Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 2012, 2014, 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.

  *

  */

 // A ClassLoaderData identifies the full set of class types that a class

 // loader's name resolution strategy produces for a given configuration of the

 // class loader.

 // Class types in the ClassLoaderData may be defined by from class file binaries

 // provided by the class loader, or from other class loader it interacts with

 // according to its name resolution strategy.

 //

 // Class loaders that implement a deterministic name resolution strategy

 // (including with respect to their delegation behavior), such as the boot, the

 // extension, and the system loaders of the JDK's built-in class loader

 // hierarchy, always produce the same linkset for a given configuration.

 //

 // ClassLoaderData carries information related to a linkset (e.g.,

 // metaspace holding its klass definitions).

 // The System Dictionary and related data structures (e.g., placeholder table,

 // loader constraints table) as well as the runtime representation of classes

 // only reference ClassLoaderData.

 //

 // Instances of java.lang.ClassLoader holds a pointer to a ClassLoaderData that

 // that represent the loader's "linking domain" in the JVM.

 //

 // The bootstrap loader (represented by NULL) also has a ClassLoaderData,

 // the singleton class the_null_class_loader_data().

 #include "precompiled.hpp"

 #include "classfile/classLoaderData.hpp"

 #include "classfile/classLoaderData.inline.hpp"

 #include "classfile/javaClasses.hpp"

 #include "classfile/metadataOnStackMark.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "code/codeCache.hpp"

 #include "memory/gcLocker.hpp"

 #include "memory/metadataFactory.hpp"

 #include "memory/metaspaceShared.hpp"

 #include "memory/oopFactory.hpp"

 #include "runtime/jniHandles.hpp"

 #include "runtime/mutex.hpp"

 #include "runtime/safepoint.hpp"

 #include "runtime/synchronizer.hpp"

 #include "utilities/growableArray.hpp"

 #include "utilities/macros.hpp"

 #include "utilities/ostream.hpp"

 #if INCLUDE_TRACE

  #include "trace/tracing.hpp"

 #endif

 ClassLoaderData * ClassLoaderData::_the_null_class_loader_data = NULL;

 ClassLoaderData::ClassLoaderData(Handle h_class_loader, bool is_anonymous, Dependencies dependencies) :

   _class_loader(h_class_loader()),

   _is_anonymous(is_anonymous), _keep_alive(is_anonymous), // initially

   _metaspace(NULL), _unloading(false), _klasses(NULL),

   _claimed(0), _jmethod_ids(NULL), _handles(NULL), _deallocate_list(NULL),

   _next(NULL), _dependencies(dependencies),

   _metaspace_lock(new Mutex(Monitor::leaf+1, "Metaspace allocation lock", true)) {

     // empty

 }

 void ClassLoaderData::init_dependencies(TRAPS) {

   assert(!Universe::is_fully_initialized(), "should only be called when initializing");

   assert(is_the_null_class_loader_data(), "should only call this for the null class loader");

   _dependencies.init(CHECK);

 }

 void ClassLoaderData::Dependencies::init(TRAPS) {

   // Create empty dependencies array to add to. CMS requires this to be

   // an oop so that it can track additions via card marks.  We think.

   _list_head = oopFactory::new_objectArray(2, CHECK);

 }

 bool ClassLoaderData::claim() {

   if (_claimed == 1) {

     return false;

   }

   return (int) Atomic::cmpxchg(1, &_claimed, 0) == 0;

 }

 void ClassLoaderData::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {

   if (must_claim && !claim()) {

     return;

   }

   f->do_oop(&_class_loader);

   _dependencies.oops_do(f);

   _handles->oops_do(f);

   if (klass_closure != NULL) {

     classes_do(klass_closure);

   }

 }

 void ClassLoaderData::Dependencies::oops_do(OopClosure* f) {

   f->do_oop((oop*)&_list_head);

 }

 void ClassLoaderData::classes_do(KlassClosure* klass_closure) {

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     klass_closure->do_klass(k);

     assert(k != k->next_link(), "no loops!");

   }

 }

 void ClassLoaderData::classes_do(void f(Klass * const)) {

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     f(k);

