YYTransaction

/**
  YYTransaction let you perform a selector once before       
  current runloop sleep
*/

@interface YYTransaction : NSObject

/**
    Creates and returns a transaction with a specified
    target and selector.
*/
+ (YYTransaction *)transactionWithTarget:(id)target selector:(SEL)selector;

/**
    commit the transaction to the main runloop

    @discussion It will perform the selector on the target 
        once before the main runloop's current loop sleep.
        If the same transaction (same target and same 
        selector) has already commit to runloop in this loop
        , this method does nothing.
*/
- (void)commit

@end

@interface Transaction()
@property (nonatomic, strong) id target;
@property (nonatomic, assign) SEL selector;
@end

static NSMutableSet *transactionSet = nil;

static void YYRunLoopObserverCallBack(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info) {
    if (transactionSet.count == 0) return;
    NSSet *currentSet = transactionSet;
    transactionSet = [NSMutableSet new];
    [currentSet enumerateObjectsUsingBlock:^(YYTransaction *transaction, BOOL *stop) {
        [transaction.target performSelector:transaction.selector]
    }];
}

static void YYTransactionSetup() {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        transactionSet = [NSMutableSet new];
        CFRunLoopRef runloop = CFRunLoopGetMain();
        CFRunLoopObserverRef observer;

        observer = CFRunLoopObserverCreate(CFAllocatorGetDefault(), kCFRunLoopBeforeWaiting | kCFRunLoopExit,true, 0xFFFFFF, YYRunLoopObserverCallBack, NULL);

        CFRunLoopAddObserver(runloop, observer, kCFRunLoopCommonModes);
        CFRelease(observer);
    });
}

@implementation YYTransaction
+ (YYTransaction *)transactionWithTarget:(id)target selector:(SEL)selector {
    if(!target || !selector) return nil;
    YYTransaction *t = [YYTransaction new];
    t.target = target;
    t.selector = selector;
    return t;
}

- (void)commit {
    if(!_target || !_selector) return;
    YYTransactionSetup();
    [transactionSet addObject:self];
}

- (NSUInteger)hash {
    long v1 = (long)((void *)_selector);
    long v2 = (long)_target;
    return v1^v2;
}

- (BOOL)isEqual:(id)object {
    if(self == object) return YES;
    if(![object isMemberOfClass:self.class]) return NO;
    YYTransaction *other = object;
    return other.selector == _selector && other.target == _target;
}

@end