packages/DocumentsUI/src/com/android/documentsui/RootsCache.java - platform/frameworks/base - Git at Google

 /*
  * Copyright (C) 2013 The Android Open Source Project
  *
  * Licensed 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 com.android.documentsui;

 import static com.android.documentsui.Shared.DEBUG;

 import android.content.BroadcastReceiver.PendingResult;
 import android.content.ContentProviderClient;
 import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager;
 import android.content.pm.ProviderInfo;
 import android.content.pm.ResolveInfo;
 import android.database.ContentObserver;
 import android.database.Cursor;
 import android.net.Uri;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.os.Handler;
 import android.os.SystemClock;
 import android.provider.DocumentsContract;
 import android.provider.DocumentsContract.Root;
 import android.support.annotation.VisibleForTesting;
 import android.util.Log;

 import com.android.documentsui.model.RootInfo;
 import com.android.internal.annotations.GuardedBy;

 import libcore.io.IoUtils;

 import com.google.common.collect.ArrayListMultimap;
 import com.google.common.collect.Multimap;

 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;

 /**
  * Cache of known storage backends and their roots.
  */
 public class RootsCache {
     public static final Uri sNotificationUri = Uri.parse(
             "content://com.android.documentsui.roots/");

     private static final String TAG = "RootsCache";

     private final Context mContext;
     private final ContentObserver mObserver;

     private final RootInfo mRecentsRoot;

     private final Object mLock = new Object();
     private final CountDownLatch mFirstLoad = new CountDownLatch(1);

     @GuardedBy("mLock")
     private boolean mFirstLoadDone;
     @GuardedBy("mLock")
     private PendingResult mBootCompletedResult;

     @GuardedBy("mLock")
     private Multimap<String, RootInfo> mRoots = ArrayListMultimap.create();
     @GuardedBy("mLock")
     private HashSet<String> mStoppedAuthorities = new HashSet<>();

     @GuardedBy("mObservedAuthorities")
     private final HashSet<String> mObservedAuthorities = new HashSet<>();

     public RootsCache(Context context) {
         mContext = context;
         mObserver = new RootsChangedObserver();

         // Create a new anonymous "Recents" RootInfo. It's a faker.
         mRecentsRoot = new RootInfo() {{
                 // Special root for recents
                 derivedIcon = R.drawable.ic_root_recent;
                 derivedType = RootInfo.TYPE_RECENTS;
                 flags = Root.FLAG_LOCAL_ONLY | Root.FLAG_SUPPORTS_IS_CHILD
                         | Root.FLAG_SUPPORTS_CREATE;
                 title = mContext.getString(R.string.root_recent);
                 availableBytes = -1;
             }};
     }

     private class RootsChangedObserver extends ContentObserver {
         public RootsChangedObserver() {
             super(new Handler());
         }

         @Override
         public void onChange(boolean selfChange, Uri uri) {
             if (uri == null) {
                 Log.w(TAG, "Received onChange event for null uri. Skipping.");
                 return;
             }
             if (DEBUG) Log.d(TAG, "Updating roots due to change at " + uri);
             updateAuthorityAsync(uri.getAuthority());
         }
     }

     /**
      * Gather roots from all known storage providers.
      */
     public void updateAsync(boolean forceRefreshAll) {

         // NOTE: This method is called when the UI language changes.
         // For that reason we update our RecentsRoot to reflect
         // the current language.
         mRecentsRoot.title = mContext.getString(R.string.root_recent);

         // Nothing else about the root should ever change.
         assert(mRecentsRoot.authority == null);
         assert(mRecentsRoot.rootId == null);
         assert(mRecentsRoot.derivedIcon == R.drawable.ic_root_recent);
         assert(mRecentsRoot.derivedType == RootInfo.TYPE_RECENTS);
         assert(mRecentsRoot.flags == (Root.FLAG_LOCAL_ONLY
                 | Root.FLAG_SUPPORTS_IS_CHILD
                 | Root.FLAG_SUPPORTS_CREATE));
         assert(mRecentsRoot.availableBytes == -1);

         new UpdateTask(forceRefreshAll, null)
                 .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }

     /**
      * Gather roots from storage providers belonging to given package name.
      */
     public void updatePackageAsync(String packageName) {
         new UpdateTask(false, packageName).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }

