/*
 * Copyright (c) 2014, 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
 * 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.File;
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.nio.file.Path;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;

import jdk.internal.loader.BootLoader;
import jdk.internal.loader.BuiltinClassLoader;
import jdk.internal.misc.JavaLangAccess;
import jdk.internal.misc.JavaLangModuleAccess;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.misc.VM;
import jdk.internal.perf.PerfCounter;

Initializes/boots the module system. The boot method is called early in the startup to initialize the module system. In summary, the boot method creates a Configuration by resolving a set of module names specified via the launcher (or equivalent) -m and --add-modules options. The modules are located on a module path that is constructed from the upgrade module path, system modules, and application module path. The Configuration is instantiated as the boot layer with each module in the configuration defined to a class loader. /**
 * Initializes/boots the module system.
 *
 * The {@link #boot() boot} method is called early in the startup to initialize
 * the module system. In summary, the boot method creates a Configuration by
 * resolving a set of module names specified via the launcher (or equivalent)
 * -m and --add-modules options. The modules are located on a module path that
 * is constructed from the upgrade module path, system modules, and application
 * module path. The Configuration is instantiated as the boot layer with each
 * module in the configuration defined to a class loader.
 */

public final class ModuleBootstrap {
    private ModuleBootstrap() { }

    private static final String JAVA_BASE = "java.base";

    // the token for "all default modules"
    private static final String ALL_DEFAULT = "ALL-DEFAULT";

    // the token for "all unnamed modules"
    private static final String ALL_UNNAMED = "ALL-UNNAMED";

    // the token for "all system modules"
    private static final String ALL_SYSTEM = "ALL-SYSTEM";

    // the token for "all modules on the module path"
    private static final String ALL_MODULE_PATH = "ALL-MODULE-PATH";

    // access to java.lang/module
    private static final JavaLangModuleAccess JLMA
        = SharedSecrets.getJavaLangModuleAccess();

    // The ModulePatcher for the initial configuration
    private static final ModulePatcher patcher = initModulePatcher();

    
Returns the ModulePatcher for the initial configuration.
/**
     * Returns the ModulePatcher for the initial configuration.
     */
    public static ModulePatcher patcher() {
        return patcher;
    }

    // ModuleFinders for the initial configuration
    private static volatile ModuleFinder unlimitedFinder;
    private static volatile ModuleFinder limitedFinder;

    
Returns the ModuleFinder for the initial configuration before
observability is limited by the --limit-modules command line option.
API Note:
Used to support locating modules java.instrument and jdk.management.agent modules when they are loaded dynamically./**
     * Returns the ModuleFinder for the initial configuration before
     * observability is limited by the --limit-modules command line option.
     *
     * @apiNote Used to support locating modules {@code java.instrument} and
     * {@code jdk.management.agent} modules when they are loaded dynamically.
     */
    public static ModuleFinder unlimitedFinder() {
        ModuleFinder finder = unlimitedFinder;
        if (finder == null) {
            return ModuleFinder.ofSystem();
        } else {
            return finder;
        }
    }

    
Returns the ModuleFinder for the initial configuration.
API Note:
Used to support "java --list-modules"./**
     * Returns the ModuleFinder for the initial configuration.
     *
     * @apiNote Used to support "{@code java --list-modules}".
     */
    public static ModuleFinder limitedFinder() {
        ModuleFinder finder = limitedFinder;
        if (finder == null) {
            return unlimitedFinder();
        } else {
            return finder;
        }
    }

    
Initialize the module system, returning the boot layer.
See Also:
initPhase2.initPhase2(boolean, boolean)/**
     * Initialize the module system, returning the boot layer.
     *
     * @see java.lang.System#initPhase2(boolean, boolean)
     */
    public static ModuleLayer boot() throws Exception {

        // Step 0: Command line options

        long t0 = System.nanoTime();

        ModuleFinder upgradeModulePath = finderFor("jdk.module.upgrade.path");
        ModuleFinder appModulePath = finderFor("jdk.module.path");
        boolean isPatched = patcher.hasPatches();

        String mainModule = System.getProperty("jdk.module.main");
        Set<String> addModules = addModules();
        Set<String> limitModules = limitModules();

