internal/module/ModuleBootstrap.java

/*
 * Copyright (c) 2014, 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.  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.nio.file.Paths;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;

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

/**
 * 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 the configuration defined to a class loader.
 */

public final class ModuleBootstrap {
    private ModuleBootstrap() { }

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

    private static final String JAVA_SE = "java.se";

    // 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";

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

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

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

    /**
     * Returns the ModuleFinder for the initial configuration before observability
     * is limited by the --limit-modules command line option.
     */
    public static ModuleFinder unlimitedFinder() {
        assert unlimitedFinder != null;
        return unlimitedFinder;
    }

    /**
     * Returns the ModuleFinder for the initial configuration.
     */
    public static ModuleFinder limitedFinder() {
        assert limitedFinder != null;
        return limitedFinder;
    }

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

        // Step 1: Locate system modules (may be patched)

        long t1 = System.nanoTime();
        ModuleFinder systemModules = ModuleFinder.ofSystem();
        PerfCounters.systemModulesTime.addElapsedTimeFrom(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 = systemModules.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);

        PerfCounters.defineBaseTime.addElapsedTimeFrom(t2);


        // Step 2a: If --validate-modules is specified then the VM needs to
        // start with only java.base, all other options are ignored.

        String propValue = getAndRemoveProperty("jdk.module.minimumBoot");
        if (propValue != null) {
            return createMinimalBootLayer();
        }


        // Step 3: Construct the module path and the set of root modules to
        // resolve. If --limit-modules is specified then it limits the set
        // modules that are observable.

        long t3 = System.nanoTime();

        // --upgrade-module-path option specified to launcher
        ModuleFinder upgradeModulePath
            = createModulePathFinder("jdk.module.upgrade.path");
        if (upgradeModulePath != null)
            systemModules = ModuleFinder.compose(upgradeModulePath, systemModules);

        // --module-path option specified to the launcher
        ModuleFinder appModulePath = createModulePathFinder("jdk.module.path");

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

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

        // launcher -m option to specify the main/initial module
        String mainModule = System.getProperty("jdk.module.main");
        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: getExtraAddModules()) {
            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
        unlimitedFinder = finder;
        propValue = getAndRemoveProperty("jdk.module.limitmods");
        if (propValue != null) {
            Set<String> mods = new HashSet<>();
            for (String mod: propValue.split(",")) {
                mods.add(mod);
            }
            finder = limitFinder(finder, mods, roots);
        }
        limitedFinder = finder;

        // 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 "java.se" and all (non-java.*) modules
        // that export an API. If "java.se" is not observable then all java.*
        // modules are resolved. 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) {
            boolean hasJava = false;
            if (systemModules.find(JAVA_SE).isPresent()) {
                // java.se is a system module
                if (finder == systemModules || finder.find(JAVA_SE).isPresent()) {
                    // java.se is observable
                    hasJava = true;
                    roots.add(JAVA_SE);
                }
            }

            for (ModuleReference mref : systemModules.findAll()) {
                String mn = mref.descriptor().name();
                if (hasJava && mn.startsWith("java."))
                    continue;

                if (ModuleResolution.doNotResolveByDefault(mref))
                    continue;

                // add as root if observable and exports at least one package
                if ((finder == systemModules || finder.find(mn).isPresent())) {
                    ModuleDescriptor descriptor = mref.descriptor();
                    for (ModuleDescriptor.Exports e : descriptor.exports()) {
                        if (!e.isQualified()) {
                            roots.add(mn);
                            break;
                        }
                    }
                }
            }
        }

        // If `--add-modules ALL-SYSTEM` is specified then all observable system
        // modules will be resolved.
        if (addAllSystemModules) {
            ModuleFinder f = finder;  // observable modules
            systemModules.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));
        }

        PerfCounters.optionsAndRootsTime.addElapsedTimeFrom(t3);


        // Step 4: Resolve the root modules, with service binding, to create
        // the configuration for the boot layer.

        long t4 = System.nanoTime();

        // determine if post resolution checks are needed
        boolean needPostResolutionChecks = true;
        if (baseUri.getScheme().equals("jrt")   // toLowerCase not needed here
                && (upgradeModulePath == null)
                && (appModulePath == null)
                && (patcher.isEmpty())) {
            needPostResolutionChecks = false;
        }

