src/jdk.jdwp.agent/share/native/libjdwp/classTrack.c

*** 1,7 ****
  /*
!  * Copyright (c) 2001, 2005, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
--- 1,7 ----
  /*
!  * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
*** 59,68 ****
--- 59,104 ----
   * to a linked list of KlassNode.
   */
  static KlassNode **table;
  
  /*
+  * The JVMTI env we use to keep track of klass tags which allows us to detect class-unloads.
+  */
+ static jvmtiEnv *trackingEnv;
+ 
+ /*
+  * The current highest tag number in use by the trackingEnv.
+  *
+  * No need for synchronization since everything is done under the handlerLock.
+  */
+ static jlong currentKlassTag;
+ 
+ /*
+  * A lock to protect access to 'deletedTagBag'
+  */
+ static jrawMonitorID deletedTagLock;
+ 
+ /*
+  * A flag indicating whether classes have been unloaded.
+  *
+  * It is cleared each time classTrack_processUnloads is called.
+  */
+ jboolean hasUnloadedClasses;
+ 
+ /*
+  * The callback for when classes are freed. Only classes are called because this is registered with
+  * the trackingEnv which only tags classes.
+  */
+ static void JNICALL
+ cbTrackingObjectFree(jvmtiEnv* jvmti_env, jlong tag)
+ {
+     debugMonitorEnter(deletedTagLock);
+     hasUnloadedClasses = JNI_TRUE;
+     debugMonitorExit(deletedTagLock);
+ }
+ 
+ /*
   * Return slot in hash table to use for this class.
   */
  static jint
  hashKlass(jclass klass)
  {
*** 175,185 ****
--- 211,228 ----
  
              jint classCount;
              jclass *classes;
              jvmtiError error;
              int i;
+             jboolean hasUnloaded = JNI_FALSE;
+ 
+             debugMonitorEnter(deletedTagLock);
+             hasUnloaded = hasUnloadedClasses;
+             hasUnloadedClasses = JNI_FALSE;
+             debugMonitorExit(deletedTagLock);
  
+             if (hasUnloaded) {
                  error = allLoadedClasses(&classes, &classCount);
                  if ( error != JVMTI_ERROR_NONE ) {
                      jvmtiDeallocate(newTable);
                      EXIT_ERROR(error,"loaded classes");
                  } else {
*** 193,203 ****
  
                  /* Delete old table, install new one */
                  unloadedSignatures = deleteTable(env, table);
                  table = newTable;
              }
! 
          } END_WITH_LOCAL_REFS(env)
  
      }
  
      return unloadedSignatures;
--- 236,246 ----
  
                      /* Delete old table, install new one */
                      unloadedSignatures = deleteTable(env, table);
                      table = newTable;
                  }
!             }
          } END_WITH_LOCAL_REFS(env)
  
      }
  
      return unloadedSignatures;
*** 232,241 ****
--- 275,291 ----
      error = classSignature(klass, &(node->signature), NULL);
      if (error != JVMTI_ERROR_NONE) {
          jvmtiDeallocate(node);
          EXIT_ERROR(error,"signature");
      }
+     ++currentKlassTag;
+     error = JVMTI_FUNC_PTR(trackingEnv,SetTag)(trackingEnv, klass, currentKlassTag);
+     if (error != JVMTI_ERROR_NONE) {
+         jvmtiDeallocate(node->signature);
+         jvmtiDeallocate(node);
+         EXIT_ERROR(error,"SetTag");
+     }
      if ((node->klass = JNI_FUNC_PTR(env,NewWeakGlobalRef)(env, klass)) == NULL) {
          jvmtiDeallocate(node->signature);
          jvmtiDeallocate(node);
          EXIT_ERROR(AGENT_ERROR_NULL_POINTER,"NewWeakGlobalRef");
      }
*** 243,258 ****
--- 293,347 ----
      /* Insert the new node */
      node->next = *head;
      *head = node;
  }
  
+ static jboolean
+ setupEvents()
+ {
+     jvmtiCapabilities caps;
+     memset(&caps, 0, sizeof(caps));
+     caps.can_generate_object_free_events = 1;
+     jvmtiError error = JVMTI_FUNC_PTR(trackingEnv,AddCapabilities)(trackingEnv, &caps);
+     if (error != JVMTI_ERROR_NONE) {
+         return JNI_FALSE;
+     }
+     jvmtiEventCallbacks cb;
+     memset(&cb, 0, sizeof(cb));
+     cb.ObjectFree = cbTrackingObjectFree;
+     error = JVMTI_FUNC_PTR(trackingEnv,SetEventCallbacks)(trackingEnv, &cb, sizeof(cb));
+     if (error != JVMTI_ERROR_NONE) {
+         return JNI_FALSE;
+     }
+     error = JVMTI_FUNC_PTR(trackingEnv,SetEventNotificationMode)
+              (trackingEnv, JVMTI_ENABLE, JVMTI_EVENT_OBJECT_FREE, NULL);
+     if (error != JVMTI_ERROR_NONE) {
+         return JNI_FALSE;
+     }
+     return JNI_TRUE;
+ }
+ 
  /*
   * Called once to build the initial prepared class hash table.
   */
  void
  classTrack_initialize(JNIEnv *env)
  {
+     /* Setup the tracking env */
+     trackingEnv = getSpecialJvmti();
+     if ( trackingEnv == NULL ) {
+         EXIT_ERROR(AGENT_ERROR_INTERNAL,"Failed to allocate tag-tracking jvmtiEnv");
+     }
+     /* We want to create these before turning on the events or tagging anything. */
+     deletedTagLock = debugMonitorCreate("Deleted class tag lock");
+     hasUnloadedClasses = JNI_FALSE;
+     /* Setup the trackingEnv's ObjectFree event */
+     if (!setupEvents()) {
+         ERROR_MESSAGE(("Unable to setup class ObjectFree tracking! Class unloads will not "
+                        "be reported!"));
+     }
+     currentKlassTag = 0l;
      WITH_LOCAL_REFS(env, 1) {
  
          jint classCount;
          jclass *classes;
          jvmtiError error;