What are race conditions?

Race conditions are problems that take place due to the sharing of the same file by several processes. In such a case none of the processes is able to use the shared file. Consider the illustration of a printing queue that maintains the list of all files to be printed. As well consider a file shared by two processes P_A and P_B.

The file has obtained two variables:

                    ‘in’ pointing to the next free slot (N.F.S)                     

and

          ‘out’ pointing to the next job to be executed.       

   Primarily in the file, in=7 and out=4. Let P_A be the first process that uses the file. Then P_A sets its local variable N.F.S=7. However before placing into the queue, an interrupt occurs. At present P_B comes. P_B also sets its local variable N.F.S=7 and is placed in the queue.

Then N.F.S=N.F.S+1 which sets in=8. In such a case while implementing P_A overwrites the slot 7 that is already occupied by P_B. Thus nothing will be printed. Such a condition is an example for race condition.

The file has obtained two variables:

                        'in' pointing to the next free slot (N.F.S)                     

and

          'out' pointing to the next job to be executed.     

Primarily in the file, in=7 and out=4. Let P_A be the first process that uses the file. Then P_A sets its local variable N.F.S=7. However before placing into the queue, an interrupt occurs. At present P_B comes. P_B also sets its local variable N.F.S=7 and is placed in the queue.

Then N.F.S=N.F.S+1 which sets in=8. In such a case while implementing P_A overwrites the slot 7 that is already occupied by P_B. Thus nothing will be printed. Such a condition is an example for race condition.