Hi Manoj,
You said , "I also agree but then if child process dies with the parent process then we can never have zombies ", :
I don't undrestand the sentence : "if child process dies with the parent" ?
The situation is :
P0 is the parent of P1.
P1 is the child of P0.
Normal programming is :
1. The parent P0 should execute a wait() function before a child process terminates normally or abnormally.
2. If Child process is not sure that his parent is waiting for him , he will execute the function getppid() function and executes an exit() as soon the function getppid() returns 1 ( that means that the unix init process (pid 1) is the actual parent).
unix init process ( pid one ) inheriets all orphan processes and immediately executes a wait() function as soon as a child process exits ( normal or abnormal exit ).
It's really the Client/Server model from a process point of vue and I implement this solution in 1995.
Of course, after two systems boots !!!
The manner by which the Unix model avoid that is :
P0 forks twice ,
P0 fork and gives P1
P1 fork and gives P2
1.The first instruction of P2 is to loop till getppid() returns 1; getppid means GetParentProcessIdentification. ( init process )
2. The first instruction of P1 is exit() function.
3. P2 became ORPHAN.
4. init process become the actual parent of P2.
5. The function getppid() returns 1 now.
6. The P2 process executes its task.
7. P2 terminates normally or abnormally.
8. init process executes an immediate wait() function.
9. P2 died without being ZAMBIE.
If you follow this protocol, your application will never have zambies processes.
Hope this explain the issue.
Wainting for any discussion.
Magdi
