Use toolchains for java tasks

integration/src/test/kotlin/kotlinx/benchmark/integration/GradleTest.kt

@@ -26,7 +26,10 @@ abstract class GradleTest {
         val builder = ProjectBuilder().apply(build)
         templates.resolve(name).copyRecursively(rootProjectDir)
         file("build.gradle").modify(builder::build)
-        file("settings.gradle").writeText("") // empty settings file
+        val settingsFile = file("settings.gradle")
+        if (!settingsFile.exists()) {
+            file("settings.gradle").writeText("") // empty settings file
+        }
         return Runner(rootProjectDir, print, gradleVersion)
     }
 }

integration/src/test/kotlin/kotlinx/benchmark/integration/JvmToolchainsTest.kt

@@ -0,0 +1,12 @@
+package kotlinx.benchmark.integration
+
+import org.junit.Test
+
+class JvmToolchainsTest : GradleTest() {
+    @Test
+    fun testJvmToolchainSetup() {
+        val runner = project("kmp-with-toolchain", true, GradleTestVersion.v8_0) {
+        }
+        runner.run("jvmBenchmark")
+    }
+}

integration/src/test/resources/templates/kmp-with-toolchain/build.gradle

@@ -0,0 +1,25 @@
+kotlin {
+    jvm {
+        compilations.create('benchmark') { associateWith(compilations.main) }
+        jvmToolchain(21)
+    }
+
+    sourceSets {
+        commonMain {
+            dependencies {
+                implementation("org.jetbrains.kotlinx:kotlinx-benchmark-runtime:0.5.0-SNAPSHOT")
+            }
+        }
+        jvmMain {
+        }
+        jvmBenchmark {
+            dependsOn(jvmMain)
+        }
+    }
+}
+
+benchmark {
+    targets {
+        register("jvm")
+    }
+}

integration/src/test/resources/templates/kmp-with-toolchain/gradle.properties

@@ -0,0 +1 @@
+org.gradle.jvmargs=-Xmx2g -XX:MaxPermSize=2048m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8

integration/src/test/resources/templates/kmp-with-toolchain/settings.gradle

@@ -0,0 +1,3 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "0.8.0"
+}

integration/src/test/resources/templates/kmp-with-toolchain/src/commonMain/kotlin/CommonBenchmark.kt

@@ -0,0 +1,15 @@
+package test
+
+import kotlinx.benchmark.*
+import kotlin.math.*
+
+// Don't really need to measure anything here, just check that the benchmark works
+@State(Scope.Benchmark)
+@Warmup(iterations = 0)
+@Measurement(iterations = 1, time = 100, timeUnit = BenchmarkTimeUnit.MILLISECONDS)
+@OutputTimeUnit(BenchmarkTimeUnit.MILLISECONDS)
+@BenchmarkMode(Mode.Throughput)
+open class CommonBenchmark {
+    @Benchmark
+    open fun mathBenchmark() = 3.14
+}

plugin/main/src/kotlinx/benchmark/gradle/JmhBytecodeGeneratorTask.kt

@@ -2,6 +2,7 @@ package kotlinx.benchmark.gradle
 
 import org.gradle.api.*
 import org.gradle.api.file.*
+import org.gradle.api.provider.Provider
 import org.gradle.api.tasks.*
 import org.gradle.workers.*
 import java.io.*
@@ -28,11 +29,18 @@ open class JmhBytecodeGeneratorTask
     @InputFiles
     @PathSensitive(PathSensitivity.RELATIVE)
     lateinit var runtimeClasspath: FileCollection
+
+    @Optional
+    @Input
+    var executableProvider: Provider<String> = project.provider { null }
 
     @TaskAction
     fun generate() {
         val workQueue = workerExecutor.processIsolation { workerSpec ->
             workerSpec.classpath.setFrom(runtimeClasspath.files)
+            if (executableProvider.isPresent) {
+                workerSpec.forkOptions.executable = executableProvider.get()
+            }
         }
         workQueue.submit(JmhBytecodeGeneratorWorker::class.java) { workParameters ->
             workParameters.inputClasses.setFrom(inputClassesDirs.files)

plugin/main/src/kotlinx/benchmark/gradle/JvmTasks.kt

@@ -20,6 +20,7 @@ fun Project.createJvmBenchmarkCompileTask(target: JvmBenchmarkTarget, compileCla
         classpath = compileClasspath
         source = fileTree("$benchmarkBuildDir/sources")
         destinationDirectory.set(file("$benchmarkBuildDir/classes"))
+        javaCompiler.set(javaCompilerProvider())
     }
 
     task<Jar>(
@@ -90,6 +91,9 @@ fun Project.createJvmBenchmarkGenerateSourceTask(
         inputClassesDirs = compilationOutput
         outputResourcesDir = file("$benchmarkBuildDir/resources")
         outputSourcesDir = file("$benchmarkBuildDir/sources")
+        executableProvider = javaLauncherProvider().map {
+            it.executablePath.asFile.absolutePath
+        }
     }
 }
 
@@ -123,5 +127,6 @@ fun Project.createJvmBenchmarkExecTask(
 
         val reportFile = setupReporting(target, config)
         args(writeParameters(target.name, reportFile, traceFormat(), config))
+        javaLauncher.set(javaLauncherProvider())
     }
 }

plugin/main/src/kotlinx/benchmark/gradle/Utils.kt

@@ -5,7 +5,12 @@ import org.gradle.api.Action
 import org.gradle.api.Project
 import org.gradle.api.Task
 import org.gradle.api.invocation.Gradle
+import org.gradle.api.plugins.JavaPluginExtension
+import org.gradle.api.provider.Provider
 import org.gradle.api.tasks.TaskProvider
+import org.gradle.jvm.toolchain.JavaCompiler
+import org.gradle.jvm.toolchain.JavaLauncher
+import org.gradle.jvm.toolchain.JavaToolchainService
 import java.io.File
 import java.nio.file.Path
 import java.time.LocalDateTime
@@ -261,4 +266,16 @@ internal fun Project.getSystemProperty(key: String): String? {
     } else {
         System.getProperty(key)
     }
-}
+}
+
+fun Project.javaCompilerProvider(): Provider<JavaCompiler> = provider {
+    val toolchainService = extensions.findByType(JavaToolchainService::class.java) ?: return@provider null
+    val javaExtension = extensions.findByType(JavaPluginExtension::class.java) ?: return@provider null
+    toolchainService.compilerFor(javaExtension.toolchain).orNull
+}
+
+fun Project.javaLauncherProvider(): Provider<JavaLauncher> = provider {
+    val toolchainService = extensions.findByType(JavaToolchainService::class.java) ?: return@provider null
+    val javaExtension = extensions.findByType(JavaPluginExtension::class.java) ?: return@provider null
+    toolchainService.launcherFor(javaExtension.toolchain).orNull
+}