hotspot/src/share/vm/classfile/moduleEntry.cpp - platform/libcore - Git at Google

 /*
  * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */

 #include "precompiled.hpp"
 #include "classfile/classLoaderData.hpp"
 #include "classfile/javaClasses.hpp"
 #include "classfile/moduleEntry.hpp"
 #include "logging/log.hpp"
 #include "memory/resourceArea.hpp"
 #include "oops/symbol.hpp"
 #include "prims/jni.h"
 #include "runtime/handles.inline.hpp"
 #include "runtime/safepoint.hpp"
 #include "trace/traceMacros.hpp"
 #include "utilities/events.hpp"
 #include "utilities/growableArray.hpp"
 #include "utilities/hashtable.inline.hpp"
 #include "utilities/ostream.hpp"

 ModuleEntry* ModuleEntryTable::_javabase_module = NULL;

 void ModuleEntry::set_location(Symbol* location) {
   if (_location != NULL) {
     // _location symbol's refcounts are managed by ModuleEntry,
     // must decrement the old one before updating.
     _location->decrement_refcount();
   }

   _location = location;

   if (location != NULL) {
     location->increment_refcount();
   }
 }

 bool ModuleEntry::is_non_jdk_module() {
   ResourceMark rm;
   if (location() != NULL) {
     const char* loc = location()->as_C_string();
     if (strncmp(loc, "jrt:/java.", 10) != 0 && strncmp(loc, "jrt:/jdk.", 9) != 0) {
       return true;
     }
   }
   return false;
 }

 void ModuleEntry::set_version(Symbol* version) {
   if (_version != NULL) {
     // _version symbol's refcounts are managed by ModuleEntry,
     // must decrement the old one before updating.
     _version->decrement_refcount();
   }

   _version = version;

   if (version != NULL) {
     version->increment_refcount();
   }
 }

 // Returns the shared ProtectionDomain
 Handle ModuleEntry::shared_protection_domain() {
   return Handle(JNIHandles::resolve(_pd));
 }

 // Set the shared ProtectionDomain atomically
 void ModuleEntry::set_shared_protection_domain(ClassLoaderData *loader_data,
                                                Handle pd_h) {
   // Create a handle for the shared ProtectionDomain and save it atomically.
   // If someone beats us setting the _pd cache, the created handle is destroyed.
   jobject obj = loader_data->add_handle(pd_h);
   if (Atomic::cmpxchg_ptr(obj, &_pd, NULL) != NULL) {
     loader_data->remove_handle_unsafe(obj);
   }
 }

 // Returns true if this module can read module m
 bool ModuleEntry::can_read(ModuleEntry* m) const {
   assert(m != NULL, "No module to lookup in this module's reads list");

   // Unnamed modules read everyone and all modules
   // read java.base.  If either of these conditions
   // hold, readability has been established.
   if (!this->is_named() ||
       (m == ModuleEntryTable::javabase_moduleEntry())) {
     return true;
   }

   MutexLocker m1(Module_lock);
   // This is a guard against possible race between agent threads that redefine
   // or retransform classes in this module. Only one of them is adding the
   // default read edges to the unnamed modules of the boot and app class loaders
   // with an upcall to jdk.internal.module.Modules.transformedByAgent.
   // At the same time, another thread can instrument the module classes by
   // injecting dependencies that require the default read edges for resolution.
   if (this->has_default_read_edges() && !m->is_named()) {
     ClassLoaderData* cld = m->loader_data();
     if (cld->is_the_null_class_loader_data() || cld->is_system_class_loader_data()) {
       return true; // default read edge
     }
   }
   if (!has_reads()) {
     return false;
   } else {
     return _reads->contains(m);
   }
 }

 // Add a new module to this module's reads list
 void ModuleEntry::add_read(ModuleEntry* m) {
   MutexLocker m1(Module_lock);
   if (m == NULL) {
     set_can_read_all_unnamed();
   } else {
     if (_reads == NULL) {
       // Lazily create a module's reads list
       _reads = new (ResourceObj::C_HEAP, mtModule)GrowableArray<ModuleEntry*>(MODULE_READS_SIZE, true);
     }

     // Determine, based on this newly established read edge to module m,
     // if this module's read list should be walked at a GC safepoint.
     set_read_walk_required(m->loader_data());

