Critical Section | Critical Section Problem

Critical Section-

 

Before you go through this article, make sure that you have gone through the previous article on Process Synchronization.

 

We have discussed-

• Process Synchronization controls the execution of processes running concurrently so as to produce the consistent results.
• Critical section is a part of the program where shared resources are accessed by the process.

 

Critical Section Problem-

 

• If multiple processes access the critical section concurrently, then results produced might be inconsistent.
• This problem is called as critical section problem.

 

Synchronization Mechanisms-

 

Synchronization mechanisms allow the processes to access critical section in a synchronized manner to avoid the inconsistent results.

 

For every critical section in the program, a synchronization mechanism adds-

• An entry section before the critical section
• An exit section after the critical section

 

 

Entry Section-

 

• It acts as a gateway for a process to enter inside the critical section.
• It ensures that only one process is present inside the critical section at any time.
• It does not allow any other process to enter inside the critical section if one process is already present inside it.

 

Exit Section-

 

• It acts as an exit gate for a process to leave the critical section.
• When a process takes exit from the critical section, some changes are made so that other processes can enter inside the critical section.

 

Criteria For Synchronization Mechanisms-

 

Any synchronization mechanism proposed to handle the critical section problem should meet the following criteria-

 

 

1. Mutual Exclusion
2. Progress
3. Bounded Wait
4. Architectural Neutral

 

1. Mutual Exclusion-

 

The mechanism must ensure-

• The processes access the critical section in a mutual exclusive manner.
• Only one process is present inside the critical section at any time.
• No other process can enter the critical section until the process already present inside it completes.

 

2. Progress-

 

The mechanism must ensure-

• An entry of a process inside the critical section is not dependent on the entry of another process inside the critical section.
• A process can freely enter inside the critical section if there is no other process present inside it.
• A process enters the critical section only if it wants to enter.
• A process is not forced to enter inside the critical section if it does not want to enter.

 

3. Bounded Wait-

 

The mechanism should ensure-

• The wait of a process to enter the critical section is bounded.
• A process gets to enter the critical section before its wait gets over.

 

4. Architectural Neutral-

 

The mechanism should ensure-

• It can run on any architecture without any problem.
• There is no dependency on the architecture.

 

Important Notes-

 

Note-01:

 

• Mutual Exclusion and Progress are the mandatory criteria.
• They must be fulfilled by all the synchronization mechanisms.

 

Note-02:

 

• Bounded waiting and Architectural neutrality are the optional criteria.
• However, it is recommended to meet these criteria if possible.

 

To gain better understanding of Critical Section in OS,

Watch this Video Lecture

 

Next Article- Lock Variable | Synchronization Mechanism

 

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