Saluran Golang yang dipermudahkan!

TL;DR

Artikel tersebut menerangkan saluran Go, yang membolehkan komunikasi selamat antara gorouti. Ia merangkumi cara membuat, menghantar dan menerima data melalui saluran, membezakan antara jenis tidak buffer dan jenis buffer. Ia menekankan kepentingan menutup saluran untuk mengelakkan kebuntuan dan menambah baik pengurusan sumber. Akhir sekali, ia memperkenalkan penyataan pilih untuk menguruskan operasi berbilang saluran dengan cekap.

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Jadual Kandungan

1. Pengenalan kepada Saluran Go
2. Membuat Saluran
3. Menghantar Data
4. Menerima Data
5. Jenis Saluran dalam Go
   • Saluran Tidak Buffer
   • Saluran Timbal
6. Menutup Saluran
   • Mengapa Tutup Saluran?
7. Coretan Kod Tanpa Menutup Saluran
   • Keluaran dan Ralat yang Dijangka
8. Coretan Kod Dengan Menutup Saluran
   • Keluaran Jangkaan
9. Menggunakan Penyata pilihan
   • Contoh pilihan dengan Saluran
10. Soalan Lazim tentang pilihan
11. Memastikan Mesej daripada Kedua-dua Saluran Menggunakan WaitGroup
    • Contoh penggunaan WaitGroup
12. Kesimpulan

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Pengenalan kepada Saluran Go

Go, atau Golang, ialah bahasa pengaturcaraan berkuasa yang direka untuk kesederhanaan dan kecekapan. Salah satu ciri menonjolnya ialah konsep saluran, yang memudahkan komunikasi antara goroutine. Saluran membenarkan pertukaran data dan penyegerakan yang selamat, menjadikan pengaturcaraan serentak lebih mudah dan lebih terurus.

Dalam artikel ini, kami akan meneroka saluran dalam Go, memecahkan penciptaan, penghantaran data dan penerimaannya. Ini akan membantu anda memahami cara memanfaatkan saluran dengan berkesan dalam aplikasi anda.

Mencipta Saluran

Untuk membuat saluran dalam Go, anda menggunakan fungsi make. Berikut ialah coretan kod ringkas yang menunjukkan cara membuat saluran:

package main

import "fmt"

func main() {
    // Create a channel of type int
    ch := make(chan int)
    fmt.Println("Channel created:", ch)
}

Dalam contoh ini, kami mencipta saluran ch yang boleh menghantar dan menerima integer. Saluran tidak ditimbal secara lalai, bermakna ia akan menyekat sehingga kedua-dua pengirim dan penerima bersedia.

Apabila anda menjalankan kod Go yang disediakan, output akan kelihatan seperti ini:

Channel created: 0xc000102060

Penjelasan

1. Penciptaan Saluran:

   • Barisan ch := make(chan int) mencipta saluran baharu jenis int. Saluran ini boleh digunakan untuk menghantar dan menerima nilai integer.

2. Alamat Saluran:

   • Output 0xc000102060 ialah alamat memori saluran. Dalam Go, apabila anda mencetak saluran, ia memaparkan perwakilan dalamannya, yang termasuk alamatnya dalam ingatan.
   • Alamat ini menunjukkan tempat saluran disimpan dalam ingatan, tetapi ia tidak memberikan sebarang maklumat tentang keadaan atau kandungan saluran.

Menghantar Data

Setelah saluran dibuat, anda boleh menghantar data ke dalamnya menggunakan operator <-. Begini cara anda boleh menghantar data ke saluran:

go func() {
    ch <- 42 // Sending the value 42 to the channel
}()

Dalam coretan ini, kami memulakan goroutine baharu yang menghantar nilai integer 42 ke saluran ch. Operasi tak segerak ini membenarkan atur cara utama untuk terus melaksanakan semasa nilai dihantar.

Menerima Data

Untuk menerima data daripada saluran, anda juga menggunakan operator <-. Begini cara membaca dari saluran:

value := <-ch // Receiving data from the channel
fmt.Println("Received value:", value)

Dalam contoh ini, kita membaca dari saluran ch dan menyimpan nilai yang diterima dalam nilai pembolehubah. Atur cara akan menyekat pada baris ini sehingga nilai tersedia untuk dibaca.

Jenis Saluran dalam Go

Dalam Go, saluran boleh dikategorikan terutamanya kepada dua jenis: saluran tidak buffer dan saluran buffer. Memahami jenis ini adalah penting untuk pengaturcaraan serentak yang berkesan.

1. Saluran Tidak Dibuffer

Saluran tanpa buffer ialah jenis yang paling mudah. Ia tidak mempunyai sebarang kapasiti untuk menyimpan data; ia memerlukan kedua-dua penghantar dan penerima bersedia pada masa yang sama.

