常见应用

控制线程生命周期（线程保活）
解决NSTimer在滑动时停止工作的问题
监控应用卡顿
性能优化

控制线程生命周期（线程保活）

线程保活封装

#import <Foundation/Foundation.h>

typedef void (^WDPermenantThreadTask)(void);

@interface WDPermenantThread : NSObject

/**
 在当前子线程执行一个任务
 */
- (void)executeTask:(WDPermenantThreadTask)task;

/**
 结束线程
 */
- (void)stop;

@end

#import "WDPermenantThread.h"

/** WDThread **/
@interface WDThread : NSThread
@end
@implementation WDThread
- (void)dealloc
{
    NSLog(@"%s", __func__);
}
@end

/** WDPermenantThread **/
@interface WDPermenantThread()
@property (strong, nonatomic) WDThread *innerThread;
@property (assign, nonatomic, getter=isStopped) BOOL stopped;
@end

@implementation WDPermenantThread
#pragma mark - public methods
- (instancetype)init
{
    if (self = [super init]) {
        self.stopped = NO;
        
        __weak typeof(self) weakSelf = self;
        
        self.innerThread = [[WDThread alloc] initWithBlock:^{
            [[NSRunLoop currentRunLoop] addPort:[[NSPort alloc] init] forMode:NSDefaultRunLoopMode];
            
            while (weakSelf && !weakSelf.isStopped) {
                [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
            }
        }];
        
        [self.innerThread start];
    }
    return self;
}

- (void)executeTask:(WDPermenantThreadTask)task
{
    if (!self.innerThread || !task) return;
    
    [self performSelector:@selector(__executeTask:) onThread:self.innerThread withObject:task waitUntilDone:NO];
}

- (void)stop
{
    if (!self.innerThread) return;
    
    [self performSelector:@selector(__stop) onThread:self.innerThread withObject:nil waitUntilDone:YES];
}

- (void)dealloc
{
    NSLog(@"%s", __func__);
    
    [self stop];
}

#pragma mark - private methods
- (void)__stop
{
    self.stopped = YES;
    CFRunLoopStop(CFRunLoopGetCurrent());
    self.innerThread = nil;
}

- (void)__executeTask:(WDPermenantThreadTask)task
{
    task();
}

@end

或者

/** WDPermenantThread **/
@interface WDPermenantThread()
@property (strong, nonatomic) WDThread *innerThread;
@end

@implementation WDPermenantThread
#pragma mark - public methods
- (instancetype)init
{
    if (self = [super init]) {
        self.innerThread = [[WDThread alloc] initWithBlock:^{
            NSLog(@"begin----");
            
            // 创建上下文（要初始化一下结构体）
            CFRunLoopSourceContext context = {0};
            
            // 创建source
            CFRunLoopSourceRef source = CFRunLoopSourceCreate(kCFAllocatorDefault, 0, &context);
            
            // 往Runloop中添加source
            CFRunLoopAddSource(CFRunLoopGetCurrent(), source, kCFRunLoopDefaultMode);
            
            // 销毁source
            CFRelease(source);
            
            // 启动
            CFRunLoopRunInMode(kCFRunLoopDefaultMode, 1.0e10, false);
        }];
        
        [self.innerThread start];
    }
    return self;
}

- (void)executeTask:(WDPermenantThreadTask)task
{
    if (!self.innerThread || !task) return;
    
    [self performSelector:@selector(__executeTask:) onThread:self.innerThread withObject:task waitUntilDone:NO];
}

- (void)stop
{
    if (!self.innerThread) return;
    
    [self performSelector:@selector(__stop) onThread:self.innerThread withObject:nil waitUntilDone:YES];
}

- (void)dealloc
{
    NSLog(@"%s", __func__);
    
    [self stop];
}

#pragma mark - private methods
- (void)__stop
{
    CFRunLoopStop(CFRunLoopGetCurrent());
    self.innerThread = nil;
}

- (void)__executeTask:(WDPermenantThreadTask)task
{
    task();
}

@end

解决NSTimer在滑动时停止工作的问题

NSRunLoopCommonModes
NSDefaultRunLoopMode、UITrackingRunLoopMode才是真正存在的模式
NSRunLoopCommonModes并不是一个真的模式，它只是一个标记
timer能在_commonModes数组中存放的模式下工作

static int count = 0;
    NSTimer *timer = [NSTimer timerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
        NSLog(@"%d", ++count);
    }];
    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
    [[NSRunLoop currentRunLoop] addTimer:timer forMode:UITrackingRunLoopMode];
    
    // NSDefaultRunLoopMode、UITrackingRunLoopMode才是真正存在的模式
    // NSRunLoopCommonModes并不是一个真的模式，它只是一个标记
    // timer能在_commonModes数组中存放的模式下工作
    [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];