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	/*
	* Copyright (c) 2015, 2021, 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. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* 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.
	*/

	package jdk.internal.module;

	import java.io.PrintStream;
	import java.lang.module.Configuration;
	import java.lang.module.ModuleDescriptor;
	import java.lang.module.ModuleFinder;
	import java.lang.module.ModuleReference;
	import java.lang.module.ResolvedModule;
	import java.net.URI;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.util.Collection;
	import java.util.List;
	import java.util.Map;
	import java.util.Optional;
	import java.util.Set;
	import java.util.function.Function;
	import java.util.stream.Collectors;

	import jdk.internal.access.JavaLangModuleAccess;
	import jdk.internal.loader.BootLoader;
	import jdk.internal.loader.BuiltinClassLoader;
	import jdk.internal.loader.ClassLoaders;
	import jdk.internal.access.JavaLangAccess;
	import jdk.internal.access.SharedSecrets;

	/**
	* A helper class for creating and updating modules. This class is intended to
	* support command-line options, tests, and the instrumentation API. It is also
	* used by the VM to load modules or add read edges when agents are instrumenting
	* code that need to link to supporting classes.
	*
	* The parameters that are package names in this API are the fully-qualified
	* names of the packages as defined in section 6.5.3 of <cite>The Java
	* Language Specification </cite>, for example, {@code "java.lang"}.
	*/

	public class Modules {
	private Modules() { }

	private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
	private static final JavaLangModuleAccess JLMA = SharedSecrets.getJavaLangModuleAccess();

	/**
	* Creates a new Module. The module has the given ModuleDescriptor and
	* is defined to the given class loader.
	*
	* The resulting Module is in a larval state in that it does not read
	* any other module and does not have any exports.
	*
	* The URI is for information purposes only.
	*/
	public static Module defineModule(ClassLoader loader,
	ModuleDescriptor descriptor,
	URI uri)
	{
	return JLA.defineModule(loader, descriptor, uri);
	}

	/**
	* Updates m1 to read m2.
	* Same as m1.addReads(m2) but without a caller check.
	*/
	public static void addReads(Module m1, Module m2) {
	JLA.addReads(m1, m2);
	}

	/**
	* Update module m to read all unnamed modules.
	*/
	public static void addReadsAllUnnamed(Module m) {
	JLA.addReadsAllUnnamed(m);
	}

	/**
	* Updates module m1 to export a package to module m2.
	* Same as m1.addExports(pn, m2) but without a caller check
	*/
	public static void addExports(Module m1, String pn, Module m2) {
	JLA.addExports(m1, pn, m2);
	}

	/**
	* Updates module m to export a package unconditionally.
	*/
	public static void addExports(Module m, String pn) {
	JLA.addExports(m, pn);
	}

	/**
	* Updates module m to export a package to all unnamed modules.
	*/
	public static void addExportsToAllUnnamed(Module m, String pn) {
	JLA.addExportsToAllUnnamed(m, pn);
	}

	/**
	* Updates module m1 to open a package to module m2.
	* Same as m1.addOpens(pn, m2) but without a caller check.
	*/
	public static void addOpens(Module m1, String pn, Module m2) {
	JLA.addOpens(m1, pn, m2);
	}

	/**
	* Updates module m to open a package to all unnamed modules.
	*/
	public static void addOpensToAllUnnamed(Module m, String pn) {
	JLA.addOpensToAllUnnamed(m, pn);
	}

	/**
	* Updates module m to use a service.
	* Same as m2.addUses(service) but without a caller check.
	*/
	public static void addUses(Module m, Class<?> service) {
	JLA.addUses(m, service);
	}

	/**
	* Updates module m to provide a service
	*/
	public static void addProvides(Module m, Class<?> service, Class<?> impl) {
	ModuleLayer layer = m.getLayer();

	PrivilegedAction<ClassLoader> pa = m::getClassLoader;
	@SuppressWarnings("removal")
	ClassLoader loader = AccessController.doPrivileged(pa);

