[Vm-dev] socketRecordSize is probably not 64-bit friendly

[Eliot Miranda]

Hi David,

On Mar 22, 2015, at 10:58 AM, "David T. Lewis" <lewis at mail.msen.com> wrote:

> 
> On Sun, Mar 22, 2015 at 05:04:12PM +0100, Nicolas Cellier wrote:
>> 
>> Hi,
>> I noticed that SocketPlugin>>socketRecordSize was so defined:
>> socketRecordSize
>>    "Return the size of a Smalltalk socket record in bytes."
>> 
>>    ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [12]
>> 
>> 
>> Shouldn't it have been like its brothers in OSProcessPlugin and AioPlugin:
>> 
>> socketRecordSize
>>    "Return the size of a Smalltalk socket record in bytes."
>> 
>>    ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [Smalltalk wordSize * 3]
>> 
>> 
>> I presume we don't use self sizeof: because the Smalltalk side does not
>> have any idea of what a SQSocket is... (an opaque struct/handle)
> 
> On my machine, sizeof(SQSocket) is 16 for both 32 bits and 64 bits. I would
> have expected it to be 12 for the 32-bit case, but maybe the compiler is
> aligning it differently for some reason.
> 
> In any case, "Smalltalk wordSize * 3" would not be right, because the
> actual data structure is this:
> 
>    typedef struct
>    {
>      int   sessionID;
>      int   socketType;  /* 0 = TCP, 1 = UDP */
>      void  *privateSocketPtr;
>    }  SQSocket, *SocketPtr;
> 
> 
> In order to cover the common cases, it might be best to just change
> the implementation to this:
> 
>     ^ self cCode: 'sizeof(SQSocket)' inSmalltalk: [16]

No, no and thrice no!  :). It should /always/ be written 

     ^self sizeof: #SQSocket

and the size answered in a sizeof: implementation marked <doNotGenerate>.  That way 
- there is one def not one in potentially multiple clients
- you don't even need the sizeOfSQSocket method in the first place.

Please see VMMaker.oscog

Eliot (phone)