In the following pseudo code, how many child processes are created?

fork();
if(fork()==0)
   fork();
fork();

I did not quite understand how if statement is executed and how many child of child processes are created within if statements.

CodePudding user response：

I'll try to see if we can visualise this

Line 1 - fork() generates parent and child_1

Now both of them start running the code

Line 2 - if(fork()==0) is run both in parent and child 1:

1. parent: will generate parent and child_2
2. child_1: will generate child_1 as parent and child_3.

Line 3 - fork() inside if condition, this if condition will be true only for child_2 and child_3, as fork() returns the the id of child when parent is running, and for child id is 0. As child_2 and child_3 are the Childs generated in if condition fork() their id will be 0. After this:

1. child_2: will generate child_2 as parent and child_4.
2. child_3: will generate child_3 as parent and child_5.

After this point we have parent, child_1, child_2, child_3, child_4, child_5 running in parallel.

Now the fork() in Line 4 are run by each of them generating child_6, child_7, child_8, child_9, child_10, child_11 respectively by each of the running process.

That leads to a total of 12 process out of which 1 is parent and 11 are Child processes.
Hence there are a total of 11 child processes.