The $fork()$ and $exec()$ System Calls

• If one thread in a program calls $fork()$,
  • does the new process duplicate all threads,
  • or is the new process single-threaded?
• Some UNIX systems have chosen to have two versions of $fork()$,
  • one that duplicates all threads
  • and another that duplicates only the thread that invoked the $fork()$ system call.
• Which of the two versions of $fork()$ to use depends on the application.
  • If $exec()$ is called immediately after forking, then duplicating all threads is unnecessary, as the program specified in the parameters to $exec()$ will replace the process. In this instance, duplicating only the calling thread is appropriate.
  • If, however, the separate process does not call $exec()$ after forking, the separate process should duplicate all threads.