Replace def #{type}_func with define_singleton_method

When you run multiples pipeline and the code get evaluated the
class cache will be clear and the last evaluated code will be called
everything. The `filter_func` and the `output_func` need to be unique
for every instance of the pipeline.

This PR is based on #4254

logstash-core/lib/logstash/config/config_ast.rb

@@ -107,7 +107,10 @@ def compile
       ["filter", "output"].each do |type|
         # defines @filter_func and @output_func
 
-        definitions << "def #{type}_func(event)"
+        # This need to be defined as a singleton method
+        # so each instance of the pipeline has his own implementation
+        # of the output/filter function
+        definitions << "define_singleton_method :#{type}_func do |event|"
         definitions << "  targeted_outputs = []" if type == "output"
         definitions << "  events = [event]" if type == "filter"
         definitions << "  @logger.debug? && @logger.debug(\"#{type} received\", :event => event.to_hash)"

logstash-core/spec/logstash/pipeline_spec.rb

@@ -17,6 +17,21 @@ def close
   end
 end
 
+class DummyInputGenerator < LogStash::Inputs::Base
+  config_name "dummyinputgenerator"
+  milestone 2
+
+  def register
+  end
+
+  def run(queue)
+    queue << Logstash::Event.new while !stop?
+  end
+
+  def close
+  end
+end
+
 class DummyCodec < LogStash::Codecs::Base
   config_name "dummycodec"
   milestone 2
@@ -47,6 +62,10 @@ def initialize(params={})
 
   def register
   end
+
+  def threadsafe?
+    false
+  end
 
   def receive(event)
     @events << event
@@ -57,6 +76,10 @@ def close
   end
 end
 
+class DummyOutputMore < DummyOutput
+  config_name "dummyoutputmore"
+end
+
 class DummyFilter < LogStash::Filters::Base
   config_name "dummyfilter"
   milestone 2
@@ -362,4 +385,24 @@ class TestPipeline < LogStash::Pipeline
       pipeline.shutdown
     end
   end
+
+  context "Multiples pipelines" do
+    before do
+      allow(LogStash::Plugin).to receive(:lookup).with("input", "dummyinputgenerator").and_return(DummyInputGenerator)
+      allow(LogStash::Plugin).to receive(:lookup).with("codec", "plain").and_return(DummyCodec)
+      allow(LogStash::Plugin).to receive(:lookup).with("filter", "dummyfilter").and_return(DummyFilter)
+      allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput").and_return(DummyOutput)
+      allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutputmore").and_return(DummyOutputMore)
+    end
+
+    let(:pipeline1) { LogStash::Pipeline.new("input { dummyinputgenerator {} } filter { dummyfilter {} } output { dummyoutput {}}") }
+    let(:pipeline2) { LogStash::Pipeline.new("input { dummyinputgenerator {} } filter { dummyfilter {} } output { dummyoutputmore {}}") }
+
+    it "should handle evaluating different config" do
+      expect(pipeline1.output_func(LogStash::Event.new)).not_to include(nil)
+      expect(pipeline1.filter_func(LogStash::Event.new)).not_to include(nil)
+      expect(pipeline2.output_func(LogStash::Event.new)).not_to include(nil)
+      expect(pipeline1.filter_func(LogStash::Event.new)).not_to include(nil)
+    end
+  end
 end