基本內容
本節主要介紹iOS中多線程相關的內容，先簡單介紹NSOperation的使用，然后結合GCD實現任務之間的管理，比如每個任務完成之后的處理以及任務與任務之間的依賴，所有任務完成之后的處理等，通過AFNetworking源碼分析其具體實現。
NSoperation
通過NSOpeartion去完成某個任務的時候，有3種方式：
- NSInvocationOperation
- NSBlockOperation
- 自己繼承NSOperation實現具體的任務操作
NSInvocationOperation
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *ope = [[NSInvocationOperation alloc] initWithTarget:
self selector:@selector(invocationOperationCall1) object:nil];
NSInvocationOperation *ope2 = [[NSInvocationOperation alloc] initWithTarget
:self selector:@selector(invocationOperationCall2) object:nil];
[queue addOperation:ope];
[queue addOperation:ope2];
}
-(void)invocationOperationCall1{
NSLog(@"%@", NSStringFromSelector(_cmd));
NSLog(@"%@", [NSThread currentThread]);
}
-(void)invocationOperationCall2{
NSLog(@"%@", NSStringFromSelector(_cmd));
NSLog(@"%@", [NSThread currentThread]);
}
輸出：
2016-01-13 14:23:54.791 operation+dispatch_group[6032:2162368]
invocationOperationCall1------<NSThread: 0x7fb6ad8019a0>{number = 3, name = (
null)}
2016-01-13 14:23:54.791 operation+dispatch_group[6032:2162371]
invocationOperationCall2------<NSThread: 0x7fb6adaec8f0>{number = 2, name = (
null)}
從日志中看出任務分別在不同的線程中執行
NSInvocationOperation *ope = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationOperationCall1) object:nil];
NSInvocationOperation *ope2 = [[NSInvocationOperation alloc] initWithTarget:
self selector:@selector(invocationOperationCall2) object:nil];
[ope start];
[ope2 start];
輸出：
2016-01-13 14:27:38.226 operation+dispatch_group[6053:2164444]
invocationOperationCall1------<NSThread: 0x7fae69508370>{number = 1, name =
main}
2016-01-13 14:27:38.226 operation+dispatch_group[6053:2164444]
invocationOperationCall2------<NSThread: 0x7fae69508370>{number = 1, name =
main}
從日志中看出，如果不添加到queue中，則任務是同步在當前線程中執行的。
還可以添加NSOperation對象之間的依賴，讓每個任務之間按一定的順序執行
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *ope = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(invocationOperationCall1) object:nil];
NSInvocationOperation *ope2 = [[NSInvocationOperation alloc] initWithTarget:
self selector:@selector(invocationOperationCall2) object:nil];
[ope addDependency:ope2];
[queue addOperation:ope];
[queue addOperation:ope2];
輸出：
2016-01-13 19:27:49.182 operation+dispatch_group[13865:2284382]
invocationOperationCall2------<NSThread: 0x7fa26300ff40>{number = 2, name = (
null)}
2016-01-13 19:27:49.183 operation+dispatch_group[13865:2284382]
invocationOperationCall1------<NSThread: 0x7fa26300ff40>{number = 2, name = (
null)}
雖然ope和ope2之間是并行的，但是添加依賴之后ope會等到ope2執行完畢之后才開始執行。
NSBlockOperation
NSBlockOperation *ope = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"task A, %@", [NSThread currentThread]);
}];
[ope addExecutionBlock:^{
NSLog(@"task B, %@", [NSThread currentThread]);
}];
[ope addExecutionBlock:^{
NSLog(@"task C, %@", [NSThread currentThread]);
}];
[ope start];
輸出：
2016-01-13 14:17:36.594 operation+dispatch_group[5990:2158464]
task A, <NSThread: 0x7ff1217073d0>{number = 1, name = main}
2016-01-13 14:17:36.594 operation+dispatch_group[5990:2158531]
task B, <NSThread: 0x7ff1215029f0>{number = 2, name = (null)}
2016-01-13 14:17:36.594 operation+dispatch_group[5990:2158532]
task C, <NSThread: 0x7ff1217a6af0>{number = 3, name = (null)}
自定義NSOperation(結合AFNetworking源碼)
AFNetworking源代碼：
AFURLConnectionOperation.m
@interface AFURLConnectionOperation : NSOperation <NSURLConnectionDelegate,
NSURLConnectionDataDelegate, NSSecureCoding, NSCopying>
AFURLConnectionOperation是繼承自NSOperation
AFURLConnectionOperation.m
- (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;
//使用AFNetworking網絡線程去調用OperationDidStart函數
[self performSelector:@selector(operationDidStart) onThread:[[self
class] networkRequestThread] withObject:nil waitUntilDone:NO modes:[
self.runLoopModes allObjects]];
}
[self.lock unlock];
}
//類方法 獲取網絡線程 全局唯一的
+ (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;
}
//初始化網絡線程
+ (void)networkRequestThreadEntryPoint:(id)__unused object {
@autoreleasepool {
[[NSThread currentThread] setName:@"AFNetworking"];
