Opening image multiple times - bug or feature?

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Opening image multiple times - bug or feature?

Schwab,Wilhelm K
Hello all,

I'm getting Ubuntu configured on my new $400 laptop, and just noticed that I can load one Pharo image at least twice w/o any error messages.  Is that good or bad?  I'm inclined to say it is bad, with caveats below.

I mentioned caveats: I have mixed feelings about Pharo's emulated/MDI GUI.  There have been (rare) times when it would have been nice to be able to do something similar on Dolphin.  If there is a reason to run multiple IDEs on one box, having them clearly separated by a single main window has some advantages.

Bill


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Re: Opening image multiple times - bug or feature?

Michael van der Gulik-2


On Fri, Sep 25, 2009 at 7:14 AM, Schwab,Wilhelm K <[hidden email]> wrote:
Hello all,

I'm getting Ubuntu configured on my new $400 laptop, and just noticed that I can load one Pharo image at least twice w/o any error messages.  Is that good or bad?  I'm inclined to say it is bad, with caveats below.

I mentioned caveats: I have mixed feelings about Pharo's emulated/MDI GUI.  There have been (rare) times when it would have been nice to be able to do something similar on Dolphin.  If there is a reason to run multiple IDEs on one box, having them clearly separated by a single main window has some advantages.


Did Pharo implement image locking to prevent this?

You'll notice that if you save code from both running instances, your .changes file will be corrupted. Otherwise it works fine.

Gulik

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Re: Opening image multiple times - bug or feature?

Miguel Cobá
In reply to this post by Schwab,Wilhelm K
El jue, 24-09-2009 a las 15:14 -0400, Schwab,Wilhelm K escribió:
> Hello all,
>
> I'm getting Ubuntu configured on my new $400 laptop, and just noticed that I can load one Pharo image at least twice w/o any error messages.  Is that good or bad?  I'm inclined to say it is bad, with caveats below.
>
Isn't a problem at all, at least as you don't save both images because
the share the changes files.

> I mentioned caveats: I have mixed feelings about Pharo's emulated/MDI GUI.  There have been (rare) times when it would have been nice to be able to do something similar on Dolphin.  If there is a reason to run multiple IDEs on one box, having them clearly separated by a single main window has some advantages.
>

By exploting this feature, you can launch a lot of running images from
the same disk image and, as long as you don't save them, you can, for
example, scale Seaside applications.

> Bill
>
>
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> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
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Miguel Cobá
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Re: Opening image multiple times - bug or feature?

johnmci
In reply to this post by Schwab,Wilhelm K
It's a feature, the virtual machines take care to only open the image  
file as read-only and read it into memory, then close it.
Optionally on the macintosh, and always on the iPhone the image could  
be mmapped by the Virtual memory manager's  file vnode mapper instead  
of being read into memory in a single read.

It's only opened as writeable if you save the image.

The changes and source file if found are opened and managed like so:

/Users/johnmci/Documents/Squeak3.8.0/build/SqueakV39.sources
{If found, this is opened read only}

/Users/johnmci/Shared/PharoCore-1.0-10451-BETA/PharoCore-1.0-10451-
BETA.changes
{If found, this is opened first as read/write, but can fall back to  
read only}

The error generated by not finding the changes/sources depends on your  
image preferences. IE ignore missing changes/source file

On 2009-09-24, at 12:14 PM, Schwab,Wilhelm K wrote:

> Hello all,
>
> I'm getting Ubuntu configured on my new $400 laptop, and just  
> noticed that I can load one Pharo image at least twice w/o any error  
> messages.  Is that good or bad?  I'm inclined to say it is bad, with  
> caveats below.
>
> I mentioned caveats: I have mixed feelings about Pharo's emulated/
> MDI GUI.  There have been (rare) times when it would have been nice  
> to be able to do something similar on Dolphin.  If there is a reason  
> to run multiple IDEs on one box, having them clearly separated by a  
> single main window has some advantages.
>
> Bill
>
>
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

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========================================================================
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squeaker68882
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
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Re: Opening image multiple times - bug or feature?

Douglas Brebner
In reply to this post by Schwab,Wilhelm K
Schwab,Wilhelm K wrote:
> Hello all,
>
> I'm getting Ubuntu configured on my new $400 laptop, and just noticed that I can load one Pharo image at least twice w/o any error messages.  Is that good or bad?  I'm inclined to say it is bad, with caveats below.
>  

It's because unix allows you to open a file for write multiple times.
This also applies to in-image code which can make for interesting
platform dependant bugs when running on platforms that don't allow this,
like windows.

