iOS 多线程简单使用的具体解释

2023-08-12 16:49:04

主线程

一个iOS程序执行后。默认会开启1条线程，称为“主线程”或“UI线程”（刷新UI界面最好在主线程中做。在子线程中可能会出现莫名其妙的BUG）
主线程的作用
- 显示\刷新UI界面
- 处理UI事件（比方点击事件、滚动事件、拖拽事件等）
注意点
- 别将比較耗时的操作放到主线程中
- 耗时操作会卡住主线程，严重影响UI的流畅度，给用户一种“卡”的坏体验
iOS中多线程的实现方案
- pthread（c语言。程序猿管理）
  - 一套通用的多线程API
  - 适用于Unix\Linux\Windows等系统
  - 跨平台\可移植
  - 使用难度大
- NSThread（oc语言，程序猿管理）
  - 使用更加面向对象
  - 简单易用。可直接操作线程对象
- GCD（c语言，自己主动管理）
  - 旨在替代NSThread等线程技术
  - 充分利用设备的多核
- NSOperation（oc语言，自己主动管理）
  - 基于GCD（底层是GCD）
  - 比GCD多了一些更简单有用的功能
  - 使用更加面向对象

NSThread

一个NSThread对象就代表一条线程
创建、启动线程

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *thread = [[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> alloc] initWithTarget:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> selector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) object:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];

[thread start];

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 线程一启动。就会在线程thread中运行self的run方法</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

常见相关使用方法

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">+ (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *)mainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得主线程</span>

- (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isMainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 是否为主线程</span>

+ (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isMainThread; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 是否为主线程</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获取当前线程</span>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> *current = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread];

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 线程的名字</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setName:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)n;

- (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)name;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

其它创建线程方式
- 长处：简单快捷
- 缺点：无法对线程进行更具体的设置

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建线程后自己主动启动线程</span>

[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> detachNewThreadSelector:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) toTarget:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> withObject:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 隐式创建并启动线程</span>

[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> performSelectorInBackground:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@selector</span>(run) withObject:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

控制线程的状态

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 启动线程</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)start;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入就绪状态 -> 执行状态。当线程任务执行完成，自己主动进入死亡状态</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 堵塞（暂停）线程</span>

+ (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)sleepUntilDate:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDate</span> *)date;

+ (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)sleepForTimeInterval:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSTimeInterval</span>)ti;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入堵塞状态</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 强制停止线程</span>

+ (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)exit;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 进入死亡状态</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：一旦线程停止（死亡）了，就不能再次开启任务</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

相互排斥锁

相互排斥锁使用格式

<code class="hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-at_rule" style="box-sizing: border-box;">@<span class="hljs-function" style="box-sizing: border-box;">synchronized(锁对象)</span> {</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 须要锁定的代码  }</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：锁定1份代码仅仅用1把锁。用多把锁是无效的</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

原子和非原子属性

OC在定义属性时有nonatomic和atomic两种选择
- atomic：原子属性，为setter方法加锁（默认就是atomic）
- nonatomic：非原子属性。不会为setter方法加锁
nonatomic和atomic对照
- atomic：线程安全，须要消耗大量的资源
- nonatomic：非线程安全。适合内存小的移动设备
iOS开发的建议
- 全部属性都声明为nonatomic
- 尽量避免多线程抢夺同一块资源
- 尽量将加锁、资源抢夺的业务逻辑交给server端处理，减小移动client的压力

线程间的通信

什么叫做线程间通信
- 在1个进程中。线程往往不是孤立存在的。多个线程之间须要常常进行通信
线程间通信的体现
- 1个线程传递数据给另1个线程
- 在1个线程中运行完特定任务后，转到另1个线程继续运行任务
线程间通信经常用法

<code class="hljs erlang has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-pp" style="box-sizing: border-box;">- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>performSelectorOnMainThread:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">SEL</span>)</span>aSelector withObject:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(id)</span>arg waitUntilDone:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">BOOL</span>)</span>wait;

- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>performSelector:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">SEL</span>)</span>aSelector onThread:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">NSThread</span> *)</span>thr withObject:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(id)</span>arg waitUntilDone:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">BOOL</span>)</span>wait;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

GCD

本质及长处
- 全称是Grand Central Dispatch，可译为“牛逼的中枢调度器”
- GCD会自己主动管理线程的生命周期（创建线程、调度任务、销毁线程）
- 程序猿仅仅须要告诉GCD想要运行什么任务，不须要编写不论什么线程管理代码
使用GCD的步骤
- 定制任务
  - 确定想做的事情
- 将任务加入到队列中
  - GCD会自己主动将队列中的任务取出，放到相应的线程中运行
  - 任务的取出遵循队列的FIFO原则：先进先出，后进后出
运行任务经常使用的函数