        PrintStream traceOutput = null;
        String trace = getAndRemoveProperty("jdk.module.showModuleResolution");
        if (trace != null && Boolean.parseBoolean(trace))
            traceOutput = System.out;


        // Step 1: The observable system modules, either all system modules
        // or the system modules pre-generated for the initial module (the
        // initial module may be the unnamed module). If the system modules
        // are pre-generated for the initial module then resolution can be
        // skipped.

        long t1 = System.nanoTime();

        SystemModules systemModules = null;
        ModuleFinder systemModuleFinder;

        boolean haveModulePath = (appModulePath != null || upgradeModulePath != null);
        boolean needResolution = true;
        boolean canArchive = false;

        // If the java heap was archived at CDS dump time and the environment
        // at dump time matches the current environment then use the archived
        // system modules and finder.
        ArchivedModuleGraph archivedModuleGraph = ArchivedModuleGraph.get(mainModule);
        if (archivedModuleGraph != null
                && !haveModulePath
                && addModules.isEmpty()
                && limitModules.isEmpty()
                && !isPatched) {
            systemModules = archivedModuleGraph.systemModules();
            systemModuleFinder = archivedModuleGraph.finder();
            needResolution = (traceOutput != null);
        } else {
            if (!haveModulePath && addModules.isEmpty() && limitModules.isEmpty()) {
                systemModules = SystemModuleFinders.systemModules(mainModule);
                if (systemModules != null && !isPatched) {
                    needResolution = (traceOutput != null);
                    canArchive = true;
                }
            }
            if (systemModules == null) {
                // all system modules are observable
                systemModules = SystemModuleFinders.allSystemModules();
            }
            if (systemModules != null) {
                // images build
                systemModuleFinder = SystemModuleFinders.of(systemModules);
            } else {
                // exploded build or testing
                systemModules = new ExplodedSystemModules();
                systemModuleFinder = SystemModuleFinders.ofSystem();
            }
        }

        Counters.add("jdk.module.boot.1.systemModulesTime", t1);


        // Step 2: Define and load java.base. This patches all classes loaded
        // to date so that they are members of java.base. Once java.base is
        // loaded then resources in java.base are available for error messages
        // needed from here on.

        long t2 = System.nanoTime();

        ModuleReference base = systemModuleFinder.find(JAVA_BASE).orElse(null);
        if (base == null)
            throw new InternalError(JAVA_BASE + " not found");
        URI baseUri = base.location().orElse(null);
        if (baseUri == null)
            throw new InternalError(JAVA_BASE + " does not have a location");
        BootLoader.loadModule(base);
        Modules.defineModule(null, base.descriptor(), baseUri);

        Counters.add("jdk.module.boot.2.defineBaseTime", t2);


        // Step 2a: Scan all modules when --validate-modules specified

        if (getAndRemoveProperty("jdk.module.validation") != null) {
            int errors = ModulePathValidator.scanAllModules(System.out);
            if (errors > 0) {
                fail("Validation of module path failed");
            }
        }


        // Step 3: If resolution is needed then create the module finder and
        // the set of root modules to resolve.

        long t3 = System.nanoTime();

        ModuleFinder savedModuleFinder = null;
        ModuleFinder finder;
        Set<String> roots;
        if (needResolution) {

            // upgraded modules override the modules in the run-time image
            if (upgradeModulePath != null)
                systemModuleFinder = ModuleFinder.compose(upgradeModulePath,
                                                          systemModuleFinder);

            // The module finder: [--upgrade-module-path] system [--module-path]
            if (appModulePath != null) {
                finder = ModuleFinder.compose(systemModuleFinder, appModulePath);
            } else {
                finder = systemModuleFinder;
            }

            // The root modules to resolve
            roots = new HashSet<>();

            // launcher -m option to specify the main/initial module
            if (mainModule != null)
                roots.add(mainModule);

            // additional module(s) specified by --add-modules
            boolean addAllDefaultModules = false;
            boolean addAllSystemModules = false;
            boolean addAllApplicationModules = false;
            for (String mod : addModules) {
                switch (mod) {
                    case ALL_DEFAULT:
                        addAllDefaultModules = true;
                        break;
                    case ALL_SYSTEM:
                        addAllSystemModules = true;
                        break;
                    case ALL_MODULE_PATH:
                        addAllApplicationModules = true;
                        break;
                    default:
                        roots.add(mod);
                }
            }

