Operations On Process

Process Creation

• Parent process creates children processes, which, in turn create other processes, forming a tree of processes.
• Resource sharing
  -Parent and children share all resources.
  -Children share subset of parent’s resources.
  -Parent and child share no resources.
• Execution
  -Parent and children execute concurrently.
  -Parent waits until children terminate.
  -Address space
  -Child duplicate of parent.
  -Child has a program loaded into it.
• UNIX examples
  -fork system call creates new process
  -fork returns 0 to child , process id of child for parent
  -exec system call used after a fork to replace the process’ memory space with a new program.
  
  

Process Termination

• Process executes last statement and asks the operating system to delete it (exit)
  -Output data from child to parent (via wait)
  -Process’ resources are deallocated by operating system
• Parent may terminate execution of children processes (abort)
  -Child has exceeded allocated resources
  -Task assigned to child is no longer required
• If parent is exiting
  -Some operating system do not allow child to continue if its parent terminates
  -All children terminated - cascading termination