     // Establish readability to module m
     _reads->append_if_missing(m);
   }
 }

 // If the module's loader, that a read edge is being established to, is
 // not the same loader as this module's and is not one of the 3 builtin
 // class loaders, then this module's reads list must be walked at GC
 // safepoint. Modules have the same life cycle as their defining class
 // loaders and should be removed if dead.
 void ModuleEntry::set_read_walk_required(ClassLoaderData* m_loader_data) {
   assert_locked_or_safepoint(Module_lock);
   if (!_must_walk_reads &&
       loader_data() != m_loader_data &&
       !m_loader_data->is_builtin_class_loader_data()) {
     _must_walk_reads = true;
     if (log_is_enabled(Trace, module)) {
       ResourceMark rm;
       log_trace(module)("ModuleEntry::set_read_walk_required(): module %s reads list must be walked",
                         (name() != NULL) ? name()->as_C_string() : UNNAMED_MODULE);
     }
   }
 }

 bool ModuleEntry::has_reads() const {
   assert_locked_or_safepoint(Module_lock);
   return ((_reads != NULL) && !_reads->is_empty());
 }

 // Purge dead module entries out of reads list.
 void ModuleEntry::purge_reads() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

   if (_must_walk_reads && has_reads()) {
     // This module's _must_walk_reads flag will be reset based
     // on the remaining live modules on the reads list.
     _must_walk_reads = false;

     if (log_is_enabled(Trace, module)) {
       ResourceMark rm;
       log_trace(module)("ModuleEntry::purge_reads(): module %s reads list being walked",
                         (name() != NULL) ? name()->as_C_string() : UNNAMED_MODULE);
     }

     // Go backwards because this removes entries that are dead.
     int len = _reads->length();
     for (int idx = len - 1; idx >= 0; idx--) {
       ModuleEntry* module_idx = _reads->at(idx);
       ClassLoaderData* cld_idx = module_idx->loader_data();
       if (cld_idx->is_unloading()) {
         _reads->delete_at(idx);
       } else {
         // Update the need to walk this module's reads based on live modules
         set_read_walk_required(cld_idx);
       }
     }
   }
 }

 void ModuleEntry::module_reads_do(ModuleClosure* const f) {
   assert_locked_or_safepoint(Module_lock);
   assert(f != NULL, "invariant");

   if (has_reads()) {
     int reads_len = _reads->length();
     for (int i = 0; i < reads_len; ++i) {
       f->do_module(_reads->at(i));
     }
   }
 }

 void ModuleEntry::delete_reads() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
   delete _reads;
   _reads = NULL;
 }

 ModuleEntryTable::ModuleEntryTable(int table_size)
   : Hashtable<Symbol*, mtModule>(table_size, sizeof(ModuleEntry)), _unnamed_module(NULL)
 {
 }

 ModuleEntryTable::~ModuleEntryTable() {
   assert_locked_or_safepoint(Module_lock);

   // Walk through all buckets and all entries in each bucket,
   // freeing each entry.
   for (int i = 0; i < table_size(); ++i) {
     for (ModuleEntry* m = bucket(i); m != NULL;) {
       ModuleEntry* to_remove = m;
       // read next before freeing.
       m = m->next();

       ResourceMark rm;
       if (to_remove->name() != NULL) {
         log_info(module, unload)("unloading module %s", to_remove->name()->as_C_string());
       }
       log_debug(module)("ModuleEntryTable: deleting module: %s", to_remove->name() != NULL ?
                         to_remove->name()->as_C_string() : UNNAMED_MODULE);

       // Clean out the C heap allocated reads list first before freeing the entry
       to_remove->delete_reads();
       if (to_remove->name() != NULL) {
         to_remove->name()->decrement_refcount();
       }
       if (to_remove->version() != NULL) {
         to_remove->version()->decrement_refcount();
       }
       if (to_remove->location() != NULL) {
         to_remove->location()->decrement_refcount();
       }

       // Unlink from the Hashtable prior to freeing
       unlink_entry(to_remove);
       FREE_C_HEAP_ARRAY(char, to_remove);
     }
   }
   assert(number_of_entries() == 0, "should have removed all entries");
   assert(new_entry_free_list() == NULL, "entry present on ModuleEntryTable's free list");
   free_buckets();
 }

 void ModuleEntryTable::create_unnamed_module(ClassLoaderData* loader_data) {
   assert(Module_lock->owned_by_self(), "should have the Module_lock");

