Question

To Implement Mutual Exclusion some Parameters must be taken into consideration. Explain them, Also State the Attempts to Implement Mutual Exclusion.

Answer 1

There are mainly three parameters needed to achieve mutual exclusion. they are:

1. Interrupts.
2. Lock variable or mutex.
3. semaphores.

Interrupts:

• process disables interrupts while entering critical section.
• It re enables interrupts while leaving critical section.
• cpu cannot be switched when interrupts are turned off.
• occurs within kernel of operating system.

Lock or mutex:

• single shared variable initially 0.
• when a process enters critical section it sets lock to 1.
• when it leaves critical section it again sets it back to 0.
• if lock value is already 1 then the process waits.

semaphore:

• integer variable.
• controls access of resources by multiple processors.
• accessed through two operations signal and wait.
• implements mutual exclusion.
• two types: binary semaphore(0 and 1), counting semaphore ( arbitary resource count).

Implementation of mutual exclusion:

• when one process is in critical section no other process can enter it. this is called mutual exclusion.
• when a process wants to enter the critical section it disables all the interrrupts.
• and uses the critical section.
• it will then set the lock variable to 1.
• so no other process can enter the critical section.
• when the process has completed using the critical section it will re enable all the interrupts.
• and set the lock variable back to 0.
• now the other processes can compete to enter the critical section.
• This is also possible using the semaphore variable using the functions signal and wait.
• when a process wants to enter critical section it will call the function wait on the semaphore.
• during this time no other process can enter the critical section.
• when it leaves the critical section it will call the signal function on the semaphore variable.
• and then set the lock variable back to 0.
• hence ensuring mutual exclusion.

hope this was helpful!