Copyright (c) 2012, 2017 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2012, 2017 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.container;

import java.security.Permission;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CancellationException;
import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.felix.resolver.Logger;
import org.apache.felix.resolver.ResolutionError;
import org.apache.felix.resolver.ResolverImpl;
import org.eclipse.osgi.container.ModuleRequirement.DynamicModuleRequirement;
import org.eclipse.osgi.container.namespaces.EquinoxFragmentNamespace;
import org.eclipse.osgi.internal.container.InternalUtils;
import org.eclipse.osgi.internal.debug.Debug;
import org.eclipse.osgi.internal.framework.EquinoxConfiguration;
import org.eclipse.osgi.internal.framework.EquinoxContainer;
import org.eclipse.osgi.internal.messages.Msg;
import org.eclipse.osgi.report.resolution.ResolutionReport;
import org.eclipse.osgi.report.resolution.ResolutionReport.Entry;
import org.eclipse.osgi.report.resolution.ResolutionReport.Entry.Type;
import org.eclipse.osgi.service.debug.DebugOptions;
import org.osgi.framework.BundleException;
import org.osgi.framework.Version;
import org.osgi.framework.hooks.resolver.ResolverHook;
import org.osgi.framework.namespace.BundleNamespace;
import org.osgi.framework.namespace.ExecutionEnvironmentNamespace;
import org.osgi.framework.namespace.HostNamespace;
import org.osgi.framework.namespace.IdentityNamespace;
import org.osgi.framework.namespace.PackageNamespace;
import org.osgi.framework.wiring.BundleCapability;
import org.osgi.framework.wiring.BundleRequirement;
import org.osgi.framework.wiring.BundleRevision;
import org.osgi.resource.Capability;
import org.osgi.resource.Namespace;
import org.osgi.resource.Requirement;
import org.osgi.resource.Resource;
import org.osgi.resource.Wire;
import org.osgi.resource.Wiring;
import org.osgi.service.resolver.HostedCapability;
import org.osgi.service.resolver.ResolutionException;
import org.osgi.service.resolver.ResolveContext;
import org.osgi.service.resolver.Resolver;

The module resolver handles calls to the Resolver service for resolving modules in a module container. /**
 * The module resolver handles calls to the {@link Resolver} service for resolving modules
 * in a module {@link ModuleContainer container}.
 */
final class ModuleResolver {
	static final String SEPARATOR = System.getProperty("line.separator"); //$NON-NLS-1$
	static final char TAB = '\t';

	private static final String OPTION_RESOLVER = EquinoxContainer.NAME + "/resolver"; //$NON-NLS-1$
	private static final String OPTION_ROOTS = OPTION_RESOLVER + "/roots"; //$NON-NLS-1$
	private static final String OPTION_PROVIDERS = OPTION_RESOLVER + "/providers"; //$NON-NLS-1$
	private static final String OPTION_HOOKS = OPTION_RESOLVER + "/hooks"; //$NON-NLS-1$
	private static final String OPTION_USES = OPTION_RESOLVER + "/uses"; //$NON-NLS-1$
	private static final String OPTION_WIRING = OPTION_RESOLVER + "/wiring"; //$NON-NLS-1$
	private static final String OPTION_REPORT = OPTION_RESOLVER + "/report"; //$NON-NLS-1$

	boolean DEBUG_ROOTS = false;
	boolean DEBUG_PROVIDERS = false;
	boolean DEBUG_HOOKS = false;
	boolean DEBUG_USES = false;
	boolean DEBUG_WIRING = false;
	boolean DEBUG_REPORT = false;

	private static final int DEFAULT_BATCH_SIZE = Integer.MAX_VALUE;
	private static final int BATCH_MIN_TIMEOUT = (int) TimeUnit.SECONDS.toMillis(5);
	private static final int DEFAULT_BATCH_TIMEOUT = (int) TimeUnit.MINUTES.toMillis(2);
	final int resolverRevisionBatchSize;
	final int resolverBatchTimeout;

	void setDebugOptions() {
		DebugOptions options = adaptor.getDebugOptions();
		// may be null if debugging is not enabled
		if (options == null)
			return;
		boolean debugAll = options.getBooleanOption(OPTION_RESOLVER, false);
		DEBUG_ROOTS = debugAll || options.getBooleanOption(OPTION_ROOTS, false);
		DEBUG_PROVIDERS = debugAll || options.getBooleanOption(OPTION_PROVIDERS, false);
		DEBUG_HOOKS = debugAll || options.getBooleanOption(OPTION_HOOKS, false);
		DEBUG_USES = debugAll || options.getBooleanOption(OPTION_USES, false);
		DEBUG_WIRING = debugAll || options.getBooleanOption(OPTION_WIRING, false);
		DEBUG_REPORT = debugAll || options.getBooleanOption(OPTION_REPORT, false);
	}

	static final Collection<String> NON_PAYLOAD_CAPABILITIES = Arrays.asList(IdentityNamespace.IDENTITY_NAMESPACE);
	static final Collection<String> NON_PAYLOAD_REQUIREMENTS = Arrays.asList(HostNamespace.HOST_NAMESPACE, ExecutionEnvironmentNamespace.EXECUTION_ENVIRONMENT_NAMESPACE);
	static final Collection<String> NON_SUBSTITUTED_REQUIREMENTS = Arrays.asList(PackageNamespace.PACKAGE_NAMESPACE, BundleNamespace.BUNDLE_NAMESPACE);

	final ThreadLocal<Boolean> threadResolving = new ThreadLocal<>();
	final ModuleContainerAdaptor adaptor;

	
Constructs the module resolver with the specified resolver hook factory
and resolver.
Params:
adaptor – the container adaptor/**
	 * Constructs the module resolver with the specified resolver hook factory
	 * and resolver.
	 * @param adaptor the container adaptor
	 */
	ModuleResolver(final ModuleContainerAdaptor adaptor) {
		this.adaptor = adaptor;

		setDebugOptions();

		String batchSizeConfig = this.adaptor.getProperty(EquinoxConfiguration.PROP_RESOLVER_REVISION_BATCH_SIZE);
		this.resolverRevisionBatchSize = parseInteger(batchSizeConfig, DEFAULT_BATCH_SIZE, 1);
		String batchTimeoutConfig = this.adaptor.getProperty(EquinoxConfiguration.PROP_RESOLVER_BATCH_TIMEOUT);
		this.resolverBatchTimeout = parseInteger(batchTimeoutConfig, DEFAULT_BATCH_TIMEOUT, BATCH_MIN_TIMEOUT);

	}

	private static int parseInteger(String sInteger, int defaultValue, int minValue) {
		try {
			int result = sInteger == null ? defaultValue : Integer.parseInt(sInteger);
			return result < minValue ? minValue : result;
		} catch (NumberFormatException e) {
			return defaultValue;
		}
	}

	
Attempts to resolve all unresolved modules installed in the specified module database.
returns a delta containing the new wirings or modified wirings that should be 
merged into the specified moduleDatabase.

This method only does read operations on the database no wirings are modified
directly by this method.  The returned wirings need to be merged into 
the database.
Params:
triggers – the triggers that caused the resolver operation to occur
triggersMandatory – true if the triggers must be resolved by the resolve process
unresolved – a snapshot of unresolved revisions
wiringCopy – the wirings snapshot of the currently resolved revisions
moduleDatabase – the module database.
Throws:
ResolutionException – 
Returns:
a delta container the new wirings or modified wirings that should be
merged into the moduleDatabase/**
	 * Attempts to resolve all unresolved modules installed in the specified module database.
	 * returns a delta containing the new wirings or modified wirings that should be 
	 * merged into the specified moduleDatabase.
	 * <p>
	 * This method only does read operations on the database no wirings are modified
	 * directly by this method.  The returned wirings need to be merged into 
	 * the database.
	 * @param triggers the triggers that caused the resolver operation to occur
	 * @param triggersMandatory true if the triggers must be resolved by the resolve process
	 * @param unresolved a snapshot of unresolved revisions
	 * @param wiringCopy the wirings snapshot of the currently resolved revisions
	 * @param moduleDatabase the module database.
	 * @return a delta container the new wirings or modified wirings that should be
	 * merged into the moduleDatabase
	 * @throws ResolutionException
	 */
	ModuleResolutionReport resolveDelta(Collection<ModuleRevision> triggers, boolean triggersMandatory, Collection<ModuleRevision> unresolved, Map<ModuleRevision, ModuleWiring> wiringCopy, ModuleDatabase moduleDatabase) {
		ResolveProcess resolveProcess = new ResolveProcess(unresolved, triggers, triggersMandatory, wiringCopy, moduleDatabase);
		return resolveProcess.resolve();
	}

	ModuleResolutionReport resolveDynamicDelta(DynamicModuleRequirement dynamicReq, Collection<ModuleRevision> unresolved, Map<ModuleRevision, ModuleWiring> wiringCopy, ModuleDatabase moduleDatabase) {
		ResolveProcess resolveProcess = new ResolveProcess(unresolved, dynamicReq, wiringCopy, moduleDatabase);
		return resolveProcess.resolve();
	}