   // Each ModuleEntryTable has exactly one unnamed module
   if (loader_data->is_the_null_class_loader_data()) {
     // For the boot loader, the java.lang.Module for the unnamed module
     // is not known until a call to JVM_SetBootLoaderUnnamedModule is made. At
     // this point initially create the ModuleEntry for the unnamed module.
     _unnamed_module = new_entry(0, Handle(NULL), NULL, NULL, NULL, loader_data);
   } else {
     // For all other class loaders the java.lang.Module for their
     // corresponding unnamed module can be found in the java.lang.ClassLoader object.
     oop module = java_lang_ClassLoader::unnamedModule(loader_data->class_loader());
     _unnamed_module = new_entry(0, Handle(module), NULL, NULL, NULL, loader_data);

     // Store pointer to the ModuleEntry in the unnamed module's java.lang.Module
     // object.
     java_lang_Module::set_module_entry(module, _unnamed_module);
   }

   // Add to bucket 0, no name to hash on
   add_entry(0, _unnamed_module);
 }

 ModuleEntry* ModuleEntryTable::new_entry(unsigned int hash, Handle module_handle, Symbol* name,
                                          Symbol* version, Symbol* location,
                                          ClassLoaderData* loader_data) {
   assert(Module_lock->owned_by_self(), "should have the Module_lock");
   ModuleEntry* entry = (ModuleEntry*) NEW_C_HEAP_ARRAY(char, entry_size(), mtModule);

   // Initialize everything BasicHashtable would
   entry->set_next(NULL);
   entry->set_hash(hash);
   entry->set_literal(name);

   // Initialize fields specific to a ModuleEntry
   entry->init();
   if (name != NULL) {
     name->increment_refcount();
   } else {
     // Unnamed modules can read all other unnamed modules.
     entry->set_can_read_all_unnamed();
   }

   if (!module_handle.is_null()) {
     entry->set_module(loader_data->add_handle(module_handle));
   }

   entry->set_loader_data(loader_data);
   entry->set_version(version);
   entry->set_location(location);

   if (ClassLoader::is_in_patch_mod_entries(name)) {
     entry->set_is_patched();
     if (log_is_enabled(Trace, module, patch)) {
       ResourceMark rm;
       log_trace(module, patch)("Marked module %s as patched from --patch-module", name->as_C_string());
     }
   }

   TRACE_INIT_ID(entry);

   return entry;
 }

 void ModuleEntryTable::add_entry(int index, ModuleEntry* new_entry) {
   assert(Module_lock->owned_by_self(), "should have the Module_lock");
   Hashtable<Symbol*, mtModule>::add_entry(index, (HashtableEntry<Symbol*, mtModule>*)new_entry);
 }

 ModuleEntry* ModuleEntryTable::locked_create_entry_or_null(Handle module_handle,
                                                            Symbol* module_name,
                                                            Symbol* module_version,
                                                            Symbol* module_location,
                                                            ClassLoaderData* loader_data) {
   assert(module_name != NULL, "ModuleEntryTable locked_create_entry_or_null should never be called for unnamed module.");
   assert(Module_lock->owned_by_self(), "should have the Module_lock");
   // Check if module already exists.
   if (lookup_only(module_name) != NULL) {
     return NULL;
   } else {
     ModuleEntry* entry = new_entry(compute_hash(module_name), module_handle, module_name,
                                    module_version, module_location, loader_data);
     add_entry(index_for(module_name), entry);
     return entry;
   }
 }

 // lookup_only by Symbol* to find a ModuleEntry.
 ModuleEntry* ModuleEntryTable::lookup_only(Symbol* name) {
   if (name == NULL) {
     // Return this table's unnamed module
     return unnamed_module();
   }
   int index = index_for(name);
   for (ModuleEntry* m = bucket(index); m != NULL; m = m->next()) {
     if (m->name()->fast_compare(name) == 0) {
       return m;
     }
   }
   return NULL;
 }

 // Remove dead modules from all other alive modules' reads list.
 // This should only occur at class unloading.
 void ModuleEntryTable::purge_all_module_reads() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
   for (int i = 0; i < table_size(); i++) {
     for (ModuleEntry* entry = bucket(i);
                       entry != NULL;
                       entry = entry->next()) {
       entry->purge_reads();
     }
   }
 }

 void ModuleEntryTable::finalize_javabase(Handle module_handle, Symbol* version, Symbol* location) {
   assert(Module_lock->owned_by_self(), "should have the Module_lock");
   ClassLoaderData* boot_loader_data = ClassLoaderData::the_null_class_loader_data();
   ModuleEntryTable* module_table = boot_loader_data->modules();

   assert(module_table != NULL, "boot loader's ModuleEntryTable not defined");

   if (module_handle.is_null()) {
     fatal("Unable to finalize module definition for " JAVA_BASE_NAME);
   }

