source: trunk/eraser6/Eraser.Manager/DirectExecutor.cs @ 1872

/* 
 * $Id$
 * Copyright 2008-2010 The Eraser Project
 * Original Author: Joel Low <lowjoel@users.sourceforge.net>
 * Modified By: Kasra Nassiri <cjax@users.sourceforge.net> @17/10/2008
 * Modified By: 
 * 
 * This file is part of Eraser.
 * 
 * Eraser is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * Eraser is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 * 
 * A copy of the GNU General Public License can be found at
 * <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Threading;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

using Eraser.Util;
using Eraser.Util.ExtensionMethods;

namespace Eraser.Manager
{
    /// <summary>
    /// The DirectExecutor class is used by the Eraser GUI directly when the program
    /// is run without the help of a Service.
    /// </summary>
    public class DirectExecutor : Executor
    {
        public DirectExecutor()
        {
            TaskAdded += OnTaskAdded;
            TaskDeleted += OnTaskDeleted;
            tasks = new DirectExecutorTasksCollection(this);
            thread = new Thread(Main);
        }

        protected override void Dispose(bool disposing)
        {
            if (thread == null || schedulerInterrupt == null)
                return;

            if (disposing)
            {
                thread.Abort();
                schedulerInterrupt.Set();

                //Wait for the executor thread to exit -- we call some event functions
                //and these events may need invocation on the main thread. So,
                //pump messages from the main thread until the thread exits.
                if (System.Windows.Forms.Application.MessageLoop)
                {
                    if (!thread.Join(new TimeSpan(0, 0, 0, 0, 100)))
                        System.Windows.Forms.Application.DoEvents();
                }

                //If we are disposing on a secondary thread, or a thread without
                //a message loop, just wait for the thread to exit indefinitely
                else
                    thread.Join();

                schedulerInterrupt.Close();
            }

            thread = null;
            schedulerInterrupt = null;
            base.Dispose(disposing);
        }

        public override void Run()
        {
            thread.CurrentUICulture = Thread.CurrentThread.CurrentUICulture;
            thread.Start();
        }

        public override void QueueTask(Task task)
        {
            lock (tasksLock)
            {
                //Queue the task to be run immediately.
                DateTime executionTime = DateTime.Now;
                if (!scheduledTasks.ContainsKey(executionTime))
                    scheduledTasks.Add(executionTime, new List<Task>());
                scheduledTasks[executionTime].Add(task);
                schedulerInterrupt.Set();
            }
        }

        public override void ScheduleTask(Task task)
        {
            RecurringSchedule schedule = task.Schedule as RecurringSchedule;
            if (schedule == null)
                return;

            DateTime executionTime = (schedule.MissedPreviousSchedule &&
                ManagerLibrary.Settings.ExecuteMissedTasksImmediately) ?
                    DateTime.Now : schedule.NextRun;

            lock (tasksLock)
            {
                if (!scheduledTasks.ContainsKey(executionTime))
                    scheduledTasks.Add(executionTime, new List<Task>());
                scheduledTasks[executionTime].Add(task);
            }
        }

        public override void QueueRestartTasks()
        {
            lock (tasksLock)
            {
                foreach (Task task in Tasks)
                    if (task.Schedule == Schedule.RunOnRestart)
                        QueueTask(task);
            }
        }

        public override void UnqueueTask(Task task)
        {
            lock (tasksLock)
                for (int i = 0; i != scheduledTasks.Count; ++i)
                    for (int j = 0; j < scheduledTasks.Values[i].Count; )
                    {
                        Task currentTask = scheduledTasks.Values[i][j];
                        if (currentTask == task &&
                            (!(currentTask.Schedule is RecurringSchedule) ||
                                ((RecurringSchedule)currentTask.Schedule).NextRun != scheduledTasks.Keys[i]))
                        {
                            scheduledTasks.Values[i].RemoveAt(j);
                        }
                        else
                        {
                            ++j;
                        }
                    }
        }

