48、Grand Central Dispatch, Background Processing, and App State Management

Grand Central Dispatch, Background Processing, and App State Management

1. Grand Central Dispatch Basics

Grand Central Dispatch (GCD) is a powerful tool for handling background processing. When using __block to define a variable, it becomes directly available to all blocks within the same scope. A notable feature is that __block - qualified variables aren’t duplicated or retained inside a block.

In terms of UIKit thread - safety, messaging GUI objects from a background thread is prohibited. GCD offers a solution: we can use dispatch_async() along with dispatch_get_main_queue() to send work back to the main thread. Here is an example of the doWork: method: