Channel Basics

A Queue Between Coroutines

A Channel<T> is like a BlockingQueue for coroutines: one coroutine sends, another receives. Both are suspend functions, so nothing blocks a thread. Unlike a flow, a channel is hot and each value is received by exactly one receiver.

producer ──send()──► [ channel ] ──receive()──► consumer

Example

close() tells the receiver no more values will come; the for loop then ends.

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*

fun main() = runBlocking {
    val orders = Channel<String>()
    launch {
        for (dish in listOf("Pizza", "Burger", "Biryani")) {
            println("Kitchen sends $dish")
            orders.send(dish)
        }
        orders.close()
    }
    for (order in orders) {
        println("Rider picks $order")
    }
    println("No more orders")
}

Output

Kitchen sends Pizza
Kitchen sends Burger
Rider picks Pizza
Rider picks Burger
Kitchen sends Biryani
Rider picks Biryani
No more orders

Channel API

Function	Does
`send(x)`	suspends if the buffer is full
`receive()`	suspends until a value arrives; throws if closed
`trySend(x)` / `tryReceive()`	non-suspending versions, return a result object
`receiveCatching()`	like receive, but returns a closed result instead of throwing
`close()`	no more sends; remaining values can still be received
`for (x in channel)` / `consumeEach`	receive until closed