Merge branch 'fix-method-instrumentation' into 'master'

Use Module#prepend for method instrumentation

cc @pcarranza 

See merge request !3754

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.7.0 (unreleased)
+  - Method instrumentation now uses Module#prepend instead of aliasing methods
   - The Projects::HousekeepingService class has extra instrumentation
   - All service classes (those residing in app/services) are now instrumented
   - Developers can now add custom tags to transactions

lib/gitlab/metrics/instrumentation.rb

@@ -11,6 +11,8 @@ module Gitlab
     module Instrumentation
       SERIES = 'method_calls'
 
+      PROXY_IVAR = :@__gitlab_instrumentation_proxy
+
       def self.configure
         yield self
       end
@@ -91,6 +93,18 @@ module Gitlab
         end
       end
 
+      # Returns true if a module is instrumented.
+      #
+      # mod - The module to check
+      def self.instrumented?(mod)
+        mod.instance_variable_defined?(PROXY_IVAR)
+      end
+
+      # Returns the proxy module (if any) of `mod`.
+      def self.proxy_module(mod)
+        mod.instance_variable_get(PROXY_IVAR)
+      end
+
       # Instruments a method.
       #
       # type - The type (:class or :instance) of method to instrument.
@@ -100,7 +114,6 @@ module Gitlab
         return unless Metrics.enabled?
 
         name   = name.to_sym
-        alias_name = :"_original_#{name}"
         target = type == :instance ? mod : mod.singleton_class
 
         if type == :instance
@@ -113,6 +126,12 @@ module Gitlab
           method = mod.method(name)
         end
 
+        unless instrumented?(target)
+          target.instance_variable_set(PROXY_IVAR, Module.new)
+        end
+
+        proxy_module = self.proxy_module(target)
+
         # Some code out there (e.g. the "state_machine" Gem) checks the arity of
         # a method to make sure it only passes arguments when the method expects
         # any. If we were to always overwrite a method to take an `*args`
@@ -125,17 +144,13 @@ module Gitlab
           args_signature = '*args, &block'
         end
 
-        send_signature = "__send__(#{alias_name.inspect}, #{args_signature})"
-
-        target.class_eval <<-EOF, __FILE__, __LINE__ + 1
-          alias_method #{alias_name.inspect}, #{name.inspect}
-
+        proxy_module.class_eval <<-EOF, __FILE__, __LINE__ + 1
           def #{name}(#{args_signature})
             trans = Gitlab::Metrics::Instrumentation.transaction
 
             if trans
               start    = Time.now
-              retval   = #{send_signature}
+              retval   = super
               duration = (Time.now - start) * 1000.0
 
               if duration >= Gitlab::Metrics.method_call_threshold
@@ -148,10 +163,12 @@ module Gitlab
 
               retval
             else
-              #{send_signature}
+              super
             end
           end
         EOF
+
+        target.prepend(proxy_module)
       end
 
       # Small layer of indirection to make it easier to stub out the current

spec/lib/gitlab/metrics/instrumentation_spec.rb

@@ -33,8 +33,16 @@ describe Gitlab::Metrics::Instrumentation do
         described_class.instrument_method(@dummy, :foo)
       end
 
-      it 'renames the original method' do
-        expect(@dummy).to respond_to(:_original_foo)
+      it 'instruments the Class' do
+        target = @dummy.singleton_class
+
+        expect(described_class.instrumented?(target)).to eq(true)
+      end
+
+      it 'defines a proxy method' do
+        mod = described_class.proxy_module(@dummy.singleton_class)
+
+        expect(mod.method_defined?(:foo)).to eq(true)
       end
 
       it 'calls the instrumented method with the correct arguments' do
@@ -76,6 +84,14 @@ describe Gitlab::Metrics::Instrumentation do
 
         expect(dummy.method(:test).arity).to eq(0)
       end
+
+      describe 'when a module is instrumented multiple times' do
+        it 'calls the instrumented method with the correct arguments' do
+          described_class.instrument_method(@dummy, :foo)
+
+          expect(@dummy.foo).to eq('foo')
+        end
+      end
     end
 
     describe 'with metrics disabled' do
@@ -86,7 +102,9 @@ describe Gitlab::Metrics::Instrumentation do
       it 'does not instrument the method' do
         described_class.instrument_method(@dummy, :foo)
 
-        expect(@dummy).to_not respond_to(:_original_foo)
+        target = @dummy.singleton_class
+
+        expect(described_class.instrumented?(target)).to eq(false)
       end
     end
   end
@@ -100,8 +118,14 @@ describe Gitlab::Metrics::Instrumentation do
           instrument_instance_method(@dummy, :bar)
       end
 
-      it 'renames the original method' do
-        expect(@dummy.method_defined?(:_original_bar)).to eq(true)
+      it 'instruments instances of the Class' do
+        expect(described_class.instrumented?(@dummy)).to eq(true)
+      end
+
+      it 'defines a proxy method' do
+        mod = described_class.proxy_module(@dummy)
+
+        expect(mod.method_defined?(:bar)).to eq(true)
       end
 
       it 'calls the instrumented method with the correct arguments' do
@@ -144,7 +168,7 @@ describe Gitlab::Metrics::Instrumentation do
         described_class.
           instrument_instance_method(@dummy, :bar)
 
-        expect(@dummy.method_defined?(:_original_bar)).to eq(false)
+        expect(described_class.instrumented?(@dummy)).to eq(false)
       end
     end
   end
@@ -167,18 +191,17 @@ describe Gitlab::Metrics::Instrumentation do
     it 'recursively instruments a class hierarchy' do
       described_class.instrument_class_hierarchy(@dummy)
 
-      expect(@child1).to respond_to(:_original_child1_foo)
-      expect(@child2).to respond_to(:_original_child2_foo)
+      expect(described_class.instrumented?(@child1.singleton_class)).to eq(true)
+      expect(described_class.instrumented?(@child2.singleton_class)).to eq(true)
 
-      expect(@child1.method_defined?(:_original_child1_bar)).to eq(true)
-      expect(@child2.method_defined?(:_original_child2_bar)).to eq(true)
+      expect(described_class.instrumented?(@child1)).to eq(true)
+      expect(described_class.instrumented?(@child2)).to eq(true)
     end
 
     it 'does not instrument the root module' do
       described_class.instrument_class_hierarchy(@dummy)
 
-      expect(@dummy).to_not respond_to(:_original_foo)
-      expect(@dummy.method_defined?(:_original_bar)).to eq(false)
+      expect(described_class.instrumented?(@dummy)).to eq(false)
     end
   end
 
@@ -190,7 +213,7 @@ describe Gitlab::Metrics::Instrumentation do
     it 'instruments all public class methods' do
       described_class.instrument_methods(@dummy)
 
-      expect(@dummy).to respond_to(:_original_foo)
+      expect(described_class.instrumented?(@dummy.singleton_class)).to eq(true)
     end
 
     it 'only instruments methods directly defined in the module' do
@@ -223,7 +246,7 @@ describe Gitlab::Metrics::Instrumentation do
     it 'instruments all public instance methods' do
       described_class.instrument_instance_methods(@dummy)
 
-      expect(@dummy.method_defined?(:_original_bar)).to eq(true)
+      expect(described_class.instrumented?(@dummy)).to eq(true)
     end
 
     it 'only instruments methods directly defined in the module' do