Add Sender.queue_size limits

README.md

@@ -180,6 +180,13 @@ There are three different kinds of messages:
 
 There is also an implicit message which closes the queue which will cause the sender thread to finish processing and exit.
 
+
+```ruby
+statsd = Datadog::Statsd.new('localhost', 8125)
+```
+
+The message queue's maximum size (in messages) is given by the `sender_queue_size` argument, and has appropriate defaults for UDP (2048) and UDS (512).
+
 The `buffer_flush_interval`, if enabled, is implemented with an additional thread which manages the timing of those flushes.  This additional thread is used even if `single_thread: true`.
 
 ### Usual workflow

lib/datadog/statsd.rb

@@ -45,7 +45,12 @@ class Error < StandardError
     UDP_DEFAULT_BUFFER_SIZE = 1_432
     UDS_DEFAULT_BUFFER_SIZE = 8_192
     DEFAULT_BUFFER_POOL_SIZE = Float::INFINITY
+
+    UDP_DEFAULT_SENDER_QUEUE_SIZE = 2048
+    UDS_DEFAULT_SENDER_QUEUE_SIZE = 512
+
     MAX_EVENT_SIZE = 8 * 1_024
+
     # minimum flush interval for the telemetry in seconds
     DEFAULT_TELEMETRY_FLUSH_INTERVAL = 10
 
@@ -74,6 +79,7 @@ def tags
     # @option [Logger] logger for debugging
     # @option [Integer] buffer_max_payload_size max bytes to buffer
     # @option [Integer] buffer_max_pool_size max messages to buffer
+    # @option [Integer] sender_queue_size size of the sender queue in number of buffers (multi-thread only)
     # @option [Numeric] buffer_flush_interval interval in second to flush buffer
     # @option [String] socket_path unix socket path
     # @option [Float] default sample rate if not overridden
@@ -92,6 +98,8 @@ def initialize(
       buffer_overflowing_stategy: :drop,
       buffer_flush_interval: nil,
 
+      sender_queue_size: nil,
+
       logger: nil,
 
       single_thread: false,
@@ -138,6 +146,8 @@ def initialize(
         buffer_overflowing_stategy: buffer_overflowing_stategy,
         buffer_flush_interval: buffer_flush_interval,
 
+        sender_queue_size: sender_queue_size,
+
         telemetry_flush_interval: telemetry_enable ? telemetry_flush_interval : nil,
       )
     end

lib/datadog/statsd/connection.rb

@@ -38,7 +38,7 @@ def write(payload)
           end
         end
 
-        telemetry.dropped(packets: 1, bytes: payload.length) if telemetry
+        telemetry.dropped_writer(packets: 1, bytes: payload.length) if telemetry
         logger.error { "Statsd: #{boom.class} #{boom}" } if logger
         nil
       end

lib/datadog/statsd/forwarder.rb

@@ -14,6 +14,8 @@ def initialize(
         buffer_overflowing_stategy: :drop,
         buffer_flush_interval: nil,
 
+        sender_queue_size: nil,
+
         telemetry_flush_interval: nil,
         global_tags: [],
 
@@ -49,7 +51,21 @@ def initialize(
           max_pool_size: buffer_max_pool_size || DEFAULT_BUFFER_POOL_SIZE,
           overflowing_stategy: buffer_overflowing_stategy,
         )
-        @sender = (single_thread ? SingleThreadSender : Sender).new(buffer, logger: logger, flush_interval: buffer_flush_interval)
+
+        sender_queue_size ||= (@transport_type == :udp ?
+                               UDP_DEFAULT_SENDER_QUEUE_SIZE : UDS_DEFAULT_SENDER_QUEUE_SIZE)
+
+        @sender = single_thread ?
+          SingleThreadSender.new(
+            buffer,
+            logger: logger,
+            flush_interval: buffer_flush_interval) :
+          Sender.new(
+            buffer,
+            logger: logger,
+            flush_interval: buffer_flush_interval,
+            telemetry: @telemetry,
+            queue_size: sender_queue_size)
         @sender.start
       end
 

lib/datadog/statsd/sender.rb

@@ -12,10 +12,14 @@ class Statsd
     class Sender
       CLOSEABLE_QUEUES = Queue.instance_methods.include?(:close)
 