	Map<ModuleRevision, ModuleWiring> generateDelta(Map<Resource, List<Wire>> result, Map<ModuleRevision, ModuleWiring> wiringCopy) {
		Map<ModuleRevision, Map<ModuleCapability, List<ModuleWire>>> provided = new HashMap<>();
		Map<ModuleRevision, List<ModuleWire>> required = new HashMap<>();
		// First populate the list of provided and required wires for revision
		// This is done this way to share the wire object between both the provider and requirer
		for (Map.Entry<Resource, List<Wire>> resultEntry : result.entrySet()) {
			ModuleRevision revision = (ModuleRevision) resultEntry.getKey();
			List<ModuleWire> requiredWires = new ArrayList<>(resultEntry.getValue().size());
			for (Wire wire : resultEntry.getValue()) {
				ModuleWire moduleWire = new ModuleWire((ModuleCapability) wire.getCapability(), (ModuleRevision) wire.getProvider(), (ModuleRequirement) wire.getRequirement(), (ModuleRevision) wire.getRequirer());
				requiredWires.add(moduleWire);
				Map<ModuleCapability, List<ModuleWire>> providedWiresMap = provided.get(moduleWire.getProvider());
				if (providedWiresMap == null) {
					providedWiresMap = new HashMap<>();
					provided.put(moduleWire.getProvider(), providedWiresMap);
				}
				List<ModuleWire> providedWires = providedWiresMap.get(moduleWire.getCapability());
				if (providedWires == null) {
					providedWires = new ArrayList<>();
					providedWiresMap.put(moduleWire.getCapability(), providedWires);
				}
				providedWires.add(moduleWire);
			}
			required.put(revision, requiredWires);
		}

		Map<ModuleRevision, ModuleWiring> delta = new HashMap<>();
		// now create the ModuleWiring for the newly resolved revisions
		for (ModuleRevision revision : required.keySet()) {
			ModuleWiring existingWiring = wiringCopy.get(revision);
			if (existingWiring == null) {
				delta.put(revision, createNewWiring(revision, provided, required));
			} else {
				// this is to handle dynamic imports
				delta.put(revision, createWiringDelta(revision, existingWiring, provided.get(revision), required.get(revision)));
			}
		}
		// Also need to create the wiring deltas for already resolved bundles
		// This should only include updating provided wires and
		// for fragments it may include new hosts
		for (ModuleRevision revision : provided.keySet()) {
			ModuleWiring existingWiring = wiringCopy.get(revision);
			if (existingWiring != null && !delta.containsKey(revision)) {
				delta.put(revision, createWiringDelta(revision, existingWiring, provided.get(revision), required.get(revision)));
			}
		}
		return delta;
	}

	private ModuleWiring createNewWiring(ModuleRevision revision, Map<ModuleRevision, Map<ModuleCapability, List<ModuleWire>>> provided, Map<ModuleRevision, List<ModuleWire>> required) {
		Map<ModuleCapability, List<ModuleWire>> providedWireMap = provided.get(revision);
		if (providedWireMap == null)
			providedWireMap = Collections.emptyMap();
		List<ModuleWire> requiredWires = required.get(revision);
		if (requiredWires == null)
			requiredWires = Collections.emptyList();

		List<ModuleCapability> capabilities = new ArrayList<>(revision.getModuleCapabilities(null));
		ListIterator<ModuleCapability> iCapabilities = capabilities.listIterator(capabilities.size());
		List<ModuleRequirement> requirements = new ArrayList<>(revision.getModuleRequirements(null));
		ListIterator<ModuleRequirement> iRequirements = requirements.listIterator(requirements.size());

		// if revision is a fragment remove payload requirements and capabilities
		if ((BundleRevision.TYPE_FRAGMENT & revision.getTypes()) != 0) {
			removePayloadContent(iCapabilities, iRequirements);
		} else {
			// add fragment capabilities and requirements
			List<ModuleCapability> hostCapabilities = revision.getModuleCapabilities(HostNamespace.HOST_NAMESPACE);
			ModuleCapability hostCapability = hostCapabilities.isEmpty() ? null : hostCapabilities.get(0);
			if (hostCapability != null) {
				addPayloadContent(providedWireMap.get(hostCapability), iCapabilities, iRequirements);
			}
		}

		removeNonEffectiveCapabilities(iCapabilities);
		removeNonEffectiveRequirements(iRequirements, requiredWires);
		Collection<String> substituted = removeSubstitutedCapabilities(iCapabilities, requiredWires);

		List<ModuleWire> providedWires = new ArrayList<>();
		addProvidedWires(providedWireMap, providedWires, capabilities);

		InternalUtils.filterCapabilityPermissions(capabilities);
		return new ModuleWiring(revision, capabilities, requirements, providedWires, requiredWires, substituted);
	}

	private static void removePayloadContent(ListIterator<ModuleCapability> iCapabilities, ListIterator<ModuleRequirement> iRequirements) {
		rewind(iCapabilities);
		while (iCapabilities.hasNext()) {
			if (!NON_PAYLOAD_CAPABILITIES.contains(iCapabilities.next().getNamespace())) {
				iCapabilities.remove();
			}
		}

		rewind(iRequirements);
		while (iRequirements.hasNext()) {
			if (!NON_PAYLOAD_REQUIREMENTS.contains(iRequirements.next().getNamespace())) {
				iRequirements.remove();
			}
		}
	}

	private static Collection<String> removeSubstitutedCapabilities(ListIterator<ModuleCapability> iCapabilities, List<ModuleWire> requiredWires) {
		Collection<String> substituted = null;
		for (ModuleWire moduleWire : requiredWires) {
			if (!PackageNamespace.PACKAGE_NAMESPACE.equals(moduleWire.getCapability().getNamespace()))
				continue;
			String packageName = (String) moduleWire.getCapability().getAttributes().get(PackageNamespace.PACKAGE_NAMESPACE);
			rewind(iCapabilities);
			while (iCapabilities.hasNext()) {
				ModuleCapability capability = iCapabilities.next();
				if (PackageNamespace.PACKAGE_NAMESPACE.equals(capability.getNamespace())) {
					if (packageName.equals(capability.getAttributes().get(PackageNamespace.PACKAGE_NAMESPACE))) {
						// found a package capability with the same name as a package that got imported
						// this indicates a substitution
						iCapabilities.remove();
						if (substituted == null) {
							substituted = new ArrayList<>();
						}
						if (!substituted.contains(packageName)) {
							substituted.add(packageName);
						}
					}
				}
			}
		}
		return substituted == null ? Collections.<String> emptyList() : substituted;
	}

	private static void removeNonEffectiveRequirements(ListIterator<ModuleRequirement> iRequirements, List<ModuleWire> requiredWires) {

		Set<ModuleRequirement> wireRequirements = new HashSet<>();
		for (ModuleWire mw : requiredWires) {
			wireRequirements.add(mw.getRequirement());
		}

		rewind(iRequirements);
		while (iRequirements.hasNext()) {
			ModuleRequirement requirement = iRequirements.next();
			// check the effective directive;
			Object effective = requirement.getDirectives().get(Namespace.REQUIREMENT_EFFECTIVE_DIRECTIVE);
			if (effective != null && !Namespace.EFFECTIVE_RESOLVE.equals(effective)) {
				iRequirements.remove();
			} else {

				if (!wireRequirements.contains(requirement)) {
					if (!PackageNamespace.PACKAGE_NAMESPACE.equals(requirement.getNamespace())) {
						iRequirements.remove();
					} else {
						Object resolution = requirement.getDirectives().get(Namespace.REQUIREMENT_RESOLUTION_DIRECTIVE);
						if (!PackageNamespace.RESOLUTION_DYNAMIC.equals(resolution)) {
							iRequirements.remove();
						}
					}
				}
			}
		}
	}

	void removeNonEffectiveCapabilities(ListIterator<ModuleCapability> iCapabilities) {
		rewind(iCapabilities);
		while (iCapabilities.hasNext()) {
			Capability capability = iCapabilities.next();
			Object effective = capability.getDirectives().get(Namespace.CAPABILITY_EFFECTIVE_DIRECTIVE);
			if (effective != null && !Namespace.EFFECTIVE_RESOLVE.equals(effective)) {
				iCapabilities.remove();
				if (DEBUG_PROVIDERS) {
					Debug.println(new StringBuilder("RESOLVER: Capability filtered because it was not effective") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB) //
							.append(capability) //
							.append(SEPARATOR).append(TAB).append(TAB) //
							.append("of resource") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
							.append(capability.getResource()) //
							.toString());
				}
			}
		}
	}

