[squeak-dev] Better VM <-> plugin API

Greg A. Woods; Planix, Inc. woods at planix.ca
Fri Nov 21 17:04:25 UTC 2008

On 21-Nov-2008, at 11:50 AM, Igor Stasenko wrote:

> I was pretty unhappy with some places in VM, where it loads a function
> from plugin by calling ioLoadFunction...
> Also, even more painful to see when one plugin wants to call another
> plugin function.

I know very little about the VM, but I agree what you describe is ugly  
and inelegant, even at a very generic level.

> Now, plugins first, should declare the atoms they would want to use or
> provide. This can be done once at plugin initialization stage, for
> instance:
> static sqInt bitBlitAtom = makeAtom('ioBitBlt');
> Now, after acquiring atom, plugin can register a service fn under  
> this atom:
> registerService(bitBlitAtom, (void*) bitBlt);
> and upon unloading
> unregisterService(bitBlitAtom);
> now, any other plugin can do:
> bitBltFn = getService(bitBlitAtom);

Everything looked good until I got here.

How is another plugin supposed to access this 'bitBlitAtom' handle  
that is effectively always in the first plugin's private storage and  
literally (as you've declared it above) also in the other plugin  
module's private symbol namespace?  (i.e. if it's compiled as a  
"static" variable in the first plugin module then there's no way the  
second plugin can use the same symbol to refer to the same storage)

Perhaps you meant to add a getAtom() function to your API?  Then the  
second plugin would first do:

	static sqInt theAtom;

	theAtom = getAtom("ioBitBlt");

And then it could do the call above as:

	if (theAtom != 0)
		bitBltFn = getService(theAtom);

> if (bitBltFn) { bitBltFn( a, b,c blabla); }

					Greg A. Woods; Planix, Inc.
					<woods at planix.ca>

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