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 /*

  * Copyright (c) 2003, 2013, 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.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #include "precompiled.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "jvmtifiles/jvmtiEnv.hpp"

 #include "oops/objArrayKlass.hpp"

 #include "oops/objArrayOop.hpp"

 #include "prims/jvmtiEnvBase.hpp"

 #include "prims/jvmtiEventController.inline.hpp"

 #include "prims/jvmtiExtensions.hpp"

 #include "prims/jvmtiImpl.hpp"

 #include "prims/jvmtiManageCapabilities.hpp"

 #include "prims/jvmtiTagMap.hpp"

 #include "prims/jvmtiThreadState.inline.hpp"

 #include "runtime/biasedLocking.hpp"

 #include "runtime/deoptimization.hpp"

 #include "runtime/interfaceSupport.hpp"

 #include "runtime/jfieldIDWorkaround.hpp"

 #include "runtime/objectMonitor.hpp"

 #include "runtime/objectMonitor.inline.hpp"

 #include "runtime/signature.hpp"

 #include "runtime/thread.inline.hpp"

 #include "runtime/vframe.hpp"

 #include "runtime/vframe_hp.hpp"

 #include "runtime/vmThread.hpp"

 #include "runtime/vm_operations.hpp"

 ///////////////////////////////////////////////////////////////

 //

 // JvmtiEnvBase

 //

 JvmtiEnvBase* JvmtiEnvBase::_head_environment = NULL;

 bool JvmtiEnvBase::_globally_initialized = false;

 volatile bool JvmtiEnvBase::_needs_clean_up = false;

 jvmtiPhase JvmtiEnvBase::_phase = JVMTI_PHASE_PRIMORDIAL;

 volatile int JvmtiEnvBase::_dying_thread_env_iteration_count = 0;

 extern jvmtiInterface_1_ jvmti_Interface;

 extern jvmtiInterface_1_ jvmtiTrace_Interface;

 // perform initializations that must occur before any JVMTI environments

 // are released but which should only be initialized once (no matter

 // how many environments are created).

 void

 JvmtiEnvBase::globally_initialize() {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(), "sanity check");

   assert(_globally_initialized == false, "bad call");

   JvmtiManageCapabilities::initialize();

   // register extension functions and events

   JvmtiExtensions::register_extensions();

 #ifdef JVMTI_TRACE

   JvmtiTrace::initialize();

 #endif

   _globally_initialized = true;

 }

 void

 JvmtiEnvBase::initialize() {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(), "sanity check");

   // Add this environment to the end of the environment list (order is important)

   {

     // This block of code must not contain any safepoints, as list deallocation

     // (which occurs at a safepoint) cannot occur simultaneously with this list

     // addition.  Note: No_Safepoint_Verifier cannot, currently, be used before

     // threads exist.

     JvmtiEnvIterator it;

     JvmtiEnvBase *previous_env = NULL;

     for (JvmtiEnvBase* env = it.first(); env != NULL; env = it.next(env)) {

       previous_env = env;

     }

     if (previous_env == NULL) {

       _head_environment = this;

     } else {

       previous_env->set_next_environment(this);

     }

   }

   if (_globally_initialized == false) {

     globally_initialize();

   }

 }

 bool

 JvmtiEnvBase::is_valid() {

   jint value = 0;

   // This object might not be a JvmtiEnvBase so we can't assume

   // the _magic field is properly aligned. Get the value in a safe

   // way and then check against JVMTI_MAGIC.

   switch (sizeof(_magic)) {

   case 2:

     value = Bytes::get_native_u2((address)&_magic);

     break;

   case 4:

     value = Bytes::get_native_u4((address)&_magic);

     break;

   case 8:

     value = Bytes::get_native_u8((address)&_magic);

     break;

   default:

     guarantee(false, "_magic field is an unexpected size");

   }

   return value == JVMTI_MAGIC;

 }

 bool

 JvmtiEnvBase::use_version_1_0_semantics() {

   int major, minor, micro;

   JvmtiExport::decode_version_values(_version, &major, &minor, &micro);

   return major == 1 && minor == 0;  // micro version doesn't matter here

 }

 bool

 JvmtiEnvBase::use_version_1_1_semantics() {

   int major, minor, micro;

   JvmtiExport::decode_version_values(_version, &major, &minor, &micro);

   return major == 1 && minor == 1;  // micro version doesn't matter here

 }

 bool

 JvmtiEnvBase::use_version_1_2_semantics() {

   int major, minor, micro;

   JvmtiExport::decode_version_values(_version, &major, &minor, &micro);

   return major == 1 && minor == 2;  // micro version doesn't matter here

 }

 JvmtiEnvBase::JvmtiEnvBase(jint version) : _env_event_enable() {

   _version = version;

   _env_local_storage = NULL;

   _tag_map = NULL;

   _native_method_prefix_count = 0;

   _native_method_prefixes = NULL;

   _next = NULL;

   _class_file_load_hook_ever_enabled = false;

   // Moot since ClassFileLoadHook not yet enabled.

   // But "true" will give a more predictable ClassFileLoadHook behavior

   // for environment creation during ClassFileLoadHook.

   _is_retransformable = true;

   // all callbacks initially NULL

   memset(&_event_callbacks,0,sizeof(jvmtiEventCallbacks));

   // all capabilities initially off

   memset(&_current_capabilities, 0, sizeof(_current_capabilities));

   // all prohibited capabilities initially off

   memset(&_prohibited_capabilities, 0, sizeof(_prohibited_capabilities));

   _magic = JVMTI_MAGIC;

   JvmtiEventController::env_initialize((JvmtiEnv*)this);

 #ifdef JVMTI_TRACE

   _jvmti_external.functions = TraceJVMTI != NULL ? &jvmtiTrace_Interface : &jvmti_Interface;

 #else

   _jvmti_external.functions = &jvmti_Interface;

 #endif

 }

 void

 JvmtiEnvBase::dispose() {

 #ifdef JVMTI_TRACE

   JvmtiTrace::shutdown();

 #endif

   // Dispose of event info and let the event controller call us back

   // in a locked state (env_dispose, below)

   JvmtiEventController::env_dispose(this);

 }

 void

 JvmtiEnvBase::env_dispose() {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(), "sanity check");

   // We have been entered with all events disabled on this environment.

   // A race to re-enable events (by setting callbacks) is prevented by

   // checking for a valid environment when setting callbacks (while

   // holding the JvmtiThreadState_lock).