-      def initialize(message_buffer, logger: nil, flush_interval: nil)
+      def initialize(message_buffer, telemetry: nil, queue_size: UDP_DEFAULT_BUFFER_SIZE, logger: nil, flush_interval: nil, queue_class: Queue, thread_class: Thread)
         @message_buffer = message_buffer
+        @telemetry = telemetry
+        @queue_size = queue_size
         @logger = logger
         @mx = Mutex.new
+        @queue_class = queue_class
+        @thread_class = thread_class
         if flush_interval
           @flush_timer = Datadog::Statsd::Timer.new(flush_interval) { flush(sync: true) }
         end
@@ -45,7 +49,7 @@ def rendez_vous
         return unless message_queue
 
         # Initialize and get the thread's sync queue
-        queue = (Thread.current[:statsd_sync_queue] ||= Queue.new)
+        queue = (@thread_class.current[:statsd_sync_queue] ||= @queue_class.new)
         # tell sender-thread to notify us in the current
         # thread's queue
         message_queue.push(queue)
@@ -75,16 +79,20 @@ def add(message)
           }
         end
 
-        message_queue << message
+        if message_queue.length <= @queue_size
+          message_queue << message
+        else
+          @telemetry.dropped_queue(packets: 1, bytes: message.bytesize) if @telemetry
+        end
       end
 
       def start
         raise ArgumentError, 'Sender already started' if message_queue
 
         # initialize a new message queue for the background thread
-        @message_queue = Queue.new
+        @message_queue = @queue_class.new
         # start background thread
-        @sender_thread = Thread.new(&method(:send_loop))
+        @sender_thread = @thread_class.new(&method(:send_loop))
         @sender_thread.name = "Statsd Sender" unless Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.3')
         @flush_timer.start if @flush_timer
       end
@@ -131,7 +139,7 @@ def send_loop
             case message
             when :flush
               message_buffer.flush
-            when Queue
+            when @queue_class
               message.push(:go_on)
             else
               message_buffer.add(message)
@@ -153,7 +161,7 @@ def send_loop
               break
             when :flush
               message_buffer.flush
-            when Queue
+            when @queue_class
               message.push(:go_on)
             else
               message_buffer.add(message)

lib/datadog/statsd/telemetry.rb

@@ -9,8 +9,12 @@ class Telemetry
       attr_reader :service_checks
       attr_reader :bytes_sent
       attr_reader :bytes_dropped
+      attr_reader :bytes_dropped_queue
+      attr_reader :bytes_dropped_writer
       attr_reader :packets_sent
       attr_reader :packets_dropped
+      attr_reader :packets_dropped_queue
+      attr_reader :packets_dropped_writer
 
       # Rough estimation of maximum telemetry message size without tags
       MAX_TELEMETRY_MESSAGE_SIZE_WT_TAGS = 50 # bytes
@@ -40,8 +44,12 @@ def reset
         @service_checks = 0
         @bytes_sent = 0
         @bytes_dropped = 0
+        @bytes_dropped_queue = 0
+        @bytes_dropped_writer = 0
         @packets_sent = 0
         @packets_dropped = 0
+        @packets_dropped_queue = 0
+        @packets_dropped_writer = 0
         @next_flush_time = now_in_s + @flush_interval
       end
 
@@ -54,9 +62,18 @@ def sent(metrics: 0, events: 0, service_checks: 0, bytes: 0, packets: 0)
         @packets_sent += packets
       end
 
-      def dropped(bytes: 0, packets: 0)
+      def dropped_queue(bytes: 0, packets: 0)
         @bytes_dropped += bytes
+        @bytes_dropped_queue += bytes
         @packets_dropped += packets
+        @packets_dropped_queue += packets
+      end
+
+      def dropped_writer(bytes: 0, packets: 0)
+        @bytes_dropped += bytes
+        @bytes_dropped_writer += bytes
+        @packets_dropped += packets
+        @packets_dropped_writer += packets
       end
 
       def should_flush?
@@ -70,8 +87,12 @@ def flush
           sprintf(pattern, 'service_checks', @service_checks),
           sprintf(pattern, 'bytes_sent', @bytes_sent),
           sprintf(pattern, 'bytes_dropped', @bytes_dropped),
+          sprintf(pattern, 'bytes_dropped_queue', @bytes_dropped_queue),
+          sprintf(pattern, 'bytes_dropped_writer', @bytes_dropped_writer),
           sprintf(pattern, 'packets_sent', @packets_sent),
           sprintf(pattern, 'packets_dropped', @packets_dropped),
+          sprintf(pattern, 'packets_dropped_queue', @packets_dropped_queue),
+          sprintf(pattern, 'packets_dropped_writer', @packets_dropped_writer),
         ]
       end