            // --limit-modules
            savedModuleFinder = finder;
            if (!limitModules.isEmpty()) {
                finder = limitFinder(finder, limitModules, roots);
            }

            // If there is no initial module specified then assume that the initial
            // module is the unnamed module of the application class loader. This
            // is implemented by resolving all observable modules that export an
            // API. Modules that have the DO_NOT_RESOLVE_BY_DEFAULT bit set in
            // their ModuleResolution attribute flags are excluded from the
            // default set of roots.
            if (mainModule == null || addAllDefaultModules) {
                roots.addAll(DefaultRoots.compute(systemModuleFinder, finder));
            }

            // If `--add-modules ALL-SYSTEM` is specified then all observable system
            // modules will be resolved.
            if (addAllSystemModules) {
                ModuleFinder f = finder;  // observable modules
                systemModuleFinder.findAll()
                    .stream()
                    .map(ModuleReference::descriptor)
                    .map(ModuleDescriptor::name)
                    .filter(mn -> f.find(mn).isPresent())  // observable
                    .forEach(mn -> roots.add(mn));
            }

            // If `--add-modules ALL-MODULE-PATH` is specified then all observable
            // modules on the application module path will be resolved.
            if (appModulePath != null && addAllApplicationModules) {
                ModuleFinder f = finder;  // observable modules
                appModulePath.findAll()
                    .stream()
                    .map(ModuleReference::descriptor)
                    .map(ModuleDescriptor::name)
                    .filter(mn -> f.find(mn).isPresent())  // observable
                    .forEach(mn -> roots.add(mn));
            }
        } else {
            // no resolution case
            finder = systemModuleFinder;
            roots = null;
        }

        Counters.add("jdk.module.boot.3.optionsAndRootsTime", t3);

        // Step 4: Resolve the root modules, with service binding, to create
        // the configuration for the boot layer. If resolution is not needed
        // then create the configuration for the boot layer from the
        // readability graph created at link time.

        long t4 = System.nanoTime();

        Configuration cf;
        if (needResolution) {
            cf = JLMA.resolveAndBind(finder, roots, traceOutput);
        } else {
            if (archivedModuleGraph != null) {
                cf = archivedModuleGraph.configuration();
            } else {
                Map<String, Set<String>> map = systemModules.moduleReads();
                cf = JLMA.newConfiguration(systemModuleFinder, map);
            }
        }

        // check that modules specified to --patch-module are resolved
        if (isPatched) {
            patcher.patchedModules()
                    .stream()
                    .filter(mn -> !cf.findModule(mn).isPresent())
                    .forEach(mn -> warnUnknownModule(PATCH_MODULE, mn));
        }

        Counters.add("jdk.module.boot.4.resolveTime", t4);


        // Step 5: Map the modules in the configuration to class loaders.
        // The static configuration provides the mapping of standard and JDK
        // modules to the boot and platform loaders. All other modules (JDK
        // tool modules, and both explicit and automatic modules on the
        // application module path) are defined to the application class
        // loader.

        long t5 = System.nanoTime();

        // mapping of modules to class loaders
        Function<String, ClassLoader> clf = ModuleLoaderMap.mappingFunction(cf);

        // check that all modules to be mapped to the boot loader will be
        // loaded from the runtime image
        if (haveModulePath) {
            for (ResolvedModule resolvedModule : cf.modules()) {
                ModuleReference mref = resolvedModule.reference();
                String name = mref.descriptor().name();
                ClassLoader cl = clf.apply(name);
                if (cl == null) {
                    if (upgradeModulePath != null
                            && upgradeModulePath.find(name).isPresent())
                        fail(name + ": cannot be loaded from upgrade module path");
                    if (!systemModuleFinder.find(name).isPresent())
                        fail(name + ": cannot be loaded from application module path");
                }
            }
        }

        // check for split packages in the modules mapped to the built-in loaders
        if (systemModules.hasSplitPackages() || isPatched || haveModulePath) {
            checkSplitPackages(cf, clf);
        }

        // load/register the modules with the built-in class loaders
        loadModules(cf, clf);

        Counters.add("jdk.module.boot.5.loadModulesTime", t5);