     /**
      * Gather roots from storage providers belonging to given authority.
      */
     public void updateAuthorityAsync(String authority) {
         final ProviderInfo info = mContext.getPackageManager().resolveContentProvider(authority, 0);
         if (info != null) {
             updatePackageAsync(info.packageName);
         }
     }

     public void setBootCompletedResult(PendingResult result) {
         synchronized (mLock) {
             // Quickly check if we've already finished loading, otherwise hang
             // out until first pass is finished.
             if (mFirstLoadDone) {
                 result.finish();
             } else {
                 mBootCompletedResult = result;
             }
         }
     }

     /**
      * Block until the first {@link UpdateTask} pass has finished.
      *
      * @return {@code true} if cached roots is ready to roll, otherwise
      *         {@code false} if we timed out while waiting.
      */
     private boolean waitForFirstLoad() {
         boolean success = false;
         try {
             success = mFirstLoad.await(15, TimeUnit.SECONDS);
         } catch (InterruptedException e) {
         }
         if (!success) {
             Log.w(TAG, "Timeout waiting for first update");
         }
         return success;
     }

     /**
      * Load roots from authorities that are in stopped state. Normal
      * {@link UpdateTask} passes ignore stopped applications.
      */
     private void loadStoppedAuthorities() {
         final ContentResolver resolver = mContext.getContentResolver();
         synchronized (mLock) {
             for (String authority : mStoppedAuthorities) {
                 if (DEBUG) Log.d(TAG, "Loading stopped authority " + authority);
                 mRoots.putAll(authority, loadRootsForAuthority(resolver, authority, true));
             }
             mStoppedAuthorities.clear();
         }
     }

     /**
      * Load roots from a stopped authority. Normal {@link UpdateTask} passes
      * ignore stopped applications.
      */
     private void loadStoppedAuthority(String authority) {
         final ContentResolver resolver = mContext.getContentResolver();
         synchronized (mLock) {
             if (!mStoppedAuthorities.contains(authority)) {
                 return;
             }
             if (DEBUG) {
                 Log.d(TAG, "Loading stopped authority " + authority);
             }
             mRoots.putAll(authority, loadRootsForAuthority(resolver, authority, true));
             mStoppedAuthorities.remove(authority);
         }
     }

     private class UpdateTask extends AsyncTask<Void, Void, Void> {
         private final boolean mForceRefreshAll;
         private final String mForceRefreshPackage;

         private final Multimap<String, RootInfo> mTaskRoots = ArrayListMultimap.create();
         private final HashSet<String> mTaskStoppedAuthorities = new HashSet<>();

         /**
          * Create task to update roots cache.
          *
          * @param forceRefreshAll when true, all previously cached values for
          *            all packages should be ignored.
          * @param forceRefreshPackage when non-null, all previously cached
          *            values for this specific package should be ignored.
          */
         public UpdateTask(boolean forceRefreshAll, String forceRefreshPackage) {
             mForceRefreshAll = forceRefreshAll;
             mForceRefreshPackage = forceRefreshPackage;
         }

         @Override
         protected Void doInBackground(Void... params) {
             final long start = SystemClock.elapsedRealtime();

             mTaskRoots.put(mRecentsRoot.authority, mRecentsRoot);

             final ContentResolver resolver = mContext.getContentResolver();
             final PackageManager pm = mContext.getPackageManager();

             // Pick up provider with action string
             final Intent intent = new Intent(DocumentsContract.PROVIDER_INTERFACE);
             final List<ResolveInfo> providers = pm.queryIntentContentProviders(intent, 0);
             for (ResolveInfo info : providers) {
                 handleDocumentsProvider(info.providerInfo);
             }

             final long delta = SystemClock.elapsedRealtime() - start;
             if (DEBUG)
                 Log.d(TAG, "Update found " + mTaskRoots.size() + " roots in " + delta + "ms");
             synchronized (mLock) {
                 mFirstLoadDone = true;
                 if (mBootCompletedResult != null) {
                     mBootCompletedResult.finish();
                     mBootCompletedResult = null;
                 }
                 mRoots = mTaskRoots;
                 mStoppedAuthorities = mTaskStoppedAuthorities;
             }
             mFirstLoad.countDown();
             resolver.notifyChange(sNotificationUri, null, false);
             return null;
         }

