AFNetworking?中如何運(yùn)用?Runloop?
AFURLConnectionOperation?這個(gè)類是基于?NSURLConnection?構(gòu)建的，其希望能在后臺(tái)線程接收?Delegate?回調(diào)。為此?AFNetworking?單獨(dú)創(chuàng)建了一個(gè)線程，并在這個(gè)線程中啟動(dòng)了一個(gè)?RunLoop：
+ (void)networkRequestThreadEntryPoint:(id)__unused object {
? ? @autoreleasepool {
? ? ? ? [[NSThread currentThread] setName:@"AFNetworking"];
? ? ? ? NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
? ? ? ? [runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];
? ? ? ? [runLoop run];
? ? }
}
AFNetworking 2.0的常駐線程為什么一開始要自動(dòng)釋放池
Each thread in a Cocoa application maintains its own stack of autorelease pool blocks. If you are writing a Foundation-only program or if you detach a thread, you need to create your own autorelease pool block.
當(dāng)新建線程的時(shí)候，需要使用自動(dòng)釋放池。并且設(shè)計(jì)到Cocoa編程在合適的地方也要設(shè)置自動(dòng)釋放池。
- 為了在釋放池塊后，立即釋放對(duì)象
- 開啟新的線程時(shí)，需要維護(hù)自動(dòng)釋放池棧
@autoreleasepool {
? ? ? ? [[NSThread currentThread] setName:@"AFNetworking"];
? ? ? ? NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
? ? ? ? [runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];
? ? ? ? [runLoop run];
? ? }
所以上面的代碼邏輯是給子線程創(chuàng)建runloop和維持線程等待消息。自動(dòng)釋放池存在的邏輯不是為了釋放對(duì)象，而是新建線程需要**維護(hù)自動(dòng)釋放池棧**。參考整個(gè)app的main函數(shù)app啟動(dòng)
+ (NSThread *)networkRequestThread {
? ? static NSThread *_networkRequestThread = nil;
? ? static dispatch_once_t oncePredicate;
? ? dispatch_once(&oncePredicate, ^{
? ? ? ? _networkRequestThread = [[NSThread alloc] initWithTarget:self selector:@selector(networkRequestThreadEntryPoint:) object:nil];
? ? ? ? [_networkRequestThread start];
? ? });
? ? return _networkRequestThread;
}
RunLoop?啟動(dòng)前內(nèi)部必須要有至少一個(gè)?Timer/Observer/Source，所以?AFNetworking?在?[runLoop run]?之前先創(chuàng)建了一個(gè)新的?NSMachPort?添加進(jìn)去了。通常情況下，調(diào)用者需要持有這個(gè)?NSMachPort (mach_port)?并在外部線程通過這個(gè)?port?發(fā)送消息到?loop?內(nèi)；但此處添加?port?只是為了讓?RunLoop?不至于退出，并沒有用于實(shí)際的發(fā)送消息。
- (void)start {
? ? [self.lock lock];
? ? if ([self isCancelled]) {
? ? ? ? [self performSelector:@selector(cancelConnection) onThread:[[self class] networkRequestThread] withObject:nil waitUntilDone:NO modes:[self.runLoopModes allObjects]];
? ? } else if ([self isReady]) {
? ? ? ? self.state = AFOperationExecutingState;
? ? ? ? [self performSelector:@selector(operationDidStart) onThread:[[self class] networkRequestThread] withObject:nil waitUntilDone:NO modes:[self.runLoopModes allObjects]];
? ? }
? ? [self.lock unlock];
}
當(dāng)需要這個(gè)后臺(tái)線程執(zhí)行任務(wù)時(shí)，AFNetworking?通過調(diào)用?[NSObject performSelector:onThread:..]?將這個(gè)任務(wù)扔到了后臺(tái)線程的?RunLoop?中。
