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Kotlin Academy · Lesson

Channel Basics: send, receive, and close

Create channels, send and receive values, and close them properly.

What Is a Channel?

A Channel is a coroutine primitive for communicating between coroutines — like a blocking queue but suspending. Think of it as a pipe: one side sends, the other receives.

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val channel = Channel<Int>()
    launch {
        for (i in 1..5) channel.send(i)
        channel.close()
    }
    for (x in channel) println(x) // 1 2 3 4 5
}

send and receive

send(value) suspends until the receiver is ready. receive() suspends until a value is available.

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val ch = Channel<String>()
    launch {
        ch.send("ping")
        println("sent")
    }
    val msg = ch.receive()
    println("received: $msg")
}

All lessons in this course

  1. Channel Basics: send, receive, and close
  2. Channel Types: Rendezvous, Buffered, Conflated, Unlimited
  3. Mutex and Semaphore for Shared State
  4. Actors and Structured State Management
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