        // Step 6: Define all modules to the VM

        long t6 = System.nanoTime();
        ModuleLayer bootLayer = ModuleLayer.empty().defineModules(cf, clf);
        Counters.add("jdk.module.boot.6.layerCreateTime", t6);


        // Step 7: Miscellaneous

        // check incubating status
        if (systemModules.hasIncubatorModules() || haveModulePath) {
            checkIncubatingStatus(cf);
        }

        // --add-reads, --add-exports/--add-opens, and --illegal-access
        long t7 = System.nanoTime();
        addExtraReads(bootLayer);
        boolean extraExportsOrOpens = addExtraExportsAndOpens(bootLayer);
        addIllegalAccess(upgradeModulePath, systemModules, bootLayer, extraExportsOrOpens);
        Counters.add("jdk.module.boot.7.adjustModulesTime", t7);

        // save module finders for later use
        if (savedModuleFinder != null) {
            unlimitedFinder = new SafeModuleFinder(savedModuleFinder);
            if (savedModuleFinder != finder)
                limitedFinder = new SafeModuleFinder(finder);
        }

        // Module graph can be archived at CDS dump time. Only allow the
        // unnamed module case for now.
        if (canArchive && (mainModule == null)) {
            ArchivedModuleGraph.archive(mainModule, systemModules,
                                        systemModuleFinder, cf);
        }

        // total time to initialize
        Counters.add("jdk.module.boot.totalTime", t0);
        Counters.publish();

        return bootLayer;
    }

    
Load/register the modules to the built-in class loaders.
/**
     * Load/register the modules to the built-in class loaders.
     */
    private static void loadModules(Configuration cf,
                                    Function<String, ClassLoader> clf) {
        for (ResolvedModule resolvedModule : cf.modules()) {
            ModuleReference mref = resolvedModule.reference();
            String name = resolvedModule.name();
            ClassLoader loader = clf.apply(name);
            if (loader == null) {
                // skip java.base as it is already loaded
                if (!name.equals(JAVA_BASE)) {
                    BootLoader.loadModule(mref);
                }
            } else if (loader instanceof BuiltinClassLoader) {
                ((BuiltinClassLoader) loader).loadModule(mref);
            }
        }
    }

    
Checks for split packages between modules defined to the built-in class
loaders.
/**
     * Checks for split packages between modules defined to the built-in class
     * loaders.
     */
    private static void checkSplitPackages(Configuration cf,
                                           Function<String, ClassLoader> clf) {
        Map<String, String> packageToModule = new HashMap<>();
        for (ResolvedModule resolvedModule : cf.modules()) {
            ModuleDescriptor descriptor = resolvedModule.reference().descriptor();
            String name = descriptor.name();
            ClassLoader loader = clf.apply(name);
            if (loader == null || loader instanceof BuiltinClassLoader) {
                for (String p : descriptor.packages()) {
                    String other = packageToModule.putIfAbsent(p, name);
                    if (other != null) {
                        String msg = "Package " + p + " in both module "
                                     + name + " and module " + other;
                        throw new LayerInstantiationException(msg);
                    }
                }
            }
        }
    }

    
Returns a ModuleFinder that limits observability to the given root
modules, their transitive dependences, plus a set of other modules.
/**
     * Returns a ModuleFinder that limits observability to the given root
     * modules, their transitive dependences, plus a set of other modules.
     */
    private static ModuleFinder limitFinder(ModuleFinder finder,
                                            Set<String> roots,
                                            Set<String> otherMods)
    {
        // resolve all root modules
        Configuration cf = Configuration.empty().resolve(finder,
                                                         ModuleFinder.of(),
                                                         roots);

        // module name -> reference
        Map<String, ModuleReference> map = new HashMap<>();

        // root modules and their transitive dependences
        cf.modules().stream()
            .map(ResolvedModule::reference)
            .forEach(mref -> map.put(mref.descriptor().name(), mref));

        // additional modules
        otherMods.stream()
            .map(finder::find)
            .flatMap(Optional::stream)
            .forEach(mref -> map.putIfAbsent(mref.descriptor().name(), mref));

        // set of modules that are observable
        Set<ModuleReference> mrefs = new HashSet<>(map.values());

        return new ModuleFinder() {
            @Override
            public Optional<ModuleReference> find(String name) {
                return Optional.ofNullable(map.get(name));
            }
            @Override
            public Set<ModuleReference> findAll() {
                return mrefs;
            }
        };
    }

