Re: Sharing a single mutex between a socket and its PCB

  > Seigo Tanimura <[e-mail]> writes:

  > As some socket operations (eg sosend(), soreceive(), ...) modify both
  > a socket and its PCB at once, both of them should be locked by a
  > single mutex.  Since hsu has already locked down struct inpcb, I would
  > like to protect a socket by the mutex of the PCB.

  > In order for the socket subsystem to lock and unlock opaquely, two new
  > usrreq methods will be added:

  > - pru_lock() locks the PCB of a socket.
  > - pru_unlock() unlocks the PCB of a socket.

  > If the PCB has its own mutex, those methods simply lock and unlock the
  > mutex.  Otherwise, those methods lock and unlock the Giant lock.  This
  > is so that we can push down Giant for the socket subsystem later.

  > Comments?

Let's stick with the BSD/OS design, which is to have a separate socket buffer
lock.  It's better for concurrency this way.  (BSD/OS also shows there's no
need to have a separate socket lock.  The socket buffer lock doubles as a
socket lock.)


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