Re: What's the status of sanei-thread?

From: Karl Heinz Kremer (khk@khk.net)
Date: Mon Jul 02 2001 - 18:35:29 PDT

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    On Mon, Jul 02, 2001 at 11:16:24PM +0200, Oliver Rauch wrote:
    > Is there no driver based command queueing for USB?

    Not for the scanner driver, or at least not without modifications
    to the scanner driver.

    > Also if there is no queueing, you can do:
    >
    > 1) read on buffer1
    > 2) initiate read of buffer2
    > 3) sane_read can get buffer1, when buffer1
    > is empty wait until buffer2 is read (should already
    > be done) and initiate read of buffer1 again.
    > etc.
    >
    > There are two problems with the reader_process
    > 1) fork does not work on all systems

    My plan actually was to make this a compile time option so that the
    original non-read-process version would still be available.

    > 2) the pipe as IPC is not very good because the
    > buffer is very small (about 4KB on most systems).
    > This can(unnecessaryly) slow down scanning on slow
    > systems.

    Pipes are not the only IPC mechanism. Shared memory would probably be
    a lot faster. This of course may open up a totally different can of
    incompatibility worms.

    Do you have any comparison data between a non-threaded and the threaded
    approach?

    What was the original idea behind implementing the second process in
    some of the backends?

    Karl Heinz

    -- 
    Karl Heinz Kremer                                  khk@khk.net
    PGP Key at http://www.freecolormanagement.com/download/khk.asc
    EPSON Sane Backend:         http://www.freecolormanagement.com
    


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