多线程之NSThread

一、介绍
NSThread用来创建多线程、监视线程的运行时情况等，线程管理需要程序员自己手动操作。

二、API

@interface NSThread : NSObject  {
@private
    id _private;
    uint8_t _bytes[44];
}

// 当前线程
@property (class, readonly, strong) NSThread *currentThread;

// 类方法 不用调用start即可执行
+ (void)detachNewThreadWithBlock:(void (^)(void))block API_AVAILABLE(macosx(10.12), ios(10.0), watchos(3.0), tvos(10.0));
+ (void)detachNewThreadSelector:(SEL)selector toTarget:(id)target withObject:(nullable id)argument;

// 应用是否是多线程
+ (BOOL)isMultiThreaded;
// 线程存储的信息 可以自己写入一些数据
@property (readonly, retain) NSMutableDictionary *threadDictionary;

// 睡眠（阻塞线程）
+ (void)sleepUntilDate:(NSDate *)date;
+ (void)sleepForTimeInterval:(NSTimeInterval)ti;

// 退出当前线程
+ (void)exit;

//  线程优先级:决定线程被CPU调用的频率，不保证调用的顺序
+ (double)threadPriority;
+ (BOOL)setThreadPriority:(double)p;
@property NSQualityOfService qualityOfService; // read-only after the thread is started

// 堆区的一些信息
@property (class, readonly, copy) NSArray *callStackReturnAddresses;
@property (class, readonly, copy) NSArray *callStackSymbols;

@property (nullable, copy) NSString *name;

@property NSUInteger stackSize;

@property (readonly) BOOL isMainThread;
@property (class, readonly) BOOL isMainThread; // reports whether current thread is main
@property (class, readonly, strong) NSThread *mainThread;

// 实例方法创建对象
- (instancetype)init;
- (instancetype)initWithTarget:(id)target selector:(SEL)selector object:(nullable id)argument;
- (instancetype)initWithBlock:(void (^)(void))block;

// 执行
@property (readonly, getter=isExecuting) BOOL executing;
// 完成
@property (readonly, getter=isFinished) BOOL finished;
// 取消
@property (readonly, getter=isCancelled) BOOL cancelled ;

- (void)cancel;

- (void)start;

- (void)main;   // thread body method

@end

// 通知相关
FOUNDATION_EXPORT NSNotificationName const NSWillBecomeMultiThreadedNotification;
FOUNDATION_EXPORT NSNotificationName const NSDidBecomeSingleThreadedNotification;
FOUNDATION_EXPORT NSNotificationName const NSThreadWillExitNotification;

@interface NSObject (NSThreadPerformAdditions)

// 在主线程搞事情
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray *)array;
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
    // equivalent to the first method with kCFRunLoopCommonModes

// 在某个线程搞事情
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray *)array;
- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
    // equivalent to the first method with kCFRunLoopCommonModes

// NSObject创建子线程
- (void)performSelectorInBackground:(SEL)aSelector withObject:(nullable id)arg API_AVAILABLE(macos(10.5), ios(2.0), watchos(2.0), tvos(9.0));

@end

注意点：
1、exit：谨慎使用:
①、不要再主线程使用
②、调用该方法时先清理线程中的资源，防止内存泄漏

2、- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray *)array;
参数理解：
aSelector：SEL，一个方法名
arg：参数
wait:yes会阻塞当前线程，no当前线程继续执行
array:runloop的mode

例子：

- (void)threadDemonstration{
    [NSThread detachNewThreadWithBlock:^{
        for (int i = 0; i < 10; i++) {
            if (i == 6) {
                // yes会阻塞当前线程，no当前线程继续执行
                [self performSelectorOnMainThread:@selector(check) withObject:nil waitUntilDone:YES];
            }
            NSLog(@"%@在执行%d",[NSThread currentThread],i);
        }
    }];

}

- (void)check{
    
    NSLog(@"haha");
}

wait:YES时：check会先于NSLog(@"%@在执行%d",[NSThread currentThread],i);执行

屏幕快照 2018-04-12 下午1.26.22.png

wait:NO时：check最后执行

屏幕快照 2018-04-12 下午1.28.11.png

3、main
线程的主要入口。
如果继承NSThread，则可以重写此方法，并使用它来实现线程的主体。 如果这样做，不需要调用super。

注：这篇文章写的比较详细，可作参考