Ruby Idiom To Retry open() Upto N Times Before Giving Up

ruby-talk
1

I write a lot of scripts that I run once or infrequently that uses open-rui. Occasionally I run into a web site that times out or is unavailable for a period of time. My normal solution is to just rerun the script manually at a later time and the problem goes away. What I would like to start doing is rescuing the open() and retrying the open() after a delay. What would be the most idiomatic way to try opening a url say n times before giving up? Here is my crude code for trying twice:

begin
open("http://www.example.com/foo.html")
rescue
begin
open("http://www.example.com/foo.html")
rescue
#tried twice - giving up
end
end

I would like a more general approach using ruby idioms where I could specify the maximum number of attempts and delay before giving up. Thanks for your help.

2

You can use "retry":

irb(main):017:0> attempts = 3
=> 3
irb(main):018:0> begin
irb(main):019:1* raise "Error, attempt = #{attempts}"
irb(main):020:1> rescue => e
irb(main):021:1> puts e
irb(main):022:1> attempts -= 1
irb(main):023:1> retry if attempts > 0
irb(main):024:1> puts "giving up"
irb(main):025:1> end
Error, attempt = 3
Error, attempt = 2
Error, attempt = 1
giving up
=> nil
irb(main):026:0>

Kind regards

  robert

···

On 22.02.2010 19:53, Dan wrote:

I write a lot of scripts that I run once or infrequently that uses open-rui Occasionally I run into a web site that times out or is unavailable for a period of time. My normal solution is to just rerun the script manually at a later time and the problem goes away. What I would like to start doing is rescuing the open() and retrying the open() after a delay. What would be the most idiomatic way to try opening a url say n times before giving up? Here is my crude code for trying twice:

begin open("http://www.example.com/foo.html"\)
rescue begin open("http://www.example.com/foo.html"\)
    rescue #tried twice - giving up end end

I would like a more general approach using ruby idioms where I could specify the maximum number of attempts and delay before giving up. Thanks for your help.

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

3

I write a lot of scripts that I run once or infrequently that uses open-rui. Occasionally I run into a web site that times out or is unavailable for a period of time. My normal solution is to just rerun the script manually at a later time and the problem goes away. What I would like to start doing is rescuing the open() and retrying the open() after a delay. What would be the most idiomatic way to try opening a url say n times before giving up? Here is my crude code for trying twice:

begin
open("http://www.example.com/foo.html"\)
rescue
begin
open("http://www.example.com/foo.html"\)
rescue
#tried twice - giving up
end
end

Use 'retry'.

This is a simple sketch of the concept:

irb(main):001:0> n = 0
=> 0
irb(main):002:0> begin
irb(main):003:1* raise "#{n} tries"
irb(main):004:1> rescue
irb(main):005:1> n += 1
irb(main):006:1> retry unless n == 3
irb(main):007:1> raise
irb(main):008:1> end
RuntimeError: 2 tries
        from (irb):3

Kirk Haines

···

On Mon, Feb 22, 2010 at 11:53 AM, Dan <dandiebolt@yahoo.com> wrote:
        from :0

4

Something along the lines of:

def open_with_retry(url, n=10, delay=1)
    1.upto(n) do
        begin
            open(url) do |handle|
                yield handle
            end
            break
        rescue
            puts "Sleeping ..."
            sleep delay
        end
    end
end

open_with_retry('http://does.not.resolve.tld/&#39;, 5, 2) do |h|
    puts "Doing something with #{h.inspect}"
end

Note that this sleeps even if the last attempt failed.

Marcelo

···

On Mon, Feb 22, 2010 at 12:53, Dan <dandiebolt@yahoo.com> wrote:

I would like a more general approach using ruby idioms where I could specify the maximum number of attempts and delay before giving up. Thanks for your help.

5

attempt() looks actually pretty cool.

Wonder if it would support this as well :smiley:

attempt("twice", "10 minutes"){
  open('http://www.example.com/foo.html')
}

hehe :smiley:

···

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