Ciri-ciri:

• Tingkah Laku Menyekat: Sekat operasi menghantar dan menerima sehingga kedua-dua pihak bersedia. Ini memastikan penyegerakan antara goroutine.
• Kes Penggunaan: Terbaik untuk senario yang anda inginkan penyegerakan yang ketat atau apabila komunikasi jarang dilakukan.

Contoh:

ch := make(chan int) // Unbuffered channel
go func() {
    ch <- 1 // Sends data; blocks until received
}()
value := <-ch // Receives data; blocks until sent
fmt.Println("Received:", value)

2. Saluran Penampan

Saluran buffer membolehkan anda menentukan kapasiti, bermakna ia boleh menyimpan bilangan nilai yang terhad sebelum menyekat penghantaran.

Characteristics:

• Non-blocking Sends: A send operation only blocks when the buffer is full. This allows for greater flexibility and can improve performance in certain scenarios.
• Use Case: Useful when you want to decouple the sender and receiver, allowing the sender to continue executing until the buffer is filled.

Example:

ch := make(chan int, 2) // Buffered channel with capacity of 2
ch <- 1 // Does not block
ch <- 2 // Does not block
// ch <- 3 // Would block since the buffer is full
fmt.Println("Values sent to buffered channel.")

What is Closing a Channel?

In Go, closing a channel is an operation that signals that no more values will be sent on that channel. This is done using the close(channel) function. Once a channel is closed, it cannot be reopened or sent to again.

Why Do We Need to Close Channels?

1. Signal Completion: Closing a channel indicates to the receiving goroutine that no more values will be sent. This allows the receiver to know when to stop waiting for new messages.

2. Preventing Deadlocks: If a goroutine is reading from a channel that is never closed, it can lead to deadlocks where the program hangs indefinitely, waiting for more data that will never arrive.

3. Resource Management: Closing channels helps in managing resources effectively, as it allows the garbage collector to reclaim memory associated with the channel once it is no longer in use.

4. Iteration Control: When using a for range loop to read from a channel, closing the channel provides a clean way to exit the loop once all messages have been processed.

In this section, we will explore a Go code snippet that demonstrates the use of unbuffered channels. We will analyze the behavior of the code with and without closing the channel, as well as the implications of each approach.

Code Snippet Without Closing the Channel

Here’s the original code snippet without the close statement:

package main

import (
    "fmt"
)

func main() {
    messages := make(chan string)

    go func() {
        messages <- "Message 1"
        messages <- "Message 2"
        messages <- "Message 3"
        // close(messages) // This line is removed
    }()

    for msg := range messages {
        fmt.Println(msg)
    }
}

Expected Output and Error

fatal error: all goroutines are asleep - deadlock!

When you run this code, it will compile and execute, but it will hang indefinitely without producing the expected output. The reason is that the for msg := range messages loop continues to wait for more messages, and since the channel is never closed, the loop has no way of knowing when to terminate. This results in a deadlock situation, causing the program to hang.

Code Snippet With Closing the Channel

Now, let’s add the close statement back into the code:

package main

import (
    "fmt"
)

func main() {
    messages := make(chan string)

    go func() {
        messages <- "Message 1"
        messages <- "Message 2"
        messages <- "Message 3"
        close(messages) // Close the channel when done
    }()

    for msg := range messages {
        fmt.Println(msg)
    }
}

Expected Output

With the close statement included, the output of this code will be:

Message 1
Message 2
Message 3

Explanation of Closure Behavior

In this version of the code:

• The close(messages) statement signals that no more messages will be sent on the messages channel.
• The for msg := range messages loop can now terminate gracefully once all messages have been received.
• Closing the channel allows the range loop to exit after processing all messages, preventing any deadlock situation.

Again, what if you don't close the channel?

Let's imagine a scenario where channels in Go are like people in a conversation.

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Scene: A Coffee Shop

Characters:

• Alice: Always eager to share ideas.
• Bob: Takes a long time to respond.

Conversation:

Alice: "Hey Bob, did you hear about the new project? We need to brainstorm!"

Bob sips his coffee, staring blankly. The conversation is paused.

Alice: "Hello? Are you there?"

Bob looks up, still processing.

Bob: "Oh, sorry! I was... uh... thinking."

Minutes pass. Alice starts to wonder if Bob is even still in the chat.

Alice: "Should I keep talking or just wait for a signal?"

Bob finally responds, but it’s completely off-topic.

Bob: "Did you know that sloths can hold their breath longer than dolphins?"

Alice facepalms.

Alice: "Great, but what about the project?"

Bob shrugs, lost in thought again. The coffee shop becomes awkwardly silent.

