NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];

NSOperationQueue *queue = [[NSOperationQueue alloc] init];

NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"currentThread = %@ ", [NSThread currentThread]);
}];
[queue addOperation:operation];

NSOperationQueue *queue = [[NSOperationQueue alloc] init];

NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"currentThread = %@ ", [NSThread currentThread]);
}];

NSOperation *invocationOperation = [[NSInvocationOperation alloc]
                                    initWithTarget:self
                                    selector:@selector(invocationOperation:)
                                    object:@{@"name": @"lucaslee"}];

NSArray *operations = @[blockOperation, invocationOperation];

[queue addOperations:operations waitUntilFinished:NO];

[queue addOperationWithBlock:^{
    NSLog(@"task 1 currentThread = %@ ", [NSThread currentThread]);
}];

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 1;

NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"task 1 currentThread = %@ ", [NSThread currentThread]);
}];
[queue addOperation:blockOperation];

blockOperation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"task 2 currentThread = %@ ", [NSThread currentThread]);
}];

[queue addOperation:blockOperation];

[queue addOperationWithBlock:^{
    NSLog(@"task 3 currentThread = %@ ", [NSThread currentThread]);
}];

[queue addOperationWithBlock:^{
    NSLog(@"task 4 currentThread = %@ ", [NSThread currentThread]);
}];

[queue addOperationWithBlock:^{
    NSLog(@"task 5 currentThread = %@ ", [NSThread currentThread]);
}];

task 1 currentThread = <NSThread: 0x608000276d00>{number = 3, name = (null)}
task 2 currentThread = <NSThread: 0x600000273a40>{number = 4, name = (null)}
task 3 currentThread = <NSThread: 0x608000276d00>{number = 3, name = (null)}
task 4 currentThread = <NSThread: 0x608000276d00>{number = 3, name = (null)}
task 5 currentThread = <NSThread: 0x608000276d00>{number = 3, name = (null)}

queue.maxConcurrentOperationCount = 5;

task 3 currentThread = <NSThread: 0x6000002732c0>{number = 3, name = (null)}
task 4 currentThread = <NSThread: 0x608000264bc0>{number = 6, name = (null)}
task 2 currentThread = <NSThread: 0x608000267000>{number = 4, name = (null)}
task 5 currentThread = <NSThread: 0x600000273500>{number = 7, name = (null)}
task 1 currentThread = <NSThread: 0x608000264b40>{number = 5, name = (null)}

queue.qualityOfService = NSQualityOfServiceUserInteractive;

queue.suspended = YES;

[self.queue cancelAllOperations];

[operation cancel];

[operation waitUntilFinished];

[queue waitUntilAllOperationsAreFinished];

queue.name = @"com.lucaslz.queue";

NSOperationQueue *queue = [[NSOperationQueue alloc] init];

NSOperation *operation1 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"task 1 currentThread = %@ ", [NSThread currentThread]);
}];
NSOperation *operation2 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"task 2 currentThread = %@ ", [NSThread currentThread]);
}];
NSOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"task 3 currentThread = %@ ", [NSThread currentThread]);
}];
[queue addOperation:operation1];
[queue addOperation:operation2];
[queue addOperation:operation3];

task 2 currentThread = <NSThread: 0x600000078100>{number = 3, name = (null)}
task 1 currentThread = <NSThread: 0x60000026a280>{number = 4, name = (null)}
task 3 currentThread = <NSThread: 0x60800007e180>{number = 5, name = (null)}

[operation1 addDependency:operation2];
[operation2 addDependency:operation3];

task 3 currentThread = <NSThread: 0x60000006adc0>{number = 3, name = (null)}
task 2 currentThread = <NSThread: 0x608000262d00>{number = 4, name = (null)}
task 1 currentThread = <NSThread: 0x60000006adc0>{number = 3, name = (null)}

NSOperationQueue *queue2 = [[NSOperationQueue alloc] init];
[queue2 addOperation:operation2];

task 3 currentThread = <NSThread: 0x608000275380>{number = 3, name = (null)}
task 2 currentThread = <NSThread: 0x600000273c80>{number = 4, name = (null)}
task 1 currentThread = <NSThread: 0x608000275380>{number = 3, name = (null)}

[operation1 addDependency:operation2];
[operation2 addDependency:operation3];
[operation3 addDependency:operation1];

NSOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"currentThread = %@ ", [NSThread currentThread]);
}];
[operation start];

[operation addExecutionBlock:^{
    NSLog(@"追加任务 task1 currentThread = %@ ", [NSThread currentThread]);
}];

