- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"begin");    
    // 隊列
    dispatch_queue_t queue = dispatch_get_main_queue();
    // 創建定時器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    // 設置時間
    uint64_t start = 2.0;
    uint64_t interval = 1.0;
    dispatch_source_set_timer(timer,
                              dispatch_time(DISPATCH_TIME_NOW, start * NSEC_PER_SEC),
                              interval * NSEC_PER_SEC, 0);
    
    // 設置回調
    dispatch_source_set_event_handler(timer, ^{
        NSLog(@"111");
    });
    // 啟動定時器
    dispatch_resume(timer);
    
    self.timer = timer;
}

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface RHGCDTimer : NSObject

+ (NSString *)timerWithBlockTask:(void(^)(void))blockTask
                      star:(float)star
                  interval:(float)interval
                    repeat:(BOOL)repeat
                     async:(BOOL)async;

+ (void)cancelTask:(NSString *)name;

@end

NS_ASSUME_NONNULL_END

#import "RHGCDTimer.h"

static NSMutableDictionary *timersDict;
static dispatch_semaphore_t semaphore;

@implementation RHGCDTimer

+ (void)initialize
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        timersDict = [NSMutableDictionary dictionary];
        semaphore = dispatch_semaphore_create(1);//創建一個信號量，只允許一個線程操作
    });
}

+ (NSString *)timerWithBlockTask:(void (^)(void))blockTask star:(float)star interval:(float)interval repeat:(BOOL)repeat async:(BOOL)async
{
    
    if (!blockTask || star<0 || (repeat && interval <= 0)) return nil;
    
    //創建隊列，隊列決定到時候任務是在哪個線程執行
    dispatch_queue_t queue = async ? dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL) : dispatch_get_main_queue();

    //創建一個定時器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    /**
    dispatch_source_set_timer 上面的定時器
    dispatch_time_t start 開始時間  (typedef uint64_t dispatch_time_t;)
    uint64_t interval 間隔
    uint64_t leeway 誤差一般寫0
    */
    dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, star * NSEC_PER_SEC), interval *NSEC_PER_SEC, 0);

    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);//信號量
    //定時器唯一標識
    static int i = 0;
    NSString *name = [NSString stringWithFormat:@"%d", i++];
    
    //放進字典，就會產生強引用
    timersDict[name] = timer;
    dispatch_semaphore_signal(semaphore);
    
    //設置回調
    dispatch_source_set_event_handler(timer, ^{
        blockTask();
        if (!repeat) {//如果非重復執行
            [self cancelTask:name];//取消定時器
        }
    });
    //啟動定時器
    dispatch_resume(timer);
    //GCD不需要銷毀
    return name;
}

+ (void)cancelTask:(NSString *)name
{
    if (name.length == 0) return;
    
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    
    dispatch_source_t timer = timersDict[name];
    if (!timer) return;
    dispatch_source_cancel(timer);
    [timersDict removeObjectForKey:name];
    
    dispatch_semaphore_signal(semaphore);
}

@end

#import "ViewController.h"

#import "RHGCDTimer.h"

@interface ViewController ()

@property (copy, nonatomic) NSString *task;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.task = [RHGCDTimer timerWithBlockTask:^{
        NSLog(@"執行任務---%@", [NSThread currentThread]);
    } star:2.0 interval:1.0 repeat:YES async:YES];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    [RHGCDTimer cancelTask:self.task];
}

@end