iOS I/O与多线程

作者: owenqi | 来源:发表于2017-02-10 11:53 被阅读0次

沙盒模型

特点

安全
隐私
整洁

sandbox

Bundle Container
- yixin.app
- [[NSBundle mainBundle] pathForResource:@"name" ofType:@"type"]
Data Container
- NSHomeDirectory()
- Documents
- [NSSearchPathForDirectoriesInDomains(NSDocumentDictionary, NSUserDomainMask, YES) firstObject]
- Library
- Temp
- NSTemporaryDirectory()

资源管理器

发现资源 : 遍历目录
修改资源 : 创建目录, 创建文件, 修改目录, 修改文件, 读写目录, 读写文件

NSFileManager *manager = [[NSFileManager alloc] init];
NSFileManager *defaultManager = [NSFileManager defaultManager];

多线程

线程生而不平等 : 主线程 & 后台线程; 线程有优先级的关系
线程是一个被模拟出来的概念 : CPU 通过分配时间片模拟出多线程同时工作的状态

NSThread

// 初始化
- (instancetype)initWithTarget:(id)target selector:(SEL)selector object:(nullable id)argument;
// 启动
- (void)start;

// 类方法, 会自动启动
+ (void)detachNewThreadSelector:(SEL)selector toTarget:(id)target withObject:(nullable id)argument;

// 使用继承, 需要使用 start 方法启动, 使用 delegate 将线程执行的结果传出
@interface MyThread : NSThread
@end
@implementation
- (void)main {
    // 在这里重写线程实现的方法
    NSLog(@"thread start");
}
@end

- (void)viewDidLoad {
    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(downloadImage:) object:nil];
    [thread start];
}
- (void)downloadImage:(id)arg {
    NSURL *url = [NSURL urlWithString:@"http://xxx.com/image.jpg"];
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *image = [UIImage imageWithData:data];
    
    [self performSelectorOnMainThread:@selector(onImageDone:) withObject:image waitUntilDone:NO];
}
- (void)onImageDone:(id)arg {
    if ([arg isKindOfClass:[UIImage class]]) {
        self.imageView.image = (UIImage *)arg;
    }
}

使用 cancel 将线程状态标记成取消状态

+ (BOOL)isMainThread;
+ (NSThread *)mainThread;
+ (NSThread *)currentThread;

// 暂停线程
+ (void)sleepUntilDate:(NSDate *)date;
+ (void)sleepForTimeInterval:(NSTimeInterval)ti;
unsigned int sleep(unsigned int);

// 线程通信
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
- (void)performSelectorOnBackground:(SEL)aSelector withObject:(nullable id)argA;

多线程优缺点

优点
- 提高 APP 实时响应性
- 充分利用计算资源
缺点
- 额外的系统开销
- 线程同步问题
- 程序复杂度上升

多线程同时访问资源

使用 NSLock

@property (nonatomic, strong) NSLock *lock;
_lock = [[NSLock alloc] init];

[_lock lock]; // 加锁
// 这里执行的代码会把使用的成员变量锁住
[_lock unlock]; // 解锁

// 过程猜测: 使用 [_lock lock] 的时候, 如果 _lock 在锁住状态, 则这个操作会一直等待, 
// 等到操作执行完之后, _lock 被解锁, 才能执行下次加锁操作

使用 @synchronized
- 简单
- 不需要自己 unlock, 不容易产生死锁

@synchronized (self) {
    // 执行操作, 这里的操作会被加锁, 执行完后退出 synchronized 则会被解锁
}

死锁状态

GCD (Grand Central Dispatch)

// 队列
dispatch_quequ_t

// 创建
dispatch_queue_t
dispatch_queue_create(const char *label, dispatch_queue_attr_t attr);

// 使用
void
dispatch_async(dispatch_queue_t queue, dispatch_block_t block);
void
dispatch_sync(dispatch_queue_t queue, dispatch_block_t block);

单例

+ (instancetype)sharedObject {
    static SingletonObject *instance = nil;
    
    // 下面的两行代码只会被之行一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[SingletonObject alloc] init];
    });
    return instance;
}

dispatch_semaphore (信号量)

dispatch_semaphore_t

// 创建
dispatch_semaphore_t
dispatch_semaphore_create(long value);

