[hpoj-devel] Laserjet 1220 hangs on the second job - possible cause

[Tomasz M. <tm...@du...>]

I have the same problem as the one mentioned at the end of the
message:

http://sourceforge.net/mailarchive/message.php?msg_id=2306606

The difference is that the problem happens almost always on my
system. After I print one job and I send another one, the printer
usually hangs as described in the mentioned message. I suspect that
this is caused by a race condition, so whether the printer hangs or
not may depend on computer speed, CPU load etc.

I have Intel Pentium III 800 MHz CPU running Debian Woody. I use CUPS
as a spooler. I have HP Laserjet 1220 connected via USB.

When I investigated the problem, I was using sources from CVS.
I was printing files using ptal-print this way:

ptal-print <test.prn

where test.prn was a CUPS output for some postscript file. I tried it
also with Windows drivers output.

The suspected race condition goes as follows:

- ptal-print sends the job, job data are buffered waiting for ptal-mlcd
  to receive them
- after sending all the data, ptal-print closes a socket and exits
- ptal-mlcd receives part of the job data
- as ptal-mlcd has some reverse data from the previous job (it ended
  with @PJL ECHO EOJ), it tries to send it to ptal-print
- the connection to ptal-print is broken, so ptal-mlcd receives
  SIGPIPE, write failes and (in ExMgr::sessionServiceOutput) it
  duplicates the /dev/null file descriptor in place of the session
  socket
- ptal-mlcd hits EOF on /dev/null when trying to receive the rest of
  the job and the printer does not receive the entire job

I have been redirecting data read in ExMgr::pullForwardData to a file
and the second job was in fact truncated there.

I commented out nullDup call in ExMgr::sessionServiceOutput and
everything started to work fine. I have not yet written a more elegant
solution, but it seems that after a failed write to a session socket,
ptal-mlcd should continue to read from the socket, but drop buffers
waiting to be written to it and all the buffers that will be added to
pReverseBdrQueue later.

Tomasz Malesinski