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ipcReadProcess returns empty string, when nil is expected

marcelpreda

Hi *,

I have some problems with ipcReadProcess() calls.

I was expecting when child process end, to get nil so I know when there is nothing to read and to end the loop.

The output that I'm trying to parse is just few lines of text (less then 10 lines).

But the ipcReadProcess() returns empty string and because of it I'm in a loop which never ends.

I was trying to use also the ipcWaitForProcess() before first ipcReadProcess(), but no success too.

After many trials I've ended with a small procedure which doesn't work too, see below.

Any idea?

I'm 100% sure that I've did similar lops in the past (older virtuoso versions) and they were working properly.

virtuoso "sub-version  IC6.1.8-64b.500.6.EHF7461 "  

procedure( TestIpcRead()
 pid = ipcBeginProcess("ls")
 outStr = ipcReadProcess(pid 10)
 while( outStr != nil
 info("Debug outStr = %L\n" outStr)
 outStr = ipcReadProcess(pid)
 )
)

And here is the output is.

Debug outStr = "CDS.log\nCDS.log.17079.gz\nCDS.log.19935\nCDS.log.19935.cdslck\nCDS.log.24278\n"
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""
Debug outStr = ""

Thank you,
Marcel
Parents

  • Hi Marcel,

    The behaviour is the same in IC5141, so it's not changed recently.

    The key is that you have not specified a timeout for the second ipcReadProcess() and hence it is a non-blocking read which only reads buffered data. You can't even then use ipcIsAliveProcess in the loop to determine whether the process is alive or not - because it never has a chance to update the status. 

    If you give a small timeout (e.g. ipcReadProcess(pid 1) for the call within the while loop, it behaves as you are expecting.

    Andrew

  • in reply to Andrew Beckett

    Hi Andrew,

    The timeout argument did the trick, thanks.

    Marcel

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