Review

Author: mvicsokolova

kotlinx-coroutines-core/build.gradle.kts

@@ -167,7 +167,7 @@ fun setupManifest(jar: Jar) {
     jar.manifest {
         attributes(
             mapOf(
-                "Premain-Class" to "kotlinx.coroutines.debug.internal.SafeAgentPremain",
+                "Premain-Class" to "kotlinx.coroutines.debug.internal.AgentPremain",
                 "Can-Retransform-Classes" to "true",
             )
         )

kotlinx-coroutines-core/jvm/src/debug/internal/AgentPremain.kt

@@ -15,6 +15,23 @@ import java.security.*
 @SuppressLint("all")
 @IgnoreJRERequirement // Never touched on Android
 internal object AgentPremain {
+    // This should be the first property to ensure the check happens first! Add new properties only below!
+    private val dummy = checkIfStdlibIsAvailable()
+
+    /**
+     * This check ensures that kotlin-stdlib classes are loaded by the time AgentPremain is initialized;
+     * otherwise the debug session would fail with `java.lang.NoClassDefFoundError: kotlin/Result`.
+     */
+    private fun checkIfStdlibIsAvailable() {
+        try {
+            Result.success(42)
+        } catch (t: Throwable) {
+            error("kotlinx.coroutines debug agent failed to load.\n" +
+                "Please ensure that the Kotlin standard library is present in the classpath.\n" +
+                "Alternatively, you can disable kotlinx.coroutines debug agent by removing `-javaagent=/path/kotlinx-coroutines-core.jar` from your VM arguments.\n" +
+                t.cause)
+        }
+    }
 
     private val enableCreationStackTraces = runCatching {
         System.getProperty("kotlinx.coroutines.debug.enable.creation.stack.trace")?.toBoolean()
@@ -69,25 +86,3 @@ internal object AgentPremain {
         }
     }
 }
-
-/**
- * This class is loaded if and only if kotlinx-coroutines-core was used as a javaagent argument.
- * It serves as a "safe" wrapper around [AgentPremain] that does not require any kotlin-stdlib classes to be loaded for its initialization.
- *
- * Initialization of [AgentPremain] may fail, e.g., because it started before the required kotlin-stdlib classes were loaded.
- * If `kotlinx.coroutines.apply.debug.agent` is set to `false`, the coroutine debug agent will not be applied.
- */
-@Suppress("unused")
-internal object SafeAgentPremain {
-    @JvmStatic
-    fun premain(args: String?, instrumentation: Instrumentation) {
-        try {
-            AgentPremain.premain(args, instrumentation)
-        } catch (t: Throwable) {
-            error("Something went wrong while loading kotlinx.coroutines debug agent.\n" +
-                "Please ensure that Kotlin Stdlib is present in the classpath.\n" +
-                "Alternatively, to disable coroutines debug agent you can remove `-javaagent=/path/kotlinx-coroutines-core.jar` from your VM arguments.\n" +
-                t.cause)
-        }
-    }
-}