RunLoop的实际运用

.h代码：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

__attribute__((objc_subclassing_restricted))
@interface RLTransaction : NSObject

+ (void)commitAction:(void (^)(void))action;

@end

NS_ASSUME_NONNULL_END

.m代码：

#import "RLTransaction.h"


@interface RLTransaction ()
@property (nonatomic, copy) void (^action)(void);
@end


static NSMutableArray *g_transactionArray = nil;
static dispatch_queue_t g_actionQueue = nil;

static void RLTransactionSetup()
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        g_transactionArray = @[].mutableCopy;
        g_actionQueue = dispatch_queue_create("action_queue", NULL);
        CFRunLoopRef runloop = CFRunLoopGetMain();
        CFRunLoopObserverRef observer;
        
        observer = CFRunLoopObserverCreateWithHandler(CFAllocatorGetDefault(),
                                                      kCFRunLoopBeforeWaiting | kCFRunLoopExit,
                                                      true,
                                                      0xFFFFFF,
                                                      ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity)
        {
          if (g_transactionArray.count == 0)
              return;
          
            dispatch_sync(g_actionQueue, ^{
                NSArray *tasks = g_transactionArray.copy;
                [g_transactionArray removeAllObjects];
                
                [tasks enumerateObjectsUsingBlock:^(RLTransaction *obj, NSUInteger idx, BOOL * stop) {
                    obj.action();
                }];
            });
        });
        
        CFRunLoopAddObserver(runloop, observer, kCFRunLoopCommonModes);
        CFRelease(observer);
    });
}


@implementation RLTransaction

+ (void)commitAction:(void (^)(void))action
{
    RLTransaction *transaction =  [RLTransaction new];
    transaction.action = action;
    RLTransactionSetup();
    [g_transactionArray addObject:transaction];
}

@end