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From jwr...@apache.org
Subject svn commit: r1328953 [2/4] - in /aries/trunk/subsystem/subsystem-core/src/main/java/org/apache: aries/subsystem/core/ aries/subsystem/core/archive/ aries/subsystem/core/internal/ aries/subsystem/core/resource/ aries/subsystem/core/resource/tmp/ felix/r...
Date Sun, 22 Apr 2012 19:49:22 GMT
Added: aries/trunk/subsystem/subsystem-core/src/main/java/org/apache/felix/resolver/Candidates.java
URL: http://svn.apache.org/viewvc/aries/trunk/subsystem/subsystem-core/src/main/java/org/apache/felix/resolver/Candidates.java?rev=1328953&view=auto
==============================================================================
--- aries/trunk/subsystem/subsystem-core/src/main/java/org/apache/felix/resolver/Candidates.java
(added)
+++ aries/trunk/subsystem/subsystem-core/src/main/java/org/apache/felix/resolver/Candidates.java
Sun Apr 22 19:49:20 2012
@@ -0,0 +1,1052 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.felix.resolver;
+
+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.Map.Entry;
+import java.util.Set;
+import java.util.TreeMap;
+import org.osgi.framework.Version;
+import org.osgi.framework.namespace.HostNamespace;
+import org.osgi.framework.namespace.PackageNamespace;
+import org.osgi.resource.Capability;
+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;
+
+class Candidates
+{
+    public static final int MANDATORY = 0;
+    public static final int OPTIONAL = 1;
+    public static final int ON_DEMAND = 2;
+
+    private final Set<Resource> m_mandatoryResources;
+    // Maps a capability to requirements that match it.
+    private final Map<Capability, Set<Requirement>> m_dependentMap;
+    // Maps a requirement to the capability it matches.
+    private final Map<Requirement, List<Capability>> m_candidateMap;
+    // Maps a bundle revision to its associated wrapped revision; this only happens
+    // when a revision being resolved has fragments to attach to it.
+    private final Map<Resource, WrappedResource> m_allWrappedHosts;
+    // Map used when populating candidates to hold intermediate and final results.
+    private final Map<Resource, Object> m_populateResultCache;
+
+    // Flag to signal if fragments are present in the candidate map.
+    private boolean m_fragmentsPresent = false;
+
+    /**
+     * Private copy constructor used by the copy() method.
+     * @param dependentMap the capability dependency map.
+     * @param candidateMap the requirement candidate map.
+     * @param hostFragments the fragment map.
+     * @param wrappedHosts the wrapped hosts map.
+    **/
+    private Candidates(
+        Set<Resource> mandatoryResources,
+        Map<Capability, Set<Requirement>> dependentMap,
+        Map<Requirement, List<Capability>> candidateMap,
+        Map<Resource, WrappedResource> wrappedHosts, Map<Resource, Object> populateResultCache,
+        boolean fragmentsPresent)
+    {
+        m_mandatoryResources = mandatoryResources;
+        m_dependentMap = dependentMap;
+        m_candidateMap = candidateMap;
+        m_allWrappedHosts = wrappedHosts;
+        m_populateResultCache = populateResultCache;
+        m_fragmentsPresent = fragmentsPresent;
+    }
+
+    /**
+     * Constructs an empty Candidates object.
+    **/
+    public Candidates()
+    {
+        m_mandatoryResources = new HashSet<Resource>();
+        m_dependentMap = new HashMap<Capability, Set<Requirement>>();
+        m_candidateMap = new HashMap<Requirement, List<Capability>>();
+        m_allWrappedHosts = new HashMap<Resource, WrappedResource>();
+        m_populateResultCache = new HashMap<Resource, Object>();
+    }
+
+    /**
+     * Populates candidates for the specified revision. How a revision is
+     * resolved depends on its resolution type as follows:
+     * <ul>
+     *   <li><tt>MANDATORY</tt> - must resolve and failure to do so throws
+     *       an exception.</li>
+     *   <li><tt>OPTIONAL</tt> - attempt to resolve, but no exception is
thrown
+     *       if the resolve fails.</li>
+     *   <li><tt>ON_DEMAND</tt> - only resolve on demand; this only applies
to
+     *       fragments and will only resolve a fragment if its host is already
+     *       selected as a candidate.</li>
+     * </ul>
+     * @param state the resolver state used for populating the candidates.
+     * @param revision the revision whose candidates should be populated.
+     * @param resolution indicates the resolution type.
+     */
+    public final void populate(
+        ResolveContext rc, Resource resource, int resolution) throws ResolutionException
+    {
+        // Get the current result cache value, to make sure the revision
+        // hasn't already been populated.
+        Object cacheValue = m_populateResultCache.get(resource);
+        // Has been unsuccessfully populated.