Alice: "Is this conversation ever going to close, or will I just be here forever?"

Bob, now fascinated by the barista, mutters something about coffee beans.

Alice: "This is like a Go channel that never gets closed! I feel like I’m stuck in an infinite loop!"

Bob finally looks back, grinning.

Bob: "So... about those sloths?"

---

Moral of the Story: Sometimes, when channels (or conversations) don’t close, you end up with endless topics and no resolution—just like a chat that drags on forever without a conclusion!

Go Channels and the select Statement

Go's concurrency model is built around goroutines and channels, which facilitate communication between concurrent processes. The select statement is vital for managing multiple channel operations effectively.

Using select with Channels

Here's an example of using select with channels:

package main

import (
    "fmt"
    "time"
)

func main() {
    ch1 := make(chan string)
    ch2 := make(chan string)

    go func() {
        time.Sleep(1 * time.Second)
        ch1 <- "Result from channel 1"
    }()

    go func() {
        time.Sleep(2 * time.Second)
        ch2 <- "Result from channel 2"
    }()

    select {
    case msg1 := <-ch1:
        fmt.Println(msg1)
    case msg2 := <-ch2:
        fmt.Println(msg2)
    }
}

Output with select:

Result from channel 1

Why Does It Print Only One Output?

In Go, the select statement is a powerful construct used for handling multiple channel operations. When working with channels, you might wonder why a program prints only one output when multiple channels are involved. Let’s explore this concept through a simple example.

Scenario Overview

Consider the program that involves two channels: ch1 and ch2. Each channel receives a message after a delay, but only one message is printed at the end. You might ask, "Why does it only print one output?"

Timing and Concurrency

1. Channel Initialization: Both ch1 and ch2 are created to handle string messages.

2. Goroutines:

   • A goroutine sends a message to ch1 after a 1-second delay.
   • Another goroutine sends a message to ch2 after a 2-second delay.

3. Select Statement: The select statement listens for messages from both channels. It blocks until one of the channels is ready to send a message.

Execution Flow

• When the program runs, it waits for either ch1 or ch2 to send a message.
• After 1 second, ch1 is ready, allowing the select statement to execute the case for ch1.
• Importantly, select can only execute one case at a time. Once a case is selected, it exits the select block.

FAQ on select

Q: Is it possible to wait for all channels in select to print all outputs?

A: No, the select statement is designed to handle one case at a time. To wait for multiple channels and print all outputs, you would need to use a loop or wait group.

Q: What happens if both channels are ready at the same time?

A: If both channels are ready simultaneously, Go will choose one at random to process, so the output may vary between executions.

Q: Can I handle timeouts with select?

A: Yes, you can include a timeout case in the select statement, allowing you to specify a duration to wait for a message.

Q: How can I ensure I receive messages from both channels?

A: To receive messages from both channels, consider using a loop with a select statement inside it, or use a sync.WaitGroup to wait for multiple goroutines to complete their tasks.

Ensuring Messages from Both Channels Using WaitGroup in Go

To ensure you receive messages from both channels in Go, you can use a sync.WaitGroup. This allows you to wait for multiple goroutines to complete before proceeding.

Here’s an example:

package main

import (
    "fmt"
    "sync"
    "time"
)

func main() {
    ch1 := make(chan string)
    ch2 := make(chan string)
    var wg sync.WaitGroup

    // Start goroutine for channel 1
    wg.Add(1)
    go func() {
        defer wg.Done()
        time.Sleep(1 * time.Second)
        ch1 <- "Result from channel 1"
    }()

    // Start goroutine for channel 2
    wg.Add(1)
    go func() {
        defer wg.Done()
        time.Sleep(2 * time.Second)
        ch2 <- "Result from channel 2"
    }()

    // Wait for both goroutines to finish
    go func() {
        wg.Wait()
        close(ch1)
        close(ch2)
    }()

    // Collect results from both channels
    results := []string{}
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-ch1:
            results = append(results, msg1)
        case msg2 := <-ch2:
            results = append(results, msg2)
        }
    }

    // Print all results
    for _, result := range results {
        fmt.Println(result)
    }
}

Output

Result from channel 1
Result from channel 2

Explanation

1. Channels and WaitGroup: Two channels, ch1 and ch2, are created. A sync.WaitGroup is used to wait for both goroutines to finish.

2. Goroutines: Each goroutine sends a message to its channel after a delay. The wg.Done() is called to signal completion.

3. Closing Channels: After all goroutines are done, the channels are closed to prevent any further sends.

4. Collecting Results: A loop with a select statement is used to receive messages from both channels until both messages are collected.

5. Final Output: The collected messages are printed.

This method ensures that you wait for both channels to send their messages before proceeding.

