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*/
ClassLoaderData* SystemDictionary::register_loader(Handle class_loader, bool create_mirror_cld) { if (create_mirror_cld) { // Add a new class loader data to the graph. return ClassLoaderDataGraph::add(class_loader, true);
} else { return (class_loader() == NULL) ? ClassLoaderData::the_null_class_loader_data() :
ClassLoaderDataGraph::find_or_create(class_loader);
}
}
// ---------------------------------------------------------------------------- // Parallel class loading check
bool is_parallelCapable(Handle class_loader) { if (class_loader.is_null()) returntrue; return java_lang_ClassLoader::parallelCapable(class_loader());
} // ---------------------------------------------------------------------------- // ParallelDefineClass flag does not apply to bootclass loader bool is_parallelDefine(Handle class_loader) { if (class_loader.is_null()) returnfalse; if (AllowParallelDefineClass && java_lang_ClassLoader::parallelCapable(class_loader())) { returntrue;
} returnfalse;
}
// Returns true if the passed class loader is the builtin application class loader // or a custom system class loader. A customer system class loader can be // specified via -Djava.system.class.loader. bool SystemDictionary::is_system_class_loader(oop class_loader) { if (class_loader == NULL) { returnfalse;
} return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_AppClassLoader_klass() ||
class_loader == _java_system_loader.peek());
}
// Returns true if the passed class loader is the platform class loader. bool SystemDictionary::is_platform_class_loader(oop class_loader) { if (class_loader == NULL) { returnfalse;
} return (class_loader->klass() == vmClasses::jdk_internal_loader_ClassLoaders_PlatformClassLoader_klass());
}
Handle SystemDictionary::get_loader_lock_or_null(Handle class_loader) { // If class_loader is NULL or parallelCapable, the JVM doesn't acquire a lock while loading. if (is_parallelCapable(class_loader)) { return Handle();
} else { return class_loader;
}
}
// ---------------------------------------------------------------------------- // Resolving of classes
Symbol* SystemDictionary::class_name_symbol(constchar* name, Symbol* exception, TRAPS) { if (name == NULL) {
THROW_MSG_0(exception, "No class name given");
} if ((int)strlen(name) > Symbol::max_length()) { // It's impossible to create this class; the name cannot fit // into the constant pool.
Exceptions::fthrow(THREAD_AND_LOCATION, exception, "Class name exceeds maximum length of %d: %s",
Symbol::max_length(),
name); return NULL;
} // Callers should ensure that the name is never an illegal UTF8 string.
assert(UTF8::is_legal_utf8((constunsignedchar*)name, (int)strlen(name), false), "Class name is not a valid utf8 string.");
// Make a new symbol for the class name. return SymbolTable::new_symbol(name);
}
#ifdef ASSERT // Used to verify that class loading succeeded in adding k to the dictionary. void verify_dictionary_entry(Symbol* class_name, InstanceKlass* k) {
MutexLocker mu(SystemDictionary_lock);
ClassLoaderData* loader_data = k->class_loader_data();
Dictionary* dictionary = loader_data->dictionary();
assert(class_name == k->name(), "Must be the same");
InstanceKlass* kk = dictionary->find_class(JavaThread::current(), class_name);
assert(kk == k, "should be present in dictionary");
} #endif
staticvoid handle_resolution_exception(Symbol* class_name, bool throw_error, TRAPS) { if (HAS_PENDING_EXCEPTION) { // If we have a pending exception we forward it to the caller, unless throw_error is true, // in which case we have to check whether the pending exception is a ClassNotFoundException, // and convert it to a NoClassDefFoundError and chain the original ClassNotFoundException. if (throw_error && PENDING_EXCEPTION->is_a(vmClasses::ClassNotFoundException_klass())) {
ResourceMark rm(THREAD);
Handle e(THREAD, PENDING_EXCEPTION);
CLEAR_PENDING_EXCEPTION;
THROW_MSG_CAUSE(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string(), e);
} else { return; // the caller will throw the incoming exception
}
} // If the class is not found, ie, caller has checked that klass is NULL, throw the appropriate // error or exception depending on the value of throw_error.
ResourceMark rm(THREAD); if (throw_error) {
THROW_MSG(vmSymbols::java_lang_NoClassDefFoundError(), class_name->as_C_string());
} else {
THROW_MSG(vmSymbols::java_lang_ClassNotFoundException(), class_name->as_C_string());
}
}
// Forwards to resolve_or_null
Klass* SystemDictionary::resolve_or_fail(Symbol* class_name, Handle class_loader, Handle protection_domain, bool throw_error, TRAPS) {
Klass* klass = resolve_or_null(class_name, class_loader, protection_domain, THREAD); // Check for pending exception or null klass, and throw exception if (HAS_PENDING_EXCEPTION || klass == NULL) {
handle_resolution_exception(class_name, throw_error, CHECK_NULL);
} return klass;
}
// Forwards to resolve_array_class_or_null or resolve_instance_class_or_null
// Must be called for any superclass or superinterface resolution // during class definition to allow class circularity checking // superinterface callers: // parse_interfaces - from defineClass // superclass callers: // ClassFileParser - from defineClass // load_shared_class - while loading a class from shared archive // resolve_instance_class_or_null: // via: handle_parallel_super_load // when resolving a class that has an existing placeholder with // a saved superclass [i.e. a defineClass is currently in progress] // If another thread is trying to resolve the class, it must do // superclass checks on its own thread to catch class circularity and // to avoid deadlock. // // resolve_super_or_fail adds a LOAD_SUPER placeholder to the placeholder table before calling // resolve_instance_class_or_null. ClassCircularityError is detected when a LOAD_SUPER or LOAD_INSTANCE // placeholder for the same thread, class, classloader is found. // This can be seen with logging option: -Xlog:class+load+placeholders=debug. //
InstanceKlass* SystemDictionary::resolve_super_or_fail(Symbol* class_name,
Symbol* super_name,
Handle class_loader,
Handle protection_domain, bool is_superclass,
TRAPS) {
assert(super_name != NULL, "null superclass for resolving");
assert(!Signature::is_array(super_name), "invalid superclass name"); #if INCLUDE_CDS if (DumpSharedSpaces) { // Special processing for handling UNREGISTERED shared classes.
InstanceKlass* k = SystemDictionaryShared::lookup_super_for_unregistered_class(class_name,
super_name, is_superclass); if (k) { return k;
}
} #endif// INCLUDE_CDS
// If klass is already loaded, just return the superclass or superinterface. // Make sure there's a placeholder for the class_name before resolving. // This is used as a claim that this thread is currently loading superclass/classloader // and for ClassCircularity checks.
// can't throw error holding a lock bool throw_circularity_error = false;
{
MutexLocker mu(THREAD, SystemDictionary_lock);
InstanceKlass* klassk = dictionary->find_class(THREAD, class_name);
InstanceKlass* quicksuperk; // To support parallel loading: if class is done loading, just return the superclass // if the super_name matches class->super()->name() and if the class loaders match. // Otherwise, a LinkageError will be thrown later. if (klassk != NULL && is_superclass &&
((quicksuperk = klassk->java_super()) != NULL) &&
((quicksuperk->name() == super_name) &&
(quicksuperk->class_loader() == class_loader()))) { return quicksuperk;
} else { // Must check ClassCircularity before checking if superclass is already loaded.
PlaceholderEntry* probe = PlaceholderTable::get_entry(class_name, loader_data); if (probe && probe->check_seen_thread(THREAD, PlaceholderTable::LOAD_SUPER)) {
log_circularity_error(class_name, probe);
throw_circularity_error = true;
}
}
if (!throw_circularity_error) { // Be careful not to exit resolve_super without removing this placeholder.
PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(class_name,
loader_data,
PlaceholderTable::LOAD_SUPER,
super_name, THREAD);
}
}
if (throw_circularity_error) {
ResourceMark rm(THREAD);
THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), class_name->as_C_string());
}
// Resolve the superclass or superinterface, check results on return
InstanceKlass* superk =
SystemDictionary::resolve_instance_class_or_null(super_name,
class_loader,
protection_domain,
THREAD);
// Check for pending exception or null superk, and throw exception if (HAS_PENDING_EXCEPTION || superk == NULL) {
handle_resolution_exception(super_name, true, CHECK_NULL);
}
return superk;
}
// We only get here if this thread finds that another thread // has already claimed the placeholder token for the current operation, // but that other thread either never owned or gave up the // object lock // Waits on SystemDictionary_lock to indicate placeholder table updated // On return, caller must recheck placeholder table state // // We only get here if // 1) custom classLoader, i.e. not bootstrap classloader // 2) custom classLoader has broken the class loader objectLock // so another thread got here in parallel // // lockObject must be held. // Complicated dance due to lock ordering: // Must first release the classloader object lock to // allow initial definer to complete the class definition // and to avoid deadlock // Reclaim classloader lock object with same original recursion count // Must release SystemDictionary_lock after notify, since // class loader lock must be claimed before SystemDictionary_lock // to prevent deadlocks // // The notify allows applications that did an untimed wait() on // the classloader object lock to not hang. staticvoid double_lock_wait(JavaThread* thread, Handle lockObject) {
assert_lock_strong(SystemDictionary_lock);
assert(EnableWaitForParallelLoad, "Only called when enabling legacy parallel class loading logic " "for non-parallel capable class loaders");
assert(lockObject() != NULL, "lockObject must be non-NULL"); bool calledholdinglock
= ObjectSynchronizer::current_thread_holds_lock(thread, lockObject);
assert(calledholdinglock, "must hold lock for notify");
assert(!is_parallelCapable(lockObject), "lockObject must not be parallelCapable"); // These don't throw exceptions.
ObjectSynchronizer::notifyall(lockObject, thread);
intx recursions = ObjectSynchronizer::complete_exit(lockObject, thread);
SystemDictionary_lock->wait();
SystemDictionary_lock->unlock();
ObjectSynchronizer::reenter(lockObject, recursions, thread);
SystemDictionary_lock->lock();
}
// If the class in is in the placeholder table, class loading is in progress. // For cases where the application changes threads to load classes, it // is critical to ClassCircularity detection that we try loading // the superclass on the new thread internally, so we do parallel // superclass loading here. This avoids deadlock for ClassCircularity // detection for parallelCapable class loaders that lock on a per-class lock. staticvoid handle_parallel_super_load(Symbol* name,
Symbol* superclassname,
Handle class_loader,
Handle protection_domain, TRAPS) {
// superk is not used; resolve_super_or_fail is called for circularity check only.
Klass* superk = SystemDictionary::resolve_super_or_fail(name,
superclassname,
class_loader,
protection_domain, true,
CHECK);
}
// Bootstrap and non-parallel capable class loaders use the LOAD_INSTANCE placeholder to // wait for parallel class loading and to check for circularity error for Xcomp when loading // signature classes. // parallelCapable class loaders do NOT wait for parallel loads to complete staticbool needs_load_placeholder(Handle class_loader) { return class_loader.is_null() || !is_parallelCapable(class_loader);
}
// For bootstrap and non-parallelCapable class loaders, check and wait for // another thread to complete loading this class.
InstanceKlass* SystemDictionary::handle_parallel_loading(JavaThread* current,
Symbol* name,
ClassLoaderData* loader_data,
Handle lockObject, bool* throw_circularity_error) {
PlaceholderEntry* oldprobe = PlaceholderTable::get_entry(name, loader_data); if (oldprobe != NULL) { // only need check_seen_thread once, not on each loop // 6341374 java/lang/Instrument with -Xcomp if (oldprobe->check_seen_thread(current, PlaceholderTable::LOAD_INSTANCE)) {
log_circularity_error(name, oldprobe);
*throw_circularity_error = true; return NULL;
} else { // Wait until the first thread has finished loading this class. Also wait until all the // threads trying to load its superclass have removed their placeholders. while (oldprobe != NULL &&
(oldprobe->instance_load_in_progress() || oldprobe->super_load_in_progress())) {
// We only get here if the application has released the // classloader lock when another thread was in the middle of loading a // superclass/superinterface for this class, and now // this thread is also trying to load this class. // To minimize surprises, the first thread that started to // load a class should be the one to complete the loading // with the classfile it initially expected. // This logic has the current thread wait once it has done // all the superclass/superinterface loading it can, until // the original thread completes the class loading or fails // If it completes we will use the resulting InstanceKlass // which we will find below in the systemDictionary.
// Check if classloading completed while we were waiting
InstanceKlass* check = loader_data->dictionary()->find_class(current, name); if (check != NULL) { // Klass is already loaded, so just return it return check;
} // check if other thread failed to load and cleaned up
oldprobe = PlaceholderTable::get_entry(name, loader_data);
}
}
} return NULL;
}
// SystemDictionary::resolve_instance_class_or_null is the main function for class name resolution. // After checking if the InstanceKlass already exists, it checks for ClassCircularityError and // whether the thread must wait for loading in parallel. It eventually calls load_instance_class, // which will load the class via the bootstrap loader or call ClassLoader.loadClass(). // This can return NULL, an exception or an InstanceKlass.
InstanceKlass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
Handle class_loader,
Handle protection_domain,
TRAPS) { // name must be in the form of "java/lang/Object" -- cannot be "Ljava/lang/Object;"
assert(name != NULL && !Signature::is_array(name) &&
!Signature::has_envelope(name), "invalid class name");
EventClassLoad class_load_start_event;
HandleMark hm(THREAD);
// Fix for 4474172; see evaluation for more details
class_loader = Handle(THREAD, java_lang_ClassLoader::non_reflection_class_loader(class_loader()));
ClassLoaderData* loader_data = register_loader(class_loader);
Dictionary* dictionary = loader_data->dictionary();
// Do lookup to see if class already exists and the protection domain // has the right access. // This call uses find which checks protection domain already matches // All subsequent calls use find_class, and set loaded_class so that // before we return a result, we call out to java to check for valid protection domain.
InstanceKlass* probe = dictionary->find(THREAD, name, protection_domain); if (probe != NULL) return probe;
// Non-bootstrap class loaders will call out to class loader and // define via jvm/jni_DefineClass which will acquire the // class loader object lock to protect against multiple threads // defining the class in parallel by accident. // This lock must be acquired here so the waiter will find // any successful result in the SystemDictionary and not attempt // the define. // ParallelCapable class loaders and the bootstrap classloader // do not acquire lock here.
Handle lockObject = get_loader_lock_or_null(class_loader);
ObjectLocker ol(lockObject, THREAD);
assert(THREAD->can_call_java(), "can not load classes with compiler thread: class=%s, classloader=%s",
name->as_C_string(),
class_loader.is_null() ? "null" : class_loader->klass()->name()->as_C_string());
// Check again (after locking) if the class already exists in SystemDictionary
{
MutexLocker mu(THREAD, SystemDictionary_lock);
InstanceKlass* check = dictionary->find_class(THREAD, name); if (check != NULL) { // InstanceKlass is already loaded, but we still need to check protection domain below.
loaded_class = check;
} else {
PlaceholderEntry* placeholder = PlaceholderTable::get_entry(name, loader_data); if (placeholder != NULL && placeholder->super_load_in_progress()) {
super_load_in_progress = true;
superclassname = placeholder->supername();
assert(superclassname != NULL, "superclass has to have a name");
}
}
}
// If the class is in the placeholder table with super_class set, // handle superclass loading in progress. if (super_load_in_progress) {
handle_parallel_super_load(name, superclassname,
class_loader,
protection_domain,
CHECK_NULL);
}
// Add placeholder entry to record loading instance class // Four cases: // case 1. Bootstrap classloader // This classloader supports parallelism at the classloader level // but only allows a single thread to load a class/classloader pair. // The LOAD_INSTANCE placeholder is the mechanism for mutual exclusion. // case 2. parallelCapable user level classloaders // These class loaders lock a per-class object lock when ClassLoader.loadClass() // is called. A LOAD_INSTANCE placeholder isn't used for mutual exclusion. // case 3. traditional classloaders that rely on the classloader object lock // There should be no need for need for LOAD_INSTANCE, except: // case 4. traditional class loaders that break the classloader object lock // as a legacy deadlock workaround. Detection of this case requires that // this check is done while holding the classloader object lock, // and that lock is still held when calling classloader's loadClass. // For these classloaders, we ensure that the first requestor // completes the load and other requestors wait for completion.
{
MutexLocker mu(THREAD, SystemDictionary_lock); if (needs_load_placeholder(class_loader)) {
loaded_class = handle_parallel_loading(THREAD,
name,
loader_data,
lockObject,
&throw_circularity_error);
}
// Recheck if the class has been loaded for all class loader cases and // add a LOAD_INSTANCE placeholder while holding the SystemDictionary_lock. if (!throw_circularity_error && loaded_class == NULL) {
InstanceKlass* check = dictionary->find_class(THREAD, name); if (check != NULL) {
loaded_class = check;
} elseif (needs_load_placeholder(class_loader)) { // Add the LOAD_INSTANCE token. Threads will wait on loading to complete for this thread, // and check for ClassCircularityError with -Xcomp.
