Test and Set Lock(TSL)

Question

In case of TSL we are aware of the following instructions:

 

     1.   TSL LOCK, Ro

     2.   CMP Ro, #0

     3.   JNZ step1

 

Now, the initial value of LOCK is 0

 

If process Po comes and executes line 1 and if it gets preempted, then Ro = 0 and LOCK = 1

Now, If process P1 comes and executes line 1, then it will store the value of LOCK variable(i.e 1) in Ro and set LOCK as 1...right?

Now, suppose P1 gets preempted and Po comes back execute line 2. Now, the value of Ro is set as 1(as P1 made it to 1) and Po should not be able to enter the CS...right? 

 

So, in this way, Po and P1 both will get stuck...right? and so is there a chance of deadlock?

Comments

 

TSL LOCK, Ro -----------> 1) LOAD LOCK ,Ro

                                             2)Store #1,LOCK     [LOCK = 0  vacant]   [LOCK = 1 ---> occupy]

Note that after you LOAD and before you STORE there shouldn't be any preemption , which means this 1) and   2)

instruction executed as a atomic Operation .

P₀ process  ist  load the R0

 

             

 

        

 

 

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I think when p0 will come back it will compare with the previous Ro it has seen i.e 0 , and will compare with o and will enter cs , isn't it @Magma