From 9ef6aee3d18d97d8efff35cf8928f4d1c85c0d3a Mon Sep 17 00:00:00 2001
From: Ryan Huffman <ryanhuffman@gmail.com>
Date: Sun, 16 Oct 2016 10:26:57 -0700
Subject: [PATCH] Fix race condition in BatchLoader

---
 libraries/script-engine/src/BatchLoader.cpp | 20 ++++++++++----------
 libraries/script-engine/src/BatchLoader.h   |  3 +++
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/libraries/script-engine/src/BatchLoader.cpp b/libraries/script-engine/src/BatchLoader.cpp
index 15b3b6c853..692c0ecd7a 100644
--- a/libraries/script-engine/src/BatchLoader.cpp
+++ b/libraries/script-engine/src/BatchLoader.cpp
@@ -48,6 +48,11 @@ void BatchLoader::start() {
             if (!self) {
                 return;
             }
+
+            // Because the ScriptCache may call this callback from differents threads,
+            // we need to make sure this is thread-safe.
+            std::lock_guard<std::mutex> lock(_dataLock);
+
             if (isURL && success) {
                 _data.insert(url, contents);
                 qCDebug(scriptengine) << "Loaded: " << url;
@@ -55,16 +60,11 @@ void BatchLoader::start() {
                 _data.insert(url, QString());
                 qCDebug(scriptengine) << "Could not load" << url;
             }
-            checkFinished();
+
+            if (!_finished && _urls.size() == _data.size()) {
+                _finished = true;
+                emit finished(_data);
+            }
         }, false);
     }
-
-    checkFinished();
-}
-
-void BatchLoader::checkFinished() {
-    if (!_finished && _urls.size() == _data.size()) {
-        _finished = true;
-        emit finished(_data);
-    }
 }
diff --git a/libraries/script-engine/src/BatchLoader.h b/libraries/script-engine/src/BatchLoader.h
index cda040d219..40b43d23b6 100644
--- a/libraries/script-engine/src/BatchLoader.h
+++ b/libraries/script-engine/src/BatchLoader.h
@@ -19,6 +19,8 @@
 #include <QString>
 #include <QUrl>
 
+#include <mutex>
+
 class BatchLoader : public QObject {
     Q_OBJECT
 public:
@@ -37,6 +39,7 @@ private:
     bool _finished;
     QSet<QUrl> _urls;
     QMap<QUrl, QString> _data;
+    std::mutex _dataLock;
 };
 
 #endif // hifi_BatchLoader_h