PlaceholderEntry* newprobe = PlaceholderTable::find_and_add(name, loader_data,
PlaceholderTable::LOAD_INSTANCE,
NULL,
THREAD);
load_placeholder_added = true;
}
}
}
// Must throw error outside of owning lock if (throw_circularity_error) {
assert(!HAS_PENDING_EXCEPTION && !load_placeholder_added, "circularity error cleanup");
ResourceMark rm(THREAD);
THROW_MSG_NULL(vmSymbols::java_lang_ClassCircularityError(), name->as_C_string());
}
// Be careful when modifying this code: once you have run // PlaceholderTable::find_and_add(PlaceholderTable::LOAD_INSTANCE), // you need to find_and_remove it before returning. // So be careful to not exit with a CHECK_ macro between these calls.
if (loaded_class == NULL) { // Do actual loading
loaded_class = load_instance_class(name, class_loader, THREAD);
}
if (load_placeholder_added) { // clean up placeholder entries for LOAD_INSTANCE success or error // This brackets the SystemDictionary updates for both defining // and initiating loaders
MutexLocker mu(THREAD, SystemDictionary_lock);
PlaceholderTable::find_and_remove(name, loader_data, PlaceholderTable::LOAD_INSTANCE, THREAD);
SystemDictionary_lock->notify_all();
}
}
if (HAS_PENDING_EXCEPTION || loaded_class == NULL) { return NULL;
}
if (class_load_start_event.should_commit()) {
post_class_load_event(&class_load_start_event, loaded_class, loader_data);
}
// Make sure we have the right class in the dictionary
DEBUG_ONLY(verify_dictionary_entry(name, loaded_class));
// Check if the protection domain is present it has the right access if (protection_domain() != NULL) { // Verify protection domain. If it fails an exception is thrown
dictionary->validate_protection_domain(loaded_class, class_loader, protection_domain, CHECK_NULL);
}
return loaded_class;
}
// This routine does not lock the system dictionary. // // Since readers don't hold a lock, we must make sure that system // dictionary entries are added to in a safe way (all links must // be updated in an MT-safe manner). All entries are removed during class // unloading, when this class loader is no longer referenced. // // Callers should be aware that an entry could be added just after // Dictionary is read here, so the caller will not see // the new entry.
// The result of this call should be consistent with the result // of the call to resolve_instance_class_or_null(). // See evaluation 6790209 and 4474172 for more details.
oop class_loader_oop = java_lang_ClassLoader::non_reflection_class_loader(class_loader());
ClassLoaderData* loader_data = ClassLoaderData::class_loader_data_or_null(class_loader_oop);
if (loader_data == NULL) { // If the ClassLoaderData has not been setup, // then the class loader has no entries in the dictionary. return NULL;
}
// Look for a loaded instance or array klass by name. Do not do any loading. // return NULL in case of error.
Klass* SystemDictionary::find_instance_or_array_klass(Thread* current,
Symbol* class_name,
Handle class_loader,
Handle protection_domain) {
Klass* k = NULL;
assert(class_name != NULL, "class name must be non NULL");
if (Signature::is_array(class_name)) { // The name refers to an array. Parse the name. // dimension and object_key in FieldArrayInfo are assigned as a // side-effect of this call
SignatureStream ss(class_name, false); int ndims = ss.skip_array_prefix(); // skip all '['s
BasicType t = ss.type(); if (t != T_OBJECT) {
k = Universe::typeArrayKlassObj(t);
} else {
k = SystemDictionary::find_instance_klass(current, ss.as_symbol(), class_loader, protection_domain);
} if (k != NULL) {
k = k->array_klass_or_null(ndims);
}
} else {
k = find_instance_klass(current, class_name, class_loader, protection_domain);
} return k;
}
// Note: this method is much like resolve_class_from_stream, but // does not publish the classes in the SystemDictionary. // Handles Lookup.defineClass hidden.
InstanceKlass* SystemDictionary::resolve_hidden_class_from_stream(
ClassFileStream* st,
Symbol* class_name,
Handle class_loader, const ClassLoadInfo& cl_info,
TRAPS) {
// - for hidden classes that are not strong: create a new CLD that has a class holder and // whose loader is the Lookup class's loader. // - for hidden class: add the class to the Lookup class's loader's CLD.
assert (cl_info.is_hidden(), "only used for hidden classes"); bool create_mirror_cld = !cl_info.is_strong_hidden();
loader_data = register_loader(class_loader, create_mirror_cld);
// Parse stream and create a klass.
InstanceKlass* k = KlassFactory::create_from_stream(st,
class_name,
loader_data,
cl_info,
CHECK_NULL);
assert(k != NULL, "no klass created");
// Hidden classes that are not strong must update ClassLoaderData holder // so that they can be unloaded when the mirror is no longer referenced. if (!cl_info.is_strong_hidden()) {
k->class_loader_data()->initialize_holder(Handle(THREAD, k->java_mirror()));
}
{
MutexLocker mu_r(THREAD, Compile_lock); // Add to class hierarchy, and do possible deoptimizations.
add_to_hierarchy(k); // But, do not add to dictionary.
}
k->link_class(CHECK_NULL);
// notify jvmti if (JvmtiExport::should_post_class_load()) {
JvmtiExport::post_class_load(THREAD, k);
} if (class_load_start_event.should_commit()) {
post_class_load_event(&class_load_start_event, k, loader_data);
}
return k;
}
// Add a klass to the system from a stream (called by jni_DefineClass and // JVM_DefineClass). // Note: class_name can be NULL. In that case we do not know the name of // the class until we have parsed the stream. // This function either returns an InstanceKlass or throws an exception. It does // not return NULL without a pending exception.
InstanceKlass* SystemDictionary::resolve_class_from_stream(
ClassFileStream* st,
Symbol* class_name,
Handle class_loader, const ClassLoadInfo& cl_info,
TRAPS) {
// Classloaders that support parallelism, e.g. bootstrap classloader, // do not acquire lock here
Handle lockObject = get_loader_lock_or_null(class_loader);
ObjectLocker ol(lockObject, THREAD);
// Parse the stream and create a klass. // Note that we do this even though this klass might // already be present in the SystemDictionary, otherwise we would not // throw potential ClassFormatErrors.
InstanceKlass* k = NULL;
#if INCLUDE_CDS if (!DumpSharedSpaces) {
k = SystemDictionaryShared::lookup_from_stream(class_name,
class_loader,
cl_info.protection_domain(),
st,
CHECK_NULL);
} #endif
if (k == NULL) {
k = KlassFactory::create_from_stream(st, class_name, loader_data, cl_info, CHECK_NULL);
}
assert(k != NULL, "no klass created");
Symbol* h_name = k->name();
assert(class_name == NULL || class_name == h_name, "name mismatch");
// Add class just loaded // If a class loader supports parallel classloading, handle parallel define requests. // find_or_define_instance_class may return a different InstanceKlass, // in which case the old k would be deallocated if (is_parallelCapable(class_loader)) {
k = find_or_define_instance_class(h_name, class_loader, k, CHECK_NULL);
} else {
define_instance_class(k, class_loader, THREAD);
// If defining the class throws an exception register 'k' for cleanup. if (HAS_PENDING_EXCEPTION) {
assert(k != NULL, "Must have an instance klass here!");
loader_data->add_to_deallocate_list(k); return NULL;
}
}
// Make sure we have an entry in the SystemDictionary on success
DEBUG_ONLY(verify_dictionary_entry(h_name, k));
#if INCLUDE_CDS // Check if a shared class can be loaded by the specific classloader. bool SystemDictionary::is_shared_class_visible(Symbol* class_name,
InstanceKlass* ik,
PackageEntry* pkg_entry,
Handle class_loader) {
assert(!ModuleEntryTable::javabase_moduleEntry()->is_patched(), "Cannot use sharing if java.base is patched");
// (1) Check if we are loading into the same loader as in dump time.
