2[10];
pid_t senders[1];
pid_t handlers[4];
pid_t reporter;
void catcher(int sig) {
printf("Signal catcher called for %d",sig);
}
int main(int argc, char *argv[]) {
void signal_catcher_int(int);
pid_t pid,w;
int status;
if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) {
perror("1");
return 1;
}
if(signal(SIGUSR2 ,SIG_IGN) == SIG_ERR) {
perror("2");
return 2;
}
if(signal(SIGINT,signal_catcher_int) == SIG_ERR) {
perror("3");
return 2;
}
//Registering the signal handler
for(int i=0; i<4; i++) {
if((pid = fork()) == 0) {
cout << i << endl;
//struct sigaction sigact;
sigset_t sigset;
int sig;
int result = 0;
sigemptyset(&sigset);
if(i%2 == 0) {
if(signal(SIGUSR2, SIG_IGN) == SIG_ERR) {
perror("2");
return 2;
}
sigaddset(&sigset, SIGUSR1);
sigprocmask(SIG_BLOCK, &sigset, NULL);
} else {
if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) {
perror("2");
return 2;
}
sigaddset(&sigset, SIGUSR2);
sigprocmask(SIG_BLOCK, &sigset, NULL);
}
while(true) {
int result = sigwait(&sigset, &sig);
if(result == 0) {
cout << "The caught signal is " << sig << endl;
}
}
exit(0);
} else {
cout << "Registerd the handler " << pid << endl;
handlers[i] = pid;
}
}
//Registering the monitoring process
if((pid = fork()) == 0) {
sigset_t sigset;
int sig;
int result = 0;
sigemptyset(&sigset);
sigaddset(&sigset, SIGUSR1);
sigaddset(&sigset, SIGUSR2);
sigprocmask(SIG_BLOCK, &sigset, NULL);
while(true) {
int result = sigwait(&sigset, &sig);
if(result == 0) {
cout << "The monitored signal is " << sig << endl;
} else {
cout << "error" << endl;
}
}
} else {
reporter = pid;
}
sleep(3);
//Registering the signal generator
for(int i=0; i<1; i++) {
if((pid = fork()) == 0) {
if(signal(SIGUSR1, SIG_IGN) == SIG_ERR) {
perror("1");
return 1;
}
if(signal(SIGUSR2, SIG_IGN) == SIG_ERR) {
perror("2");
return 2;
}
srand(time(0));
while(true) {
volatile int signal_id = rand()%2 + 1;
cout << "Generating the signal " << signal_id << endl;
if(signal_id == 1) {
killpg(getpgid(getpid()), SIGUSR1);
} else {
killpg(getpgid(getpid()), SIGUSR2);
}
int r = rand()%10 + 1;
double s = (double)r/100;
sleep(s);
}
exit(0);
} else {
cout << "Registered the sender " << pid << endl;
senders[i] = pid;
}
}
while(w = wait(&status)) {
cout << "Wait on PID " << w << endl;
}
}
void signal_catcher_int(int the_sig) {
//cout << "Handling the Ctrl C signal " << endl;
for(int i=0; i<1; i++) {
kill(senders[i],SIGKILL);
}
for(int i=0; i<4; i++) {
kill(handlers[i],SIGKILL);
}
kill(reporter,SIGKILL);
exit(3);
}
Any suggestions?
Here is a sample of the output as well
In the beginning
Registerd the handler 9544
Registerd the handler 9545
1
Registerd the handler 9546
Registerd the handler 9547
2
3
0
Registered the sender 9550
Generating the signal 1
The caught signal is 10
The monitored signal is 10
The caught signal is 10
Generating the signal 1
The caught signal is 10
The monitored signal is 10
The caught signal is 10
Generating the signal 1
The caught signal is 10
The monitored signal is 10
The caught signal is 10
Generating the signal 1
The caught signal is 10
The monitored signal is 10
The caught signal is 10
Generating the signal 2
The caught signal is 12
The caught signal is 12
The monitored signal is 12
Generating the signal 2
Generating the signal 2
The caught signal is 12
The caught signal is 12
Generating the signal 1
The caught signal is 12
The monitored signal is 10
The monitored signal is 12
Generating the signal 1
Generating the signal 2
The caught signal is 12
Generating the signal 1
Generating the signal 2
10
The monitored signal is 10
The caught signal is 12
Generating the signal 1
The caught signal is 12
The monitored signal is GenThe caught signal is TheThe caught signal is 10
Generating the signal 2
Later on
The monitored signal is GenThe monitored signal is 10
Generating the signal 1
Generating the signal 2
The caught signal is 10
The caught signal is 10
The caught signal is 10
The caught signal is 12
Generating the signal 1
Generating the signal 2
Generating the signal 1
Generating the signal 1
Generating the signal 2
Generating the signal 2
Generating the signal 2
Generating the signal 2
Generating the signal 2
Generating the signal 1
The caught signal is 12
The caught signal is 10
The caught signal is 10
Generating the signal 2
Generating the signal 1
Generating the signal 1
Generating the signal 2
Generating the signal 1
Generating the signal 2
Generating the signal 2
Generating the signal 2
Generating the signal 1
Generating the signal 2
Generating the signal 1
Generating the signal 2
Generating the signal 2
The caught signal is 10
Generating the signal 2
Generating the signal 1
Generating the signal 1
As you can see initially, the signal was generated and handled both by my signal handlers and monitoring
processes. But later on the signal was generated a lot, but it was not quite
processes in the same magnitude as before. Further I could see very less signal processing by the monitoring process
Can anyone please provide some insights. What's going on?
