start inputs only when all WorkerLoop are fully initialized

logstash-core/lib/logstash/java_pipeline.rb

@@ -244,18 +244,28 @@ def start_workers
 
       filter_queue_client.set_batch_dimensions(batch_size, batch_delay)
 
-      pipeline_workers.times do |t|
+      # First launch WorkerLoop initialization in separate threads which concurrently
+      # compiles and initializes the worker pipelines
+
+      worker_loops = pipeline_workers.times
+        .map { Thread.new { init_worker_loop } }
+        .map(&:value)
+
+      fail("Some worker(s) were not correctly initialized") if worker_loops.any?{|v| v.nil?}
+
+      # Once all WorkerLoop have been initialized run them in separate threads
+
+      worker_loops.each_with_index do |worker_loop, t|
         thread = Thread.new do
           Util.set_thread_name("[#{pipeline_id}]>worker#{t}")
           ThreadContext.put("pipeline.id", pipeline_id)
-          org.logstash.execution.WorkerLoop.new(
-              lir_execution, filter_queue_client, @events_filtered, @events_consumed,
-              @flushRequested, @flushing, @shutdownRequested, @drain_queue).run
+          worker_loop.run
         end
         @worker_threads << thread
       end
 
-      # inputs should be started last, after all workers
+      # Finally inputs should be started last, after all workers have been initialized and started
+
       begin
         start_inputs
       rescue => e
@@ -466,6 +476,26 @@ def inspect
 
   private
 
+  # @return [WorkerLoop] a new WorkerLoop instance or nil upon construction exception
+  def init_worker_loop
+    begin
+      org.logstash.execution.WorkerLoop.new(
+        lir_execution,
+        filter_queue_client,
+        @events_filtered,
+        @events_consumed,
+        @flushRequested,
+        @flushing,
+        @shutdownRequested,
+        @drain_queue)
+    rescue => e
+      @logger.error(
+        "Worker loop initialization error",
+        default_logging_keys(:error => e.message, :exception => e.class, :stacktrace => e.backtrace.join("\n")))
+      nil
+    end
+  end
+
   def maybe_setup_out_plugins
     if @outputs_registered.make_true
       register_plugins(outputs)