if (ik->is_shared_boot_class()) { if (class_loader() != NULL) { returnfalse;
}
} elseif (ik->is_shared_platform_class()) { if (class_loader() != java_platform_loader()) { returnfalse;
}
} elseif (ik->is_shared_app_class()) { if (class_loader() != java_system_loader()) { returnfalse;
}
} else { // ik was loaded by a custom loader during dump time if (class_loader_data(class_loader)->is_builtin_class_loader_data()) { returnfalse;
} else { returntrue;
}
}
// (2) Check if we are loading into the same module from the same location as in dump time.
if (MetaspaceShared::use_optimized_module_handling()) { // Class visibility has not changed between dump time and run time, so a class // that was visible (and thus archived) during dump time is always visible during runtime.
assert(SystemDictionary::is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader), "visibility cannot change between dump time and runtime"); returntrue;
} return is_shared_class_visible_impl(class_name, ik, pkg_entry, class_loader);
}
bool SystemDictionary::is_shared_class_visible_impl(Symbol* class_name,
InstanceKlass* ik,
PackageEntry* pkg_entry,
Handle class_loader) { int scp_index = ik->shared_classpath_index();
assert(!ik->is_shared_unregistered_class(), "this function should be called for built-in classes only");
assert(scp_index >= 0, "must be");
SharedClassPathEntry* scp_entry = FileMapInfo::shared_path(scp_index); if (!Universe::is_module_initialized()) {
assert(scp_entry != NULL, "must be"); // At this point, no modules have been defined yet. KlassSubGraphInfo::check_allowed_klass() // has restricted the classes can be loaded at this step to be only: // [1] scp_entry->is_modules_image(): classes in java.base, or, // [2] HeapShared::is_a_test_class_in_unnamed_module(ik): classes in bootstrap/unnamed module
assert(scp_entry->is_modules_image() || HeapShared::is_a_test_class_in_unnamed_module(ik), "only these classes can be loaded before the module system is initialized");
assert(class_loader.is_null(), "sanity"); returntrue;
}
if (pkg_entry == NULL) { // We might have looked up pkg_entry before the module system was initialized. // Need to reload it now.
TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name); if (pkg_name != NULL) {
pkg_entry = ClassLoaderData::class_loader_data(class_loader())->packages()->lookup_only(pkg_name);
}
}
if (was_archived_from_named_module) { if (should_be_in_named_module) { // Is the module loaded from the same location as during dump time?
visible = mod_entry->shared_path_index() == scp_index; if (visible) {
assert(!mod_entry->is_patched(), "cannot load archived classes for patched module");
}
} else { // During dump time, this class was in a named module, but at run time, this class should be // in an unnamed module.
visible = false;
}
} else { if (should_be_in_named_module) { // During dump time, this class was in an unnamed, but at run time, this class should be // in a named module.
visible = false;
} else {
visible = true;
}
}
// Quick check if the super type has been already loaded. // + Don't do it for unregistered classes -- they can be unloaded so // super_type->class_loader_data() could be stale. // + Don't check if loader data is NULL, ie. the super_type isn't fully loaded. if (!super_type->is_shared_unregistered_class() && super_type->class_loader_data() != NULL) { // Check if the superclass is loaded by the current class_loader
Symbol* name = super_type->name();
InstanceKlass* check = find_instance_klass(THREAD, name, class_loader, protection_domain); if (check == super_type) { returntrue;
}
}
Klass *found = resolve_super_or_fail(klass->name(), super_type->name(),
class_loader, protection_domain, is_superclass, CHECK_0); if (found == super_type) { returntrue;
} else { // The dynamically resolved super type is not the same as the one we used during dump time, // so we cannot use the class. returnfalse;
}
}
bool SystemDictionary::check_shared_class_super_types(InstanceKlass* ik, Handle class_loader,
Handle protection_domain, TRAPS) { // Check the superclass and interfaces. They must be the same // as in dump time, because the layout of <ik> depends on // the specific layout of ik->super() and ik->local_interfaces(). // // If unexpected superclass or interfaces are found, we cannot // load <ik> from the shared archive.
Array<InstanceKlass*>* interfaces = ik->local_interfaces(); int num_interfaces = interfaces->length(); for (int index = 0; index < num_interfaces; index++) { if (!check_shared_class_super_type(ik, interfaces->at(index), class_loader, protection_domain, false, THREAD)) { returnfalse;
}
}
returntrue;
}
InstanceKlass* SystemDictionary::load_shared_lambda_proxy_class(InstanceKlass* ik,
Handle class_loader,
Handle protection_domain,
PackageEntry* pkg_entry,
TRAPS) {
InstanceKlass* shared_nest_host = SystemDictionaryShared::get_shared_nest_host(ik);
assert(shared_nest_host->is_shared(), "nest host must be in CDS archive");
Symbol* cn = shared_nest_host->name();
Klass *s = resolve_or_fail(cn, class_loader, protection_domain, true, CHECK_NULL); if (s != shared_nest_host) { // The dynamically resolved nest_host is not the same as the one we used during dump time, // so we cannot use ik. return NULL;
} else {
assert(s->is_shared(), "must be");
}
if (loaded_ik != NULL) {
assert(shared_nest_host->is_same_class_package(ik), "lambda proxy class and its nest host must be in the same package");
}
// The lambda proxy class and its nest host have the same class loader and class loader data, // as verified in SystemDictionaryShared::add_lambda_proxy_class()
assert(shared_nest_host->class_loader() == class_loader(), "mismatched class loader");
assert(shared_nest_host->class_loader_data() == ClassLoaderData::class_loader_data(class_loader()), "mismatched class loader data");
ik->set_nest_host(shared_nest_host);
return loaded_ik;
}
InstanceKlass* SystemDictionary::load_shared_class(InstanceKlass* ik,
Handle class_loader,
Handle protection_domain, const ClassFileStream *cfs,
PackageEntry* pkg_entry,
TRAPS) {
assert(ik != NULL, "sanity");
assert(!ik->is_unshareable_info_restored(), "shared class can be loaded only once");
Symbol* class_name = ik->name();
if (!is_shared_class_visible(class_name, ik, pkg_entry, class_loader)) { return NULL;
}
if (!check_shared_class_super_types(ik, class_loader, protection_domain, THREAD)) { return NULL;
}
InstanceKlass* new_ik = NULL; // CFLH check is skipped for VM hidden classes (see KlassFactory::create_from_stream). // It will be skipped for shared VM hidden lambda proxy classes. if (!SystemDictionaryShared::is_hidden_lambda_proxy(ik)) {
new_ik = KlassFactory::check_shared_class_file_load_hook(
ik, class_name, class_loader, protection_domain, cfs, CHECK_NULL);
} if (new_ik != NULL) { // The class is changed by CFLH. Return the new class. The shared class is // not used. return new_ik;
}
// Adjust methods to recover missing data. They need addresses for // interpreter entry points and their default native method address // must be reset.
// Shared classes are all currently loaded by either the bootstrap or // internal parallel class loaders, so this will never cause a deadlock // on a custom class loader lock. // Since this class is already locked with parallel capable class // loaders, including the bootstrap loader via the placeholder table, // this lock is currently a nop.
// For boot loader, ensure that GetSystemPackage knows that a class in this // package was loaded. if (loader_data->is_the_null_class_loader_data()) { int path_index = ik->shared_classpath_index();
ik->set_classpath_index(path_index);
}
// notify a class loaded from shared object
ClassLoadingService::notify_class_loaded(ik, true/* shared class */);
}
// Find the package in the boot loader's package entry table.
TempNewSymbol pkg_name = ClassLoader::package_from_class_name(class_name); if (pkg_name != NULL) {
pkg_entry = loader_data->packages()->lookup_only(pkg_name);
}
// Prior to attempting to load the class, enforce the boot loader's // visibility boundaries. if (!Universe::is_module_initialized()) { // During bootstrapping, prior to module initialization, any // class attempting to be loaded must be checked against the // java.base packages in the boot loader's PackageEntryTable. // No class outside of java.base is allowed to be loaded during // this bootstrapping window. if (pkg_entry == NULL || pkg_entry->in_unnamed_module()) { // Class is either in the unnamed package or in // a named package within the unnamed module. Either // case is outside of java.base, do not attempt to // load the class post java.base definition. If // java.base has not been defined, let the class load // and its package will be checked later by // ModuleEntryTable::verify_javabase_packages. if (ModuleEntryTable::javabase_defined()) { return NULL;
}
} else { // Check that the class' package is defined within java.base.
