Question

Is there any rules to access shared memory at the same time in multicores?
If one core is writing the shared memory, another core is reading the same memory at the exact same time, is there any problem with that?
SHALL This kind of scenario be avoided?

Answer 1

This is called a race condition and the result of such code will be unpredictable. You HAVE to avoid it. You can either:

• change the algorithm to use separate memory, or
• synchronize access by using atomic operations, or
• synchronize access by using higher-level synchronization constructs, like critical section or a mutex.

As @DanDan said, only reading from several threads is not a problem.