src/com/android/mtp/DocumentLoader.java - platform/packages/services/Mtp - Git at Google

 /*
  * Copyright (C) 2015 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.mtp;

 import android.annotation.Nullable;
 import android.annotation.WorkerThread;
 import android.content.ContentResolver;
 import android.database.Cursor;
 import android.mtp.MtpConstants;
 import android.mtp.MtpObjectInfo;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.Process;
 import android.provider.DocumentsContract;
 import android.util.Log;

 import com.android.internal.util.Preconditions;

 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.LinkedList;

 /**
  * Loader for MTP document.
  * At the first request, the loader returns only first NUM_INITIAL_ENTRIES. Then it launches
  * background thread to load the rest documents and caches its result for next requests.
  * TODO: Rename this class to ObjectInfoLoader
  */
 class DocumentLoader implements AutoCloseable {
     static final int NUM_INITIAL_ENTRIES = 10;
     static final int NUM_LOADING_ENTRIES = 20;
     static final int NOTIFY_PERIOD_MS = 500;

     private final MtpDeviceRecord mDevice;
     private final MtpManager mMtpManager;
     private final ContentResolver mResolver;
     private final MtpDatabase mDatabase;
     private final TaskList mTaskList = new TaskList();
     private Thread mBackgroundThread;

     DocumentLoader(MtpDeviceRecord device, MtpManager mtpManager, ContentResolver resolver,
                    MtpDatabase database) {
         mDevice = device;
         mMtpManager = mtpManager;
         mResolver = resolver;
         mDatabase = database;
     }

     /**
      * Queries the child documents of given parent.
      * It loads the first NUM_INITIAL_ENTRIES of object info, then launches the background thread
      * to load the rest.
      */
     synchronized Cursor queryChildDocuments(String[] columnNames, Identifier parent)
             throws IOException {
         assert parent.mDeviceId == mDevice.deviceId;

         LoaderTask task = mTaskList.findTask(parent);
         if (task == null) {
             if (parent.mDocumentId == null) {
                 throw new FileNotFoundException("Parent not found.");
             }
             // TODO: Handle nit race around here.
             // 1. getObjectHandles.
             // 2. putNewDocument.
             // 3. startAddingChildDocuemnts.
             // 4. stopAddingChildDocuments - It removes the new document added at the step 2,
             //     because it is not updated between start/stopAddingChildDocuments.
             task = new LoaderTask(mMtpManager, mDatabase, mDevice.operationsSupported, parent);
             task.loadObjectHandles();
             task.loadObjectInfoList(NUM_INITIAL_ENTRIES);
         } else {
             // Once remove the existing task in order to add it to the head of the list.
             mTaskList.remove(task);
         }

         mTaskList.addFirst(task);
         if (task.getState() == LoaderTask.STATE_LOADING) {
             resume();
         }
         return task.createCursor(mResolver, columnNames);
     }

     /**
      * Resumes a background thread.
      */
     synchronized void resume() {
         if (mBackgroundThread == null) {
             mBackgroundThread = new BackgroundLoaderThread();
             mBackgroundThread.start();
         }
     }

     /**
      * Obtains next task to be run in background thread, or release the reference to background
      * thread.
      *
      * Worker thread that receives null task needs to exit.
      */
     @WorkerThread
     synchronized @Nullable LoaderTask getNextTaskOrReleaseBackgroundThread() {
         Preconditions.checkState(mBackgroundThread != null);

         for (final LoaderTask task : mTaskList) {
             if (task.getState() == LoaderTask.STATE_LOADING) {
                 return task;
             }
         }

         final Identifier identifier = mDatabase.getUnmappedDocumentsParent(mDevice.deviceId);
         if (identifier != null) {
             final LoaderTask existingTask = mTaskList.findTask(identifier);
             if (existingTask != null) {
                 Preconditions.checkState(existingTask.getState() != LoaderTask.STATE_LOADING);
                 mTaskList.remove(existingTask);
             }
             final LoaderTask newTask = new LoaderTask(
                     mMtpManager, mDatabase, mDevice.operationsSupported, identifier);
             newTask.loadObjectHandles();
             mTaskList.addFirst(newTask);
             return newTask;
         }

         mBackgroundThread = null;
         return null;
     }

     /**
      * Terminates background thread.
      */
     @Override
     public void close() throws InterruptedException {
         final Thread thread;
         synchronized (this) {
             mTaskList.clear();
             thread = mBackgroundThread;
         }
         if (thread != null) {
             thread.interrupt();
             thread.join();
         }
     }

     synchronized void clearCompletedTasks() {
         mTaskList.clearCompletedTasks();
     }

