基本內(nèi)容

本節(jié)主要介紹iOS中多線程相關(guān)的內(nèi)容麻裳，先簡單介紹NSOperation的使用骂租，然后結(jié)合GCD實現(xiàn)任務之間的管理洋访，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镣陕，所有任務完成之后的處理等，通過AFNetworking源碼分析其具體實現(xiàn)姻政。

NSoperation

通過NSOpeartion去完成某個任務的時候呆抑，有3種方式：

• NSInvocationOperation
• NSBlockOperation
• 自己繼承NSOperation實現(xiàn)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(zhí)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中汁展，則任務是同步在當前線程中執(zhí)行的鹊碍。

還可以添加NSOperation對象之間的依賴厌殉，讓每個任務之間按一定的順序執(zhí)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(zhí)行完畢之后才開始執(zhí)行侈咕。

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(jié)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(wǎng)絡線程去調(diào)用OperationDidStart函數(shù)
        [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(wǎng)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(wǎng)絡線程
+ (void)networkRequestThreadEntryPoint:(id)__unused object {

    @autoreleasepool {

        [[NSThread currentThread] setName:@"AFNetworking"];
//新建網(wǎng)絡線程的runloop對象
        NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
//保證網(wǎng)絡線程在沒有任何port消息的時候一直處于活躍狀態(tài)公罕，防止進入休眠，隨時處理網(wǎng)絡請求或者數(shù)據(jù)返回耀销。
        [runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];
//開始運行網(wǎng)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(wǎng)絡請求相關(guān)的事件源添加到網(wǎng)絡線程的runloop中楼眷，網(wǎng)絡回調(diào)和數(shù)據(jù)返回都依賴于網(wǎng)絡線程runloop去監(jiān)聽
            [self.connection scheduleInRunLoop:runLoop forMode:runLoopMode];
//將流相關(guān)的事件源添加到網(wǎng)絡線程的runloop中，流的讀寫都依賴于網(wǎng)絡線程runloop去監(jiān)聽
            [self.outputStream scheduleInRunLoop:runLoop forMode:runLoopMode];
        }
        [self.outputStream open];
//開始網(wǎng)絡請求
        [self.connection start];

    }
    [self.lock unlock];

//讓主線程去觸發(fā)”已經(jīng)開始網(wǎng)絡請求“這一事件树姨。
    dispatch_async(dispatch_get_main_queue(), ^{
        [[NSNotificationCenter defaultCenter] postNotificationName:
        AFNetworkingOperationDidStartNotification object:self];
    });
}

AFURLConnectionOperation自己重寫了NSOperation中的start方法摩桶，具體指定了需要執(zhí)行的任務。多個請求同時進行的時候帽揪，對網(wǎng)絡數(shù)據(jù)回調(diào)的處理都是由AFNetworking的網(wǎng)絡線程進行的硝清。

多個線程任務之間的管理

有時候，可能需要在所有網(wǎng)絡請求完成之后需要做一件事情或者是不同的網(wǎng)絡請求直接還有一定的依賴關(guān)系或者是順序關(guān)系转晰，這種情況下需要使用GCD的group去處理芦拿。

GCD group簡單介紹：

通過group可以對多個task進行統(tǒng)一管理，比如現(xiàn)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(zhí)行完之后最后進行處理查邢。

AFNetworking中多任務之間的管理實現(xiàn)

+ (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蔗崎，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中處理扰藕。
                if (originalCompletionBlock) {

                    originalCompletionBlock();

                }

//過濾出已經(jīng)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任務的依賴缓苛，保證batchedOperation最后處理。
        [batchedOperation addDependency:operation];

    }
    return [operations arrayByAddingObject:batchedOperation];
}

這個函數(shù)是將多個任務進行打包處理邓深，并能顯示出完成進度未桥，以及最后等待所有任務完成之后進行最后的處理。