Programming

Hi all,
i'm reading Andrew S.Tanenbaum's book --- Modern Operating System.At the part of discussing race condition.And the author gives a solution with using the TSL instruction,say that one process must call the enter_region function before entering the critical regions and call the leave_region after finish hes job,as following:

Code:

enter_region:
       TSL  REGISTER,LOCK
       CMP REGISTER,$0
       JNE enter_region
       RET

leave_region:
      MOVE LOCK,$0
      RET

and i'm ok with that code,but the author gives another similar code and says it is essentially the same as the solution with TSL,code is following:

Code:

enter_region:
       MOVE  REGISTER,$1
       XCHG  REGISTER,LOCK
       CMP    REGISTER,$0
#my question is :
#what if the scheduler choose another process 
#to run now and set the LOCK to 1 and 
#enter the critical region?
       JNE enter_region
       RET

leave_region:
      MOVE LOCK,$0
      RET

---------- Post updated at 04:36 AM ---------- Previous update was at 04:32 AM ----------



---------- Post updated at 04:39 AM ---------- Previous update was at 04:36 AM ----------

sorry I forget now the LOCK is already 1 and no process can enter it.....