3) Operations on Process (Process Operations)

PROCESS CREATION
~ Parent process create 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
>>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 OS to delete it (exit)
>>Output data from child to parent (via wait)
>>Process’ resources are deallocated by OS

~ 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 OS do not allow child to continue if its parent terminates
--All children terminated - cascading termination