     /**
      * Cancels the task for |parentIdentifier|.
      *
      * Task is removed from the cached list and it will create new task when |parentIdentifier|'s
      * children are queried next.
      */
     void cancelTask(Identifier parentIdentifier) {
         final LoaderTask task;
         synchronized (this) {
             task = mTaskList.findTask(parentIdentifier);
         }
         if (task != null) {
             task.cancel();
             mTaskList.remove(task);
         }
     }

     /**
      * Background thread to fetch object info.
      */
     private class BackgroundLoaderThread extends Thread {
         /**
          * Finds task that needs to be processed, then loads NUM_LOADING_ENTRIES of object info and
          * store them to the database. If it does not find a task, exits the thread.
          */
         @Override
         public void run() {
             Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
             while (!Thread.interrupted()) {
                 final LoaderTask task = getNextTaskOrReleaseBackgroundThread();
                 if (task == null) {
                     return;
                 }
                 task.loadObjectInfoList(NUM_LOADING_ENTRIES);
                 final boolean shouldNotify =
                         task.getState() != LoaderTask.STATE_CANCELLED &&
                         (task.mLastNotified.getTime() <
                          new Date().getTime() - NOTIFY_PERIOD_MS ||
                          task.getState() != LoaderTask.STATE_LOADING);
                 if (shouldNotify) {
                     task.notify(mResolver);
                 }
             }
         }
     }

     /**
      * Task list that has helper methods to search/clear tasks.
      */
     private static class TaskList extends LinkedList<LoaderTask> {
         LoaderTask findTask(Identifier parent) {
             for (int i = 0; i < size(); i++) {
                 if (get(i).mIdentifier.equals(parent))
                     return get(i);
             }
             return null;
         }

         void clearCompletedTasks() {
             int i = 0;
             while (i < size()) {
                 if (get(i).getState() == LoaderTask.STATE_COMPLETED) {
                     remove(i);
                 } else {
                     i++;
                 }
             }
         }
     }

     /**
      * Loader task.
      * Each task is responsible for fetching child documents for the given parent document.
      */
     private static class LoaderTask {
         static final int STATE_START = 0;
         static final int STATE_LOADING = 1;
         static final int STATE_COMPLETED = 2;
         static final int STATE_ERROR = 3;
         static final int STATE_CANCELLED = 4;

         final MtpManager mManager;
         final MtpDatabase mDatabase;
         final int[] mOperationsSupported;
         final Identifier mIdentifier;
         int[] mObjectHandles;
         int mState;
         Date mLastNotified;
         int mPosition;
         IOException mError;

         LoaderTask(MtpManager manager, MtpDatabase database, int[] operationsSupported,
                 Identifier identifier) {
             assert operationsSupported != null;
             assert identifier.mDocumentType != MtpDatabaseConstants.DOCUMENT_TYPE_DEVICE;
             mManager = manager;
             mDatabase = database;
             mOperationsSupported = operationsSupported;
             mIdentifier = identifier;
             mObjectHandles = null;
             mState = STATE_START;
             mPosition = 0;
             mLastNotified = new Date();
         }

         synchronized void loadObjectHandles() {
             assert mState == STATE_START;
             mPosition = 0;
             int parentHandle = mIdentifier.mObjectHandle;
             // Need to pass the special value MtpManager.OBJECT_HANDLE_ROOT_CHILDREN to
             // getObjectHandles if we would like to obtain children under the root.
             if (mIdentifier.mDocumentType == MtpDatabaseConstants.DOCUMENT_TYPE_STORAGE) {
                 parentHandle = MtpManager.OBJECT_HANDLE_ROOT_CHILDREN;
             }
             try {
                 mObjectHandles = mManager.getObjectHandles(
                         mIdentifier.mDeviceId, mIdentifier.mStorageId, parentHandle);
                 mState = STATE_LOADING;
             } catch (IOException error) {
                 mError = error;
                 mState = STATE_ERROR;
             }
         }

