GCD implementation and arc, blocks, GCD usage examples

Dispatch Queue

Usually , The code for thread management written in the application should be implemented at the system level .

No matter how hard programmers try to write code to manage threads , In terms of performance, it is impossible to surpass XNU Implemented at the kernel level GCD.

Used to implement Dispatch Queue And the software components used ：

1. libdispatch Provide technology ：Dispatch Queue;
2. Libc（pthreads） Provide technology ：pthread_workqueue;
3. XNU kernel Provide technology ：workqueue;

GCD Of API All are included in libdispatch In the library C Language functions .

Dispatch Queue Through the structure and linked list, it is realized as FIFO queue . The queue manager passed dispatch_async Function Block.

Block Join first Dispatch Continuation this dispatch_continuation_t Type structure , And then we're going to add FIFO In line . The Dispatch Continuation For memory Block Of Dispatch Group And other information , It is equivalent to the execution context .

dispatch_set_target_queue Function can be set Dispatch Queue For another Dispatch Queue The goal of . It can be like stringing beads , Set up multiple connected Dispatch Queue. At the end of the connection, it must be set to Main Dispatch Queue, Or various priorities Global Dispatch Queue Or to be used for Serial Dispatch Queue Of various priorities Global Dispatch Queue.

Main Dispatch Queue stay RunLoop In the implementation of Block.

Global Dispatch Queue Yes 8 Types .

ARC、Blocks、GCD Examples of use

Implement from the specified URL Download data , Parse the data in another thread and use its parsing results in the main thread ：

NSString *url = @"https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fphoto.16pic.com%2F00%2F54%2F75%2F16pic_5475997_b.jpg&refer=http%3A%2F%2Fphoto.16pic.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=jpeg?sec=1617284495&t=3bacab64a5d8233a37c94e2cc7f47492";
// In the main thread , From the specified url Start asynchronous network download 
NSURL *postUrl = [NSURL URLWithString:url];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:postUrl];
request.HTTPMethod = @"GET";
[request setTimeoutInterval:15];
request.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];

NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error)
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^
    {
        // It does not prevent the main thread from processing the acquired data for a long time 
        dispatch_async(dispatch_get_main_queue(), ^
        {
            // React to the interface 
        });
    });
}];

[task resume];
[session finishTasksAndInvalidate];

Cocoa The framework provides for asynchronous network communication API, Therefore, threads cannot be used in network programming . Be sure to use API.

We are based on NSURLSession Encapsulated asynchronous network request ：

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

typedef void (^completeBlock_t) (NSData *data);
typedef void (^errorBlock_t) (NSError *error);

@interface ASyncURLSession : NSURLSession

{
    /**
     * because ARC It works , So the following variables that do not show additional ownership modifiers ,
     * All attached __strong Modifier variables .
     */
    NSMutableData *data;
    completeBlock_t completeBlock_;
    errorBlock_t errorBlock_;
}

+(id)request:(NSString *)requestURL
completeBlock:(completeBlock_t)completeBlock
  errorBlock:(errorBlock_t)errorBlock;

-(id)initWithRequest:(NSString *)requestURL
       completeBlock:(completeBlock_t)completeBlock
          errorBlock:(errorBlock_t)errorBlock;

@end

NS_ASSUME_NONNULL_END