[Glass] Problem with #fork and #performOnServer?

Mariano Martinez Peck via Glass glass at lists.gemtalksystems.com
Mon Jul 3 19:16:02 PDT 2017

On Mon, Jul 3, 2017 at 4:52 PM, Petr Fischer via Glass <
glass at lists.gemtalksystems.com> wrote:

> > Hi guys,
> >
> > I am trying to accomplish something easy: I have a main gem that iterates
> > some "reports" and exports each report into a PDF by calling a unix lib.
> > This PDF export takes some seconds. So what I wanted to do is something
> > like this pseudo code:
> >
> > self reports do: [:aReport | [  System performOnServer: (self
> > pdfExportStringFor: aReport)  ] fork ].
> >
> > What I wanted to do with that is that each unix process for the PDF tool
> > was executed on separate CPU cores than the GEM (my current GemStone
> > license does allow all cores). However, I am not sure I am getting that
> > behavior. It looks like I am still using 1 core and being sequential.
> >
> > Finally, I couldn't even reproduce a single test case with that I had in
> > mind:
> >
> > 1 to: 6 do: [:index |
> > [ System performOnServer: 'tar -zcvf test', index asString, '.tar.gz
> > /home/quuve/GsDevKit_home/server/stones/xxx_333/extents' ] fork.
> > ].
> >
> > I would have expected those lines to burn my server and use 6 cpu cores
> at
> > 100%. But no, nothing happens. What is funny is that if I call the very
> > same line without the #fork I do get the 100% CPU process:
> Just a note:
> tar/gzip is not written with multicore support IMHO, so you always utilize
> single core only to 100%. But there is "parallel gzip" (pigz), which
> definitelly turns CPU cooler to speed.
> Usage: tar --use-compress-program=pigz ...

Sure, that was a dummy example to see CPU in usage and test my thoughts
(not the real unix command called)

> Is performOnServer: really non blocking for whole image/gem (or the whole
> VM simply wait for command to complete)?
Yeah, that's the thing, I think you are right, the #performOnServer: may be
blocking at gem level.

For OSSubprocess I was able to allow specifying/managing none blocking
pipes for standard streams.

And now, I am reading GsHostProcess and it also supports none blocking

I see that #_waitChild does indeed call waitpid() so.... I should be able
to do a busy waiting around #childHasExited

BTW,  for OSSubprocesses I added a SIGCHLD kind of waiting to avoid
polling.... but of course, you must be careful because you may need to
force reading from streams (depending on how much the process writes)



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