         /**
          * Returns a cursor that traverses the child document of the parent document handled by the
          * task.
          * The returned task may have a EXTRA_LOADING flag.
          */
         synchronized Cursor createCursor(ContentResolver resolver, String[] columnNames)
                 throws IOException {
             final Bundle extras = new Bundle();
             switch (getState()) {
                 case STATE_LOADING:
                     extras.putBoolean(DocumentsContract.EXTRA_LOADING, true);
                     break;
                 case STATE_ERROR:
                     throw mError;
             }
             final Cursor cursor =
                     mDatabase.queryChildDocuments(columnNames, mIdentifier.mDocumentId);
             cursor.setExtras(extras);
             cursor.setNotificationUri(resolver, createUri());
             return cursor;
         }

         /**
          * Stores object information into database.
          */
         void loadObjectInfoList(int count) {
             synchronized (this) {
                 if (mState != STATE_LOADING) {
                     return;
                 }
                 if (mPosition == 0) {
                     try{
                         mDatabase.getMapper().startAddingDocuments(mIdentifier.mDocumentId);
                     } catch (FileNotFoundException error) {
                         mError = error;
                         mState = STATE_ERROR;
                         return;
                     }
                 }
             }
             final ArrayList<MtpObjectInfo> infoList = new ArrayList<>();
             for (int chunkEnd = mPosition + count;
                     mPosition < mObjectHandles.length && mPosition < chunkEnd;
                     mPosition++) {
                 try {
                     infoList.add(mManager.getObjectInfo(
                             mIdentifier.mDeviceId, mObjectHandles[mPosition]));
                 } catch (IOException error) {
                     Log.e(MtpDocumentsProvider.TAG, "Failed to load object info", error);
                 }
             }
             final long[] objectSizeList = new long[infoList.size()];
             for (int i = 0; i < infoList.size(); i++) {
                 final MtpObjectInfo info = infoList.get(i);
                 // Compressed size is 32-bit unsigned integer but getCompressedSize returns the
                 // value in Java int (signed 32-bit integer). Use getCompressedSizeLong instead
                 // to get the value in Java long.
                 if (info.getCompressedSizeLong() != 0xffffffffl) {
                     objectSizeList[i] = info.getCompressedSizeLong();
                     continue;
                 }

                 if (!MtpDeviceRecord.isSupported(
                         mOperationsSupported,
                         MtpConstants.OPERATION_GET_OBJECT_PROP_DESC) ||
                         !MtpDeviceRecord.isSupported(
                                 mOperationsSupported,
                                 MtpConstants.OPERATION_GET_OBJECT_PROP_VALUE)) {
                     objectSizeList[i] = -1;
                     continue;
                 }

                 // Object size is more than 4GB.
                 try {
                     objectSizeList[i] = mManager.getObjectSizeLong(
                             mIdentifier.mDeviceId,
                             info.getObjectHandle(),
                             info.getFormat());
                 } catch (IOException error) {
                     Log.e(MtpDocumentsProvider.TAG, "Failed to get object size property.", error);
                     objectSizeList[i] = -1;
                 }
             }
             synchronized (this) {
                 // Check if the task is cancelled or not.
                 if (mState != STATE_LOADING) {
                     return;
                 }
                 try {
                     mDatabase.getMapper().putChildDocuments(
                             mIdentifier.mDeviceId,
                             mIdentifier.mDocumentId,
                             mOperationsSupported,
                             infoList.toArray(new MtpObjectInfo[infoList.size()]),
                             objectSizeList);
                 } catch (FileNotFoundException error) {
                     // Looks like the parent document information is removed.
                     // Adding documents has already cancelled in Mapper so we don't need to invoke
                     // stopAddingDocuments.
                     mError = error;
                     mState = STATE_ERROR;
                     return;
                 }
                 if (mPosition >= mObjectHandles.length) {
                     try{
                         mDatabase.getMapper().stopAddingDocuments(mIdentifier.mDocumentId);
                         mState = STATE_COMPLETED;
                     } catch (FileNotFoundException error) {
                         mError = error;
                         mState = STATE_ERROR;
                         return;
                     }
                 }
             }
         }

         /**
          * Cancels the task.
          */
         synchronized void cancel() {
             mDatabase.getMapper().cancelAddingDocuments(mIdentifier.mDocumentId);
             mState = STATE_CANCELLED;
         }

         /**
          * Returns a state of the task.
          */
         int getState() {
             return mState;
         }

