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One of the challenges with writing a Facebook or Bebo application is staying within a limit it gives you to respond with data before it shows the Application Did Not Respond page to a user. Having a content reach application calling external APIs, like Amazon or YouTube, with response times beyond your control, forces you to keep such calls short to allow extra time for processing. We usually wrap them in aggressive timeouts with a retry. As an example is this code from the Ruby Amazon E-Commerce REST Service API gem rewritten to limit a single call attempt to two seconds with one more retry.
Original Codemodule Amazon class Ecs def self.send_request(opts) request_url = prepare_url(opts) res = Net::HTTP.get_response(URI::parse(request_url)) unless res.kind_of? Net::HTTPSuccess raise Amazon::RequestError, "HTTP Response: #{res.code} #{res.message}" end Response.new(res.body) end end end
module Amazon class Ecs class EmptyResponse def items; []; end def total_pages; 0; end end def self.send_request(opts) res = timed_try(request_url, 2) do |url| uri = URI::parse(url) req = Net::HTTP.new(uri.host, uri.port) # Agressive timeouts req.open_timeout = 1 req.read_timeout = 2 req.start { |http| http.request_get(url) } end res.kind_of?(Net::HTTPSuccess) ? Response.new(res.body) : EmptyResponse.new end private def timed_try(url, attempts, &block) attempt = 1 begin block.call(url) rescue Timeout::Error if attempt >= attempts RAILS_DEFAULT_LOGGER.warn "[amazon_api] gave up after attempt ##{ attempt } to get data from #{ url }" nil else RAILS_DEFAULT_LOGGER.warn "[amazon_api] attempt ##{ attempt } timed out on getting data from #{ url }" attempt += 1 retry end end end end end
