iOS多线程2 Opertaion补充

   Operation 可以添加依赖

  [operation1 addDependency:operation2];</span>

 这样保证operation1在operation2之后执行.有添加依赖就有删除依赖

[operation1 removeDependency:operation2];</span>

operation还可以设置优先级

[operation1 setQueuePriority:NSOperationQueuePriorityLow];</span>

优先级可以选择

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

取消operation

 [operation1 cancel];

Operation 符合KVO通知，可以在线程中了解操作到哪一步。

Operation KVO的状态有

• isCancelled
• isConcurrent
• isExecuting
• isFinished
• isReady
• dependencies
• queuePriority
• completionBlock
• 注意多线程造成死锁，

Operation的并发数是由系统决定的，系统会控制有多少并发数。