iOS开发-多线程

多线程-NSOperation

用线程是为了什么

• 完成一个费事的任务，且不影响UI响应
  • 不如封装一下，省得反复写例行代码
    • NSOperation:封装任务部分
      • 用selector编写任务：NSInvocationOperation
      • 用block编写任务：NSBlockOperation
      • 任务可以用依赖关系穿起来
    • NSOperationQueue：封装线程管理部分

NSOperation 抽象基类

• 执行
  • -start 启动
    • 设置状态然后调用-main
  • cancel 取消
  • -waitUntilFinished
• 任务定义
  • main
    • 默认啥也不干
    • 会在NSOperation提供的AutoreleasePool理智型
    • 定义NSOperation子类时并覆盖之

NSInvocationOperation

• 创建
  • -initWithTarget:(id) selector:(SEL) boject:(id)
  • -initWithInvocation:(NSInvocation *)

NSBlockOperation

• 创建
  • • blcokOperationWithBlock:(void (^)(void))
• 追加
  • -(void)addExecutionBlock:(void (^)(void))
• Operation 会copy参数block

NSOperation 依赖关系

• -(void)addDependency:(NSOperation *)dep
  • dep 完成后，本operation才会开始执行
  • 注意不要写出唤醒依赖！！
  • 依赖链中的operation即时已经完成，也不会从连中移除，除非调用-removeDependency:

NSOperation 状态 （iOS8+)

• .name
• .ready： 依赖都满足了没
• .executing,.finished,.cancelled
• .asynchronous
  • 默认都是NO，制度，只有子类能改变之
  • synchronized, in calling thread
• -setCompletionBlock:(^void))/*copy*/
  • iOS4+,但iOS8+block开始执行后会置nil

NSOperationQueue

• Queue operations
  • add
    • [q addOperation:anOp];
    • [q addOperations:anArrayOfOps waitUntilFinished:NO];
    • [q addOperationWithBlock:^{...}];
  • exec control
    • run once added
    • -setMaxConcurrentOperationCount;
    • operation -addDependency;
    • queue -cancelAllOperations
    • queue -setSuspended:(BOOL)
  • waitUntilAllOperationsAreFinished

Dispatch Queue

• GCD Dispatch Queue is C API!
• Queue Type :Serial,Concurrent,Main
• Usage
  • get a queue
  • dispatch a block using the queue

在Objective-C里，dispatch objects 也是ObjC对象，支持ARC

Predefined Queue

• Global Concurrent Queue
  • dispatch_get_global_queue(id,0)
    • returns dispatch_queue_t,falgs alwasy 0
    • id
      • QOS_CLASS_USER_INTERACTIVE/INITIATED/UNILITY/BACKGROUND
      • DISPATCH_QUEUE_PRIORITY_HIGH/DEFAULT/LOW/BACKGROUND
  • Main queue(serial)
    • dispatch_get_main_queue();

Create Queue

tips: 只能创建串行queue

• dispatch_queue_create("com.my.q",NULL);
• QueueOP
  • dispatch_suspend()/dispatch_resume()
  • on queue cleanup:dispatch_set_finalizer_f(func)

Queue the Tasks

• dispatch_sysc(q,block) : don't do this on q's thread
• dispatch_asysnc(q,block)
  • on task complete：dispatch a block at end of task
    • dispatch inside
      • dispatch_retain(q) before queue the task
      • dispatch_release(q) before queue complete block
  • get queue in block: dispatch_get_current_queue()

Special Tasks

• singleton
  • dispatch_once(dispatch_once_t *,block);
• timer
  • dispatch_after(dispatch_time_t,q,block);
• for-loop
  • dispatch_apply(count,q,^(size_t i){....})

Dispatch Group

• how to wait a group of tasks to finished
  • dispatch_group_t group = dispatch_group_create()；
  • dispatch_group_async(g,q,^{});
  • dispatch_group_wait(g)

同步

• dispatch_semaphore_t
  • dispatch_semaphore_create(long)
  • long dispatch_semaphore_wait(sema,timeout);
  • dispatch_semaphore_signal(sema)
• barrier
  • dispatch_barrier_async(q,block)
  • dispatch_barrier_sync(q,block)

Dispatch Source

• 用以接受各类事件
  • Timer
  • UNIX signal/FD/Process/Mach port
  • Custom
• 用法
  • 创建
    • -dispatch_source_create(type,handle,mask,q)
  • 配置
    • -dispatch_source_set_event_handler(src,block)
      • dispatch_source_get_data/handle/mask(src)
    • dispatch_source_set_cancel_handler(src,block)
  • 启动：dispatch_resume(src)
  • 撤销：dispatch_source_cancel(src)

数据存储

数据持久化

• 本地
  • 文件 NSHomeDirectiory()/Documents
  • 数据库
• 云端
  • iCloud
    • 文件
    • key-value数据库
  • 第三方