CUPS: end-user usability issues

[Michael Sweet]

Georgi Kuzmanov wrote:
> ...
>  1. When jobs reach a printer via different paths (such as in the
> example above), is there any real coordination between the queues, or
> do they just fight it out so the first queue to get a hold of an open
> socket to port 9100 of that printer gets to send its job first?  What
> happens if the two or more queues are on two or more print servers?
> What is the mechanism which decides the sequence in which jobs 1a,
> 2a, 3a coming through CUPS server A and jobs 1b, 2b, 3b, 4b, 5b, 6b
> and 7b coming through CUPS server B will get printed?

Network printers typically only allow 1 job at a time, so it will be
first-come, first-serve.  It is possible (but unlikely) that one
server/queue will be "starved" by the other server/queue always
accessing the printer before the first one has a chance to retry
the connection.

The sequence of server a/b jobs that get printed is essentially
random, however jobs sent to a single server will always come out
in priority+submission order.

> 2. If an accounting script for job "1a" from CUPS server A gets a
> reading of the page counter by sending a PS or PCL print job
> "before1a" before job 1a and PS or PCL job "after1a" and an
> accounting script for job "2b" form CUPS server B gets a reading of
> the page counter through job "before2b" before, and again through job
> "after2b" after it has sent job 2b, is there a possible racing
> condition, or is there a mechanism that could guarantee the jobs will
> be sent in the order:

The idea is that you keep the connection to the printer open until the
job is completed, and then query the page counter using in-band
methods.  Since you are holding the connection open, only you can
affect the page counter and thus the print job is "atomic".

Out-of-band methods only work when you have a single system talking
to the printer or when the method provides a way to differentiate
between jobs like IPP does...

-- 
______________________________________________________________________
Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software          http://www.easysw.com