What is the difference between thread synchronization and Asynchrony? How does multi-threaded synchronization work in iOS?

1. Thread synchronization is multiple threads accessing the same resource at the same time, waiting for resource access to end, wasting time, inefficient, serial execution of tasks

Thread Async: Access resources while idle wait while accessing other resources, implement multithreading mechanism, execute task 1.2.3 mode in parallel

Use GCD's primary queue. Use Nsoperationqueue to set the maximum number of threads (concurrency) to 1 1.1.1

How is the interaction between all the objects implemented in 2.OC?

Method of implementing object---by message sending mechanism

3. Describe the implementation mechanism for pull-up loading and pull-down refreshes?

Inheriting from the scrolling view, the two properties of the scrolling view offset (x, y) represent offsets, inset (top,left) when the Y value is not negative, the height of the scrolling view--Displays the view height +100 (if the offset 100 is refreshed), refreshes the data again.

4. What do you think about performance optimization?

Lazy loading, memory management, timely release of memory,

Program background runs using push notifications

Rendering reduction (reduces video card usage)

TableView Reuse

What is the difference between thread synchronization and Asynchrony? How does multi-threaded synchronization work in iOS?