Closing Channels

This Go code demonstrates the use of a combination of channels and goroutines to synchronize the sending and receiving of messages. Let's go through it with inline comments:

package main

import "fmt"

func main() {
    // Creating a buffered channel 'jobs' with a capacity of 5
    jobs := make(chan int, 5)

    // Creating an unbuffered channel 'done' for signaling when all jobs are received
    done := make(chan bool)

    // Launching a goroutine to receive jobs from the 'jobs' channel
    go func() {
        for {
            // Attempting to receive a job from 'jobs'
            j, more := <-jobs
            if more {
                fmt.Println("received job", j)
            } else {
                // If 'more' is false, it means the 'jobs' channel is closed
                fmt.Println("received all jobs")
                // Signaling that all jobs are received by sending true to 'done'
                done <- true
                return
            }
        }
    }()

    // Sending three jobs to the 'jobs' channel
    for j := 1; j <= 3; j++ {
        jobs <- j
        fmt.Println("sent job", j)
    }

    // Closing the 'jobs' channel to indicate that no more jobs will be sent
    close(jobs)
    fmt.Println("sent all jobs")

    // Waiting for the 'done' channel to receive a signal indicating all jobs are received
    <-done

    // Attempting to receive from the closed 'jobs' channel
    _, ok := <-jobs
    fmt.Println("received more jobs:", ok)
}

Output

sent job 1
received job 1
sent job 2
received job 2
sent job 3
received job 3
sent all jobs
received all jobs
received more jobs: false

Explanation:

1. package main: Indicates that this Go file belongs to the main executable package.

2. import "fmt": Imports the "fmt" package for formatting and printing.

3. func main() { ... }: The main function, where the execution of the program begins.

4. jobs := make(chan int, 5): Creates a buffered channel named 'jobs' with a capacity of 5.

5. done := make(chan bool): Creates an unbuffered channel named 'done' for signaling when all jobs are received.

6. A goroutine is launched to receive jobs from the 'jobs' channel. It loops indefinitely, attempting to receive jobs until the 'jobs' channel is closed.

7. Inside the goroutine, more is a boolean value that indicates whether there are more values to receive from the 'jobs' channel.

8. The main goroutine sends three jobs to the 'jobs' channel and prints a message for each sent job.

9. close(jobs): Closes the 'jobs' channel to indicate that no more jobs will be sent.

10. <-done: Waits for the 'done' channel to receive a signal (true) indicating that all jobs are received.

11. _, ok := <-jobs: Attempts to receive from the closed 'jobs' channel. Since the channel is closed, ok will be false, and it prints "received more jobs: false."

In summary, this code demonstrates how to use channels and goroutines to coordinate the sending and receiving of messages, and how to signal the completion of tasks using channels. The close operation on the 'jobs' channel is used to signal that no more jobs will be sent.