Improve thread safety to avoid race conditions during shutdown.

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 7.4.1
+  - Improve thread safety to avoid race conditions during shutdown and integration tests. [#67](https://github.com/logstash-plugins/logstash-integration-rabbitmq/pull/66)
+
 ## 7.4.0
   - Removed obsolete `verify_ssl` and `debug` options [#60](https://github.com/logstash-plugins/logstash-integration-rabbitmq/pull/60)
 

lib/logstash/inputs/rabbitmq.rb

@@ -59,6 +59,7 @@ module Inputs
     class RabbitMQ < LogStash::Inputs::Threadable
 
       java_import java.util.concurrent.TimeUnit
+      java_import java.util.concurrent.CountDownLatch
 
       include ::LogStash::PluginMixins::RabbitMQConnection
 
@@ -189,6 +190,7 @@ def setup!
         connect!
         declare_queue!
         bind_exchange!
+        @poison_latch = CountDownLatch.new(1)
         @hare_info.channel.prefetch = @prefetch_count
       rescue => e
         # when encountering an exception during shut-down,
@@ -268,7 +270,11 @@ def internal_queue_consume!
             next
           end
 
-          break if payload == INTERNAL_QUEUE_POISON
+          if payload == INTERNAL_QUEUE_POISON
+            @logger.info("RabbitMQ consumer thread received shutdown signal, exiting")
+            @poison_latch.countDown
+            break
+          end
 
           metadata, data = payload
           @codec.decode(data) do |event|
@@ -302,11 +308,22 @@ def decorate(event, metadata, data)
       end
 
       def stop
-        @internal_queue.put(INTERNAL_QUEUE_POISON)
+        stop_consumer_thread
         shutdown_consumer
         close_connection
       end
 
+      def stop_consumer_thread
+        # After sending the poison pill, we need to wait for the consumer thread to actually exit.
+        # Closing channel right away may lead to messages not being acked properly or a race condition
+        # where the consumer thread tries to ack a message on a closed channel.
+        @internal_queue.put(INTERNAL_QUEUE_POISON)
+        timed_out = !@poison_latch.await(2, TimeUnit::SECONDS)
+        if timed_out
+          @logger.warn("Timeout waiting for RabbitMQ consumer thread to terminate")
+        end
+      end
+
       def shutdown_consumer
         # There are two possible flows to shutdown consumers. When the plugin is the one shutting down, it should send a channel
         # cancellation message by invoking channel.basic_cancel(consumer_tag) and waiting for the consumer to terminate

logstash-integration-rabbitmq.gemspec

@@ -1,6 +1,6 @@
 Gem::Specification.new do |s|
   s.name            = 'logstash-integration-rabbitmq'
-  s.version         = '7.4.0'
+  s.version         = '7.4.1'
   s.licenses        = ['Apache License (2.0)']
   s.summary         = "Integration with RabbitMQ - input and output plugins"
   s.description     = "This gem is a Logstash plugin required to be installed on top of the Logstash core pipeline "+

spec/inputs/rabbitmq_spec.rb

@@ -33,7 +33,6 @@
     let(:connection) { double("MarchHare Connection") }
     let(:channel) { double("Channel") }
     let(:exchange) { double("Exchange") }
-    let(:channel) { double("Channel") }
     let(:queue) { double("queue") }
 
     # Doing this in a before block doesn't give us enough control over scope
@@ -76,6 +75,12 @@
         allow(consumer).to receive(:consumer_tag).and_return(consumer_tag)
       end
 
+      after do
+        # This unit tests don't initialize consumer thread, so sync signal should be manually sent.
+        instance.instance_variable_get(:@poison_latch).countDown
+        instance.stop
+      end
+
       context "with a cancelled consumer" do
         before do
           allow(consumer).to receive(:cancelled?).and_return(true)
@@ -84,7 +89,6 @@
 
         it "should not call basic_cancel" do
           expect(channel).to_not receive(:basic_cancel)
-          instance.stop
         end
       end
 
@@ -96,7 +100,6 @@
 
         it "should not call basic_cancel" do
           expect(channel).to_not receive(:basic_cancel)
-          instance.stop
         end
       end
 
@@ -108,13 +111,11 @@
 
         it "should call basic_cancel" do
           expect(channel).to receive(:basic_cancel).with(consumer_tag)
-          instance.stop
         end
 
         it "should log terminating info" do
           allow(channel).to receive(:basic_cancel).with(consumer_tag)
           expect(instance.logger).to receive(:info).with(/Waiting for RabbitMQ consumer to terminate before stopping/, anything)
-          instance.stop
         end
       end
     end
@@ -384,24 +385,30 @@
   let(:hare_info) { instance.instance_variable_get(:@hare_info) }
   let(:output_queue) { Queue.new }
 
-  # Spawn a connection in the bg and wait up (n) seconds
+  # Spawn a connection and waits for it to be ready.
   def spawn_and_wait(instance)
     instance.register
 
     output_queue # materialize in this thread
 
-    Thread.new {
+    @consumer_thread = Thread.new {
       instance.run(output_queue)
     }
 
-    20.times do
-      instance.send(:connection_open?) ? break : sleep(0.1)
+    # Ensure that the connection and channel are fully started.
+    Timeout.timeout(2, Timeout::Error, "Timeout waiting for connection to open and channel to be available") do
+      until instance.send(:connection_open?) && instance.instance_variable_get(:@hare_info)&.channel
+        sleep 0.05
+      end
     end
 
-    # Extra time to make sure the consumer can attach
-    # Without this there's a chance the shutdown code will execute
-    # before consumption begins. This is tricky to do more elegantly
-    sleep 4
+    # Ensure that the consumer is fully started.
+    hare_info = instance.instance_variable_get(:@hare_info)
+    Timeout.timeout(10, Timeout::Error, "Timeout waiting for channel to have consumers.") do
+      until hare_info.channel.consumers && !hare_info.channel.consumers.empty?
+        sleep 0.05
+      end
+    end
   end
 
   let(:test_connection) { MarchHare.connect(instance.send(:rabbitmq_settings)) }
@@ -418,6 +425,11 @@ def spawn_and_wait(instance)
 
   after do
     instance.stop()
+    # Stop the thread gracefully before tearing down connections.
+    @consumer_thread.join
+    # Exchange deletion needs to be placed after thread is finished,
+    # as the exchange may be dynamically created during the test context initialization.
+    exchange&.delete if defined?(exchange)
     test_channel.close
     test_connection.close
   end
@@ -440,10 +452,6 @@ def spawn_and_wait(instance)
     #let(:queue) { test_channel.queue(queue_name, :auto_delete => true) }
     let(:queue_name) { "logstash-input-rabbitmq-#{rand(0xFFFFFFFF)}" }
 
-    after do
-      exchange.delete
-    end
-
     context "when the message has a payload but no message headers" do
       before do
         exchange.publish(message)