// 触发信号量
long
dispatch_semaphore_signal(dispatch_semaphore_t dsema);

// 等待信号量
long 
dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout);

NSOperation

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

创建 NSOperation 子类对象 : 重写 NSOperation 任务执行函数

@interface  MyOperation : NSOperation
@end
@implementation MyOperation
- (void)main {
    // 任务执行函数
}

将 NSOperation 的子类对象加入 NSOperationQueue : [queue addOperation:operation];

设置子类对象的 completionBlock, 在 block 中进行剩余的 UI 操作

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
MyOperation *op = [[MyOperation alloc] init];
__weak typeof(op) weakOp = op;
op.completionBlock = ^(){
    // 执行完毕之后需要进行的操作
    // 在此的操作也是在子线程进行的, 所以如果涉及到 UI 的操作需要手动放到主线程中
}

NSBlockOperation

+ (instancetype)blockOperationWithBlock:(void (^)(void))block;

NSInvocationOperation

+ (nullable instancetype)initWithTarget:(id)target selector:(SEL)sel object:(nullable id)arg;

Serial vs Concurrent

@property NSInteger maxConcurrentOperationCount;
// maxConcurrentOperationCount = 1      Serial Queue
// maxConcurrentOperationCount > 1      Concurrent Queue
// [NSOperationQueue mainQueue]         dispatch_get_main_queue()
@property (readonly) NSUinteger operationCount;

GCD vs NSOperation

NSOperation 支持取消
- 标记成取消状态, 当执行到这个任务的时候, 任务不会被执行但是 completetionBlock 仍然会被执行
封装, 能适应更复杂的操作和提供更精细化的操控

NSOperation 等待

创建两个 OperationQueue : uploadQueue, finalQueue
在 uploadQueue 中添加所有的操作
在 finalQueue 中添加后续的操作 finalOperation, 中间加入代码
- [uploadQueue waitUntilAllOperationsAreFinished];
- finalOperation 会等待到所有的 uploadQueue 中任务执行完然后执行

使用 dependency 等待任务

@interface NSOperation : NSObject
- (void)addDependency:(NSOperation *)op; // 添加依赖任务
- (void)removeDependency:(NSOperation *)op; // 移除依赖任务
@property (readonly, copy) NSArray<NSOperation *> *dependencies;

循环依赖
- 显式循环依赖
- 隐式循环依赖 : 串行队列中, 前面的任务依赖于后面的任务, 导致任务循环依赖

优先级

@interface NSOperation : NSObject
@property NSOperationQueuePriority queuePriority;

typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
    NSOperationQueuePriorityVeryLow = -8L;
    NSOperationQueuePriorityLow     = -4L;
    NSOperationQueuePriorityNormal  = 0;
    NSOperationQueuePriorityHigh        = 4;
    NSOperationQueuePriorityVeryHigh    = 8;
}

RunLoop 常驻的主线程

和线程一一对应, 每个线程有且只有一个 RunLoop
线程创建的时候并未有 RunLoop, 需要手动创建, 主线程除外
RunLoop 的创建发生在第一次获取它的时候(单例)
只能在线程内部获取对应的 RunLoop (主线程 RunLoop 除外)

@interface NSRunLoop : NSObject
+ (NSRunLoop *)currentRunLoop;
+ (NSRunLoop *)mainRunLoop;

- (void)run;
- (void)runUntilDate:(NSDate *)limitDate;
@end

常驻的后台线程

将有繁重的操作的回调指定到固定的线程中执行
perform selector 指定到固定的线程执行

RunLoop Mode

NSDefaultRunLoopMode
NSRunLoopCommonModes
- default mode
- modal mode
- tracking mode UITrackingRunLoopMode

@interface NSRunLoop : NSObject
- (void)addTimer:(NSTimer *)timer forMode:(NSString *);
@end

iOS 网络基础

NSURLRequest

/********** 创建请求 **********/
@interface NSURLRequest : NSObject
// 各种属性都不可设置
+ (instancetype)requestWithURL:(NSURL *)URL;
- (instancetype)initWithURL:(NSURL *)URL;
@property (nullable, readonly, copy) NSURL *URL;