   }

 }

 void ClassLoaderData::loaded_classes_do(KlassClosure* klass_closure) {

   // Lock to avoid classes being modified/added/removed during iteration

   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     // Do not filter ArrayKlass oops here...

     if (k->oop_is_array() || (k->oop_is_instance() && InstanceKlass::cast(k)->is_loaded())) {

       klass_closure->do_klass(k);

     }

   }

 }

 void ClassLoaderData::classes_do(void f(InstanceKlass*)) {

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     if (k->oop_is_instance()) {

       f(InstanceKlass::cast(k));

     }

     assert(k != k->next_link(), "no loops!");

   }

 }

 void ClassLoaderData::record_dependency(Klass* k, TRAPS) {

   ClassLoaderData * const from_cld = this;

   ClassLoaderData * const to_cld = k->class_loader_data();

   // Dependency to the null class loader data doesn't need to be recorded

   // because the null class loader data never goes away.

   if (to_cld->is_the_null_class_loader_data()) {

     return;

   }

   oop to;

   if (to_cld->is_anonymous()) {

     // Anonymous class dependencies are through the mirror.

     to = k->java_mirror();

   } else {

     to = to_cld->class_loader();

     // If from_cld is anonymous, even if it's class_loader is a parent of 'to'

     // we still have to add it.  The class_loader won't keep from_cld alive.

     if (!from_cld->is_anonymous()) {

       // Check that this dependency isn't from the same or parent class_loader

       oop from = from_cld->class_loader();

       oop curr = from;

       while (curr != NULL) {

         if (curr == to) {

           return; // this class loader is in the parent list, no need to add it.

         }

         curr = java_lang_ClassLoader::parent(curr);

       }

     }

   }

   // It's a dependency we won't find through GC, add it. This is relatively rare

   // Must handle over GC point.

   Handle dependency(THREAD, to);

   from_cld->_dependencies.add(dependency, CHECK);

 }

 void ClassLoaderData::Dependencies::add(Handle dependency, TRAPS) {

   // Check first if this dependency is already in the list.

   // Save a pointer to the last to add to under the lock.

   objArrayOop ok = _list_head;

   objArrayOop last = NULL;

   while (ok != NULL) {

     last = ok;

     if (ok->obj_at(0) == dependency()) {

       // Don't need to add it

       return;

     }

     ok = (objArrayOop)ok->obj_at(1);

   }

   // Must handle over GC points

   assert (last != NULL, "dependencies should be initialized");

   objArrayHandle last_handle(THREAD, last);

   // Create a new dependency node with fields for (class_loader or mirror, next)

   objArrayOop deps = oopFactory::new_objectArray(2, CHECK);

   deps->obj_at_put(0, dependency());

   // Must handle over GC points

   objArrayHandle new_dependency(THREAD, deps);

   // Add the dependency under lock

   locked_add(last_handle, new_dependency, THREAD);

 }

 void ClassLoaderData::Dependencies::locked_add(objArrayHandle last_handle,

                                                objArrayHandle new_dependency,

                                                Thread* THREAD) {

   // Have to lock and put the new dependency on the end of the dependency

   // array so the card mark for CMS sees that this dependency is new.

   // Can probably do this lock free with some effort.

   ObjectLocker ol(Handle(THREAD, _list_head), THREAD);

   oop loader_or_mirror = new_dependency->obj_at(0);

   // Since the dependencies are only added, add to the end.

   objArrayOop end = last_handle();

   objArrayOop last = NULL;

   while (end != NULL) {

     last = end;

     // check again if another thread added it to the end.

     if (end->obj_at(0) == loader_or_mirror) {

       // Don't need to add it

       return;

     }

     end = (objArrayOop)end->obj_at(1);

   }

   assert (last != NULL, "dependencies should be initialized");

   // fill in the first element with the oop in new_dependency.

   if (last->obj_at(0) == NULL) {

     last->obj_at_put(0, new_dependency->obj_at(0));

   } else {

     last->obj_at_put(1, new_dependency());

   }

 }

 void ClassLoaderDataGraph::clear_claimed_marks() {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     cld->clear_claimed();

