iOS development: Multithreading with GCD

In addition to the previous article on the nsthread thread, there is also a gcd (Grand Central Dispath), a new Apple-developed solution for multi-core programming, leveraging CPU resources to put all tasks into a single task queue for scheduling. GCD provides a global concurrency queue by default, which is used by the entire application and does not need to be created.

• The difference between synchronous and asynchronous
  • Dispatch_sync Sync: Does not have the ability to open threads
  • Dispatch_async Async : Ability to open threads

• how tasks are executed
  • concurrent queues: Multiple tasks are executed concurrently and can only be performed under one-step functions " Async"
  • Serial queue: Let the task run one after another

Note: commonly used in actual development it's dispatch_async.

Here are a few common queue usage

One: The most commonly used global concurrency queue:

 　　     //Get global concurrency queueLet queue = Dispatch_get_global_queue (Dispatch_queue_priority_default,0)        //add a task to a queue and execute concurrentlyDispatch_async (queue) {(), Voidinch            //dosomething ... Task 1} dispatch_async (queue) {()-Voidinch            //dosomething ... Task 2} dispatch_async (queue) {()-Voidinch            //dosomething ... Task 3        }                //pausing a queuedispatch_suspend (queue)//Continue queueDispatch_resume (Queue)

Two: Serial queue, the tasks in the queue will not be executed concurrently, one task will be executed after the completion of another task

 //Create a serial queueLet Serialqueue = Dispatch_queue_create ("Dispatch_queue_name", nil)//add a task to a queue one task executes before another task is executedDispatch_async (Serialqueue) {() Voidinch            //dosomething ... Task 1} dispatch_async (Serialqueue) {()-Voidinch            //dosomething ... Task 2} dispatch_async (Serialqueue) {()-Voidinch            //dosomething ... Task 3}

Three: GCD communication between threads, usually used for sub-threads to request data, back to the main thread update UI

// inter-thread communication     0 inch            // Doing something on a child thread            inch                // update UI on main thread ...             })        }

Four: Thread-deferred execution

// thread-Deferred execution        3.0 = Dispatch_time (Dispatch_time_now, Int64 (second * Double (nsec_per_sec)))                //          3s back to the main thread to perform the task        inch                     }        //3s will open a new thread to execute the task        in the queue 0 inch                     }

Five: A one-time code, as the name implies, within the application lifecycle, block blocks will only be executed once.

  0         dispatch_once (            in// only once during the application life cycle         )      

Six: Queue groups: Some tasks are put into a queue group, and when all tasks are completed, the notify of the group is executed.

/ ********************************** Queue Group ******************************************/Let group=dispatch_group_create () let Groupqueue= Dispatch_get_global_queue (Dispatch_queue_priority_default,0) Dispatch_group_async (group, Groupqueue) {()-Voidinch            //Task 1} dispatch_group_async (Group, Groupqueue) {()-Voidinch            //Task 2} dispatch_group_async (Group, Groupqueue) {()-Voidinch            //Task 3} dispatch_group_notify (Group, Groupqueue) {()-Voidinch            //will wait for Task 1, Task 2, Task 3 execution after completion}

Finish!

iOS development: Multithreading with GCD