RACScheduler //RAC封装的多线程/单线程block调用接口。
特点：可以递归执行block／可以在后台线程环境下执行block／可以在指定的时间执行block／可以在指定时间开始，一定时间间隔重复执行block

RACScheduler    // scheduler默认创建的RACTargetQueueScheduler。  RACScheduler的初始化没有队列，只是得到个名字。因此这个类似于抽象类。schedule的调用，依赖于继承类。或者是调用RACScheduler.currentScheduler类方法--RACScheduler.mainThreadScheduler主线程或者是当前线程NSThread.currentThread.threadDictionary[RACSchedulerCurrentSchedulerKey]


    ->RACTestScheduler//


    ->RACSubscriptionScheduler      //subscriptionScheduler单例。实际包括一条RACTargetQueueScheduler类型的backgroundScheduler实例，由此来工作。 

    ->RACQueueScheduler//
        ->RACTargetQueueScheduler   //RACScheduler.mainThreadScheduler就是这个类型，只不过dispatch_set_target_queue是dispatch_get_main_queue()。




    ->RACImmediateScheduler//immediateScheduler单例

RACScheduler+Private.h

import "RACScheduler.h"

extern NSString * const RACSchedulerCurrentSchedulerKey;
扩展的作用。 私有
@interface RACScheduler ()

• (instancetype)subscriptionScheduler;

• (instancetype)initWithName:(nullable NSString )name;
  @end
  配合使用
  spec.private_header_files = 'Headers/Private/.h'

@implementation RACQueueScheduler

pragma mark Lifecycle

• (instancetype)initWithName:(NSString *)name queue:(dispatch_queue_t)queue {
  NSCParameterAssert(queue != NULL);

  self = [super initWithName:name];

  _queue = queue;

if !OS_OBJECT_USE_OBJC

dispatch_retain(_queue);

endif

return self;

}

@implementation RACTargetQueueScheduler

• (instancetype)initWithName:(NSString *)name targetQueue:(dispatch_queue_t)targetQueue {
  NSCParameterAssert(targetQueue != NULL);

  if (name == nil) {
  name = [NSString stringWithFormat:@"org.reactivecocoa.ReactiveObjC.RACTargetQueueScheduler(%s)", dispatch_queue_get_label(targetQueue)];
  }

  dispatch_queue_t queue = dispatch_queue_create(name.UTF8String, DISPATCH_QUEUE_SERIAL);
  if (queue == NULL) return nil;

  dispatch_set_target_queue(queue, targetQueue);
  //这里奇妙。调用父类也可以在自己初始化完成后再调用！！！
  return [super initWithName:name queue:queue];
  }

//栈
//堆
//数据区、只读数据区
//代码段

//结论：
//1、数据区的作用域很大，block直接访问。
//2、栈变量。 __block。 改变指针。 指针指向的内容也改变。
//3、栈变量。 不改变指针，指针指向的内容改变。
//4、栈变量。 block里面改变指针。
//5、栈变量。加了__block的dispatch跟数据区的相同，block直接访问。

• (RACDisposable *)schedule:(void (^)(void))block {
  NSCParameterAssert(block != NULL);
  2018-01-17 17:57:33.987843+0800 ReactiveCocoaTest[25141:1238160] 777770x604000010fa0
  2018-01-17 17:57:33.988021+0800 ReactiveCocoaTest[25141:1238160] 888880x604000010fa0
  2018-01-17 17:57:33.988030+0800 ReactiveCocoaTest[25141:1238159] 999990x604000010fa0
  RACDisposable *disposable = [[RACDisposable alloc] init];
  NSLog(@"77777%p",disposable);
  dispatch_async(self.queue, ^{
  NSLog(@"99999%p",disposable);
  if (disposable.disposed) return;
  [self performAsCurrentScheduler:block];
  });
  NSLog(@"88888%p",disposable);
  return disposable;
  }

双目运算符可以省略冒号的值。

RACScheduler *scheduler = RACScheduler.currentScheduler ?: self.backgroundScheduler;

block懒加载

• (instancetype)init {
  self = [super init];
• (instancetype)initWithDisposables:(NSArray *)otherDisposables {
  self = [self init];

• (RACDisposable *)after:(NSDate *)date repeatingEvery:(NSTimeInterval)interval withLeeway:(NSTimeInterval)leeway schedule:(void (^)(void))block {
  NSCParameterAssert(date != nil);
  NSCParameterAssert(interval > 0.0 && interval < INT64_MAX / NSEC_PER_SEC);
  NSCParameterAssert(leeway >= 0.0 && leeway < INT64_MAX / NSEC_PER_SEC);
  NSCParameterAssert(block != NULL);

  uint64_t intervalInNanoSecs = (uint64_t)(interval * NSEC_PER_SEC);
  uint64_t leewayInNanoSecs = (uint64_t)(leeway * NSEC_PER_SEC);

  dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, self.queue);
  dispatch_source_set_timer(timer, [self.class wallTimeWithDate:date], intervalInNanoSecs, leewayInNanoSecs);
  dispatch_source_set_event_handler(timer, block);
  dispatch_resume(timer);

  return [RACDisposable disposableWithBlock:^{
  //只有加了这句11
  dispatch_source_cancel(timer);
  }];
  }

//并且加了这句22。 定时器才能用。
self.dispose= [[RACScheduler schedulerWithPriority:RACSchedulerPriorityDefault name:@"111"] after:
[NSDate dateWithTimeIntervalSinceNow:5] repeatingEvery:5 withLeeway:1 schedule:^{
NSLog(@"22222");
}];

dispatch_time_t (^datesblock)(NSDate*d)=^(NSDate *date) {
    double seconds = 0;
    double frac = modf(date.timeIntervalSince1970, &seconds);

    struct timespec walltime = {
        .tv_sec = (time_t)fmin(fmax(seconds, LONG_MIN), LONG_MAX),
        .tv_nsec = (long)fmin(fmax(frac * NSEC_PER_SEC, LONG_MIN), LONG_MAX)
    };

    dispatch_time_t tim=    dispatch_walltime(&walltime, 0);
    return tim;
};
dispatch_time_t tim3 = dispatch_time(DISPATCH_TIME_NOW, 5*NSEC_PER_SEC);
dispatch_time_t tim1 = dispatch_time_delay(5);
dispatch_time_t tim2 =datesblock([NSDate dateWithTimeIntervalSinceNow:5]);

dispatch_time_t的长整型值并没有必然联系,但是作用是等效的。
2018-01-18 16:29:33.964167+0800 ReactiveCocoaTest[11843:455353] 26853368747865===26853368747970===16930479894745437666

把可变参数转化为NSString

• (instancetype)setNameWithFormat:(NSString *)format, ... {
  if (getenv("RAC_DEBUG_SIGNAL_NAMES") == NULL) return self;

  NSCParameterAssert(format != nil);

  va_list args;
  va_start(args, format);

  NSString *str = [[NSString alloc] initWithFormat:format arguments:args];
  va_end(args);

  self.name = str;
  return self;
  }