iOS中GCD定时器详解

目录

前言：CADisplayLink、NSTimer 不准时
一、GCD 定时器
二、GCD 定时器的实现方案

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"begin");    
    // 队列
    dispatch_queue_t queue = dispatch_get_main_queue();
    // 创建定时器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    // 设置时间
    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);

    // 设置回调
    dispatch_source_set_event_handler(timer, ^{
        NSLog(@"111");
    });
    // 启动定时器
    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);//创建一个信号量，只允许一个线程操作
    });
}
+ (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;

    //创建队列，队列决定到时候任务是在哪个线程执行
    dispatch_queue_t queue = async ? dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL) : dispatch_get_main_queue();
    //创建一个定时器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    /**
    dispatch_source_set_timer 上面的定时器
    dispatch_time_t start 开始时间  (typedef uint64_t dispatch_time_t;)
    uint64_t interval 间隔
    uint64_t leeway 误差一般写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);//信号量
    //定时器唯一标识
    static int i = 0;
    NSString *name = [NSString stringWithFormat:@"%d", i++];

    //放进字典，就会产生强引用
    timersDict[name] = timer;
    dispatch_semaphore_signal(semaphore);

    //设置回调
    dispatch_source_set_event_handler(timer, ^{
        blockTask();
        if (!repeat) {//如果非重复执行
            [self cancelTask:name];//取消定时器
        }
    });
    //启动定时器
    dispatch_resume(timer);
    //GCD不需要销毁
    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(@"执行任务---%@", [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

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