พื้นฐาน Channel: send, receive และ close

แชนเนลคืออะไร

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 และ receive

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")
}

การปิดแชนเนล

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val ch = Channel<Int>(3)
    launch {
        repeat(3) { ch.send(it) }
        ch.close()  // signal done
    }
    for (v in ch) println(v) // 0 1 2, then loop ends
    println("Channel consumed")
}

isClosedForSend / isClosedForReceive

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val ch = Channel<Int>()
    launch {
        ch.send(1)
        ch.close()
    }
    println(ch.receive())
    println("isClosedForReceive: ${ch.isClosedForReceive}")
}

ตัวสร้าง produce

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun CoroutineScope.squares(n: Int) = produce<Int> {
    for (i in 1..n) send(i * i)
}
fun main() = runBlocking {
    val sq = squares(5)
    for (v in sq) println(v) // 1 4 9 16 25
}

ส่วนขยาย consumeEach

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val ch = produce<String> {
        send("a"); send("b"); send("c")
    }
    ch.consumeEach { println(it) }
}

tryReceive และ trySend

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val ch = Channel<Int>(1)
    val sendResult = ch.trySend(42)
    println("Sent: ${sendResult.isSuccess}")
    val recvResult = ch.tryReceive()
    println("Got: ${recvResult.getOrNull()}")
}

Fan-Out: ผู้ใช้หลายราย

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val tasks = produce { repeat(6) { send(it) } }
    repeat(3) { worker ->
        launch {
            for (task in tasks) {
                println("Worker $worker: task $task")
            }
        }
    }
}

Fan-In: ผู้ผลิตหลายราย

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun main() = runBlocking {
    val results = Channel<String>()
    repeat(3) { i ->
        launch { results.send("result-$i") }
    }
    launch {
        repeat(3) { println(results.receive()) }
        results.close()
    }
}

รูปแบบไปป์ไลน์

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
fun CoroutineScope.numbers() = produce { for (i in 1..5) send(i) }
fun CoroutineScope.doubled(input: ReceiveChannel<Int>) = produce { for (v in input) send(v * 2) }
fun main() = runBlocking {
    val nums = numbers()
    val doubled = doubled(nums)
    for (v in doubled) println(v) // 2 4 6 8 10
    coroutineContext.cancelChildren()
}

แชนเนลกับโฟลว์

import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.flow.*
// Flow (cold): each collect() re-runs the block
// Channel (hot): shared; multiple receivers share the same stream
fun main() = runBlocking { println("Flow = cold; Channel = hot") }

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