+        if (cacheValue instanceof ResolutionException)
+        {
+            return;
+        }
+        // Has been successfully populated.
+        else if (cacheValue instanceof Boolean)
+        {
+            return;
+        }
+
+        // We will always attempt to populate fragments, since this is necessary
+        // for ondemand attaching of fragment. However, we'll only attempt to
+        // populate optional non-fragment revisions if they aren't already
+        // resolved.
+        boolean isFragment = Util.isFragment(resource);
+        if (!isFragment && rc.getWirings().containsKey(resource))
+        {
+            return;
+        }
+
+        // Always attempt to populate mandatory or optional revisions.
+        // However, for on-demand fragments only populate if their host
+        // is already populated.
+        if ((resolution != ON_DEMAND)
+            || (isFragment && populateFragmentOndemand(rc, resource)))
+        {
+            if (resolution == MANDATORY)
+            {
+                m_mandatoryResources.add(resource);
+            }
+            try
+            {
+                // Try to populate candidates for the optional revision.
+                populateResource(rc, resource);
+            }
+            catch (ResolutionException ex)
+            {
+                // Only throw an exception if resolution is mandatory.
+                if (resolution == MANDATORY)
+                {
+                    throw ex;
+                }
+            }
+        }
+    }
+
+    /**
+     * Populates candidates for the specified revision.
+     * @param state the resolver state used for populating the candidates.
+     * @param revision the revision whose candidates should be populated.
+     */
+// TODO: FELIX3 - Modify to not be recursive.
+    private void populateResource(ResolveContext rc, Resource resource) throws ResolutionException
+    {
+        // Determine if we've already calculated this revision's candidates.
+        // The result cache will have one of three values:
+        //   1. A resolve exception if we've already attempted to populate the
+        //      revision's candidates but were unsuccessful.
+        //   2. Boolean.TRUE indicating we've already attempted to populate the
+        //      revision's candidates and were successful.
+        //   3. An array containing the cycle count, current map of candidates
+        //      for already processed requirements, and a list of remaining
+        //      requirements whose candidates still need to be calculated.
+        // For case 1, rethrow the exception. For case 2, simply return immediately.
+        // For case 3, this means we have a cycle so we should continue to populate
+        // the candidates where we left off and not record any results globally
+        // until we've popped completely out of the cycle.
+
+        // Keeps track of the number of times we've reentered this method
+        // for the current revision.
+        Integer cycleCount = null;
+
+        // Keeps track of the candidates we've already calculated for the
+        // current revision's requirements.
+        Map<Requirement, List<Capability>> localCandidateMap = null;
+
+        // Keeps track of the current revision's requirements for which we
+        // haven't yet found candidates.
+        List<Requirement> remainingReqs = null;
+
+        // Get the cache value for the current revision.
+        Object cacheValue = m_populateResultCache.get(resource);
+
+        // This is case 1.
+        if (cacheValue instanceof ResolutionException)
+        {
+            throw (ResolutionException) cacheValue;
+        }
+        // This is case 2.
+        else if (cacheValue instanceof Boolean)
+        {
+            return;
+        }
+        // This is case 3.
+        else if (cacheValue != null)
+        {
+            // Increment and get the cycle count.
+            cycleCount = (Integer)
+                (((Object[]) cacheValue)[0]
+                    = new Integer(((Integer) ((Object[]) cacheValue)[0]).intValue() + 1));
+            // Get the already populated candidates.
+            localCandidateMap = (Map) ((Object[]) cacheValue)[1];
+            // Get the remaining requirements.
+            remainingReqs = (List) ((Object[]) cacheValue)[2];
+        }
+
+        // If there is no cache value for the current revision, then this is
+        // the first time we are attempting to populate its candidates, so
+        // do some one-time checks and initialization.
+        if ((remainingReqs == null) && (localCandidateMap == null))
+        {
+            // Record cycle count.
+            cycleCount = new Integer(0);
+
+            // Create a local map for populating candidates first, just in case
+            // the revision is not resolvable.
+            localCandidateMap = new HashMap();
+
+            // Create a modifiable list of the revision's requirements.
+            remainingReqs = new ArrayList(resource.getRequirements(null));
+
+            // Add these value to the result cache so we know we are
+            // in the middle of populating candidates for the current
+            // revision.
+            m_populateResultCache.put(resource,
+                cacheValue = new Object[] { cycleCount, localCandidateMap, remainingReqs
});
+        }
+
+        // If we have requirements remaining, then find candidates for them.
+        while (!remainingReqs.isEmpty())
+        {
+            Requirement req = remainingReqs.remove(0);
+
+            // Ignore non-effective and dynamic requirements.
+            String resolution = req.getDirectives()
+                .get(PackageNamespace.REQUIREMENT_RESOLUTION_DIRECTIVE);
+            if (!rc.isEffective(req)
+                || ((resolution != null)
+                    && resolution.equals(PackageNamespace.RESOLUTION_DYNAMIC)))
+            {
+                continue;
+            }
+
+            // Process the candidates, removing any candidates that
+            // cannot resolve.