   // Set java.lang.Module, version and location for java.base
   ModuleEntry* jb_module = javabase_moduleEntry();
   assert(jb_module != NULL, JAVA_BASE_NAME " ModuleEntry not defined");
   jb_module->set_version(version);
   jb_module->set_location(location);
   // Once java.base's ModuleEntry _module field is set with the known
   // java.lang.Module, java.base is considered "defined" to the VM.
   jb_module->set_module(boot_loader_data->add_handle(module_handle));

   // Store pointer to the ModuleEntry for java.base in the java.lang.Module object.
   java_lang_Module::set_module_entry(module_handle(), jb_module);
 }

 // Within java.lang.Class instances there is a java.lang.Module field that must
 // be set with the defining module.  During startup, prior to java.base's definition,
 // classes needing their module field set are added to the fixup_module_list.
 // Their module field is set once java.base's java.lang.Module is known to the VM.
 void ModuleEntryTable::patch_javabase_entries(Handle module_handle) {
   if (module_handle.is_null()) {
     fatal("Unable to patch the module field of classes loaded prior to "
           JAVA_BASE_NAME "'s definition, invalid java.lang.Module");
   }

   // Do the fixups for the basic primitive types
   java_lang_Class::set_module(Universe::int_mirror(), module_handle());
   java_lang_Class::set_module(Universe::float_mirror(), module_handle());
   java_lang_Class::set_module(Universe::double_mirror(), module_handle());
   java_lang_Class::set_module(Universe::byte_mirror(), module_handle());
   java_lang_Class::set_module(Universe::bool_mirror(), module_handle());
   java_lang_Class::set_module(Universe::char_mirror(), module_handle());
   java_lang_Class::set_module(Universe::long_mirror(), module_handle());
   java_lang_Class::set_module(Universe::short_mirror(), module_handle());
   java_lang_Class::set_module(Universe::void_mirror(), module_handle());

   // Do the fixups for classes that have already been created.
   GrowableArray <Klass*>* list = java_lang_Class::fixup_module_field_list();
   int list_length = list->length();
   for (int i = 0; i < list_length; i++) {
     Klass* k = list->at(i);
     assert(k->is_klass(), "List should only hold classes");
     java_lang_Class::fixup_module_field(KlassHandle(k), module_handle);
     k->class_loader_data()->dec_keep_alive();
   }

   delete java_lang_Class::fixup_module_field_list();
   java_lang_Class::set_fixup_module_field_list(NULL);
 }

 void ModuleEntryTable::print(outputStream* st) {
   st->print_cr("Module Entry Table (table_size=%d, entries=%d)",
                table_size(), number_of_entries());
   for (int i = 0; i < table_size(); i++) {
     for (ModuleEntry* probe = bucket(i);
                               probe != NULL;
                               probe = probe->next()) {
       probe->print(st);
     }
   }
 }

 void ModuleEntry::print(outputStream* st) {
   ResourceMark rm;
   st->print_cr("entry " PTR_FORMAT " name %s module " PTR_FORMAT " loader %s version %s location %s strict %s next " PTR_FORMAT,
                p2i(this),
                name() == NULL ? UNNAMED_MODULE : name()->as_C_string(),
                p2i(module()),
                loader_data()->loader_name(),
                version() != NULL ? version()->as_C_string() : "NULL",
                location() != NULL ? location()->as_C_string() : "NULL",
                BOOL_TO_STR(!can_read_all_unnamed()), p2i(next()));
 }

 void ModuleEntryTable::verify() {
   int element_count = 0;
   for (int i = 0; i < table_size(); i++) {
     for (ModuleEntry* probe = bucket(i);
                               probe != NULL;
                               probe = probe->next()) {
       probe->verify();
       element_count++;
     }
   }
   guarantee(number_of_entries() == element_count,
             "Verify of Module Entry Table failed");
   DEBUG_ONLY(verify_lookup_length((double)number_of_entries() / table_size(), "Module Entry Table"));
 }

 void ModuleEntry::verify() {
   guarantee(loader_data() != NULL, "A module entry must be associated with a loader.");
 }
	/*
	* Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*
	*/

