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Re: [libvirt] PATCH: 8/25: Concurrent dispatch of RPC methods

Jim Meyering <jim meyering net> wrote:
> "Daniel P. Berrange" <berrange redhat com> wrote:
>> This patch re-writes the code for dispatching RPC calls in the
>> remote driver to allow use from multiple threads. Only one thread
>> is allowed to send/recv on the socket at a time though. If another
>> thread comes along it will put itself on a queue and go to sleep.
>> The first thread may actually get around to transmitting the 2nd
>> thread's request while it is waiting for its own reply. It may
>> even get the 2nd threads reply, if its own RPC call is being really
>> slow. So when a thread wakes up from sleeping, it has to check
>> whether its own RPC call has already been processed. Likewise when
>> a thread owning the socket finishes with its own wor, it may have
>> to pass the buck to another thread. The upshot of this, is that
>> we have mutliple RPC calls executing in parallel, and requests+reply
>> are no longer guarenteed to be FIFO on the wire if talking to a new
>> enough server.
>> This refactoring required use of a self-pipe/poll trick for sync
>> between threads, but fortunately gnulib now provides this on Windows
>> too, so there's no compatability problem there.
> Quick summary: dense ;-)
> though lots of moved code.
> I haven't finished,...

Modulo the things I mentioned, and the following nits,
the rest looked fine.

Typo in a comment:

    $ g grep -n EGAIN
    src/remote_internal.c:6110:     * EGAIN

printing a raw errno value (rather than a strerror-style string)
in a DEBUG statement:

    $ g grep -n 'DEB.*, errno'
    src/remote_internal.c:6190: \
      DEBUG("Poll unexpectedly failed %d\n", errno);

comment typos:

    +        /* Two reasons we can be woken up
    +         *  1. Other thread has got our reply ready for us
    +         *  2. Other thread is all done, and its out turn to
    +         *     be the dispatcher to finish waiting for
    +         *     out reply
    +         */

s/its out/it's our/
s/out reply/our reply/

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