Vulkan has just become the world’s first graphics API with a formal memory model.  So, what is a memory model and why should I care?

Khronos has released a provisional Vulkan Memory Model Specification that includes extensions for Vulkan, SPIR-V, and GLSL and gives Vulkan developers additional control over how their shaders synchronize access to should cooperate safely over memory operations in a parallel execution environment. In tandem with the extension specification, Khronos has released memory model extension conformance tests to enable implementers to do early tests on their shader compilers to ensure that the specified memory synchronization is implemented correctly. The memory model will have an Alloy description of the extension functionality to enable formal modeling and experimentation.