Operations on Processes

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.
* Parent is exiting.
= Operating system does not allow child to continue if its parent terminates.
= Cascading termination.
* In Unix, if parent exits children are assigned init as parent