ModuleEntry* mod_entry = pkg_entry->module();
Symbol* mod_entry_name = mod_entry->name(); if (mod_entry_name->fast_compare(vmSymbols::java_base()) != 0) { return NULL;
}
}
} else { // After the module system has been initialized, check if the class' // package is in a module defined to the boot loader. if (pkg_name == NULL || pkg_entry == NULL || pkg_entry->in_unnamed_module()) { // Class is either in the unnamed package, in a named package // within a module not defined to the boot loader or in a // a named package within the unnamed module. In all cases, // limit visibility to search for the class only in the boot // loader's append path. if (!ClassLoader::has_bootclasspath_append()) { // If there is no bootclasspath append entry, no need to continue // searching. return NULL;
}
search_only_bootloader_append = true;
}
}
// Prior to bootstrapping's module initialization, never load a class outside // of the boot loader's module path
assert(Universe::is_module_initialized() ||
!search_only_bootloader_append, "Attempt to load a class outside of boot loader's module path");
// Search for classes in the CDS archive.
InstanceKlass* k = NULL;
#if INCLUDE_CDS if (UseSharedSpaces)
{
PerfTraceTime vmtimer(ClassLoader::perf_shared_classload_time());
InstanceKlass* ik = SystemDictionaryShared::find_builtin_class(class_name); if (ik != NULL && ik->is_shared_boot_class() && !ik->shared_loading_failed()) {
SharedClassLoadingMark slm(THREAD, ik);
k = load_shared_class(ik, class_loader, Handle(), NULL, pkg_entry, CHECK_NULL);
}
} #endif
if (k == NULL) { // Use VM class loader
PerfTraceTime vmtimer(ClassLoader::perf_sys_classload_time());
k = ClassLoader::load_class(class_name, search_only_bootloader_append, CHECK_NULL);
}
// find_or_define_instance_class may return a different InstanceKlass if (k != NULL) {
CDS_ONLY(SharedClassLoadingMark slm(THREAD, k);)
k = find_or_define_instance_class(class_name, class_loader, k, CHECK_NULL);
} return k;
} else { // Use user specified class loader to load class. Call loadClass operation on class_loader.
ResourceMark rm(THREAD);
// Translate to external class name format, i.e., convert '/' chars to '.'
Handle string = java_lang_String::externalize_classname(class_name, CHECK_NULL);
// Call public unsynchronized loadClass(String) directly for all class loaders. // For parallelCapable class loaders, JDK >=7, loadClass(String, boolean) will // acquire a class-name based lock rather than the class loader object lock. // JDK < 7 already acquire the class loader lock in loadClass(String, boolean).
JavaCalls::call_virtual(&result,
class_loader,
spec_klass,
vmSymbols::loadClass_name(),
vmSymbols::string_class_signature(),
string,
CHECK_NULL);
// Primitive classes return null since forName() can not be // used to obtain any of the Class objects representing primitives or void if ((obj != NULL) && !(java_lang_Class::is_primitive(obj))) {
InstanceKlass* k = InstanceKlass::cast(java_lang_Class::as_Klass(obj)); // For user defined Java class loaders, check that the name returned is // the same as that requested. This check is done for the bootstrap // loader when parsing the class file. if (class_name == k->name()) { return k;
}
} // Class is not found or has the wrong name, return NULL return NULL;
}
}
// If everything was OK (no exceptions, no null return value), and // class_loader is NOT the defining loader, do a little more bookkeeping. if (loaded_class != NULL &&
loaded_class->class_loader() != class_loader()) {
// Record dependency for non-parent delegation. // This recording keeps the defining class loader of the klass (loaded_class) found // from being unloaded while the initiating class loader is loaded // even if the reference to the defining class loader is dropped // before references to the initiating class loader.
ClassLoaderData* loader_data = class_loader_data(class_loader);
loader_data->record_dependency(loaded_class);
{ // Grabbing the Compile_lock prevents systemDictionary updates // during compilations.
MutexLocker mu(THREAD, Compile_lock);
update_dictionary(THREAD, loaded_class, class_loader);
}
if (JvmtiExport::should_post_class_load()) {
JvmtiExport::post_class_load(THREAD, loaded_class);
}
} return loaded_class;
}
ClassLoaderData* loader_data = k->class_loader_data();
assert(loader_data->class_loader() == class_loader(), "they must be the same");
// Bootstrap and other parallel classloaders don't acquire a lock, // they use placeholder token. // If a parallelCapable class loader calls define_instance_class instead of // find_or_define_instance_class to get here, we have a timing // hole with systemDictionary updates and check_constraints if (!is_parallelCapable(class_loader)) {
assert(ObjectSynchronizer::current_thread_holds_lock(THREAD,
get_loader_lock_or_null(class_loader)), "define called without lock");
}
// Check class-loading constraints. Throw exception if violation is detected. // Grabs and releases SystemDictionary_lock // The check_constraints/find_class call and update_dictionary sequence // must be "atomic" for a specific class/classloader pair so we never // define two different instanceKlasses for that class/classloader pair. // Existing classloaders will call define_instance_class with the // classloader lock held // Parallel classloaders will call find_or_define_instance_class // which will require a token to perform the define class
Symbol* name_h = k->name();
Dictionary* dictionary = loader_data->dictionary();
check_constraints(k, class_loader, true, CHECK);
// Register class just loaded with class loader (placed in ArrayList) // Note we do this before updating the dictionary, as this can // fail with an OutOfMemoryError (if it does, we will *not* put this // class in the dictionary and will not update the class hierarchy). // JVMTI FollowReferences needs to find the classes this way. if (k->class_loader() != NULL) {
methodHandle m(THREAD, Universe::loader_addClass_method());
JavaValue result(T_VOID);
JavaCallArguments args(class_loader);
args.push_oop(Handle(THREAD, k->java_mirror()));
JavaCalls::call(&result, m, &args, CHECK);
}
// Add the new class. We need recompile lock during update of CHA.
{
MutexLocker mu_r(THREAD, Compile_lock);
// Add to class hierarchy, and do possible deoptimizations.
add_to_hierarchy(k);
// Add to systemDictionary - so other classes can see it. // Grabs and releases SystemDictionary_lock
update_dictionary(THREAD, k, class_loader);
}
// Support parallel classloading // All parallel class loaders, including bootstrap classloader // lock a placeholder entry for this class/class_loader pair // to allow parallel defines of different classes for this class loader // With AllowParallelDefine flag==true, in case they do not synchronize around // FindLoadedClass/DefineClass, calls, we check for parallel // loading for them, wait if a defineClass is in progress // and return the initial requestor's results // This flag does not apply to the bootstrap classloader. // With AllowParallelDefine flag==false, call through to define_instance_class // which will throw LinkageError: duplicate class definition. // False is the requested default. // For better performance, the class loaders should synchronize // findClass(), i.e. FindLoadedClass/DefineClassIfAbsent or they // potentially waste time reading and parsing the bytestream. // Note: VM callers should ensure consistency of k/class_name,class_loader // Be careful when modifying this code: once you have run // PlaceholderTable::find_and_add(PlaceholderTable::DEFINE_CLASS), // you need to find_and_remove it before returning. // So be careful to not exit with a CHECK_ macro between these calls.
InstanceKlass* SystemDictionary::find_or_define_helper(Symbol* class_name, Handle class_loader,
InstanceKlass* k, TRAPS) {
Symbol* name_h = k->name(); // passed in class_name may be null
ClassLoaderData* loader_data = class_loader_data(class_loader);
Dictionary* dictionary = loader_data->dictionary();
// Hold SD lock around find_class and placeholder creation for DEFINE_CLASS
{
MutexLocker mu(THREAD, SystemDictionary_lock); // First check if class already defined if (is_parallelDefine(class_loader)) {
InstanceKlass* check = dictionary->find_class(THREAD, name_h); if (check != NULL) { return check;
}
}
// Acquire define token for this class/classloader
PlaceholderEntry* probe = PlaceholderTable::find_and_add(name_h, loader_data,
PlaceholderTable::DEFINE_CLASS, NULL, THREAD); // Wait if another thread defining in parallel // All threads wait - even those that will throw duplicate class: otherwise // caller is surprised by LinkageError: duplicate, but findLoadedClass fails // if other thread has not finished updating dictionary while (probe->definer() != NULL) {
SystemDictionary_lock->wait();
} // Only special cases allow parallel defines and can use other thread's results // Other cases fall through, and may run into duplicate defines // caught by finding an entry in the SystemDictionary if (is_parallelDefine(class_loader) && (probe->instance_klass() != NULL)) {
InstanceKlass* ik = probe->instance_klass();
PlaceholderTable::find_and_remove(name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
SystemDictionary_lock->notify_all(); #ifdef ASSERT
InstanceKlass* check = dictionary->find_class(THREAD, name_h);
assert(check != NULL, "definer missed recording success"); #endif return ik;
} else { // This thread will define the class (even if earlier thread tried and had an error)
probe->set_definer(THREAD);
}
}
// If a class loader supports parallel classloading handle parallel define requests. // find_or_define_instance_class may return a different InstanceKlass
InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_name, Handle class_loader,
InstanceKlass* k, TRAPS) {
InstanceKlass* defined_k = find_or_define_helper(class_name, class_loader, k, THREAD); // Clean up original InstanceKlass if duplicate or error if (!HAS_PENDING_EXCEPTION && defined_k != k) { // If a parallel capable class loader already defined this class, register 'k' for cleanup.