If you're interested in learning more about using sync.WaitGroup in Go, check out this article on concurrency: Golang Concurrency: A Fun and Fast Ride.

Real world example

Let's compare the two versions of a program in terms of their structure, execution, and timing.

Sequential Execution Version

This version processes the jobs sequentially, one after the other.

package main

import (
    "fmt"
    "time"
)

func worker(id int, job int) string {
    time.Sleep(time.Second) // Simulate work
    return fmt.Sprintf("Worker %d completed job %d", id, job)
}

func main() {
    start := time.Now()
    results := make([]string, 5)

    for j := 1; j <= 5; j++ {
        results[j-1] = worker(1, j) // Call the worker function directly
    }

    for _, result := range results {
        fmt.Println(result)
    }

    duration := time.Since(start)
    fmt.Printf("It took %s to execute!", duration)
}

Output:

Worker 1 completed job 1
Worker 1 completed job 2
Worker 1 completed job 3
Worker 1 completed job 4
Worker 1 completed job 5
It took 5.048703s to execute!

Concurrent Execution Version

This version processes the jobs concurrently using goroutines and channels.

package main

import (
    "fmt"
    "time"
)

func worker(id int, jobs <-chan int, results chan<- string) {
    for job := range jobs {
        time.Sleep(time.Second) // Simulate work
        results <- fmt.Sprintf("Worker %d completed job %d", id, job)
    }
}

func main() {
    start := time.Now()
    jobs := make(chan int, 5)
    results := make(chan string)

    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }

    for j := 1; j <= 5; j++ {
        jobs <- j
    }
    close(jobs)

    for a := 1; a <= 5; a++ {
        fmt.Println(<-results)
    }

    duration := time.Since(start)
    fmt.Printf("It took %s to execute!", duration)
}

Output:

Worker 1 completed job 1
Worker 2 completed job 2
Worker 3 completed job 3
Worker 1 completed job 4
Worker 2 completed job 5
It took 2.0227664s to execute!

Comparison

Structure:

• Versi Berjujukan: Memanggil fungsi pekerja terus dalam gelung. Tiada kesesuaian.
• Versi Serentak: Menggunakan gorout untuk menjalankan berbilang fungsi pekerja secara serentak dan saluran untuk pengagihan kerja dan pengumpulan hasil.

Pelaksanaan:

• Versi Berjujukan: Setiap kerja diproses satu demi satu, mengambil masa 1 saat bagi setiap kerja, membawa kepada jumlah masa pelaksanaan kira-kira sama dengan bilangan kerja (5 saat untuk 5 kerja).
• Versi Serentak: Berbilang pekerja (3 dalam kes ini) memproses kerja secara serentak, mengurangkan jumlah masa pelaksanaan dengan ketara. Pekerjaan diedarkan di kalangan pekerja dan keputusan dikumpulkan melalui saluran.

Masa:

• Versi Berjujukan: Mengambil kira-kira 5.048703 saat.
• Versi Serentak: Mengambil kira-kira 2.0227664 saat.

Versi serentak jauh lebih pantas kerana ia memanfaatkan pelaksanaan selari, membolehkan berbilang kerja diproses secara serentak. Ini mengurangkan jumlah masa pelaksanaan kepada sekitar masa yang diperlukan untuk menyelesaikan kerja terpanjang, dibahagikan dengan bilangan pekerja, dan bukannya menjumlahkan masa untuk setiap kerja seperti dalam versi berurutan.

Rujukan Dokumentasi Rasmi

1. Go Documentation - Goroutines
   
   Goroutines

2. Go Documentation - Saluran
   
   Saluran

3. Blog Go - Concurrency in Go
   
   Concurrency dalam Go

4. Go Documentation - Penyata pilihan
   
   Pilih Pernyataan

5. Go Tour - Saluran
   
   Lawatan Pergi: Saluran

Kesimpulan

Ringkasnya, artikel itu memberikan gambaran keseluruhan saluran yang jelas dan ringkas dalam Go, menekankan peranannya dalam memudahkan komunikasi selamat antara goroutin. Dengan menerangkan konsep saluran tidak buffer dan buffer, artikel itu menyerlahkan gelagat berbeza dan kes penggunaan yang sesuai. Selain itu, ia menekankan kepentingan menutup saluran untuk mengelakkan kebuntuan dan memastikan pengurusan sumber yang cekap. Dengan contoh kod praktikal dan analogi yang boleh dikaitkan, artikel itu melengkapkan pembaca dengan pemahaman asas tentang cara menggunakan saluran secara berkesan dalam aplikasi Go mereka, membuka jalan untuk pengaturcaraan serentak yang lebih mantap.

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