+            List<Capability> candidates = rc.findProviders(req);
+            ResolutionException rethrow = processCandidates(rc, resource, candidates);
+
+            // First, due to cycles, makes sure we haven't already failed in
+            // a deeper recursion.
+            Object result = m_populateResultCache.get(resource);
+            if (result instanceof ResolutionException)
+            {
+                throw (ResolutionException) result;
+            }
+            // Next, if are no candidates remaining and the requirement is not
+            // not optional, then record and throw a resolve exception.
+            else if (candidates.isEmpty() && !Util.isOptional(req))
+            {
+                String msg = "Unable to resolve " + resource
+                    + ": missing requirement " + req;
+                if (rethrow != null)
+                {
+                    msg = msg + " [caused by: " + rethrow.getMessage() + "]";
+                }
+                rethrow = new ResolutionException(msg, null, Collections.singleton(req));
+                m_populateResultCache.put(resource, rethrow);
+                throw rethrow;
+            }
+            // Otherwise, if we actually have candidates for the requirement, then
+            // add them to the local candidate map.
+            else if (candidates.size() > 0)
+            {
+                localCandidateMap.put(req, candidates);
+            }
+        }
+
+        // If we are exiting from a cycle then decrement
+        // cycle counter, otherwise record the result.
+        if (cycleCount.intValue() > 0)
+        {
+            ((Object[]) cacheValue)[0] = new Integer(cycleCount.intValue() - 1);
+        }
+        else if (cycleCount.intValue() == 0)
+        {
+            // Record that the revision was successfully populated.
+            m_populateResultCache.put(resource, Boolean.TRUE);
+
+            // Merge local candidate map into global candidate map.
+            if (localCandidateMap.size() > 0)
+            {
+                add(localCandidateMap);
+            }
+        }
+    }
+
+    private boolean populateFragmentOndemand(ResolveContext rc, Resource resource)
+        throws ResolutionException
+    {
+        // Create a modifiable list of the revision's requirements.
+        List<Requirement> remainingReqs =
+            new ArrayList(resource.getRequirements(null));
+        // Find the host requirement.
+        Requirement hostReq = null;
+        for (Iterator<Requirement> it = remainingReqs.iterator();
+            it.hasNext(); )
+        {
+            Requirement r = it.next();
+            if (r.getNamespace().equals(HostNamespace.HOST_NAMESPACE))
+            {
+                hostReq = r;
+                it.remove();
+                break;
+            }
+        }
+        // Get candidates hosts and keep any that have been populated.
+        List<Capability> hosts = rc.findProviders(hostReq);
+        for (Iterator<Capability> it = hosts.iterator(); it.hasNext(); )
+        {
+            Capability host = it.next();
+            if (!isPopulated(host.getResource()))
+            {
+                it.remove();
+            }
+        }
+        // If there aren't any populated hosts, then we can just
+        // return since this fragment isn't needed.
+        if (hosts.isEmpty())
+        {
+            return false;
+        }
+
+        // If there are populated host candidates, then prepopulate
+        // the result cache with the work we've done so far.
+        // Record cycle count, but start at -1 since it will
+        // be incremented again in populate().
+        Integer cycleCount = new Integer(-1);
+        // Create a local map for populating candidates first, just in case
+        // the revision is not resolvable.
+        Map<Requirement, List<Capability>> localCandidateMap =
+            new HashMap<Requirement, List<Capability>>();
+        // Add the discovered host candidates to the local candidate map.
+        localCandidateMap.put(hostReq, hosts);
+        // Add these value to the result cache so we know we are
+        // in the middle of populating candidates for the current
+        // revision.
+        m_populateResultCache.put(resource,
+            new Object[] { cycleCount, localCandidateMap, remainingReqs });
+        return true;
+    }
+
+    public void populateDynamic(
+        ResolveContext rc, Resource resource,
+        Requirement req, List<Capability> candidates) throws ResolutionException
+    {
+        // Record the revision associated with the dynamic require
+        // as a mandatory revision.
+        m_mandatoryResources.add(resource);
+
+        // Add the dynamic imports candidates.
+        add(req, candidates);
+
+        // Process the candidates, removing any candidates that
+        // cannot resolve.
+        ResolutionException rethrow = processCandidates(rc, resource, candidates);
+
+        if (candidates.isEmpty())
+        {
+            if (rethrow == null)
+            {
+                rethrow = new ResolutionException(
+                    "Dynamic import failed.", null, Collections.singleton(req));
+            }
+            throw rethrow;
+        }
+
+        m_populateResultCache.put(resource, Boolean.TRUE);
+    }
+
+    /**
+     * This method performs common processing on the given set of candidates.