   }

 }

 void ClassLoaderData::add_class(Klass* k) {

   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

   Klass* old_value = _klasses;

   k->set_next_link(old_value);

   // link the new item into the list

   _klasses = k;

   if (TraceClassLoaderData && Verbose && k->class_loader_data() != NULL) {

     ResourceMark rm;

     tty->print_cr("[TraceClassLoaderData] Adding k: " PTR_FORMAT " %s to CLD: "

                   PTR_FORMAT " loader: " PTR_FORMAT " %s",

                   k,

                   k->external_name(),

                   k->class_loader_data(),

                   (void *)k->class_loader(),

                   loader_name());

   }

 }

 // This is called by InstanceKlass::deallocate_contents() to remove the

 // scratch_class for redefine classes.  We need a lock because there it may not

 // be called at a safepoint if there's an error.

 void ClassLoaderData::remove_class(Klass* scratch_class) {

   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

   Klass* prev = NULL;

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     if (k == scratch_class) {

       if (prev == NULL) {

         _klasses = k->next_link();

       } else {

         Klass* next = k->next_link();

         prev->set_next_link(next);

       }

       return;

     }

     prev = k;

     assert(k != k->next_link(), "no loops!");

   }

   ShouldNotReachHere();   // should have found this class!!

 }

 void ClassLoaderData::unload() {

   _unloading = true;

   // Tell serviceability tools these classes are unloading

   classes_do(InstanceKlass::notify_unload_class);

   if (TraceClassLoaderData) {

     ResourceMark rm;

     tty->print("[ClassLoaderData: unload loader data "PTR_FORMAT, this);

     tty->print(" for instance "PTR_FORMAT" of %s", (void *)class_loader(),

                loader_name());

     if (is_anonymous()) {

       tty->print(" for anonymous class  "PTR_FORMAT " ", _klasses);

     }

     tty->print_cr("]");

   }

 }

 bool ClassLoaderData::is_alive(BoolObjectClosure* is_alive_closure) const {

   bool alive =

     is_anonymous() ?

        is_alive_closure->do_object_b(_klasses->java_mirror()) :

        class_loader() == NULL || is_alive_closure->do_object_b(class_loader());

   assert(!alive || claimed(), "must be claimed");

   return alive;

 }

 ClassLoaderData::~ClassLoaderData() {

   // Release C heap structures for all the classes.

   classes_do(InstanceKlass::release_C_heap_structures);

   Metaspace *m = _metaspace;

   if (m != NULL) {

     _metaspace = NULL;

     // release the metaspace

     delete m;

     // release the handles

     if (_handles != NULL) {

       JNIHandleBlock::release_block(_handles);

       _handles = NULL;

     }

   }

   // Clear all the JNI handles for methods

   // These aren't deallocated and are going to look like a leak, but that's

   // needed because we can't really get rid of jmethodIDs because we don't

   // know when native code is going to stop using them.  The spec says that

   // they're "invalid" but existing programs likely rely on their being

   // NULL after class unloading.

   if (_jmethod_ids != NULL) {

     Method::clear_jmethod_ids(this);

   }

   // Delete lock

   delete _metaspace_lock;

   // Delete free list

   if (_deallocate_list != NULL) {

     delete _deallocate_list;

   }

 }

 /**

  * Returns true if this class loader data is for the extension class loader.

  */

 bool ClassLoaderData::is_ext_class_loader_data() const {

   return SystemDictionary::is_ext_class_loader(class_loader());

 }

 Metaspace* ClassLoaderData::metaspace_non_null() {

   assert(!DumpSharedSpaces, "wrong metaspace!");

   // If the metaspace has not been allocated, create a new one.  Might want

   // to create smaller arena for Reflection class loaders also.

