8319932: [JVMCI] class unloading related tests can fail on libgraal

Backport-of: 7d53559d2f8f3c27f4d764f081fb031f7660c50b

Author: GoeLin

test/hotspot/jtreg/runtime/ClassInitErrors/InitExceptionUnloadTest.java

@@ -37,6 +37,8 @@
 
 import java.io.ByteArrayOutputStream;
 import java.io.PrintStream;
+import java.util.Set;
+import java.util.List;
 
 import jdk.test.whitebox.WhiteBox;
 import jdk.test.lib.classloader.ClassUnloadCommon;
@@ -122,10 +124,9 @@ static void test() throws Throwable {
             }
         }
         cl = null;
-        ClassUnloadCommon.triggerUnloading();  // should unload these classes
-        for (String className : classNames) {
-          ClassUnloadCommon.failIf(wb.isClassAlive(className), "should be unloaded");
-        }
+
+        Set<String> aliveClasses = ClassUnloadCommon.triggerUnloading(List.of(classNames));
+        ClassUnloadCommon.failIf(!aliveClasses.isEmpty(), "should be unloaded: " + aliveClasses);
     }
     public static void main(java.lang.String[] unused) throws Throwable {
         test();

test/lib/jdk/test/lib/classloader/ClassUnloadCommon.java

@@ -39,6 +39,9 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
 import java.util.stream.Stream;
 
 public class ClassUnloadCommon {
@@ -71,6 +74,41 @@ public static void triggerUnloading() {
         wb.fullGC();  // will do class unloading
     }
 
+    /**
+     * Calls triggerUnloading() in a retry loop for 2 seconds or until WhiteBox.isClassAlive
+     * determines that no classes named in classNames are alive.
+     *
+     * This variant of triggerUnloading() accommodates the inherent raciness
+     * of class unloading. For example, it's possible for a JIT compilation to hold
+     * strong roots to types (e.g. in virtual call or instanceof profiles) that
+     * are not released or converted to weak roots until the compilation completes.
+     *
+     * @param classNames the set of classes that are expected to be unloaded
+     * @return the set of classes that have not been unloaded after exiting the retry loop
+     */
+    public static Set<String> triggerUnloading(List<String> classNames) {
+        WhiteBox wb = WhiteBox.getWhiteBox();
+        Set<String> aliveClasses = new HashSet<>(classNames);
+        int attempt = 0;
+        while (!aliveClasses.isEmpty() && attempt < 20) {
+            ClassUnloadCommon.triggerUnloading();
+            for (String className : classNames) {
+                if (aliveClasses.contains(className)) {
+                    if (wb.isClassAlive(className)) {
+                        try {
+                            Thread.sleep(100);
+                        } catch (InterruptedException ex) {
+                        }
+                    } else {
+                        aliveClasses.remove(className);
+                    }
+                }
+            }
+            attempt++;
+        }
+        return aliveClasses;
+    }
+
     /**
      * Creates a class loader that loads classes from {@code ${test.class.path}}
      * before delegating to the system class loader.