Preliminary understanding of GCD and understanding of GCD

Preliminary understanding of GCD and understanding of GCD

// (1) use an asynchronous function to add tasks to the concurrent queue. // conclusion: Enable three subthreads at the same time-(void) test1 {// 1. obtain the global concurrent queue dispatch_queue_t queue = dispatch_get_global_queue (DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); // 2. after adding a task to the queue, You can execute the task // asynchronous function: With the ability to enable the new thread dispatch_async (queue, ^ {NSLog (@ "Download image 1 ---- % @", [NSThread currentThread]);}); dispatch_async (queue, ^ {NSLog (@ "Download Image 2 ---- % @", [NSThread currentThread]);}); dispatch_async (queue, ^ {NSLog (@ "Download Image 3 ---- % @", [NSThread currentThread]) ;}); // print the main thread NSLog (@ "main thread ---- % @", [NSThread mainThread]);}

// (2) use an asynchronous function to add a task to the serial queue // conclusion: the thread is enabled, but only one thread is enabled-(void) test2 {// print the main thread NSLog (@ "main thread ---- % @", [NSThread mainThread]); // create a serial queue dispatch_queue_t queue = dispatch_queue_create ("tqh ", NULL); // The first parameter is the name of the serial queue, which is a C string // The second parameter is the queue attribute. Generally, no attribute is assigned to the serial queue, therefore, a NULL value (NULL) is usually input. // 2. add the task to the queue and execute dispatch_async (queue, ^ {NSLog (@ "Download image 1 ---- % @", [NSThread currentThread]);}); dispatch_async (queue, ^ {NSLog (@ "Download Image 2 ---- % @", [NSThread currentThread]) ;}); dispatch_async (queue, ^ {NSLog (@ "Download Image 3 ---- % @", [NSThread currentThread]) ;}); // 3. release resources // dispatch_release (queue );}

// 3) use the synchronous function to add tasks to the concurrent queue // conclusion: no new threads are enabled, and the concurrent queue loses the concurrent function-(void) test3 {// print the main thread NSLog (@ "main thread ---- % @", [NSThread mainThread]); // create a serial queue dispatch_queue_t queue = dispatch_get_global_queue (queue, 0 ); // 2. add a task to the queue and execute dispatch_sync (queue, ^ {NSLog (@ "Download image 1 ---- % @", [NSThread currentThread]) ;}); dispatch_sync (queue, ^ {NSLog (@ "Download Image 2 ---- % @", [NSThread currentThread]) ;}); dispatch_sync (queue, ^ {NSLog (@ "Download Image 3 ---- % @", [NSThread currentThread]) ;});}

// (4) use the synchronous function to add tasks to the serial queue // conclusion: no new thread is enabled-(void) test4 {NSLog (@ "add a task to the serial queue using the synchronization function"); // print the main thread NSLog (@ "main thread ---- % @", [NSThread mainThread]); // create a serial queue dispatch_queue_t queue = dispatch_queue_create ("tqh", NULL); // 2. add a task to the queue and execute dispatch_sync (queue, ^ {NSLog (@ "Download image 1 ---- % @", [NSThread currentThread]) ;}); dispatch_sync (queue, ^ {NSLog (@ "Download Image 2 ---- % @", [NSThread currentThread]) ;}); dispatch_sync (queue, ^ {NSLog (@ "Download Image 3 ---- % @", [NSThread currentThread]) ;});}

/** Supplement: queue name: in future debugging, you can see the queue in which the task is executed. Note: Synchronous functions do not have the ability to enable threads. threads are not enabled in any queue. asynchronous functions can enable threads, the number of threads enabled is determined by the queue (only one new thread is enabled for the serial queue and multiple threads are enabled for the concurrent Queue ). Synchronous function (1) Concurrent queue: no thread (2) Serial queue: no thread asynchronous function (1) Concurrent queue: N threads enabled (2) Serial queue: enable one thread supplement: All functions with the words "create \ copy \ new \ retain" in their names need to be release when this data is not needed. The data type of GCD does not need to be release in the ARC environment. The data type of CF (core Foundation) still needs to be release in the ARC environment. Asynchronous functions have the ability to open threads, but do not necessarily open threads */