	#include "precompiled.hpp"
	#include "classfile/classLoaderData.hpp"
	#include "classfile/javaClasses.hpp"
	#include "classfile/moduleEntry.hpp"
	#include "logging/log.hpp"
	#include "memory/resourceArea.hpp"
	#include "oops/symbol.hpp"
	#include "prims/jni.h"
	#include "runtime/handles.inline.hpp"
	#include "runtime/safepoint.hpp"
	#include "trace/traceMacros.hpp"
	#include "utilities/events.hpp"
	#include "utilities/growableArray.hpp"
	#include "utilities/hashtable.inline.hpp"
	#include "utilities/ostream.hpp"

	ModuleEntry* ModuleEntryTable::_javabase_module = NULL;

	void ModuleEntry::set_location(Symbol* location) {
	if (_location != NULL) {
	// _location symbol's refcounts are managed by ModuleEntry,
	// must decrement the old one before updating.
	_location->decrement_refcount();
	}

	_location = location;

	if (location != NULL) {
	location->increment_refcount();
	}
	}

	bool ModuleEntry::is_non_jdk_module() {
	ResourceMark rm;
	if (location() != NULL) {
	const char* loc = location()->as_C_string();
	if (strncmp(loc, "jrt:/java.", 10) != 0 && strncmp(loc, "jrt:/jdk.", 9) != 0) {
	return true;
	}
	}
	return false;
	}

	void ModuleEntry::set_version(Symbol* version) {
	if (_version != NULL) {
	// _version symbol's refcounts are managed by ModuleEntry,
	// must decrement the old one before updating.
	_version->decrement_refcount();
	}

	_version = version;

	if (version != NULL) {
	version->increment_refcount();
	}
	}

	// Returns the shared ProtectionDomain
	Handle ModuleEntry::shared_protection_domain() {
	return Handle(JNIHandles::resolve(_pd));
	}

	// Set the shared ProtectionDomain atomically
	void ModuleEntry::set_shared_protection_domain(ClassLoaderData *loader_data,
	Handle pd_h) {
	// Create a handle for the shared ProtectionDomain and save it atomically.
	// If someone beats us setting the _pd cache, the created handle is destroyed.
	jobject obj = loader_data->add_handle(pd_h);
	if (Atomic::cmpxchg_ptr(obj, &_pd, NULL) != NULL) {
	loader_data->remove_handle_unsafe(obj);
	}
	}

	// Returns true if this module can read module m
	bool ModuleEntry::can_read(ModuleEntry* m) const {
	assert(m != NULL, "No module to lookup in this module's reads list");

	// Unnamed modules read everyone and all modules
	// read java.base. If either of these conditions
	// hold, readability has been established.
	if (!this->is_named() \|\|
	(m == ModuleEntryTable::javabase_moduleEntry())) {
	return true;
	}

	MutexLocker m1(Module_lock);
	// This is a guard against possible race between agent threads that redefine
	// or retransform classes in this module. Only one of them is adding the
	// default read edges to the unnamed modules of the boot and app class loaders
	// with an upcall to jdk.internal.module.Modules.transformedByAgent.
	// At the same time, another thread can instrument the module classes by
	// injecting dependencies that require the default read edges for resolution.
	if (this->has_default_read_edges() && !m->is_named()) {
	ClassLoaderData* cld = m->loader_data();
	if (cld->is_the_null_class_loader_data() \|\| cld->is_system_class_loader_data()) {
	return true; // default read edge
	}
	}
	if (!has_reads()) {
	return false;
	} else {
	return _reads->contains(m);
	}
	}

	// Add a new module to this module's reads list
	void ModuleEntry::add_read(ModuleEntry* m) {
	MutexLocker m1(Module_lock);
	if (m == NULL) {
	set_can_read_all_unnamed();
	} else {
	if (_reads == NULL) {
	// Lazily create a module's reads list
	_reads = new (ResourceObj::C_HEAP, mtModule)GrowableArray<ModuleEntry*>(MODULE_READS_SIZE, true);
	}

	// Determine, based on this newly established read edge to module m,
	// if this module's read list should be walked at a GC safepoint.
	set_read_walk_required(m->loader_data());

