Trying to write a plugin - how to store a pointer

[John M McIntosh]

Handles?
Sure you did, in that case you could use small integers and ignore  
the 32/64 bit issue. With a range check of course on the array you  
are indexing (32 or 64 bit addresses)
and a register as external object and cross check, or do a shutdown/ 
startup check to prevent passing in a bogus handle.

I'll also add you can say rtid := self LIB_NewRuntime: size   of  
course, the compiler will complain, but it will change that  into  
rtid = LIB_NewRuntime(size)


On 23-Jan-06, at 11:00 PM, Andreas Raab wrote:

> > Is there a good way to make it future proof for 64 bit addresses?
>
> Generally, it's safer to use indexes (handles) that the VM maps to  
> appropriate pointers... wait ... I wrote that before, didn't I?
>
> ;-)
>
>
> Todd Blanchard wrote:
>> My plan is to add the class containing the pointer to the startup/  
>> shutdown lists and make them zombies (I can't reasonably re- 
>> animate  them with full state I don't think).
>> So I've got this:
>> primNewRuntime: bytesToAllocate
>>     | rtid size |
>>     self export: true.
>>     self var: #rtid type: 'void *'.
>>     self var: #size type: 'unsigned int'.
>>     size := interpreterProxy positive32BitValueOf:  bytesToAllocate.
>>     rtid := self cCode: 'LIB_NewRuntime(size)'.
>>     ^interpreterProxy positive32BitIntegerFor:  rtid.
>> Look OK?
>> Is there a good way to make it future proof for 64 bit  
>> addresses?   Off the top of my head I can think of:
>> primNewRuntime: bytesToAllocate
>>     | rtid size |
>>     self export: true.
>>     self var: #rtid type: 'void *'.
>>     self var: #size type: 'unsigned int'.
>>     (self cCode: 'sizeof(void*)') = 4 ifTrue:
>>     [
>>         size := interpreterProxy positive32BitValueOf:   
>> bytesToAllocate.
>>         rtid := self cCode: 'LIB_NewRuntime(size)'.
>>         ^interpreterProxy positive32BitIntegerFor:  rtid.
>>     ]
>>     ifFalse:
>>     [
>>         size := interpreterProxy positive64BitValueOf:   
>> bytesToAllocate.
>>         rtid := self cCode: 'LIB_NewRuntime(size)'.
>>         ^interpreterProxy positive64BitIntegerFor:  rtid.
>>     ]
>> Maybe you know a better way?
>> On Jan 23, 2006, at 3:29 PM, John M McIntosh wrote:
>>> Although this seems correct at first, you run into trouble  
>>> because  SmallInteger has a finite range smaller than a 32bit  
>>> integer.
>>> Ignoring the 64bit needs  you would pass the value in as a Oops   
>>> then do this
>>>
>>>     pv := interpreterProxy positive32BitValueOf:  anAddressOops.
>>> or perhaps
>>> use positive64BitIntegerFor:  ?
>>>
>>> on return you do this to pass the bits back.
>>>     ^ interpreterProxy positive32BitIntegerFor:  address
>>>
>>> It's likely you need to look at finalization and registering an   
>>> external object (Smalltalk registerExternalObject: )
>>> to ensure you free things when the smalltalk object is GCed, and  
>>> to  check to see if the object is still valid save after an  
>>> image  restart to
>>> prevent passing in a bogus address which your C plugin would   
>>> cheerfully attempt to use.  MPEGFile has some example code in it.
>>>
>>>
>>> On 23-Jan-06, at 3:01 PM, Todd Blanchard wrote:
>>>
>>>> For various reasons, I'm wanting to build a plugin to a library   
>>>> that requires me to hold onto pointers to things.  This means I   
>>>> need to store the pointer in an ivar in a squeak object and use  
>>>> it  on subsequent calls.
>>>>
>>>> Can I get away with using a SmallInteger for this?  Basically   
>>>> doing something like:
>>>>
>>>> primNewContext
>>>>     | ctx |
>>>>
>>>>     self export: true.
>>>>     self primitive: 'primCreateContext' parameters: #().        
>>>> self var: #ctx type: 'int'.
>>>>     ctx := self cCode: 'LIB_NewContext()'.
>>>>     ^ctx.
>>>>
>>>> primDestroyContext: ctx
>>>>     self export: true.
>>>>     self primitive: 'primDestroyContext' parameters: # 
>>>> (SmallInteger).       self cCode: 'LIB_DestroyContext((void*)ctx)'.
>>>>
>>>> Or is this evil and I should consider a different technique?
>>>> If this is evil, what is the good way to store external  
>>>> addresses  in ivars?
>>>>
>>>> Thanks
>>>
>>>
>>> -- 
>>> ==================================================================== 
>>> == =====
>>> John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
>>> Corporate Smalltalk Consulting Ltd.  http://  
>>> www.smalltalkconsulting.com
>>> ==================================================================== 
>>> == =====
>>>

--
======================================================================== 
===
John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
======================================================================== 
===