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

Atomic Operations on Images

The number of applications for simply being able to store randomly into images and buffers is limited. However, GLSL provides many more built-in functions for manipulating images. These include atomic functions that perform simple mathematical operations directly on the image in an atomic fashion. Atomic operations (or atomics) are important in these applications because multiple shader instances could attempt to write to the same memory location. OpenGL does not guarantee the order of operations for shader invocations produced by the same draw command or even between invocations produced by separate drawing commands. It is this undefined ordering that allows OpenGL to be implemented on massively parallel architectures ...