	private static void addPayloadContent(List<ModuleWire> hostWires, ListIterator<ModuleCapability> iCapabilities, ListIterator<ModuleRequirement> iRequirements) {
		if (hostWires == null)
			return;
		for (ModuleWire hostWire : hostWires) {
			// add fragment capabilities
			String currentNamespace = null;
			List<ModuleCapability> fragmentCapabilities = hostWire.getRequirer().getModuleCapabilities(null);
			for (ModuleCapability fragmentCapability : fragmentCapabilities) {
				if (NON_PAYLOAD_CAPABILITIES.contains(fragmentCapability.getNamespace())) {
					continue; // don't include, not a payload capability
				}
				if (!fragmentCapability.getNamespace().equals(currentNamespace)) {
					currentNamespace = fragmentCapability.getNamespace();
					fastForward(iCapabilities);
					while (iCapabilities.hasPrevious()) {
						if (iCapabilities.previous().getNamespace().equals(currentNamespace)) {
							iCapabilities.next(); // put position after the last one
							break;
						}
					}
				}
				iCapabilities.add(fragmentCapability);
			}
			// add fragment requirements
			currentNamespace = null;
			List<ModuleRequirement> fragmentRequriements = hostWire.getRequirer().getModuleRequirements(null);
			for (ModuleRequirement fragmentRequirement : fragmentRequriements) {
				if (NON_PAYLOAD_REQUIREMENTS.contains(fragmentRequirement.getNamespace())) {
					continue; // don't inlcude, not a payload requirement
				}
				if (!fragmentRequirement.getNamespace().equals(currentNamespace)) {
					currentNamespace = fragmentRequirement.getNamespace();
					boolean isDynamic = isDynamic(fragmentRequirement);
					fastForward(iRequirements);
					while (iRequirements.hasPrevious()) {
						ModuleRequirement previous = iRequirements.previous();
						if (previous.getNamespace().equals(currentNamespace)) {
							if (isDynamic || !isDynamic(previous)) {
								iRequirements.next(); // put position after the last one
								break;
							}
						}
					}
				}
				iRequirements.add(fragmentRequirement);
			}
		}
	}

	static boolean isDynamic(Requirement requirement) {
		return PackageNamespace.PACKAGE_NAMESPACE.equals(requirement.getNamespace()) && PackageNamespace.RESOLUTION_DYNAMIC.equals(requirement.getDirectives().get(Namespace.REQUIREMENT_RESOLUTION_DIRECTIVE));
	}

	private static void addProvidedWires(Map<ModuleCapability, List<ModuleWire>> toAdd, List<ModuleWire> existing, final List<ModuleCapability> orderedCapabilities) {
		if (toAdd == null)
			return;
		int originalSize = existing.size();
		for (ModuleCapability capability : orderedCapabilities) {
			List<ModuleWire> newWires = toAdd.get(capability);
			if (newWires != null) {
				existing.addAll(newWires);
			}
		}
		if (originalSize != 0) {
			Collections.sort(existing, new Comparator<ModuleWire>() {
				@Override
				public int compare(ModuleWire w1, ModuleWire w2) {
					int index1 = orderedCapabilities.indexOf(w1.getCapability());
					int index2 = orderedCapabilities.indexOf(w2.getCapability());
					return index1 - index2;
				}
			});
		}
	}

	private static void addRequiredWires(List<ModuleWire> toAdd, List<ModuleWire> existing, final List<ModuleRequirement> orderedRequirements) {
		if (toAdd == null)
			return;
		int originalSize = existing.size();
		existing.addAll(toAdd);
		if (originalSize != 0) {
			Collections.sort(existing, new Comparator<ModuleWire>() {
				@Override
				public int compare(ModuleWire w1, ModuleWire w2) {
					int index1 = orderedRequirements.indexOf(w1.getRequirement());
					int index2 = orderedRequirements.indexOf(w2.getRequirement());
					return index1 - index2;
				}
			});
		}
	}

	private static void fastForward(ListIterator<?> listIterator) {
		while (listIterator.hasNext())
			listIterator.next();
	}

	static void rewind(ListIterator<?> listIterator) {
		while (listIterator.hasPrevious())
			listIterator.previous();
	}

	private static ModuleWiring createWiringDelta(ModuleRevision revision, ModuleWiring existingWiring, Map<ModuleCapability, List<ModuleWire>> providedWireMap, List<ModuleWire> requiredWires) {
		// No null checks are done here on the wires since this is a copy.
		List<ModuleWire> existingProvidedWires = existingWiring.getProvidedModuleWires(null);
		List<ModuleCapability> existingCapabilities = existingWiring.getModuleCapabilities(null);
		List<ModuleWire> existingRequiredWires = existingWiring.getRequiredModuleWires(null);
		List<ModuleRequirement> existingRequirements = existingWiring.getModuleRequirements(null);

		// First, add newly resolved fragment capabilities and requirements
		if (providedWireMap != null) {
			List<ModuleCapability> hostCapabilities = revision.getModuleCapabilities(HostNamespace.HOST_NAMESPACE);
			ModuleCapability hostCapability = hostCapabilities.isEmpty() ? null : hostCapabilities.get(0);
			List<ModuleWire> newHostWires = hostCapability == null ? null : providedWireMap.get(hostCapability);
			if (newHostWires != null) {
				addPayloadContent(newHostWires, existingCapabilities.listIterator(), existingRequirements.listIterator());
			}
		}

		// Create a ModuleWiring that only contains the new ordered list of provided wires
		addProvidedWires(providedWireMap, existingProvidedWires, existingCapabilities);

		// Also need to include any new required wires that may have be added for fragment hosts
		// Also will be needed for dynamic imports
		addRequiredWires(requiredWires, existingRequiredWires, existingRequirements);

		InternalUtils.filterCapabilityPermissions(existingCapabilities);
		return new ModuleWiring(revision, existingCapabilities, existingRequirements, existingProvidedWires, existingRequiredWires, Collections.EMPTY_LIST);
	}

	static boolean isSingleton(ModuleRevision revision) {
		List<Capability> identities = revision.getCapabilities(IdentityNamespace.IDENTITY_NAMESPACE);
		if (identities.isEmpty())
			return false;
		return "true".equals(identities.get(0).getDirectives().get(IdentityNamespace.CAPABILITY_SINGLETON_DIRECTIVE)); //$NON-NLS-1$
	}

	static Version getVersion(Capability c) {
		String versionAttr = null;
		String namespace = c.getNamespace();
		if (IdentityNamespace.IDENTITY_NAMESPACE.equals(namespace)) {
			versionAttr = IdentityNamespace.CAPABILITY_VERSION_ATTRIBUTE;
		} else if (PackageNamespace.PACKAGE_NAMESPACE.equals(namespace)) {
			versionAttr = PackageNamespace.CAPABILITY_VERSION_ATTRIBUTE;
		} else if (BundleNamespace.BUNDLE_NAMESPACE.equals(namespace)) {
			versionAttr = BundleNamespace.CAPABILITY_BUNDLE_VERSION_ATTRIBUTE;
		} else if (HostNamespace.HOST_NAMESPACE.equals(namespace)) {
			versionAttr = HostNamespace.CAPABILITY_BUNDLE_VERSION_ATTRIBUTE;
		} else {
			// Just default to version attribute
			versionAttr = IdentityNamespace.CAPABILITY_VERSION_ATTRIBUTE;
		}
		Object version = c.getAttributes().get(versionAttr);
		return version instanceof Version ? (Version) version : Version.emptyVersion;
	}

	class ResolveProcess extends ResolveContext implements Comparator<Capability>, Executor {

		class ResolveLogger extends Logger {
			private Map<Resource, ResolutionException> errors = null;

			public ResolveLogger() {
				super(DEBUG_USES ? Logger.LOG_DEBUG : 0);
			}

			@Override
			public void logUsesConstraintViolation(Resource resource, ResolutionError error) {
				if (errors == null) {
					errors = new HashMap<>();
				}
				errors.put(resource, error.toException());
				if (DEBUG_USES) {
					Debug.println(new StringBuilder("RESOLVER: Uses constraint violation") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB) //
							.append("Resource") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB).append(TAB) //
							.append(resource) //
							.append(SEPARATOR).append(TAB) //
							.append("Error") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB).append(TAB) //
							.append(error.getMessage()) //
							.toString());
				}
			}

			Map<Resource, ResolutionException> getUsesConstraintViolations() {
				return errors == null ? Collections.<Resource, ResolutionException> emptyMap() : errors;
			}

			@Override
			public boolean isDebugEnabled() {
				return DEBUG_USES;
			}

			@Override
			protected void doLog(int level, String msg, Throwable throwable) {
				Debug.println("RESOLVER: " + msg + SEPARATOR + (throwable != null ? (TAB + TAB + throwable.getMessage()) : "")); //$NON-NLS-1$ //$NON-NLS-2$
			}