   // Mark as invalid.

   _magic = DISPOSED_MAGIC;

   // Relinquish all capabilities.

   jvmtiCapabilities *caps = get_capabilities();

   JvmtiManageCapabilities::relinquish_capabilities(caps, caps, caps);

   // Same situation as with events (see above)

   set_native_method_prefixes(0, NULL);

   JvmtiTagMap* tag_map_to_deallocate = _tag_map;

   set_tag_map(NULL);

   // A tag map can be big, deallocate it now

   if (tag_map_to_deallocate != NULL) {

     delete tag_map_to_deallocate;

   }

   _needs_clean_up = true;

 }

 JvmtiEnvBase::~JvmtiEnvBase() {

   assert(SafepointSynchronize::is_at_safepoint(), "sanity check");

   // There is a small window of time during which the tag map of a

   // disposed environment could have been reallocated.

   // Make sure it is gone.

   JvmtiTagMap* tag_map_to_deallocate = _tag_map;

   set_tag_map(NULL);

   // A tag map can be big, deallocate it now

   if (tag_map_to_deallocate != NULL) {

     delete tag_map_to_deallocate;

   }

   _magic = BAD_MAGIC;

 }

 void

 JvmtiEnvBase::periodic_clean_up() {

   assert(SafepointSynchronize::is_at_safepoint(), "sanity check");

   // JvmtiEnvBase reference is saved in JvmtiEnvThreadState. So

   // clean up JvmtiThreadState before deleting JvmtiEnv pointer.

   JvmtiThreadState::periodic_clean_up();

   // Unlink all invalid environments from the list of environments

   // and deallocate them

   JvmtiEnvIterator it;

   JvmtiEnvBase* previous_env = NULL;

   JvmtiEnvBase* env = it.first();

   while (env != NULL) {

     if (env->is_valid()) {

       previous_env = env;

       env = it.next(env);

     } else {

       // This one isn't valid, remove it from the list and deallocate it

       JvmtiEnvBase* defunct_env = env;

       env = it.next(env);

       if (previous_env == NULL) {

         _head_environment = env;

       } else {

         previous_env->set_next_environment(env);

       }

       delete defunct_env;

     }

   }

 }

 void

 JvmtiEnvBase::check_for_periodic_clean_up() {

   assert(SafepointSynchronize::is_at_safepoint(), "sanity check");

   class ThreadInsideIterationClosure: public ThreadClosure {

    private:

     bool _inside;

    public:

     ThreadInsideIterationClosure() : _inside(false) {};

     void do_thread(Thread* thread) {

       _inside |= thread->is_inside_jvmti_env_iteration();

     }

     bool is_inside_jvmti_env_iteration() {

       return _inside;

     }

   };

   if (_needs_clean_up) {

     // Check if we are currently iterating environment,

     // deallocation should not occur if we are

     ThreadInsideIterationClosure tiic;

     Threads::threads_do(&tiic);

     if (!tiic.is_inside_jvmti_env_iteration() &&

              !is_inside_dying_thread_env_iteration()) {

       _needs_clean_up = false;

       JvmtiEnvBase::periodic_clean_up();

     }

   }

 }

 void

 JvmtiEnvBase::record_first_time_class_file_load_hook_enabled() {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(),

          "sanity check");

   if (!_class_file_load_hook_ever_enabled) {

     _class_file_load_hook_ever_enabled = true;

     if (get_capabilities()->can_retransform_classes) {

       _is_retransformable = true;

     } else {

       _is_retransformable = false;

       // cannot add retransform capability after ClassFileLoadHook has been enabled

       get_prohibited_capabilities()->can_retransform_classes = 1;

     }

   }

 }

 void

 JvmtiEnvBase::record_class_file_load_hook_enabled() {

   if (!_class_file_load_hook_ever_enabled) {

     if (Threads::number_of_threads() == 0) {

       record_first_time_class_file_load_hook_enabled();

     } else {

       MutexLocker mu(JvmtiThreadState_lock);

       record_first_time_class_file_load_hook_enabled();

     }

   }

 }

 jvmtiError

 JvmtiEnvBase::set_native_method_prefixes(jint prefix_count, char** prefixes) {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(),

          "sanity check");

   int old_prefix_count = get_native_method_prefix_count();

   char **old_prefixes = get_native_method_prefixes();

   // allocate and install the new prefixex

   if (prefix_count == 0 || !is_valid()) {

     _native_method_prefix_count = 0;

     _native_method_prefixes = NULL;

   } else {

     // there are prefixes, allocate an array to hold them, and fill it

     char** new_prefixes = (char**)os::malloc((prefix_count) * sizeof(char*), mtInternal);

     if (new_prefixes == NULL) {

       return JVMTI_ERROR_OUT_OF_MEMORY;

     }

     for (int i = 0; i < prefix_count; i++) {

       char* prefix = prefixes[i];

       if (prefix == NULL) {

         for (int j = 0; j < (i-1); j++) {

           os::free(new_prefixes[j]);

         }

         os::free(new_prefixes);

         return JVMTI_ERROR_NULL_POINTER;

       }

       prefix = os::strdup(prefixes[i]);

       if (prefix == NULL) {

         for (int j = 0; j < (i-1); j++) {

           os::free(new_prefixes[j]);

         }

         os::free(new_prefixes);

         return JVMTI_ERROR_OUT_OF_MEMORY;

       }

       new_prefixes[i] = prefix;

     }

     _native_method_prefix_count = prefix_count;

     _native_method_prefixes = new_prefixes;

   }

   // now that we know the new prefixes have been successfully installed we can

   // safely remove the old ones

   if (old_prefix_count != 0) {

     for (int i = 0; i < old_prefix_count; i++) {

       os::free(old_prefixes[i]);

     }

     os::free(old_prefixes);

   }

   return JVMTI_ERROR_NONE;

 }

 // Collect all the prefixes which have been set in any JVM TI environments

 // by the SetNativeMethodPrefix(es) functions.  Be sure to maintain the

 // order of environments and the order of prefixes within each environment.