assert(defined_k != NULL, "Should have a klass if there's no exception");
k->class_loader_data()->add_to_deallocate_list(k);
} elseif (HAS_PENDING_EXCEPTION) {
assert(defined_k == NULL, "Should not have a klass if there's an exception");
k->class_loader_data()->add_to_deallocate_list(k);
} return defined_k;
}
// ---------------------------------------------------------------------------- // Update hierarchy. This is done before the new klass has been added to the SystemDictionary. The Compile_lock // is held, to ensure that the compiler is not using the class hierarchy, and that deoptimization will kick in // before a new class is used.
k->set_init_state(InstanceKlass::loaded); // make sure init_state store is already done. // The compiler reads the hierarchy outside of the Compile_lock. // Access ordering is used to add to hierarchy.
// Link into hierarchy.
k->append_to_sibling_list(); // add to superklass/sibling list
k->process_interfaces(); // handle all "implements" declarations
// Now flush all code that depended on old class hierarchy. // Note: must be done *after* linking k into the hierarchy (was bug 12/9/97) if (Universe::is_fully_initialized()) {
CodeCache::flush_dependents_on(k);
}
}
// ---------------------------------------------------------------------------- // GC support
// Assumes classes in the SystemDictionary are only unloaded at a safepoint bool SystemDictionary::do_unloading(GCTimer* gc_timer) {
bool unloading_occurred; bool is_concurrent = !SafepointSynchronize::is_at_safepoint();
{
GCTraceTime(Debug, gc, phases) t("ClassLoaderData", gc_timer);
assert_locked_or_safepoint(ClassLoaderDataGraph_lock); // caller locks. // First, mark for unload all ClassLoaderData referencing a dead class loader.
unloading_occurred = ClassLoaderDataGraph::do_unloading(); if (unloading_occurred) {
MutexLocker ml2(is_concurrent ? Module_lock : NULL);
JFR_ONLY(Jfr::on_unloading_classes();)
MANAGEMENT_ONLY(FinalizerService::purge_unloaded();)
MutexLocker ml1(is_concurrent ? SystemDictionary_lock : NULL);
ClassLoaderDataGraph::clean_module_and_package_info();
LoaderConstraintTable::purge_loader_constraints();
ResolutionErrorTable::purge_resolution_errors();
}
}
if (unloading_occurred) {
SymbolTable::trigger_cleanup();
if (java_lang_System::allow_security_manager()) { // Oops referenced by the protection domain cache table may get unreachable independently // of the class loader (eg. cached protection domain oops). So we need to // explicitly unlink them here. // All protection domain oops are linked to the caller class, so if nothing // unloads, this is not needed.
ProtectionDomainCacheTable::trigger_cleanup();
} else {
assert(ProtectionDomainCacheTable::number_of_entries() == 0, "should be empty");
}
// Resolve basic classes
vmClasses::resolve_all(CHECK); // Resolve classes used by archived heap objects if (UseSharedSpaces) {
HeapShared::resolve_classes(THREAD);
}
}
// Constraints on class loaders. The details of the algorithm can be // found in the OOPSLA'98 paper "Dynamic Class Loading in the Java // Virtual Machine" by Sheng Liang and Gilad Bracha. The basic idea is // that the dictionary needs to maintain a set of constraints that // must be satisfied by all classes in the dictionary. // if defining is true, then LinkageError if already in dictionary // if initiating loader, then ok if InstanceKlass matches existing entry
{
Symbol *name = k->name();
ClassLoaderData *loader_data = class_loader_data(class_loader);
MutexLocker mu(THREAD, SystemDictionary_lock);
InstanceKlass* check = loader_data->dictionary()->find_class(THREAD, name); if (check != NULL) { // If different InstanceKlass - duplicate class definition, // else - ok, class loaded by a different thread in parallel. // We should only have found it if it was done loading and ok to use.
if (throwException == false) { if (LoaderConstraintTable::check_or_update(k, class_loader, name) == false) {
throwException = true;
ss.print("loader constraint violation: loader %s", loader_data->loader_name_and_id());
ss.print(" wants to load %s %s.",
k->external_kind(), k->external_name());
Klass *existing_klass = LoaderConstraintTable::find_constrained_klass(name, class_loader); if (existing_klass != NULL && existing_klass->class_loader() != class_loader()) {
ss.print(" A different %s with the same name was previously loaded by %s. (%s)",
existing_klass->external_kind(),
existing_klass->class_loader_data()->loader_name_and_id(),
existing_klass->class_in_module_of_loader(false, true));
} else {
ss.print(" (%s)", k->class_in_module_of_loader(false, true));
}
}
}
}
// Throw error now if needed (cannot throw while holding // SystemDictionary_lock because of rank ordering) if (throwException == true) {
THROW_MSG(vmSymbols::java_lang_LinkageError(), ss.as_string());
}
}
// Update class loader data dictionary - done after check_constraint and add_to_hierarchy // have been called. void SystemDictionary::update_dictionary(JavaThread* current,
InstanceKlass* k,
Handle class_loader) { // Compile_lock prevents systemDictionary updates during compilations
assert_locked_or_safepoint(Compile_lock);
Symbol* name = k->name();
ClassLoaderData *loader_data = class_loader_data(class_loader);
{
MutexLocker mu1(SystemDictionary_lock);
// Make a new dictionary entry.
Dictionary* dictionary = loader_data->dictionary();
InstanceKlass* sd_check = dictionary->find_class(current, name); if (sd_check == NULL) {
dictionary->add_klass(current, name, k);
}
SystemDictionary_lock->notify_all();
}
}
// Try to find a class name using the loader constraints. The // loader constraints might know about a class that isn't fully loaded // yet and these will be ignored.
Klass* SystemDictionary::find_constrained_instance_or_array_klass(
Thread* current, Symbol* class_name, Handle class_loader) {
// First see if it has been loaded directly. // Force the protection domain to be null. (This removes protection checks.)
Handle no_protection_domain;
Klass* klass = find_instance_or_array_klass(current, class_name, class_loader,
no_protection_domain); if (klass != NULL) return klass;
// Now look to see if it has been loaded elsewhere, and is subject to // a loader constraint that would require this loader to return the // klass that is already loaded. if (Signature::is_array(class_name)) { // For array classes, their Klass*s are not kept in the // constraint table. The element Klass*s are.
SignatureStream ss(class_name, false); int ndims = ss.skip_array_prefix(); // skip all '['s
BasicType t = ss.type(); if (t != T_OBJECT) {
klass = Universe::typeArrayKlassObj(t);
} else {
MutexLocker mu(current, SystemDictionary_lock);
klass = LoaderConstraintTable::find_constrained_klass(ss.as_symbol(), class_loader);
} // If element class already loaded, allocate array klass if (klass != NULL) {
klass = klass->array_klass_or_null(ndims);
}
} else {
MutexLocker mu(current, SystemDictionary_lock); // Non-array classes are easy: simply check the constraint table.
klass = LoaderConstraintTable::find_constrained_klass(class_name, class_loader);
}
if (!Signature::is_array(class_name)) {
constraint_name = class_name;
} else { // For array classes, their Klass*s are not kept in the // constraint table. The element classes are.
