会有多少个进程和线程？

Question

How many processes and threads will be created?

pid_t pid;
pid = fork();
if (pid == 0)
{
/* child process */
fork();
thread.create(...);
}
else
{
/* parent process */
fork();
thread.create(...);
}
fork();

I think there are 8 threads and 6 processes.

Answer 1

Let's walk through it line by line (format edits and comments added):

pid_t pid;
pid = fork(); //Parent spawns child 1
if (pid == 0)
{
  /* child process */
  fork(); //Child 1 spawns child 2
  thread.create(...); //Child 1 and child 2 spawn threads 1 and 2 respectively
}
else
{
  /* parent process */
  fork(); //Parent spawns child 3
  thread.create(...); //Parent and child 3 spawn threads 3 and 4 respectively
}
fork(); //Parent and children 1,2, and 3 spawn children 4, 5, 6, and 7

So at the end of our program we have 8 processes and 4 threads.

If you don't believe me try running this program and count the number of times "Thread" and "Process" are printed out.

int main(){
  if(fork()){
    fork();
    printf("Thread\n"); //Simulate spawning a thread that prints "Thread"
  }
  else{
    fork();
    printf("Thread\n"); //Simulate spawning a thread that prints "Thread"
  }
  fork();
  printf("Process\n"); //Have each forked process sound off
}

You also might mean thread_create() instead of thread.create()