 // Return in a resource allocated array.

 char**

 JvmtiEnvBase::get_all_native_method_prefixes(int* count_ptr) {

   assert(Threads::number_of_threads() == 0 ||

          SafepointSynchronize::is_at_safepoint() ||

          JvmtiThreadState_lock->is_locked(),

          "sanity check");

   int total_count = 0;

   GrowableArray<char*>* prefix_array =new GrowableArray<char*>(5);

   JvmtiEnvIterator it;

   for (JvmtiEnvBase* env = it.first(); env != NULL; env = it.next(env)) {

     int prefix_count = env->get_native_method_prefix_count();

     char** prefixes = env->get_native_method_prefixes();

     for (int j = 0; j < prefix_count; j++) {

       // retrieve a prefix and so that it is safe against asynchronous changes

       // copy it into the resource area

       char* prefix = prefixes[j];

       char* prefix_copy = NEW_RESOURCE_ARRAY(char, strlen(prefix)+1);

       strcpy(prefix_copy, prefix);

       prefix_array->at_put_grow(total_count++, prefix_copy);

     }

   }

   char** all_prefixes = NEW_RESOURCE_ARRAY(char*, total_count);

   char** p = all_prefixes;

   for (int i = 0; i < total_count; ++i) {

     *p++ = prefix_array->at(i);

   }

   *count_ptr = total_count;

   return all_prefixes;

 }

 void

 JvmtiEnvBase::set_event_callbacks(const jvmtiEventCallbacks* callbacks,

                                                jint size_of_callbacks) {

   assert(Threads::number_of_threads() == 0 || JvmtiThreadState_lock->is_locked(), "sanity check");

   size_t byte_cnt = sizeof(jvmtiEventCallbacks);

   // clear in either case to be sure we got any gap between sizes

   memset(&_event_callbacks, 0, byte_cnt);

   // Now that JvmtiThreadState_lock is held, prevent a possible race condition where events

   // are re-enabled by a call to set event callbacks where the DisposeEnvironment

   // occurs after the boiler-plate environment check and before the lock is acquired.

   if (callbacks != NULL && is_valid()) {

     if (size_of_callbacks < (jint)byte_cnt) {

       byte_cnt = size_of_callbacks;

     }

     memcpy(&_event_callbacks, callbacks, byte_cnt);

   }

 }

 // Called from JVMTI entry points which perform stack walking. If the

 // associated JavaThread is the current thread, then wait_for_suspend

 // is not used. Otherwise, it determines if we should wait for the

 // "other" thread to complete external suspension. (NOTE: in future

 // releases the suspension mechanism should be reimplemented so this

 // is not necessary.)

 //

 bool

 JvmtiEnvBase::is_thread_fully_suspended(JavaThread* thr, bool wait_for_suspend, uint32_t *bits) {

   // "other" threads require special handling

   if (thr != JavaThread::current()) {

     if (wait_for_suspend) {

       // We are allowed to wait for the external suspend to complete

       // so give the other thread a chance to get suspended.

       if (!thr->wait_for_ext_suspend_completion(SuspendRetryCount,

           SuspendRetryDelay, bits)) {

         // didn't make it so let the caller know

         return false;

       }

     }

     // We aren't allowed to wait for the external suspend to complete

     // so if the other thread isn't externally suspended we need to

     // let the caller know.

     else if (!thr->is_ext_suspend_completed_with_lock(bits)) {

       return false;

     }

   }

   return true;

 }

 // In the fullness of time, all users of the method should instead

 // directly use allocate, besides being cleaner and faster, this will

 // mean much better out of memory handling

 unsigned char *

 JvmtiEnvBase::jvmtiMalloc(jlong size) {

   unsigned char* mem;

   jvmtiError result = allocate(size, &mem);

   assert(result == JVMTI_ERROR_NONE, "Allocate failed");

   return mem;

 }

 //

 // Threads

 //

 jobject *

 JvmtiEnvBase::new_jobjectArray(int length, Handle *handles) {

   if (length == 0) {

     return NULL;

   }

   jobject *objArray = (jobject *) jvmtiMalloc(sizeof(jobject) * length);

   NULL_CHECK(objArray, NULL);

   for (int i=0; i<length; i++) {

     objArray[i] = jni_reference(handles[i]);

   }

   return objArray;

 }

 jthread *

 JvmtiEnvBase::new_jthreadArray(int length, Handle *handles) {

   return (jthread *) new_jobjectArray(length,handles);

 }

 jthreadGroup *

 JvmtiEnvBase::new_jthreadGroupArray(int length, Handle *handles) {

   return (jthreadGroup *) new_jobjectArray(length,handles);

 }

 JavaThread *

 JvmtiEnvBase::get_JavaThread(jthread jni_thread) {

   oop t = JNIHandles::resolve_external_guard(jni_thread);

   if (t == NULL || !t->is_a(SystemDictionary::Thread_klass())) {

     return NULL;

   }

   // The following returns NULL if the thread has not yet run or is in

   // process of exiting

   return java_lang_Thread::thread(t);

 }

 // return the vframe on the specified thread and depth, NULL if no such frame

 vframe*

 JvmtiEnvBase::vframeFor(JavaThread* java_thread, jint depth) {

   if (!java_thread->has_last_Java_frame()) {

     return NULL;

   }

   RegisterMap reg_map(java_thread);

   vframe *vf = java_thread->last_java_vframe(&reg_map);

   int d = 0;

   while ((vf != NULL) && (d < depth)) {

     vf = vf->java_sender();

     d++;

   }

   return vf;

 }

 //

 // utilities: JNI objects

 //

 jclass

 JvmtiEnvBase::get_jni_class_non_null(Klass* k) {

   assert(k != NULL, "k != NULL");

   return (jclass)jni_reference(k->java_mirror());

 }

 //

 // Field Information

 //

 bool

 JvmtiEnvBase::get_field_descriptor(Klass* k, jfieldID field, fieldDescriptor* fd) {

   if (!jfieldIDWorkaround::is_valid_jfieldID(k, field)) {

     return false;

   }

   bool found = false;

   if (jfieldIDWorkaround::is_static_jfieldID(field)) {

     JNIid* id = jfieldIDWorkaround::from_static_jfieldID(field);

     found = id->find_local_field(fd);

   } else {

     // Non-static field. The fieldID is really the offset of the field within the object.

     int offset = jfieldIDWorkaround::from_instance_jfieldID(k, field);

     found = InstanceKlass::cast(k)->find_field_from_offset(offset, false, fd);

   }

   return found;

 }

 //

 // Object Monitor Information

 //

 //

 // Count the number of objects for a lightweight monitor. The hobj

 // parameter is object that owns the monitor so this routine will

 // count the number of times the same object was locked by frames

 // in java_thread.

