DRb question

ruby-talk
1

I am trying to write a simple remote execution framework, and am running into a
DRb problem I can’t seem to figure out. The system consists of a controller and
a number of clients; the controller sends commands to the clients (these
commands in turn will eventually talk to a server). The problem is that when I
make the same method call twice in a row I see the following error on the
controller side:

Terminal A: running the client:

lizzy:~/public_html/ruby/webrun% ./webrun-client.rb
Starting WebRun service on localhost:12345
WebRunClient.add(u1)
users=[u1]
cmd=load_file

Terminal B: running the controller:

lizzy:~/public_html/ruby/webrun% ./webrun-control.rb
assigning proxy for localhost
#<UserPool:0x8174ba8 @userlist={“u1”=>#<User:0x8174b30 @client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
#<UserPool:0x8174234 @userlist={“u1”=>#<User:0x81741bc @client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
user u1 -> client localhost:12345
execute cmd load_file on client localhost:12345 for users [u1]

2nd call fails:
#<DRb::DRbUnknown:0x8172d44 @buf="\004\010o:\rUserPool\006:\016@userlist{\006"\au1o:\tUser\n:\022@client_class"\016Client_u1:\v@klassc\024User::Client_u1:\016@filename"\fproc.rb:\f@thread0:\n@name"\au1", @name=“User::Client_u1”>
#<DRb::DRbUnknown:0x8172060 @buf="\004\010o:\rUserPool\006:\016@userlist{\006"\au1o:\tUser\n:\022@client_class"\016Client_u1:\v@klassc\024User::Client_u1:\016@filename"\fproc.rb:\f@thread0:\n@name"\au1", @name=“User::Client_u1”>
./webrun.rb:29:in has_user?': undefined methodhas_user?’ for #DRb::DRbUnknown:0x81719d0 (NoMethodError)
from ./webrun.rb:82:in where_is_user' from ./webrun.rb:80:ineach’
from ./webrun.rb:75:in each' from ./webrun.rb:75:ineach’
from ./webrun.rb:87:in where_is_user' from ./webrun.rb:138:inexecute_each_user’
from ./webrun.rb:137:in each' from ./webrun.rb:137:inexecute_each_user’
from ./webrun-control.rb:17

The code is at:

http://lizzy.dyndns.org/~jos/ruby/webrun/webrun.rb
http://lizzy.dyndns.org/~jos/ruby/webrun/webrun-client.rb
http://lizzy.dyndns.org/~jos/ruby/webrun/webrun-control.rb
http://lizzy.dyndns.org/~jos/ruby/webrun/proc.rb

Does anybody have any idea what I could be doing wrong or how to debug this
problem?

Thanks,

···

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’

2

Hi Jos,

I am trying to write a simple remote execution framework, and am running
into a

Interesting … keep us posted.

DRb problem I can’t seem to figure out. The system consists of a
controller and
a number of clients; the controller sends commands to the clients (these
commands in turn will eventually talk to a server).

Looking at the code makes me feel that the controller is a DRb client
and your client is actually a DRb server. Not a big issue at all … just
tripped
me initially.

The problem is that when I
make the same method call twice in a row I see the following error on the
controller side:

Terminal A: running the client:

lizzy:~/public_html/ruby/webrun% ./webrun-client.rb
Starting WebRun service on localhost:12345
WebRunClient.add(u1)
users=[u1]
cmd=load_file

Terminal B: running the controller:

lizzy:~/public_html/ruby/webrun% ./webrun-control.rb
assigning proxy for localhost
#<UserPool:0x8174ba8 @userlist={“u1”=>#<User:0x8174b30
@client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
#<UserPool:0x8174234 @userlist={“u1”=>#<User:0x81741bc
@client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
user u1 → client localhost:12345
execute cmd load_file on client localhost:12345 for users [u1]

2nd call fails:
#<DRb::DRbUnknown:0x8172d44
@buf="\004\010o:\rUserPool\006:\016@userlist{\006
^^^^^^^^^^^^^^^
I tried hard to track down the source of this object … but was not very
successful :frowning:

/webrun.rb:29:in has_user?': undefined method has_user?’ for
#DRb::DRbUnknown:0x81719d0

This was my starting point of investigation

NoMethodError)
from ./webrun.rb:82:in where_is_user' from ./webrun.rb:80:in each’
from ./webrun.rb:75:in each' from ./webrun.rb:75:in each’
from ./webrun.rb:87:in where_is_user' from ./webrun.rb:138:in execute_each_user’
from ./webrun.rb:137:in each' from ./webrun.rb:137:in execute_each_user’
from ./webrun-control.rb:17

Does anybody have any idea what I could be doing wrong or how to debug
this
problem?

