Don't submit the queue when empty

[cyx]

Currently it's checking queued.empty? which always turns out to be non-empty if you provide a source.

This check relies on just empty? which only utilizes @queued without the merging of the global metadata.

[mikehale]

I think the definition of empty? on Librato::Metrics::Queue also needs to change, to look something like this:

def empty?
  gauges.empty? && counters.empty? && measurements.empty?
end

[chancefeick]

Hi @cyx. Thanks for the report and contribution.

Currently it's checking queued.empty? which always turns out to be non-empty if you provide a source.

Could you elaborate on this with an example to reproduce? Seems like the expected behavior:

q1 = Librato::Metrics::Queue.new
q1.empty?
# => true
q1.add foo: { value: 1, source: 'bar' }
q1.queued
# => {:gauges=>[{:value=>1, :source=>"bar", :name=>"foo", :measure_time=>1489707683}]}
q1.empty?
# => false
q2 = Librato::Metrics::Queue.new(source: 'test')
q2.empty?
# => true
q2.add foo: { value: 1, source: 'bar' }
q2.queued
# => {:gauges=>[{:value=>1, :source=>"bar", :name=>"foo", :measure_time=>1489707741}], :source=>"test"}
q2.empty?
# => false

[cyx]

I'm afk now, will try to provide tomorrow.

[mikehale]

@chancefeick here are the steps to reproduce:

> aggregator = Librato::Metrics::Aggregator.new
> queue = Librato::Metrics::Queue.new(source: 'test')
> queue.empty?
=> true
> queue.merge!(aggregator)
> queue.empty?
=> false
> queue.queued
=> {:gauges=>[], :source=>"test"}

[chancefeick]

Thanks for the example, that's definitely not the intended behavior.

These changes make sense to me 👍 Can you please include specs around this fix so we can ensure it doesn't unintentionally break in a future version?

[mikehale]

@cyx I came up with the following. If you think it looks good you can just add it to your branch:

diff --git a/spec/unit/metrics/queue_spec.rb b/spec/unit/metrics/queue_spec.rb
index 163f34f..ea874ff 100644
--- a/spec/unit/metrics/queue_spec.rb
+++ b/spec/unit/metrics/queue_spec.rb
@@ -301,6 +301,11 @@ module Librato
           subject.add foo: {type: :gauge, value: 121212}
           expect(subject.empty?).to be false
         end
+
+        it "returns true when nothing merged" do
+          subject.merge!(Librato::Metrics::Aggregator.new)
+          expect(subject.empty?).to be true
+        end
       end

       describe "#gauges" do
@@ -544,6 +549,14 @@ module Librato
             expect(subject.queued).not_to be_empty
           end
         end
+
+        context "when there are no metrics" do
+          it "it does not persist and returns true" do
+            subject.merge!(Librato::Metrics::Aggregator.new)
+            subject.persister.return_value(false)
+            expect(subject.submit).to be true
+          end
+        end
       end

       describe "#time" do

[cyx]

@mikehale thanks! Pushed the commit.

[cyx]

@chancefeick can you check and see if it's all good now?

[chancefeick]

@cyx LGTM 👍

Released in v2.1.1. Thanks again for your contribution.

[mikehale]

Thanks!