Here's a hang inside the runtime. rdar://13210148

runtimeHang.m

//
//  AppDelegate.m
//  RuntimeHang
//
//  Created by BJ Homer on 2/13/13.
//  Copyright (c) 2013 BJ Homer. All rights reserved.
//

#import "AppDelegate.h"


// ----------------- CKObject Implementation ---------------- //

@interface CKObject : NSObject
@end

@implementation CKObject

+ (void)initialize {
    [super initialize];
    
    NSString *str = [[NSString alloc] initWithFormat:@"%s", __PRETTY_FUNCTION__];
#pragma unused (str)
    // When this string is deallocated, if we are inside a call to objc_storeWeak(), we will hang
}
@end





// ----------------- AppDelegate Implementation ---------------- //

@interface AppDelegate ()

@property (weak) CKObject *someObject;  // Important; this MUST be a weak property
@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

    // This code will hang inside +[CKObject initialize]. It happens when an NSKVONotifying_CKObject is assigned to a weak property.
    // The bug only happens on iOS devices (tested with iOS 6.1.1). It does not happen in the 6.1 simulator shipped with Xcode 4.6 release.
    
    
    CKObject *obj = [CKObject new];
    
    [obj addObserver:self forKeyPath:@"foo" options:0 context:0];
    

    NSLog(@"Starting the test. If the bug still exists, you will see no logging after this point.");
    self.someObject = obj;
    NSLog(@"If you see this, the bug is fixed.");
    
    [obj removeObserver:self forKeyPath:@"foo"];
    
    return YES;
}

@end