    
Creates a finder from the module path that is the value of the given
system property and optionally patched by --patch-module
/**
     * Creates a finder from the module path that is the value of the given
     * system property and optionally patched by --patch-module
     */
    private static ModuleFinder finderFor(String prop) {
        String s = System.getProperty(prop);
        if (s == null) {
            return null;
        } else {
            String[] dirs = s.split(File.pathSeparator);
            Path[] paths = new Path[dirs.length];
            int i = 0;
            for (String dir: dirs) {
                paths[i++] = Path.of(dir);
            }
            return ModulePath.of(patcher, paths);
        }
    }

    
Initialize the module patcher for the initial configuration passed on the
value of the --patch-module options.
/**
     * Initialize the module patcher for the initial configuration passed on the
     * value of the --patch-module options.
     */
    private static ModulePatcher initModulePatcher() {
        Map<String, List<String>> map = decode("jdk.module.patch.",
                                               File.pathSeparator,
                                               false);
        return new ModulePatcher(map);
    }

    
Returns the set of module names specified by --add-module options.
/**
     * Returns the set of module names specified by --add-module options.
     */
    private static Set<String> addModules() {
        String prefix = "jdk.module.addmods.";
        int index = 0;
        // the system property is removed after decoding
        String value = getAndRemoveProperty(prefix + index);
        if (value == null) {
            return Set.of();
        } else {
            Set<String> modules = new HashSet<>();
            while (value != null) {
                for (String s : value.split(",")) {
                    if (!s.isEmpty())
                        modules.add(s);
                }
                index++;
                value = getAndRemoveProperty(prefix + index);
            }
            return modules;
        }
    }

    
Returns the set of module names specified by --limit-modules.
/**
     * Returns the set of module names specified by --limit-modules.
     */
    private static Set<String> limitModules() {
        String value = getAndRemoveProperty("jdk.module.limitmods");
        if (value == null) {
            return Set.of();
        } else {
            Set<String> names = new HashSet<>();
            for (String name : value.split(",")) {
                if (name.length() > 0) names.add(name);
            }
            return names;
        }
    }

    
Process the --add-reads options to add any additional read edges that
are specified on the command-line.
/**
     * Process the --add-reads options to add any additional read edges that
     * are specified on the command-line.
     */
    private static void addExtraReads(ModuleLayer bootLayer) {

        // decode the command line options
        Map<String, List<String>> map = decode("jdk.module.addreads.");
        if (map.isEmpty())
            return;

        for (Map.Entry<String, List<String>> e : map.entrySet()) {

            // the key is $MODULE
            String mn = e.getKey();
            Optional<Module> om = bootLayer.findModule(mn);
            if (!om.isPresent()) {
                warnUnknownModule(ADD_READS, mn);
                continue;
            }
            Module m = om.get();

            // the value is the set of other modules (by name)
            for (String name : e.getValue()) {
                if (ALL_UNNAMED.equals(name)) {
                    Modules.addReadsAllUnnamed(m);
                } else {
                    om = bootLayer.findModule(name);
                    if (om.isPresent()) {
                        Modules.addReads(m, om.get());
                    } else {
                        warnUnknownModule(ADD_READS, name);
                    }
                }
            }
        }
    }

    
Process the --add-exports and --add-opens options to export/open
additional packages specified on the command-line.
/**
     * Process the --add-exports and --add-opens options to export/open
     * additional packages specified on the command-line.
     */
    private static boolean addExtraExportsAndOpens(ModuleLayer bootLayer) {
        boolean extraExportsOrOpens = false;

        // --add-exports
        String prefix = "jdk.module.addexports.";
        Map<String, List<String>> extraExports = decode(prefix);
        if (!extraExports.isEmpty()) {
            addExtraExportsOrOpens(bootLayer, extraExports, false);
            extraExportsOrOpens = true;
        }


        // --add-opens
        prefix = "jdk.module.addopens.";
        Map<String, List<String>> extraOpens = decode(prefix);
        if (!extraOpens.isEmpty()) {
            addExtraExportsOrOpens(bootLayer, extraOpens, true);
            extraExportsOrOpens = true;
        }

        return extraExportsOrOpens;
    }

    private static void addExtraExportsOrOpens(ModuleLayer bootLayer,
                                               Map<String, List<String>> map,
                                               boolean opens)
    {
        String option = opens ? ADD_OPENS : ADD_EXPORTS;
        for (Map.Entry<String, List<String>> e : map.entrySet()) {

