iOS Metal：命令缓冲区执行顺序

Question

Suppose I commit two commands buffers modifying the same texture, generated from the same queue:

var a: MTLCommandBuffer
var b: MTLCommandBuffer
...
a.commit()
b.commit()

Then, suppose I wait for the second one to complete:

b.waitUntilCompleted()

Is it possible that b gets completed before a ? According to the documentation for commit() ,

The command buffer is executed after any command buffers enqueued before it on the same command queue

Does this imply that b will finish executing after a finishes or that it will just begin executing after a begins executing?

Answer 1

From the documentation of commit , assuming here the buffers are in the same queue:

The command buffer is executed after any command buffers enqueued before it on the same command queue.

This is logical since one MTLCommandQueue will only execute one buffer at a time. So b will start executing after a has executed and waiting for it means both will have finished when it has finished.