[Daemon] Change default Kotlin daemon JVM options

Now, the Kotlin daemon enables parallel GC and uses code cache flushing by default. Also, the default reserved code cache size is adjusted.

^KT-64283 Verification Pending

compiler/daemon/daemon-client/src/main/kotlin/KotlinCompilerClient.kt

@@ -470,11 +470,18 @@ object KotlinCompilerClient {
             if (javaVersion != null && javaVersion >= 16)
                 listOf("--add-exports", "java.base/sun.nio.ch=ALL-UNNAMED")
             else emptyList()
+        val jvmArguments = daemonJVMOptions.mappers.flatMap { it.toArgs("-") }
+        val additionalOptimizationOptions = listOfNotNull(
+            "-XX:+UseCodeCacheFlushing",
+            // enable parallel gc only if it's not explicitly disabled and no other GC is selected
+            "-XX:+UseParallelGC".takeIf { jvmArguments.none { it == "-XX:-UseParallelGC" || (it.startsWith("-XX:+Use") && it.endsWith("GC")) } },
+        )
         val args = listOf(
             javaExecutable.absolutePath, "-cp", compilerId.compilerClasspath.joinToString(File.pathSeparator)
         ) +
                 platformSpecificOptions +
-                daemonJVMOptions.mappers.flatMap { it.toArgs("-") } +
+                jvmArguments +
+                additionalOptimizationOptions +
                 javaIllegalAccessWorkaround +
                 COMPILER_DAEMON_CLASS_FQN +
                 daemonOptions.mappers.flatMap { it.toArgs(COMPILE_DAEMON_CMDLINE_OPTIONS_PREFIX) } +

compiler/daemon/daemon-common/src/org/jetbrains/kotlin/daemon/common/DaemonParams.kt

@@ -181,7 +181,7 @@ fun Iterable<String>.filterExtractProps(vararg groups: OptionsGroup, prefix: Str
 data class DaemonJVMOptions(
         var maxMemory: String = "",
         var maxMetaspaceSize: String = "",
-        var reservedCodeCacheSize: String = "",
+        var reservedCodeCacheSize: String = "320m",
         var jvmParams: MutableCollection<String> = arrayListOf()
 ) : OptionsGroup {
     override val mappers: List<PropMapper<*, *, *>>

compiler/daemon/daemon-tests/test/org/jetbrains/kotlin/daemon/BaseDaemonSessionTest.kt

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.daemon
 
 import org.jetbrains.kotlin.cli.common.CompilerSystemProperties
 import org.jetbrains.kotlin.daemon.client.CompileServiceSession
+import org.jetbrains.kotlin.daemon.client.DaemonReportMessage
 import org.jetbrains.kotlin.daemon.client.DaemonReportingTargets
 import org.jetbrains.kotlin.daemon.client.KotlinCompilerClient
 import org.jetbrains.kotlin.daemon.common.CompileService
@@ -74,6 +75,7 @@ abstract class BaseDaemonSessionTest {
         jvmOptions: DaemonJVMOptions = defaultDaemonJvmOptions,
         daemonOptions: DaemonOptions = defaultDaemonOptions,
         logFile: File? = null,
+        daemonMessagesCollector: MutableCollection<DaemonReportMessage>? = null,
     ): CompileServiceSession {
         val actualJvmOptions = logFile?.let { jvmOptions.withLogFile(it) } ?: jvmOptions
         println("Leasing a session with $actualJvmOptions and $daemonOptions")
@@ -85,7 +87,7 @@ abstract class BaseDaemonSessionTest {
             clientMarkerFile,
             actualJvmOptions,
             daemonOptions,
-            DaemonReportingTargets(out = System.err),
+            DaemonReportingTargets(messages = daemonMessagesCollector, out = System.err),
             autostart = true,
             leaseSession = true,
             sessionAliveFlagFile = sessionMarkerFile,

compiler/daemon/daemon-tests/test/org/jetbrains/kotlin/daemon/JvmArgumentsModificationTest.kt

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2010-2024 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.daemon
+
+import org.jetbrains.kotlin.daemon.client.DaemonReportMessage
+import org.jetbrains.kotlin.daemon.common.filterExtractProps
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import kotlin.test.assertContains
+import kotlin.test.assertEquals
+
+class JvmArgumentsModificationTest : BaseDaemonSessionTest() {
+    @DisplayName("Default jvm arguments contain expected gc and code cache options")
+    @Test
+    fun testDefaultGcArguments() {
+        val commandParts = leaseSessionAndExtractCommand()
+        val xmxArgument = commandParts.single { it.startsWith("-Xmx") }
+        val codeCacheSizeArgument = commandParts.single { it.startsWith("-XX:ReservedCodeCacheSize") }
+        val useGcArgument = commandParts.single { it.startsWith("-XX:+Use") && it.endsWith("GC") }
+        assertEquals("-Xmx384m", xmxArgument)
+        assertEquals("-XX:ReservedCodeCacheSize=320m", codeCacheSizeArgument)
+        assertEquals("-XX:+UseParallelGC", useGcArgument)
+        assertContains(commandParts, "-XX:+UseCodeCacheFlushing")
+    }
+
+    @DisplayName("Gc and code cache options may be properly overridden")
+    @Test
+    fun testModification() {
+        val commandParts = leaseSessionAndExtractCommand(listOf("Xmx400m", "XX:ReservedCodeCacheSize=280m", "XX:+UseG1GC"))
+        val xmxArgument = commandParts.single { it.startsWith("-Xmx") }
+        val codeCacheSizeArgument = commandParts.single { it.startsWith("-XX:ReservedCodeCacheSize") }
+        val useGcArgument = commandParts.single { it.startsWith("-XX:+Use") && it.endsWith("GC") }
+        assertEquals("-Xmx400m", xmxArgument)
+        assertEquals("-XX:ReservedCodeCacheSize=280m", codeCacheSizeArgument)
+        assertEquals("-XX:+UseG1GC", useGcArgument)
+        assertContains(commandParts, "-XX:+UseCodeCacheFlushing")
+    }
+
+    @DisplayName("-XX:-UseParallelGC is handled")
+    @Test
+    fun testDisablingParallelGC() {
+        val commandParts = leaseSessionAndExtractCommand(listOf("XX:-UseParallelGC"))
+        assert(commandParts.none { it.startsWith("-XX:+Use") && it.endsWith("GC") }) {
+            "Expected no explicitly enabled garbage collector via JVM arguments: $commandParts"
+        }
+    }
+
+    private fun leaseSessionAndExtractCommand(additionalJvmArguments: List<String> = emptyList()): List<String> {
+        val daemonMessagesCollector = mutableListOf<DaemonReportMessage>()
+        leaseSession(
+            daemonMessagesCollector = daemonMessagesCollector,
+            jvmOptions = defaultDaemonJvmOptions.copy().apply {
+                jvmParams.addAll(
+                    additionalJvmArguments.filterExtractProps(mappers, "", restMapper)
+                )
+            }
+        )
+        val prefix = "starting the daemon as: "
+        return daemonMessagesCollector.single { it.message.startsWith(prefix) }.message.substring(prefix.length).split(" ")
+    }
+}