         private void handleDocumentsProvider(ProviderInfo info) {
             // Ignore stopped packages for now; we might query them
             // later during UI interaction.
             if ((info.applicationInfo.flags & ApplicationInfo.FLAG_STOPPED) != 0) {
                 if (DEBUG) Log.d(TAG, "Ignoring stopped authority " + info.authority);
                 mTaskStoppedAuthorities.add(info.authority);
                 return;
             }

             final boolean forceRefresh = mForceRefreshAll
                     || Objects.equals(info.packageName, mForceRefreshPackage);
             mTaskRoots.putAll(info.authority, loadRootsForAuthority(mContext.getContentResolver(),
                     info.authority, forceRefresh));
         }
     }

     /**
      * Bring up requested provider and query for all active roots.
      */
     private Collection<RootInfo> loadRootsForAuthority(ContentResolver resolver, String authority,
             boolean forceRefresh) {
         if (DEBUG) Log.d(TAG, "Loading roots for " + authority);

         synchronized (mObservedAuthorities) {
             if (mObservedAuthorities.add(authority)) {
                 // Watch for any future updates
                 final Uri rootsUri = DocumentsContract.buildRootsUri(authority);
                 mContext.getContentResolver().registerContentObserver(rootsUri, true, mObserver);
             }
         }

         final Uri rootsUri = DocumentsContract.buildRootsUri(authority);
         if (!forceRefresh) {
             // Look for roots data that we might have cached for ourselves in the
             // long-lived system process.
             final Bundle systemCache = resolver.getCache(rootsUri);
             if (systemCache != null) {
                 if (DEBUG) Log.d(TAG, "System cache hit for " + authority);
                 return systemCache.getParcelableArrayList(TAG);
             }
         }

         final ArrayList<RootInfo> roots = new ArrayList<>();
         ContentProviderClient client = null;
         Cursor cursor = null;
         try {
             client = DocumentsApplication.acquireUnstableProviderOrThrow(resolver, authority);
             cursor = client.query(rootsUri, null, null, null, null);
             while (cursor.moveToNext()) {
                 final RootInfo root = RootInfo.fromRootsCursor(authority, cursor);
                 roots.add(root);
             }
         } catch (Exception e) {
             Log.w(TAG, "Failed to load some roots from " + authority + ": " + e);
         } finally {
             IoUtils.closeQuietly(cursor);
             ContentProviderClient.releaseQuietly(client);
         }

         // Cache these freshly parsed roots over in the long-lived system
         // process, in case our process goes away. The system takes care of
         // invalidating the cache if the package or Uri changes.
         final Bundle systemCache = new Bundle();
         systemCache.putParcelableArrayList(TAG, roots);
         resolver.putCache(rootsUri, systemCache);

         return roots;
     }

     /**
      * Return the requested {@link RootInfo}, but only loading the roots for the
      * requested authority. This is useful when we want to load fast without
      * waiting for all the other roots to come back.
      */
     public RootInfo getRootOneshot(String authority, String rootId) {
         synchronized (mLock) {
             RootInfo root = getRootLocked(authority, rootId);
             if (root == null) {
                 mRoots.putAll(authority,
                         loadRootsForAuthority(mContext.getContentResolver(), authority, false));
                 root = getRootLocked(authority, rootId);
             }
             return root;
         }
     }

     public RootInfo getRootBlocking(String authority, String rootId) {
         waitForFirstLoad();
         loadStoppedAuthorities();
         synchronized (mLock) {
             return getRootLocked(authority, rootId);
         }
     }

     private RootInfo getRootLocked(String authority, String rootId) {
         for (RootInfo root : mRoots.get(authority)) {
             if (Objects.equals(root.rootId, rootId)) {
                 return root;
             }
         }
         return null;
     }

     public boolean isIconUniqueBlocking(RootInfo root) {
         waitForFirstLoad();
         loadStoppedAuthorities();
         synchronized (mLock) {
             final int rootIcon = root.derivedIcon != 0 ? root.derivedIcon : root.icon;
             for (RootInfo test : mRoots.get(root.authority)) {
                 if (Objects.equals(test.rootId, root.rootId)) {
                     continue;
                 }
                 final int testIcon = test.derivedIcon != 0 ? test.derivedIcon : test.icon;
                 if (testIcon == rootIcon) {
                     return false;
                 }
             }
             return true;
         }
     }