            // the key is $MODULE/$PACKAGE
            String key = e.getKey();
            String[] s = key.split("/");
            if (s.length != 2)
                fail(unableToParse(option, "<module>/<package>", key));

            String mn = s[0];
            String pn = s[1];
            if (mn.isEmpty() || pn.isEmpty())
                fail(unableToParse(option, "<module>/<package>", key));

            // The exporting module is in the boot layer
            Module m;
            Optional<Module> om = bootLayer.findModule(mn);
            if (!om.isPresent()) {
                warnUnknownModule(option, mn);
                continue;
            }

            m = om.get();

            if (!m.getDescriptor().packages().contains(pn)) {
                warn("package " + pn + " not in " + mn);
                continue;
            }

            // the value is the set of modules to export to (by name)
            for (String name : e.getValue()) {
                boolean allUnnamed = false;
                Module other = null;
                if (ALL_UNNAMED.equals(name)) {
                    allUnnamed = true;
                } else {
                    om = bootLayer.findModule(name);
                    if (om.isPresent()) {
                        other = om.get();
                    } else {
                        warnUnknownModule(option, name);
                        continue;
                    }
                }
                if (allUnnamed) {
                    if (opens) {
                        Modules.addOpensToAllUnnamed(m, pn);
                    } else {
                        Modules.addExportsToAllUnnamed(m, pn);
                    }
                } else {
                    if (opens) {
                        Modules.addOpens(m, pn, other);
                    } else {
                        Modules.addExports(m, pn, other);
                    }
                }

            }
        }
    }

    
Process the --illegal-access option (and its default) to open packages
of system modules in the boot layer to code in unnamed modules.
/**
     * Process the --illegal-access option (and its default) to open packages
     * of system modules in the boot layer to code in unnamed modules.
     */
    private static void addIllegalAccess(ModuleFinder upgradeModulePath,
                                         SystemModules systemModules,
                                         ModuleLayer bootLayer,
                                         boolean extraExportsOrOpens) {
        String value = getAndRemoveProperty("jdk.module.illegalAccess");
        IllegalAccessLogger.Mode mode = IllegalAccessLogger.Mode.ONESHOT;
        if (value != null) {
            switch (value) {
                case "deny":
                    return;
                case "permit":
                    break;
                case "warn":
                    mode = IllegalAccessLogger.Mode.WARN;
                    break;
                case "debug":
                    mode = IllegalAccessLogger.Mode.DEBUG;
                    break;
                default:
                    fail("Value specified to --illegal-access not recognized:"
                            + " '" + value + "'");
                    return;
            }
        }
        IllegalAccessLogger.Builder builder
            = new IllegalAccessLogger.Builder(mode, System.err);

        Map<String, Set<String>> map1 = systemModules.concealedPackagesToOpen();
        Map<String, Set<String>> map2 = systemModules.exportedPackagesToOpen();
        if (map1.isEmpty() && map2.isEmpty()) {
            // need to generate (exploded build)
            IllegalAccessMaps maps = IllegalAccessMaps.generate(limitedFinder());
            map1 = maps.concealedPackagesToOpen();
            map2 = maps.exportedPackagesToOpen();
        }

        // open specific packages in the system modules
        for (Module m : bootLayer.modules()) {
            ModuleDescriptor descriptor = m.getDescriptor();
            String name = m.getName();

            // skip open modules
            if (descriptor.isOpen()) {
                continue;
            }

            // skip modules loaded from the upgrade module path
            if (upgradeModulePath != null
                && upgradeModulePath.find(name).isPresent()) {
                continue;
            }

            Set<String> concealedPackages = map1.getOrDefault(name, Set.of());
            Set<String> exportedPackages = map2.getOrDefault(name, Set.of());

