Race condition: Min and Max range of an integer

Your threads are updating a variable which is is not volatile that means it does not guarantee that every thread will see the updated value of num. Let consider the below execution flow of threads:

Thread 1: 0->1->2 (2 iteration left)
Thread 2: 0->1->2->3 (1 iteration left)
Thread 3: 0->1->2->3 (1 iteration left)
Thread 4: 0->1->2->3 (1 iteration left)
Thread 5: 0->1->2->3 (1 iteration left)

At this point, Thread 1 flushes the value 2 of num to memory and Thread 2,3,4,5 decide to read the num from the memory again (for any reason). Now:

Thread 1: 2->3->4 (completed 2 iteration)
Thread 2: 2->3 (completed 1 iteration)
Thread 3: 2->3 (completed 1 iteration)
Thread 4: 2->3 (completed 1 iteration)
Thread 5: 2->3 (completed 1 iteration)

Thread 1 flushes the value 4 to the memory and after that Theard 2,3,4.. flushes the value to the memory show the current value of the number will be 3 instead of 5

I claim the minimum value possible is 2.

The key to this is the non-atomicity of num++, i.e., it is a read and a write, which may have other operations in between.

Call the threads T1..T5:

• T1 reads 0, T2 reads 0;
• T1 writes 1, and then reads and writes 3 times.
• Then T2 writes 1;
• Then T1 reads 1;
• Then T2-5 do all of their work
• Then, finally, T1 writes 2.

(Note: the result 2 is not dependent either on the number of threads, or the number of iterations, provided there are at least 2 of each.)

But the honest answer to this is: it really doesn't matter. There is a data race, as defined in JLS 17.4.5:

When a program contains two conflicting accesses (§17.4.1 ["Two accesses to (reads of or writes to) the same variable are said to be conflicting if at least one of the accesses is a write."]) that are not ordered by a happens-before relationship, it is said to contain a data race.

(There is an absence of happens-before relationships between the actions in the threads)

So you can't usefully rely on whatever it does. It is simply incorrect code.

(Moreover, I know the answer to this not because of some hard-won battle debugging multithreaded code, or deep technical reading: I know this because I have read this answer before elsewhere. It's a parlour trick, nothing more, and so asking the minimum value isn't a very good interview question).