صےےہ

9. Pointer to queue of messages. It is considered as a special case of resources that are usable once. ft
because messages from the OS also queue up to be controlled by a process. 59

10. Pointer to access permissions descriptor for sharing a set of resources globally, and with another Process

11. ID by which identification is made by the process manager .

8.2.2 Management of the Created Processes

Recall process, thread and task definitions in Sections 7.1 to 7.3. A process (or thread or task) is considered
a unit in which sequential running is feasible only under the control of an OS, with each process having a
independent control block (descriptor of the process at an instant). (Recall the PCB and TCB described in
Sections 7.1 and 7.3.)

Process manager is a unit of the OS that is the entity responsible for controlling a process execution. Process
management enables process creation, activation, running, blocking, resumption, deactivation and deletion. A
process manager facilitates the following. Each process of a multiple process (or multitasking or multithreading)
system is executed such that a process state can switch from one to another. A process does the following
sequential execution of the states: ‘created’, ‘ready or activate’, ‘spawn’ (means Create and activate), ‘running’,
‘blocked’ or ‘suspended’, ‘resumed’ and ‘finished’ and ‘ready’ after ‘finish’ (when there is an infinite loop in
a process) and finally ‘deleted’. Blocking and resuming can take place several times in a long process. The
different OSes make the provisions for possible states between creation and deletion differently.

The process manager executes a process request for a resource or OS service and then grants that request
to let the processes share the resources. For example, an LCD display is a shared resource. The LCD display
can be used only by one task or thread at an instance. A running process requests by two methods, which ४९
listed in Table 8.3.

The process manager (i) makes it feasible for a process to sequentially (or concurrently) execute oF block
when needing a resource and to resume when it becomes available; (ii) implements the logical link to te
resource manager for resources management (including scheduling of processes on the CPU); (iii) allows
specific resources sharing between specified processes only; (iv) allocates the resources as per the resource
allocation mechanism of the system and (४) manages the processes and resources of the given system.

A process manager creates the processes, allocates to each a PCB, manages access to resources and facilitates
switching from one process state to another. The PCB defines the process structure for a process-stale-

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