# MyBook

**Repository Path**: sunjian2012/MyBook

## Basic Information

- **Project Name**: MyBook
- **Description**: 上课电子课件
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2016-04-19
- **Last Updated**: 2020-12-19

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# iOS多线程编程

## 一.简介

### ① iOS有三种多线程编程技术

    1.NSThread
    2.Cocoa NSOperation
    3.GCD(Grand Central Dispatch)
    这三种编程方式从上到下,城乡度层次是从低到高的,抽象度越高的使用越简单,也是Apple最推荐使用的.
    
### ② 三种方式的优缺点
    NSThread
      优点:比其他两个轻量级
      缺点:需要自己管理线程的生命周期,线程同步.线程同步对数据的加锁会有一定的系统开销

   
NSThread实现的技术有下面三种

| Technology | Description |
| -- | -- |
| Cocoa threads | Cocoa implements threads using the NSThread class. Cocoa also provides methods on NSObject for spawning new threads and executing code on already-running threads. For more information, see “Using NSThread” and “Using NSObject to Spawn a Thread.” |
| POSIX threads | POSIX threads provide a C-based interface for creating threads. If you are not writing a Cocoa application, this is the best choice for creating threads. The POSIX interface is relatively simple to use and offers ample flexibility for configuring your threads. For more information, see “Using POSIX Threads” |
| Multiprocessing Services | Multiprocessing Services is a legacy C-based interface used by applications transitioning from older versions of Mac OS. This technology is available in OS X only and should be avoided for any new development. Instead, you should use the NSThread class or POSIX threads. If you need more information on this technology, see Multiprocessing Services Programming Guide. |


  一般使用Cocoa threads技术

    Cocoa operation 
        优点：不需要关心线程管理，数据同步的事情，可以把精力放在自己需要执行的操作上。
        Cocoa operation 相关的类是 NSOperation ，NSOperationQueue。
        NSOperation是个抽象类，使用它必须用它的子类，可以实现它或者使用它定义好的两个子类：NSInvocationOperation 和 NSBlockOperation。创建NSOperation子类的对象，把对象添加到NSOperationQueue队列里执行。

    GCD
        Grand Central Dispatch (GCD)是Apple开发的一个多核编程的解决方法。在iOS4.0开始之后才能使用。
        GCD是一个替代诸如NSThread, NSOperationQueue, NSInvocationOperation等技术的很高效和强大的技术。现在的iOS系统都升级到6了，所以不用担心该技术不能使用。