ntdll: Use lockfree implementation for get_cached_fd. (try 2)

[Ken Thomases]

On May 31, 2014, at 12:05 PM, Sebastian Lackner wrote:

> Changes in try 2:
> 
> * Always try to access the fd cache two times - this ensures that we
> don't release a file descriptor when its still in use by a second thread.

Heh.  Well, you can ignore that part of my reply to your previous try.  :)


> * Replace interlocked_xchg() with an assert(). The original code looks
> like its valid that the fd is nonzero at this point, but in fact this
> would cause releasing a file descriptor which is still in use.

I'll leave it to others to comment on that.

> Replacing with an assert() also saves a couple of CPU cycles.

I understand that this is an attempt to improve performance, but I don't think it's necessary to squeeze every last CPU cycle out of this code.

-Ken