通过对通道进行多次写入来理解 golang 阻塞通道行为

package main

import (
    "log"
    "time"
)

func Greet2(c chan string) {
    // logging to Stdout is not an atomic operation
    // so artificially, sleep for some time
    time.Sleep(2 * time.Second)
    
    // 5. until below line reads and unblock the channel
    log.Printf("5. Read Greet2:: %s\n\n", <-c)
}

func Greet(c chan string) {
    // 4. Push a new value to the channel, this will block
    // Process will look for other go routines to execute
    log.Printf("4. Add 'Greet::John' to the channel, block until it is read. Remember, 'Greet' goroutine will block and only other goroutines can run even though this go routine can pull the value out from the channel.\n\n")
    c <- "Greet::John!"
    
    // 8. This statement will never execute
    log.Printf("8. Read Greet:: %s !\n\n", <-c)
}

func main() {

    c := make(chan string)

    log.Println("1. Main start")
    
    // 2. Both go routine will be declared and both will
    // for a value to be inserted in the channel
    log.Println("2. Declare go routines.\n\n")
    go Greet(c)
    go Greet2(c)
    
    // 3. write will block
    log.Println("3. Add 'main::Hello' to the channel, block until it is read. Remember, 'main' goroutine will block and only other goroutines can run even though this go routine can pull the value out from the channel.\n\n")
    c <- "main::Hello"
    
    // Sleep to give time goroutines to execute
    time.Sleep(time.Second)
    
    // 6. read the channel value.
    log.Printf("6. Read main:: %s \n\n", <-c)
    
    // 7. Insert a new value to the channel
    log.Println("7. Add 'main::Bye' to the channel, block until it is read.\n")
    c <- "main::Bye"
    
    // Sleep to give time goroutines to execute
    time.Sleep(time.Second)
    log.Println("9. Main stop")

}

2023/09/02 21:58:07 1. Main start
2023/09/02 21:58:07 2. Declare go routines.


2023/09/02 21:58:07 3. Add 'main::Hello' to the channel, block until it is read. Remember, 'main' goroutine will block and only other goroutines can run even though this go routine can pull the value out from the channel.


2023/09/02 21:58:07 4. Add 'Greet::John' to the channel, block until it is read. Remember, 'Greet' goroutine will block and only other goroutines can run even though this go routine can pull the value out from the channel.

2023/09/02 21:58:10 5. Read Greet2:: main::Hello

2023/09/02 21:58:11 6. Read main:: Greet::John!

2023/09/02 21:58:11 7. Add 'main::Bye' to the channel, block until it is read.

2023/09/02 21:58:11 8. Read Greet:: main::Bye !

2023/09/02 21:58:12 9. Main stop

package main

import (
        "fmt"
)

func do2(c chan int) {
        fmt.Println(<-c)
}

func do(c chan int) {
        // 4. this statement is trying to write another value "2" to the channel
        // Channel already contains "1" as the value which has not been read yet.
        // this statement will wait for "1" to get read and block the execution.
        // Scheduler will look for other goroutines that can execute.
        // However, this("do") is blocked as well as "main" is blocked too and
        // there are no other goroutines to execute.
        // Hence, will result in a "Deadlock" fatal error.
        c <- 2
        fmt.Println(<-c)
}

func main() {

        // 1. Declare a channel
        c := make(chan int)
        // 2. Declare "do" goroutine
        go do(c)
        // 3. write "1" to the channel
        // This will block and wait for program's other goroutines to read the value.
        // however, there is only "do" goroutine is defined can run at this point.
        // Scheduler, will try to run "do" goroutine.
        c <- 1
        go do2(c)

}