 //

 jint

 JvmtiEnvBase::count_locked_objects(JavaThread *java_thread, Handle hobj) {

   jint ret = 0;

   if (!java_thread->has_last_Java_frame()) {

     return ret;  // no Java frames so no monitors

   }

   ResourceMark rm;

   HandleMark   hm;

   RegisterMap  reg_map(java_thread);

   for(javaVFrame *jvf=java_thread->last_java_vframe(&reg_map); jvf != NULL;

                                                  jvf = jvf->java_sender()) {

     GrowableArray<MonitorInfo*>* mons = jvf->monitors();

     if (!mons->is_empty()) {

       for (int i = 0; i < mons->length(); i++) {

         MonitorInfo *mi = mons->at(i);

         if (mi->owner_is_scalar_replaced()) continue;

         // see if owner of the monitor is our object

         if (mi->owner() != NULL && mi->owner() == hobj()) {

           ret++;

         }

       }

     }

   }

   return ret;

 }

 jvmtiError

 JvmtiEnvBase::get_current_contended_monitor(JavaThread *calling_thread, JavaThread *java_thread, jobject *monitor_ptr) {

 #ifdef ASSERT

   uint32_t debug_bits = 0;

 #endif

   assert((SafepointSynchronize::is_at_safepoint() ||

           is_thread_fully_suspended(java_thread, false, &debug_bits)),

          "at safepoint or target thread is suspended");

   oop obj = NULL;

   ObjectMonitor *mon = java_thread->current_waiting_monitor();

   if (mon == NULL) {

     // thread is not doing an Object.wait() call

     mon = java_thread->current_pending_monitor();

     if (mon != NULL) {

       // The thread is trying to enter() or raw_enter() an ObjectMonitor.

       obj = (oop)mon->object();

       // If obj == NULL, then ObjectMonitor is raw which doesn't count

       // as contended for this API

     }

     // implied else: no contended ObjectMonitor

   } else {

     // thread is doing an Object.wait() call

     obj = (oop)mon->object();

     assert(obj != NULL, "Object.wait() should have an object");

   }

   if (obj == NULL) {

     *monitor_ptr = NULL;

   } else {

     HandleMark hm;

     Handle     hobj(obj);

     *monitor_ptr = jni_reference(calling_thread, hobj);

   }

   return JVMTI_ERROR_NONE;

 }

 jvmtiError

 JvmtiEnvBase::get_owned_monitors(JavaThread *calling_thread, JavaThread* java_thread,

                                  GrowableArray<jvmtiMonitorStackDepthInfo*> *owned_monitors_list) {

   jvmtiError err = JVMTI_ERROR_NONE;

 #ifdef ASSERT

   uint32_t debug_bits = 0;

 #endif

   assert((SafepointSynchronize::is_at_safepoint() ||

           is_thread_fully_suspended(java_thread, false, &debug_bits)),

          "at safepoint or target thread is suspended");

   if (java_thread->has_last_Java_frame()) {

     ResourceMark rm;

     HandleMark   hm;

     RegisterMap  reg_map(java_thread);

     int depth = 0;

     for (javaVFrame *jvf = java_thread->last_java_vframe(&reg_map); jvf != NULL;

          jvf = jvf->java_sender()) {

       if (depth++ < MaxJavaStackTraceDepth) {  // check for stack too deep

         // add locked objects for this frame into list

         err = get_locked_objects_in_frame(calling_thread, java_thread, jvf, owned_monitors_list, depth-1);

         if (err != JVMTI_ERROR_NONE) {

           return err;

         }

       }

     }

   }

   // Get off stack monitors. (e.g. acquired via jni MonitorEnter).

   JvmtiMonitorClosure jmc(java_thread, calling_thread, owned_monitors_list, this);

   ObjectSynchronizer::monitors_iterate(&jmc);

   err = jmc.error();

   return err;

 }

 // Save JNI local handles for any objects that this frame owns.

 jvmtiError

 JvmtiEnvBase::get_locked_objects_in_frame(JavaThread* calling_thread, JavaThread* java_thread,

                                  javaVFrame *jvf, GrowableArray<jvmtiMonitorStackDepthInfo*>* owned_monitors_list, int stack_depth) {

   jvmtiError err = JVMTI_ERROR_NONE;

   ResourceMark rm;

   GrowableArray<MonitorInfo*>* mons = jvf->monitors();

   if (mons->is_empty()) {

     return err;  // this javaVFrame holds no monitors

   }

   HandleMark hm;

   oop wait_obj = NULL;

   {

     // save object of current wait() call (if any) for later comparison

     ObjectMonitor *mon = java_thread->current_waiting_monitor();

     if (mon != NULL) {

       wait_obj = (oop)mon->object();

     }

   }

   oop pending_obj = NULL;

   {

     // save object of current enter() call (if any) for later comparison

     ObjectMonitor *mon = java_thread->current_pending_monitor();

     if (mon != NULL) {

       pending_obj = (oop)mon->object();

     }

   }

   for (int i = 0; i < mons->length(); i++) {

     MonitorInfo *mi = mons->at(i);

     if (mi->owner_is_scalar_replaced()) continue;

     oop obj = mi->owner();

     if (obj == NULL) {

       // this monitor doesn't have an owning object so skip it

       continue;

     }

     if (wait_obj == obj) {

       // the thread is waiting on this monitor so it isn't really owned

       continue;

     }

     if (pending_obj == obj) {

       // the thread is pending on this monitor so it isn't really owned

       continue;

     }

     if (owned_monitors_list->length() > 0) {

       // Our list has at least one object on it so we have to check

       // for recursive object locking

       bool found = false;

       for (int j = 0; j < owned_monitors_list->length(); j++) {

         jobject jobj = ((jvmtiMonitorStackDepthInfo*)owned_monitors_list->at(j))->monitor;

         oop check = JNIHandles::resolve(jobj);

         if (check == obj) {

           found = true;  // we found the object

           break;

         }

       }

       if (found) {

         // already have this object so don't include it

         continue;

       }

     }

     // add the owning object to our list

     jvmtiMonitorStackDepthInfo *jmsdi;

     err = allocate(sizeof(jvmtiMonitorStackDepthInfo), (unsigned char **)&jmsdi);

     if (err != JVMTI_ERROR_NONE) {

         return err;

     }

     Handle hobj(obj);

     jmsdi->monitor = jni_reference(calling_thread, hobj);

     jmsdi->stack_depth = stack_depth;

     owned_monitors_list->append(jmsdi);

   }

   return err;