		}

		private final ModuleResolutionReport.Builder reportBuilder = new ModuleResolutionReport.Builder();
		/*
		 * Contains the revisions that were requested to be resolved and is not
		 * modified post instantiation.
		 */
		private final Collection<ModuleRevision> unresolved;
		/*
		 * Contains unresolved revisions that should not be resolved as part of
		 * this process. The reasons they should not be resolved will vary. For 
		 * example, some might have been filtered out by the resolver hook while
		 * others represent singleton collisions. It is assumed that all
		 * unresolved revisions are disabled at the start of the resolve
		 * process (see initialization in constructors). Any not filtered out
		 * by ResolverHook.filterResolvable are then removed but may be added 
		 * back later for other reasons.
		 */
		private final Collection<ModuleRevision> disabled;
		private final Collection<ModuleRevision> triggers;
		private final Collection<ModuleRevision> optionals;
		private final boolean triggersMandatory;
		final ModuleDatabase moduleDatabase;
		final Map<ModuleRevision, ModuleWiring> wirings;
		private final Set<ModuleRevision> previouslyResolved;
		private final DynamicModuleRequirement dynamicReq;
		private volatile ResolverHook hook = null;
		private volatile Map<String, Collection<ModuleRevision>> byName = null;
		private volatile List<Resource> currentlyResolving = null;
		private volatile boolean currentlyResolvingMandatory = false;
		private final Set<Resource> transitivelyResolveFailures = new LinkedHashSet<>();
		private final Set<Resource> failedToResolve = new HashSet<>();
		private AtomicBoolean scheduleTimeout = new AtomicBoolean(true);
		private AtomicReference<ScheduledFuture<?>> timoutFuture = new AtomicReference<>();
		/*
		 * Used to generate the UNRESOLVED_PROVIDER resolution report entries.
		 * 
		 * The inner map associates a requirement to the set of all matching
		 * capabilities that were found. The outer map associates the requiring
		 * resource to the inner map so that its contents may easily be looked
		 * up from the set of unresolved resources, if any, after the resolution
		 * has occurred.
		 */
		private final Map<Resource, Map<Requirement, Set<Capability>>> unresolvedProviders = new HashMap<>();

		ResolveProcess(Collection<ModuleRevision> unresolved, Collection<ModuleRevision> triggers, boolean triggersMandatory, Map<ModuleRevision, ModuleWiring> wirings, ModuleDatabase moduleDatabase) {
			this.unresolved = unresolved;
			this.disabled = new HashSet<>(unresolved);
			this.triggers = new ArrayList<>(triggers);
			this.triggersMandatory = triggersMandatory;
			this.optionals = new LinkedHashSet<>(unresolved);
			if (this.triggersMandatory) {
				// do this the hard way because the 'optimization' in removeAll hurts us
				for (ModuleRevision triggerRevision : triggers) {
					this.optionals.remove(triggerRevision);
				}
			}
			this.wirings = new HashMap<>(wirings);
			this.previouslyResolved = new HashSet<>(wirings.keySet());
			this.moduleDatabase = moduleDatabase;
			this.dynamicReq = null;
		}

		ResolveProcess(Collection<ModuleRevision> unresolved, DynamicModuleRequirement dynamicReq, Map<ModuleRevision, ModuleWiring> wirings, ModuleDatabase moduleDatabase) {
			this.unresolved = unresolved;
			this.disabled = new HashSet<>(unresolved);
			ModuleRevision revision = dynamicReq.getRevision();
			this.triggers = new ArrayList<>(1);
			this.triggers.add(revision);
			this.triggersMandatory = false;
			this.optionals = new ArrayList<>(unresolved);
			this.wirings = wirings;
			this.previouslyResolved = new HashSet<>(wirings.keySet());
			this.moduleDatabase = moduleDatabase;
			this.dynamicReq = dynamicReq;
		}

		@Override
		public List<Capability> findProviders(Requirement requirement) {
			Requirement origReq = requirement;
			Requirement lookupReq = dynamicReq == null || dynamicReq.getOriginal() != requirement ? requirement : dynamicReq;
			return findProviders0(origReq, lookupReq);
		}

		private List<Capability> findProviders0(Requirement origReq, Requirement lookupReq) {
			if (DEBUG_PROVIDERS) {
				Debug.println(new StringBuilder("RESOLVER: Finding capabilities for requirement") //$NON-NLS-1$
						.append(SEPARATOR).append(TAB) //
						.append(origReq) //
						.append(SEPARATOR).append(TAB).append(TAB) //
						.append("of resource") //$NON-NLS-1$
						.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
						.append(origReq.getResource()) //
						.toString());
			}
			List<ModuleCapability> candidates = moduleDatabase.findCapabilities(lookupReq);
			List<Capability> result = filterProviders(origReq, candidates);
			if (DEBUG_PROVIDERS) {
				StringBuilder builder = new StringBuilder("RESOLVER: Capabilities being returned to the resolver"); //$NON-NLS-1$
				int i = 0;
				for (Capability capability : result) {
					builder.append(SEPARATOR).append(TAB) //
							.append("[").append(++i).append("] ") //$NON-NLS-1$ //$NON-NLS-2$
							.append(capability) //
							.append(SEPARATOR).append(TAB).append(TAB) //
							.append("of resource") //$NON-NLS-1$
							.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
							.append(capability.getResource());
				}
				Debug.println(builder.toString());
			}
			return result;
		}

		private List<Capability> filterProviders(Requirement requirement, List<ModuleCapability> candidates) {
			return filterProviders(requirement, candidates, true);
		}

		List<Capability> filterProviders(Requirement requirement, List<ModuleCapability> candidates, boolean filterResolvedHosts) {
			ListIterator<ModuleCapability> iCandidates = candidates.listIterator();
			filterDisabled(iCandidates);
			removeNonEffectiveCapabilities(iCandidates);
			removeSubstituted(iCandidates);
			filterPermissions((BundleRequirement) requirement, iCandidates);

			List<ModuleCapability> filteredMatches = null;
			if (DEBUG_PROVIDERS || DEBUG_HOOKS) {
				filteredMatches = new ArrayList<>(candidates);
			}
			hook.filterMatches((BundleRequirement) requirement, InternalUtils.asListBundleCapability(candidates));
			if (DEBUG_PROVIDERS || DEBUG_HOOKS) {
				filteredMatches.removeAll(candidates);
				if (!filteredMatches.isEmpty()) {
					StringBuilder builder = new StringBuilder("RESOLVER: Capabilities filtered by ResolverHook.filterMatches"); //$NON-NLS-1$
					int i = 0;
					for (Capability capability : filteredMatches) {
						builder.append(SEPARATOR).append(TAB) //
								.append("[").append(++i).append("] ") //$NON-NLS-1$ //$NON-NLS-2$
								.append(capability) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(capability.getResource());
					}
					Debug.println(builder.toString());
				}
			}

			// filter resolved hosts after calling hooks to allow hooks to see the host capability
			filterResolvedHosts(requirement, candidates, filterResolvedHosts);

			if (candidates.isEmpty()) {
				if (!wirings.containsKey(requirement.getResource()) || isDynamic(requirement)) {
					reportBuilder.addEntry(requirement.getResource(), Entry.Type.MISSING_CAPABILITY, requirement);
					String resolution = requirement.getDirectives().get(Namespace.REQUIREMENT_RESOLUTION_DIRECTIVE);
					if ((resolution == null || Namespace.RESOLUTION_MANDATORY.equals(resolution))) {
						transitivelyResolveFailures.add(requirement.getResource());
					}
				}
			} else {
				computeUnresolvedProviders(requirement, candidates);
			}

			filterFailedToResolve(candidates);

			Collections.sort(candidates, this);
			return InternalUtils.asListCapability(candidates);
		}

		private void filterFailedToResolve(List<ModuleCapability> candidates) {
			for (Iterator<ModuleCapability> iCandidates = candidates.iterator(); iCandidates.hasNext();) {
				ModuleCapability capability = iCandidates.next();
				if (failedToResolve.contains(capability.getRevision())) {
					iCandidates.remove();
					if (DEBUG_PROVIDERS) {
						Debug.println(new StringBuilder("RESOLVER: Capability filtered because its resource was not resolved") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append(capability) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(capability.getResource()) //
								.toString());
					}
				}
			}
		}

		private void filterResolvedHosts(Requirement requirement, List<ModuleCapability> candidates, boolean filterResolvedHosts) {
			if (filterResolvedHosts && HostNamespace.HOST_NAMESPACE.equals(requirement.getNamespace())) {
				for (Iterator<ModuleCapability> iCandidates = candidates.iterator(); iCandidates.hasNext();) {
					if (wirings.containsKey(iCandidates.next().getRevision())) {
						iCandidates.remove();
					}
				}
			}
		}

		private void filterPermissions(BundleRequirement requirement, ListIterator<ModuleCapability> iCandidates) {
			rewind(iCandidates);
			if (System.getSecurityManager() == null || !iCandidates.hasNext()) {
				return;
			}

			if (requirement.getRevision().getBundle() == null) {
				// this container is not modeling a real framework, no permission check is done
				return;
			}

			candidates: while (iCandidates.hasNext()) {
				ModuleCapability candidate = iCandidates.next();
				// TODO this is a hack for when a bundle imports and exports the same package
				if (PackageNamespace.PACKAGE_NAMESPACE.equals(requirement.getNamespace())) {
					if (requirement.getRevision().equals(candidate.getRevision())) {
						continue candidates;
					}
				}
				Permission requirePermission = InternalUtils.getRequirePermission(candidate);
				Permission providePermission = InternalUtils.getProvidePermission(candidate);
				if (!requirement.getRevision().getBundle().hasPermission(requirePermission)) {
					iCandidates.remove();
					if (DEBUG_PROVIDERS) {
						Debug.println(new StringBuilder("RESOLVER: Capability filtered because requirer did not have permission") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append(candidate) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(candidate.getResource()) //
								.toString());
					}
				} else if (!candidate.getRevision().getBundle().hasPermission(providePermission)) {
					iCandidates.remove();
					if (DEBUG_PROVIDERS) {
						Debug.println(new StringBuilder("RESOLVER: Capability filtered because provider did not have permission") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append(candidate) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(candidate.getResource()) //
								.toString());
					}
				}
			}
		}

		private void filterDisabled(ListIterator<ModuleCapability> iCandidates) {
			rewind(iCandidates);
			while (iCandidates.hasNext()) {
				Capability capability = iCandidates.next();
				if (disabled.contains(capability.getResource())) {
					iCandidates.remove();
					if (DEBUG_PROVIDERS) {
						Debug.println(new StringBuilder("RESOLVER: Capability filtered because it was disabled") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append(capability) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(capability.getResource()) //
								.toString());
					}
				}
			}
		}

		private void removeSubstituted(ListIterator<ModuleCapability> iCapabilities) {
			rewind(iCapabilities);
			while (iCapabilities.hasNext()) {
				ModuleCapability capability = iCapabilities.next();
				ModuleWiring wiring = wirings.get(capability.getRevision());
				if (wiring != null && wiring.isSubtituted(capability)) {
					iCapabilities.remove();
					if (DEBUG_PROVIDERS) {
						Debug.println(new StringBuilder("RESOLVER: Capability filtered because it was substituted") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append(capability) //
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append("of resource") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB).append(TAB) //
								.append(capability.getResource()) //
								.toString());
					}
				}
			}
		}

