Operations on Process in Process Scheduling

Operations on Process in Process Scheduling:

The operating system is responsible for providing a mechanism to create and destroy processes dynamically.

Process Creation:

Parent process creates children processes. The children processes can also create other processes forming a tree of processes.

A process may create zero or more new child processes. Process creation may be limited by the amount of resources that a parent process has. If a parent process creates a child process, child process may create child processes of its own, creating a tree of processes.

When a child process is created, it may be able to obtain resources directly from the parent. It may only be able to obtain a subset of the parent's resources or it must acquire its own resources. It is usually a good idea to limit the resources of child process as a single user process could create hundreds of child processes. Each might be able to acquire resources of their own, leaving no resources for other processes and effectively giving control of the machine to a single user process.

When a process creates a new process, the parent may continue to execute concurrently with its children or it must wait until some or all its children have terminated execution.

In terms of address space, the child may be an exact duplicate of the parent. This would allow the child and parent to communicate very easily as they share the same address space. It should be possible to load a new program into the address space of the child (typically we want the child to do something different to its parent).
It is also possible to create an entirely new process and place a new program into it. This makes it more difficult for the child and parent to communicate since they have nothing in common.

Process Termination:

A process normally terminates when it has finished executing its last statement. It typically tells the operating system by issuing some form of the exit() system call. At this point, if the process is a child it may output some data to its parent. Eventually the process has all its resources removed from it and is no longer part of the job pool.

A child process may be terminated by its parent using the abort () system call. This may occur because the child has asked for too many resources, the child is no longer wanted, or possibly if the parent is terminating. The operating system may or may not allow a child process to continue executing after its parent terminates.

In some instances it does not make sense for the child to keep going, especially if its job was to compute something and to return a result. In other instance, a child process may continue after the parent has finished e.g. a web browser may allow you to download files in the background after the web browser has been closed.