 }

 jvmtiError

 JvmtiEnvBase::get_stack_trace(JavaThread *java_thread,

                               jint start_depth, jint max_count,

                               jvmtiFrameInfo* frame_buffer, jint* count_ptr) {

 #ifdef ASSERT

   uint32_t debug_bits = 0;

 #endif

   assert((SafepointSynchronize::is_at_safepoint() ||

           is_thread_fully_suspended(java_thread, false, &debug_bits)),

          "at safepoint or target thread is suspended");

   int count = 0;

   if (java_thread->has_last_Java_frame()) {

     RegisterMap reg_map(java_thread);

     Thread* current_thread = Thread::current();

     ResourceMark rm(current_thread);

     javaVFrame *jvf = java_thread->last_java_vframe(&reg_map);

     HandleMark hm(current_thread);

     if (start_depth != 0) {

       if (start_depth > 0) {

         for (int j = 0; j < start_depth && jvf != NULL; j++) {

           jvf = jvf->java_sender();

         }

         if (jvf == NULL) {

           // start_depth is deeper than the stack depth

           return JVMTI_ERROR_ILLEGAL_ARGUMENT;

         }

       } else { // start_depth < 0

         // we are referencing the starting depth based on the oldest

         // part of the stack.

         // optimize to limit the number of times that java_sender() is called

         javaVFrame *jvf_cursor = jvf;

         javaVFrame *jvf_prev = NULL;

         javaVFrame *jvf_prev_prev;

         int j = 0;

         while (jvf_cursor != NULL) {

           jvf_prev_prev = jvf_prev;

           jvf_prev = jvf_cursor;

           for (j = 0; j > start_depth && jvf_cursor != NULL; j--) {

             jvf_cursor = jvf_cursor->java_sender();

           }

         }

         if (j == start_depth) {

           // previous pointer is exactly where we want to start

           jvf = jvf_prev;

         } else {

           // we need to back up further to get to the right place

           if (jvf_prev_prev == NULL) {

             // the -start_depth is greater than the stack depth

             return JVMTI_ERROR_ILLEGAL_ARGUMENT;

           }

           // j now is the number of frames on the stack starting with

           // jvf_prev, we start from jvf_prev_prev and move older on

           // the stack that many, the result is -start_depth frames

           // remaining.

           jvf = jvf_prev_prev;

           for (; j < 0; j++) {

             jvf = jvf->java_sender();

           }

         }

       }

     }

     for (; count < max_count && jvf != NULL; count++) {

       frame_buffer[count].method = jvf->method()->jmethod_id();

       frame_buffer[count].location = (jvf->method()->is_native() ? -1 : jvf->bci());

       jvf = jvf->java_sender();

     }

   } else {

     if (start_depth != 0) {

       // no frames and there is a starting depth

       return JVMTI_ERROR_ILLEGAL_ARGUMENT;

     }

   }

   *count_ptr = count;

   return JVMTI_ERROR_NONE;

 }

 jvmtiError

 JvmtiEnvBase::get_frame_count(JvmtiThreadState *state, jint *count_ptr) {

   assert((state != NULL),

          "JavaThread should create JvmtiThreadState before calling this method");

   *count_ptr = state->count_frames();

   return JVMTI_ERROR_NONE;

 }

 jvmtiError

 JvmtiEnvBase::get_frame_location(JavaThread *java_thread, jint depth,

                                  jmethodID* method_ptr, jlocation* location_ptr) {

 #ifdef ASSERT

   uint32_t debug_bits = 0;

 #endif

   assert((SafepointSynchronize::is_at_safepoint() ||

           is_thread_fully_suspended(java_thread, false, &debug_bits)),

          "at safepoint or target thread is suspended");

   Thread* current_thread = Thread::current();

   ResourceMark rm(current_thread);

   vframe *vf = vframeFor(java_thread, depth);

   if (vf == NULL) {

     return JVMTI_ERROR_NO_MORE_FRAMES;

   }

   // vframeFor should return a java frame. If it doesn't

   // it means we've got an internal error and we return the

   // error in product mode. In debug mode we will instead

   // attempt to cast the vframe to a javaVFrame and will

   // cause an assertion/crash to allow further diagnosis.

 #ifdef PRODUCT

   if (!vf->is_java_frame()) {

     return JVMTI_ERROR_INTERNAL;

   }

 #endif

   HandleMark hm(current_thread);

   javaVFrame *jvf = javaVFrame::cast(vf);

   Method* method = jvf->method();

   if (method->is_native()) {

     *location_ptr = -1;

   } else {

     *location_ptr = jvf->bci();

   }

   *method_ptr = method->jmethod_id();

   return JVMTI_ERROR_NONE;

 }

 jvmtiError

 JvmtiEnvBase::get_object_monitor_usage(JavaThread* calling_thread, jobject object, jvmtiMonitorUsage* info_ptr) {

   HandleMark hm;

   Handle hobj;

   bool at_safepoint = SafepointSynchronize::is_at_safepoint();

   // Check arguments

   {

     oop mirror = JNIHandles::resolve_external_guard(object);

     NULL_CHECK(mirror, JVMTI_ERROR_INVALID_OBJECT);

     NULL_CHECK(info_ptr, JVMTI_ERROR_NULL_POINTER);

     hobj = Handle(mirror);

   }

   JavaThread *owning_thread = NULL;

   ObjectMonitor *mon = NULL;

   jvmtiMonitorUsage ret = {

       NULL, 0, 0, NULL, 0, NULL

   };

   uint32_t debug_bits = 0;

   // first derive the object's owner and entry_count (if any)

   {

     // Revoke any biases before querying the mark word

     if (SafepointSynchronize::is_at_safepoint()) {

       BiasedLocking::revoke_at_safepoint(hobj);

     } else {

       BiasedLocking::revoke_and_rebias(hobj, false, calling_thread);

     }

     address owner = NULL;

     {

       markOop mark = hobj()->mark();

       if (!mark->has_monitor()) {

         // this object has a lightweight monitor

         if (mark->has_locker()) {

           owner = (address)mark->locker(); // save the address of the Lock word

         }

         // implied else: no owner

       } else {

         // this object has a heavyweight monitor

         mon = mark->monitor();

         // The owner field of a heavyweight monitor may be NULL for no

         // owner, a JavaThread * or it may still be the address of the

         // Lock word in a JavaThread's stack. A monitor can be inflated

         // by a non-owning JavaThread, but only the owning JavaThread

         // can change the owner field from the Lock word to the

         // JavaThread * and it may not have done that yet.

         owner = (address)mon->owner();

       }

     }

     if (owner != NULL) {

       // This monitor is owned so we have to find the owning JavaThread.