            // refresh the set of concealed and exported packages if needed
            if (extraExportsOrOpens) {
                concealedPackages = new HashSet<>(concealedPackages);
                exportedPackages = new HashSet<>(exportedPackages);
                Iterator<String> iterator = concealedPackages.iterator();
                while (iterator.hasNext()) {
                    String pn = iterator.next();
                    if (m.isExported(pn, BootLoader.getUnnamedModule())) {
                        // concealed package is exported to ALL-UNNAMED
                        iterator.remove();
                        exportedPackages.add(pn);
                    }
                }
                iterator = exportedPackages.iterator();
                while (iterator.hasNext()) {
                    String pn = iterator.next();
                    if (m.isOpen(pn, BootLoader.getUnnamedModule())) {
                        // exported package is opened to ALL-UNNAMED
                        iterator.remove();
                    }
                }
            }

            // log reflective access to all types in concealed packages
            builder.logAccessToConcealedPackages(m, concealedPackages);

            // log reflective access to non-public members/types in exported packages
            builder.logAccessToExportedPackages(m, exportedPackages);

            // open the packages to unnamed modules
            JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
            jla.addOpensToAllUnnamed(m, concat(concealedPackages.iterator(),
                                               exportedPackages.iterator()));
        }

        builder.complete();
    }

    
Decodes the values of --add-reads, -add-exports, --add-opens or
--patch-modules options that are encoded in system properties.
Params:
prefix – the system property prefix
@praam
regex the regex for splitting the RHS of the option value/**
     * Decodes the values of --add-reads, -add-exports, --add-opens or
     * --patch-modules options that are encoded in system properties.
     *
     * @param prefix the system property prefix
     * @praam regex the regex for splitting the RHS of the option value
     */
    private static Map<String, List<String>> decode(String prefix,
                                                    String regex,
                                                    boolean allowDuplicates) {
        int index = 0;
        // the system property is removed after decoding
        String value = getAndRemoveProperty(prefix + index);
        if (value == null)
            return Map.of();

        Map<String, List<String>> map = new HashMap<>();

        while (value != null) {

            int pos = value.indexOf('=');
            if (pos == -1)
                fail(unableToParse(option(prefix), "<module>=<value>", value));
            if (pos == 0)
                fail(unableToParse(option(prefix), "<module>=<value>", value));

            // key is <module> or <module>/<package>
            String key = value.substring(0, pos);

            String rhs = value.substring(pos+1);
            if (rhs.isEmpty())
                fail(unableToParse(option(prefix), "<module>=<value>", value));

            // value is <module>(,<module>)* or <file>(<pathsep><file>)*
            if (!allowDuplicates && map.containsKey(key))
                fail(key + " specified more than once to " + option(prefix));
            List<String> values = map.computeIfAbsent(key, k -> new ArrayList<>());
            int ntargets = 0;
            for (String s : rhs.split(regex)) {
                if (!s.isEmpty()) {
                    values.add(s);
                    ntargets++;
                }
            }
            if (ntargets == 0)
                fail("Target must be specified: " + option(prefix) + " " + value);

            index++;
            value = getAndRemoveProperty(prefix + index);
        }

        return map;
    }

    
Decodes the values of --add-reads, -add-exports or --add-opens
which use the "," to separate the RHS of the option value.
/**
     * Decodes the values of --add-reads, -add-exports or --add-opens
     * which use the "," to separate the RHS of the option value.
     */
    private static Map<String, List<String>> decode(String prefix) {
        return decode(prefix, ",", true);
    }

    
Gets and remove the named system property
/**
     * Gets and remove the named system property
     */
    private static String getAndRemoveProperty(String key) {
        return (String)System.getProperties().remove(key);
    }

    
Checks incubating status of modules in the configuration
/**
     * Checks incubating status of modules in the configuration
     */
    private static void checkIncubatingStatus(Configuration cf) {
        String incubating = null;
        for (ResolvedModule resolvedModule : cf.modules()) {
            ModuleReference mref = resolvedModule.reference();

            // emit warning if the WARN_INCUBATING module resolution bit set
            if (ModuleResolution.hasIncubatingWarning(mref)) {
                String mn = mref.descriptor().name();
                if (incubating == null) {
                    incubating = mn;
                } else {
                    incubating += ", " + mn;
                }
            }
        }
        if (incubating != null)
            warn("Using incubator modules: " + incubating);
    }

