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8184289: Obsolete -XX:+UnsyncloadClass and -XX:+MustCallLoadClassInternal options

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Add comments, fix a small issue with the boot loader, and add an assert.

Reviewed-by: coleenp, alanb, acorn, dholmes
This commit is contained in:
Harold Seigel 2018-02-21 11:18:52 -05:00
parent 6be7841937
commit 7d1735efbb
12 changed files with 37 additions and 143 deletions
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101
src/hotspot/share/classfile/systemDictionary.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1997, 2018, 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
@ -106,7 +106,6 @@ InstanceKlass* SystemDictionary::_box_klasses[T_VOID+1] = { NULL /*,
oop SystemDictionary::_java_system_loader = NULL;
oop SystemDictionary::_java_platform_loader = NULL;
bool SystemDictionary::_has_loadClassInternal = false;
bool SystemDictionary::_has_checkPackageAccess = false;
// lazily initialized klass variables
@ -159,7 +158,7 @@ ClassLoaderData* SystemDictionary::register_loader(Handle class_loader, TRAPS) {
// Parallel class loading check
bool SystemDictionary::is_parallelCapable(Handle class_loader) {
if (UnsyncloadClass || class_loader.is_null()) return true;
if (class_loader.is_null()) return true;
if (AlwaysLockClassLoader) return false;
return java_lang_ClassLoader::parallelCapable(class_loader());
}
@ -503,8 +502,7 @@ void SystemDictionary::validate_protection_domain(InstanceKlass* klass,
//
// We only get here if
// 1) custom classLoader, i.e. not bootstrap classloader
// 2) UnsyncloadClass not set
// 3) custom classLoader has broken the class loader objectLock
// 2) custom classLoader has broken the class loader objectLock
// so another thread got here in parallel
//
// lockObject must be held.
@ -594,7 +592,6 @@ InstanceKlass* SystemDictionary::handle_parallel_super_load(
} else {
placeholder = placeholders()->get_entry(p_index, p_hash, name, loader_data);
if (placeholder && placeholder->super_load_in_progress() ){
// Before UnsyncloadClass:
// 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
@ -687,9 +684,9 @@ Klass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
// 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 Classloaders and the bootstrap classloader,
// or all classloaders with UnsyncloadClass do not acquire lock here
// the define.
// ParallelCapable Classloaders and the bootstrap classloader
// do not acquire lock here.
bool DoObjectLock = true;
if (is_parallelCapable(class_loader)) {
DoObjectLock = false;
@ -765,14 +762,11 @@ Klass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
// 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.
// case 3. UnsyncloadClass - don't use objectLocker
// With this flag, we allow parallel classloading of a
// class/classloader pair
// case4. Bootstrap classloader - don't own objectLocker
// case 3. Bootstrap classloader - don't own objectLocker
// This classloader supports parallelism at the classloader level,
// but only allows a single load of a class/classloader pair.
// No performance benefit and no deadlock issues.
// case 5. parallelCapable user level classloaders - without objectLocker
// case 4. parallelCapable user level classloaders - without objectLocker
// Allow parallel classloading of a class/classloader pair
{
@ -788,7 +782,7 @@ Klass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
// case 1: traditional: should never see load_in_progress.
while (!class_has_been_loaded && oldprobe && oldprobe->instance_load_in_progress()) {
// case 4: bootstrap classloader: prevent futile classloading,
// case 3: bootstrap classloader: prevent futile classloading,
// wait on first requestor
if (class_loader.is_null()) {
SystemDictionary_lock->wait();
@ -811,7 +805,7 @@ Klass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
}
}
// All cases: add LOAD_INSTANCE holding SystemDictionary_lock
// case 3: UnsyncloadClass || case 5: parallelCapable: allow competing threads to try
// case 4: parallelCapable: allow competing threads to try
// LOAD_INSTANCE in parallel
if (!throw_circularity_error && !class_has_been_loaded) {
@ -844,28 +838,6 @@ Klass* SystemDictionary::resolve_instance_class_or_null(Symbol* name,
// Do actual loading
k = load_instance_class(name, class_loader, THREAD);
// For UnsyncloadClass only
// If they got a linkageError, check if a parallel class load succeeded.
