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Re: problems in Perl process management

On Wed, May 18, 2005 at 01:01:48PM +1000, Sonam Chauhan wrote:
>[Note, I'm no Cygwin expert, so please correct any misunderstandings.]
>> >>or fix it in this module XS. It's really easy with the cygwin provided
>> >>translation functions.
>> >>   See
>> > After all, Proc::ProcessTable misreports the PID and
>> > PPID only under certain conditions -- this would indicate a complex
>> issue in
>> > Proc::ProcessTable XS code, right?
>> No. Just the translation is needed, but one has to specify somehow which
>>   pid's he wants. The cygwin pid's or the winpid's.
>> Both have their merits and usecases.
>Why are two usecases needed? The code that builds the process table
>(returned by Proc::ProcessTable->table) should return the same PID and PPID
>that 'ps' reports - no exceptions - right? 
>I had a look in Proc::ProcessTable's .xs and os/cygwin.c. There seem to be a
>problem with the process table data returned by this code in the
>OS_get_table() function:
>This defines an internal Cygwin query to return process information:
>	cygwin_getinfo_types query = CW_GETPINFO_FULL;
>This executes the query within a for loop:
>	p = (external_pinfo *) cygwin_internal (query, pid | CW_NEXTPID);
>From what I gather, the root problem is that for some processes (as
>demonstrated by my testcase script), the CW_GETPINFO_FULL query returns:
>1. Invalid PPIDs 

Only PPIDs for cygwin processes are returned.  Everything else should be 0.
Orphaned cygwin processes or processes started from the command line have
a PPID of 1.

>2. WINPID instead of Cygwin PID. 

A cygwin pid can actually be spread across two processes.  You see this with
"ps -W" if you do something like:

  bash -c "exec sleep 20"

in one window and:

  ps -W

in another window.

ps -W will also not always properly report on execed processes in
general.  Since ps -W uses CW_GETPINFO_FULL, you can use that command to
see what is going on.


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