     public RootInfo getRecentsRoot() {
         return mRecentsRoot;
     }

     public boolean isRecentsRoot(RootInfo root) {
         return mRecentsRoot.equals(root);
     }

     public Collection<RootInfo> getRootsBlocking() {
         waitForFirstLoad();
         loadStoppedAuthorities();
         synchronized (mLock) {
             return mRoots.values();
         }
     }

     public Collection<RootInfo> getMatchingRootsBlocking(State state) {
         waitForFirstLoad();
         loadStoppedAuthorities();
         synchronized (mLock) {
             return getMatchingRoots(mRoots.values(), state);
         }
     }

     /**
      * Returns a list of roots for the specified authority. If not found, then
      * an empty list is returned.
      */
     public Collection<RootInfo> getRootsForAuthorityBlocking(String authority) {
         waitForFirstLoad();
         loadStoppedAuthority(authority);
         synchronized (mLock) {
             final Collection<RootInfo> roots = mRoots.get(authority);
             return roots != null ? roots : Collections.<RootInfo>emptyList();
         }
     }

     /**
      * Returns the default root for the specified state.
      */
     public RootInfo getDefaultRootBlocking(State state) {
         for (RootInfo root : getMatchingRoots(getRootsBlocking(), state)) {
             if (root.isDownloads()) {
                 return root;
             }
         }
         return mRecentsRoot;
     }

     @VisibleForTesting
     static List<RootInfo> getMatchingRoots(Collection<RootInfo> roots, State state) {
         final List<RootInfo> matching = new ArrayList<>();
         for (RootInfo root : roots) {

             if (DEBUG) Log.d(TAG, "Evaluating " + root);

             if (state.action == State.ACTION_CREATE && !root.supportsCreate()) {
                 if (DEBUG) Log.d(TAG, "Excluding read-only root because: ACTION_CREATE.");
                 continue;
             }

             if (state.action == State.ACTION_PICK_COPY_DESTINATION
                     && !root.supportsCreate()) {
                 if (DEBUG) Log.d(
                         TAG, "Excluding read-only root because: ACTION_PICK_COPY_DESTINATION.");
                 continue;
             }

             if (state.action == State.ACTION_OPEN_TREE && !root.supportsChildren()) {
                 if (DEBUG) Log.d(
                         TAG, "Excluding root !supportsChildren because: ACTION_OPEN_TREE.");
                 continue;
             }

             if (!state.showAdvanced && root.isAdvanced()) {
                 if (DEBUG) Log.d(TAG, "Excluding root because: unwanted advanced device.");
                 continue;
             }

             if (state.localOnly && !root.isLocalOnly()) {
                 if (DEBUG) Log.d(TAG, "Excluding root because: unwanted non-local device.");
                 continue;
             }

             if (state.directoryCopy && root.isDownloads()) {
                 if (DEBUG) Log.d(
                         TAG, "Excluding downloads root because: unsupported directory copy.");
                 continue;
             }

             if (state.action == State.ACTION_OPEN && root.isEmpty()) {
                 if (DEBUG) Log.d(TAG, "Excluding empty root because: ACTION_OPEN.");
                 continue;
             }

             if (state.action == State.ACTION_GET_CONTENT && root.isEmpty()) {
                 if (DEBUG) Log.d(TAG, "Excluding empty root because: ACTION_GET_CONTENT.");
                 continue;
             }

             final boolean overlap =
                     MimePredicate.mimeMatches(root.derivedMimeTypes, state.acceptMimes) ||
                     MimePredicate.mimeMatches(state.acceptMimes, root.derivedMimeTypes);
             if (!overlap) {
                 if (DEBUG) Log.d(
                         TAG, "Excluding root because: unsupported content types > "
                         + state.acceptMimes);
                 continue;
             }

             if (state.excludedAuthorities.contains(root.authority)) {
                 if (DEBUG) Log.d(TAG, "Excluding root because: owned by calling package.");
                 continue;
             }

             if (DEBUG) Log.d(TAG, "Including " + root);
             matching.add(root);
         }
         return matching;
     }
 }
	/*
	* Copyright (C) 2013 The Android Open Source Project
	*
	* Licensed 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 com.android.documentsui;

