From: ts <decoux@...>
Date: 2003-06-27T17:21:28+09:00
Subject: Re: collect info about ruby-api

>>>>> "S" == Simon Strandgaard <0bz63fz3m1qt3001@sneakemail.com> writes:

S> I don't know what plruby_call_handler() does.. but it definitly uses
S> Init_stack()  

 plruby_call_handler() is the entry point for plruby : each time that
 postgres need to call a procedural function written in ruby it will call
 plruby_call_handler() 

S> int pl_call_level;   hmmm, don't know what this is either.

 a procedural function written in ruby can call another procedural function
 written in ruby : pl_call_level will say if it's the first call or if it's
 a "recursive" call.

S> Any hints ? :-)

 Normally ruby_init() (which call Init_stack()) must be called at the
 beginning of the program (postgres in this case) to make sure that ruby
 has the right value for the beginning of the stack.

 It's not possible (and I don't want) to modify postgres to be sure that
 ruby_init() will be called at the right place (in main()). The
 consequence is that plruby will call ruby_init() (to initialize ruby) the
 first time that a procedural function written in ruby is called.

 Now where is the problem : imagine this case (the values for the stack are
 just examples) 

 * The first time that postgres call plruby_call_handler() the value of the
 stack is 0xe0000000

  - ruby_init() is called, and ruby will remember that the beginning of
    the stack is 0xe0000000

  - ruby will store VALUE from 0xe0000000 to 0xc0000000 (this is just an
    example) 

 * Another procedural function is called latter (and this is not a
   "recursive" call) but this time the value for the stack is 0xf0000000
   (i.e. postgres use less stack when it call plruby_call_handler())

  - ruby will store VALUE from 0xf0000000 to 0xd0000000

  - if ruby call the GC, the GC will mark the objects from 0xe0000000
    (beginning of the stack when ruby_init() was called) to 0xd0000000.
    When ruby run the sweep phase, it will remove all objects which are
    stored in 0xf0000000-0xe0000000

  - now after the GC, if plruby try to access objects stored in
    0xf0000000-0xe0000000, it just crash.

 * To correct this : each time that plruby_call_handler() is called (and
   this is not a "recursive" call) it call Init_stack() to be sure that
   ruby has the right value for the beginning of the stack when it run the
   GC 



Guy Decoux