Documents USE_BLOCKS_BASED_LOCKING define. Refs #10.

README.markdown

@@ -18,6 +18,8 @@ App Store
 
 For iOS work, or Mac App Store work, you will probably want to set both COREFOUNDATION_HACK_LEVEL and KVO_HACK_LEVEL to `0`. In this mode, MAZeroingWeakRef uses no private APIs.
 
+Also, if you need your app to run on iOS 3.x you need to disable blocks based code setting USE_BLOCKS_BASED_LOCKING to `0`.
+
 Source Code
 -----------
 

Source/MAZeroingWeakRef.m

@@ -48,6 +48,19 @@
 #define KVO_HACK_LEVEL 1
 #endif
 
+/*
+ The USE_BLOCKS_BASED_LOCKING macro allows control on the code structure used
+ during lock checking. You want to disable blocks if you want your app to work
+ on iOS 3.x devices. iOS 4.x and above can use blocks.
+
+ 1 - Use blocks for lock checks.
+
+ 0 - Don't use blocks for lock checks.
+ */
+#ifndef USE_BLOCKS_BASED_LOCKING
+#define USE_BLOCKS_BASED_LOCKING 1
+#endif
+
 #if KVO_HACK_LEVEL >= 1
 @interface NSObject (KVOPrivateMethod)
 
@@ -192,7 +205,6 @@ + (void)initialize
     }
 }
 
-#define USE_BLOCKS_BASED_LOCKING 1
 #if USE_BLOCKS_BASED_LOCKING
 #define BLOCK_QUALIFIER __block
 static void WhileLocked(void (^block)(void))