Process & Fork

Hello,

I'm running the following program with two simple processes (the main one
and a forked process):

[
  | i |
  i := 0.
  [ true ] whileTrue: [
    i := i + 1.
    i displayNl.
    (Delay forSeconds: 1) wait
  ]
] fork.

[ true ] whileTrue: [
  Processor yield
]

I was expecting these two processes to run indefinitely, but the program
hangs after printing a few lines:

1
2
3

And then I have to interrupt it.

I'm wondering if there's something basic I'm missing here. Maybe I don't
understand how "Process yield" works, but I thought it was just going to
suspend the current process and let the forked process run.

Any help is appreciated,
    Quenio
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> On 20. Jul 2019, at 21:36, Quenio dos Santos <[hidden email]> wrote:


Hi!


>
> And then I have to interrupt it.
>
> I'm wondering if there's something basic I'm missing here. Maybe I don't
> understand how "Process yield" works, but I thought it was just going to
> suspend the current process and let the forked process run.

Can you try with the master branch? I suspect some known (and fixed) undefined
behavior in 3.2.5.



holger
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I haven't been able to compiler master on MacOS. I installed GCC and
configured as follows, but it still seems to be using CLANG:

$ configure --prefix=/usr/local/Cellar/gcc/9.1.0
--with-gmp=/usr/local/Cellar/gcc/9.1.0
...
$ make
...
cd packages/net && /Applications/Xcode.app/Contents/Developer/usr/bin/make
  CC       gnutls-wrapper.o
  CCLD     gnutls-wrapper
Undefined symbols for architecture x86_64:
  "_gnutls_alert_send", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_alert_send_appropriate", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_anon_allocate_client_credentials", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_anon_free_client_credentials", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_bye", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_certificate_allocate_credentials", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_certificate_free_credentials", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_credentials_set", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_deinit", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_error_is_fatal", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_global_deinit", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_global_init", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_handshake", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_init", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_perror", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_record_recv", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_record_send", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_set_default_priority", referenced from:
      _main in gnutls-wrapper.o
  "_gnutls_transport_set_ptr", referenced from:
      _main in gnutls-wrapper.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
make[3]: *** [gnutls-wrapper] Error 1
make[2]: *** [NetClients.star] Error 2
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2


On Sat, Jul 20, 2019 at 12:00 PM Holger Freyther <[hidden email]> wrote:
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Hi Quenio,

I can't speak for GNU Smalltalk, but yield in general is a tricky business,
and does often not mean what one might think. A good way of thinking of
yield is: "Hi scheduler, I'm not done yet, but if you have something
important to do, I will yield now". In particular, yield MAY be a no-op, so
never put it in a busy-wait loop.

Anyways, puting a delay in the main process makes the two processes take
turns on the cpu. This may be a bug, a feature, or per design, I have
really no idea. Just don't ever put yield in a busy-wait loop, and
everyone will be fine. :-)

/Tommy

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Thanks for the explanation, Tommy.

I did try it with a delay instead of yielding in the main process, but got
the same hanging behavior.

I was looking at the implementation of Delay, and suspect the
non-synchronized queue used there might be causing this problem.

On Sat, 20 Jul 2019 at 17:35 Tommy Pettersson <[hidden email]> wrote:
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If it's not working with a delay in the main process it sounds like a bug.
What if you put a counter in the main process and print it as well, does
the main process stop too, or is it just the forked process?

Btw, on my Linux machine your original example works the way you expect. I
get the output:

   1 2 3 4 5 6 7 ... and so on, until I interrupt it.

Both with v3.2.5 and current master branch.

/Tommy

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It hangs as well when I put the counter on the main process with a delay.

i := 0.
[ true ] whileTrue: [
  i := i + 1.
  i displayNl.
  (Delay forSeconds: 1) wait.
]


$ gst counter.st
1
2
3


On Sun, Jul 21, 2019 at 8:20 AM Tommy Pettersson <[hidden email]> wrote:
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I'm running gst 3.2.5 on Ubuntu 18.04.2 LTS (bionic) and it works fine there.