追加任务 task1 currentThread = <NSThread: 0x60000006f040>{number = 1, name = main}
追加任务 task3 currentThread = <NSThread: 0x60800026c540>{number = 5, name = (null)}
追加任务 task2 currentThread = <NSThread: 0x600000264f40>{number = 4, name = (null)}
currentThread = <NSThread: 0x60800026c4c0>{number = 3, name = (null)}

NSOperation *operation = [[NSInvocationOperation alloc]
                       initWithTarget:self
                             selector:@selector(invocationOperation:)
                               object:@{@"name": @"lucaslee"}];
[operation start];
    
- (void)invocationOperation:(NSDictionary *)info {
    NSLog(@"currentThread = %@, info = %@", [NSThread currentThread], info);
}

@interface LZCustomOperation : NSOperation
@end

@implementation LZCustomOperation

- (void)main {
    NSLog(@"currentThread = %@", [NSThread currentThread]);
}

@end

NSOperation *operation = [[LZCustomOperation alloc] init];
[operation start];

@property (readonly, getter=isCancelled) BOOL cancelled;

- (void)cancel;

@property (readonly, getter=isReady) BOOL ready;

@property (readonly, getter=isExecuting) BOOL executing;

@property (readonly, getter=isFinished) BOOL finished;

dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());

dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(15ull * NSEC_PER_SEC));
dispatch_source_set_timer(timer, start, DISPATCH_TIME_FOREVER, (int64_t)(1ull * NSEC_PER_SEC));

dispatch_source_set_event_handler(timer, ^{
    NSLog(@"唤醒了定时器");
    dispatch_source_cancel(timer);
});

dispatch_source_set_cancel_handler(timer, ^{
    NSLog(@"取消");
});

dispatch_resume(timer);

@interface LZTimer ()

@property (nonatomic, assign) dispatch_source_t source;

@property (nonatomic, copy) dispatch_block_t block;

@end

@implementation LZTimer

+ (LZTimer *)timerRepeatintWithTimeInterval:(NSTimeInterval)seconds block:(dispatch_block_t)block {
    
    NSParameterAssert(seconds);
    NSParameterAssert(block);
    
    LZTimer *timer = [[self alloc] init];
    timer.block = block;
    timer.source = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    
    uint64_t nsec = (uint64_t)(seconds * NSEC_PER_SEC);
    
    dispatch_source_set_timer(timer.source, dispatch_time(DISPATCH_TIME_NOW, nsec), nsec, 0);
    
    dispatch_source_set_event_handler(timer.source, block);
    
    dispatch_resume(timer.source);
    
    return timer;
}

- (void)invalidate {
    if (self.source) {
        dispatch_source_cancel(self.source);
        self.source = nil;
    }
    self.block = nil;
}

- (void)dealloc {
    [self invalidate];
}

- (void)fire {
    self.block();
}

@end

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    // 初始化
});

+ (instancetype)sharedInstance {
    static id sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] init];
    });
    return sharedInstance;
}

static NSString *LZStringFromDateISO8601(NSDate *date) {
    static NSDateFormatter *formatter = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        formatter = [[NSDateFormatter alloc] init];
        [formatter setDateFormat:@"yyyy-MM-dd"];
    });
    return [formatter stringFromDate:date];
}

NSCalendar *LZTimeOfDayReferenceCalendar() {
    static NSCalendar *calendar;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
    });
    return calendar;
}

static CGFloat screenScale = 1.0;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    screenScale = [UIScreen mainScreen].scale;
});

dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);

NSMutableArray *array = [NSMutableArray array];

for (NSUInteger index = 0; index < 1000; index++) {
    dispatch_async(queue, ^{
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        [array addObject:@(index)];
        dispatch_semaphore_signal(semaphore);
    });
}

- (NSArray *)tasksForKeyPath:(NSString *)keyPath {
    __block NSArray *tasks = nil;
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
        if ([keyPath isEqualToString:NSStringFromSelector(@selector(dataTasks))]) {
            tasks = dataTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(uploadTasks))]) {
            tasks = uploadTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(downloadTasks))]) {
            tasks = downloadTasks;
        } else if ([keyPath isEqualToString:NSStringFromSelector(@selector(tasks))]) {
            tasks = [@[dataTasks, uploadTasks, downloadTasks] valueForKeyPath:@"@unionOfArrays.self"];
        }

        dispatch_semaphore_signal(semaphore);
    }];

    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    return tasks;
}