Is it safe to read an integer variable that's being concurrently modified without locking?

Question

Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect re

Answer 1

While it would probably be safe to read ints on 32 bit systems without synchronization. I would not risk it. While multiple concurrent reads are not a problem, I do not like writes to happen at the same time as reads.

I would recommend placing the reads in the Critical Section too and then stress test your application on multiple cores to see if this is causing too much contention. Finding concurrency bugs is a nightmare I prefer to avoid. What happens if in the future some one decides to change the int to a long long or a double, so they can hold larger numbers?

If you have a nice thread library like boost.thread or zthread then you should have read/writer locks. These would be ideal for your situation as they allow multiple reads while protecting writes.