07 - RAC與多線程
RAC怎么實現多線程并發處理訂閱?RAC多線程模式怎么解決資源搶奪?RAC怎么實現取消訂閱的?
首選先我們 沿著
信息訂閱這條路往后走:
- (RACDisposable *)subscribe:(id<RACSubscriber>)subscriber {
NSCParameterAssert(subscriber != nil);
RACCompoundDisposable *disposable = [RACCompoundDisposable compoundDisposable];
subscriber = [[RACPassthroughSubscriber alloc] initWithSubscriber:subscriber signal:self disposable:disposable];
if (self.didSubscribe != NULL) {
// 創建調度者, 執行訂閱
RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
RACDisposable *innerDisposable = self.didSubscribe(subscriber);
[disposable addDisposable:innerDisposable];
}];
[disposable addDisposable:schedulingDisposable];
}
return disposable;
}
-
RACSchedulerSchedulers are used to control when and where work is performed
在RAC中真正執行訂閱的block是由
RACScheduler調度者去執行的.
RACScheduler本質上就是對隊列的封裝, 就是一個Queue且調度者由
RACScheduler子類去實現, 其本身無法使用.
- 1.0 訂閱信息的block
// 1.0 訂閱信息的block
RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
RACDisposable *innerDisposable = self.didSubscribe(subscriber);
[disposable addDisposable:innerDisposable];
}];
- 2.0 創建
subscriptionScheduler
// 其本身是一個單列, 在整個程序中存在一份; 畢竟調度者只要一個就好, 無需更多浪費資源
+ (instancetype) subscriptionScheduler {
static dispatch_once_t onceToken;
static RACScheduler *subscriptionScheduler;
dispatch_once(&onceToken, ^{
subscriptionScheduler = [[RACSubscriptionScheduler alloc] init];
});
return subscriptionScheduler;
}
-
3.0 執行
schedule當期的
RACScheduler.currentScheduler為nil時, 表示沒有調度者, 則把block交由backgroundScheduler去調度當期的
RACScheduler.currentScheduler不為nil時,表示當前存在調度者, 則立即執行block
- (RACDisposable *)schedule:(void (^)(void))block {
NSCParameterAssert(block != NULL);
if (RACScheduler.currentScheduler == nil) return [self.backgroundScheduler schedule:block];
block();
return nil;
}
// 獲取`當前的Scheduler`
+ (instancetype)currentScheduler {
// 首先去線程字典中獲取`當前的Scheduler`
RACScheduler *scheduler = NSThread.currentThread.threadDictionary[RACSchedulerCurrentSchedulerKey];
if (scheduler != nil) return scheduler;
// 當在主線程時 `當前的Scheduler`為 `mainThreadScheduler`
if ([self.class isOnMainThread]) return RACScheduler.mainThreadScheduler;
// 此時表示當前執行在子線程, 且沒有`當前的Scheduler`
return nil;
}
// 獲取 `_backgroundScheduler`
- (id)init {
self = [super initWithName:@"com.ReactiveCocoa.RACScheduler.subscriptionScheduler"];
if (self == nil) return nil;
_backgroundScheduler = [RACScheduler scheduler];
return self;
}
+ (instancetype)scheduler {
return [self schedulerWithPriority:RACSchedulerPriorityDefault];
}
+ (instancetype)schedulerWithPriority:(RACSchedulerPriority)priority {
return [self schedulerWithPriority:priority name:@"com.ReactiveCocoa.RACScheduler.backgroundScheduler"];
}
+ (instancetype)schedulerWithPriority:(RACSchedulerPriority)priority name:(NSString *)name {
return [[RACTargetQueueScheduler alloc] initWithName:name targetQueue:dispatch_get_global_queue(priority, 0)];
}
// RACTargetQueueScheduler實現
