Will atomic operations block other threads?

Question

I am trying to make \"atomic vs non atomic\" concept settled in my mind. My first problem is I could not find \"real-life analogy\" on that. Like customer/restaurant relationshi

Answer 1

Atomic operation means the system performs an operation in its entirety or not at all. Reading or writing an int64 is atomic (64bits System & 64bits CLR) because the system read/write the 8 bytes in one single operation, readers do not see half of the new value being stored and half of the old value. But be carefull :

long n = 0; // writing 'n' is atomic, 64bits OS & 64bits CLR
long m = n; // reading 'n' is atomic
....// some code
long o = n++; // is not atomic : n = n + 1 is doing a read then a write in 2 separate operations

To make atomicity happens to the n++ you can use the Interlocked API :

long o = Interlocked.Increment(ref n); // other threads are blocked while the atomic operation is running