Nicholas Clark wrote:

>  On Wed, Jan 29, 2003 at 02:12:01PM +0100, Leopold Toetsch wrote:

>  

> >The variable layout of interpreter->code (actually the packfile) doesn't 

> >fit very good for multiple code segments. There is only one ->byte_code 

> >pointer, the byte_code_size is in bytes and converted zig times into 

> >opcode_t's and so on.


>  Would it be better to store the value as a length in opcode_t's, and convert

>  back to bytes where needed?



Yep. The value in length of op's comes out for free by reading the 
packfile. The length in bytes is not needed at all (AFAIK).


> >3) one PBC file has exactly one const_table (or none if no constants are 

> >used) and may have multiple code segments


>  If I understand you correctly, every time an eval happens, more code is

>  created, and that code's associated constants are appended to the constant

>  table. 



... only if they are not yet there.

>  ... As is, this feels like an effective leak - in a long running process

>  (eg mod_parrot) there is the potential for something to cause repeated

>  evals, where the code is used only once then discarded. The parrot code

>  block can be released, GCed and recycled, but the constant table will keep

>  growing.



Normally constants are folded. I think, there are 2 or 3 kinds of code 
to be evaled:
- code is static - need to be compiled only once
- code changes but constants are the same
- all dynamic

The latter would need a constant_table per eval/code_block, which then 
get's recycled. But as it seems not too easy to detect, if an evaled 
code in a loop does produces always the same constants, it might be 
necessary to always regenerated (and GC) the constant table too.


>  Maybe code blocks should keep their own constants, so that they can be

>  released together. Maybe they should even be in the same bit of allocated

>  memory, so that locality helps caching and VM performance.



Do you like to append the constants to the "normal" code block, to the 
prederefed or to the JITed ;-)


>  Nicholas Clark


leo