- (id)initWithName:(NSString *)name targetQueue:(dispatch_queue_t)targetQueue {
NSCParameterAssert(targetQueue != NULL);
if (name == nil) {
name = [NSString stringWithFormat:@"com.ReactiveCocoa.RACTargetQueueScheduler(%s)", dispatch_queue_get_label(targetQueue)];
}
// 創建一個串行隊列, 且把當前隊列的執行階層設置為 `dispatch_get_global_queue`
dispatch_queue_t queue = dispatch_queue_create(name.UTF8String, DISPATCH_QUEUE_SERIAL);
if (queue == NULL) return nil;
dispatch_set_target_queue(queue, targetQueue);
return [super initWithName:name queue:queue];
}
-
subscriptionScheduler執行schedule
- (RACDisposable *)schedule:(void (^)(void))block {
NSCParameterAssert(block != NULL);
RACDisposable *disposable = [[RACDisposable alloc] init];
// 把操作追加到 `self.queue 串行隊列`
dispatch_async(self.queue, ^{
if (disposable.disposed) return;
[self performAsCurrentScheduler:block];
});
return disposable;
}
// 執行訂閱的block
- (void)performAsCurrentScheduler:(void (^)(void))block {
NSCParameterAssert(block != NULL);
RACScheduler *previousScheduler = RACScheduler.currentScheduler;
NSThread.currentThread.threadDictionary[RACSchedulerCurrentSchedulerKey] = self;
@autoreleasepool {
block();
}
if (previousScheduler != nil) {
NSThread.currentThread.threadDictionary[RACSchedulerCurrentSchedulerKey] = previousScheduler;
} else {
[NSThread.currentThread.threadDictionary removeObjectForKey:RACSchedulerCurrentSchedulerKey];
}
}
-
RAC多線程模式怎么解決資源搶奪?
1.0 模擬RAC多線程并發
for (NSInteger i = 0; i < 5; i++) {
dispatch_async(dispatch_queue_create("", DISPATCH_QUEUE_CONCURRENT), ^{
RACSignal *s1 = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
[subscriber sendNext:@5];
return nil;
}];
[s1 subscribeNext:^(id x) {
}];
});
}
2.0 因為實在子線程處理ARC;
故 `RACScheduler.currentScheduler == nil`即當前schedule一直是nil, 則把block交給 bacggroundSchedule.
3.0 追加任務到隊列, 此時由于是在子線程追加任務, 故線程各不相同
NSLog(@"追加任務到隊列:%@ 追加線程:%@", self.queue, [NSThread currentThread]);
dispatch_async(self.queue, ^{
if (disposable.disposed) return;
[self performAsCurrentScheduler:block];
});
4.0 `bacggroundSchedule`是一個單列, 故追加任務的隊列都是同一個queue (self.queue), 且該隊列是串行隊列
5.0 故開多線程出處理RAC, 其僅僅是把`訂閱的block`追加到`同一個串行隊列`這步操作在不同線程處理而已;
但真正執行訂閱的block, 還是由串行隊列+異步執行; 即每次只會開一條子線程去處理任務, 不會發生資源搶奪問題.
-
RAC怎么實現取消訂閱的?
RACDisposable *schedulingDisposable = [RACScheduler.subscriptionScheduler schedule:^{
// 訂閱的block
}];
[disposable addDisposable:schedulingDisposable];
}
// 返回 schedulingDisposable
- (RACDisposable *)schedule:(void (^)(void))block {
NSCParameterAssert(block != NULL);
RACDisposable *disposable = [[RACDisposable alloc] init];
dispatch_async(self.queue, ^{
if (disposable.disposed) return;
[self performAsCurrentScheduler:block];
});
return disposable;
}
1.0 執行 `schedule:` 創建一個新的 RACDisposable 即`schedulingDisposable`, 并添加到 外部的`disposable`;
2.0 把訂閱的block執行過程, 以異步的方式追加到同一個串行隊列, 故只有當當前線程所有程序都執行完, 串行隊列才會開啟線程 `執行訂閱的block`
3.0 當外面的disposable 釋放后, 其里面的子disposable都會被釋放, 當GCD回過頭來執行訂閱的block時, 發現自己的disposable被釋放, 就立即結束不再執行block.
