As an excersise, I wrote a C program that handles Signals and counts them etc. The program itself is actually "working" as intended, however:
The program uses fork() several times, creating a single child first, which in turn then forks two more children (i.e. grandchildren of the top-level parent). The top-level parent waits for the child to finish, and before that, the child waits for its children to finish.
Trying to understand what's going on I printed a little debug message everytime the child code executes (to make sure its only executing once - as intended).
This is what I get though:
Note: Child PID: 28411
Note: Grandchild 2 PID: 28413
Note: Child PID: 28411
Note: Grandchild 1 PID: 28412
Note: Child PID: 28411
Grandchild with PID 28413 called SIGUSR2 1139226 times
Grandchild with PID 28412 called SIGUSR1 1140378 times
Print to console successful
All done!
[Done] exited with code=0 in 5.493 seconds
The first child call is correct, the grandchildren are fine as well. However, the child code, for some reason, is executed two more times. Its also not a new process, since the PID is the same.
This is how I fork the child:
pid_t child = fork();
if (child == -1) {
perror("Failure to fork in main\n");
exit(-1);
}
else if (child == 0) {
childCode();
}
else {
wait(NULL);
}
And this is how I fork the grandchildren:
pid_t grandchild1 = fork();
if (grandchild1 == -1) {
// Error
perror("Failure to fork first grandchild");
}
else if (grandchild1 == 0)
// Grandchild
grandchildCode(1);
else {
// Child
pid_t grandchild2 = fork();
if (grandchild2 == -1) {
// Error
perror("Failure to fork second grandchild");
exit(-1);
}
else if (grandchild2 == 0) {
// Grandchild
grandchildCode(2);
}
else {
// Child
wait(NULL);
}
}
Because I dont want to clutter this thread with useless code, here is the full program on Pastebin: https://pastebin.com/XnZEaaNZ (or should I include it here?)
I would be very thankful for any information on this. I can't figure it out.
