implement feedback from CR

Author: Picazsoo

modules/openapi-generator-gradle-plugin/README.adoc

@@ -446,16 +446,16 @@ file states is output.
 |`process`
 a|Controls how the code-generation work action is isolated from the Gradle daemon.
 
-`process` (default):: Runs generation in a separate forked JVM. Generator classes are fully unloaded when the worker
+`classloader` (default):: Runs generation inside the Gradle daemon JVM using a separate `ClassLoader`. Avoids the per-task JVM
+startup overhead, but generator classes accumulate in the daemon's Metaspace across tasks and builds. Suitable for
+single-module projects or local developer loops where Metaspace pressure is not a concern.
+
+`process`:: Runs generation in a separate forked JVM. Generator classes are fully unloaded when the worker
 exits, preventing Metaspace accumulation in the Gradle daemon. A small per-task JVM startup cost is incurred (~1–2 s
 amortized across parallel builds). Recommended for CI/CD and multi-project builds to avoid the
 https://docs.gradle.org/current/userguide/build_environment.html#sec:configuring_jvm_memory[metaspace exhaustion
 warning].
 
-`classloader`:: Runs generation inside the Gradle daemon JVM using a separate `ClassLoader`. Avoids the per-task JVM
-startup overhead, but generator classes accumulate in the daemon's Metaspace across tasks and builds. Suitable for
-single-module projects or local developer loops where Metaspace pressure is not a concern.
-
 |maxWorkerHeapSize
 |String / Provider<String>
 |Gradle default (~512 MiB)

modules/openapi-generator-gradle-plugin/src/main/kotlin/org/openapitools/generator/gradle/plugin/extensions/OpenApiGeneratorGenerateExtension.kt

@@ -412,14 +412,14 @@ open class OpenApiGeneratorGenerateExtension(private val project: Project) {
     /**
      * Controls how the code generation worker is isolated from the Gradle daemon.
      *
-     * - "process" (default): runs in a separate JVM. Metaspace is isolated from the daemon and freed
+     * - "classloader" (default): runs inside the Gradle daemon JVM with a separate ClassLoader. No process
+     *   startup overhead, but generator classes accumulate in daemon Metaspace. Suitable for projects
+     *   with very few generation tasks.
+     *
+     * - "process": runs in a separate JVM. Metaspace is isolated from the daemon and freed
      *   when the worker exits. Gradle reuses the worker process across tasks that share the same
      *   classpath, so the JVM startup cost is typically paid only once per parallel slot.
      *   Best for projects with many generation tasks.
-     *
-     * - "classloader": runs inside the Gradle daemon JVM with a separate ClassLoader. No process
-     *   startup overhead, but generator classes accumulate in daemon Metaspace. Suitable for projects
-     *   with very few generation tasks.
      */
     val workerIsolation = project.objects.property<String>()
 

modules/openapi-generator-gradle-plugin/src/main/kotlin/org/openapitools/generator/gradle/plugin/tasks/GenerateTask.kt

@@ -891,23 +891,14 @@ abstract class GenerateTask : DefaultTask() {
         }
 
 // Submit generation work using the configured isolation mode.
-// "process" (default): worker runs in a separate JVM; Metaspace is freed after each worker daemon
+// "classloader" (default): worker runs inside the Gradle daemon JVM with a separate ClassLoader; no startup
+//   overhead but generator classes accumulate in daemon Metaspace across all tasks.
+// "process": worker runs in a separate JVM; Metaspace is freed after each worker daemon
 //   exits, and Gradle reuses the same worker daemon across tasks that share the same classpath,
 //   so startup cost is amortized — typically paid only once per parallel slot.
-// "classloader": worker runs inside the Gradle daemon JVM with a separate ClassLoader; no startup
-//   overhead but generator classes accumulate in daemon Metaspace across all tasks.
-        val isolation = workerIsolation.getOrElse("process").lowercase()
+        val isolation = workerIsolation.getOrElse("classloader").lowercase()
         val workQueue = when (isolation) {
-            "classloader" -> {
-                logger.lifecycle(
-                    "[openApiGenerate] Worker isolation: classloader " +
-                            "(fast startup, but generator classes accumulate in Gradle daemon Metaspace - " +
-                            "consider workerIsolation = \"process\" if you hit metaspace pressure)"
-                )
-                workerExecutor.classLoaderIsolation()
-            }
-
-            else -> {
+            "process" -> {
                 val heapMsg = maxWorkerHeapSize.orNull?.let { " (maxHeapSize=$it)" } ?: ""
                 logger.lifecycle(
                     "[openApiGenerate] Worker isolation: process$heapMsg " +
@@ -918,6 +909,17 @@ abstract class GenerateTask : DefaultTask() {
                     maxWorkerHeapSize.orNull?.let { forkOptions.maxHeapSize = it }
                 }
             }
+
+            "classloader" -> {
+                logger.lifecycle(
+                    "[openApiGenerate] Worker isolation: classloader " +
+                            "(fast startup, but generator classes accumulate in Gradle daemon Metaspace - " +
+                            "consider workerIsolation = \"process\" if you hit metaspace pressure)"
+                )
+                workerExecutor.classLoaderIsolation()
+            }
+
+            else -> throw GradleException("Invalid workerIsolation mode: $isolation. Supported values are 'process' and 'classloader'.")
         }
 
         workQueue.submit(OpenApiWorkAction::class.java, object : Action<OpenApiWorkParameters> {