Well, I can point you to some obvious typos (see line 15 in webrun.rb):

  @proxy = DRbObject.new(nil, "druby://#@name:#@port")
                                                              ^^^^

^^^^
Don’t you want this to be:

 @proxy = DRbObject.new(nil, "druby://#{@name}:#{@port}")

Search for #@ in your code and you will find few more occurances

And line 17:

 yield @proxy if block_given? and @proxy

I would rewrite as:

yield @proxy if (block_given? and @proxy)

just to be on the safe side…“and” has very low precedence.

Unfortunately, even after changing this and using ruby 1.8.1 on Win XP,
I got the same errors as before. I tried running in the debugger mode (with
-rdebug option) and I got even more errors, even for the first call.

All I can suggest is: try single-threaded, non-distributed version first, if
possible
and slowly introduce the more advanced features. Best of luck !

– shanko

3

Never mind, I found the problem in my code triggering this error after
studying drb.rb and adding some debugging code to it. The User::Client_u1
class apparently wasn’t being defined properly in my code, causing the above
error. @name holds the name of the undefined class/module, which was the clue
I was missing.

DRb rulez :slight_smile:

···

On Sat, Jan 03, 2004 at 02:52:02PM +0900, Jos Backus wrote:

#<DRb::DRbUnknown:0x8172060 @buf=“\004\010o:\rUserPool\006:\016@userlist{\006"\au1o:\tUser\n:\022@client_class"\016Client_u1:\v@klassc\024User::Client_u1:\016@filename"\fproc.rb:\f@thread0:\n@name"\au1”, @name=“User::Client_u1”>
./webrun.rb:29:in has_user?': undefined method has_user?’ for #DRb::DRbUnknown:0x81719d0 (NoMethodError)

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’

4

Jos Backus wrote:

I am trying to write a simple remote execution framework,

Btw, do you know that Phil Tomson’s TaskMaster
http://raa.ruby-lang.org/list.rhtml?name=taskmaster has exactly this
purpose?

(although I don’t know which is its status, nor if it has been ported to
ruby 1.8)

Can you explain in which way your framework is different, please?

Ciao,
Giuliano

···

–
If you want to send me an email in the address you have to write ‘p’,
then a dot, followed by ‘bossi’ at ‘quinary’, another dot and ‘com’ at last

5

#@varname and #$globalname get expanded to #{@varname} and
#{$globalname}. #$0 is seen sometimes in usage messages like this:

STDERR.puts “#$0: some usage message here about how to run this thing”

I tend not to use them, because the {} tell me where interpolation
begins/ends properly.

···

Shashank Date (sdate@everestkc.net) wrote:

Well, I can point you to some obvious typos (see line 15 in webrun.rb):

  @proxy = DRbObject.new(nil, "druby://#@name:#@port")

Don’t you want this to be:

 @proxy = DRbObject.new(nil, "druby://#{@name}:#{@port}")

–
Eric Hodel - drbrain@segment7.net - http://segment7.net
All messages signed with fingerprint:
FEC2 57F1 D465 EB15 5D6E 7C11 332A 551C 796C 9F04

6

Btw, this is with ruby-1.8.1 and dRuby 2.0.4 on a recent FreeBSD -current,
installed from ports. I should also add that what’s weird is that the second
identical call fails in the controller, i.e.:

cp.execute_each_user(:load_file, args, usernames)
puts "\n2nd call fails:"
cp.execute_each_user(:load_file, args, usernames)

I am trying to write a simple remote execution framework, and am running
into a

Interesting … keep us posted.

Sure.

DRb problem I can’t seem to figure out. The system consists of a
controller and
a number of clients; the controller sends commands to the clients (these
commands in turn will eventually talk to a server).

Looking at the code makes me feel that the controller is a DRb client
and your client is actually a DRb server. Not a big issue at all … just
tripped
me initially.

Yeah, that is why I gave the short description. The clients will eventually be
making HTTP calls to a web server, which is why I called them clients, even
though from the controller’s perspective they are really servers.

The problem is that when I
make the same method call twice in a row I see the following error on the
controller side:

Terminal A: running the client:

lizzy:~/public_html/ruby/webrun% ./webrun-client.rb
Starting WebRun service on localhost:12345
WebRunClient.add(u1)
users=[u1]
cmd=load_file

Terminal B: running the controller:

lizzy:~/public_html/ruby/webrun% ./webrun-control.rb
assigning proxy for localhost
#<UserPool:0x8174ba8 @userlist={“u1”=>#<User:0x8174b30
@client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
#<UserPool:0x8174234 @userlist={“u1”=>#<User:0x81741bc
@client_class=“Client_u1”, @name=“u1”, @filename=nil, @thread=nil>}>
user u1 → client localhost:12345
execute cmd load_file on client localhost:12345 for users [u1]

2nd call fails:
#<DRb::DRbUnknown:0x8172d44
@buf="\004\010o:\rUserPool\006:\016@userlist{\006
^^^^^^^^^^^^^^^
I tried hard to track down the source of this object … but was not very
successful :frowning:

Same here :frowning:

/webrun.rb:29:in has_user?': undefined method has_user?’ for
#DRb::DRbUnknown:0x81719d0

This was my starting point of investigation

NoMethodError)
from ./webrun.rb:82:in where_is_user' from ./webrun.rb:80:in each’
from ./webrun.rb:75:in each' from ./webrun.rb:75:in each’
from ./webrun.rb:87:in where_is_user' from ./webrun.rb:138:in execute_each_user’
from ./webrun.rb:137:in each' from ./webrun.rb:137:in execute_each_user’
from ./webrun-control.rb:17

Does anybody have any idea what I could be doing wrong or how to debug
this
problem?