         /**
          * Notifies a change of child list of the document.
          */
         void notify(ContentResolver resolver) {
             resolver.notifyChange(createUri(), null, false);
             mLastNotified = new Date();
         }

         private Uri createUri() {
             return DocumentsContract.buildChildDocumentsUri(
                     MtpDocumentsProvider.AUTHORITY, mIdentifier.mDocumentId);
         }
     }
 }
	/*
	* Copyright (C) 2015 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.mtp;

	import android.annotation.Nullable;
	import android.annotation.WorkerThread;
	import android.content.ContentResolver;
	import android.database.Cursor;
	import android.mtp.MtpConstants;
	import android.mtp.MtpObjectInfo;
	import android.net.Uri;
	import android.os.Bundle;
	import android.os.Process;
	import android.provider.DocumentsContract;
	import android.util.Log;

	import com.android.internal.util.Preconditions;

	import java.io.FileNotFoundException;
	import java.io.IOException;
	import java.util.ArrayList;
	import java.util.Date;
	import java.util.LinkedList;

	/**
	* Loader for MTP document.
	* At the first request, the loader returns only first NUM_INITIAL_ENTRIES. Then it launches
	* background thread to load the rest documents and caches its result for next requests.
	* TODO: Rename this class to ObjectInfoLoader
	*/
	class DocumentLoader implements AutoCloseable {
	static final int NUM_INITIAL_ENTRIES = 10;
	static final int NUM_LOADING_ENTRIES = 20;
	static final int NOTIFY_PERIOD_MS = 500;

	private final MtpDeviceRecord mDevice;
	private final MtpManager mMtpManager;
	private final ContentResolver mResolver;
	private final MtpDatabase mDatabase;
	private final TaskList mTaskList = new TaskList();
	private Thread mBackgroundThread;

	DocumentLoader(MtpDeviceRecord device, MtpManager mtpManager, ContentResolver resolver,
	MtpDatabase database) {
	mDevice = device;
	mMtpManager = mtpManager;
	mResolver = resolver;
	mDatabase = database;
	}

	/**
	* Queries the child documents of given parent.
	* It loads the first NUM_INITIAL_ENTRIES of object info, then launches the background thread
	* to load the rest.
	*/
	synchronized Cursor queryChildDocuments(String[] columnNames, Identifier parent)
	throws IOException {
	assert parent.mDeviceId == mDevice.deviceId;

	LoaderTask task = mTaskList.findTask(parent);
	if (task == null) {
	if (parent.mDocumentId == null) {
	throw new FileNotFoundException("Parent not found.");
	}
	// TODO: Handle nit race around here.
	// 1. getObjectHandles.
	// 2. putNewDocument.
	// 3. startAddingChildDocuemnts.
	// 4. stopAddingChildDocuments - It removes the new document added at the step 2,
	// because it is not updated between start/stopAddingChildDocuments.
	task = new LoaderTask(mMtpManager, mDatabase, mDevice.operationsSupported, parent);
	task.loadObjectHandles();
	task.loadObjectInfoList(NUM_INITIAL_ENTRIES);
	} else {
	// Once remove the existing task in order to add it to the head of the list.
	mTaskList.remove(task);
	}

	mTaskList.addFirst(task);
	if (task.getState() == LoaderTask.STATE_LOADING) {
	resume();
	}
	return task.createCursor(mResolver, columnNames);
	}

	/**
	* Resumes a background thread.
	*/
	synchronized void resume() {
	if (mBackgroundThread == null) {
	mBackgroundThread = new BackgroundLoaderThread();
	mBackgroundThread.start();
	}
	}

	/**
	* Obtains next task to be run in background thread, or release the reference to background
	* thread.
	*
	* Worker thread that receives null task needs to exit.
	*/
	@WorkerThread
	synchronized @Nullable LoaderTask getNextTaskOrReleaseBackgroundThread() {
	Preconditions.checkState(mBackgroundThread != null);

	for (final LoaderTask task : mTaskList) {
	if (task.getState() == LoaderTask.STATE_LOADING) {
	return task;
	}
	}

	final Identifier identifier = mDatabase.getUnmappedDocumentsParent(mDevice.deviceId);
	if (identifier != null) {
	final LoaderTask existingTask = mTaskList.findTask(identifier);
	if (existingTask != null) {
	Preconditions.checkState(existingTask.getState() != LoaderTask.STATE_LOADING);
	mTaskList.remove(existingTask);
	}
	final LoaderTask newTask = new LoaderTask(
	mMtpManager, mDatabase, mDevice.operationsSupported, identifier);
	newTask.loadObjectHandles();
	mTaskList.addFirst(newTask);
	return newTask;
	}

