Beyond Number of Cores

About

In this exame we illustrate the Dispatchers.IO re-using the same OS thread for 2 different executions.

This is illustrated in these lines of output:

[2024-06-09T04:23:29.653692Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-21/tid:41] Fetching data... task 19
[2024-06-09T04:23:29.653867Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-21/tid:41] Fetching data... task 22

Code

package gt.sandbox

import gt.sandbox.internal.output.Out
import kotlinx.coroutines.*

val out = Out.standard()

suspend fun fetchData(s: String) {
    out.println("Fetching data... $s")
    delay(1000) // This suspends the coroutine for 1 second without blocking the thread
    out.println("Data fetched $s")
}

fun main(): Unit = runBlocking {
    val availableCores = Runtime.getRuntime().availableProcessors()
    out.println("Number of available cores: $availableCores")

    for (i in 1..(availableCores* 2) + 2) {
        launch(Dispatchers.IO) {
            fetchData("task $i")
        }
    }
}

Command to reproduce:

gt.sandbox.checkout.commit 95c0ae2 \
&& cd "${GT_SANDBOX_REPO}" \
&& cmd.run.announce "./gradlew run"

Recorded output of command:

> Task :app:checkKotlinGradlePluginConfigurationErrors SKIPPED
> Task :app:processResources NO-SOURCE
> Task :app:compileKotlin
> Task :app:compileJava NO-SOURCE
> Task :app:classes UP-TO-DATE

> Task :app:run
[2024-06-09T04:23:29.630413Z][ms-elapsed-since-start:   47][tname:main/tid:1] Number of available cores: 10
[2024-06-09T04:23:29.651359Z][ms-elapsed-since-start:   59][tname:DefaultDispatcher-worker-1/tid:21] Fetching data... task 1
[2024-06-09T04:23:29.651570Z][ms-elapsed-since-start:   59][tname:DefaultDispatcher-worker-3/tid:23] Fetching data... task 2
[2024-06-09T04:23:29.651777Z][ms-elapsed-since-start:   59][tname:DefaultDispatcher-worker-5/tid:25] Fetching data... task 3
[2024-06-09T04:23:29.651815Z][ms-elapsed-since-start:   59][tname:DefaultDispatcher-worker-2/tid:22] Fetching data... task 4
[2024-06-09T04:23:29.651846Z][ms-elapsed-since-start:   59][tname:DefaultDispatcher-worker-4/tid:24] Fetching data... task 5
[2024-06-09T04:23:29.652016Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-8/tid:28] Fetching data... task 6
[2024-06-09T04:23:29.652160Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-7/tid:27] Fetching data... task 7
[2024-06-09T04:23:29.652243Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-6/tid:26] Fetching data... task 8
[2024-06-09T04:23:29.652418Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-11/tid:31] Fetching data... task 9
[2024-06-09T04:23:29.652762Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-10/tid:30] Fetching data... task 10
[2024-06-09T04:23:29.652811Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-14/tid:34] Fetching data... task 11
[2024-06-09T04:23:29.652945Z][ms-elapsed-since-start:   60][tname:DefaultDispatcher-worker-13/tid:33] Fetching data... task 12
[2024-06-09T04:23:29.653149Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-18/tid:38] Fetching data... task 13
[2024-06-09T04:23:29.653555Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-9/tid:29] Fetching data... task 15
[2024-06-09T04:23:29.653556Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-21/tid:41] Fetching data... task 14
[2024-06-09T04:23:29.653623Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-7/tid:27] Fetching data... task 16
[2024-06-09T04:23:29.653651Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-9/tid:29] Fetching data... task 17
[2024-06-09T04:23:29.653676Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-13/tid:33] Fetching data... task 18
[2024-06-09T04:23:29.653717Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-7/tid:27] Fetching data... task 20
[2024-06-09T04:23:29.653692Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-21/tid:41] Fetching data... task 19
[2024-06-09T04:23:29.653867Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-21/tid:41] Fetching data... task 22
[2024-06-09T04:23:29.653732Z][ms-elapsed-since-start:   61][tname:DefaultDispatcher-worker-9/tid:29] Fetching data... task 21
[2024-06-09T04:23:30.661370Z][ms-elapsed-since-start: 1069][tname:DefaultDispatcher-worker-17/tid:37] Data fetched task 7
[2024-06-09T04:23:30.661588Z][ms-elapsed-since-start: 1069][tname:DefaultDispatcher-worker-15/tid:35] Data fetched task 4
[2024-06-09T04:23:30.662263Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-15/tid:35] Data fetched task 8
[2024-06-09T04:23:30.661870Z][ms-elapsed-since-start: 1069][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 2
[2024-06-09T04:23:30.662439Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-15/tid:35] Data fetched task 3
[2024-06-09T04:23:30.662540Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 6
[2024-06-09T04:23:30.662606Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-15/tid:35] Data fetched task 1
[2024-06-09T04:23:30.662685Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 10
[2024-06-09T04:23:30.662824Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 11
[2024-06-09T04:23:30.662870Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-24/tid:45] Data fetched task 13
[2024-06-09T04:23:30.662972Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 15
[2024-06-09T04:23:30.663027Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-24/tid:45] Data fetched task 14
[2024-06-09T04:23:30.661376Z][ms-elapsed-since-start: 1069][tname:DefaultDispatcher-worker-18/tid:38] Data fetched task 9
[2024-06-09T04:23:30.663206Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-24/tid:45] Data fetched task 17
[2024-06-09T04:23:30.663273Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-18/tid:38] Data fetched task 18
[2024-06-09T04:23:30.663533Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-6/tid:26] Data fetched task 19
[2024-06-09T04:23:30.663124Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-19/tid:39] Data fetched task 16
[2024-06-09T04:23:30.662265Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-17/tid:37] Data fetched task 5
[2024-06-09T04:23:30.662858Z][ms-elapsed-since-start: 1070][tname:DefaultDispatcher-worker-15/tid:35] Data fetched task 12
[2024-06-09T04:23:30.663355Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-24/tid:45] Data fetched task 20
[2024-06-09T04:23:30.663540Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-18/tid:38] Data fetched task 22
[2024-06-09T04:23:30.663689Z][ms-elapsed-since-start: 1071][tname:DefaultDispatcher-worker-6/tid:26] Data fetched task 21

BUILD SUCCESSFUL in 1s
2 actionable tasks: 2 executed

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