Well, I can point you to some obvious typos (see line 15 in webrun.rb):

  @proxy = DRbObject.new(nil, "druby://#@name:#@port")
                                                              ^^^^

^^^^
Don’t you want this to be:

 @proxy = DRbObject.new(nil, "druby://#{@name}:#{@port}")

Search for #@ in your code and you will find few more occurances

This syntax is actually permissible, see

http://www.rubycentral.com/book/tut_classes.html

for some examples. It’s smelly in some ways.

And line 17:

 yield @proxy if block_given? and @proxy

I would rewrite as:

yield @proxy if (block_given? and @proxy)

just to be on the safe side…“and” has very low precedence.

Fortunately it doesn’t matter in this case. Thanks for the reminder though.

Unfortunately, even after changing this and using ruby 1.8.1 on Win XP,
I got the same errors as before. I tried running in the debugger mode (with
-rdebug option) and I got even more errors, even for the first call.

All I can suggest is: try single-threaded, non-distributed version first, if
possible
and slowly introduce the more advanced features. Best of luck !

Thanks. I may have to simplify it some more. Taking out the threading stuff
didn’t seem to make any difference though.

···

On Sun, Jan 04, 2004 at 06:06:46AM +0900, Shashank Date wrote:

– shanko

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’

7

“Jos Backus” jos@catnook.com wrote in message

Never mind, I found the problem in my code triggering this error after
studying drb.rb and adding some debugging code to it. The User::Client_u1
class apparently wasn’t being defined properly in my code, causing the
above
error. @name holds the name of the undefined class/module, which was the
clue
I was missing.

Is the working code available for study?
Thanks,
– shanko

8

Jos Backus wrote:

I am trying to write a simple remote execution framework,

Btw, do you know that Phil Tomson’s TaskMaster
http://raa.ruby-lang.org/list.rhtml?name=taskmaster has exactly this
purpose?

No, thanks for the pointer! It looks very interesting.

(although I don’t know which is its status, nor if it has been ported to
ruby 1.8)

Can you explain in which way your framework is different, please?

My “framework” needs to be able to execute multiple tasks/scripts in parallel
on each slave/client, to achieve better scalability. I suppose I could write a
TaskMaster task that handles the threading internally and still lets the
end-user write scripts without having to worry about the threading issue but
I’m not sure how I’d go about that. Sure would be cool though.

···

On Thu, Jan 08, 2004 at 01:36:45AM +0900, Piergiuliano Bossi wrote:

Ciao,
Giuliano

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’

9

“Jos Backus” jos@catnook.com wrote in message

Never mind, I found the problem in my code triggering this error after
studying drb.rb and adding some debugging code to it. The User::Client_u1
class apparently wasn’t being defined properly in my code, causing the
above
error. @name holds the name of the undefined class/module, which was the
clue
I was missing.

Is the working code available for study?

I just updated the code on the website. This is far from complete though, it
needs much more work to be useful :slight_smile: As a first step, there’s a file named
loadtest.rb that I need to integrate.

Jos

···

On Wed, Jan 07, 2004 at 12:06:42PM +0900, Shashank Date wrote:

Thanks,
– shanko

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’

10

“Jos Backus” jos@catnook.com wrote in message

···

On Wed, Jan 07, 2004 at 12:06:42PM +0900, Shashank Date wrote:

Is the working code available for study?

I just updated the code on the website.

Thanks ! Where can I find apollo.rb ?

I searched on RAA and found a Delphi/Ruby project with that name.
Is it the same one?

– Shashank

11

“Jos Backus” jos@catnook.com wrote in message

Is the working code available for study?

I just updated the code on the website.

Thanks ! Where can I find apollo.rb ?

Actually, you’ll want common.rb, I just put it up.

I searched on RAA and found a Delphi/Ruby project with that name.
Is it the same one?

No.

···

On Thu, Jan 08, 2004 at 09:01:40AM +0900, Shashank Date wrote:

On Wed, Jan 07, 2004 at 12:06:42PM +0900, Shashank Date wrote:

– Shashank

–
Jos Backus / /// Sunnyvale, CA
_/ _/ _/
/ ///
_/ _/ _/ /
jos at catnook.com // /// require ‘std/disclaimer’