OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Atomic-Counter Functions

The atomic-counter operations in this section operate atomically with respect to each other. They are atomic for any single counter, meaning any of these operations on a specific counter in one shader instantiation will be indivisible by any of these operations on the same counter from another shader instantiation. There is no guarantee that these operations are atomic with respect to other forms of access to the counter or that they are serialized when applied to separate counters. Such cases would require additional use of fences, barriers, or other forms of synchronization, if atomicity or serialization is desired. The value returned by an atomic-counter function is the value of an atomic counter, which may be returned ...