Question

1. [15 points] Give careful definitions for each term (in the context of computer operating systems):
   1. Process Control Block

2. Blocking send and Non-blocking send

3. Race condition

4. Critical-Section problem

5. Deadlock

Answer 1

Process Control Block : Process Control Block is a data structure that contains information about the process related to it.The process control block is also known as a task control block.

Structure of the process control block is

Process State Process Number Program Counter Registers Memory Limits List of Open Files Process Control Block (PCB)

Process State

This specifies the process state i.e. new, ready, running, waiting or terminated.

Process Number

This shows the number of the particular process.

Program Counter

This contains the address of the next instruction that needs to be executed in the process.

Registers

This specifies the registers that are used by the process. They may include accumulators, index registers, stack pointers, general purpose registers etc.

List of Open Files

These are the different files that are associated with the process.

Blocking send : Sender blocked until message is received by receiver(by a mailbox),

Non-Blocking Send : The sending process sends a message and can continue other tasks immediately while the message passing mechanism delivers the message.

Race Condition : A race condition is an undesirable situation that occurs when a device or system attempts to perform two or more operations at the same time, but because of the nature of the device or system, the operations must be done in the proper sequence to be done correctly.

Another way to define Race condition

A race condition occurs when two or more threads can access shared data and they try to change it at the same time. Because the thread scheduling algorithm can swap between threads at any time, you don't know the order in which the threads will attempt to access the shared data.

Critical Section Problem :

Critical Section is the part of a program which tries to access shared resources. That resource may be any resource in a computer like a memory location, Data structure, CPU or any IO device.

The critical section cannot be executed by more than one process at the same time; operating system faces the difficulties in allowing and disallowing the processes from entering the critical section.

The critical section problem is used to design a set of protocols which can ensure that the Race condition among the process will never arise.

Process P2 Process P1 Process P3 Process P4

Process P1 Process P4 Process P2 Process P3

Deadlock : A deadlock happens in operating system when two or more processes need some resource to complete their execution that is held by the other process.

Process 1 Resource 1 Resource 2 Process 2 Deadlock in Operating System

In the above diagram, the process 1 has resource 1 and needs to acquire resource 2. Similarly process 2 has resource 2 and needs to acquire resource 1. Process 1 and process 2 are in deadlock as each of them needs the other’s resource to complete their execution but neither of them is willing to relinquish their resources.