    
Throws a RuntimeException with the given message
/**
     * Throws a RuntimeException with the given message
     */
    static void fail(String m) {
        throw new RuntimeException(m);
    }

    static void warn(String m) {
        System.err.println("WARNING: " + m);
    }

    static void warnUnknownModule(String option, String mn) {
        warn("Unknown module: " + mn + " specified to " + option);
    }

    static String unableToParse(String option, String text, String value) {
        return "Unable to parse " +  option + " " + text + ": " + value;
    }

    private static final String ADD_MODULES  = "--add-modules";
    private static final String ADD_EXPORTS  = "--add-exports";
    private static final String ADD_OPENS    = "--add-opens";
    private static final String ADD_READS    = "--add-reads";
    private static final String PATCH_MODULE = "--patch-module";


    /*
     * Returns the command-line option name corresponds to the specified
     * system property prefix.
     */
    static String option(String prefix) {
        switch (prefix) {
            case "jdk.module.addexports.":
                return ADD_EXPORTS;
            case "jdk.module.addopens.":
                return ADD_OPENS;
            case "jdk.module.addreads.":
                return ADD_READS;
            case "jdk.module.patch.":
                return PATCH_MODULE;
            case "jdk.module.addmods.":
                return ADD_MODULES;
            default:
                throw new IllegalArgumentException(prefix);
        }
    }

    
Returns an iterator that yields all elements of the first iterator
followed by all the elements of the second iterator.
/**
     * Returns an iterator that yields all elements of the first iterator
     * followed by all the elements of the second iterator.
     */
    static <T> Iterator<T> concat(Iterator<T> iterator1, Iterator<T> iterator2) {
        return new Iterator<T>() {
            @Override
            public boolean hasNext() {
                return iterator1.hasNext() || iterator2.hasNext();
            }
            @Override
            public T next() {
                if (iterator1.hasNext()) return iterator1.next();
                if (iterator2.hasNext()) return iterator2.next();
                throw new NoSuchElementException();
            }
        };
    }

    
Wraps a (potentially not thread safe) ModuleFinder created during startup
for use after startup.
/**
     * Wraps a (potentially not thread safe) ModuleFinder created during startup
     * for use after startup.
     */
    static class SafeModuleFinder implements ModuleFinder {
        private final Set<ModuleReference> mrefs;
        private volatile Map<String, ModuleReference> nameToModule;

        SafeModuleFinder(ModuleFinder finder) {
            this.mrefs = Collections.unmodifiableSet(finder.findAll());
        }
        @Override
        public Optional<ModuleReference> find(String name) {
            Objects.requireNonNull(name);
            Map<String, ModuleReference> nameToModule = this.nameToModule;
            if (nameToModule == null) {
                this.nameToModule = nameToModule = mrefs.stream()
                        .collect(Collectors.toMap(m -> m.descriptor().name(),
                                                  Function.identity()));
            }
            return Optional.ofNullable(nameToModule.get(name));
        }
        @Override
        public Set<ModuleReference> findAll() {
            return mrefs;
        }
    }

    
Counters for startup performance analysis.
/**
     * Counters for startup performance analysis.
     */
    static class Counters {
        private static final boolean PUBLISH_COUNTERS;
        private static final boolean PRINT_COUNTERS;
        private static Map<String, Long> counters;
        static {
            String s = System.getProperty("jdk.module.boot.usePerfData");
            if (s == null) {
                PUBLISH_COUNTERS = false;
                PRINT_COUNTERS = false;
            } else {
                PUBLISH_COUNTERS = true;
                PRINT_COUNTERS = s.equals("debug");
                counters = new LinkedHashMap<>();  // preserve insert order
            }
        }

        
Add a counter
/**
         * Add a counter
         */
        static void add(String name, long start) {
            if (PUBLISH_COUNTERS || PRINT_COUNTERS) {
                counters.put(name, (System.nanoTime() - start));
            }
        }

        
Publish the counters to the instrumentation buffer or stdout.
/**
         * Publish the counters to the instrumentation buffer or stdout.
         */
        static void publish() {
            if (PUBLISH_COUNTERS || PRINT_COUNTERS) {
                for (Map.Entry<String, Long> e : counters.entrySet()) {
                    String name = e.getKey();
                    long value = e.getValue();
                    if (PUBLISH_COUNTERS)
                        PerfCounter.newPerfCounter(name).set(value);
                    if (PRINT_COUNTERS)
                        System.out.println(name + " = " + value);
                }
            }
        }
    }
}