	import static com.android.documentsui.Shared.DEBUG;

	import android.content.BroadcastReceiver.PendingResult;
	import android.content.ContentProviderClient;
	import android.content.ContentResolver;
	import android.content.Context;
	import android.content.Intent;
	import android.content.pm.ApplicationInfo;
	import android.content.pm.PackageManager;
	import android.content.pm.ProviderInfo;
	import android.content.pm.ResolveInfo;
	import android.database.ContentObserver;
	import android.database.Cursor;
	import android.net.Uri;
	import android.os.AsyncTask;
	import android.os.Bundle;
	import android.os.Handler;
	import android.os.SystemClock;
	import android.provider.DocumentsContract;
	import android.provider.DocumentsContract.Root;
	import android.support.annotation.VisibleForTesting;
	import android.util.Log;

	import com.android.documentsui.model.RootInfo;
	import com.android.internal.annotations.GuardedBy;

	import libcore.io.IoUtils;

	import com.google.common.collect.ArrayListMultimap;
	import com.google.common.collect.Multimap;

	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.Collections;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Objects;
	import java.util.concurrent.CountDownLatch;
	import java.util.concurrent.TimeUnit;

	/**
	* Cache of known storage backends and their roots.
	*/
	public class RootsCache {
	public static final Uri sNotificationUri = Uri.parse(
	"content://com.android.documentsui.roots/");

	private static final String TAG = "RootsCache";

	private final Context mContext;
	private final ContentObserver mObserver;

	private final RootInfo mRecentsRoot;

	private final Object mLock = new Object();
	private final CountDownLatch mFirstLoad = new CountDownLatch(1);

	@GuardedBy("mLock")
	private boolean mFirstLoadDone;
	@GuardedBy("mLock")
	private PendingResult mBootCompletedResult;

	@GuardedBy("mLock")
	private Multimap<String, RootInfo> mRoots = ArrayListMultimap.create();
	@GuardedBy("mLock")
	private HashSet<String> mStoppedAuthorities = new HashSet<>();

	@GuardedBy("mObservedAuthorities")
	private final HashSet<String> mObservedAuthorities = new HashSet<>();

	public RootsCache(Context context) {
	mContext = context;
	mObserver = new RootsChangedObserver();

	// Create a new anonymous "Recents" RootInfo. It's a faker.
	mRecentsRoot = new RootInfo() {{
	// Special root for recents
	derivedIcon = R.drawable.ic_root_recent;
	derivedType = RootInfo.TYPE_RECENTS;
	flags = Root.FLAG_LOCAL_ONLY \| Root.FLAG_SUPPORTS_IS_CHILD
	\| Root.FLAG_SUPPORTS_CREATE;
	title = mContext.getString(R.string.root_recent);
	availableBytes = -1;
	}};
	}

	private class RootsChangedObserver extends ContentObserver {
	public RootsChangedObserver() {
	super(new Handler());
	}

	@Override
	public void onChange(boolean selfChange, Uri uri) {
	if (uri == null) {
	Log.w(TAG, "Received onChange event for null uri. Skipping.");
	return;
	}
	if (DEBUG) Log.d(TAG, "Updating roots due to change at " + uri);
	updateAuthorityAsync(uri.getAuthority());
	}
	}

	/**
	* Gather roots from all known storage providers.
	*/
	public void updateAsync(boolean forceRefreshAll) {

	// NOTE: This method is called when the UI language changes.
	// For that reason we update our RecentsRoot to reflect
	// the current language.
	mRecentsRoot.title = mContext.getString(R.string.root_recent);

	// Nothing else about the root should ever change.
	assert(mRecentsRoot.authority == null);
	assert(mRecentsRoot.rootId == null);
	assert(mRecentsRoot.derivedIcon == R.drawable.ic_root_recent);
	assert(mRecentsRoot.derivedType == RootInfo.TYPE_RECENTS);
	assert(mRecentsRoot.flags == (Root.FLAG_LOCAL_ONLY
	\| Root.FLAG_SUPPORTS_IS_CHILD
	\| Root.FLAG_SUPPORTS_CREATE));
	assert(mRecentsRoot.availableBytes == -1);

	new UpdateTask(forceRefreshAll, null)
	.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
	}