-----Original Message-----
From: help-smalltalk <help-smalltalk-bounces+mdbratch=[hidden email]> On Behalf Of Quenio dos Santos
Sent: Sunday, July 21, 2019 11:04 AM
To: Tommy Pettersson <[hidden email]>
Cc: [hidden email]
Subject: Re: [Help-smalltalk] Process & Fork

It hangs as well when I put the counter on the main process with a delay.

i := 0.
[ true ] whileTrue: [
  i := i + 1.
  i displayNl.
  (Delay forSeconds: 1) wait.
]


$ gst counter.st
1
2
3


On Sun, Jul 21, 2019 at 8:20 AM Tommy Pettersson <[hidden email]> wrote:
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> On 21. Jul 2019, at 00:59, Quenio dos Santos <[hidden email]> wrote:

Hi!


> I haven't been able to compiler master on MacOS. I installed GCC and configured as follows, but it still seems to be using CLANG:


You can use CC=/usr/loca.../gcc on configure and make ti pick GCC but either clang or
gcc should be fine.


> $ configure --prefix=/usr/local/Cellar/gcc/9.1.0 --with-gmp=/usr/local/Cellar/gcc/9.1.0
> ...
> $ make
> ...
> cd packages/net && /Applications/Xcode.app/Contents/Developer/usr/bin/make
>   CC       gnutls-wrapper.o
>   CCLD     gnutls-wrapper

can you use make V=1 to show me the link line? It seems it is not linking to GNUtls at all.
Maybe have a look at config.log as well to see how gnutls support was found.

But. At this stage you should already have a ./gst in the build/src directory. Can you see
if it handles the process switching better?



holger
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Hello Holger,

I've run into more problems as seen below.

At this point, I'm ready to give up on getting the build working on my Mac.

I'll keep using 3.2.5 for small scripts, and I'll start using Pharo for
anything larger.

Thanks for your help,
    Quenio

On Mon, Jul 22, 2019 at 8:53 AM Holger Freyther <[hidden email]> wrote:

On MacOS, the gcc command actually runs CLANG.

I'm getting a segmentation fault when using the built gst:

Quenios-MacBook-Pro:smalltalk-playground quenio$
~/Projects/gnu-smalltalk/smalltalk/gst --kernel-directory
/usr/local/Cellar/gnu-smalltalk/3.2.5_8/share/smalltalk/kernel/ counter.im
"Global garbage collection... done, heap grown"
"Global garbage collection... done, heap grown"
Segmentation fault: 11


>
> holger
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> On 22. Jul 2019, at 20:52, Quenio dos Santos <[hidden email]> wrote:
>
> Hello Holger,
>
> I've run into more problems as seen below.
>
> At this point, I'm ready to give up on getting the build working on my Mac.

I have Macos too and we can share notes.



Was there a reason to provide an image and use the 3.2.5 kernel instead of master?


holger




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Hello Holger,

Sorry for the delay on replying. I got really busy the last couple of days.

I was able to finally get the counter.st running continuously on my Mac
with the master branch:

$ ~/Projects/gnu-smalltalk/smalltalk/gst --kernel-directory
~/Projects/gnu-smalltalk/smalltalk/kernel counter.st
1
2
3
....
225
226
...

It looks like master has the fix for MacOS.

Thanks for your help,
    Quenio


On Tue, Jul 23, 2019 at 12:51 PM Holger Freyther <[hidden email]> wrote:
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> On 26. Jul 2019, at 20:07, Quenio dos Santos <[hidden email]> wrote:
>
> Hello Holger,

Hey!



fantastic. Can you help to get homebrew apply http://git.savannah.gnu.org/cgit/smalltalk.git/commit/?id=72ada189aba0283c551ead16635c1983968080b8?

thank you

holger


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Hi Holger,

I’ll hopefully look into it this weekend. I’ll get back to you when I have
some progress.

Thanks,
    Quenio

On Fri, 26 Jul 2019 at 09:32 Holger Freyther <[hidden email]> wrote:
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Your two blocks run okay on my Ubuntu 20.04 laptop running 3.2.5 GNU
Smalltalk.



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