golang 片段7 for https://medium.com/@francesc/why-are-there-nil-channels-in-go-9877cc0b2308

Posted 2021-05-24

func merge(a, b <-chan int) <-chan int {
	c := make(chan int)
	go func() {
		defer close(c)
		for a != nil || b != nil {
			select {
			case v, ok := <-a:
				if !ok {
					fmt.Println("a is done")
					a = nil
					continue
				}
				c <- v
			case v, ok := <-b:
				if !ok {
					fmt.Println("b is done")
					b = nil
					continue
				}
				c <- v
			}
		}
	}()
	return c
}

golang 转到片段以观察运行时行为和内存分配

// This snippet is helpful for observing OS threads as the runtime is creating
// blocked out of the gate goroutines. These should immediately be going off of
// CPU and remaining this way for the entirety of the process's lifetime.
package main

import (
	"fmt"
	"os"
	"runtime"
	"time"

	"net/http"
	_ "net/http/pprof"
)

func main() {
	const limit = 100000
	go func() {
		fmt.Println(http.ListenAndServe(":9876", nil))
	}()

	for i := 0; i < limit; i++ {

		c := make(chan struct{})
		go func() {
			<-c
		}()
	}

	fmt.Fprintf(os.Stdout, "Number of goroutines: %d\n", runtime.NumGoroutine())
	<-time.NewTimer(600 * time.Second).C
}

// This snippet is helpful for observing OS threads as the runtime is creating
// blocked out of the gate goroutines. These should immediately be going off of
// CPU and remaining this way for the entirety of the process's lifetime.
package main

import (
	"fmt"
	"os"
	"runtime"
	"time"
)

func main() {
	for {
		fmt.Fprintf(os.Stderr, "%d ", runtime.NumGoroutine())
		c := make(chan struct{})
		go func() {
			<-c
		}()
		<-time.NewTimer(time.Second).C
	}
}