	// Establish readability to module m
	_reads->append_if_missing(m);
	}
	}

	// If the module's loader, that a read edge is being established to, is
	// not the same loader as this module's and is not one of the 3 builtin
	// class loaders, then this module's reads list must be walked at GC
	// safepoint. Modules have the same life cycle as their defining class
	// loaders and should be removed if dead.
	void ModuleEntry::set_read_walk_required(ClassLoaderData* m_loader_data) {
	assert_locked_or_safepoint(Module_lock);
	if (!_must_walk_reads &&
	loader_data() != m_loader_data &&
	!m_loader_data->is_builtin_class_loader_data()) {
	_must_walk_reads = true;
	if (log_is_enabled(Trace, module)) {
	ResourceMark rm;
	log_trace(module)("ModuleEntry::set_read_walk_required(): module %s reads list must be walked",
	(name() != NULL) ? name()->as_C_string() : UNNAMED_MODULE);
	}
	}
	}

	bool ModuleEntry::has_reads() const {
	assert_locked_or_safepoint(Module_lock);
	return ((_reads != NULL) && !_reads->is_empty());
	}

	// Purge dead module entries out of reads list.
	void ModuleEntry::purge_reads() {
	assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");

	if (_must_walk_reads && has_reads()) {
	// This module's _must_walk_reads flag will be reset based
	// on the remaining live modules on the reads list.
	_must_walk_reads = false;

	if (log_is_enabled(Trace, module)) {
	ResourceMark rm;
	log_trace(module)("ModuleEntry::purge_reads(): module %s reads list being walked",
	(name() != NULL) ? name()->as_C_string() : UNNAMED_MODULE);
	}

	// Go backwards because this removes entries that are dead.
	int len = _reads->length();
	for (int idx = len - 1; idx >= 0; idx--) {
	ModuleEntry* module_idx = _reads->at(idx);
	ClassLoaderData* cld_idx = module_idx->loader_data();
	if (cld_idx->is_unloading()) {
	_reads->delete_at(idx);
	} else {
	// Update the need to walk this module's reads based on live modules
	set_read_walk_required(cld_idx);
	}
	}
	}
	}

	void ModuleEntry::module_reads_do(ModuleClosure* const f) {
	assert_locked_or_safepoint(Module_lock);
	assert(f != NULL, "invariant");

	if (has_reads()) {
	int reads_len = _reads->length();
	for (int i = 0; i < reads_len; ++i) {
	f->do_module(_reads->at(i));
	}
	}
	}

	void ModuleEntry::delete_reads() {
	assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
	delete _reads;
	_reads = NULL;
	}

	ModuleEntryTable::ModuleEntryTable(int table_size)
	: Hashtable<Symbol*, mtModule>(table_size, sizeof(ModuleEntry)), _unnamed_module(NULL)
	{
	}

	ModuleEntryTable::~ModuleEntryTable() {
	assert_locked_or_safepoint(Module_lock);

	// Walk through all buckets and all entries in each bucket,
	// freeing each entry.
	for (int i = 0; i < table_size(); ++i) {
	for (ModuleEntry* m = bucket(i); m != NULL;) {
	ModuleEntry* to_remove = m;
	// read next before freeing.
	m = m->next();

	ResourceMark rm;
	if (to_remove->name() != NULL) {
	log_info(module, unload)("unloading module %s", to_remove->name()->as_C_string());
	}
	log_debug(module)("ModuleEntryTable: deleting module: %s", to_remove->name() != NULL ?
	to_remove->name()->as_C_string() : UNNAMED_MODULE);

	// Clean out the C heap allocated reads list first before freeing the entry
	to_remove->delete_reads();
	if (to_remove->name() != NULL) {
	to_remove->name()->decrement_refcount();
	}
	if (to_remove->version() != NULL) {
	to_remove->version()->decrement_refcount();
	}
	if (to_remove->location() != NULL) {
	to_remove->location()->decrement_refcount();
	}

	// Unlink from the Hashtable prior to freeing
	unlink_entry(to_remove);
	FREE_C_HEAP_ARRAY(char, to_remove);
	}
	}
	assert(number_of_entries() == 0, "should have removed all entries");
	assert(new_entry_free_list() == NULL, "entry present on ModuleEntryTable's free list");
	free_buckets();
	}

	void ModuleEntryTable::create_unnamed_module(ClassLoaderData* loader_data) {
	assert(Module_lock->owned_by_self(), "should have the Module_lock");