		@Override
		public int insertHostedCapability(List<Capability> capabilities, HostedCapability hostedCapability) {
			int index = Collections.binarySearch(capabilities, hostedCapability, this);
			if (index < 0)
				index = -index - 1;
			capabilities.add(index, hostedCapability);
			return index;
		}

		@Override
		public boolean isEffective(Requirement requirement) {
			String effective = requirement.getDirectives().get(Namespace.REQUIREMENT_EFFECTIVE_DIRECTIVE);
			return effective == null || Namespace.EFFECTIVE_RESOLVE.equals(effective);
		}

		@SuppressWarnings("unchecked")
		@Override
		public Map<Resource, Wiring> getWirings() {
			Map<?, ?> raw = wirings;
			return Collections.unmodifiableMap((Map<Resource, Wiring>) raw);
		}

		@Override
		public Collection<Resource> getMandatoryResources() {
			if (currentlyResolvingMandatory) {
				return Collections.unmodifiableList(currentlyResolving);
			}
			return Collections.emptyList();
		}

		@Override
		public Collection<Resource> getOptionalResources() {
			if (!currentlyResolvingMandatory) {
				return Collections.unmodifiableList(currentlyResolving);
			}
			return Collections.emptyList();
		}

		@Override
		public Collection<Resource> findRelatedResources(Resource host) {
			// for the container we only care about fragments for related resources
			List<ModuleCapability> hostCaps = ((ModuleRevision) host).getModuleCapabilities(HostNamespace.HOST_NAMESPACE);
			if (hostCaps.isEmpty()) {
				return Collections.emptyList();
			}

			Collection<Resource> relatedFragments = new ArrayList<>();
			for (String hostBSN : getHostBSNs(hostCaps)) {
				String matchFilter = "(" + EquinoxFragmentNamespace.FRAGMENT_NAMESPACE + "=" + hostBSN + ")"; //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$
				Requirement fragmentRequirement = ModuleContainer.createRequirement(EquinoxFragmentNamespace.FRAGMENT_NAMESPACE, Collections.<String, String> singletonMap(Namespace.REQUIREMENT_FILTER_DIRECTIVE, matchFilter), Collections.<String, Object> emptyMap());
				List<ModuleCapability> candidates = moduleDatabase.findCapabilities(fragmentRequirement);
				// filter out disabled fragments and singletons
				filterDisabled(candidates.listIterator());
				for (ModuleCapability candidate : candidates) {
					ModuleRequirement hostReq = candidate.getRevision().getModuleRequirements(HostNamespace.HOST_NAMESPACE).get(0);
					for (ModuleCapability hostCap : hostCaps) {
						if (hostReq.matches(hostCap)) {
							relatedFragments.add(candidate.getResource());
							break;
						}
					}
				}
			}

			return relatedFragments;
		}

		private Collection<String> getHostBSNs(List<ModuleCapability> hostCaps) {
			if (hostCaps.size() == 1) {
				// optimization and likely the only case since you are not supposed to have multiple host caps
				return getHostBSNs(hostCaps.get(0));
			}
			Set<String> result = new HashSet<>();
			for (ModuleCapability hostCap : hostCaps) {
				result.addAll(getHostBSNs(hostCap));
			}
			return result;
		}

		@SuppressWarnings("unchecked")
		private Collection<String> getHostBSNs(ModuleCapability moduleCapability) {
			Object namesAttr = moduleCapability.getAttributes().get(HostNamespace.HOST_NAMESPACE);
			if (namesAttr instanceof String) {
				return Collections.singletonList((String) namesAttr);
			}
			if (namesAttr instanceof String[]) {
				return Arrays.asList((String[]) namesAttr);
			}
			if (namesAttr instanceof Collection) {
				return (Collection<String>) namesAttr;
			}
			return Collections.emptyList();
		}

		ModuleResolutionReport resolve() {
			if (threadResolving()) {
				// throw up a runtime exception, if this is caused by a resolver hook
				// then it will get caught at the call to the resolver hook and a proper exception is thrown
				throw new IllegalStateException(Msg.ModuleResolver_RecursiveError);
			}
			threadResolving.set(Boolean.TRUE);
			try {
				try {
					hook = adaptor.getResolverHookFactory().begin(InternalUtils.asListBundleRevision((List<? extends BundleRevision>) triggers));
				} catch (RuntimeException e) {
					if (e.getCause() instanceof BundleException) {
						BundleException be = (BundleException) e.getCause();
						if (be.getType() == BundleException.REJECTED_BY_HOOK) {
							return new ModuleResolutionReport(null, Collections.<Resource, List<Entry>> emptyMap(), new ResolutionException(be));
						}
					}
					throw e;
				}
				Map<Resource, List<Wire>> result = null;
				ResolutionException re = null;
				ModuleResolutionReport report;
				ResolveLogger logger = new ResolveLogger();
				try {
					filterResolvable();
					selectSingletons();
					// remove disabled from optional and triggers to prevent the resolver from resolving them
					optionals.removeAll(disabled);
					if (triggers.removeAll(disabled) && triggersMandatory) {
						throw new ResolutionException(Msg.ModuleResolver_SingletonDisabledError + disabled);
					}
					if (dynamicReq != null) {
						result = resolveDynamic();
					} else {
						result = new HashMap<>();
						Map<Resource, List<Wire>> dynamicAttachWirings = resolveNonPayLoadFragments();
						applyInterimResultToWiringCopy(dynamicAttachWirings);
						if (!dynamicAttachWirings.isEmpty()) {
							// be sure to remove the revisions from the optional and triggers 
							// so they no longer attempt to be resolved
							Set<Resource> fragmentResources = dynamicAttachWirings.keySet();
							triggers.removeAll(fragmentResources);
							optionals.removeAll(fragmentResources);

							result.putAll(dynamicAttachWirings);
						}
						if (triggersMandatory) {
							resolveRevisionsInBatch(triggers, true, logger, result);
						}

						resolveRevisionsInBatch(optionals, false, logger, result);
					}
				} catch (ResolutionException e) {
					re = e;
				} finally {
					ScheduledFuture<?> f = timoutFuture.getAndSet(null);
					if (f != null) {
						f.cancel(true);
					}
					computeUnresolvedProviderResolutionReportEntries(result);
					computeUsesConstraintViolations(logger.getUsesConstraintViolations());
					if (DEBUG_WIRING) {
						printWirings(result);
					}
					report = reportBuilder.build(result, re);
					if (DEBUG_REPORT) {
						if (report.getResolutionException() != null) {
							Debug.printStackTrace(report.getResolutionException());
						}
						Set<Resource> resources = report.getEntries().keySet();
						if (!resources.isEmpty()) {
							Debug.println("RESOLVER: Resolution report"); //$NON-NLS-1$
							for (Resource resource : report.getEntries().keySet()) {
								Debug.println(report.getResolutionReportMessage(resource));
							}
						}
					}
					if (hook instanceof ResolutionReport.Listener)
						((ResolutionReport.Listener) hook).handleResolutionReport(report);
					hook.end();
				}
				return report;
			} finally {
				threadResolving.set(Boolean.FALSE);
			}
		}

		private void printWirings(Map<Resource, List<Wire>> wires) {
			StringBuilder builder = new StringBuilder("RESOLVER: Wirings for resolved bundles:"); //$NON-NLS-1$
			if (wires == null) {
				Debug.println(" null wires!"); //$NON-NLS-1$
				return;
			}
			for (Map.Entry<Resource, List<Wire>> entry : wires.entrySet()) {
				builder.append(SEPARATOR).append(TAB) //
						.append("Resource") //$NON-NLS-1$
						.append(SEPARATOR).append(TAB).append(TAB) //
						.append(entry.getKey()) //
						.append(SEPARATOR).append(TAB) //
						.append("Wiring"); //$NON-NLS-1$
				int i = 0;
				for (Wire wire : entry.getValue()) {
					builder.append(SEPARATOR).append(TAB).append(TAB) //
							.append('[').append(++i).append("] ") //$NON-NLS-1$
							.append(wire);
				}

