Asp Forum - Win32OLE: Output parameters, Dispatch IDs

Dave Burt

12/7/2005 3:04:00 PM

Hi,

x1 recently asked about an issue with a WMI script that had an output parameter.
I guess you can get a result from an output parameter via WIN32OLE#_invoke (with
VT_BYREF?) if you have the Dispatch ID for the method. But for a few WMI objects
I've seen recently, I haven't been able to get a WIN32OLE_METHOD instance for a
lot of methods, even ones that I can invoke. For example:

# Get a Win32_Process WMI object
wmi_svc = WIN32OLE.connect("winmgmts:\\\\.\\root\\cimv2:Win32_Process")
# Try to get the method
wmi_svc.ole_method("Create") #=> WIN32OLERuntimeError: Not found Create
# Invoke the method
wmi_svc.invoke("Create", "notepad", nil, nil, nil) #=> (Creates notepad.exe
process)

That last parameter is an output parameter which should return the PID of the
created process as a uint32.

Is there a way I can get info on a method like that, and how do I get the result
of an output parameter?

Cheers,
Dave

9 Answers

x1

12/8/2005 5:35:00 AM

I have not been able to figure anything out yet myself.

Do you know off hand how one would be able to find any variable
names(if exist) that are pointing to a given object?

For instance when looking at ObjectSpace.cantremembermethodname(Array)
You get something like:
["notepad", nil, nil, 333]

How would one be able to determine the object id and / or any variable
names associated with it?

On 12/7/05, Dave Burt <dave@burt.id.au> wrote:
> Hi,
>
> x1 recently asked about an issue with a WMI script that had an output parameter.
> I guess you can get a result from an output parameter via WIN32OLE#_invoke (with
> VT_BYREF?) if you have the Dispatch ID for the method. But for a few WMI objects
> I've seen recently, I haven't been able to get a WIN32OLE_METHOD instance for a
> lot of methods, even ones that I can invoke. For example:
>
> # Get a Win32_Process WMI object
> wmi_svc = WIN32OLE.connect("winmgmts:\\\\.\\root\\cimv2:Win32_Process")
> # Try to get the method
> wmi_svc.ole_method("Create") #=> WIN32OLERuntimeError: Not found Create
> # Invoke the method
> wmi_svc.invoke("Create", "notepad", nil, nil, nil) #=> (Creates notepad.exe
> process)
>
> That last parameter is an output parameter which should return the PID of the
> created process as a uint32.
>
> Is there a way I can get info on a method like that, and how do I get the result
> of an output parameter?
>
> Cheers,
> Dave
>
>
>

Dave Burt

12/8/2005 6:41:00 AM

x1 wrote:
> I have not been able to figure anything out yet myself.

I figured.

> Do you know off hand how one would be able to find any variable
> names(if exist) that are pointing to a given object?

Just last week, Joel VanderWerf wrote, in "Re: Memory Leaks: How to see GC
Roots?":
> There's a ruby patch to show what objects are reachable from the roots
> (and the chain of references in each case):
>
> http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/151854?151...
>
> It should easy to modify it to just show the roots.

In the same thread, Stephen Kellett posted a link to a product called Ruby
Memory Validator, which lists as a feature "References view. Display the
object reference graph for the application," and the screenshot looks like
it would deal well with this issue.
http://www.softwareverify.com/rubyMemoryValidator/fe...

I have not actually operated either of these two possible solutions.

> For instance when looking at ObjectSpace.cantremembermethodname(Array)
> You get something like:
> ["notepad", nil, nil, 333]
>
> How would one be able to determine the object id and / or any variable
> names associated with it?

But, it just occurred to me, you could cheat and do something like this to
get the array:
pid = nil
ObjectSpace.each_object(Array) do |arr|
pid = arr[3] if arr.size == 4 && arr[0, 3] == ["notepad", nil, nil]
end

There you go - recover it from the object pool without knowing where the
references to it are/were.

