How to find and close opened file descriptor


#1

During my testing, I found that ruby doesn’t create IO object for each
opened file descriptor which are inherited from parent process. So we
have to close all these opened file descriptor except stdin, stdout and
stderr by following way:

 3.upto(1023) do |fd|
    begin
      if io = IO::new(fd)
        io.close
      end
    rescue
    end
  end

But I really don’t like this way. Is there better way that I can find
all opened file descriptors.

And now I am assuming the maximum file no is 1023. Is there any way that
I can get the maximum file no?

Thanks.


#2

And now I am assuming the maximum file no is 1023. Is there any way that
I can get the maximum file no?

You could run a loop at the beginning of your script which detects it :slight_smile:

count = 0
all = []
begin
loop { all << File.open(‘test’,‘w’) }
rescue Exception
count = all.length
for file in all do; file.close; end
end
count

But getting back to your original question, another way to close
descriptors is
GC.each_object(IO) do |io| io.close; end

I guess. Not totally sure what you mean by “doesnt create file
descriptors for each inherited object” ?
Thanks.
-=r


#3

Roger P. wrote:

And now I am assuming the maximum file no is 1023. Is there any way that
I can get the maximum file no?

You could run a loop at the beginning of your script which detects it :slight_smile:

count = 0
all = []
begin
loop { all << File.open(‘test’,‘w’) }
rescue Exception
count = all.length
for file in all do; file.close; end
end
count

But getting back to your original question, another way to close
descriptors is
GC.each_object(IO) do |io| io.close; end

I guess. Not totally sure what you mean by “doesnt create file
descriptors for each inherited object” ?
Thanks.
-=r

At first, I also try to find all IO objects and close. Here is the code:

ObjectSpace.each_object(IO) do |io|
begin
unless io.closed?
io.close
end
rescue ::Exception
end
end

But it doesn’t work because ruby doesn’t create IO object for the open
file descriptor which are inherited from parent process.


#4

On 8 May 2009, at 14:55, Oliver P. wrote:

end

But it doesn’t work because ruby doesn’t create IO object for the open
file descriptor which are inherited from parent process.

You should probably describe how your parent process is opening these
file descriptors as clearly it’s not via objects in the IO hierarchy
or they would be accessible in the child process. As a general rule
though, if you have control over where and when the file descriptors
are coming into play you can use the IO.for_fd(file_descriptor) method
and store them in a shudder global variable or constant…

OPEN_FILES = []


fd = some_method_that_opens_file_and_returns_descriptor
OPEN_FILES << IO.for_fd(fd)

Then in the spawned child process closing these would be as simple as:

OPEN_FILES.each { |file| file.close }

Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net

raise ArgumentError unless @reality.responds_to? :reason


#5

I believe this is the standard idiom on *nix type systems to close all
file descriptors when you have no particular knowledge of which ones
are open.

I think that’s right except for maybe solaris has a helper or something,
but there’s no standard.
-=r


#6

On May 7, 9:54 am, Oliver P. removed_email_address@domain.invalid wrote:

    rescue
    end
  end

But I really don’t like this way. Is there better way that I can find
all opened file descriptors.

And now I am assuming the maximum file no is 1023. Is there any way that
I can get the maximum file no?

The io-extra library might be able to help you, depending on your
platform.

gem install io-extra.

Take a look at the IO.closefrom and IO.fdwalk methods.

Regards,

Dan


#7

On May 7, 2009, at 11:54 AM, Oliver P. wrote:

     end
   rescue
   end
 end

But I really don’t like this way. Is there better way that I can find
all opened file descriptors.

I believe this is the standard idiom on *nix type systems to close all
file descriptors when you have no particular knowledge of which ones
are open.

In other words there is no standard way to ask the OS for a list of
open descriptors via a simple system call.

A possible alternative is to parse the output of utilities like ‘lsof’
to determine what file descriptors are open or to dig into the various
platform specific ways that those utilities query the kernel for this
information.

Gary W.