	mBackgroundThread = null;
	return null;
	}

	/**
	* Terminates background thread.
	*/
	@Override
	public void close() throws InterruptedException {
	final Thread thread;
	synchronized (this) {
	mTaskList.clear();
	thread = mBackgroundThread;
	}
	if (thread != null) {
	thread.interrupt();
	thread.join();
	}
	}

	synchronized void clearCompletedTasks() {
	mTaskList.clearCompletedTasks();
	}

	/**
	* Cancels the task for \|parentIdentifier\|.
	*
	* Task is removed from the cached list and it will create new task when \|parentIdentifier\|'s
	* children are queried next.
	*/
	void cancelTask(Identifier parentIdentifier) {
	final LoaderTask task;
	synchronized (this) {
	task = mTaskList.findTask(parentIdentifier);
	}
	if (task != null) {
	task.cancel();
	mTaskList.remove(task);
	}
	}

	/**
	* Background thread to fetch object info.
	*/
	private class BackgroundLoaderThread extends Thread {
	/**
	* Finds task that needs to be processed, then loads NUM_LOADING_ENTRIES of object info and
	* store them to the database. If it does not find a task, exits the thread.
	*/
	@Override
	public void run() {
	Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
	while (!Thread.interrupted()) {
	final LoaderTask task = getNextTaskOrReleaseBackgroundThread();
	if (task == null) {
	return;
	}
	task.loadObjectInfoList(NUM_LOADING_ENTRIES);
	final boolean shouldNotify =
	task.getState() != LoaderTask.STATE_CANCELLED &&
	(task.mLastNotified.getTime() <
	new Date().getTime() - NOTIFY_PERIOD_MS \|\|
	task.getState() != LoaderTask.STATE_LOADING);
	if (shouldNotify) {
	task.notify(mResolver);
	}
	}
	}
	}

	/**
	* Task list that has helper methods to search/clear tasks.
	*/
	private static class TaskList extends LinkedList<LoaderTask> {
	LoaderTask findTask(Identifier parent) {
	for (int i = 0; i < size(); i++) {
	if (get(i).mIdentifier.equals(parent))
	return get(i);
	}
	return null;
	}

	void clearCompletedTasks() {
	int i = 0;
	while (i < size()) {
	if (get(i).getState() == LoaderTask.STATE_COMPLETED) {
	remove(i);
	} else {
	i++;
	}
	}
	}
	}

	/**
	* Loader task.
	* Each task is responsible for fetching child documents for the given parent document.
	*/
	private static class LoaderTask {
	static final int STATE_START = 0;
	static final int STATE_LOADING = 1;
	static final int STATE_COMPLETED = 2;
	static final int STATE_ERROR = 3;
	static final int STATE_CANCELLED = 4;

	final MtpManager mManager;
	final MtpDatabase mDatabase;
	final int[] mOperationsSupported;
	final Identifier mIdentifier;
	int[] mObjectHandles;
	int mState;
	Date mLastNotified;
	int mPosition;
	IOException mError;

	LoaderTask(MtpManager manager, MtpDatabase database, int[] operationsSupported,
	Identifier identifier) {
	assert operationsSupported != null;
	assert identifier.mDocumentType != MtpDatabaseConstants.DOCUMENT_TYPE_DEVICE;
	mManager = manager;
	mDatabase = database;
	mOperationsSupported = operationsSupported;
	mIdentifier = identifier;
	mObjectHandles = null;
	mState = STATE_START;
	mPosition = 0;
	mLastNotified = new Date();
	}

	synchronized void loadObjectHandles() {
	assert mState == STATE_START;
	mPosition = 0;
	int parentHandle = mIdentifier.mObjectHandle;
	// Need to pass the special value MtpManager.OBJECT_HANDLE_ROOT_CHILDREN to
	// getObjectHandles if we would like to obtain children under the root.
	if (mIdentifier.mDocumentType == MtpDatabaseConstants.DOCUMENT_TYPE_STORAGE) {
	parentHandle = MtpManager.OBJECT_HANDLE_ROOT_CHILDREN;
	}
	try {
	mObjectHandles = mManager.getObjectHandles(
	mIdentifier.mDeviceId, mIdentifier.mStorageId, parentHandle);
	mState = STATE_LOADING;
	} catch (IOException error) {
	mError = error;
	mState = STATE_ERROR;
	}
	}