Cheers,
Dave

x1

12/9/2005 2:14:00 AM

ObjectSpace.each_object(Array) do |arr|
pid = arr[3] if arr.size == 4 && arr[0, 3] == ["notepad", nil, nil]
end

--not sure how accurate this would be once 2 or more instances of
"notepad" are running simultaneously.

On 12/8/05, Dave Burt <dave@burt.id.au> wrote:
> x1 wrote:
> > I have not been able to figure anything out yet myself.
>
> I figured.
>
> > Do you know off hand how one would be able to find any variable
> > names(if exist) that are pointing to a given object?
>
> Just last week, Joel VanderWerf wrote, in "Re: Memory Leaks: How to see GC
> Roots?":
> > There's a ruby patch to show what objects are reachable from the roots
> > (and the chain of references in each case):
> >
> > http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/151854?151...
> >
> > It should easy to modify it to just show the roots.
>
> In the same thread, Stephen Kellett posted a link to a product called Ruby
> Memory Validator, which lists as a feature "References view. Display the
> object reference graph for the application," and the screenshot looks like
> it would deal well with this issue.
> http://www.softwareverify.com/rubyMemoryValidator/fe...
>
> I have not actually operated either of these two possible solutions.
>
> > For instance when looking at ObjectSpace.cantremembermethodname(Array)
> > You get something like:
> > ["notepad", nil, nil, 333]
> >
> > How would one be able to determine the object id and / or any variable
> > names associated with it?
>
> But, it just occurred to me, you could cheat and do something like this to
> get the array:
> pid = nil
> ObjectSpace.each_object(Array) do |arr|
> pid = arr[3] if arr.size == 4 && arr[0, 3] == ["notepad", nil, nil]
> end
>
> There you go - recover it from the object pool without knowing where the
> references to it are/were.
>
> Cheers,
> Dave
>
>
>
>

dave.burt

12/9/2005 5:12:00 AM

x1 complained:
> --not sure how accurate this would be once 2 or more instances of
> "notepad" are running simultaneously.

pids = []
ObjectSpace.each_object(Array) do |arr|
pid << arr[3] if arr.size == 4 && arr[0, 3] == ["notepad", nil, nil]
end

You can easily collect them all. If you get one list before the Create
call and one after, the difference is likely to be the PID you're
after.

Of course, in practical Ruby, it's going to be easier to use
Process.create #=> pid from the Win32-Utils library, or even to use
Win32API or DL to call CreateProcess() directly.

Cheers,
Dave

x1

12/9/2005 6:14:00 AM

I find it strange that the win32ole package cant handle out params.

Hunting in ObjectSpace with a semi-production script doesn't give me
the "warm and fuzzies".

Creating a basic .vbs file and calling it as such:
pid = `cscript.exe exec.vbs`.split("\n")[3]
...works, but it's still a hack IMO.

Thanks again for the kind suggestions but since I'm still learning
ruby, knowing the precise problem or solution with this scenario would
be optimal.

On 12/9/05, dave.burt@gmail.com <dave.burt@gmail.com> wrote:
> x1 complained:
> > --not sure how accurate this would be once 2 or more instances of
> > "notepad" are running simultaneously.
>
> pids = []
> ObjectSpace.each_object(Array) do |arr|
> pid << arr[3] if arr.size == 4 && arr[0, 3] == ["notepad", nil, nil]
> end
>
> You can easily collect them all. If you get one list before the Create
> call and one after, the difference is likely to be the PID you're
> after.
>
> Of course, in practical Ruby, it's going to be easier to use
> Process.create #=> pid from the Win32-Utils library, or even to use
> Win32API or DL to call CreateProcess() directly.
>
> Cheers,
> Dave
>
>
>

Dave Burt

12/9/2005 7:36:00 AM

x1 wrote:
> I find it strange that the win32ole package cant handle out params.

That's the thing, though, it _does_ explicitly handle out params. The only
way I know of using them, though, is via "_invoke", and you need a dispid
(method handle) to call that.

> Hunting in ObjectSpace with a semi-production script doesn't give me
> the "warm and fuzzies".

Fair enough, if you're then doing something destructive with the PID.

