Opening image multiple times - bug or feature?

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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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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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:

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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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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:

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

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


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