       // Since owning_thread_from_monitor_owner() grabs a lock, GC can

       // move our object at this point. However, our owner value is safe

       // since it is either the Lock word on a stack or a JavaThread *.

       owning_thread = Threads::owning_thread_from_monitor_owner(owner, !at_safepoint);

       // Cannot assume (owning_thread != NULL) here because this function

       // may not have been called at a safepoint and the owning_thread

       // might not be suspended.

       if (owning_thread != NULL) {

         // The monitor's owner either has to be the current thread, at safepoint

         // or it has to be suspended. Any of these conditions will prevent both

         // contending and waiting threads from modifying the state of

         // the monitor.

         if (!at_safepoint && !JvmtiEnv::is_thread_fully_suspended(owning_thread, true, &debug_bits)) {

           // Don't worry! This return of JVMTI_ERROR_THREAD_NOT_SUSPENDED

           // will not make it back to the JVM/TI agent. The error code will

           // get intercepted in JvmtiEnv::GetObjectMonitorUsage() which

           // will retry the call via a VM_GetObjectMonitorUsage VM op.

           return JVMTI_ERROR_THREAD_NOT_SUSPENDED;

         }

         HandleMark hm;

         Handle     th(owning_thread->threadObj());

         ret.owner = (jthread)jni_reference(calling_thread, th);

       }

       // implied else: no owner

     }

     if (owning_thread != NULL) {  // monitor is owned

       if ((address)owning_thread == owner) {

         // the owner field is the JavaThread *

         assert(mon != NULL,

           "must have heavyweight monitor with JavaThread * owner");

         ret.entry_count = mon->recursions() + 1;

       } else {

         // The owner field is the Lock word on the JavaThread's stack

         // so the recursions field is not valid. We have to count the

         // number of recursive monitor entries the hard way. We pass

         // a handle to survive any GCs along the way.

         ResourceMark rm;

         ret.entry_count = count_locked_objects(owning_thread, hobj);

       }

     }

     // implied else: entry_count == 0

   }

   int nWant,nWait;

   if (mon != NULL) {

     // this object has a heavyweight monitor

     nWant = mon->contentions(); // # of threads contending for monitor

     nWait = mon->waiters();     // # of threads in Object.wait()

     ret.waiter_count = nWant + nWait;

     ret.notify_waiter_count = nWait;

   } else {

     // this object has a lightweight monitor

     ret.waiter_count = 0;

     ret.notify_waiter_count = 0;

   }

   // Allocate memory for heavyweight and lightweight monitor.

   jvmtiError err;

   err = allocate(ret.waiter_count * sizeof(jthread *), (unsigned char**)&ret.waiters);

   if (err != JVMTI_ERROR_NONE) {

     return err;

   }

   err = allocate(ret.notify_waiter_count * sizeof(jthread *),

                  (unsigned char**)&ret.notify_waiters);

   if (err != JVMTI_ERROR_NONE) {

     deallocate((unsigned char*)ret.waiters);

     return err;

   }

   // now derive the rest of the fields

   if (mon != NULL) {

     // this object has a heavyweight monitor

     // Number of waiters may actually be less than the waiter count.

     // So NULL out memory so that unused memory will be NULL.

     memset(ret.waiters, 0, ret.waiter_count * sizeof(jthread *));

     memset(ret.notify_waiters, 0, ret.notify_waiter_count * sizeof(jthread *));

     if (ret.waiter_count > 0) {

       // we have contending and/or waiting threads

       HandleMark hm;

       if (nWant > 0) {

         // we have contending threads

         ResourceMark rm;

         // get_pending_threads returns only java thread so we do not need to

         // check for  non java threads.

         GrowableArray<JavaThread*>* wantList = Threads::get_pending_threads(

           nWant, (address)mon, !at_safepoint);

         if (wantList->length() < nWant) {

           // robustness: the pending list has gotten smaller

           nWant = wantList->length();

         }

         for (int i = 0; i < nWant; i++) {

           JavaThread *pending_thread = wantList->at(i);

           // If the monitor has no owner, then a non-suspended contending

           // thread could potentially change the state of the monitor by

           // entering it. The JVM/TI spec doesn't allow this.

           if (owning_thread == NULL && !at_safepoint &

               !JvmtiEnv::is_thread_fully_suspended(pending_thread, true, &debug_bits)) {

             if (ret.owner != NULL) {

               destroy_jni_reference(calling_thread, ret.owner);

             }

             for (int j = 0; j < i; j++) {

               destroy_jni_reference(calling_thread, ret.waiters[j]);

             }

             deallocate((unsigned char*)ret.waiters);

             deallocate((unsigned char*)ret.notify_waiters);

             return JVMTI_ERROR_THREAD_NOT_SUSPENDED;

           }

           Handle th(pending_thread->threadObj());

           ret.waiters[i] = (jthread)jni_reference(calling_thread, th);

         }

       }

       if (nWait > 0) {

         // we have threads in Object.wait()

         int offset = nWant;  // add after any contending threads

         ObjectWaiter *waiter = mon->first_waiter();

         for (int i = 0, j = 0; i < nWait; i++) {

           if (waiter == NULL) {

             // robustness: the waiting list has gotten smaller

             nWait = j;

             break;

           }

           Thread *t = mon->thread_of_waiter(waiter);

           if (t != NULL && t->is_Java_thread()) {

             JavaThread *wjava_thread = (JavaThread *)t;

             // If the thread was found on the ObjectWaiter list, then

             // it has not been notified. This thread can't change the

             // state of the monitor so it doesn't need to be suspended.

             Handle th(wjava_thread->threadObj());

             ret.waiters[offset + j] = (jthread)jni_reference(calling_thread, th);

             ret.notify_waiters[j++] = (jthread)jni_reference(calling_thread, th);

           }

           waiter = mon->next_waiter(waiter);

         }

       }

     }

     // Adjust count. nWant and nWait count values may be less than original.

     ret.waiter_count = nWant + nWait;

     ret.notify_waiter_count = nWait;

   } else {

     // this object has a lightweight monitor and we have nothing more

     // to do here because the defaults are just fine.

