Merge pull request #475 from newrelic/vince/fix-backoff-samp

Fix: Make sure we trigger backoff sampler cycles

lib/new_relic/distributed_trace/backoff_sampler.ex

@@ -26,6 +26,7 @@ defmodule NewRelic.DistributedTrace.BackoffSampler do
     :persistent_term.put({__MODULE__, :counter}, new(@size, []))
     put(@sampling_target, AgentRun.lookup(:sampling_target) || 10)
 
+    trigger_next_cycle()
     {:ok, %{}}
   end
 
@@ -94,7 +95,7 @@ defmodule NewRelic.DistributedTrace.BackoffSampler do
 
   def trigger_next_cycle() do
     cycle_period = AgentRun.lookup(:sampling_target_period) || 60_000
-    Process.send_after(self(), :cycle, cycle_period)
+    Process.send_after(__MODULE__, :cycle, cycle_period)
   end
 
   def update_state(false = _sampled?) do

test/backoff_sampler_test.exs

@@ -19,7 +19,7 @@ defmodule BackoffSamplerTest do
     assert BackoffSampler.sample?()
     assert BackoffSampler.sample?()
 
-    # The rest will be ignored
+    # The rest will be dropped
     refute BackoffSampler.sample?()
     refute BackoffSampler.sample?()
     refute BackoffSampler.sample?()
@@ -96,4 +96,48 @@ defmodule BackoffSamplerTest do
       decided_count_last: 0
     })
   end
+
+  test "cycles trigger" do
+    Application.put_env(:new_relic_agent, :sampling_target_period, 100)
+
+    BackoffSampler.reset()
+    BackoffSampler.trigger_next_cycle()
+
+    # Target is 10, so it will sample the first 10
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+    assert BackoffSampler.sample?()
+
+    # The rest will be dropped
+    refute BackoffSampler.sample?()
+    refute BackoffSampler.sample?()
+    refute BackoffSampler.sample?()
+    refute BackoffSampler.sample?()
+
+    # Wait until the next cycle
+    Process.sleep(110)
+
+    # Next cycle it will adjust and take some, but not all
+    decisions = [
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?(),
+      BackoffSampler.sample?()
+    ]
+
+    assert true in decisions
+    assert false in decisions
+  end
 end