If multiple pixel shader invocations write a value to the same location of a texture, then all of the writes will happen by the time the draw/dispatch call finishes. However you will have no guarantee as to the order in which they occur, so one of the threads will "win" by being last to write its value. If all of the threads are writing the same value then this shouldn't matter, that value should be written to the texture and visible in any subsequent draw/dispatch calls. AFAIK this is guaranteed in D3D, although the public docs are notoriously vague about this sort of thing. The one place you could get into trouble is if you try to read from a location in memory that was written to earlier in the same shader. In such cases writes from one thread group aren't guaranteed to be visible to threads in other thread groups, unless you use globallycoherent to ensure that sync calls wait for pending writes to be finished and flushed across different GPU cores.