			}
			Debug.println(builder);
		}

		private void resolveRevisionsInBatch(Collection<ModuleRevision> revisions, boolean isMandatory, ResolveLogger logger, Map<Resource, List<Wire>> result) throws ResolutionException {
			long startTime = System.currentTimeMillis();
			long initialFreeMemory = Runtime.getRuntime().freeMemory();
			long maxUsedMemory = 0;

			// make a copy so we do not modify the input
			revisions = new LinkedList<>(revisions);
			List<Resource> toResolve = new ArrayList<>();
			try {
				for (Iterator<ModuleRevision> iResources = revisions.iterator(); iResources.hasNext();) {
					ModuleRevision single = iResources.next();
					iResources.remove();
					if (!wirings.containsKey(single) && !failedToResolve.contains(single)) {
						toResolve.add(single);
					}
					if (toResolve.size() == resolverRevisionBatchSize || !iResources.hasNext()) {
						if (DEBUG_ROOTS) {
							Debug.println("Resolver: resolving " + toResolve.size() + " in batch."); //$NON-NLS-1$ //$NON-NLS-2$
							for (Resource root : toResolve) {
								Debug.println("    Resolving root bundle: " + root); //$NON-NLS-1$
							}
						}
						resolveRevisions(toResolve, isMandatory, logger, result);
						toResolve.clear();
					}
					maxUsedMemory = Math.max(maxUsedMemory, Runtime.getRuntime().freeMemory() - initialFreeMemory);
				}
			} catch (ResolutionException resolutionException) {
				if (resolutionException.getCause() instanceof CancellationException) {
					// revert back to single bundle resolves
					resolveRevisionsIndividually(isMandatory, logger, result, toResolve, revisions);
				} else {
					throw resolutionException;
				}
			} catch (OutOfMemoryError memoryError) {
				// revert back to single bundle resolves
				resolveRevisionsIndividually(isMandatory, logger, result, toResolve, revisions);
			}

			if (DEBUG_ROOTS) {
				Debug.println("Resolver: resolve batch size:  " + resolverRevisionBatchSize); //$NON-NLS-1$
				Debug.println("Resolver: time to resolve:  " + (System.currentTimeMillis() - startTime) + "ms"); //$NON-NLS-1$ //$NON-NLS-2$
				Debug.println("Resolver: max used memory: " + maxUsedMemory / (1024 * 1024) + "Mo"); //$NON-NLS-1$ //$NON-NLS-2$
			}
		}

		private void resolveRevisionsIndividually(boolean isMandatory, ResolveLogger logger, Map<Resource, List<Wire>> result, Collection<Resource> toResolve, Collection<ModuleRevision> revisions) throws ResolutionException {
			scheduleTimeout.set(false);
			for (Resource resource : toResolve) {
				if (!wirings.containsKey(resource) && !failedToResolve.contains(resource)) {
					resolveRevisions(Collections.singletonList(resource), isMandatory, logger, result);
				}
			}
			for (Resource resource : revisions) {
				if (!wirings.containsKey(resource) && !failedToResolve.contains(resource)) {
					resolveRevisions(Collections.singletonList(resource), isMandatory, logger, result);
				}
			}
		}

		private void resolveRevisions(List<Resource> revisions, boolean isMandatory, ResolveLogger logger, Map<Resource, List<Wire>> result) throws ResolutionException {
			boolean applyTransitiveFailures = true;
			currentlyResolving = revisions;
			currentlyResolvingMandatory = isMandatory;
			transitivelyResolveFailures.clear();
			Map<Resource, List<Wire>> interimResults = null;
			try {
				transitivelyResolveFailures.addAll(revisions);
				interimResults = new ResolverImpl(logger, this).resolve(this);
				applyInterimResultToWiringCopy(interimResults);
				if (DEBUG_ROOTS) {
					Debug.println("Resolver: resolved " + interimResults.size() + " bundles."); //$NON-NLS-1$ //$NON-NLS-2$
				}
				// now apply the simple wires to the results
				for (Map.Entry<Resource, List<Wire>> interimResultEntry : interimResults.entrySet()) {
					if (DEBUG_ROOTS) {
						Debug.println("    Resolved bundle: " + interimResultEntry.getKey()); //$NON-NLS-1$
					}
					List<Wire> existingWires = result.get(interimResultEntry.getKey());
					if (existingWires != null) {
						existingWires.addAll(interimResultEntry.getValue());
					} else {
						result.put(interimResultEntry.getKey(), interimResultEntry.getValue());
					}
				}
			} catch (ResolutionException resolutionException) {
				if (resolutionException.getCause() instanceof CancellationException) {
					applyTransitiveFailures = false;
				}
				throw resolutionException;
			} catch (OutOfMemoryError memoryError) {
				applyTransitiveFailures = false;
				throw memoryError;
			} finally {
				if (applyTransitiveFailures) {
					transitivelyResolveFailures.addAll(logger.getUsesConstraintViolations().keySet());
					if (interimResults != null) {
						transitivelyResolveFailures.removeAll(interimResults.keySet());
					}
					// what is left did not resolve
					if (!transitivelyResolveFailures.isEmpty()) {
						failedToResolve.addAll(transitivelyResolveFailures);
					}
				}
				currentlyResolving = null;
				currentlyResolvingMandatory = false;
			}
		}

		private void applyInterimResultToWiringCopy(Map<Resource, List<Wire>> interimResult) {
			if (!interimResult.isEmpty()) {
				// update the copy of wirings to include interim results
				Map<ModuleRevision, ModuleWiring> updatedWirings = generateDelta(interimResult, wirings);
				for (Map.Entry<ModuleRevision, ModuleWiring> updatedWiring : updatedWirings.entrySet()) {
					wirings.put(updatedWiring.getKey(), updatedWiring.getValue());
				}
			}
		}

		private void computeUsesConstraintViolations(Map<Resource, ResolutionException> usesConstraintViolations) {
			for (Map.Entry<Resource, ResolutionException> usesConstraintViolation : usesConstraintViolations.entrySet()) {
				reportBuilder.addEntry(usesConstraintViolation.getKey(), Type.USES_CONSTRAINT_VIOLATION, usesConstraintViolation.getValue());
			}
		}

		/*
		 * Given the results of a resolution, compute which, if any, of the
		 * enabled, resolving resources are still unresolved. For those that are
		 * unresolved, generate resolution report entries for unresolved
		 * providers, if necessary.
		 */
		private void computeUnresolvedProviderResolutionReportEntries(Map<Resource, List<Wire>> resolution) {
			// Create a collection representing the resources asked to be
			// resolved.
			Collection<Resource> shouldHaveResolvedResources = new ArrayList<Resource>(unresolved);
			// Remove disabled resources.
			shouldHaveResolvedResources.removeAll(disabled);
			// Remove resolved resources, if necessary. The resolution will be
			// null if the resolver threw an exception because the triggers
			// were mandatory but didn't resolve.
			if (resolution != null)
				shouldHaveResolvedResources.removeAll(resolution.keySet());
			// What remains are resources that should have resolved but didn't.
			// For each resource, add report entries for any unresolved
			// providers.
			for (Resource shouldHaveResolvedResource : shouldHaveResolvedResources) {
				Map<Requirement, Set<Capability>> requirementToCapabilities = unresolvedProviders.get(shouldHaveResolvedResource);
				if (requirementToCapabilities == null)
					continue;
				// If nothing resolved then there are no resolved resources to
				// filter out.
				if (resolution != null) {
					// Filter out capability providers that resolved.
					for (Iterator<Set<Capability>> values = requirementToCapabilities.values().iterator(); values.hasNext();) {
						Set<Capability> value = values.next();
						for (Iterator<Capability> capabilities = value.iterator(); capabilities.hasNext();)
							if (resolution.containsKey(capabilities.next().getResource()))
								// Remove the resolved capability provider.
								capabilities.remove();
						if (value.isEmpty())
							// Remove the requirement that has no unresolved
							// capability providers.
							values.remove();
					}
				}
				// Add a report entry if there are any remaining requirements
				// pointing to unresolved capability providers.
				if (!requirementToCapabilities.isEmpty())
					reportBuilder.addEntry(shouldHaveResolvedResource, Entry.Type.UNRESOLVED_PROVIDER, requirementToCapabilities);
			}
		}

		/*
		 * Given a requirement and its matching capabilities, map the
		 * requirement's resource to the requirement and matching capabilities.
		 * This data is used to compute report entries for resources that did
		 * not resolve because a provider did not resolve.
		 */
		private void computeUnresolvedProviders(Requirement requirement, Collection<? extends Capability> capabilities) {
			Resource requirer = requirement.getResource();
			Map<Requirement, Set<Capability>> requirementToCapabilities = unresolvedProviders.get(requirer);
			if (requirementToCapabilities == null) {
				requirementToCapabilities = new HashMap<>();
				unresolvedProviders.put(requirer, requirementToCapabilities);
			}
			Set<Capability> value = requirementToCapabilities.get(requirement);
			if (value == null) {
				value = new HashSet<>(capabilities.size());
				requirementToCapabilities.put(requirement, value);
			}
			for (Capability capability : capabilities)
				if (!wirings.containsKey(capability.getResource()))
					value.add(capability);
		}

		class DynamicFragments {
			private final ModuleCapability hostCapability;
			private final Map<String, ModuleRevision> fragments = new HashMap<>();
			private final Set<ModuleRevision> validProviders = new HashSet<>();
			boolean fragmentAdded = false;