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

        // run the resolver to create the configuration
        Configuration cf = SharedSecrets.getJavaLangModuleAccess()
                .resolveAndBind(finder,
                                roots,
                                needPostResolutionChecks,
                                traceOutput);

        PerfCounters.resolveTime.addElapsedTimeFrom(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 (needPostResolutionChecks) {
            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 (!systemModules.find(name).isPresent())
                        fail(name + ": cannot be loaded from application module path");
                }
            }

            // check if module specified in --patch-module is present
            for (String mn: patcher.patchedModules()) {
                if (!cf.findModule(mn).isPresent()) {
                    warnUnknownModule(PATCH_MODULE, mn);
                }
            }
        }

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

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

        PerfCounters.loadModulesTime.addElapsedTimeFrom(t5);


        // Step 6: Define all modules to the VM

        long t6 = System.nanoTime();
        ModuleLayer bootLayer = ModuleLayer.empty().defineModules(cf, clf);
        PerfCounters.layerCreateTime.addElapsedTimeFrom(t6);


        // Step 7: Miscellaneous

        // check incubating status
        checkIncubatingStatus(cf);

        // --add-reads, --add-exports/--add-opens, and -illegal-access
        long t7 = System.nanoTime();
        addExtraReads(bootLayer);
        boolean extraExportsOrOpens = addExtraExportsAndOpens(bootLayer);
        addIllegalAccess(bootLayer, upgradeModulePath, extraExportsOrOpens);
        PerfCounters.adjustModulesTime.addElapsedTimeFrom(t7);

        // total time to initialize
        PerfCounters.bootstrapTime.addElapsedTimeFrom(t1);

        return bootLayer;
    }

    /**
     * Create a "minimal" boot module layer that only contains java.base.
     */
    private static ModuleLayer createMinimalBootLayer() {
        Configuration cf = SharedSecrets.getJavaLangModuleAccess()
            .resolveAndBind(ModuleFinder.ofSystem(),
                            Set.of(JAVA_BASE),
                            false,
                            null);

        Function<String, ClassLoader> clf = ModuleLoaderMap.mappingFunction(cf);
        return ModuleLayer.empty().defineModules(cf, clf);
    }

    /**
     * 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.
     */
    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.
     */
    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
     */
    private static ModuleFinder createModulePathFinder(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++] = Paths.get(dir);
            }
            return ModulePath.of(patcher, paths);
        }
    }

    /**
     * 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 via --add-modules options
     * on the command line
     */
    private static Set<String> getExtraAddModules() {
        String prefix = "jdk.module.addmods.";
        int index = 0;

        // the system property is removed after decoding
        String value = getAndRemoveProperty(prefix + index);
        if (value == null) {
            return Collections.emptySet();
        }

        Set<String> modules = new HashSet<>();
        while (value != null) {
            for (String s : value.split(",")) {
                if (s.length() > 0) modules.add(s);
            }
            index++;
            value = getAndRemoveProperty(prefix + index);
        }

        return modules;
    }

    /**
     * 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.
     */
    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.
     */
    private static void addIllegalAccess(ModuleLayer bootLayer,
                                         ModuleFinder upgradeModulePath,
                                         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 maps when on 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.
     *
     * @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 Collections.emptyMap();

        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.length() > 0) {
                    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.
     */
    private static Map<String, List<String>> decode(String prefix) {
        return decode(prefix, ",", true);
    }

    /**
     * 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
     */
    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
     */
    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);
        }
    }

    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();
            }
        };
    }

    static class PerfCounters {

        static PerfCounter systemModulesTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.systemModulesTime");
        static PerfCounter defineBaseTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.defineBaseTime");
        static PerfCounter optionsAndRootsTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.optionsAndRootsTime");
        static PerfCounter resolveTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.resolveTime");
        static PerfCounter layerCreateTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.layerCreateTime");
        static PerfCounter loadModulesTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.loadModulesTime");
        static PerfCounter adjustModulesTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.adjustModulesTime");
        static PerfCounter bootstrapTime
            = PerfCounter.newPerfCounter("jdk.module.bootstrap.totalTime");
    }
}