   }

   // we don't update return parameter unless everything worked

   *info_ptr = ret;

   return JVMTI_ERROR_NONE;

 }

 ResourceTracker::ResourceTracker(JvmtiEnv* env) {

   _env = env;

   _allocations = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<unsigned char*>(20, true);

   _failed = false;

 }

 ResourceTracker::~ResourceTracker() {

   if (_failed) {

     for (int i=0; i<_allocations->length(); i++) {

       _env->deallocate(_allocations->at(i));

     }

   }

   delete _allocations;

 }

 jvmtiError ResourceTracker::allocate(jlong size, unsigned char** mem_ptr) {

   unsigned char *ptr;

   jvmtiError err = _env->allocate(size, &ptr);

   if (err == JVMTI_ERROR_NONE) {

     _allocations->append(ptr);

     *mem_ptr = ptr;

   } else {

     *mem_ptr = NULL;

     _failed = true;

   }

   return err;

  }

 unsigned char* ResourceTracker::allocate(jlong size) {

   unsigned char* ptr;

   allocate(size, &ptr);

   return ptr;

 }

 char* ResourceTracker::strdup(const char* str) {

   char *dup_str = (char*)allocate(strlen(str)+1);

   if (dup_str != NULL) {

     strcpy(dup_str, str);

   }

   return dup_str;

 }

 struct StackInfoNode {

   struct StackInfoNode *next;

   jvmtiStackInfo info;

 };

 // Create a jvmtiStackInfo inside a linked list node and create a

 // buffer for the frame information, both allocated as resource objects.

 // Fill in both the jvmtiStackInfo and the jvmtiFrameInfo.

 // Note that either or both of thr and thread_oop

 // may be null if the thread is new or has exited.

 void

 VM_GetMultipleStackTraces::fill_frames(jthread jt, JavaThread *thr, oop thread_oop) {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   jint state = 0;

   struct StackInfoNode *node = NEW_RESOURCE_OBJ(struct StackInfoNode);

   jvmtiStackInfo *infop = &(node->info);

   node->next = head();

   set_head(node);

   infop->frame_count = 0;

   infop->thread = jt;

   if (thread_oop != NULL) {

     // get most state bits

     state = (jint)java_lang_Thread::get_thread_status(thread_oop);

   }

   if (thr != NULL) {    // add more state bits if there is a JavaThead to query

     // same as is_being_ext_suspended() but without locking

     if (thr->is_ext_suspended() || thr->is_external_suspend()) {

       state |= JVMTI_THREAD_STATE_SUSPENDED;

     }

     JavaThreadState jts = thr->thread_state();

     if (jts == _thread_in_native) {

       state |= JVMTI_THREAD_STATE_IN_NATIVE;

     }

     OSThread* osThread = thr->osthread();

     if (osThread != NULL && osThread->interrupted()) {

       state |= JVMTI_THREAD_STATE_INTERRUPTED;

     }

   }

   infop->state = state;

   if (thr != NULL || (state & JVMTI_THREAD_STATE_ALIVE) != 0) {

     infop->frame_buffer = NEW_RESOURCE_ARRAY(jvmtiFrameInfo, max_frame_count());

     env()->get_stack_trace(thr, 0, max_frame_count(),

                            infop->frame_buffer, &(infop->frame_count));

   } else {

     infop->frame_buffer = NULL;

     infop->frame_count = 0;

   }

   _frame_count_total += infop->frame_count;

 }

 // Based on the stack information in the linked list, allocate memory

 // block to return and fill it from the info in the linked list.

 void

 VM_GetMultipleStackTraces::allocate_and_fill_stacks(jint thread_count) {

   // do I need to worry about alignment issues?

   jlong alloc_size =  thread_count       * sizeof(jvmtiStackInfo)

                     + _frame_count_total * sizeof(jvmtiFrameInfo);

   env()->allocate(alloc_size, (unsigned char **)&_stack_info);

   // pointers to move through the newly allocated space as it is filled in

   jvmtiStackInfo *si = _stack_info + thread_count;      // bottom of stack info

   jvmtiFrameInfo *fi = (jvmtiFrameInfo *)si;            // is the top of frame info

   // copy information in resource area into allocated buffer

   // insert stack info backwards since linked list is backwards

   // insert frame info forwards

   // walk the StackInfoNodes

   for (struct StackInfoNode *sin = head(); sin != NULL; sin = sin->next) {

     jint frame_count = sin->info.frame_count;

     size_t frames_size = frame_count * sizeof(jvmtiFrameInfo);

     --si;

     memcpy(si, &(sin->info), sizeof(jvmtiStackInfo));

     if (frames_size == 0) {

       si->frame_buffer = NULL;

     } else {

       memcpy(fi, sin->info.frame_buffer, frames_size);

       si->frame_buffer = fi;  // point to the new allocated copy of the frames

       fi += frame_count;

     }

   }

   assert(si == _stack_info, "the last copied stack info must be the first record");

   assert((unsigned char *)fi == ((unsigned char *)_stack_info) + alloc_size,

          "the last copied frame info must be the last record");

 }

 void

 VM_GetThreadListStackTraces::doit() {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   ResourceMark rm;

   for (int i = 0; i < _thread_count; ++i) {

     jthread jt = _thread_list[i];

     oop thread_oop = JNIHandles::resolve_external_guard(jt);

     if (thread_oop == NULL || !thread_oop->is_a(SystemDictionary::Thread_klass())) {

       set_result(JVMTI_ERROR_INVALID_THREAD);

       return;

     }

     fill_frames(jt, java_lang_Thread::thread(thread_oop), thread_oop);

   }

   allocate_and_fill_stacks(_thread_count);

 }

 void

 VM_GetAllStackTraces::doit() {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   ResourceMark rm;

   _final_thread_count = 0;

   for (JavaThread *jt = Threads::first(); jt != NULL; jt = jt->next()) {

     oop thread_oop = jt->threadObj();

     if (thread_oop != NULL &&

         !jt->is_exiting() &&

         java_lang_Thread::is_alive(thread_oop) &&

         !jt->is_hidden_from_external_view()) {

       ++_final_thread_count;

       // Handle block of the calling thread is used to create local refs.

       fill_frames((jthread)JNIHandles::make_local(_calling_thread, thread_oop),

                   jt, thread_oop);

     }

   }

   allocate_and_fill_stacks(_final_thread_count);

 }

 // Verifies that the top frame is a java frame in an expected state.

 // Deoptimizes frame if needed.

 // Checks that the frame method signature matches the return type (tos).

 // HandleMark must be defined in the caller only.