	/**
	* Gather roots from storage providers belonging to given package name.
	*/
	public void updatePackageAsync(String packageName) {
	new UpdateTask(false, packageName).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
	}

	/**
	* Gather roots from storage providers belonging to given authority.
	*/
	public void updateAuthorityAsync(String authority) {
	final ProviderInfo info = mContext.getPackageManager().resolveContentProvider(authority, 0);
	if (info != null) {
	updatePackageAsync(info.packageName);
	}
	}

	public void setBootCompletedResult(PendingResult result) {
	synchronized (mLock) {
	// Quickly check if we've already finished loading, otherwise hang
	// out until first pass is finished.
	if (mFirstLoadDone) {
	result.finish();
	} else {
	mBootCompletedResult = result;
	}
	}
	}

	/**
	* Block until the first {@link UpdateTask} pass has finished.
	*
	* @return {@code true} if cached roots is ready to roll, otherwise
	* {@code false} if we timed out while waiting.
	*/
	private boolean waitForFirstLoad() {
	boolean success = false;
	try {
	success = mFirstLoad.await(15, TimeUnit.SECONDS);
	} catch (InterruptedException e) {
	}
	if (!success) {
	Log.w(TAG, "Timeout waiting for first update");
	}
	return success;
	}

	/**
	* Load roots from authorities that are in stopped state. Normal
	* {@link UpdateTask} passes ignore stopped applications.
	*/
	private void loadStoppedAuthorities() {
	final ContentResolver resolver = mContext.getContentResolver();
	synchronized (mLock) {
	for (String authority : mStoppedAuthorities) {
	if (DEBUG) Log.d(TAG, "Loading stopped authority " + authority);
	mRoots.putAll(authority, loadRootsForAuthority(resolver, authority, true));
	}
	mStoppedAuthorities.clear();
	}
	}

	/**
	* Load roots from a stopped authority. Normal {@link UpdateTask} passes
	* ignore stopped applications.
	*/
	private void loadStoppedAuthority(String authority) {
	final ContentResolver resolver = mContext.getContentResolver();
	synchronized (mLock) {
	if (!mStoppedAuthorities.contains(authority)) {
	return;
	}
	if (DEBUG) {
	Log.d(TAG, "Loading stopped authority " + authority);
	}
	mRoots.putAll(authority, loadRootsForAuthority(resolver, authority, true));
	mStoppedAuthorities.remove(authority);
	}
	}

	private class UpdateTask extends AsyncTask<Void, Void, Void> {
	private final boolean mForceRefreshAll;
	private final String mForceRefreshPackage;

	private final Multimap<String, RootInfo> mTaskRoots = ArrayListMultimap.create();
	private final HashSet<String> mTaskStoppedAuthorities = new HashSet<>();

	/**
	* Create task to update roots cache.
	*
	* @param forceRefreshAll when true, all previously cached values for
	* all packages should be ignored.
	* @param forceRefreshPackage when non-null, all previously cached
	* values for this specific package should be ignored.
	*/
	public UpdateTask(boolean forceRefreshAll, String forceRefreshPackage) {
	mForceRefreshAll = forceRefreshAll;
	mForceRefreshPackage = forceRefreshPackage;
	}

	@Override
	protected Void doInBackground(Void... params) {
	final long start = SystemClock.elapsedRealtime();

	mTaskRoots.put(mRecentsRoot.authority, mRecentsRoot);

	final ContentResolver resolver = mContext.getContentResolver();
	final PackageManager pm = mContext.getPackageManager();

	// Pick up provider with action string
	final Intent intent = new Intent(DocumentsContract.PROVIDER_INTERFACE);
	final List<ResolveInfo> providers = pm.queryIntentContentProviders(intent, 0);
	for (ResolveInfo info : providers) {
	handleDocumentsProvider(info.providerInfo);
	}

	final long delta = SystemClock.elapsedRealtime() - start;
	if (DEBUG)
	Log.d(TAG, "Update found " + mTaskRoots.size() + " roots in " + delta + "ms");
	synchronized (mLock) {
	mFirstLoadDone = true;
	if (mBootCompletedResult != null) {
	mBootCompletedResult.finish();
	mBootCompletedResult = null;
	}
	mRoots = mTaskRoots;
	mStoppedAuthorities = mTaskStoppedAuthorities;
	}
	mFirstLoad.countDown();
	resolver.notifyChange(sNotificationUri, null, false);
	return null;
	}