+     * Specifically, it removes any candidates which cannot resolve and it
+     * synthesizes candidates for any candidates coming from any attached
+     * fragments, since fragment capabilities only appear once, but technically
+     * each host represents a unique capability.
+     * @param state the resolver state.
+     * @param revision the revision being resolved.
+     * @param candidates the candidates to process.
+     * @return a resolve exception to be re-thrown, if any, or null.
+     */
+    private ResolutionException processCandidates(
+        ResolveContext rc,
+        Resource resource,
+        List<Capability> candidates)
+    {
+        // Get satisfying candidates and populate their candidates if necessary.
+        ResolutionException rethrow = null;
+        Set<Capability> fragmentCands = null;
+        for (Iterator<Capability> itCandCap = candidates.iterator();
+            itCandCap.hasNext(); )
+        {
+            Capability candCap = itCandCap.next();
+
+            boolean isFragment = Util.isFragment(candCap.getResource());
+
+            // If the capability is from a fragment, then record it
+            // because we have to insert associated host capabilities
+            // if the fragment is already attached to any hosts.
+            if (isFragment)
+            {
+                if (fragmentCands == null)
+                {
+                    fragmentCands = new HashSet<Capability>();
+                }
+                fragmentCands.add(candCap);
+            }
+
+            // If the candidate revision is a fragment, then always attempt
+            // to populate candidates for its dependency, since it must be
+            // attached to a host to be used. Otherwise, if the candidate
+            // revision is not already resolved and is not the current version
+            // we are trying to populate, then populate the candidates for
+            // its dependencies as well.
+            // NOTE: Technically, we don't have to check to see if the
+            // candidate revision is equal to the current revision, but this
+            // saves us from recursing and also simplifies exceptions messages
+            // since we effectively chain exception messages for each level
+            // of recursion; thus, any avoided recursion results in fewer
+            // exceptions to chain when an error does occur.
+            if ((isFragment || !rc.getWirings().containsKey(candCap.getResource()))
+                && !candCap.getResource().equals(resource))
+            {
+                try
+                {
+                    populateResource(rc, candCap.getResource());
+                }
+                catch (ResolutionException ex)
+                {
+                    if (rethrow == null)
+                    {
+                        rethrow = ex;
+                    }
+                    // Remove the candidate since we weren't able to
+                    // populate its candidates.
+                    itCandCap.remove();
+                }
+            }
+        }
+
+        // If any of the candidates for the requirement were from a fragment,
+        // then also insert synthesized hosted capabilities for any other host
+        // to which the fragment is attached since they are all effectively
+        // unique capabilities.
+        if (fragmentCands != null)
+        {
+            for (Capability fragCand : fragmentCands)
+            {
+                // Only necessary for resolved fragments.
+                Wiring wiring = rc.getWirings().get(fragCand.getResource());
+                if (wiring != null)
+                {
+                    // Fragments only have host wire, so each wire represents
+                    // an attached host.
+                    for (Wire wire : wiring.getRequiredResourceWires(null))
+                    {
+                        // If the capability is a package, then make sure the
+                        // host actually provides it in its resolved capabilities,
+                        // since it may be a substitutable export.
+                        if (!fragCand.getNamespace().equals(PackageNamespace.PACKAGE_NAMESPACE)
+                            || rc.getWirings().get(wire.getProvider())
+                                .getResourceCapabilities(null).contains(fragCand))
+                        {
+                            // Note that we can just add this as a candidate
+                            // directly, since we know it is already resolved.
+                            // NOTE: We are synthesizing a hosted capability here,
+                            // but we are not using a ShadowList like we do when
+                            // we synthesizing capabilities for unresolved hosts.
+                            // It is not necessary to use the ShadowList here since
+                            // the host is resolved, because in that case we can
+                            // calculate the proper package space by traversing
+                            // the wiring. In the unresolved case, this isn't possible
+                            // so we need to use the ShadowList so we can keep
+                            // a reference to a synthesized resource with attached
+                            // fragments so we can correctly calculate its package
+                            // space.
+                            rc.insertHostedCapability(
+                                candidates,
+                                new WrappedCapability(
+                                    wire.getCapability().getResource(),
+                                    fragCand));
+                        }
+                    }
+                }
+            }
+        }
+
+        return rethrow;
+    }
+
+    public boolean isPopulated(Resource resource)
+    {
+        Object value = m_populateResultCache.get(resource);
+        return ((value != null) && (value instanceof Boolean));
+    }
+
+    public ResolutionException getResolveException(Resource resource)
+    {
+        Object value = m_populateResultCache.get(resource);
+        return ((value != null) && (value instanceof ResolutionException))
+            ? (ResolutionException) value : null;
+    }
+
+    /**
+     * Adds a requirement and its matching candidates to the internal data
+     * structure. This method assumes it owns the data being passed in and
+     * does not make a copy. It takes the data and processes, such as calculating
+     * which requirements depend on which capabilities and recording any fragments
+     * it finds for future merging.