> Creating a basic .vbs file and calling it as such:
> pid = `cscript.exe exec.vbs`.split("\n")[3]
> ..works, but it's still a hack IMO.

You haven't tried win32-utils? I imagine if you're doing this kind of thing
you'll find it very useful.

http://rubyforge.org/projects/...

> Thanks again for the kind suggestions but since I'm still learning
> ruby, knowing the precise problem or solution with this scenario would
> be optimal.

You're welcome. I actually emailed the start of this thread directly to the
Win32OLE maintainer in hope he can enlighten us - he has sometimes taken a
bit of time to get around to responding, so let's be patient on that front.

Cheers,
Dave

Masaki Suketa

12/9/2005 9:01:00 AM

Hello,

In message "Re: Win32OLE: Output parameters, Dispatch IDs"
on 05/12/09, "Dave Burt" <dave@burt.id.au> writes:

> You're welcome. I actually emailed the start of this thread directly to the
> Win32OLE maintainer in hope he can enlighten us - he has sometimes taken a
> bit of time to get around to responding, so let's be patient on that front.
Sorry for being too late to reply.

> # Get a Win32_Process WMI object
> wmi_svc = WIN32OLE.connect("winmgmts:\\\\.\\root\\cimv2:Win32_Process")
> # Try to get the method
> wmi_svc.ole_method("Create") #=> WIN32OLERuntimeError: Not found Create
> # Invoke the method
> wmi_svc.invoke("Create", "notepad", nil, nil, nil) #=> (Creates notepad.exe process)
(snip)
> Is there a way I can get info on a method like that, and how do I get the result
> of an output parameter?

You can get the result of an output parameter using WIN32OLE::ARGV.

wmi_svc = WIN32OLE.connect("winmgmts:\\\\.\\root\\cimv2:Win32_Process")
wmi_svc.invoke("Create", "notepad", nil, nil, nil)
p WIN32OLE::ARGV # => ["notepad", -2147352572, -2147352572, 1704]

I am going to investigate why ole_method is failed.
Please wait for a while.

Regards,
Masaki Suketa

Dave Burt

12/9/2005 3:25:00 PM

Hi,

Masaki Suketa wrote:
> Sorry for being too late to reply.

No need to apologize! And you're not even late - the thread's still warm
after less than 2 days.

>> Is there a way I can get info on a method like that, and how do I get the
>> result
>> of an output parameter?
>
> You can get the result of an output parameter using WIN32OLE::ARGV.

Thanks. That makes it easy.

It's not documented in the RDoc; I don't think RDoc supports constants in C
code yet.

> I am going to investigate why ole_method is failed.
> Please wait for a while.

I came across a similar problem a while back, using ADSI, I think. Like
Daniel's issue here:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-t...

Thanks a lot for looking into this and for all the effort you've put into
this library over the years - you're a champ, Masaki Suketa!

Cheers,
Dave

x1

12/10/2005 5:33:00 AM

On 12/9/05, Dave Burt <dave@burt.id.au> wrote:
<trim>
> Fair enough, if you're then doing something destructive with the PID.

Indeed I am! "-9 destructive" to be exact :D

> You haven't tried win32-utils? I imagine if you're doing this kind of thing
> you'll find it very useful.

Actually, I've looked at it but have a few reasons not to use it:
1) requires compilation with VC

2) portability. With pid handling needed on multiple systems, I prefer
to let the "ruby one click installer" be the only required component
for a complete restoration(apart from the scripts themselves)

3) still learning ruby. What better way than to get down and dirty? :-)

On 12/9/05, Dave Burt <dave@burt.id.au> wrote:
<trim>
> Thanks a lot for looking into this and for all the effort you've put into
> this library over the years - you're a champ, Masaki Suketa!
>
> Cheers,
> Dave

Agreed! Masaki, thanks so much for your time and concern.

comp.lang.ruby

Win32OLE: Output parameters, Dispatch IDs

Dave Burt

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Dave Burt

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dave.burt

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Dave Burt

Masaki Suketa

Dave Burt

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