   // The reason for the delayed allocation is because some class loaders are

   // simply for delegating with no metadata of their own.

   if (_metaspace == NULL) {

     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

     // Check again if metaspace has been allocated while we were getting this lock.

     if (_metaspace != NULL) {

       return _metaspace;

     }

     if (this == the_null_class_loader_data()) {

       assert (class_loader() == NULL, "Must be");

       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::BootMetaspaceType));

     } else if (is_anonymous()) {

       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {

         tty->print_cr("is_anonymous: %s", class_loader()->klass()->internal_name());

       }

       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::AnonymousMetaspaceType));

     } else if (class_loader()->is_a(SystemDictionary::reflect_DelegatingClassLoader_klass())) {

       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {

         tty->print_cr("is_reflection: %s", class_loader()->klass()->internal_name());

       }

       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::ReflectionMetaspaceType));

     } else {

       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::StandardMetaspaceType));

     }

   }

   return _metaspace;

 }

 JNIHandleBlock* ClassLoaderData::handles() const           { return _handles; }

 void ClassLoaderData::set_handles(JNIHandleBlock* handles) { _handles = handles; }

 jobject ClassLoaderData::add_handle(Handle h) {

   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

   if (handles() == NULL) {

     set_handles(JNIHandleBlock::allocate_block());

   }

   return handles()->allocate_handle(h());

 }

 // Add this metadata pointer to be freed when it's safe.  This is only during

 // class unloading because Handles might point to this metadata field.

 void ClassLoaderData::add_to_deallocate_list(Metadata* m) {

   // Metadata in shared region isn't deleted.

   if (!m->is_shared()) {

     MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

     if (_deallocate_list == NULL) {

       _deallocate_list = new (ResourceObj::C_HEAP, mtClass) GrowableArray<Metadata*>(100, true);

     }

     _deallocate_list->append_if_missing(m);

   }

 }

 // Deallocate free metadata on the free list.  How useful the PermGen was!

 void ClassLoaderData::free_deallocate_list() {

   // Don't need lock, at safepoint

   assert(SafepointSynchronize::is_at_safepoint(), "only called at safepoint");

   if (_deallocate_list == NULL) {

     return;

   }

   // Go backwards because this removes entries that are freed.

   for (int i = _deallocate_list->length() - 1; i >= 0; i--) {

     Metadata* m = _deallocate_list->at(i);

     if (!m->on_stack()) {

       _deallocate_list->remove_at(i);

       // There are only three types of metadata that we deallocate directly.

       // Cast them so they can be used by the template function.

       if (m->is_method()) {

         MetadataFactory::free_metadata(this, (Method*)m);

       } else if (m->is_constantPool()) {

         MetadataFactory::free_metadata(this, (ConstantPool*)m);

       } else if (m->is_klass()) {

         MetadataFactory::free_metadata(this, (InstanceKlass*)m);

       } else {

         ShouldNotReachHere();

       }

     }

   }

 }

 // These anonymous class loaders are to contain classes used for JSR292

 ClassLoaderData* ClassLoaderData::anonymous_class_loader_data(oop loader, TRAPS) {

   // Add a new class loader data to the graph.

   return ClassLoaderDataGraph::add(loader, true, CHECK_NULL);

 }

 const char* ClassLoaderData::loader_name() {

   // Handles null class loader

   return SystemDictionary::loader_name(class_loader());

 }

 #ifndef PRODUCT

 // Define to dump klasses

 #undef CLD_DUMP_KLASSES

 void ClassLoaderData::dump(outputStream * const out) {

   ResourceMark rm;

   out->print("ClassLoaderData CLD: "PTR_FORMAT", loader: "PTR_FORMAT", loader_klass: "PTR_FORMAT" %s {",

       this, (void *)class_loader(),

       class_loader() != NULL ? class_loader()->klass() : NULL, loader_name());

   if (claimed()) out->print(" claimed ");

   if (is_unloading()) out->print(" unloading ");

   out->print(" handles " INTPTR_FORMAT, handles());

   out->cr();

   if (metaspace_or_null() != NULL) {

     out->print_cr("metaspace: " PTR_FORMAT, metaspace_or_null());

     metaspace_or_null()->dump(out);

   } else {

     out->print_cr("metaspace: NULL");

   }

 #ifdef CLD_DUMP_KLASSES

   if (Verbose) {

     ResourceMark rm;