 // It is to keep a ret_ob_h handle alive after return to the caller.

 jvmtiError

 JvmtiEnvBase::check_top_frame(JavaThread* current_thread, JavaThread* java_thread,

                               jvalue value, TosState tos, Handle* ret_ob_h) {

   ResourceMark rm(current_thread);

   vframe *vf = vframeFor(java_thread, 0);

   NULL_CHECK(vf, JVMTI_ERROR_NO_MORE_FRAMES);

   javaVFrame *jvf = (javaVFrame*) vf;

   if (!vf->is_java_frame() || jvf->method()->is_native()) {

     return JVMTI_ERROR_OPAQUE_FRAME;

   }

   // If the frame is a compiled one, need to deoptimize it.

   if (vf->is_compiled_frame()) {

     if (!vf->fr().can_be_deoptimized()) {

       return JVMTI_ERROR_OPAQUE_FRAME;

     }

     Deoptimization::deoptimize_frame(java_thread, jvf->fr().id());

   }

   // Get information about method return type

   Symbol* signature = jvf->method()->signature();

   ResultTypeFinder rtf(signature);

   TosState fr_tos = as_TosState(rtf.type());

   if (fr_tos != tos) {

     if (tos != itos || (fr_tos != btos && fr_tos != ctos && fr_tos != stos)) {

       return JVMTI_ERROR_TYPE_MISMATCH;

     }

   }

   // Check that the jobject class matches the return type signature.

   jobject jobj = value.l;

   if (tos == atos && jobj != NULL) { // NULL reference is allowed

     Handle ob_h = Handle(current_thread, JNIHandles::resolve_external_guard(jobj));

     NULL_CHECK(ob_h, JVMTI_ERROR_INVALID_OBJECT);

     KlassHandle ob_kh = KlassHandle(current_thread, ob_h()->klass());

     NULL_CHECK(ob_kh, JVMTI_ERROR_INVALID_OBJECT);

     // Method return type signature.

     char* ty_sign = 1 + strchr(signature->as_C_string(), ')');

     if (!VM_GetOrSetLocal::is_assignable(ty_sign, ob_kh(), current_thread)) {

       return JVMTI_ERROR_TYPE_MISMATCH;

     }

     *ret_ob_h = ob_h;

   }

   return JVMTI_ERROR_NONE;

 } /* end check_top_frame */

 // ForceEarlyReturn<type> follows the PopFrame approach in many aspects.

 // Main difference is on the last stage in the interpreter.

 // The PopFrame stops method execution to continue execution

 // from the same method call instruction.

 // The ForceEarlyReturn forces return from method so the execution

 // continues at the bytecode following the method call.

 // Threads_lock NOT held, java_thread not protected by lock

 // java_thread - pre-checked

 jvmtiError

 JvmtiEnvBase::force_early_return(JavaThread* java_thread, jvalue value, TosState tos) {

   JavaThread* current_thread = JavaThread::current();

   HandleMark   hm(current_thread);

   uint32_t debug_bits = 0;

   // retrieve or create the state

   JvmtiThreadState* state = JvmtiThreadState::state_for(java_thread);

   if (state == NULL) {

     return JVMTI_ERROR_THREAD_NOT_ALIVE;

   }

   // Check if java_thread is fully suspended

   if (!is_thread_fully_suspended(java_thread,

                                  true /* wait for suspend completion */,

                                  &debug_bits)) {

     return JVMTI_ERROR_THREAD_NOT_SUSPENDED;

   }

   // Check to see if a ForceEarlyReturn was already in progress

   if (state->is_earlyret_pending()) {

     // Probably possible for JVMTI clients to trigger this, but the

     // JPDA backend shouldn't allow this to happen

     return JVMTI_ERROR_INTERNAL;

   }

   {

     // The same as for PopFrame. Workaround bug:

     //  4812902: popFrame hangs if the method is waiting at a synchronize

     // Catch this condition and return an error to avoid hanging.

     // Now JVMTI spec allows an implementation to bail out with an opaque

     // frame error.

     OSThread* osThread = java_thread->osthread();

     if (osThread->get_state() == MONITOR_WAIT) {

       return JVMTI_ERROR_OPAQUE_FRAME;

     }

   }

   Handle ret_ob_h = Handle();

   jvmtiError err = check_top_frame(current_thread, java_thread, value, tos, &ret_ob_h);

   if (err != JVMTI_ERROR_NONE) {

     return err;

   }

   assert(tos != atos || value.l == NULL || ret_ob_h() != NULL,

          "return object oop must not be NULL if jobject is not NULL");

   // Update the thread state to reflect that the top frame must be

   // forced to return.

   // The current frame will be returned later when the suspended

   // thread is resumed and right before returning from VM to Java.

   // (see call_VM_base() in assembler_<cpu>.cpp).

   state->set_earlyret_pending();

   state->set_earlyret_oop(ret_ob_h());

   state->set_earlyret_value(value, tos);

   // Set pending step flag for this early return.

   // It is cleared when next step event is posted.

   state->set_pending_step_for_earlyret();

   return JVMTI_ERROR_NONE;

 } /* end force_early_return */

 void

 JvmtiMonitorClosure::do_monitor(ObjectMonitor* mon) {

   if ( _error != JVMTI_ERROR_NONE) {

     // Error occurred in previous iteration so no need to add

     // to the list.

     return;

   }

   if (mon->owner() == _java_thread ) {

     // Filter out on stack monitors collected during stack walk.

     oop obj = (oop)mon->object();

     bool found = false;

     for (int j = 0; j < _owned_monitors_list->length(); j++) {

       jobject jobj = ((jvmtiMonitorStackDepthInfo*)_owned_monitors_list->at(j))->monitor;

       oop check = JNIHandles::resolve(jobj);

       if (check == obj) {

         // On stack monitor already collected during the stack walk.

         found = true;

         break;

       }

     }

     if (found == false) {

       // This is off stack monitor (e.g. acquired via jni MonitorEnter).

       jvmtiError err;

       jvmtiMonitorStackDepthInfo *jmsdi;

       err = _env->allocate(sizeof(jvmtiMonitorStackDepthInfo), (unsigned char **)&jmsdi);

       if (err != JVMTI_ERROR_NONE) {

         _error = err;

         return;

       }

       Handle hobj(obj);

       jmsdi->monitor = _env->jni_reference(_calling_thread, hobj);

       // stack depth is unknown for this monitor.

       jmsdi->stack_depth = -1;

       _owned_monitors_list->append(jmsdi);

     }

   }

 }