3)OPERATION PROCESS

a)Process Creation

-Parent process create children processes, which, in turn create other processes, forming a tree of processes.

• Resource sharing
  

1. Parent and children share all resources.
   



2. Children share subset of parent’s resources.
   



3. Parent and child share no resources.
   

• Execution
  

1. Parent and children execute concurrently.
   



2. Parent waits until children terminate.

• Address space
  

1. Child duplicate of parent.



2. Child has a program loaded into it.

• UNIX examples
  

1. fork system call creates new process
   



2. exec system call used after a fork to replace the process’ memory space with a new program.
   

b)Process Termination

• Process executes last statement and asks the operating system to decide it (exit).

1. Output data from child to parent (via wait).
   



2. Process resources are deallocated by operating system.

• Parent may terminate execution of children processes (abort).
  

1. Child has exceeded allocated resources.
   



2. Task assigned to child is no longer required.
   

-Parent is exiting.

1. Operating system does not allow child to continue if its parent terminates.
   



2. Cascading termination.