Hi Martin,


On Fri, May 22, 2020 at 10:35:08PM +0200, Martin Kuball wrote:
> Hi David,
> 
> I finally found a solution to my problem. Successfully converted 1300 images in
> a couple of minutes. The code I come up with is roughly the following (using
> the wc program here as a proof of concept before switching to tesseract and
> image data for the input):
> 
> | input output stdErr proc accessProtect res err |
> input := ExternalPipe nonBlockingPipe.
> output := ExternalPipe blockingPipe.
> stdErr := ExternalPipe nonBlockingPipe.
> proc := ExternalOSProcess concreteClass
> 	programName: '/usr/bin/wc'
> 	arguments: #('-w')
> 	initialEnvironment: nil.
> proc initialStdIn: input reader.
> proc initialStdOut: output writer.
> proc initialStdErr: stdErr writer.
> accessProtect := Semaphore forMutualExclusion.
> accessProtect critical: [
> 	proc value.
> 	input nextPutAll: 'this is a test'.
> 	input closeWriter.
> 	res := output upToEndOfFile.
> 	err := stdErr upToEndOfFile
> ].
> proc waitForTermination.
> output close.
> stdErr close.
> proc exitStatus ~= 0
> 	ifTrue: [^ 'error ' , proc exitStatus , ': ' , err].
> 	ifFalse: [^res]
> 

I'm glad it worked out for you!

> 
> Mybe it is possible to reuse more of your high-level code. But I wanted low
> overhead and complete control over the input and output streams.


Indeed, it can be interesting to work with this at a lower level so you
can see exactly what is going on.


> 
> By the way uninstalling an older version of OSProcess and installing the new
> one left a OSProcess watcher with an ObsoleteUnixOSProcessAccessor running.

This does not surprise me. That would just be the child process watcher that
was left running after removing all the OSProcess classes, so I guess you would
have to terminate the old process in that case.

> 
> And a final question: If you want to get a deeper understanding of process
> handling in squeak, what would you recomend to read? Is the blue book still a
> good reference?

I think we are talking about two different things here. In Smalltalk, a
process is very lightweight, more like what you would call a thread in most
operating systems today. The blue book descriptions are still very relevant.
There have been some changes and improvements in Squeak over the years, but
the basics would still be the same.

The "processes" in OSProcess are a different thing entirely. These refer to
the processes of the underlying operating system. For an operating system
like Unix (Linux) or Windows, these processes are heavier-weight, and they
carry quite a lot of execution context in addition to the basic schedulable
unit of execution.

If you were to make a comparison, a Process in Squeak is like a "green thread"
in typical operating system lingo.

But to your question - yes I would start with the blue book, and then others
on this list (notably Eliot Miranda) can give explanations of the finer points
and the more recent chnages.

Dave


> 
> Thanks again for your help and the great code.
> 
> Martin
> 
> 
> 
> Am Samstag, 16. Mai 2020, 00:13:19 CEST schrieb David T. Lewis:
> > Hi Martin,
> >
> > On Fri, May 15, 2020 at 09:20:17PM +0200, Martin Kuball wrote:
> > > Am Donnerstag, 14. Mai 2020, 23:27:59 CEST schrieb David T. Lewis:
> > > > On Thu, May 14, 2020 at 09:37:26PM +0200, Martin Kuball wrote:
> > > > > Hi!
> > > > >
> > > > > I'm trying to do some OCR from squeak using tesseract. I installed
> > > > > OSProcess. So far so good. But I don't know what classes to use for
> > > > > stdIn
> > > > > and stdOut. My>
> > > > >
> > > > > code would look something like this:
> > > > > | proc stdIn stdOut d |
> > > > >
> > > > > stdIn := ???
> > > > > stdOut := ???
> > > > > proc := ExternalUnixOSProcess forkAndExec: '/usr/bin/tesseract'
> > > > > arguments:
> > > > > #('-' '-' '--dpi' '100') environment: nil descriptors: (Array with:
> > > > > stdIn
> > > > > with: stdOut with: nil).
> > > > > proc ifNil: [self class noAccessorAvailable].
> > > > > d := Delay forMilliseconds: 50.
> > > > > [proc runState == #complete] whileFalse: [d wait].
> > > > > " and now read the text from stdOut..."
> > > > >
> >  > > > Can someone fill in the blanks or point me to code that does similar
> > > > >
> > > > > things? Thanks very much.
> > > >
> > > > Hi Martin,
> > > >
> > > > First, please also install CommandShell in addition to OSProcess. Get
> > > > the
> > > > latest versions of both OSProcess and CommandShell, regardless of the
> > > > version of Squeak you are using. If you are using SqueakMap to load
> > > > them,
> > > > then please select the versions labelled "(head)".
> > > >
> > > > Start out by trying something like this:
> > > >     OSProcess outputOf: 'tesseract - - --dpi 100'
> > > >
> > > > I'm not sure if this will do what you want but please give it a try,
> > > > and if it does not work I'll try to give a better answer.
> > > >
> > > > This uses a couple of new methods that I added to OSPrecess recently,
> > > > but have not mentioned until now. If it proves to be useful you, you
> > > > will be the first :-)
> > > >
> > > > Assuming that it works, here is what will have happened:
> > > >
> > > > - The argument string is parsed into a unix-style command pipeline
> > > >
> > > > - The pipeline is all objects, with OS process proxies doing the work
> > > >
> > > > - When evaluated, and stderr result will show up in an error notifier
> > > >
> > > >   in your image (proceed though the notifier)
> > > >
> > > > - Command stdout is collected and answered as the result of #outputOf:
> > > >
> > > > I would recommend running this in a debugger so you can step through
> > > > it and see what is going on.
> > > >
> > > > Dave
> > >
> > > Hi Dave,
> > >
> > > thanks for your answer. Acutally I did install CommandShell because I
> > > thougth it might help me understand the usage of OSProcess. And maybe it
> > > will if I give it more time.
> > >
> > > So here is what I did: I configure the following repository:
> > >
> > > MCHttpRepository
> > >
> > > 	location: 'http://www.squeaksource.com/OSProcess'
> > > 	user: ''
> > > 	password: ''
> > >
> > > and installed OSProcess-Base dtl.71, OSProcess-AIO dlt.9 and
> > > OSProcess-Unix
> > > dtl.35. But I do not see any mention of a head label. So where did I go
> > > wrong?
> > From the OSProcess repository, load OSProcess-dtl.118. From the CommandShell
> > repository, load CommandShell-dtl.109. These are currently the most recent
> > versions. Ignore the sub-packages such as "OSProcess-Unix", that is
> > something I did to support Pharo (something of a fools errand if I may say
> > so). All of the sub-packages are included in the full OSProcess and
> > CommandShell packages.
> >
> > A shortcut to do this is:
> >
> > 	Installer ss project: 'OSProcess'; install: 'OSProcess'.
> > 	Installer ss project: 'CommandShell'; install: 'CommandShell'.
> >
> > The "(head)" version labels in the SqueakMap package loader do the same
> > thing, except for the alarming warning messages which you can safely ignore.
> > > The command you suggested worked. At least if I provide the image to
> > > tesseract as a file. I will go on with the debugger and try to find out
> > > how to feed the image data to stdIn.
> >
> > The basic Unix shell redirector operators #> and #< should work. For
> > example, try evaluating this:
> >
> >    OSProcess outputOf: 'cat < /etc/services | edit'
> >
> > I am not familiar with tesseract, but you can probably use the same
> > approach.
> >
> > Dave
> 
> 
> 
> 
>