Lazily start TelemetryEventBuffer threads (#2832)

* Lazily start `TelemetryEventBuffer`s

* move ensure_thread inside mutex

Author: sl0thentr0py

CHANGELOG.md

@@ -61,6 +61,7 @@
 - Unify Logs and Metrics implementations ([#2826](https://github.com/getsentry/sentry-ruby/pull/2826))
 - Unify LogEventBuffer and MetricEventBuffer logic ([#2830](https://github.com/getsentry/sentry-ruby/pull/2830))
 - Add maximum limits on LogEventBuffer (1k) and MetricEventBuffer (10k) for protection from memory blowup ([#2831](https://github.com/getsentry/sentry-ruby/pull/2831))
+- Lazily start LogEventBuffer and MetricEventBuffer threads ([#2832](https://github.com/getsentry/sentry-ruby/pull/2832))
 
 ## 6.2.0
 

sentry-ruby/lib/sentry/client.rb

@@ -49,11 +49,11 @@ def initialize(configuration)
       @spotlight_transport = SpotlightTransport.new(configuration) if configuration.spotlight
 
       if configuration.enable_logs
-        @log_event_buffer = LogEventBuffer.new(configuration, self).start
+        @log_event_buffer = LogEventBuffer.new(configuration, self)
       end
 
       if configuration.enable_metrics
-        @metric_event_buffer = MetricEventBuffer.new(configuration, self).start
+        @metric_event_buffer = MetricEventBuffer.new(configuration, self)
       end
     end
 

sentry-ruby/lib/sentry/telemetry_event_buffer.rb

@@ -14,7 +14,7 @@ class TelemetryEventBuffer < ThreadedPeriodicWorker
     FLUSH_INTERVAL = 5 # seconds
 
     # @!visibility private
-    attr_reader :pending_items, :envelope_type, :data_category
+    attr_reader :pending_items, :envelope_type, :data_category, :thread
 
     def initialize(configuration, client, event_class:, max_items:, max_items_before_drop:, envelope_type:, envelope_content_type:, before_send:)
       super(configuration.sdk_logger, FLUSH_INTERVAL)
@@ -36,11 +36,6 @@ def initialize(configuration, client, event_class:, max_items:, max_items_before
       log_debug("[#{self.class}] Initialized buffer with max_items=#{@max_items}, flush_interval=#{FLUSH_INTERVAL}s")
     end
 
-    def start
-      ensure_thread
-      self
-    end
-
     def flush
       @mutex.synchronize do
         return if empty?
@@ -55,12 +50,9 @@ def flush
     alias_method :run, :flush
 
     def add_item(item)
-      unless item.is_a?(@event_class)
-        log_debug("[#{self.class}] expected a #{@event_class}, got #{item.class}")
-        return
-      end
-
       @mutex.synchronize do
+        return unless ensure_thread
+
         if size >= @max_items_before_drop
           log_debug("[#{self.class}] exceeded max capacity, dropping event")
           @client.transport.record_lost_event(:queue_overflow, @data_category)

sentry-ruby/spec/support/shared_examples_for_telemetry_event_buffers.rb

@@ -24,6 +24,18 @@
   describe "#add_item" do
     let(:max_items) { 3 }
 
+    it "spawns only one thread" do
+      expect do
+        subject.add_item(event)
+      end.to change { Thread.list.count }.by(1)
+
+      expect(subject.thread).to receive(:alive?).and_return(true)
+
+      expect do
+        subject.add_item(event)
+      end.to change { Thread.list.count }.by(0)
+    end
+
     it "does nothing when there are no pending items" do
       expect(client).not_to receive(:capture_envelope)
 
@@ -156,9 +168,8 @@
 
       it "keeps the background thread alive after an error" do
         subject.add_item(event)
-        subject.start
 
-        thread = subject.instance_variable_get(:@thread)
+        thread = subject.thread
 
         expect(thread).to be_alive
         expect { subject.flush }.not_to raise_error