+     * @param req the requirement to add.
+     * @param candidates the candidates matching the requirement.
+    **/
+    private void add(Requirement req, List<Capability> candidates)
+    {
+        if (req.getNamespace().equals(HostNamespace.HOST_NAMESPACE))
+        {
+            m_fragmentsPresent = true;
+        }
+
+        // Record the candidates.
+        m_candidateMap.put(req, candidates);
+    }
+
+    /**
+     * Adds requirements and candidates in bulk. The outer map is not retained
+     * by this method, but the inner data structures are, so they should not
+     * be further modified by the caller.
+     * @param candidates the bulk requirements and candidates to add.
+    **/
+    private void add(Map<Requirement, List<Capability>> candidates)
+    {
+        for (Entry<Requirement, List<Capability>> entry : candidates.entrySet())
+        {
+            add(entry.getKey(), entry.getValue());
+        }
+    }
+
+    /**
+     * Returns the wrapped module associated with the given module. If the module
+     * was not wrapped, then the module itself is returned. This is really only
+     * needed to determine if the root modules of the resolve have been wrapped.
+     * @param m the module whose wrapper is desired.
+     * @return the wrapper module or the module itself if it was not wrapped.
+    **/
+    public Resource getWrappedHost(Resource r)
+    {
+        Resource wrapped = m_allWrappedHosts.get(r);
+        return (wrapped == null) ? r : wrapped;
+    }
+
+    /**
+     * Gets the candidates associated with a given requirement.
+     * @param req the requirement whose candidates are desired.
+     * @return the matching candidates or null.
+    **/
+    public List<Capability> getCandidates(Requirement req)
+    {
+        return m_candidateMap.get(req);
+    }
+
+    /**
+     * Merges fragments into their hosts. It does this by wrapping all host
+     * modules and attaching their selected fragments, removing all unselected
+     * fragment modules, and replacing all occurrences of the original fragments
+     * in the internal data structures with the wrapped host modules instead.
+     * Thus, fragment capabilities and requirements are merged into the appropriate
+     * host and the candidates for the fragment now become candidates for the host.
+     * Likewise, any module depending on a fragment now depend on the host. Note
+     * that this process is sort of like multiplication, since one fragment that
+     * can attach to two hosts effectively gets multiplied across the two hosts.
+     * So, any modules being satisfied by the fragment will end up having the
+     * two hosts as potential candidates, rather than the single fragment.
+     * @param existingSingletons existing resolved singletons.
+     * @throws ResolveException if the removal of any unselected fragments result
+     *         in the root module being unable to resolve.
+    **/
+    public void prepare(ResolveContext rc) throws ResolutionException
+    {
+        // Maps a host capability to a map containing its potential fragments;
+        // the fragment map maps a fragment symbolic name to a map that maps
+        // a version to a list of fragments requirements matching that symbolic
+        // name and version.
+        Map<Capability, Map<String, Map<Version, List<Requirement>>>>
+            hostFragments = Collections.EMPTY_MAP;
+        if (m_fragmentsPresent)
+        {
+            hostFragments = populateDependents();
+        }
+
+        // This method performs the following steps:
+        // 1. Select the fragments to attach to a given host.
+        // 2. Wrap hosts and attach fragments.
+        // 3. Remove any unselected fragments. This is necessary because
+        //    other revisions may depend on the capabilities of unselected
+        //    fragments, so we need to remove the unselected fragments and
+        //    any revisions that depends on them, which could ultimately cause
+        //    the entire resolve to fail.
+        // 4. Replace all fragments with any host it was merged into
+        //    (effectively multiplying it).
+        //    * This includes setting candidates for attached fragment
+        //      requirements as well as replacing fragment capabilities
+        //      with host's attached fragment capabilities.
+
+        // Steps 1 and 2
+        List<WrappedResource> hostResources = new ArrayList<WrappedResource>();
+        List<Resource> unselectedFragments = new ArrayList<Resource>();
+        for (Entry<Capability, Map<String, Map<Version, List<Requirement>>>>
+            hostEntry : hostFragments.entrySet())
+        {
+            // Step 1
+            Capability hostCap = hostEntry.getKey();
+            Map<String, Map<Version, List<Requirement>>> fragments
+                = hostEntry.getValue();
+            List<Resource> selectedFragments = new ArrayList<Resource>();
+            for (Entry<String, Map<Version, List<Requirement>>> fragEntry
+                : fragments.entrySet())
+            {
+                boolean isFirst = true;
+                for (Entry<Version, List<Requirement>> versionEntry
+                    : fragEntry.getValue().entrySet())
+                {
+                    for (Requirement hostReq : versionEntry.getValue())
+                    {
+                        // Selecting the first fragment in each entry, which
+                        // is equivalent to selecting the highest version of
+                        // each fragment with a given symbolic name.