     Klass* k = _klasses;

     while (k != NULL) {

       out->print_cr("klass "PTR_FORMAT", %s, CT: %d, MUT: %d", k, k->name()->as_C_string(),

           k->has_modified_oops(), k->has_accumulated_modified_oops());

       assert(k != k->next_link(), "no loops!");

       k = k->next_link();

     }

   }

 #endif  // CLD_DUMP_KLASSES

 #undef CLD_DUMP_KLASSES

   if (_jmethod_ids != NULL) {

     Method::print_jmethod_ids(this, out);

   }

   out->print_cr("}");

 }

 #endif // PRODUCT

 void ClassLoaderData::verify() {

   oop cl = class_loader();

   guarantee(this == class_loader_data(cl) || is_anonymous(), "Must be the same");

   guarantee(cl != NULL || this == ClassLoaderData::the_null_class_loader_data() || is_anonymous(), "must be");

   // Verify the integrity of the allocated space.

   if (metaspace_or_null() != NULL) {

     metaspace_or_null()->verify();

   }

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     guarantee(k->class_loader_data() == this, "Must be the same");

     k->verify();

     assert(k != k->next_link(), "no loops!");

   }

 }

 bool ClassLoaderData::contains_klass(Klass* klass) {

   for (Klass* k = _klasses; k != NULL; k = k->next_link()) {

     if (k == klass) return true;

   }

   return false;

 }

 // GC root of class loader data created.

 ClassLoaderData* ClassLoaderDataGraph::_head = NULL;

 ClassLoaderData* ClassLoaderDataGraph::_unloading = NULL;

 ClassLoaderData* ClassLoaderDataGraph::_saved_head = NULL;

 // Add a new class loader data node to the list.  Assign the newly created

 // ClassLoaderData into the java/lang/ClassLoader object as a hidden field

 ClassLoaderData* ClassLoaderDataGraph::add(Handle loader, bool is_anonymous, TRAPS) {

   // We need to allocate all the oops for the ClassLoaderData before allocating the

   // actual ClassLoaderData object.

   ClassLoaderData::Dependencies dependencies(CHECK_NULL);

   No_Safepoint_Verifier no_safepoints; // we mustn't GC until we've installed the

                                        // ClassLoaderData in the graph since the CLD

                                        // contains unhandled oops

   ClassLoaderData* cld = new ClassLoaderData(loader, is_anonymous, dependencies);

   if (!is_anonymous) {

     ClassLoaderData** cld_addr = java_lang_ClassLoader::loader_data_addr(loader());

     // First, Atomically set it

     ClassLoaderData* old = (ClassLoaderData*) Atomic::cmpxchg_ptr(cld, cld_addr, NULL);

     if (old != NULL) {

       delete cld;

       // Returns the data.

       return old;

     }

   }

   // We won the race, and therefore the task of adding the data to the list of

   // class loader data

   ClassLoaderData** list_head = &_head;

   ClassLoaderData* next = _head;

   do {

     cld->set_next(next);

     ClassLoaderData* exchanged = (ClassLoaderData*)Atomic::cmpxchg_ptr(cld, list_head, next);

     if (exchanged == next) {

       if (TraceClassLoaderData) {

         ResourceMark rm;

         tty->print("[ClassLoaderData: ");

         tty->print("create class loader data "PTR_FORMAT, cld);

         tty->print(" for instance "PTR_FORMAT" of %s", (void *)cld->class_loader(),

                    cld->loader_name());

         tty->print_cr("]");

       }

       return cld;

     }

     next = exchanged;

   } while (true);

 }

 void ClassLoaderDataGraph::oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     cld->oops_do(f, klass_closure, must_claim);

   }

 }

 void ClassLoaderDataGraph::keep_alive_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     if (cld->keep_alive()) {

       cld->oops_do(f, klass_closure, must_claim);

     }

   }

 }

 void ClassLoaderDataGraph::always_strong_oops_do(OopClosure* f, KlassClosure* klass_closure, bool must_claim) {

   if (ClassUnloading) {

     ClassLoaderData::the_null_class_loader_data()->oops_do(f, klass_closure, must_claim);

     // keep any special CLDs alive.