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Re: Opening image multiple times - bug or feature?

johnmci
Actually the WIndows VM use to lie, might still, if you opened a file  
READ/WRITE but it was read only, like on a CD, then the windows VM would
say SURE no problem.  This caused grief for macintosh users using one-
click apps on a CD because we would cause a walkback saying we  
couldn't open
the file READ/WRITE.

The *fix* in etoys was to alter the file open (read/write) and  
silently fall back to saying oops try again (read-only) if it fails.  
Versus fixing all the places
where you opened a file for reading, but as read/write (by default).


On 2009-09-24, at 4:44 PM, Douglas Brebner wrote:

> Schwab,Wilhelm K wrote:
>> Hello all,
>>
>> I'm getting Ubuntu configured on my new $400 laptop, and just  
>> noticed that I can load one Pharo image at least twice w/o any  
>> error messages.  Is that good or bad?  I'm inclined to say it is  
>> bad, with caveats below.
>>
>
> It's because unix allows you to open a file for write multiple times.
> This also applies to in-image code which can make for interesting
> platform dependant bugs when running on platforms that don't allow  
> this,
> like windows.
>
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

--
=
=
=
========================================================================
John M. McIntosh <[hidden email]>   Twitter:  
squeaker68882
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
=
=
=
========================================================================





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Re: Opening image multiple times - bug or feature?

Douglas Brebner
John M McIntosh wrote:
> Actually the WIndows VM use to lie, might still, if you opened a file  
> READ/WRITE but it was read only, like on a CD, then the windows VM would
> say SURE no problem.  This caused grief for macintosh users using one-
> click apps on a CD because we would cause a walkback saying we  
> couldn't open the file READ/WRITE.
>  

The problem I had was code that was written on unix that opened the same
file twice in write mode in the initialization methods. Broke nastily on
windows with confusing exceptions and leaking file handles iirc.


BTW, opening an image twice at the same time on windows give the
"changes file not accessible" popup at startup of the second image.

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Re: Opening image multiple times - bug or feature?

Igor Stasenko
2009/9/25 Douglas Brebner <[hidden email]>:

> John M McIntosh wrote:
>> Actually the WIndows VM use to lie, might still, if you opened a file
>> READ/WRITE but it was read only, like on a CD, then the windows VM would
>> say SURE no problem.  This caused grief for macintosh users using one-
>> click apps on a CD because we would cause a walkback saying we
>> couldn't open the file READ/WRITE.
>>
>
> The problem I had was code that was written on unix that opened the same
> file twice in write mode in the initialization methods. Broke nastily on
> windows with confusing exceptions and leaking file handles iirc.
>
>
> BTW, opening an image twice at the same time on windows give the
> "changes file not accessible" popup at startup of the second image.
>
Right, because on windows you can obtain an exclusive write-lock on a
file for a process and disallow others
to open it for writing.
AFAIK, POSIX systems also allowing locking the file handle through
using ioctl().

> _______________________________________________
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> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>



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Igor Stasenko AKA sig.

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Re: Opening image multiple times - bug or feature?

Douglas Brebner
Igor Stasenko wrote:

> 2009/9/25 Douglas Brebner <[hidden email]>:
>  
>> John M McIntosh wrote:
>>    
>>> Actually the WIndows VM use to lie, might still, if you opened a file
>>> READ/WRITE but it was read only, like on a CD, then the windows VM would
>>> say SURE no problem.  This caused grief for macintosh users using one-
>>> click apps on a CD because we would cause a walkback saying we
>>> couldn't open the file READ/WRITE.
>>>
>>>      
>> The problem I had was code that was written on unix that opened the same
>> file twice in write mode in the initialization methods. Broke nastily on
>> windows with confusing exceptions and leaking file handles iirc.
>>
>>
>> BTW, opening an image twice at the same time on windows give the
>> "changes file not accessible" popup at startup of the second image.
>>
>>    
> Right, because on windows you can obtain an exclusive write-lock on a
> file for a process and disallow others
> to open it for writing.
> AFAIK, POSIX systems also allowing locking the file handle through
> using ioctl().
>
>  


Yep, and windows isn't the only one that does this by default, it's
merely the most common :)


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