+                        if (isFirst)
+                        {
+                            selectedFragments.add(hostReq.getResource());
+                            isFirst = false;
+                        }
+                        // For any fragment that wasn't selected, remove the
+                        // current host as a potential host for it and remove it
+                        // as a dependent on the host. If there are no more
+                        // potential hosts for the fragment, then mark it as
+                        // unselected for later removal.
+                        else
+                        {
+                            m_dependentMap.get(hostCap).remove(hostReq);
+                            List<Capability> hosts = m_candidateMap.get(hostReq);
+                            hosts.remove(hostCap);
+                            if (hosts.isEmpty())
+                            {
+                                unselectedFragments.add(hostReq.getResource());
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Step 2
+            WrappedResource wrappedHost =
+                new WrappedResource(hostCap.getResource(), selectedFragments);
+            hostResources.add(wrappedHost);
+            m_allWrappedHosts.put(hostCap.getResource(), wrappedHost);
+        }
+
+        // Step 3
+        for (Resource fragment : unselectedFragments)
+        {
+            removeResource(fragment,
+                new ResolutionException(
+                    "Fragment was not selected for attachment: " + fragment));
+        }
+
+        // Step 4
+        for (WrappedResource hostResource : hostResources)
+        {
+            // Replaces capabilities from fragments with the capabilities
+            // from the merged host.
+            for (Capability c : hostResource.getCapabilities(null))
+            {
+                // Don't replace the host capability, since the fragment will
+                // really be attached to the original host, not the wrapper.
+                if (!c.getNamespace().equals(HostNamespace.HOST_NAMESPACE))
+                {
+                    Capability origCap = ((HostedCapability) c).getDeclaredCapability();
+                    // Note that you might think we could remove the original cap
+                    // from the dependent map, but you can't since it may come from
+                    // a fragment that is attached to multiple hosts, so each host
+                    // will need to make their own copy.
+                    Set<Requirement> dependents = m_dependentMap.get(origCap);
+                    if (dependents != null)
+                    {
+                        dependents = new HashSet<Requirement>(dependents);
+                        m_dependentMap.put(c, dependents);
+                        for (Requirement r : dependents)
+                        {
+                            // We have synthesized hosted capabilities for all
+                            // fragments that have been attached to hosts by
+                            // wrapping the host bundle and their attached
+                            // fragments. We need to use the ResolveContext to
+                            // determine the proper priority order for hosted
+                            // capabilities since the order may depend on the
+                            // declaring host/fragment combination. However,
+                            // internally we completely wrap the host revision
+                            // and make all capabilities/requirements point back
+                            // to the wrapped host not the declaring host. The
+                            // ResolveContext expects HostedCapabilities to point
+                            // to the declaring revision, so we need two separate
+                            // candidate lists: one for the ResolveContext with
+                            // HostedCapabilities pointing back to the declaring
+                            // host and one for the resolver with HostedCapabilities
+                            // pointing back to the wrapped host. We ask the
+                            // ResolveContext to insert its appropriate HostedCapability
+                            // into its list, then we mirror the insert into a
+                            // shadow list with the resolver's HostedCapability.
+                            // We only need to ask the ResolveContext to find
+                            // the insert position for fragment caps since these
+                            // were synthesized and we don't know their priority.
+                            // However, in the resolver's candidate list we need
+                            // to replace all caps with the wrapped caps, no
+                            // matter if they come from the host or fragment,
+                            // since we are completing replacing the declaring
+                            // host and fragments with the wrapped host.
+                            List<Capability> cands = m_candidateMap.get(r);
+                            if (!(cands instanceof ShadowList))
+                            {
+                                ShadowList<Capability> shadow =
+                                    new ShadowList<Capability>(cands);
+                                m_candidateMap.put(r, shadow);
+                                cands = shadow;
+                            }
+
+                            // If the original capability is from a fragment, then
+                            // ask the ResolveContext to insert it and update the
+                            // shadow copy of the list accordingly.
+                            if (!origCap.getResource().equals(hostResource.getDeclaredResource()))
+                            {
+                                List<Capability> original = ((ShadowList) cands).getOriginal();
+                                int removeIdx = original.indexOf(origCap);
+                                if (removeIdx != -1)
+                                {
+                                    original.remove(removeIdx);
+                                    cands.remove(removeIdx);
+                                }
+                                int insertIdx = rc.insertHostedCapability(
+                                    original,
+                                    new SimpleHostedCapability(
+                                        hostResource.getDeclaredResource(),
+                                        origCap));
+                                cands.add(insertIdx, c);
+                            }
+                            // If the original capability is from the host, then
+                            // we just need to replace it in the shadow list.