//新建網絡線程的runloop對象
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
//保證網絡線程在沒有任何port消息的時候一直處于活躍狀態，防止進入休眠，隨時處理網絡請求或者數據返回。
[runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];
//開始運行網絡線程的runloop
[runLoop run];
}
}
- (void)operationDidStart {
[self.lock lock];
if (![self isCancelled]) {
self.connection = [[NSURLConnection alloc] initWithRequest:self.request
delegate:self startImmediately:NO];
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
for (NSString *runLoopMode in self.runLoopModes) {
//將網絡請求相關的事件源添加到網絡線程的runloop中，網絡回調和數據返回都依賴于網絡線程runloop去監聽
[self.connection scheduleInRunLoop:runLoop forMode:runLoopMode];
//將流相關的事件源添加到網絡線程的runloop中，流的讀寫都依賴于網絡線程runloop去監聽
[self.outputStream scheduleInRunLoop:runLoop forMode:runLoopMode];
}
[self.outputStream open];
//開始網絡請求
[self.connection start];
}
[self.lock unlock];
//讓主線程去觸發”已經開始網絡請求“這一事件。
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:
AFNetworkingOperationDidStartNotification object:self];
});
}
AFURLConnectionOperation自己重寫了NSOperation中的start方法，具體指定了需要執行的任務。多個請求同時進行的時候，對網絡數據回調的處理都是由AFNetworking的網絡線程進行的。
多個線程任務之間的管理
有時候，可能需要在所有網絡請求完成之后需要做一件事情或者是不同的網絡請求直接還有一定的依賴關系或者是順序關系，這種情況下需要使用GCD的group去處理。
GCD group簡單介紹：
通過group可以對多個task進行統一管理，比如現在需要在多個任務完成之后再去做最后的處理：
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("com.ConcurrentQueue",
DISPATCH_QUEUE_CONCURRENT);
dispatch_group_async(group, queue, ^{
NSLog(@"task A");
});
dispatch_group_async(group, queue, ^{
NSLog(@"task B");
});
dispatch_group_notify(group, queue, ^{
NSLog(@"task LAST");
});
dispatch_group_async(group, queue, ^{
NSLog(@"task C");
});
輸出
2016-01-13 19:18:13.814 operation+dispatch_group[13783:2280382] task B
2016-01-13 19:18:13.814 operation+dispatch_group[13783:2280385] task C
2016-01-13 19:18:13.814 operation+dispatch_group[13783:2280383] task A
2016-01-13 19:18:13.815 operation+dispatch_group[13783:2280383] task LAST
通過group讓task LAST等到ABC任務執行完之后最后進行處理。
AFNetworking中多任務之間的管理實現
+ (NSArray *)batchOfRequestOperations:(NSArray *)operations
progressBlock:(void (^)(NSUInteger
numberOfFinishedOperations, NSUInteger
totalNumberOfOperations))progressBlock
completionBlock:(void (^)(NSArray *operations))
completionBlock
{
if (!operations || [operations count] == 0) {
return @[[NSBlockOperation blockOperationWithBlock:^{
dispatch_async(dispatch_get_main_queue(), ^{
if (completionBlock) {
completionBlock(@[]);
}
});
}]];
}
__block dispatch_group_t group = dispatch_group_create();
//等待所有任務都完成之后最后需要處理的任務
NSBlockOperation *batchedOperation = [NSBlockOperation
blockOperationWithBlock:^{
//通過dispatch_group_notify保證completionBlock當前group
//中的主線程隊列上所有的originalCompletionBlock任務處理完之后再處理
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
if (completionBlock) {
completionBlock(operations);
}
});
}];
for (AFURLConnectionOperation *operation in operations) {
operation.completionGroup = group;
void (^originalCompletionBlock)(void) = [operation.completionBlock copy];
__weak __typeof(operation)weakOperation = operation;
//改變每個Operation的completionBlock，主要是添加了能顯示任務完成進度的功能。
operation.completionBlock = ^{
__strong __typeof(weakOperation)strongOperation = weakOperation;
//忽略行級別的編譯器警告
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
dispatch_queue_t queue = strongOperation.completionQueue ?: dispatch_get_main_queue();
#pragma clang diagnostic pop
dispatch_group_async(group, queue, ^{
//originalCompletionBlock任務可能會被放到dispatch_main_queue中處理。
if (originalCompletionBlock) {
originalCompletionBlock();
}
//過濾出已經完成的任務
NSUInteger numberOfFinishedOperations = [[operations
indexesOfObjectsPassingTest:^BOOL(id op, NSUInteger __unused
idx, BOOL __unused *stop) {
return [op isFinished];
}] count];
if (progressBlock) {
//顯示任務完成的進度
progressBlock(numberOfFinishedOperations, [operations count
]);
}
dispatch_group_leave(group);
});
};
dispatch_group_enter(group);
//添加batchedOperation對所有Operation任務的依賴，保證batchedOperation最后處理。
[batchedOperation addDependency:operation];
}
return [operations arrayByAddingObject:batchedOperation];
}
這個函數是將多個任務進行打包處理，并能顯示出完成進度，以及最后等待所有任務完成之后進行最后的處理。