SignatureStream ss(class_name, false);
ss.skip_array_prefix(); // skip all '['s if (!ss.has_envelope()) { returntrue; // primitive types always pass
}
constraint_name = ss.as_symbol(); // Increment refcount to keep constraint_name alive after // SignatureStream is destructed. It will be decremented below // before returning.
constraint_name->increment_refcount();
}
// Add entry to resolution error table to record the error when the first // attempt to resolve a reference to a class has failed. void SystemDictionary::add_resolution_error(const constantPoolHandle& pool, int which,
Symbol* error, Symbol* message,
Symbol* cause, Symbol* cause_msg) {
{
MutexLocker ml(Thread::current(), SystemDictionary_lock);
ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which); if (entry == NULL) {
ResolutionErrorTable::add_entry(pool, which, error, message, cause, cause_msg);
}
}
}
// Delete a resolution error for RedefineClasses for a constant pool is going away void SystemDictionary::delete_resolution_error(ConstantPool* pool) {
ResolutionErrorTable::delete_entry(pool);
}
// Lookup resolution error table. Returns error if found, otherwise NULL.
Symbol* SystemDictionary::find_resolution_error(const constantPoolHandle& pool, int which,
Symbol** message, Symbol** cause, Symbol** cause_msg) {
// Add an entry to resolution error table to record an error in resolving or // validating a nest host. This is used to construct informative error // messages when IllegalAccessError's occur. If an entry already exists it will // be updated with the nest host error message.
void SystemDictionary::add_nest_host_error(const constantPoolHandle& pool, int which, constchar* message) {
{
MutexLocker ml(Thread::current(), SystemDictionary_lock);
ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which); if (entry != NULL && entry->nest_host_error() == NULL) { // An existing entry means we had a true resolution failure (LinkageError) with our nest host, but we // still want to add the error message for the higher-level access checks to report. We should // only reach here under the same error condition, so we can ignore the potential race with setting // the message. If we see it is already set then we can ignore it.
entry->set_nest_host_error(message);
} else {
ResolutionErrorTable::add_entry(pool, which, message);
}
}
}
// Lookup any nest host error constchar* SystemDictionary::find_nest_host_error(const constantPoolHandle& pool, int which) {
{
MutexLocker ml(Thread::current(), SystemDictionary_lock);
ResolutionErrorEntry* entry = ResolutionErrorTable::find_entry(pool, which); if (entry != NULL) { return entry->nest_host_error();
} else { return NULL;
}
}
}
// Signature constraints ensure that callers and callees agree about // the meaning of type names in their signatures. This routine is the // intake for constraints. It collects them from several places: // // * LinkResolver::resolve_method (if check_access is true) requires // that the resolving class (the caller) and the defining class of // the resolved method (the callee) agree on each type in the // method's signature. // // * LinkResolver::resolve_interface_method performs exactly the same // checks. // // * LinkResolver::resolve_field requires that the constant pool // attempting to link to a field agree with the field's defining // class about the type of the field signature. // // * klassVtable::initialize_vtable requires that, when a class // overrides a vtable entry allocated by a superclass, that the // overriding method (i.e., the callee) agree with the superclass // on each type in the method's signature. // // * klassItable::initialize_itable requires that, when a class fills // in its itables, for each non-abstract method installed in an // itable, the method (i.e., the callee) agree with the interface // on each type in the method's signature. // // All those methods have a boolean (check_access, checkconstraints) // which turns off the checks. This is used from specialized contexts // such as bootstrapping, dumping, and debugging. // // No direct constraint is placed between the class and its // supertypes. Constraints are only placed along linked relations // between callers and callees. When a method overrides or implements // an abstract method in a supertype (superclass or interface), the // constraints are placed as if the supertype were the caller to the // overriding method. (This works well, since callers to the // supertype have already established agreement between themselves and // the supertype.) As a result of all this, a class can disagree with // its supertype about the meaning of a type name, as long as that // class neither calls a relevant method of the supertype, nor is // called (perhaps via an override) from the supertype. // // // SystemDictionary::check_signature_loaders(sig, klass_being_linked, l1, l2) // // Make sure all class components (including arrays) in the given // signature will be resolved to the same class in both loaders. // Returns the name of the type that failed a loader constraint check, or // NULL if no constraint failed. No exception except OOME is thrown. // Arrays are not added to the loader constraint table, their elements are.
Symbol* SystemDictionary::check_signature_loaders(Symbol* signature,
Klass* klass_being_linked,
Handle loader1, Handle loader2, bool is_method) { // Nothing to do if loaders are the same. if (loader1() == loader2()) { return NULL;
}
for (SignatureStream ss(signature, is_method); !ss.is_done(); ss.next()) { if (ss.is_reference()) {
Symbol* sig = ss.as_symbol(); // Note: In the future, if template-like types can take // arguments, we will want to recognize them and dig out class // names hiding inside the argument lists. if (!add_loader_constraint(sig, klass_being_linked, loader1, loader2)) { return sig;
}
}
} return NULL;
}
constint iid_as_int = vmIntrinsics::as_int(iid);
assert(MethodHandles::is_signature_polymorphic(iid) &&
MethodHandles::is_signature_polymorphic_intrinsic(iid) &&
iid != vmIntrinsics::_invokeGeneric, "must be a known MH intrinsic iid=%d: %s", iid_as_int, vmIntrinsics::name_at(iid));
{
MutexLocker ml(THREAD, InvokeMethodTable_lock);
InvokeMethodKey key(signature, iid_as_int);
Method** met = _invoke_method_intrinsic_table.get(key); if (met != nullptr) { return *met;
}
bool throw_error = false; // This function could get an OOM but it is safe to call inside of a lock because // throwing OutOfMemoryError doesn't call Java code.
methodHandle m = Method::make_method_handle_intrinsic(iid, signature, CHECK_NULL); if (!Arguments::is_interpreter_only() || iid == vmIntrinsics::_linkToNative) { // Generate a compiled form of the MH intrinsic // linkToNative doesn't have interpreter-specific implementation, so always has to go through compiled version.
AdapterHandlerLibrary::create_native_wrapper(m); // Check if have the compiled code.
throw_error = (!m->has_compiled_code());
}
if (!throw_error) {
signature->make_permanent(); // The signature is never unloaded. bool created = _invoke_method_intrinsic_table.put(key, m());
assert(created, "must be since we still hold the lock");
assert(Arguments::is_interpreter_only() || (m->has_compiled_code() &&
m->code()->entry_point() == m->from_compiled_entry()), "MH intrinsic invariant"); return m();
}
}
// Throw error outside of the lock.
THROW_MSG_NULL(vmSymbols::java_lang_VirtualMachineError(), "Out of space in CodeCache for method handle intrinsic");
}
// Helper for unpacking the return value from linkMethod and linkCallSite. static Method* unpack_method_and_appendix(Handle mname,
Klass* accessing_klass,
objArrayHandle appendix_box,
Handle* appendix_result,
TRAPS) { if (mname.not_null()) {
Method* m = java_lang_invoke_MemberName::vmtarget(mname()); if (m != NULL) {
oop appendix = appendix_box->obj_at(0);
LogTarget(Info, methodhandles) lt; if (lt.develop_is_enabled()) {
ResourceMark rm(THREAD);
LogStream ls(lt);
ls.print("Linked method=" INTPTR_FORMAT ": ", p2i(m));
m->print_on(&ls); if (appendix != NULL) { ls.print("appendix = "); appendix->print_on(&ls); }
ls.cr();
}
(*appendix_result) = Handle(THREAD, appendix); // the target is stored in the cpCache and if a reference to this // MemberName is dropped we need a way to make sure the // class_loader containing this method is kept alive.
methodHandle mh(THREAD, m); // record_dependency can safepoint.
ClassLoaderData* this_key = accessing_klass->class_loader_data();
this_key->record_dependency(m->method_holder()); return mh();
}
}
THROW_MSG_NULL(vmSymbols::java_lang_LinkageError(), "bad value from MethodHandleNatives");
}
// This should not happen. JDK code should take care of that. if (accessing_klass == NULL || method_type.is_null()) {
THROW_MSG_NULL(vmSymbols::java_lang_InternalError(), "bad invokehandle");
}
// Decide if we can globally cache a lookup of this class, to be returned to any client that asks. // We must ensure that all class loaders everywhere will reach this class, for any client. // This is a safe bet for public classes in java.lang, such as Object and String. // We also include public classes in java.lang.invoke, because they appear frequently in system-level method types. // Out of an abundance of caution, we do not include any other classes, not even for packages like java.util. staticbool is_always_visible_class(oop mirror) {
Klass* klass = java_lang_Class::as_Klass(mirror); if (klass->is_objArray_klass()) {
klass = ObjArrayKlass::cast(klass)->bottom_klass(); // check element type
} if (klass->is_typeArray_klass()) { returntrue; // primitive array
}
assert(klass->is_instance_klass(), "%s", klass->external_name()); return klass->is_public() &&
(InstanceKlass::cast(klass)->is_same_class_package(vmClasses::Object_klass()) || // java.lang
InstanceKlass::cast(klass)->is_same_class_package(vmClasses::MethodHandle_klass())); // java.lang.invoke
}
// Find or construct the Java mirror (java.lang.Class instance) for // the given field type signature, as interpreted relative to the // given class loader. Handles primitives, void, references, arrays, // and all other reflectable types, except method types. // N.B. Code in reflection should use this entry point.
