There is a period of time between checking if NativeLoader has been i…

…nitialized, and when we try to perform .init() which means a race condition can occur (as mentioned in facebook/SoLoader#60).

This change uses synchronization on the NativeLoader class, and a secondary check to verify that the initialization needs to take place just before we perform it, in order to reduce the window for a race condition to affect client code.

When combined with facebook/SoLoader#69 this will remove the race condition from the code because the initialisation inside SoLoader and inside Fresco will both be synchronized on the NativeLoad.class object.

drawee-backends/drawee-pipeline/src/main/java/com/facebook/drawee/backends/pipeline/Fresco.java

@@ -84,16 +84,16 @@ public static void initialize(
         clazz.getMethod("init", Context.class).invoke(null, context);
       } catch (ClassNotFoundException e) {
         // Failed to initialize SoLoader
-        NativeLoader.init(new SystemDelegate());
+        initializeNativeLoaderWithSystemDelegate();
       } catch (IllegalAccessException e) {
         // Failed to initialize SoLoader
-        NativeLoader.init(new SystemDelegate());
+        initializeNativeLoaderWithSystemDelegate();
       } catch (InvocationTargetException e) {
         // Failed to initialize SoLoader
-        NativeLoader.init(new SystemDelegate());
+        initializeNativeLoaderWithSystemDelegate();
       } catch (NoSuchMethodException e) {
         // Failed to initialize SoLoader
-        NativeLoader.init(new SystemDelegate());
+        initializeNativeLoaderWithSystemDelegate();
       } finally {
         if (FrescoSystrace.isTracing()) {
           FrescoSystrace.endSection();
@@ -113,6 +113,14 @@ public static void initialize(
     }
   }
 
+  private static void initializeNativeLoaderWithSystemDelegate() {
+    synchronized(NativeLoader.class) {
+      if(!NativeLoader.isInitialized()) {
+        NativeLoader.init(new SystemDelegate());
+      }
+    }
+  }
+
   /** Initializes Drawee with the specified config. */
   private static void initializeDrawee(Context context, @Nullable DraweeConfig draweeConfig) {
     if (FrescoSystrace.isTracing()) {