Question

int val = memLoc[index++];

or better yet

int val = memLoc[index++ & 0xFF];

Trying to do a threadsafe read from a shared ring buffer where each call gets the next value – and I’d love it to be lock free if at all possible as it happens a TON. No Boost / C++ 11 allowed 🙁

Answer 1

The only operation here which needs to be synchronized is the increment of the index value. Since this is just a numeric value it can be done without the use of locks via an atomic increment. The rest of the operations you listed are just reads of a shared location and don’t need to be synchronized.

On Win32 making the increment synchronized is done with the InterlockedIncrement function

int oldValue = InterlockedIncrement(&index);
int val = memLoc[oldValue & 0xFF];

There are various synchronized increment functions available on Linux. There is a fairly good discussion about the options on this stackoverflow thread

• How to perform atomic operations on Linux that work on x86, arm, GCC and icc?