Handle SystemDictionary::find_java_mirror_for_type(Symbol* signature,
Klass* accessing_klass,
Handle class_loader,
Handle protection_domain,
SignatureStream::FailureMode failure_mode,
TRAPS) {
assert(accessing_klass == NULL || (class_loader.is_null() && protection_domain.is_null()), "one or the other, or perhaps neither");
// What we have here must be a valid field descriptor, // and all valid field descriptors are supported. // Produce the same java.lang.Class that reflection reports. if (accessing_klass != NULL) {
class_loader = Handle(THREAD, accessing_klass->class_loader());
protection_domain = Handle(THREAD, accessing_klass->protection_domain());
}
ResolvingSignatureStream ss(signature, class_loader, protection_domain, false);
oop mirror_oop = ss.as_java_mirror(failure_mode, CHECK_NH); if (mirror_oop == NULL) { return Handle(); // report failure this way
}
Handle mirror(THREAD, mirror_oop);
// Ask Java code to find or construct a java.lang.invoke.MethodType for the given // signature, as interpreted relative to the given class loader. // Because of class loader constraints, all method handle usage must be // consistent with this loader.
Handle SystemDictionary::find_method_handle_type(Symbol* signature,
Klass* accessing_klass,
TRAPS) {
Handle empty;
OopHandle* o;
{
MutexLocker ml(THREAD, InvokeMethodTable_lock);
o = _invoke_method_type_table.get(signature);
}
if (o != nullptr) {
oop mt = o->resolve();
assert(java_lang_invoke_MethodType::is_instance(mt), ""); return Handle(THREAD, mt);
} elseif (!THREAD->can_call_java()) {
warning("SystemDictionary::find_method_handle_type called from compiler thread"); // FIXME return Handle(); // do not attempt from within compiler, unless it was cached
}
Handle class_loader, protection_domain; if (accessing_klass != NULL) {
class_loader = Handle(THREAD, accessing_klass->class_loader());
protection_domain = Handle(THREAD, accessing_klass->protection_domain());
} bool can_be_cached = true; int npts = ArgumentCount(signature).size();
objArrayHandle pts = oopFactory::new_objArray_handle(vmClasses::Class_klass(), npts, CHECK_(empty)); int arg = 0;
Handle rt; // the return type from the signature
ResourceMark rm(THREAD); for (SignatureStream ss(signature); !ss.is_done(); ss.next()) {
oop mirror = NULL; if (can_be_cached) { // Use neutral class loader to lookup candidate classes to be placed in the cache.
mirror = ss.as_java_mirror(Handle(), Handle(),
SignatureStream::ReturnNull, CHECK_(empty)); if (mirror == NULL || (ss.is_reference() && !is_always_visible_class(mirror))) { // Fall back to accessing_klass context.
can_be_cached = false;
}
} if (!can_be_cached) { // Resolve, throwing a real error if it doesn't work.
mirror = ss.as_java_mirror(class_loader, protection_domain,
SignatureStream::NCDFError, CHECK_(empty));
}
assert(mirror != NULL, "%s", ss.as_symbol()->as_C_string()); if (ss.at_return_type())
rt = Handle(THREAD, mirror); else
pts->obj_at_put(arg++, mirror);
if (can_be_cached) { // We can cache this MethodType inside the JVM.
MutexLocker ml(THREAD, InvokeMethodTable_lock); bool created = false;
assert(method_type != NULL, "unexpected null");
OopHandle* h = _invoke_method_type_table.get(signature); if (h == nullptr) {
signature->make_permanent(); // The signature is never unloaded.
OopHandle elem = OopHandle(Universe::vm_global(), method_type()); bool created = _invoke_method_type_table.put(signature, elem);
assert(created, "better be created");
}
} // report back to the caller with the MethodType return method_type;
}
// Ask Java code to find or construct a method handle constant.
Handle SystemDictionary::link_method_handle_constant(Klass* caller, int ref_kind, //e.g., JVM_REF_invokeVirtual
Klass* callee,
Symbol* name,
Symbol* signature,
TRAPS) {
Handle empty; if (caller == NULL) {
THROW_MSG_(vmSymbols::java_lang_InternalError(), "bad MH constant", empty);
}
Handle name_str = java_lang_String::create_from_symbol(name, CHECK_(empty));
Handle signature_str = java_lang_String::create_from_symbol(signature, CHECK_(empty));
// Put symbolic info from the MH constant into freshly created MemberName and resolve it.
Handle mname = vmClasses::MemberName_klass()->allocate_instance_handle(CHECK_(empty));
java_lang_invoke_MemberName::set_clazz(mname(), callee->java_mirror());
java_lang_invoke_MemberName::set_name (mname(), name_str());
java_lang_invoke_MemberName::set_type (mname(), signature_str());
java_lang_invoke_MemberName::set_flags(mname(), MethodHandles::ref_kind_to_flags(ref_kind));
if (ref_kind == JVM_REF_invokeVirtual &&
MethodHandles::is_signature_polymorphic_public_name(callee, name)) { // Skip resolution for public signature polymorphic methods such as // j.l.i.MethodHandle.invoke()/invokeExact() and those on VarHandle // They require appendix argument which MemberName resolution doesn't handle. // There's special logic on JDK side to handle them // (see MethodHandles.linkMethodHandleConstant() and MethodHandles.findVirtualForMH()).
} else {
MethodHandles::resolve_MemberName(mname, caller, 0, false/*speculative_resolve*/, CHECK_(empty));
}
// After method/field resolution succeeded, it's safe to resolve MH signature as well.
Handle type = MethodHandles::resolve_MemberName_type(mname, caller, CHECK_(empty));
// call java.lang.invoke.MethodHandleNatives::linkMethodHandleConstant(Class caller, int refKind, Class callee, String name, Object type) -> MethodHandle
JavaCallArguments args;
args.push_oop(Handle(THREAD, caller->java_mirror())); // the referring class
args.push_int(ref_kind);
args.push_oop(Handle(THREAD, callee->java_mirror())); // the target class
args.push_oop(name_str);
args.push_oop(type);
JavaValue result(T_OBJECT);
JavaCalls::call_static(&result,
vmClasses::MethodHandleNatives_klass(),
vmSymbols::linkMethodHandleConstant_name(),
vmSymbols::linkMethodHandleConstant_signature(),
&args, CHECK_(empty)); return Handle(THREAD, result.get_oop());
}
// Ask Java to run a bootstrap method, in order to create a dynamic call site // while linking an invokedynamic op, or compute a constant for Dynamic_info CP entry // with linkage results being stored back into the bootstrap specifier. void SystemDictionary::invoke_bootstrap_method(BootstrapInfo& bootstrap_specifier, TRAPS) { // Resolve the bootstrap specifier, its name, type, and static arguments
bootstrap_specifier.resolve_bsm(CHECK);
// This should not happen. JDK code should take care of that. if (bootstrap_specifier.caller() == NULL || bootstrap_specifier.type_arg().is_null()) {
THROW_MSG(vmSymbols::java_lang_InternalError(), "Invalid bootstrap method invocation with no caller or type argument");
}
bool is_indy = bootstrap_specifier.is_method_call();
objArrayHandle appendix_box; if (is_indy) { // Some method calls may require an appendix argument. Arrange to receive it.
appendix_box = oopFactory::new_objArray_handle(vmClasses::Object_klass(), 1, CHECK);
assert(appendix_box->obj_at(0) == NULL, "");
}
// Utility for dumping dictionaries.
SystemDictionaryDCmd::SystemDictionaryDCmd(outputStream* output, bool heap) :
DCmdWithParser(output, heap),
_verbose("-verbose", "Dump the content of each dictionary entry for all class loaders", "BOOLEAN", false, "false") {
_dcmdparser.add_dcmd_option(&_verbose);
}
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