Skip to content

GCD & NSOperation.md

Latest commit

 

History

History
43 lines (31 loc) · 2.2 KB

GCD & NSOperation.md

File metadata and controls

43 lines (31 loc) · 2.2 KB

GCD & NSOperation

GCD

  • Serial and concurrent
  • Synchronous method returns control to the caller only after the task is completed
  • Asychronous method returns control to the caller immediately
  • Three main types of queues
    • Main queue (only Async)
      • Mainly used to rendering User Interface without any interferences
    • Global queues (4 types of Quality of Service from User-interactive to Background)
    • Custom queues(Default: serial queues)
  • Deadlock
    • Solutions: Make queues concurrent, avoid using locks
    • Dispatch Barries: all works prior to the barrier are guarateed to complete in the same queue
  • No need to retain or release any of the global dispatch queues, including the concurrent dispatch queues or the main dispatch queue. Any attempts to retain or release the queues are ignored
  • On iphones, discretionary and background operations including networking are paused when Low Power Mode is enabled

NSOperation

  • Operations are executed on a separate thread from GCD
  • Using dependencies to execute an operation after another one is done
  • Support KVO and KVC
    • Ready, cancelled, executed
  • Cacellation is enabled at any time duirng execution
  • NSBlockOperation
    • let blockOperation = BlockOperation{ () -> Void }
  • NSInvocationOperation (Not in Swift)
  • Operations with high priority will be executed first (5 levels)

GCD & Timer

NSTimer requires an active run loop, when initialized in Main Thread it automatically uses the main run loop. If you need to make a background timer you need attach it to the thread’s run loop and invoke run() to make it active.

  • NSTimer needs one live NSRunLoop to execute it’s events. In main thread, the NSRunLoop is always live and will never stop until the app is terminated, but in other threads, you must invoke run() to active the NSRunLoop.
  • NSTimer must invoke invalidate() to release the current timer, otherwise, the timer will retain a strong reference of the current instance of target, and it will remain in memory until invalidate() invoked or app terminated;
  • NSTimer must created and invalidated in the same thread, and a lot of times, we may forget that.
  • GCD & Timer