     ClassLoaderDataGraph::keep_alive_oops_do(f, klass_closure, must_claim);

   } else {

     ClassLoaderDataGraph::oops_do(f, klass_closure, must_claim);

   }

 }

 void ClassLoaderDataGraph::classes_do(KlassClosure* klass_closure) {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     cld->classes_do(klass_closure);

   }

 }

 void ClassLoaderDataGraph::classes_do(void f(Klass* const)) {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     cld->classes_do(f);

   }

 }

 void ClassLoaderDataGraph::loaded_classes_do(KlassClosure* klass_closure) {

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     cld->loaded_classes_do(klass_closure);

   }

 }

 void ClassLoaderDataGraph::classes_unloading_do(void f(Klass* const)) {

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

   for (ClassLoaderData* cld = _unloading; cld != NULL; cld = cld->next()) {

     cld->classes_do(f);

   }

 }

 GrowableArray<ClassLoaderData*>* ClassLoaderDataGraph::new_clds() {

   assert(_head == NULL || _saved_head != NULL, "remember_new_clds(true) not called?");

   GrowableArray<ClassLoaderData*>* array = new GrowableArray<ClassLoaderData*>();

   // The CLDs in [_head, _saved_head] were all added during last call to remember_new_clds(true);

   ClassLoaderData* curr = _head;

   while (curr != _saved_head) {

     if (!curr->claimed()) {

       array->push(curr);

       if (TraceClassLoaderData) {

         tty->print("[ClassLoaderData] found new CLD: ");

         curr->print_value_on(tty);

         tty->cr();

       }

     }

     curr = curr->_next;

   }

   return array;

 }

 // For profiling and hsfind() only.  Otherwise, this is unsafe (and slow).  This

 // is done lock free to avoid lock inversion problems.  It is safe because

 // new ClassLoaderData are added to the end of the CLDG, and only removed at

 // safepoint.  The _unloading list can be deallocated concurrently with CMS so

 // this doesn't look in metaspace for classes that have been unloaded.

 bool ClassLoaderDataGraph::contains(const void* x) {

   if (DumpSharedSpaces) {

     // There are only two metaspaces to worry about.

     ClassLoaderData* ncld = ClassLoaderData::the_null_class_loader_data();

     return (ncld->ro_metaspace()->contains(x) || ncld->rw_metaspace()->contains(x));

   }

   if (UseSharedSpaces && MetaspaceShared::is_in_shared_space(x)) {

     return true;

   }

   for (ClassLoaderData* cld = _head; cld != NULL; cld = cld->next()) {

     if (cld->metaspace_or_null() != NULL && cld->metaspace_or_null()->contains(x)) {

       return true;

     }

   }

   // Do not check unloading list because deallocation can be concurrent.

   return false;

 }

 #ifndef PRODUCT

 bool ClassLoaderDataGraph::contains_loader_data(ClassLoaderData* loader_data) {

   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {

     if (loader_data == data) {

       return true;

     }

   }

   return false;

 }

 #endif // PRODUCT

 // Move class loader data from main list to the unloaded list for unloading

 // and deallocation later.

 bool ClassLoaderDataGraph::do_unloading(BoolObjectClosure* is_alive_closure) {

   ClassLoaderData* data = _head;

   ClassLoaderData* prev = NULL;

   bool seen_dead_loader = false;

   // mark metadata seen on the stack and code cache so we can delete

   // unneeded entries.

   bool has_redefined_a_class = JvmtiExport::has_redefined_a_class();

   MetadataOnStackMark md_on_stack;

   while (data != NULL) {

     if (data->keep_alive() || data->is_alive(is_alive_closure)) {

       if (has_redefined_a_class) {

         data->classes_do(InstanceKlass::purge_previous_versions);

       }

       data->free_deallocate_list();

       prev = data;

       data = data->next();

       continue;

     }

     seen_dead_loader = true;

     ClassLoaderData* dead = data;

     dead->unload();

     data = data->next();

     // Remove from loader list.

