Faster Virtual Method Dispatch

[James Dunne]

Craig Black wrote:
> Good idea!  I suppose that every time you allocate memory you must always 
> specify a parent node in the hierarchy.  This requires a little more thought 
> than GC, because you have to consider how to organize the hierarchy so that 
> it will be easy to free memory relating to a given task once the task is 
> done.  Such a system is would be very fast, and with just a small amount of 
> preparation, memory leaks are completely eliminated.  It could potentially 
> be faster than traditional memory management, because you don't necessarily 
> have to call free on every block of memory.  Rather, one free could free the 
> entire hierarchy, or a large sub-hierarchy.  Have you experienced any 
> drawbacks?  Does this approach work well with exceptions? threads?  Also, 
> what kind of data structure do you use for this hierarchy?
> 
> -Craig 
> 
> 

Holy geez... Yes it is a good idea, but alas I cannot take credit for 
it.  You point out all the benefits that I've gotten from it so far 
quite accurately. :)

I've only used it with my compiler implementation written in C, so I'll 
discuss my experience relating to that, if that's okay with you...

Drawbacks?  Only that you have to give it that much more thought about 
what to parent to what...  There's no serious runtime penalty - it just 
adds a pointer to the parent's list of children, but that cost is tacked 
on to allocating memory in general.

Exceptions?  I'm coding in C, and I wrote my own pseudo-exception model, 
which makes use of that memory model so I don't even leak memory from 
exceptions... a good thing!

Threads?  Haven't gotten there yet, but I plan to design my threads to 
be completely independent of each other.  It's easy to do when you're 
lexing/parsing/analyzing different source files at the same time.  Only 
need to synchronize when each pass is completed.  I'll look into 
concurrency issues in the allocator code when I get to it.

The data structure is a simple list of child pointers and a single 
parent pointer for each memory block.  Linked lists.  The code still 
relies, of course, on malloc and free to actually get the memory in the 
first place.

-- 
Regards,
James Dunne