Issue 3594 - remove circular references JsEngine-JsValue-JsEngine

src/WebRequestJsObject.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
@@ skipping 12 matching lines @@
 #include "Thread.h"
 #include "Utils.h"
 #include "WebRequestJsObject.h"
 
 namespace
 {
   class WebRequestThread : public AdblockPlus::Thread
   {
   public:
     WebRequestThread(AdblockPlus::JsEnginePtr jsEngine, AdblockPlus::JsValueList& arguments)
-        : Thread(true), jsEngine(jsEngine), url(arguments[0]->AsString())
+        : Thread(true), m_jsEngine(jsEngine), url(arguments[0]->AsString())
     {
       if (!url.length())
         throw std::runtime_error("Invalid string passed as first argument to GET");
 
       {
         AdblockPlus::JsValuePtr headersObj = arguments[1];
         if (!headersObj->IsObject())
           throw std::runtime_error("Second argument to GET must be an object");
 
         std::vector<std::string> properties = headersObj->GetOwnPropertyNames();
         for (std::vector<std::string>::iterator it = properties.begin();
             it != properties.end(); ++it)
         {
           std::string header = *it;
           std::string headerValue = headersObj->GetProperty(header)->AsString();
           if (header.length() && headerValue.length())
             headers.push_back(std::pair<std::string, std::string>(header, headerValue));
         }
       }
 
       callback = arguments[2];
       if (!callback->IsFunction())
         throw std::runtime_error("Third argument to GET must be a function");
     }
 
     void Run()
     {
-      AdblockPlus::ServerResponse result = jsEngine->GetWebRequest()->GET(url, headers);
-
-      AdblockPlus::JsContext context(jsEngine);
-
-      AdblockPlus::JsValuePtr resultObject = jsEngine->NewObject();
+      // Don't keep a strong reference to JsEngine while request is being executed.
+      auto webRequest = AdblockPlus::Utils::lockJsEngine(m_jsEngine)->GetWebRequest();

[Oleksandr, 2016/11/25 10:38:04]

Is there any reason why the line above is not using jsEngine from the context as
well? 

[sergei, 2016/11/25 12:04:46]

Yes, it's in the comment. Let's say we have "locked" JsEngine and call
WebRequest::GET. At the same time we have LazyWebRequest::GET which never
returns. It means that all tests will still prevent JsEngine from destroying.
So, here we lock JsEngine, obtain webRequest and "unlock" JsEngine.
AdblockPlus::Utils::lockJsEngine and AdblockPlus::JsContext throw exception if
they cannot lock JsEngine.

+      auto result = webRequest->GET(url, headers);
+      AdblockPlus::JsContext context(m_jsEngine);
+      AdblockPlus::JsValuePtr resultObject = context.jsEngine().NewObject();
       resultObject->SetProperty("status", result.status);
       resultObject->SetProperty("responseStatus", result.responseStatus);
       resultObject->SetProperty("responseText", result.responseText);
 
-      AdblockPlus::JsValuePtr headersObject = jsEngine->NewObject();
+      AdblockPlus::JsValuePtr headersObject = context.jsEngine().NewObject();
       for (AdblockPlus::HeaderList::iterator it = result.responseHeaders.begin();
         it != result.responseHeaders.end(); ++it)
       {
         headersObject->SetProperty(it->first, it->second);
       }
       resultObject->SetProperty("responseHeaders", headersObject);
 
       AdblockPlus::JsValueList params;
       params.push_back(resultObject);
       callback->Call(params);
     }
 
   private:
-    AdblockPlus::JsEnginePtr jsEngine;
+    std::weak_ptr<AdblockPlus::JsEngine> m_jsEngine;
     std::string url;
     AdblockPlus::HeaderList headers;
     AdblockPlus::JsValuePtr callback;
   };
 
   v8::Handle<v8::Value> GETCallback(const v8::Arguments& arguments)
   {
     WebRequestThread* thread;
     try
     {
@@ skipping 13 matching lines @@
     return v8::Undefined();
   }
 }
 
 AdblockPlus::JsValuePtr AdblockPlus::WebRequestJsObject::Setup(
     AdblockPlus::JsEnginePtr jsEngine, AdblockPlus::JsValuePtr obj)
 {
   obj->SetProperty("GET", jsEngine->NewCallback(::GETCallback));
   return obj;
 }