     // This class loader data will no longer be found

     // in the ClassLoaderDataGraph.

     if (prev != NULL) {

       prev->set_next(data);

     } else {

       assert(dead == _head, "sanity check");

       _head = data;

     }

     dead->set_next(_unloading);

     _unloading = dead;

   }

   if (seen_dead_loader) {

     post_class_unload_events();

   }

   return seen_dead_loader;

 }

 void ClassLoaderDataGraph::purge() {

   ClassLoaderData* list = _unloading;

   _unloading = NULL;

   ClassLoaderData* next = list;

   while (next != NULL) {

     ClassLoaderData* purge_me = next;

     next = purge_me->next();

     delete purge_me;

   }

   Metaspace::purge();

 }

 void ClassLoaderDataGraph::post_class_unload_events(void) {

 #if INCLUDE_TRACE

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

   if (Tracing::enabled()) {

     if (Tracing::is_event_enabled(TraceClassUnloadEvent)) {

       assert(_unloading != NULL, "need class loader data unload list!");

       _class_unload_time = Ticks::now();

       classes_unloading_do(&class_unload_event);

     }

     Tracing::on_unloading_classes();

   }

 #endif

 }

 // CDS support

 // Global metaspaces for writing information to the shared archive.  When

 // application CDS is supported, we may need one per metaspace, so this

 // sort of looks like it.

 Metaspace* ClassLoaderData::_ro_metaspace = NULL;

 Metaspace* ClassLoaderData::_rw_metaspace = NULL;

 static bool _shared_metaspaces_initialized = false;

 // Initialize shared metaspaces (change to call from somewhere not lazily)

 void ClassLoaderData::initialize_shared_metaspaces() {

   assert(DumpSharedSpaces, "only use this for dumping shared spaces");

   assert(this == ClassLoaderData::the_null_class_loader_data(),

          "only supported for null loader data for now");

   assert (!_shared_metaspaces_initialized, "only initialize once");

   MutexLockerEx ml(metaspace_lock(),  Mutex::_no_safepoint_check_flag);

   _ro_metaspace = new Metaspace(_metaspace_lock, Metaspace::ROMetaspaceType);

   _rw_metaspace = new Metaspace(_metaspace_lock, Metaspace::ReadWriteMetaspaceType);

   _shared_metaspaces_initialized = true;

 }

 Metaspace* ClassLoaderData::ro_metaspace() {

   assert(_ro_metaspace != NULL, "should already be initialized");

   return _ro_metaspace;

 }

 Metaspace* ClassLoaderData::rw_metaspace() {

   assert(_rw_metaspace != NULL, "should already be initialized");

   return _rw_metaspace;

 }

 ClassLoaderDataGraphMetaspaceIterator::ClassLoaderDataGraphMetaspaceIterator() {

   _data = ClassLoaderDataGraph::_head;

 }

 ClassLoaderDataGraphMetaspaceIterator::~ClassLoaderDataGraphMetaspaceIterator() {}

 #ifndef PRODUCT

 // callable from debugger

 extern "C" int print_loader_data_graph() {

   ClassLoaderDataGraph::dump_on(tty);

   return 0;

 }

 void ClassLoaderDataGraph::verify() {

   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {

     data->verify();

   }

 }

 void ClassLoaderDataGraph::dump_on(outputStream * const out) {

   for (ClassLoaderData* data = _head; data != NULL; data = data->next()) {

     data->dump(out);

   }

   MetaspaceAux::dump(out);

 }

 #endif // PRODUCT

 void ClassLoaderData::print_value_on(outputStream* out) const {

   if (class_loader() == NULL) {

     out->print("NULL class_loader");

   } else {

     out->print("class loader "PTR_FORMAT, this);

     class_loader()->print_value_on(out);

   }

 }

 #if INCLUDE_TRACE

 Ticks ClassLoaderDataGraph::_class_unload_time;

 void ClassLoaderDataGraph::class_unload_event(Klass* const k) {

   // post class unload event

   EventClassUnload event(UNTIMED);

   event.set_endtime(_class_unload_time);

   event.set_unloadedClass(k);

   oop defining_class_loader = k->class_loader();

   event.set_definingClassLoader(defining_class_loader != NULL ?

                                 defining_class_loader->klass() : (Klass*)NULL);

   event.commit();

 }

 #endif /* INCLUDE_TRACE */