Consider the concurrent program:
x:=1;
cobegin
x:= x + x + 1|| x:= x + 2
coend;
Reading and writing of a vairable is atomic, but evaluation of an expression is not atomic. The sum of possible values of variable x at the end of execution of the program is ___.
The above question is from madeeasy test series.
Solution:
1. x=1, run x = x + 2 then x = x + x + 1 finally x will be 7
2. x=1, run x = x + 2 then x = x + x + 1 parallely then x will be 3
3. x=1, run x = x + x + 1 then x = x + 2 finally x = 5
Possible values of x would be 3, 5, 7 and Sum = 15
My Doubt:
Wont there be 1 more case where we run x = x + x + 1 but load only value of highlighted x i.e it becomes x = 1 + x + 1
and after it we will run x = x + 2 i.e x = 1 + 2 = 3
now again running x = 1+ x + 1 and now substituting the value of x as 3
x = 1 + 3 + 1 = 5
