Issue 4694 - JsEngine::{SetEventCallback,RemoveEventCallback,TriggerEvent} should be thread safe.

src/JsEngine.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 99 matching lines @@
     filename);
   CheckTryCatch(tryCatch);
   v8::Local<v8::Value> result = script->Run();
   CheckTryCatch(tryCatch);
   return JsValuePtr(new JsValue(shared_from_this(), result));
 }
 
 void AdblockPlus::JsEngine::SetEventCallback(const std::string& eventName,
     AdblockPlus::JsEngine::EventCallback callback)
 {
+  std::lock_guard<std::mutex> lock(eventCallbacksMutex);
   eventCallbacks[eventName] = callback;
 }
 
 void AdblockPlus::JsEngine::RemoveEventCallback(const std::string& eventName)
 {
+  std::lock_guard<std::mutex> lock(eventCallbacksMutex);
   eventCallbacks.erase(eventName);
 }
 
 void AdblockPlus::JsEngine::TriggerEvent(const std::string& eventName, AdblockPlus::JsValueList& params)
 {
-  EventMap::iterator it = eventCallbacks.find(eventName);
-  if (it != eventCallbacks.end())
-    it->second(params);
+  EventCallback callback;
+  {
+    std::lock_guard<std::mutex> lock(eventCallbacksMutex);
+    auto it = eventCallbacks.find(eventName);
+    if (it == eventCallbacks.end())
+      return;
+    callback = it->second;
+  }
+  callback(params);

[Oleksandr, 2017/03/20 20:00:42]

Nit: Maybe check if callback is not null JIC?

[sergei, 2017/03/20 20:08:13]

What about such check in SetEventCallback? Maybe even removing of existing
callback if an empty value is passed into SetEventCallback, though I would like
to avoid such dualism, it definitely should not be a documented way while there
is RemoveEventCallback.

[sergei, 2017/03/20 20:23:24]

Actually, I think it should be in another commit.

[Oleksandr, 2017/03/20 20:25:25]

Fair enough. It isn't that big of an issue IMO, so, again, LGTM.

 }
 
 void AdblockPlus::JsEngine::Gc()
 {
   while (!v8::V8::IdleNotification());
 }
 
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::NewValue(const std::string& val)
 {
   const JsContext context(shared_from_this());
@@ skipping 122 matching lines @@
 
 
 void AdblockPlus::JsEngine::SetGlobalProperty(const std::string& name, 
                                               AdblockPlus::JsValuePtr value)
 {
   auto global = GetGlobalObject();
   if (!global)
     throw std::runtime_error("Global object cannot be null");
   global->SetProperty(name, value);
 }