Java Projects - Second Edition

Race conditions

We talk about race conditions when the result of a calculation may be different based on the speed and CPU access of the different parallel running threads. Let's take a look at the following two methods:

   void method1(){
1       a = b; 
2       b = a+1; 
        } 
    void method2(){ 
3       c = b; 
4       b = c+2; 
        }

The order of the lines can be 1234, 1324, 1342, 3412, 3142, or 3142. Any execution order of the four lines may happen that assures that 1 runs before 2 and 3 runs before 4, but there are no other restrictions. Assuming that the value of b is zero at the start, the value of b, is either 1 or 2£ at the end of the execution of the segments. This is almost never what we want. We prefer it if the behavior of our program is not stochastic except, perhaps ...