			DynamicFragments(ModuleWiring hostWiring, ModuleCapability hostCapability) {
				this.hostCapability = hostCapability;
				validProviders.add(hostWiring.getRevision());
				for (ModuleWire hostWire : hostWiring.getProvidedModuleWires(HostNamespace.HOST_NAMESPACE)) {
					validProviders.add(hostWire.getRequirer());
					fragments.put(hostWire.getRequirer().getSymbolicName(), hostWire.getRequirer());
				}
			}

			void addFragment(ModuleRevision fragment) {
				ModuleRevision existing = fragments.get(fragment.getSymbolicName());
				if (existing == null) {
					fragments.put(fragment.getSymbolicName(), fragment);
					validProviders.add(fragment);
					fragmentAdded = true;
				}
			}

			Map<Resource, List<Wire>> getNewWires() {
				if (!fragmentAdded) {
					return Collections.emptyMap();
				}
				Map<Resource, List<Wire>> result = new HashMap<>();
				boolean retry;
				do {
					retry = false;
					result.clear();
					fragmentsLoop: for (Iterator<Map.Entry<String, ModuleRevision>> iFragments = fragments.entrySet().iterator(); iFragments.hasNext();) {
						Map.Entry<String, ModuleRevision> fragmentEntry = iFragments.next();
						if (wirings.get(fragmentEntry.getValue()) == null) {
							for (ModuleRequirement req : fragmentEntry.getValue().getModuleRequirements(null)) {
								ModuleRevision requirer = NON_PAYLOAD_REQUIREMENTS.contains(req.getNamespace()) ? req.getRevision() : hostCapability.getRevision();
								List<Wire> newWires = result.get(requirer);
								if (newWires == null) {
									newWires = new ArrayList<>();
									result.put(requirer, newWires);
								}
								if (HostNamespace.HOST_NAMESPACE.equals(req.getNamespace())) {
									newWires.add(new ModuleWire(hostCapability, hostCapability.getRevision(), req, requirer));
								} else {
									if (failToWire(req, requirer, newWires)) {
										iFragments.remove();
										validProviders.remove(req.getRevision());
										retry = true;
										break fragmentsLoop;
									}
								}
							}
						}
					}
				} while (retry);
				return result;
			}

			private boolean failToWire(ModuleRequirement requirement, ModuleRevision requirer, List<Wire> wires) {
				List<ModuleCapability> matching = moduleDatabase.findCapabilities(requirement);
				List<Wire> newWires = new ArrayList<>(0);
				filterProviders(requirement, matching, false);
				for (ModuleCapability candidate : matching) {
					// If the requirer equals the requirement revision then this is a non-payload requirement.
					// We let non-payload requirements come from anywhere.
					// Payload requirements must come from the host or one of the fragments attached to the host
					if (requirer.equals(requirement.getRevision()) || validProviders.contains(candidate.getRevision())) {
						ModuleRevision provider = NON_PAYLOAD_CAPABILITIES.contains(candidate.getNamespace()) ? candidate.getRevision() : hostCapability.getRevision();
						// if there are multiple candidates; then check for cardinality
						if (newWires.isEmpty() || Namespace.CARDINALITY_MULTIPLE.equals(requirement.getDirectives().get(Namespace.REQUIREMENT_CARDINALITY_DIRECTIVE))) {
							newWires.add(new ModuleWire(candidate, provider, requirement, requirer));
						}
					}
				}
				if (newWires.isEmpty()) {
					if (!Namespace.RESOLUTION_OPTIONAL.equals(requirement.getDirectives().get(Namespace.REQUIREMENT_RESOLUTION_DIRECTIVE))) {
						// could not resolve mandatory requirement;
						return true;
					}
				}
				// only create the wire if the namespace is a non-substituted namespace (e.g. NOT package)
				if (!NON_SUBSTITUTED_REQUIREMENTS.contains(requirement.getNamespace())) {
					wires.addAll(newWires);
				}
				return false;
			}
		}

		private Map<Resource, List<Wire>> resolveNonPayLoadFragments() {
			// This is to support dynamic attachment of fragments that do not
			// add any payload requirements to their host.
			// This is needed for framework extensions since the system bundle
			// host is always resolved.
			// It is also useful for things like NLS fragments that are installed later
			// without the need to refresh the host.
			List<ModuleRevision> dynamicAttachableFrags = new ArrayList<>();
			if (triggersMandatory) {
				for (ModuleRevision moduleRevision : triggers) {
					if ((moduleRevision.getTypes() & BundleRevision.TYPE_FRAGMENT) != 0) {
						dynamicAttachableFrags.add(moduleRevision);
					}
				}
			}
			for (ModuleRevision moduleRevision : optionals) {
				if ((moduleRevision.getTypes() & BundleRevision.TYPE_FRAGMENT) != 0) {
					dynamicAttachableFrags.add(moduleRevision);
				}
			}

			if (dynamicAttachableFrags.isEmpty()) {
				return Collections.emptyMap();
			}
			Collections.sort(dynamicAttachableFrags, new Comparator<ModuleRevision>() {
				@Override
				public int compare(ModuleRevision r1, ModuleRevision r2) {
					// we only care about versions here
					return -(r1.getVersion().compareTo(r2.getVersion()));
				}
			});

			Map<ModuleCapability, DynamicFragments> hostDynamicFragments = new HashMap<>();
			// first find the hosts to dynamically attach to
			for (ModuleRevision dynamicAttachableFragment : dynamicAttachableFrags) {
				List<ModuleRequirement> requirements = dynamicAttachableFragment.getModuleRequirements(null);
				for (ModuleRequirement requirement : requirements) {
					if (HostNamespace.HOST_NAMESPACE.equals(requirement.getNamespace())) {
						List<ModuleCapability> matchingHosts = moduleDatabase.findCapabilities(requirement);
						filterProviders(requirement, matchingHosts, false);
						for (ModuleCapability hostCandidate : matchingHosts) {
							ModuleWiring hostWiring = wirings.get(hostCandidate.getRevision());
							String attachDirective = hostCandidate.getDirectives().get(HostNamespace.CAPABILITY_FRAGMENT_ATTACHMENT_DIRECTIVE);
							boolean attachAlways = attachDirective == null || HostNamespace.FRAGMENT_ATTACHMENT_ALWAYS.equals(attachDirective);
							// only do this if the candidate host is already resolved and it allows dynamic attachment
							if (!attachAlways || hostWiring == null) {
								continue;
							}
							DynamicFragments dynamicFragments = hostDynamicFragments.get(hostCandidate);
							if (dynamicFragments == null) {
								dynamicFragments = new DynamicFragments(hostWiring, hostCandidate);
								hostDynamicFragments.put(hostCandidate, dynamicFragments);
							}
							dynamicFragments.addFragment(requirement.getRevision());
						}
					}
				}
			}
			// now try to get the new wires for each host
			Map<Resource, List<Wire>> dynamicWires = new HashMap<>();
			for (DynamicFragments dynamicFragments : hostDynamicFragments.values()) {
				dynamicWires.putAll(dynamicFragments.getNewWires());
			}
			return dynamicWires;
		}

		private Map<Resource, List<Wire>> resolveDynamic() throws ResolutionException {
			return new ResolverImpl(new Logger(0), null).resolveDynamic(this, dynamicReq.getRevision().getWiring(), dynamicReq.getOriginal());
		}

		private void filterResolvable() {
			Collection<ModuleRevision> enabledCandidates = new ArrayList<>(unresolved);
			hook.filterResolvable(InternalUtils.asListBundleRevision((List<? extends BundleRevision>) enabledCandidates));
			// do this the hard way because the 'optimization' in removeAll hurts us
			for (ModuleRevision enabledRevision : enabledCandidates) {
				disabled.remove(enabledRevision);
			}
			for (ModuleRevision revision : disabled) {
				reportBuilder.addEntry(revision, Entry.Type.FILTERED_BY_RESOLVER_HOOK, null);
				if (DEBUG_HOOKS) {
					Debug.println("RESOLVER: Resource filtered by ResolverHook.filterResolvable: " + revision); //$NON-NLS-1$
				}
			}
		}

		private void selectSingletons() {
			Map<String, Collection<ModuleRevision>> selectedSingletons = new HashMap<>();
			for (ModuleRevision revision : unresolved) {
				if (!isSingleton(revision) || disabled.contains(revision))
					continue;
				String bsn = revision.getSymbolicName();
				Collection<ModuleRevision> selected = selectedSingletons.get(bsn);
				if (selected != null)
					continue; // already processed the bsn
				selected = new ArrayList<>(1);
				selectedSingletons.put(bsn, selected);

