From: Michael Witrant <mike@...>
Date: 2002-01-07T22:57:28+09:00
Subject: Segfault with druby and fork

Hello,

While playing with DRb, I experienced some segfaults.
I tried to remove anything not related to the bug from the scripts. You
can find them below.

There are two parts:
* a Hash shared trough DRb
* a script that forks, assigns an DRbUndumped object in the Hash, waits
for the fork to exit, and calls a method on this object (that doesn't
exist anymore, since the fork exited).

I expected the second script to raise an exception because the object
doesn't respond or the remote server doesn't exist. Actually, the two
processes (the fork'ed one and its parent) share the same DRb server.
This might not be a valid DRb usage. Anyway, Ruby always says "[BUG]"
when I run these scripts, so I report it in case it helps.

I tried it with the following versions:
ruby 1.6.2 (2000-12-18) [i386-cygwin]
ruby 1.6.4 (2001-06-04) [i686-linux]
ruby 1.6.6 (2001-12-26) [i686-linux]
ruby 1.7.2 (2002-01-05) [i686-linux]

and dRuby 1.3.4.


Mike.


---------------------------------------- global_hash.rb
require 'drb'

URI = 'druby://localhost:12000'

global_hash = Hash.new
class <<global_hash
    include DRbUndumped
end

DRb.start_service(URI, global_hash)
DRb.thread.join

---------------------------------------- hash_accessor.rb
require 'drb'

class Foo
    include DRbUndumped
end

URI = 'druby://localhost:12000'

def remote_hash
    DRbObject.new(nil, URI)
end

DRb.start_service
name = "testing_segfault"

pid = fork {
    ## change this to false and it works
    if true
	remote_hash[name] = Foo.new
    else
	DRbObject.new(nil, URI)[name] = Foo.new
    end
}
Process.waitpid pid

def shared(name)
    ## change this to false and it works
    if true
	DRbObject.new(nil, URI)[name]
    else
	remote_hash[name]
    end
end

## uncomment this line and it works
# DRbObject.new(nil, URI)[name].inspect
shared(name).inspect

-------------------------------------------

The backtrace from gdb:

#0  0x809cb5a in st_lookup (table=0x0, key=0xbb9 <Address 0xbb9 out of
bounds>,     value=0xbffff0e8) at st.c:253
#1  0x8050d59 in search_method (klass=1075390032, id=3001,
origin=0xbffff124)    at eval.c:252
#2  0x8050d99 in rb_get_method_body (klassp=0xbffff174, idp=0xbffff164, 
    noexp=0xbffff168) at eval.c:270
#3  0x805a0f4 in rb_call (klass=1075390032, recv=1075390072, mid=3001,
argc=0,     argv=0x0, scope=0) at eval.c:4521
#4  0x80554ac in rb_eval (self=1075534992, n=0x401a8aa4) at eval.c:2512
#5  0x8051d68 in eval_node (self=1075534992, node=0x401a8aa4) at
eval.c:1059#6  0x80520ff in ruby_run () at eval.c:1189
#7  0x80509f6 in main (argc=2, argv=0xbffff804, envp=0xbffff810) at
main.c:50