	/**
	* Returns a cursor that traverses the child document of the parent document handled by the
	* task.
	* The returned task may have a EXTRA_LOADING flag.
	*/
	synchronized Cursor createCursor(ContentResolver resolver, String[] columnNames)
	throws IOException {
	final Bundle extras = new Bundle();
	switch (getState()) {
	case STATE_LOADING:
	extras.putBoolean(DocumentsContract.EXTRA_LOADING, true);
	break;
	case STATE_ERROR:
	throw mError;
	}
	final Cursor cursor =
	mDatabase.queryChildDocuments(columnNames, mIdentifier.mDocumentId);
	cursor.setExtras(extras);
	cursor.setNotificationUri(resolver, createUri());
	return cursor;
	}

	/**
	* Stores object information into database.
	*/
	void loadObjectInfoList(int count) {
	synchronized (this) {
	if (mState != STATE_LOADING) {
	return;
	}
	if (mPosition == 0) {
	try{
	mDatabase.getMapper().startAddingDocuments(mIdentifier.mDocumentId);
	} catch (FileNotFoundException error) {
	mError = error;
	mState = STATE_ERROR;
	return;
	}
	}
	}
	final ArrayList<MtpObjectInfo> infoList = new ArrayList<>();
	for (int chunkEnd = mPosition + count;
	mPosition < mObjectHandles.length && mPosition < chunkEnd;
	mPosition++) {
	try {
	infoList.add(mManager.getObjectInfo(
	mIdentifier.mDeviceId, mObjectHandles[mPosition]));
	} catch (IOException error) {
	Log.e(MtpDocumentsProvider.TAG, "Failed to load object info", error);
	}
	}
	final long[] objectSizeList = new long[infoList.size()];
	for (int i = 0; i < infoList.size(); i++) {
	final MtpObjectInfo info = infoList.get(i);
	// Compressed size is 32-bit unsigned integer but getCompressedSize returns the
	// value in Java int (signed 32-bit integer). Use getCompressedSizeLong instead
	// to get the value in Java long.
	if (info.getCompressedSizeLong() != 0xffffffffl) {
	objectSizeList[i] = info.getCompressedSizeLong();
	continue;
	}

	if (!MtpDeviceRecord.isSupported(
	mOperationsSupported,
	MtpConstants.OPERATION_GET_OBJECT_PROP_DESC) \|\|
	!MtpDeviceRecord.isSupported(
	mOperationsSupported,
	MtpConstants.OPERATION_GET_OBJECT_PROP_VALUE)) {
	objectSizeList[i] = -1;
	continue;
	}

	// Object size is more than 4GB.
	try {
	objectSizeList[i] = mManager.getObjectSizeLong(
	mIdentifier.mDeviceId,
	info.getObjectHandle(),
	info.getFormat());
	} catch (IOException error) {
	Log.e(MtpDocumentsProvider.TAG, "Failed to get object size property.", error);
	objectSizeList[i] = -1;
	}
	}
	synchronized (this) {
	// Check if the task is cancelled or not.
	if (mState != STATE_LOADING) {
	return;
	}
	try {
	mDatabase.getMapper().putChildDocuments(
	mIdentifier.mDeviceId,
	mIdentifier.mDocumentId,
	mOperationsSupported,
	infoList.toArray(new MtpObjectInfo[infoList.size()]),
	objectSizeList);
	} catch (FileNotFoundException error) {
	// Looks like the parent document information is removed.
	// Adding documents has already cancelled in Mapper so we don't need to invoke
	// stopAddingDocuments.
	mError = error;
	mState = STATE_ERROR;
	return;
	}
	if (mPosition >= mObjectHandles.length) {
	try{
	mDatabase.getMapper().stopAddingDocuments(mIdentifier.mDocumentId);
	mState = STATE_COMPLETED;
	} catch (FileNotFoundException error) {
	mError = error;
	mState = STATE_ERROR;
	return;
	}
	}
	}
	}

	/**
	* Cancels the task.
	*/
	synchronized void cancel() {
	mDatabase.getMapper().cancelAddingDocuments(mIdentifier.mDocumentId);
	mState = STATE_CANCELLED;
	}

	/**
	* Returns a state of the task.
	*/
	int getState() {
	return mState;
	}

	/**
	* Notifies a change of child list of the document.
	*/
	void notify(ContentResolver resolver) {
	resolver.notifyChange(createUri(), null, false);
	mLastNotified = new Date();
	}

	private Uri createUri() {
	return DocumentsContract.buildChildDocumentsUri(
	MtpDocumentsProvider.AUTHORITY, mIdentifier.mDocumentId);
	}
	}
	}