Solution of critical section problem in Operating System

Solution of critical section problem in Operating System

Two Process Solution:

  Two process solution for P0 and P1.

Algorithm 1:

 

Algorithm 1 satisfy the mutual exclusion condition because only one process can be execute in critical section but it can not satisfy the progress condition.

Algorithm 2:

Algorithm 1 can not retain the status of the process that are currently executing in critical section.

share variable: flag[0 or 1]

initially flag[0]=true;

for P0,

do 

{

  flag[0]=true; //process P0 is ready to enter in CS

while ( flag[1] != true; // check the status P1 process

C.S {P0}

flag [0]=false;

R.S

}

for P1,

do

{

flag[1]=true;

while (flag[0]!=true)

C.S {P1}

flag[1]=false

R.S

}

  

Algorithm 2 satisfy the mutual exclusion condition because only one process execute in the critical section but it can not satisfy the progress condition.

Algorithm 3:

  In Algorithm 3 we combined (Peterson's algorithm) the approach of both algorithm 1 and algorithm 2.

Shared Variable:

flag[0 or 1]=true or false

turn= 0 or 1;

initially-

                 flag[0]=flag[1]=false;

                turn=0 or1;

for P0

do

{

flag[0]true;

turn=0;      //P0 ready to enter in C.S

while(flag [1] =true && turn=1)

do not operation;

< C.S > P0

flag[0]=false;

< R.S >

}while(1);

for P1

do

{

flag[1]=true

turn=1; //P1 ready to enter in C.S

while (flag[0]=true  &&  turn=0)

turn=1;

while( flag[0]= true  &&  turn=0)

do not operation;

< C.S > P1 // P1 begin execution in CS

flag [1] = false

<R.S>

}while(1);

Problem : algorithm 3 satisfy all the three condition of C.S.

Solution:  that is mutual exclusion, progress & bounded waiting.

Mutual Exclusion:

  since at a time only flag [0]=true and turn=0 that is P0 is in critical section.

Progress: suppose both processes P0 and P1 want to enter in critical section.

flag[0]=true;

flag[1]=true;

then if turn=0;

then P0 execute in C.S

else if turn=1

then P1 execute in C.S

hence progress condition is satisfied.

Bounded waiting:

  from the above it is clear that bounded waiting is also satisfy because process must be participate in CS in there second attempt.