	ClassLoader platformClassLoader = ClassLoaders.platformClassLoader();
	if (layer == null \|\| loader == null \|\| loader == platformClassLoader) {
	// update ClassLoader catalog
	ServicesCatalog catalog;
	if (loader == null) {
	catalog = BootLoader.getServicesCatalog();
	} else {
	catalog = ServicesCatalog.getServicesCatalog(loader);
	}
	catalog.addProvider(m, service, impl);
	}

	if (layer != null) {
	// update Layer catalog
	JLA.getServicesCatalog(layer).addProvider(m, service, impl);
	}
	}

	/**
	* Resolves a collection of root modules, with service binding and the empty
	* Configuration as the parent to create a Configuration for the boot layer.
	*
	* This method is intended to be used to create the Configuration for the
	* boot layer during startup or at a link-time.
	*/
	public static Configuration newBootLayerConfiguration(ModuleFinder finder,
	Collection<String> roots,
	PrintStream traceOutput)
	{
	return JLMA.resolveAndBind(finder, roots, traceOutput);
	}

	/**
	* Called by the VM when code in the given Module has been transformed by
	* an agent and so may have been instrumented to call into supporting
	* classes on the boot class path or application class path.
	*/
	public static void transformedByAgent(Module m) {
	addReads(m, BootLoader.getUnnamedModule());
	addReads(m, ClassLoaders.appClassLoader().getUnnamedModule());
	}

	/**
	* Called by the VM to load a system module, typically "java.instrument" or
	* "jdk.management.agent". If the module is not loaded then it is resolved
	* and loaded (along with any dependences that weren't previously loaded)
	* into a child layer.
	*/
	public static synchronized Module loadModule(String name) {
	ModuleLayer top = topLayer;
	if (top == null)
	top = ModuleLayer.boot();

	Module module = top.findModule(name).orElse(null);
	if (module != null) {
	// module already loaded
	return module;
	}

	// resolve the module with the top-most layer as the parent
	ModuleFinder empty = ModuleFinder.of();
	ModuleFinder finder = ModuleBootstrap.unlimitedFinder();
	Set<String> roots = Set.of(name);
	Configuration cf = top.configuration().resolveAndBind(empty, finder, roots);

	// create the child layer
	Function<String, ClassLoader> clf = ModuleLoaderMap.mappingFunction(cf);
	ModuleLayer newLayer = top.defineModules(cf, clf);

	// add qualified exports/opens to give access to modules in child layer
	Map<String, Module> map = newLayer.modules().stream()
	.collect(Collectors.toMap(Module::getName,
	Function.identity()));
	ModuleLayer layer = top;
	while (layer != null) {
	for (Module m : layer.modules()) {
	// qualified exports
	m.getDescriptor().exports().stream()
	.filter(ModuleDescriptor.Exports::isQualified)
	.forEach(e -> e.targets().forEach(target -> {
	Module other = map.get(target);
	if (other != null) {
	addExports(m, e.source(), other);
	}}));

	// qualified opens
	m.getDescriptor().opens().stream()
	.filter(ModuleDescriptor.Opens::isQualified)
	.forEach(o -> o.targets().forEach(target -> {
	Module other = map.get(target);
	if (other != null) {
	addOpens(m, o.source(), other);
	}}));
	}

	List<ModuleLayer> parents = layer.parents();
	assert parents.size() <= 1;
	layer = parents.isEmpty() ? null : parents.get(0);
	}

	// update security manager before making types visible
	JLA.addNonExportedPackages(newLayer);

	// update the built-in class loaders to make the types visible
	for (ResolvedModule resolvedModule : cf.modules()) {
	ModuleReference mref = resolvedModule.reference();
	String mn = mref.descriptor().name();
	ClassLoader cl = clf.apply(mn);
	if (cl == null) {
	BootLoader.loadModule(mref);
	} else {
	((BuiltinClassLoader) cl).loadModule(mref);
	}
	}

	// new top layer
	topLayer = newLayer;

	// return module
	return newLayer.findModule(name)
	.orElseThrow(() -> new InternalError("module not loaded"));

	}

	/**
	* Finds the module with the given name in the boot layer or any child
	* layers created to load the "java.instrument" or "jdk.management.agent"
	* modules into a running VM.
	*/
	public static Optional<Module> findLoadedModule(String name) {
	ModuleLayer top = topLayer;
	if (top == null)
	top = ModuleLayer.boot();
	return top.findModule(name);
	}

	// the top-most layer
	private static volatile ModuleLayer topLayer;

	}

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