	// Each ModuleEntryTable has exactly one unnamed module
	if (loader_data->is_the_null_class_loader_data()) {
	// For the boot loader, the java.lang.Module for the unnamed module
	// is not known until a call to JVM_SetBootLoaderUnnamedModule is made. At
	// this point initially create the ModuleEntry for the unnamed module.
	_unnamed_module = new_entry(0, Handle(NULL), NULL, NULL, NULL, loader_data);
	} else {
	// For all other class loaders the java.lang.Module for their
	// corresponding unnamed module can be found in the java.lang.ClassLoader object.
	oop module = java_lang_ClassLoader::unnamedModule(loader_data->class_loader());
	_unnamed_module = new_entry(0, Handle(module), NULL, NULL, NULL, loader_data);

	// Store pointer to the ModuleEntry in the unnamed module's java.lang.Module
	// object.
	java_lang_Module::set_module_entry(module, _unnamed_module);
	}

	// Add to bucket 0, no name to hash on
	add_entry(0, _unnamed_module);
	}

	ModuleEntry* ModuleEntryTable::new_entry(unsigned int hash, Handle module_handle, Symbol* name,
	Symbol* version, Symbol* location,
	ClassLoaderData* loader_data) {
	assert(Module_lock->owned_by_self(), "should have the Module_lock");
	ModuleEntry* entry = (ModuleEntry*) NEW_C_HEAP_ARRAY(char, entry_size(), mtModule);

	// Initialize everything BasicHashtable would
	entry->set_next(NULL);
	entry->set_hash(hash);
	entry->set_literal(name);

	// Initialize fields specific to a ModuleEntry
	entry->init();
	if (name != NULL) {
	name->increment_refcount();
	} else {
	// Unnamed modules can read all other unnamed modules.
	entry->set_can_read_all_unnamed();
	}

	if (!module_handle.is_null()) {
	entry->set_module(loader_data->add_handle(module_handle));
	}

	entry->set_loader_data(loader_data);
	entry->set_version(version);
	entry->set_location(location);

	if (ClassLoader::is_in_patch_mod_entries(name)) {
	entry->set_is_patched();
	if (log_is_enabled(Trace, module, patch)) {
	ResourceMark rm;
	log_trace(module, patch)("Marked module %s as patched from --patch-module", name->as_C_string());
	}
	}

	TRACE_INIT_ID(entry);

	return entry;
	}

	void ModuleEntryTable::add_entry(int index, ModuleEntry* new_entry) {
	assert(Module_lock->owned_by_self(), "should have the Module_lock");
	Hashtable<Symbol, mtModule>::add_entry(index, (HashtableEntry<Symbol, mtModule>*)new_entry);
	}

	ModuleEntry* ModuleEntryTable::locked_create_entry_or_null(Handle module_handle,
	Symbol* module_name,
	Symbol* module_version,
	Symbol* module_location,
	ClassLoaderData* loader_data) {
	assert(module_name != NULL, "ModuleEntryTable locked_create_entry_or_null should never be called for unnamed module.");
	assert(Module_lock->owned_by_self(), "should have the Module_lock");
	// Check if module already exists.
	if (lookup_only(module_name) != NULL) {
	return NULL;
	} else {
	ModuleEntry* entry = new_entry(compute_hash(module_name), module_handle, module_name,
	module_version, module_location, loader_data);
	add_entry(index_for(module_name), entry);
	return entry;
	}
	}

	// lookup_only by Symbol* to find a ModuleEntry.
	ModuleEntry* ModuleEntryTable::lookup_only(Symbol* name) {
	if (name == NULL) {
	// Return this table's unnamed module
	return unnamed_module();
	}
	int index = index_for(name);
	for (ModuleEntry* m = bucket(index); m != NULL; m = m->next()) {
	if (m->name()->fast_compare(name) == 0) {
	return m;
	}
	}
	return NULL;
	}

	// Remove dead modules from all other alive modules' reads list.
	// This should only occur at class unloading.
	void ModuleEntryTable::purge_all_module_reads() {
	assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
	for (int i = 0; i < table_size(); i++) {
	for (ModuleEntry* entry = bucket(i);
	entry != NULL;
	entry = entry->next()) {
	entry->purge_reads();
	}
	}
	}

	void ModuleEntryTable::finalize_javabase(Handle module_handle, Symbol* version, Symbol* location) {
	assert(Module_lock->owned_by_self(), "should have the Module_lock");
	ClassLoaderData* boot_loader_data = ClassLoaderData::the_null_class_loader_data();
	ModuleEntryTable* module_table = boot_loader_data->modules();

	assert(module_table != NULL, "boot loader's ModuleEntryTable not defined");

	if (module_handle.is_null()) {
	fatal("Unable to finalize module definition for " JAVA_BASE_NAME);
	}