+                            else
+                            {
+                                int idx = cands.indexOf(origCap);
+                                cands.set(idx, c);
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Copy candidates for fragment requirements to the host.
+            for (Requirement r : hostResource.getRequirements(null))
+            {
+                Requirement origReq = ((WrappedRequirement) r).getDeclaredRequirement();
+                List<Capability> cands = m_candidateMap.get(origReq);
+                if (cands != null)
+                {
+                    m_candidateMap.put(r, new ArrayList<Capability>(cands));
+                    for (Capability cand : cands)
+                    {
+                        Set<Requirement> dependents = m_dependentMap.get(cand);
+                        dependents.remove(origReq);
+                        dependents.add(r);
+                    }
+                }
+            }
+        }
+
+        // Lastly, verify that all mandatory revisions are still
+        // populated, since some might have become unresolved after
+        // selecting fragments/singletons.
+        for (Resource resource : m_mandatoryResources)
+        {
+            if (!isPopulated(resource))
+            {
+                throw getResolveException(resource);
+            }
+        }
+    }
+
+    // Maps a host capability to a map containing its potential fragments;
+    // the fragment map maps a fragment symbolic name to a map that maps
+    // a version to a list of fragments requirements matching that symbolic
+    // name and version.
+    private Map<Capability,
+        Map<String, Map<Version, List<Requirement>>>> populateDependents()
+    {
+        Map<Capability, Map<String, Map<Version, List<Requirement>>>>
+            hostFragments = new HashMap<Capability,
+                Map<String, Map<Version, List<Requirement>>>>();
+        for (Entry<Requirement, List<Capability>> entry : m_candidateMap.entrySet())
+        {
+            Requirement req = entry.getKey();
+            List<Capability> caps = entry.getValue();
+            for (Capability cap : caps)
+            {
+                // Record the requirement as dependent on the capability.
+                Set<Requirement> dependents = m_dependentMap.get(cap);
+                if (dependents == null)
+                {
+                    dependents = new HashSet<Requirement>();
+                    m_dependentMap.put(cap, dependents);
+                }
+                dependents.add(req);
+
+                // Keep track of hosts and associated fragments.
+                if (req.getNamespace().equals(HostNamespace.HOST_NAMESPACE))
+                {
+                    String resSymName = Util.getSymbolicName(req.getResource());
+                    Version resVersion = Util.getVersion(req.getResource());
+
+                    Map<String, Map<Version, List<Requirement>>>
+                        fragments = hostFragments.get(cap);
+                    if (fragments == null)
+                    {
+                        fragments = new HashMap<String, Map<Version, List<Requirement>>>();
+                        hostFragments.put(cap, fragments);
+                    }
+                    Map<Version, List<Requirement>> fragmentVersions = fragments.get(resSymName);
+                    if (fragmentVersions == null)
+                    {
+                        fragmentVersions =
+                            new TreeMap<Version, List<Requirement>>(Collections.reverseOrder());
+                        fragments.put(resSymName, fragmentVersions);
+                    }
+                    List<Requirement> actual = fragmentVersions.get(resVersion);
+                    if (actual == null)
+                    {
+                        actual = new ArrayList<Requirement>();
+                        fragmentVersions.put(resVersion, actual);
+                    }
+                    actual.add(req);
+                }
+            }
+        }
+
+        return hostFragments;
+    }
+
+    /**
+     * Removes a module from the internal data structures if it wasn't selected
+     * as a fragment or a singleton. This process may cause other modules to
+     * become unresolved if they depended on the module's capabilities and there
+     * is no other candidate.
+     * @param revision the module to remove.
+     * @throws ResolveException if removing the module caused the resolve to fail.
+    **/
+    private void removeResource(Resource resource, ResolutionException ex)
+        throws ResolutionException
+    {
+        // Add removal reason to result cache.
+        m_populateResultCache.put(resource, ex);
+        // Remove from dependents.
+        Set<Resource> unresolvedResources = new HashSet<Resource>();
+        remove(resource, unresolvedResources);
+        // Remove dependents that failed as a result of removing revision.
+        while (!unresolvedResources.isEmpty())
+        {
+            Iterator<Resource> it = unresolvedResources.iterator();
+            resource = it.next();
+            it.remove();
+            remove(resource, unresolvedResources);
+        }
+    }
+
+    /**
+     * Removes the specified module from the internal data structures, which
+     * involves removing its requirements and its capabilities. This may cause
+     * other modules to become unresolved as a result.
+     * @param br the module to remove.
+     * @param unresolvedRevisions a list to containing any additional modules that
+     *        that became unresolved as a result of removing this module and will
+     *        also need to be removed.
+     * @throws ResolveException if removing the module caused the resolve to fail.