	private void handleDocumentsProvider(ProviderInfo info) {
	// Ignore stopped packages for now; we might query them
	// later during UI interaction.
	if ((info.applicationInfo.flags & ApplicationInfo.FLAG_STOPPED) != 0) {
	if (DEBUG) Log.d(TAG, "Ignoring stopped authority " + info.authority);
	mTaskStoppedAuthorities.add(info.authority);
	return;
	}

	final boolean forceRefresh = mForceRefreshAll
	\|\| Objects.equals(info.packageName, mForceRefreshPackage);
	mTaskRoots.putAll(info.authority, loadRootsForAuthority(mContext.getContentResolver(),
	info.authority, forceRefresh));
	}
	}

	/**
	* Bring up requested provider and query for all active roots.
	*/
	private Collection<RootInfo> loadRootsForAuthority(ContentResolver resolver, String authority,
	boolean forceRefresh) {
	if (DEBUG) Log.d(TAG, "Loading roots for " + authority);

	synchronized (mObservedAuthorities) {
	if (mObservedAuthorities.add(authority)) {
	// Watch for any future updates
	final Uri rootsUri = DocumentsContract.buildRootsUri(authority);
	mContext.getContentResolver().registerContentObserver(rootsUri, true, mObserver);
	}
	}

	final Uri rootsUri = DocumentsContract.buildRootsUri(authority);
	if (!forceRefresh) {
	// Look for roots data that we might have cached for ourselves in the
	// long-lived system process.
	final Bundle systemCache = resolver.getCache(rootsUri);
	if (systemCache != null) {
	if (DEBUG) Log.d(TAG, "System cache hit for " + authority);
	return systemCache.getParcelableArrayList(TAG);
	}
	}

	final ArrayList<RootInfo> roots = new ArrayList<>();
	ContentProviderClient client = null;
	Cursor cursor = null;
	try {
	client = DocumentsApplication.acquireUnstableProviderOrThrow(resolver, authority);
	cursor = client.query(rootsUri, null, null, null, null);
	while (cursor.moveToNext()) {
	final RootInfo root = RootInfo.fromRootsCursor(authority, cursor);
	roots.add(root);
	}
	} catch (Exception e) {
	Log.w(TAG, "Failed to load some roots from " + authority + ": " + e);
	} finally {
	IoUtils.closeQuietly(cursor);
	ContentProviderClient.releaseQuietly(client);
	}

	// Cache these freshly parsed roots over in the long-lived system
	// process, in case our process goes away. The system takes care of
	// invalidating the cache if the package or Uri changes.
	final Bundle systemCache = new Bundle();
	systemCache.putParcelableArrayList(TAG, roots);
	resolver.putCache(rootsUri, systemCache);

	return roots;
	}

	/**
	* Return the requested {@link RootInfo}, but only loading the roots for the
	* requested authority. This is useful when we want to load fast without
	* waiting for all the other roots to come back.
	*/
	public RootInfo getRootOneshot(String authority, String rootId) {
	synchronized (mLock) {
	RootInfo root = getRootLocked(authority, rootId);
	if (root == null) {
	mRoots.putAll(authority,
	loadRootsForAuthority(mContext.getContentResolver(), authority, false));
	root = getRootLocked(authority, rootId);
	}
	return root;
	}
	}

	public RootInfo getRootBlocking(String authority, String rootId) {
	waitForFirstLoad();
	loadStoppedAuthorities();
	synchronized (mLock) {
	return getRootLocked(authority, rootId);
	}
	}

	private RootInfo getRootLocked(String authority, String rootId) {
	for (RootInfo root : mRoots.get(authority)) {
	if (Objects.equals(root.rootId, rootId)) {
	return root;
	}
	}
	return null;
	}

	public boolean isIconUniqueBlocking(RootInfo root) {
	waitForFirstLoad();
	loadStoppedAuthorities();
	synchronized (mLock) {
	final int rootIcon = root.derivedIcon != 0 ? root.derivedIcon : root.icon;
	for (RootInfo test : mRoots.get(root.authority)) {
	if (Objects.equals(test.rootId, root.rootId)) {
	continue;
	}
	final int testIcon = test.derivedIcon != 0 ? test.derivedIcon : test.icon;
	if (testIcon == rootIcon) {
	return false;
	}
	}
	return true;
	}
	}

