iOS底层系列之＜46＞--内存管理＜2＞定时器

1、定时器相关 （a） 上一篇文章介绍了定时器相关内容，CADisplayLink 和NSTimer都是基于Runloop的定时器，但是Runloop的任务过于繁重的时候，定时器就不准了！ （b）所以，在项目中，尽量使用GCD定时器会更准确。 2、GCD定时器封装

类方法调用，但是我觉得可以封装成实例方法可能会更好一点，晚点再封装一次。
JHTimer.h文件

#import 

NS_ASSUME_NONNULL_BEGIN

//typedef (void)(^Task)(void);

@interface JHTimer : NSObject
+ (NSString *)excuteTask:(void (^)(void))task
             start:(NSTimeInterval)start
          interval:(NSTimeInterval)interval
         isRepeats:(BOOL)isRepeats
           isAsync:(BOOL)isAsync;

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

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

+ (void)restartTimer:(NSString *)name;
@end

NS_ASSUME_NONNULL_END

JHTimer.m文件

#import "JHTimer.h"

@implementation JHTimer

static NSMutableDictionary *timerDict;
static BOOL isStarted;
static BOOL isCanceled;
static BOOL isSuspended;
static BOOL isRestarted;

+ (void)initialize {
    static dispatch_once_t onecToken;
    dispatch_once(&onecToken, ^{
        timerDict = [NSMutableDictionary dictionary];
        isStarted = NO;
        isCanceled = NO;
        isSuspended = NO;
        isRestarted = NO;
    });
    
}

+ (NSString *)excuteTask:(void (^)(void))task start:(NSTimeInterval)start interval:(NSTimeInterval)interval isRepeats:(BOOL)isRepeats isAsync:(BOOL)isAsync {
    if (!task) {
        return nil;
    }
    if (timerDict.count == 1) {
        return [NSString stringWithFormat:@"%zd",timerDict.count];
    }
    
    unsigned long count = timerDict.count + 1;
    NSString *timerName = [NSString stringWithFormat:@"%zd",count++];
    
    dispatch_queue_t queue = isAsync ? dispatch_get_global_queue(0, 0) : dispatch_get_main_queue();
    
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    
    
    dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, start * NSEC_PER_SEC), interval * NSEC_PER_SEC, 0);
    
    
    dispatch_source_set_event_handler(timer, ^{
        task();
        if (!isRepeats) {
            [self __cancelTimer:timerName];
        }
    });
    
    dispatch_resume(timer);
    
    
    timerDict[timerName] = timer;
    
    isStarted = YES;
    isCanceled = NO;
    isSuspended = NO;
    isRestarted = NO;
    
    return timerName;
}

// pass
+ (void)cancelTimer:(NSString *)name {
    if ([timerDict objectForKey:name] == nil || isSuspended) {
        return;
    }
    dispatch_cancel([timerDict objectForKey:name]);
    [timerDict removeObjectForKey:name];
    isStarted = NO;
    isCanceled = NO;
    isSuspended = NO;
    isRestarted = NO;
}

// 开启状态才可以
+ (void)suspendTimer:(NSString *)name {
    if ([timerDict objectForKey:name] == nil || !isStarted || isCanceled || isSuspended) {
        return;
    }
    dispatch_suspend([timerDict objectForKey:name]);
    isStarted = YES;
    isCanceled = NO;
    isSuspended = YES;
    isRestarted = NO;
}

// suspend状态才可以
+ (void)restartTimer:(NSString *)name {
    if ([timerDict objectForKey:name] == nil || !isSuspended || isRestarted || isCanceled || !isStarted) {
        return;
    }
    dispatch_resume([timerDict objectForKey:name]);
    isStarted = YES;
    isCanceled = NO;
    isSuspended = NO;
    isRestarted = YES;
}


+ (void)__cancelTimer:(NSString *)name {
    dispatch_cancel(timerDict[name]);
    [timerDict removeObjectForKey:name];
}

@end

3、iOS程序的内存布局