Process creation and termination

Agenda of Lecture

• Why and how process are created• Resource Sharing• Execution• Address Space• System Calls

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?

Resource Sharing

They may settle three arrangements

1. Parent and children share all resources

2. Child and parent share subset of resources

3. They may share no resources

Execution

Parent has created a child Process how their execution will go on

1. Parent stops waiting for child to finish itself2. Either they perform simultaneously3. Either parents end and child continues

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?

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

Process Tree in Unix

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

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

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);

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);

Sample Code

Cooperating Processes

Advantages of Cooperating Process

• Information Sharing• Computation speedup• Modularity

Producer Consumer Problem

• Over view of the ProblemWe 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

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

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.

General Problem Description

• We have fixed size buffer ,two processes( Producer and Consumer ) .Producer produce the item. Place 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.

Semantics of the problem

Solution of the Problem

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 )

Operation for IPC

• Operation SendA process will send something to another process• Operation ReceiveA process will receive something form the sender processMessage that is sent may be unlimited or

bounded in terms of bytes

Communication means

1. Direct Communication2. Indirect Communication

Communication Channels

• Provide medium of communication• Both communication means employ medium of

communication• Few question to understand………a) How the channels are establish?b) How we may link two processesc) How many channels a cooperating process have?d) What is the capacity of the channels?e) Is the link is bidirectional or unidirectional?

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 processMessage

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)

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?

Solutions

Process Synchronization

Channels capacity