Process creation and termination In Operating System

In this Presentaion You will learn about Process Creation and Termination In Linux

1. Process creation and termination Agenda of Lecture Why and how process are created Resource Sharing Execution Address Space System Calls

2. Process Creation Tree Hierarchy Question : When a child Process is created , whether the child process will share info with their parent process and how its execution might be?

3. Resource Sharing They may settle three arrangements Parent and children share all resources Child and parent share subset of resources They may share no resources

4. Execution Parent has created a child Process how their execution will go on Parent stops waiting for child to finish itself Either they perform simultaneously Either parents end and child continues

5. Unix & Linux Unix / Linux Parent and child Process Question: If they both look the same and usually if both the process of the same are running what will be the need of it to run?

6. Unix & Linux ( Parent –Child) System calls: Fork() To create a child Process Exit() To terminate a child Process Wait() Parent Process wait for a child Process Exec() Process overwrites itself with another executable program

7. Process Tree in Unix

8. Process Termination Reasons: The allocated resources to the child has been exceeded Parent Process has created lots of child Process Child Process was created for a purpose whose task is completed

9. System Calls …… Fork() When the fork system call is executed a new process is created which consist of copy of the parent process The mechanism allows parent process to communicate easily with the child Synopsis: #include <sys/ types.h > #include< unistd.h > Pid _ t fork(void)

10. Wait() A process created a child process , process calls wait(), until a child process is terminated the parent process will remain in waiting state. Synopsis for wait system call # include <sys/ types.h > #include <sys/ wait.h > pid_t wait( int * stat_loc );

11. Exec() A process that calls EXEC() it will overwrite itself with another executable There is no return value Synopsis of execlp () is given as #include < unistd.h > int execlp ( const char *file, const,char *arg0, ..., const char * argn ,(char *)Null);

12. Sample Code

13. Cooperating Processes Advantages of Cooperating Process Information Sharing Computation speedup Modularity

14. Producer Consumer Problem Over view of the Problem We may have processes which produce something, we place them some where (file/main memory) and then there are processes who will consume these things . The place where these items are placed can be bounded on unbounded

15. Bounded Buffer consumer problem We call space a buffer which is bounded. Process that creates an item place it in an array slot called producer process Process that consume the created item is called consumer problem

16. Buffer Buffer can be filled and empty . If producer produce item at faster rate then consumer consumption then it may get full. In this case if the producer another item then it will have to wait If the buffer is empty then the consumer is consuming at faster rate then producing so then the consumer will have to wait.

17. General Problem Description We have fixed size buffer ,two processes( Producer and Consumer ) .Producer produce the item. P lace it in the right full place in the buffer updates the index variable for the next item to place. Similarly index maintain the index variable which points to the next item to be consumed.

18. Semantics of the problem

19. Solution of the Problem

20. Inter Process Communication The agenda is based on parent and child process communication. Channels required for communication Properties of channels for different communication System calls ( Read and write )

21. Operation for IPC Operation Send A process will send something to another process Operation Receive A process will receive something form the sender process Message that is sent may be unlimited or bounded in terms of bytes

22. Communication means Direct Communication Indirect Communication

23. Communication Channels Provide medium of communication Both communication means employ medium of communication Few question to understand……… How the channels are establish? How we may link two processes How many channels a cooperating process have? What is the capacity of the channels? Is the link is bidirectional or unidirectional?

24. Direct Communication In direct Communication links are establish automatically Between each pair there would be one link Link may be unidirectional or bidirectional Name of the process Message

25. Indirect Communication Sender or receiver doesn’t name to sender process or receiver process and vice versa Example Mail Box It is only possible if the process share the same mail box ( Channel)

26. Issues with indirect communication We have three processes P1, P2 and P3.P1 sends a message and P2,P3 are the receiver. Which Process will receive the message?

27. Solutions

28. Process Synchronization

29. Channels capacity