Best way to free a device

ruby-talk
1

Hi,

what is the best way to release an unix device that can't handle
multiple opens?

I've created a video device class in C, where the device gets opened
with an instanciation like:

  Wc::Cam.new '/dev/video0'

In this class i also added a destructor that closes the device. But it
is called to late. From

http://www.rubygarden.org/ruby?ResourceAcquisitionIsInitialization

i've seen, that i cant aspect a direct destruction of the object if it's
not more in use.

Is there a more elegant way to free the resources automatically, as to
create a special free or close method for my object?

Cheers
detlef

2

Hi,

what is the best way to release an unix device that can't handle
multiple opens?

        [...]

http://www.rubygarden.org/ruby?ResourceAcquisitionIsInitialization

i've seen, that i cant aspect a direct destruction of the object if it's
not more in use.

Make it a Singleton?

http://www.ruby-doc.org/stdlib/libdoc/singleton/rdoc/

Is there a more elegant way to free the resources automatically, as to
create a special free or close method for my object?

Cheers
detlef

        Hugh

···

On Wed, 2 Nov 2005, Detlef Reichl wrote:

3

Yes. Write an open method that takes a block:

def open(device_name)
  dev = do_the_opening(device_name)
  yield dev
  do_the_closing(dev)
end

And use it like this:

MyDevice.open("/dev/foo") do |dev|
  dev.write('bar')
  puts dev.read
end

regards,
Ed

···

On Wed, Nov 02, 2005 at 02:43:08AM +0900, Detlef Reichl wrote:

Is there a more elegant way to free the resources automatically, as to
create a special free or close method for my object?

4

make 'Wc::Cam::new' return a singleton object and allow new to take a block
that cleans up.

   module Wc
     class Cam
       INSTANCES = {}
       def new path
         cam =
           if INSTANCES.has_key? path
             return INSTANCES[path]
           else
             super
           end
         if block_given?
           begin
             yield cam
           ensure
             cam.close
           end
         else
           cam
         end
       end
     end
   end

that way you can write

   Wc::Cam::new('/dev/video0') do |cam|

   end

and ensure the cam is closed. when blocks dont' suffice you can write

   a = Wc::Cam::new '/dev/video0'
   b = Wc::Cam::new '/dev/video0'

and both a and b will be the same object.

regards.

-a

···

On Wed, 2 Nov 2005, Detlef Reichl wrote:

Hi,

what is the best way to release an unix device that can't handle
multiple opens?

I've created a video device class in C, where the device gets opened
with an instanciation like:

Wc::Cam.new '/dev/video0'

In this class i also added a destructor that closes the device. But it
is called to late. From

http://www.rubygarden.org/ruby?ResourceAcquisitionIsInitialization

i've seen, that i cant aspect a direct destruction of the object if it's
not more in use.

Is there a more elegant way to free the resources automatically, as to
create a special free or close method for my object?

--

email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
anything that contradicts experience and logic should be abandoned.
-- h.h. the 14th dalai lama

===============================================================================