don't do concurrent access to a static member variable

in situations where the renderer is used from multiple threads, this causes memory corruption.

fixes mapbox/node-mapbox-gl-native#7

4 files changed, 39 insertions, 12 deletions

diff --git a/include/mbgl/style/class_dictionary.hpp b/include/mbgl/style/class_dictionary.hpp
index c7f9c6a284..ecf80be3e3 100644
--- a/include/mbgl/style/class_dictionary.hpp
+++ b/include/mbgl/style/class_dictionary.hpp
@@ -14,17 +14,22 @@ enum class ClassID : uint32_t {
 };
 
 class ClassDictionary {
+private:
+    ClassDictionary();
+
 public:
+    static ClassDictionary &Get();
+
     // Returns an ID for a class name. If the class name does not yet have an ID, one is
     // auto-generated and stored for future reference.
-    static ClassID Lookup(const std::string &class_name);
+    ClassID lookup(const std::string &class_name);
 
     // Returns either Fallback, Default or Named, depending on the type of the class id.
-    static ClassID Normalize(ClassID id);
+    ClassID normalize(ClassID id);
 
 private:
-    static std::unordered_map<std::string, ClassID> store;
-    static uint32_t offset;
+    std::unordered_map<std::string, ClassID> store = { { "", ClassID::Default } };
+    uint32_t offset = 0;
 };
 
 }
diff --git a/src/style/class_dictionary.cpp b/src/style/class_dictionary.cpp
index 6e1eb5a879..ba7c0d55be 100644
--- a/src/style/class_dictionary.cpp
+++ b/src/style/class_dictionary.cpp
@@ -1,8 +1,34 @@
 #include <mbgl/style/class_dictionary.hpp>
 
+#include <uv.h>
+
 namespace mbgl {
 
-ClassID ClassDictionary::Lookup(const std::string &class_name) {
+ClassDictionary::ClassDictionary() {}
+
+ClassDictionary &ClassDictionary::Get() {
+    // Note: We should eventually switch to uv_key_* functions, but libuv 0.10 doesn't have these
+    // yet. Instead, we're using the pthread functions directly for now.
+    static pthread_once_t store_once = PTHREAD_ONCE_INIT;
+    static pthread_key_t store_key;
+
+    // Create the key.
+    pthread_once(&store_once, []() {
+        pthread_key_create(&store_key, [](void *ptr) {
+            delete reinterpret_cast<ClassDictionary *>(ptr);
+        });
+    });
+
+    ClassDictionary *ptr = reinterpret_cast<ClassDictionary *>(pthread_getspecific(store_key));
+    if (ptr == nullptr) {
+        ptr = new ClassDictionary();
+        pthread_setspecific(store_key, ptr);
+    }
+
+    return *ptr;
+}
+
+ClassID ClassDictionary::lookup(const std::string &class_name) {
     auto it = store.find(class_name);
     if (it == store.end()) {
         // Insert the class name into the store.
@@ -14,7 +40,7 @@ ClassID ClassDictionary::Lookup(const std::string &class_name) {
     }
 }
 
-ClassID ClassDictionary::Normalize(ClassID id) {
+ClassID ClassDictionary::normalize(ClassID id) {
     if (id >= ClassID::Named) {
         return ClassID::Named;
     } else {
@@ -22,8 +48,4 @@ ClassID ClassDictionary::Normalize(ClassID id) {
     }
 }
 
-
-std::unordered_map<std::string, ClassID> ClassDictionary::store = { { "", ClassID::Default } };
-uint32_t ClassDictionary::offset = 0;
-
 }
diff --git a/src/style/style_layer.cpp b/src/style/style_layer.cpp
index 4f758fe723..b1b878cc8d 100644
--- a/src/style/style_layer.cpp
+++ b/src/style/style_layer.cpp
@@ -23,7 +23,7 @@ void StyleLayer::setClasses(const std::vector<std::string> &class_names, const t
     for (auto it = class_names.rbegin(); it != class_names.rend(); it++) {
         const std::string &class_name = *it;
         // From here on, we're only dealing with IDs to avoid comparing strings all the time.
-        const ClassID class_id = ClassDictionary::Lookup(class_name);
+        const ClassID class_id = ClassDictionary::Get().lookup(class_name);
         applyClassProperties(class_id, already_applied, now, defaultTransition);
     }
 
diff --git a/src/style/style_parser.cpp b/src/style/style_parser.cpp
index 7e695e71cb..ad7694d9a9 100644
--- a/src/style/style_parser.cpp
+++ b/src/style/style_parser.cpp
@@ -554,7 +554,7 @@ void StyleParser::parseStyles(JSVal value, std::map<ClassID, ClassProperties> &s
         if (name == "style") {
             parseStyle(replaceConstant(itr->value), styles[ClassID::Default]);
         } else if (name.compare(0, 6, "style.") == 0 && name.length() > 6) {
-            const ClassID class_id = ClassDictionary::Lookup(name.substr(6));
+            const ClassID class_id = ClassDictionary::Get().lookup(name.substr(6));
             parseStyle(replaceConstant(itr->value), styles[class_id]);
         }
     }