+    **/
+    private void remove(Resource resource, Set<Resource> unresolvedResources)
+        throws ResolutionException
+    {
+        for (Requirement r : resource.getRequirements(null))
+        {
+            remove(r);
+        }
+
+        for (Capability c : resource.getCapabilities(null))
+        {
+            remove(c, unresolvedResources);
+        }
+    }
+
+    /**
+     * Removes a requirement from the internal data structures.
+     * @param req the requirement to remove.
+    **/
+    private void remove(Requirement req)
+    {
+        boolean isFragment = req.getNamespace().equals(HostNamespace.HOST_NAMESPACE);
+
+        List<Capability> candidates = m_candidateMap.remove(req);
+        if (candidates != null)
+        {
+            for (Capability cap : candidates)
+            {
+                Set<Requirement> dependents = m_dependentMap.get(cap);
+                if (dependents != null)
+                {
+                    dependents.remove(req);
+                }
+            }
+        }
+    }
+
+    /**
+     * Removes a capability from the internal data structures. This may cause
+     * other modules to become unresolved as a result.
+     * @param c the capability to remove.
+     * @param unresolvedRevisions a list to containing any additional modules that
+     *        that became unresolved as a result of removing this module and will
+     *        also need to be removed.
+     * @throws ResolveException if removing the module caused the resolve to fail.
+    **/
+    private void remove(Capability c, Set<Resource> unresolvedResources)
+        throws ResolutionException
+    {
+        Set<Requirement> dependents = m_dependentMap.remove(c);
+        if (dependents != null)
+        {
+            for (Requirement r : dependents)
+            {
+                List<Capability> candidates = m_candidateMap.get(r);
+                candidates.remove(c);
+                if (candidates.isEmpty())
+                {
+                    m_candidateMap.remove(r);
+                    if (!Util.isOptional(r))
+                    {
+                        String msg = "Unable to resolve " + r.getResource()
+                            + ": missing requirement " + r;
+                        m_populateResultCache.put(
+                            r.getResource(),
+                            new ResolutionException(msg, null, Collections.singleton(r)));
+                        unresolvedResources.add(r.getResource());
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Creates a copy of the Candidates object. This is used for creating
+     * permutations when package space conflicts are discovered.
+     * @return copy of this Candidates object.
+    **/
+    public Candidates copy()
+    {
+        Map<Capability, Set<Requirement>> dependentMap =
+            new HashMap<Capability, Set<Requirement>>();
+        for (Entry<Capability, Set<Requirement>> entry : m_dependentMap.entrySet())
+        {
+            Set<Requirement> dependents = new HashSet<Requirement>(entry.getValue());
+            dependentMap.put(entry.getKey(), dependents);
+        }
+
+        Map<Requirement, List<Capability>> candidateMap =
+            new HashMap<Requirement, List<Capability>>();
+        for (Entry<Requirement, List<Capability>> entry
+            : m_candidateMap.entrySet())
+        {
+            List<Capability> candidates =
+                new ArrayList<Capability>(entry.getValue());
+            candidateMap.put(entry.getKey(), candidates);
+        }
+
+        return new Candidates(
+            m_mandatoryResources, dependentMap, candidateMap,
+            m_allWrappedHosts, m_populateResultCache, m_fragmentsPresent);
+    }
+
+    public void dump(ResolveContext rc)
+    {
+        // Create set of all revisions from requirements.
+        Set<Resource> resources = new HashSet<Resource>();
+        for (Entry<Requirement, List<Capability>> entry
+            : m_candidateMap.entrySet())
+        {
+            resources.add(entry.getKey().getResource());
+        }
+        // Now dump the revisions.
+        System.out.println("=== BEGIN CANDIDATE MAP ===");
+        for (Resource resource : resources)
+        {
+            Wiring wiring = rc.getWirings().get(resource);
+            System.out.println("  " + resource
+                 + " (" + ((wiring != null) ? "RESOLVED)" : "UNRESOLVED)"));
+            List<Requirement> reqs = (wiring != null)
+                ? wiring.getResourceRequirements(null)
+                : resource.getRequirements(null);
+            for (Requirement req : reqs)
+            {
+                List<Capability> candidates = m_candidateMap.get(req);
+                if ((candidates != null) && (candidates.size() > 0))
+                {
+                    System.out.println("    " + req + ": " + candidates);
+                }
+            }
+            reqs = (wiring != null)
+                ? Util.getDynamicRequirements(wiring.getResourceRequirements(null))
+                : Util.getDynamicRequirements(resource.getRequirements(null));
+            for (Requirement req : reqs)
+            {
+                List<Capability> candidates = m_candidateMap.get(req);
+                if ((candidates != null) && (candidates.size() > 0))
+                {
+                    System.out.println("    " + req + ": " + candidates);
+                }
+            }
+        }
+        System.out.println("=== END CANDIDATE MAP ===");
+    }
+}
\ No newline at end of file



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