	// Set java.lang.Module, version and location for java.base
	ModuleEntry* jb_module = javabase_moduleEntry();
	assert(jb_module != NULL, JAVA_BASE_NAME " ModuleEntry not defined");
	jb_module->set_version(version);
	jb_module->set_location(location);
	// Once java.base's ModuleEntry _module field is set with the known
	// java.lang.Module, java.base is considered "defined" to the VM.
	jb_module->set_module(boot_loader_data->add_handle(module_handle));

	// Store pointer to the ModuleEntry for java.base in the java.lang.Module object.
	java_lang_Module::set_module_entry(module_handle(), jb_module);
	}

	// Within java.lang.Class instances there is a java.lang.Module field that must
	// be set with the defining module. During startup, prior to java.base's definition,
	// classes needing their module field set are added to the fixup_module_list.
	// Their module field is set once java.base's java.lang.Module is known to the VM.
	void ModuleEntryTable::patch_javabase_entries(Handle module_handle) {
	if (module_handle.is_null()) {
	fatal("Unable to patch the module field of classes loaded prior to "
	JAVA_BASE_NAME "'s definition, invalid java.lang.Module");
	}

	// Do the fixups for the basic primitive types
	java_lang_Class::set_module(Universe::int_mirror(), module_handle());
	java_lang_Class::set_module(Universe::float_mirror(), module_handle());
	java_lang_Class::set_module(Universe::double_mirror(), module_handle());
	java_lang_Class::set_module(Universe::byte_mirror(), module_handle());
	java_lang_Class::set_module(Universe::bool_mirror(), module_handle());
	java_lang_Class::set_module(Universe::char_mirror(), module_handle());
	java_lang_Class::set_module(Universe::long_mirror(), module_handle());
	java_lang_Class::set_module(Universe::short_mirror(), module_handle());
	java_lang_Class::set_module(Universe::void_mirror(), module_handle());

	// Do the fixups for classes that have already been created.
	GrowableArray <Klass> list = java_lang_Class::fixup_module_field_list();
	int list_length = list->length();
	for (int i = 0; i < list_length; i++) {
	Klass* k = list->at(i);
	assert(k->is_klass(), "List should only hold classes");
	java_lang_Class::fixup_module_field(KlassHandle(k), module_handle);
	k->class_loader_data()->dec_keep_alive();
	}

	delete java_lang_Class::fixup_module_field_list();
	java_lang_Class::set_fixup_module_field_list(NULL);
	}

	void ModuleEntryTable::print(outputStream* st) {
	st->print_cr("Module Entry Table (table_size=%d, entries=%d)",
	table_size(), number_of_entries());
	for (int i = 0; i < table_size(); i++) {
	for (ModuleEntry* probe = bucket(i);
	probe != NULL;
	probe = probe->next()) {
	probe->print(st);
	}
	}
	}

	void ModuleEntry::print(outputStream* st) {
	ResourceMark rm;
	st->print_cr("entry " PTR_FORMAT " name %s module " PTR_FORMAT " loader %s version %s location %s strict %s next " PTR_FORMAT,
	p2i(this),
	name() == NULL ? UNNAMED_MODULE : name()->as_C_string(),
	p2i(module()),
	loader_data()->loader_name(),
	version() != NULL ? version()->as_C_string() : "NULL",
	location() != NULL ? location()->as_C_string() : "NULL",
	BOOL_TO_STR(!can_read_all_unnamed()), p2i(next()));
	}

	void ModuleEntryTable::verify() {
	int element_count = 0;
	for (int i = 0; i < table_size(); i++) {
	for (ModuleEntry* probe = bucket(i);
	probe != NULL;
	probe = probe->next()) {
	probe->verify();
	element_count++;
	}
	}
	guarantee(number_of_entries() == element_count,
	"Verify of Module Entry Table failed");
	DEBUG_ONLY(verify_lookup_length((double)number_of_entries() / table_size(), "Module Entry Table"));
	}

	void ModuleEntry::verify() {
	guarantee(loader_data() != NULL, "A module entry must be associated with a loader.");
	}