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 用同步的方式运行任务</span>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// queue：队列</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// block：任务</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：使用sync函数往当前串行队列中加入任务，会卡住当前的串行队列。同步方式会堵塞当前队列。

</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 用异步的方式运行任务</span>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block);

dispatch_barrier_async(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue, dispatch_block_t block);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在前面的任务运行结束后它才运行。并且它后面的任务等它运行完毕之后才会运行</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：这个queue不能是全局的并发队列</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

同步和异步的差别
- 同步：仅仅能在当前线程中运行任务。不具备开启新线程的能力
- 异步：能够在新的线程中运行任务，具备开启新线程的能力
队列的类型
- 并发队列（Concurrent Dispatch Queue）
  - 能够让多个任务并发（同一时候）运行（自己主动开启多个线程同一时候运行任务）
  - 并发功能仅仅有在异步（dispatch_async）函数下才有效
- 串行队列（Serial Dispatch Queue）
  - 让任务一个接着一个地运行（一个任务运行完成后，再运行下一个任务）
并发队列

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建并发队列</span>

dispatch_queue_t <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"队列名称"</span>, DISPATCH_QUEUE_CONCURRENT)

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第一个參数 const char *label 队列名称 </span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第二个參数 dispatch_queue_attr_t attr 队列的类型 DISPATCH_QUEUE_CONCURRENT 表示并发队列</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得全局的并发队列</span>

dispatch_queue_t <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">queue</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第一个參数 dispatch_queue_priority_t priority 队列的优先级</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 第二个參数 unsigned long flags 此參数临时无用，用0就可以</span>

<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_HIGH <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 高</span>

<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_DEFAULT <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 默认（中）</span>

<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_LOW (<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 低</span>

<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#define</span> DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 后台</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

串行队列

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建串行队列（队列类型传递NULL或者DISPATCH_QUEUE_SERIAL）</span>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"队列名称"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获得主队列。主队列也是串行队列</span>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_get_main_queue();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

线程间的通信

<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">// 从子线程回到主线程

dispatch_async(

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{

    // 运行耗时的异步操作<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>

      dispatch_async(dispatch_get_main_queue(), ^{

        // 回到主线程，运行UI刷新操作

        });

});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

延迟操作
- iOS中延迟操作有3种
  - 调用NSObject的方法
  - 使用GCD函数
  - 使用NSTimer

<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">[self performSelector:@selector(run) withObject:nil afterDelay:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>];

// <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>秒后再调用self的run方法

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span> * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

    // <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>秒后运行这里的代码<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>

});

[NSTimer scheduledTimerWithTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span> target:self selector:@selector(test) userInfo:nil repeats:NO];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

一次性代码

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 使用dispatch_once函数能保证某段代码在程序运行过程中仅仅被运行1次</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 仅仅运行1次的代码(这里面默认是线程安全的)</span>

});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

高速迭代

<code class="hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 使用dispatch_apply函数能进行高速迭代遍历</span>

<span class="hljs-function" style="box-sizing: border-box;">dispatch_apply(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-function" style="box-sizing: border-box;">dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)</span>, ^(size_t index)</span>{

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 运行10次代码，index顺序不确定</span>

});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

队列组
- 能够满足的一种需求（当然也能够用依赖线程依赖实现，下文会提到）
  - 首先：分别异步运行2个耗时的操作
  - 其次：等2个异步操作都运行完成后，再回到主线程运行操作

<code class="hljs r has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">dispatch_group_t group =  dispatch_group_create();

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{

    // 运行<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>个耗时的异步操作

});

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{

    // 运行<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>个耗时的异步操作

});

dispatch_group_notify(group, dispatch_get_main_queue(), ^{

    // 等前面的异步操作都运行完成后，回到主线程<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>

});</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

单例模式

单例模式的作用
- 能够保证在程序执行过程，一个类仅仅有一个实例，并且该实例易于供外界訪问
- 从而方便地控制了实例个数，并节约系统资源
单例模式的使用场合
- 在整个应用程序中，共享一份资源（这份资源仅仅须要创建初始化1次）
实现步骤：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在.m中保留一个全局的static的实例</span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span> _instance;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 重写allocWithZone:方法，在这里创建唯一的实例（注意线程安全），alloc方法会调用allocWithZone:方法</span>

