Devoptab is not thread safe.

[shinyquagsire23]

Accessing files from one thread while a file operation is ongoing in another can cause one of the threads to hang indefinitely on hardware. It is possible that multiple FSCmdBlocks need to be used per-thread.

Edit: Alternatively, maybe find a way to wait for the cmd block to be processed before doing another operation, don't think it makes a difference either way in terms of performance.

[brett19]

Each operation should allocate its own FSCmdBlock locally on the stack (assuming we are talking about synchronous operations here).