Issue #4826 - Use latch to replace thread-sleeping in tests

test/JsLatch.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "JsLatch.h"
 
 namespace
 {
   /**
+   * Implementation of JS function "Arrive()" on latch objects.
    */
   v8::Handle<v8::Value> ArriveCallback(const v8::Arguments& arguments)
   {
     auto self = static_cast<JsTestingLatch *>(
       v8::Local<v8::External>::Cast(arguments.Holder()->GetInternalField(0))->Value());
     if (self)
     {
       self->GetLatch().Arrive();
     }
     return v8::Undefined();
   }
 }
 
 /**
  * \par Implementation Notes
  *    Internal field 0 of the JS object contains a copy of \c this.
  */
 V8PersistentNG<v8::Object> JsTestingLatch::JsObjectInitializer(const std::string& propertyName)
 {
+  /*
+   * N.B. Member order ensures that \c engine has been initialized before this function runs.
+   */
   V8ExecutionScope context(engine);
   // Object template
   auto jsObjectTemplate = v8::ObjectTemplate::New();
   jsObjectTemplate->SetInternalFieldCount(1);
   jsObjectTemplate->Set(engine->ToV8String("Arrive"), v8::FunctionTemplate::New(ArriveCallback));
   // Object
   auto localJsObject = jsObjectTemplate->NewInstance();
   localJsObject->SetInternalField(0, v8::External::New(this));
   // Property on global
   engine->GetGlobalObject()->Set(engine->ToV8String(propertyName), localJsObject);
   // Persistent
   return V8PersistentNG<v8::Object>(engine->GetIsolate(), localJsObject);
 }
 
 JsTestingLatch::JsTestingLatch(JsEngineInternal* engine, const std::string& propertyName, int count)
   : engine(engine), latch(count), jsObject(JsObjectInitializer(propertyName))
 {}
 
 JsTestingLatch::~JsTestingLatch()
 {
   V8ExecutionScope context(engine);
   auto obj = jsObject.Get(engine->GetIsolate());
   // ensure object still exists
   if (obj->IsObject())
   {
     obj->SetInternalField(0, v8::External::New(nullptr));
   }
   // Rather than changing the "Arrive" property, we handle a null pointer in the callback for it.
 }