Chnage concurrency to :shared and publish outside of synchronized code

lib/logstash/outputs/bigquery/batcher.rb

@@ -35,6 +35,7 @@ def enqueue_push(message, queue)
         def enqueue(message)
           @lock.write_lock.lock
 
+          orig = nil
           begin
             is_flush_request = message.nil?
 
@@ -49,15 +50,14 @@ def enqueue(message)
             if is_flush_request || length_met || size_met
               orig = @batch
               clear
-
-              yield(orig) if block_given?
-              return orig
             end
 
-            nil
           ensure
             @lock.write_lock.unlock
           end
+
+          yield(orig) if block_given? && !orig.nil?
+          return orig
         end
 
         # removes all elements from the batch

lib/logstash/outputs/google_bigquery.rb

@@ -68,7 +68,7 @@
 class LogStash::Outputs::GoogleBigQuery < LogStash::Outputs::Base
   config_name 'google_bigquery'
 
-  concurrency :single
+  concurrency :shared
 
   # Google Cloud Project ID (number, not Project Name!).
   config :project_id, validate: :string, required: true