repeated hooks

lib/datadog/di/hook.rb

@@ -1,23 +1,42 @@
+require 'concurrent-ruby'
+
 module Datadog
   module DI
     module Hook
       module_function def hook_method(cls_name, meth_name)
         cls = symbolize_class_name(cls_name)
+        id = next_id
 
         cls.class_eval do
           saved = instance_method(meth_name)
 
           remove_method(meth_name)
           define_method(meth_name) do |*args, **kwargs|
-            saved.bind(self).call(*args, **kwargs).tap do |rv|
-              yield rv: rv
+            if INSTRUMENTED[[cls_name, meth_name]] == id
+              saved.bind(self).call(*args, **kwargs).tap do |rv|
+                yield rv: rv
+              end
+            else
+              saved.bind(self).call(*args, **kwargs)
             end
           end
         end
+
+        INSTRUMENTED[[cls_name, meth_name]] = id
       end
 
       private
 
+      INSTRUMENTED = Concurrent::Map.new
+      NEXT_MUTEX = Mutex.new
+
+      module_function def next_id
+        NEXT_MUTEX.synchronize do
+          @next_id ||= 0
+          @next_id += 1
+        end
+      end
+
       module_function def symbolize_class_name(cls_name)
         Object.const_get(cls_name)
       end

spec/datadog/di/hook_spec.rb

@@ -52,5 +52,22 @@ def hook_test_method_with_kwarg(kwarg:)
         observed_calls.first.should == {rv: 2}
       end
     end
+
+    context 'when hooked twice' do
+      it 'only invokes callback once' do
+        described_class.hook_method(:HookTestClass, :hook_test_method) do |payload|
+          observed_calls << payload
+        end
+
+        described_class.hook_method(:HookTestClass, :hook_test_method) do |payload|
+          observed_calls << payload
+        end
+
+        HookTestClass.new.hook_test_method.should == 42
+
+        observed_calls.length.should == 1
+        observed_calls.first.should == {rv: 42}
+      end
+    end
   end
 end