goroutine (coroutine) in go language

Article Directory

• goroutine(coroutine)
• • • • 1. Process and thread description:
      • 2. Description of Concurrency and Parallelism:
      • 3.go coroutine and go main thread:
      • 4. Basic introduction to MPG mode
      • 5. Set the number of CPUs running in golang

goroutine(coroutine)

1. Process and thread description:

1. A process is an execution process of a program in the operating system, and it is the basic unit of resource allocation and scheduling in the system.
2. A thread is an execution instance of a process and the smallest unit of program execution. It is a basic unit smaller than a process that can run independently.
3. A process can create and destroy multiple threads, and multiple threads in the same process can execute concurrent.
4. A program has at least one process, and a process has at least one thread.

2. Description of concurrency and parallelism:

1. Multi-threaded programs running on a single core are concurrent.
2. Multi-threaded programs run on multiple cores, which is parallelism.

3.go coroutine and go main thread:

1. Go main thread (some programmers directly call it a thread/can also be understood as a process): On a go thread, multiple coroutines can be started.It can be understood as: coroutines are lightweight threads (optimized by the compiler).
2. Features of go coroutines:
   1) Independent stack space
   2) Shared program heap space
   3) Scheduling is controlled by the user
   4) Coroutines are lightweight threads

goroutine-quick start case
Case description:
Write a program to complete the following functions:
1) In the main thread (which can be understood as a process), start agoroutine, this coroutine outputs "hello, world" every second
2) The main thread also outputs "hello, golang" every second, after 10 outputs, exit the program
3) Request the main threadThreads and goroutines execute simultaneously

package mainimport ("fmt""strconv""time")//Write a function that prints "hello,world" every secondfunc test() {for i:=1;i<=10;i++ {fmt.Println("test hello,world "+strconv.Itoa(i))time.Sleep(time.Second)}}func main() {go test() //Open a coroutine to execute it at the same timefor i:=1;i<=10;i++ {fmt.Println("mian() hello,world "+strconv.Itoa(i))time.Sleep(time.Second)}}

Summary:

1. The main thread is a physical thread that acts directly on the CPU.It is heavyweight and consumes a lot of CPU resources.
2. Coroutines are started from the main thread, which are lightweight threads and logical states.Relatively small consumption of resources.
3. Golang's coroutine mechanism is an important feature, which can easily open tens of thousands of coroutines.The concurrency mechanism of other programming languages ​​is generally based on threads. Too many threads are opened, and the resource consumption is high. This highlights the advantages of Golang in concurrency.

4. Basic introduction to MPG mode

M: The main thread of the operating system (the physical thread)
P: The context required for the execution of the coroutine
G: The coroutine

5. Set the number of CPUs running in golang

package mainimport "fmt"import "runtime"func main() {//Get the number of CPUs in the current systemnum := runtime.NumCPU()//Set the cpu of num-1 to run the go program hereruntime.GOMAXPROCS(num)fmt.Println("num=",num)}//output result: num = 16

Note: After go1.8, the program runs on multiple cores by default, so it is not necessary to set it.Before go1.8, it needs to be set.

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