+ (instancetype)allocWithZone:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> _NSZone *)zone

{

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{

        _instance = [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> allocWithZone:zone];

    });

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;

}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 提供1个类方法让外界訪问唯一的实例</span>

+ (instancetype)sharedInstance

{

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{

        _instance = [[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> alloc] init];

    });

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;

}

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 实现copyWithZone:方法</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)copyWithZone:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> _NSZone *)zone

{

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> _instance;

}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>

NSOperation

NSOperation和NSOperationQueue实现多线程的详细步骤
- 先将须要运行的操作封装到一个NSOperation对象中
- 然后将NSOperation对象加入到NSOperationQueue中
- 系统会自己主动将NSOperationQueue中的NSOperation取出来
- 将取出的NSOperation封装的操作放到一条新线程中运行
NSOperation是抽象类，使用NSOperation子类的方式有3种
- NSInvocationOperation
- NSBlockOperation
- 自己定义子类继承NSOperation，实现内部对应的方法
NSInvocationOperation

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建NSInvocationOperation对象</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)initWithTarget:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)target selector:(SEL)sel object:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)arg;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 调用start方法開始运行操作</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)start;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 一旦运行操作，就会调用target的sel方法</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：默认情况下，调用了start方法后并不会开一条新线程去运行操作。而是在当前线程同步运行操作。仅仅有将NSOperation放到一个NSOperationQueue中，才会异步运行操作</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

NSBlockOperation

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建NSBlockOperation对象</span>

+ (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)blockOperationWithBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 通过addExecutionBlock:方法加入很多其它的操作</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)addExecutionBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注意：仅仅要NSBlockOperation封装的操作数 > 1。就会异步运行操作</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

NSOperationQueue

<code class="hljs erlang has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">// 加入操作到<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSOperationQueue</span>中

<span class="hljs-pp" style="box-sizing: border-box;">- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>addOperation:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(<span class="hljs-variable" style="box-sizing: border-box;">NSOperation</span> *)</span>op;

- <span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>addOperationWithBlock:<span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void (^)</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(void)</span>)block;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

相关操作

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 设置最大并发数</span>

- (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSInteger</span>)maxConcurrentOperationCount;

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setMaxConcurrentOperationCount:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSInteger</span>)cnt;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 取消队列的全部操作</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)cancelAllOperations;

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 提示：也能够调用NSOperation的- (void)cancel方法取消单个操作</span>

<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 暂停和恢复队列</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setSuspended:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)b; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// YES代表暂停队列。NO代表恢复队列</span>

- (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">BOOL</span>)isSuspended;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

操作依赖
- NSOperation之间能够设置依赖来保证运行顺序
- 能够在不同queue的NSOperation之间创建依赖关系

<code class="hljs ini has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 102, 102);">[operationB addDependency:operationA]</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // 操作B依赖于操作A</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

操作的监听

<code class="hljs cs has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 能够监听一个操作的运行完成</span>

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))completionBlock;

- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setCompletionBlock:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^)(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>))block;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

自己定义NSOperation
- 仅仅须要重写- (void)main方法。在里面实现想运行的任务
- 注意点
  - 自己创建自己主动释放池（由于假设是异步操作，无法訪问主线程的自己主动释放池）
  - 常常通过- (BOOL)isCancelled方法检測操作是否被取消，对取消做出响应

计算时间差

<code class="hljs sql has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">NSDate *<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">start</span> = [NSDate <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">date</span>];</span>

// 上下两句代码间放须要计算时间的程序

NSDate *<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> = [NSDate <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">date</span>];</span>

NSLog(@"%f", [<span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> timeIntervalSinceDate:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">start</span>]);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

<code class="hljs sql has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">CFTimeInterval <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">begin</span> = CFAbsoluteTimeGetCurrent();</span>

// 上下两句代码间放须要计算时间的程序

CFTimeInterval <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> = CFAbsoluteTimeGetCurrent();</span>

NSLog(@"%f", <span class="hljs-operator" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span> - <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">begin</span>);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

小结：

1、在GCD中，方法假设用异步函数能够开启子线程做事情。该方法中的程序会顺序运行究竟，然后再返回去开启子线程运行内部的操作。假设是同步函数。则不能开启子线程，里面的同步函数仅仅能一个一个运行下去。

2、假设在主队列中调用同步函数，easy造成死锁。

顶: 0

码农公寓

主线程

NSThread

相互排斥锁

原子和非原子属性

线程间的通信

GCD

单例模式

NSOperation

计算时间差

小结：

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