How to create a read-only channel in golang

Channel in Golang is a special data type used to communicate between multiple goroutines. Chanel supports two operations: sending and receiving. The send operation sends a value to the channel, and the receive operation receives a value from the channel.

By default, channel can be read and written, which means that any goroutine can send and receive operations through the channel. However, in some cases, we need to restrict certain goroutines to only receive but not send, or to only send but not receive. At this time, the read-only channel can come in handy.

Read-only channels can be read by multiple goroutines at the same time, but cannot be written to. It can be used to implement read-only shared data structures to avoid concurrency issues. In the Go language, there is a difference between read-only channels and ordinary channels. Read-only channels and write-only channels are of different types.

How to create a read-only channel

A read-only channel can be created by adding the <- symbol in front of the ordinary channel type. For example, if we have a normal channel:

ch := make(chan int)

To convert it to a read-only channel, we can write it as follows:

roCh := <-chan int(ch)

Here, we create a read-only channel , its type is <-chan int, which is a read-only int type channel. Note that this read-only channel is of a different type than the original ordinary channel, although they are both used to transmit int type data.

Read-only channel implementation

For a read-only channel, we can only read data from it and cannot write data into it. Therefore, when using a read-only channel, we need to pay attention to two points:

1. Cannot perform send operations on a read-only channel, otherwise it will cause compilation errors.
2. If we convert a writable channel to a read-only channel, then the read-only channel and the writable channel will point to the same block of data, so send operations can be performed on the writable channel, and Receive via a read-only channel.

The following is a simple example that demonstrates the use of a read-only channel:

package main

import "fmt"

func main() {
    ch := make(chan int, 10)
    for i := 0; i < 10; i++ {
        ch <- i
    }

    // 只读channel
    roCh := (<-chan int)(ch)

    // 从只读channel中读取数据
    for x := range roCh {
        fmt.Println("value:", x)
    }
}

In this example, we first create a writable channel and add it to it 10 integers were written. Next, we convert this writable channel to a read-only channel and read data from it through this read-only channel. Eventually, the program will output all data written to the channel.

Read-only channels are used for shared data structures

The most common use of read-only channels is for shared data structures to avoid concurrent access problems. For example, we can use a read-only channel to implement a thread-safe queue that can only read data.

The following is a simple example that demonstrates how to use a read-only channel to implement a thread-safe queue:

package main

import "fmt"

type Queue struct {
    roCh <-chan interface{}
}

func NewQueue(size int) *Queue {
    ch := make(chan interface{}, size)
    return &Queue{
        roCh: (<-chan interface{})(ch),
    }
}

func (q *Queue) Push(v interface{}) {
    ch := q.roCh.(chan<- interface{})
    ch <- v
}

func (q *Queue) Pop() interface{} {
    return <-q.roCh
}

func main() {
    q := NewQueue(10)
    for i := 0; i < 10; i++ {
        q.Push(i)
    }

    for i := 0; i < 10; i++ {
        fmt.Println(q.Pop())
    }
}

In this example, we implement a queue in which the Push method Used to add elements to the queue, the Pop method is used to pop up and return elements in the queue. Note that our queue uses a read-only channel to share data, ensuring the safety of concurrent access.

Summary

Read-only channel is a special type in Golang, which is used to restrict certain goroutines to only receive operations and not send operations. Read-only channels can be used to implement read-only shared data structures to avoid concurrency issues. Read-only channels are different types from ordinary channels and writable channels. When using a read-only channel, we need to be careful not to perform send operations on a read-only channel, otherwise it will cause compilation errors.

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