// If it did, then for bytecode resolution the specification requires
// that we return the same result we did for the other thread, i.e. the
// successfully loaded InstanceKlass
// Should not get here for classloaders that support parallelism
// with the new cleaner mechanism, even with AllowParallelDefineClass
// Bootstrap goes through here to allow for an extra guarantee check
if (UnsyncloadClass || (class_loader.is_null())) {
if (k == NULL && HAS_PENDING_EXCEPTION
&& PENDING_EXCEPTION->is_a(SystemDictionary::LinkageError_klass())) {
MutexLocker mu(SystemDictionary_lock, THREAD);
InstanceKlass* check = find_class(d_hash, name, dictionary);
if (check != NULL) {
// Klass is already loaded, so just use it
k = check;
CLEAR_PENDING_EXCEPTION;
guarantee((!class_loader.is_null()), "dup definition for bootstrap loader?");
}
}
}
// If everything was OK (no exceptions, no null return value), and
// class_loader is NOT the defining loader, do a little more bookkeeping.
if (!HAS_PENDING_EXCEPTION && k != NULL &&
@ -1097,7 +1069,7 @@ InstanceKlass* SystemDictionary::resolve_from_stream(Symbol* class_name,
HandleMark hm(THREAD);
// Classloaders that support parallelism, e.g. bootstrap classloader,
// or all classloaders with UnsyncloadClass do not acquire lock here
// do not acquire lock here
bool DoObjectLock = true;
if (is_parallelCapable(class_loader)) {
DoObjectLock = false;
@ -1556,40 +1528,17 @@ InstanceKlass* SystemDictionary::load_instance_class(Symbol* class_name, Handle
InstanceKlass* spec_klass = SystemDictionary::ClassLoader_klass();
// Call public unsynchronized loadClass(String) directly for all class loaders
// for parallelCapable class loaders. JDK >=7, loadClass(String, boolean) will
// 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),
// so the call to loadClassInternal() was not required.
//
// UnsyncloadClass flag means both call loadClass(String) and do
// not acquire the class loader lock even for class loaders that are
// not parallelCapable. This was a risky transitional
// flag for diagnostic purposes only. It is risky to call
// custom class loaders without synchronization.
// WARNING If a custom class loader does NOT synchronizer findClass, or callers of
// findClass, the UnsyncloadClass flag risks unexpected timing bugs in the field.
// Do NOT assume this will be supported in future releases.
//
// Added MustCallLoadClassInternal in case we discover in the field
// a customer that counts on this call
if (MustCallLoadClassInternal && has_loadClassInternal()) {
JavaCalls::call_special(&result,
class_loader,
spec_klass,
vmSymbols::loadClassInternal_name(),
vmSymbols::string_class_signature(),
string,
CHECK_NULL);
} else {
JavaCalls::call_virtual(&result,
class_loader,
spec_klass,
vmSymbols::loadClass_name(),
vmSymbols::string_class_signature(),
string,
CHECK_NULL);
}
// 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);
assert(result.get_type() == T_OBJECT, "just checking");
oop obj = (oop) result.get_jobject();
@ -1718,7 +1667,7 @@ InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_nam
{
MutexLocker mu(SystemDictionary_lock, THREAD);
// First check if class already defined
if (UnsyncloadClass || (is_parallelDefine(class_loader))) {
if (is_parallelDefine(class_loader)) {
InstanceKlass* check = find_class(d_hash, name_h, dictionary);
if (check != NULL) {
return check;
@ -1737,7 +1686,7 @@ InstanceKlass* SystemDictionary::find_or_define_instance_class(Symbol* class_nam
// 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 ((UnsyncloadClass || is_parallelDefine(class_loader)) && (probe->instance_klass() != NULL)) {
if (is_parallelDefine(class_loader) && (probe->instance_klass() != NULL)) {
placeholders()->find_and_remove(p_index, p_hash, name_h, loader_data, PlaceholderTable::DEFINE_CLASS, THREAD);
SystemDictionary_lock->notify_all();
#ifdef ASSERT
@ -2174,10 +2123,6 @@ void SystemDictionary::initialize_preloaded_classes(TRAPS) {
//_box_klasses[T_OBJECT] = WK_KLASS(object_klass);
//_box_klasses[T_ARRAY] = WK_KLASS(object_klass);
{ // Compute whether we should use loadClass or loadClassInternal when loading classes.
Method* method = InstanceKlass::cast(ClassLoader_klass())->find_method(vmSymbols::loadClassInternal_name(), vmSymbols::string_class_signature());
_has_loadClassInternal = (method != NULL);
}
{ // Compute whether we should use checkPackageAccess or NOT
Method* method = InstanceKlass::cast(ClassLoader_klass())->find_method(vmSymbols::checkPackageAccess_name(), vmSymbols::class_protectiondomain_signature());
_has_checkPackageAccess = (method != NULL);