Forked processes are a traditional way to structure parallel tasks, and they are a fundamental part of the Unix tool set. Forking is a straightforward way to start an independent program, whether it is different from the calling program or not. Forking is based on the notion of copying programs: when a program calls the fork routine, the operating system makes a new copy of that program and its process in memory and starts running that copy in parallel with the original. Some systems don’t really copy the original program (it’s an expensive operation), but the new copy works as if it were a literal copy.
After a fork operation, the original copy of the program is
called the parent process, and the copy
os.fork is called
the child process. In general, parents
can make any number of children, and children can create child
processes of their own; all forked processes run independently and in
parallel under the operating system’s control, and children may
continue to run after their parent exits.
This is probably simpler in practice than in theory, though. The Python script in Example 5-1 forks new child processes until you type the letter q at the console.
Example 5-1. PP4E\System\Processes\fork1.py
"forks child processes until you type 'q'" import os def child(): print('Hello from child', os.getpid()) os._exit(0) # else goes back to parent loop def parent(): while True: newpid = os.fork() if newpid == 0: child() else: print('Hello from parent', os.getpid(), ...