Best way to free a device

[Detlef Reichl]

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

 

[Hugh Sasse]

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

 

[Edward Faulkner]

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

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

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[Ara.T.Howard]

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?

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
--
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| phone :: 303.497.6469
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