				Collection<ModuleRevision> sameBSN = getRevisions(bsn);
				if (sameBSN.size() < 2) {
					selected.add(revision);
					continue;
				}
				// prime selected with resolved singleton bundles
				for (ModuleRevision singleton : sameBSN) {
					if (isSingleton(singleton) && wirings.containsKey(singleton))
						selected.add(singleton);
				}
				// get the collision map for the BSN
				Map<ModuleRevision, Collection<ModuleRevision>> collisionMap = getCollisionMap(sameBSN);
				// process the collision map
				for (ModuleRevision singleton : sameBSN) {
					if (selected.contains(singleton))
						continue; // no need to process resolved bundles
					Collection<ModuleRevision> collisions = collisionMap.get(singleton);
					if (collisions == null || disabled.contains(singleton))
						continue; // not a singleton or not resolvable
					Collection<ModuleRevision> pickOneToResolve = new ArrayList<>();
					for (ModuleRevision collision : collisions) {
						if (selected.contains(collision)) {
							// Must fail since there is already a selected bundle which is a collision of the singleton bundle
							disabled.add(singleton);
							reportBuilder.addEntry(singleton, Type.SINGLETON_SELECTION, collision);
							break;
						}
						if (!pickOneToResolve.contains(collision))
							pickOneToResolve.add(collision);
					}
					if (!disabled.contains(singleton)) {
						// need to make sure the bundle does not collide from the POV of another entry
						for (Map.Entry<ModuleRevision, Collection<ModuleRevision>> collisionEntry : collisionMap.entrySet()) {
							if (collisionEntry.getKey() != singleton && collisionEntry.getValue().contains(singleton)) {
								if (selected.contains(collisionEntry.getKey())) {
									// Must fail since there is already a selected bundle for which the singleton bundle is a collision
									disabled.add(singleton);
									reportBuilder.addEntry(singleton, Type.SINGLETON_SELECTION, collisionEntry.getKey());
									break;
								}
								if (!pickOneToResolve.contains(collisionEntry.getKey()))
									pickOneToResolve.add(collisionEntry.getKey());
							}
						}
					}
					if (!disabled.contains(singleton)) {
						pickOneToResolve.add(singleton);
						selected.add(pickOneToResolve(pickOneToResolve));
					}
				}
			}
		}

		private Collection<ModuleRevision> getRevisions(String name) {
			Map<String, Collection<ModuleRevision>> current = byName;
			if (current == null) {
				// generate the map using unresolved collection and wiring snap shot
				// this is to avoid interacting with the module database
				Set<ModuleRevision> revisions = new HashSet<>();
				revisions.addAll(unresolved);
				revisions.addAll(previouslyResolved);
				current = new HashMap<>();
				for (ModuleRevision revision : revisions) {
					Collection<ModuleRevision> sameName = current.get(revision.getSymbolicName());
					if (sameName == null) {
						sameName = new ArrayList<>();
						current.put(revision.getSymbolicName(), sameName);
					}
					sameName.add(revision);
				}
				byName = current;
			}
			Collection<ModuleRevision> result = current.get(name);
			if (result == null) {
				return Collections.emptyList();
			}
			return result;
		}

		private ModuleRevision pickOneToResolve(Collection<ModuleRevision> pickOneToResolve) {
			ModuleRevision selectedVersion = null;
			for (ModuleRevision singleton : pickOneToResolve) {
				if (selectedVersion == null)
					selectedVersion = singleton;
				boolean higherVersion = selectedVersion.getVersion().compareTo(singleton.getVersion()) < 0;
				if (higherVersion)
					selectedVersion = singleton;
			}

			for (ModuleRevision singleton : pickOneToResolve) {
				if (singleton != selectedVersion) {
					disabled.add(singleton);
					reportBuilder.addEntry(singleton, Type.SINGLETON_SELECTION, selectedVersion);
				}
			}
			return selectedVersion;
		}

		private Map<ModuleRevision, Collection<ModuleRevision>> getCollisionMap(Collection<ModuleRevision> sameBSN) {
			Map<ModuleRevision, Collection<ModuleRevision>> result = new HashMap<>();
			for (ModuleRevision singleton : sameBSN) {
				if (!isSingleton(singleton) || disabled.contains(singleton))
					continue; // ignore non-singleton and non-resolvable
				List<BundleCapability> capabilities = new ArrayList<>(sameBSN.size() - 1);
				for (ModuleRevision collision : sameBSN) {
					if (collision == singleton || !isSingleton(collision) || disabled.contains(collision))
						continue; // Ignore the bundle we are checking and non-singletons and non-resolvable
					capabilities.add(getIdentity(collision));
				}
				hook.filterSingletonCollisions(getIdentity(singleton), capabilities);
				Collection<ModuleRevision> collisionCandidates = new ArrayList<>(capabilities.size());
				for (BundleCapability identity : capabilities) {
					collisionCandidates.add((ModuleRevision) identity.getRevision());
				}
				if (DEBUG_HOOKS) {
					Collection<ModuleRevision> filteredSingletons = new ArrayList<>(sameBSN);
					filteredSingletons.removeAll(collisionCandidates);
					filteredSingletons.remove(singleton);
					if (!filteredSingletons.isEmpty()) {
						StringBuilder builder = new StringBuilder("RESOLVER: Resources filtered by ResolverHook.filterSingletonCollisions") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB) //
								.append("Singleton") //$NON-NLS-1$
								.append(SEPARATOR).append(TAB).append(TAB) //
								.append(singleton) //
								.append(" [id=") //$NON-NLS-1$
								.append(singleton.getRevisions().getModule().getId()) //
								.append(", location=") //$NON-NLS-1$
								.append(singleton.getRevisions().getModule().getLocation()) //
								.append(']') //
								.append(SEPARATOR).append(TAB) //
								.append("Collisions"); //$NON-NLS-1$
						int i = 0;
						for (ModuleRevision revision : filteredSingletons) {
							builder.append(SEPARATOR).append(TAB).append(TAB) //
									.append("[").append(++i).append("] ") //$NON-NLS-1$ //$NON-NLS-2$
									.append(revision) //
									.append(" [id=") //$NON-NLS-1$
									.append(revision.getRevisions().getModule().getId()) //
									.append(", location=") //$NON-NLS-1$
									.append(revision.getRevisions().getModule().getLocation()) //
									.append(']');
						}
						Debug.println(builder.toString());
					}
				}
				result.put(singleton, collisionCandidates);
			}
			return result;
		}

		private BundleCapability getIdentity(ModuleRevision bundle) {
			List<BundleCapability> identities = bundle.getDeclaredCapabilities(IdentityNamespace.IDENTITY_NAMESPACE);
			return identities.isEmpty() ? null : identities.get(0);
		}

		@Override
		public int compare(Capability c1, Capability c2) {
			// TODO Ideally this policy should be handled by the ModuleDatabase.
			// To do that the wirings would have to be provided since the wirings may
			// be a subset of the current wirings provided by the ModuleDatabase
			boolean resolved1 = previouslyResolved.contains(c1.getResource());
			boolean resolved2 = previouslyResolved.contains(c2.getResource());
			if (resolved1 != resolved2)
				return resolved1 ? -1 : 1;

			Version v1 = getVersion(c1);
			Version v2 = getVersion(c2);
			int versionCompare = -(v1.compareTo(v2));
			if (versionCompare != 0)
				return versionCompare;

			ModuleRevision m1 = getModuleRevision(c1);
			ModuleRevision m2 = getModuleRevision(c2);
			Long id1 = m1.getRevisions().getModule().getId();
			Long id2 = m2.getRevisions().getModule().getId();

			if (id1.equals(id2) && !m1.equals(m2)) {
				// sort based on revision ordering
				List<ModuleRevision> revisions = m1.getRevisions().getModuleRevisions();
				int index1 = revisions.indexOf(m1);
				int index2 = revisions.indexOf(m2);
				// we want to sort the indexes from highest to lowest
				return index2 - index1;
			}
			return id1.compareTo(id2);
		}

		ModuleRevision getModuleRevision(Capability c) {
			// We assume all capabilities here either come from us and have ModuleRevision resources or
			// they are HostedCapabilities which have ModuleRevision resources as the host revision
			if (c instanceof HostedCapability) {
				c = ((HostedCapability) c).getDeclaredCapability();
			}
			if (c instanceof ModuleCapability) {
				return ((ModuleCapability) c).getRevision();
			}
			// TODO is there some bug in the resolver?
			return null;
		}

		@Override
		public void execute(Runnable command) {
			adaptor.getResolverExecutor().execute(command);
		}

		@Override
		public void onCancel(Runnable callback) {
			// Note that for each resolve Process we only want timeout the initial batch resolve
			if (scheduleTimeout.compareAndSet(true, false)) {
				ScheduledExecutorService scheduledExecutor = adaptor.getScheduledExecutor();
				if (scheduledExecutor != null) {
					try {
						timoutFuture.set(scheduledExecutor.schedule(callback, resolverBatchTimeout, TimeUnit.MILLISECONDS));
					} catch (RejectedExecutionException e) {
						// ignore may have been shutdown, it is ok we will not be able to timeout
					}
				}
			}
		}

		@Override
		public List<Wire> getSubstitutionWires(Wiring wiring) {
			return ((ModuleWiring) wiring).getSubstitutionWires();
		}
	}

	protected boolean threadResolving() {
		Boolean resolvingValue = this.threadResolving.get();
		if (resolvingValue == null) {
			return false;
		}
		return resolvingValue.booleanValue();
	}
}