4 Basic Concept Synchronization
- Before writing the program is from top to bottom, from left to right, code execution order
- 1 threads perform multiple tasks, which are executed sequentially, and 1 threads perform a task at the same time
Asynchronous
Multiple threads can perform multiple tasks "at the same time"
Process
- Programs that are running on the current computer
- Each process is independent, and each process runs within its dedicated and protected memory space
- You can view the processes that are open in your Mac system through Activity Monitor
Thread
- A process contains one or more threads
- Threads are the basic unit of program execution, and all tasks in the process are run in the thread
The basic concept of multi-threaded multithreading
- Multiple threads can be opened in a process
- Multiple threads are "simultaneously" running
- Multithreading can improve the efficiency of program execution
Principle of execution
Fast switching threads through the CPU
Feature summary
- (Single core CPU) at the same time, the CPU can only handle 1 threads, and only 1 threads are executing
- Fast switching through the CPU
- Switching time is very short, resulting in "simultaneous" execution of the phenomenon
- When very many threads are turned on, CPU switching threads consume a large amount of resources resulting in less efficient execution of threads
Advantages and Disadvantages
- To be able to appropriately mention the execution efficiency of the procedure
- To improve the utilization rate of resources appropriately
- Automatic destruction of threads after all tasks have been performed
Disadvantages
- Open threads need to occupy a certain amount of memory (by default, each thread is a 512KB)
- If you open a large number of threads, it will take up a lot of memory space, reduce the performance of the program
- The more threads, the greater the overhead of the CPU on the calling thread
- More complex programming, such as inter-thread communication, multi-threaded data sharing
Main thread
- After a program is run, 1 threads are turned on by default, called the "main thread" or "UI thread"
- The main thread is typically used to refresh the UI interface and handle UI events (e.g., click, scroll, drag, etc.)
Main thread Usage Note
- Don't put time-consuming operations into the main thread
- Time-consuming operations can get stuck in the main thread, seriously affecting the smoothness of the UI, giving the user a bad experience with cards
The difference between four-in-the-middle multithreading technology in iOS
manual
|   |
|
language /th> |
Thread life cycle |
Usage frequency |
| pthread |
cross-platform POSIX, inconvenient to use |
c |
manual |
almost no |
| nsthread |
|
oc |
occasional |
| gcd |
optimized for multicore performance, easy to use |
c |
auto |
regular |
| nsopera tion |
Encapsulation of GCD, object-oriented |
oc |
auto |
regular |
Introduction to Multithreading 001------
