exfile / file locking

[Alan DeKok]

On Jul 25, 2017, at 8:29 AM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
> What I don't understand is why the code open()s to one FD but returns a dup()d FD to the caller. This seems to accomplish nothing - you're still paying for a context switch on the dup() and it's frankly hard for me to believe that saving the open() is worth the extra code complexity, but I'm assuming there's a reason.

  Hmm... I thought so, but perhaps not...

> Unless I'm missing something, the mutex around the exfile isn't dependent on the dup()ing of the FD?

  It returns from exfile_open() with the mutex held.  So the dup() is done while the mutex is locked.

  The exfile_close() releases the mutex.

  Alan DeKok.