	public RootInfo getRecentsRoot() {
	return mRecentsRoot;
	}

	public boolean isRecentsRoot(RootInfo root) {
	return mRecentsRoot.equals(root);
	}

	public Collection<RootInfo> getRootsBlocking() {
	waitForFirstLoad();
	loadStoppedAuthorities();
	synchronized (mLock) {
	return mRoots.values();
	}
	}

	public Collection<RootInfo> getMatchingRootsBlocking(State state) {
	waitForFirstLoad();
	loadStoppedAuthorities();
	synchronized (mLock) {
	return getMatchingRoots(mRoots.values(), state);
	}
	}

	/**
	* Returns a list of roots for the specified authority. If not found, then
	* an empty list is returned.
	*/
	public Collection<RootInfo> getRootsForAuthorityBlocking(String authority) {
	waitForFirstLoad();
	loadStoppedAuthority(authority);
	synchronized (mLock) {
	final Collection<RootInfo> roots = mRoots.get(authority);
	return roots != null ? roots : Collections.<RootInfo>emptyList();
	}
	}

	/**
	* Returns the default root for the specified state.
	*/
	public RootInfo getDefaultRootBlocking(State state) {
	for (RootInfo root : getMatchingRoots(getRootsBlocking(), state)) {
	if (root.isDownloads()) {
	return root;
	}
	}
	return mRecentsRoot;
	}

	@VisibleForTesting
	static List<RootInfo> getMatchingRoots(Collection<RootInfo> roots, State state) {
	final List<RootInfo> matching = new ArrayList<>();
	for (RootInfo root : roots) {

	if (DEBUG) Log.d(TAG, "Evaluating " + root);

	if (state.action == State.ACTION_CREATE && !root.supportsCreate()) {
	if (DEBUG) Log.d(TAG, "Excluding read-only root because: ACTION_CREATE.");
	continue;
	}

	if (state.action == State.ACTION_PICK_COPY_DESTINATION
	&& !root.supportsCreate()) {
	if (DEBUG) Log.d(
	TAG, "Excluding read-only root because: ACTION_PICK_COPY_DESTINATION.");
	continue;
	}

	if (state.action == State.ACTION_OPEN_TREE && !root.supportsChildren()) {
	if (DEBUG) Log.d(
	TAG, "Excluding root !supportsChildren because: ACTION_OPEN_TREE.");
	continue;
	}

	if (!state.showAdvanced && root.isAdvanced()) {
	if (DEBUG) Log.d(TAG, "Excluding root because: unwanted advanced device.");
	continue;
	}

	if (state.localOnly && !root.isLocalOnly()) {
	if (DEBUG) Log.d(TAG, "Excluding root because: unwanted non-local device.");
	continue;
	}

	if (state.directoryCopy && root.isDownloads()) {
	if (DEBUG) Log.d(
	TAG, "Excluding downloads root because: unsupported directory copy.");
	continue;
	}

	if (state.action == State.ACTION_OPEN && root.isEmpty()) {
	if (DEBUG) Log.d(TAG, "Excluding empty root because: ACTION_OPEN.");
	continue;
	}

	if (state.action == State.ACTION_GET_CONTENT && root.isEmpty()) {
	if (DEBUG) Log.d(TAG, "Excluding empty root because: ACTION_GET_CONTENT.");
	continue;
	}

	final boolean overlap =
	MimePredicate.mimeMatches(root.derivedMimeTypes, state.acceptMimes) \|\|
	MimePredicate.mimeMatches(state.acceptMimes, root.derivedMimeTypes);
	if (!overlap) {
	if (DEBUG) Log.d(
	TAG, "Excluding root because: unsupported content types > "
	+ state.acceptMimes);
	continue;
	}

	if (state.excludedAuthorities.contains(root.authority)) {
	if (DEBUG) Log.d(TAG, "Excluding root because: owned by calling package.");
	continue;
	}

	if (DEBUG) Log.d(TAG, "Including " + root);
	matching.add(root);
	}
	return matching;
	}
	}