[Vm-dev] [Fwd: Image file loading]

[David T. Lewis]

This proposal is tracked on Mantis for follow up:
  http://bugs.squeak.org/view.php?id=7459

Dave

On Tue, Jan 19, 2010 at 02:30:43PM -0800, Andreas Raab wrote:
> 
> Apologies, accidentally posted to squeak-dev instead of vm-dev.
> 
>   - A.
> 
> -------- Original Message --------
> Subject: Image file loading
> Date: Tue, 19 Jan 2010 14:06:00 -0800
> From: Andreas Raab <andreas.raab at gmx.de>
> Reply-To: The general-purpose Squeak developers list 
> <squeak-dev at lists.squeakfoundation.org>
> To: The general-purpose Squeak developers list 
> <squeak-dev at lists.squeakfoundation.org>
> Newsgroups: gmane.comp.lang.smalltalk.squeak.general
> 
> Folks -
> 
> I think that one of the more clever hacks I did for the Android VM
> deserves proper generalization in the Interpreter. Since on Android the
> image is part of the (compressed) application package it's not easily
> possible to pass a file handle into the VM and have the VM read the
> image as an external file.
> 
> Instead, I'm preloading the image file into memory and then hacked an
> implementation of the sqImageFile* and sqAlloc* functions that would
> basically operate on the image in memory. I think we should formalize
> this idea for two reasons:
> 
> a) It allows preloading the image into memory on platforms where the
> image may not be in an external file.
> 
> b) It trivially allows mmap()ing the entire image into memory (I think
> John does that on the iPhone).
> 
> What I'm proposing is an additional VM entry point, called
> 
>   Interpreter>>readImageFromHeap: heapStart size: heapSize
> 
> which takes to arguments: The pointer to the beginning of the
> (pre-allocated) memory portion where the image file has been loaded or
> mapped and a size for the allocated memory portion. The VM then assumes
> that beginning at heapStart there is an image provided that it needs to
> properly prepare (i.e., perform byte-reversal, pointer adjustment etc).
> 
> The VMs would generally use this along the lines of:
> 
>   memStart = self malloc(heapSize);
>   fread(imageFile, memStart, fsize(imageFile));
>   readImageFromHeapSize(memStart, heapSize);
> 
> and of course a backwards compatible version of
> readImageFromFile:HeapSize:StartingAt: could do the same (although I'd
> rather drop that function altogether since it removes the need for
> supporting various sqImageFile* functions).
> 
> I'd also say that the same pattern should be used for *writing* image
> files, that is we assemble the entire image in memory then call
> sqImageFileWrite(fileName, heapStart, heapSize) and sqImageFileWrite is
> really just a combo of fopen(); fwrite(); fclose();
> 
> I think this scheme is much nicer, less complicated and offers more
> options for implementing image loading than what we currently have.
> 
> Comments?
> 
> Cheers,
>   - Andreas
> 
>