GCD summary

What is? GCD

It's one of the technologies to execute tasks asynchronously . Generally, the code used for thread management of technology in applications is implemented at the system level . Developers only need to define the tasks they want to perform and append them to the appropriate Dispatch Queue in ,GCD You can generate the necessary threads and schedule tasks . As a part of the system , More efficient than previous threads .

dispatch_async(queue, ^
{
    /**
     * Long time processing 
     *
     * for example AR Image recognition 
     * For example, database access 
     */

    /**
     * End of long processing , The main thread uses this processing result .
     */
    dispatch_async(dispatch_get_main_queue(), ^
    {
        /**
         * Only in the processing that the main thread can execute 
         * For example, user interface update 
         */
    });
});

Multithreaded programming

1 individual CPU Executive CPU The command line is a Forkless path , The thread .

This bifurcated path is not only 1 strip , Multithreading occurs when there are multiple threads . In multithreading ,1 individual CPU The core executes different commands on multiple different paths .

Due to the use of multithreading, context switching can be repeated many times between a thread and other threads , So it looks like 1 individual CPU The core can execute multiple threads in parallel . And there are multiple CPU In the case of nuclear , It doesn't look like , It really provides multiple CPU The technology of executing multiple threads in parallel with the kernel .

Possible problems of multithreading ：

Data competition 、 Deadlock 、 Too many threads consume a lot of memory .

But using multithreaded programming can ensure the response performance of the application .