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

You ask a question about reading a variable and later you talk about updating a variable, which implies a read-modify-write operation.

Assuming you really mean the former, the read is safe if it is an atomic operation. For almost all architectures this is true for integers.

There are a few (and rare) exceptions:

• The read is misaligned, for example accessing a 4-byte int at an odd address. Usually you need to force the compiler with special attributes to do some misalignment.
• The size of an int is bigger than the natural size of instructions, for example using 16 bit ints on a 8 bit architecture.
• Some architectures have an artificially limited bus width. I only know of very old and outdated ones, like a 386sx or a 68008.