What is Monitor in Operating System

What is Monitor in Operating System:

Monitor: 

 Monitor is a high level implementation technique to solve the critical section problem. It provides abstraction for shared data variable.

 Syntax of monitor is as following-

type  monitor_name = monitor

Section -1 :

  Declaration of shared data variables.

Section-2:

Procedure Procedure_name P1()

{

}

Procedure Procedure_name P2()

{

}

Procedure Procedure_name P3()

{

}

Section - 3: 

   Initialization of code 

{

}

The above monitor code is consist three section-

Section - I:

  

In section first we declare all the shared data items which are use in the given problem.

Section-II:

 

In this section we declare all the methods / operations involve in the given problem.

Section -III:

  In this section we initialize the variables and procedures.

 

To access monitor the process use condition stub as following-

var : x, y : condition ; to access the shared data item only two preemptive are involve [wait () & signal ( ) ].

for example:

To block a process-

x.wait( ) function are used means that all the processes are block until another process resume it.

and Second Operation-

y . signal ( ) means that particular process are resume which are suspended by any other process or operation.

Dining Philosopher Problem using Monitor:

Syntax:

 type monitor name: DP

var : state [ 0 - - - - 4 ] of (hungry, thinking , eat );

var : self [ 0 - - - - -4 ] of condition;

procedure pickup ( i: 0 - - - - 4 ] 

begin 

state [i] =hungry;

test (i) ;

if state [i] != Eat;

self [i] .wait;

end

procedure put-up [ i: 0 - - - - 4 ]

begin

state [i] = thinking;

test (i mod 5 );

test ( i + 1 mod 5 ) ;

end

Procedure test ( i : 0 - - - - 4 )

begin 

if ( state [ i + 4  mod 5] != eat and state [ i + 1 mod 5] != eat and state [i] = hungry

begin

state [i] =Eat ;

self [i] .signal ;

end

End

initialization section:

for ( i=0 ; i<= 4 ; i ++ )

state [i] =think;

Producer Consumer Problem using Monitor:

int itemconut =0;

procedure producer ( )

{

while ( true )

{

item =produceitem( );

if ( itemcount == BUFFER_SIZE )

{

sleep ( );

}

Put itemIntoBuffer (item );

itemcount =itemcount + 1;

if (itemcount = = 1)

{

wakeup ( consumer );

}

}

}

procedure consumer ()

{

while (true)

{

if (itemcount == 0)

{

sleep();

}

item=removeitemformbuffer ();

itemcount = itemcount -1 ;

if(itemcount == BUFFER_SIZE -1 )

{

wakeup (producer);

}

consumeritem (item);

}

}