@property (nullable, readonly, copy) NSString *HTTPMethod;
@property (nullable, readonly, copy) NSDictionary<NSString *, NSString *> *allHTTPHeaderFields;
- (nullable NSString *)valueForHTTPHeaderField:(NSString *)field;
@property (nullable, readonly, copy) NSData *HTTPBody;
@end

@interface : NSMutableURLRequest : NSURLRequest
// ... 各种属性都是可以设置的

@interface NSURL : NSObject
- (nullable instancetype)initWithString:(NSString *)URLString;
+ (nullable instancetype)URLWithString:(NSString *)URLString;
@property (readonly, copy) NSString *absoluteString;
@end


/********** 发送请求 **********/
@interface NSURLConnection : NSObject // 逐步被废弃, 推荐使用 NSURLSession
- (nullable instancetype)initWithRequest:(NSURLRequest *)request delegate:(nullable id)delegate startImmediately:(BOOL)startImmediately;
- (void)start;
@end


/********** 接收响应 **********/
@protocol NSURLConnectionDataDelegate <NSURLConnectionDelegate>
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;
@end

@protocol NSURLConnectionDelegate <NSObject>
@optional
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
@end

@interface NSHTTPURLResponse : NSURLResponse
@property (readonly) NSInteger statusCode;
@property (readonly, copy) NSDictionary *allHeaderFields;
@end

@interface NSURLResponse : NSObject <NSSecureCoding, NSCopying>
@property (nullable, readonly, copy) NSURL *URL;
@end


/********** 获取数据 : 解析 JSON/XML 数据 **********/
// JSON  <==> NSData
@interface NSJSONSeriallization : NSObject
+ (BOOL)isValidJSONObject:(id)obj;
+ (nullable NSData *)dataWithJSONObject:(id)obj options:(NSJSONWritingOptions)opt error:(NSError **)error;
+ (nullable id)JSONObjectWithData:(NSData *)data options:(NSJSONReadingOptions)opt error:(NSError **)error;

流程 Demo

// 创建一个请求
NSURL *url = [NSURL URLWithString:@"http://xxx.com"];
NSMutableURLRequest *request = [NSMutableRequest requestWithURL:url];
request.HTTPMethod = @"POST";
[request setValue:@"NEDemoAgent" forHTTPHeaderField:@"User-Agent"];
[request setValue:@"Application/JSON" forHTTPHeaderField:@"Content-Type"];

// 发送请求
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[connection start];

// 接收响应
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    self.response = response;
    self.responseData = [NSMutableData data];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    // handle error.
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // handle when request finished.
    NSStringEncoding stringEncoding = NSUTF8StringEncoding;
    // 直接获取返回的字符串
    self.responseString = [[NSString alloc] initWithData:self.responseData 
                                encoding:stringEncoding];
    // self.responseInfo 是 id 类型, 在这里获取的是格式化之后的 JSON 数据, 可能是 NSArray 或者 NSDictionary
    self.responseInfo = [NSJSONSerialization JSONObjectWithData:self.responseData 
                                options:0 
                                error:nil];
}

使用 NSURLSession 代替 NSURLConnection

NSURLSession	NSURLConnection
`NSURLConnection`	`NSURLSession & NSURLSessionTask & NSURLSessionConfiguration`
`NSURLConnectionDelegate && NSURLConnectionDatDelegate`	`NSURLSessionDelegate`

@interface NSURLSession : NSObject
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration;
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration delegate:(nullable id <NSURLSessionDelegate>)delegate delegateQueue:(nullable NSOperationQueue *)queue;

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url;

- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL;
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData;

- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;

iOS I/O与多线程

沙盒模型

特点

sandbox

资源管理器

多线程

NSThread

多线程优缺点

多线程同时访问资源

死锁状态

GCD (Grand Central Dispatch)

单例

dispatch_semaphore (信号量)

NSOperation

NSBlockOperation

NSInvocationOperation

Serial vs Concurrent

GCD vs NSOperation

NSOperation 等待

使用 dependency 等待任务

优先级

RunLoop 常驻的主线程

常驻的后台线程

RunLoop Mode

iOS 网络基础

NSURLRequest

流程 Demo

使用 NSURLSession 代替 NSURLConnection

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