CODEWITHSUNDEEP
cfork
user11672305
user11672305

Reputation: 11

How do I count correctly processes created by fork?

I am having problems with C code about processes that are created with fork given by our professor to figure out the number of processes that it creates.

pid1 = fork();

if (pid1 != 0) {
   pid2 = fork();
   pid3 = fork();
}
else {
   pid4 = fork(); 
}

Upvotes: 0

Views: 54

Answers (1)

ggorlen
ggorlen

Reputation: 56905

Running the code is only somewhat helpful (and can't be done during the exam!)--better to draw a process tree. The rules are that every child process starts execution after the fork call that spawned it, parents have nonzero pid and children have a pid of zero.

         main
       /   |   \
    pid1 pid2 pid3
     /     |
  pid4   pid3

We can see main spawns three children, pid1, pid2 and pid3 (pid1 is trivial and the other two are spawned in the true if block). pid1 goes on to the else portion of the conditional and spawns pid4 before finishing. pid2 is the only trick: it spawns again at pid3 because that's where its execution starts.

Answer:

6 processes in total are created (main and 5 children)

Upvotes: 2

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