        internal override bool IsTaskQueued(Task task)
        {
            lock (tasksLock)
                foreach (KeyValuePair<DateTime, List<Task>> tasks in scheduledTasks)
                    foreach (Task i in tasks.Value)
                        if (task == i)
                            if (task.Schedule is RecurringSchedule)
                            {
                                if (((RecurringSchedule)task.Schedule).NextRun != tasks.Key)
                                    return true;
                            }
                            else
                                return true;

            return false;
        }

        private void OnTaskAdded(object sender, TaskEventArgs e)
        {
            e.Task.TaskEdited += OnTaskEdited;
        }

        private void OnTaskEdited(object sender, EventArgs e)
        {
            //Find all schedule entries containing the task - since the user cannot make
            //edits to the task when it is queued (only if it is scheduled) remove
            //all task references and add them back
            Task task = (Task)sender;
            lock (tasksLock)
                for (int i = 0; i != scheduledTasks.Count; ++i)
                    for (int j = 0; j < scheduledTasks.Values[i].Count; )
                    {
                        Task currentTask = scheduledTasks.Values[i][j];
                        if (currentTask == task)
                            scheduledTasks.Values[i].RemoveAt(j);
                        else
                            j++;
                    }

            //Then reschedule the task
            if (task.Schedule is RecurringSchedule)
                ScheduleTask(task);
        }

        private void OnTaskDeleted(object sender, TaskEventArgs e)
        {
            e.Task.TaskEdited -= OnTaskEdited;
        }

        public override ExecutorTasksCollection Tasks
        {
            get
            {
                return tasks;
            }
        }

        /// <summary>
        /// The thread entry point for this object. This object operates on a queue
        /// and hence the thread will sequentially execute tasks.
        /// </summary>
        private void Main()
        {
            //The waiting thread will utilize a polling loop to check for new
            //scheduled tasks. This will be checked every 30 seconds. However,
            //when the thread is waiting for a new task, it can be interrupted.
            while (thread.ThreadState != ThreadState.AbortRequested)
            {
                //Check for a new task
                Task task = null;
                lock (tasksLock)
                {
                    while (scheduledTasks.Count != 0)
                        if (scheduledTasks.Values[0].Count == 0)
                        {
                            //Clean all all time slots at the start of the queue which are
                            //empty
                            scheduledTasks.RemoveAt(0);
                        }
                        else
                        {
                            if (scheduledTasks.Keys[0] <= DateTime.Now)
                            {
                                List<Task> tasks = scheduledTasks.Values[0];
                                task = tasks[0];
                                tasks.RemoveAt(0);
                            }

                            //Do schedule queue maintenance: clean up all empty timeslots
                            if (task == null)
                            {
                                for (int i = 0; i < scheduledTasks.Count; )
                                    if (scheduledTasks.Values[i].Count == 0)
                                        scheduledTasks.RemoveAt(i);
                                    else
                                        ++i;
                            }

                            break;
                        }
                }

                if (task != null)
                {
                    //Start a new log session to separate this session's events
                    //from previous ones.
                    LogSink sessionLog = new LogSink();
                    task.Log.Add(sessionLog);
                    using (new LogSession(sessionLog))
                    {
                        ExecuteTask(task);
                    }
                }

                //Wait for half a minute to check for the next scheduled task.
                schedulerInterrupt.WaitOne(30000, false);
            }
        }

        /// <summary>
        /// Executes the given task.
        /// </summary>
        /// <param name="task">The task to execute.</param>
        private void ExecuteTask(Task task)
        {
            //Set the currently executing task.
            currentTask = task;

            //Prevent the system from sleeping.
            Power.ExecutionState = ExecutionState.Continuous | ExecutionState.SystemRequired;

            try
            {
                //Broadcast the task started event.
                task.Canceled = false;
                task.OnTaskStarted();

                //Run the task
                foreach (ErasureTarget target in task.Targets)
                    try
                    {
                        UnusedSpaceTarget unusedSpaceTarget =
                            target as UnusedSpaceTarget;
                        FileSystemObjectTarget fileSystemObjectTarget =
                            target as FileSystemObjectTarget;

                        if (unusedSpaceTarget != null)
                            EraseUnusedSpace(task, unusedSpaceTarget);
                        else if (fileSystemObjectTarget != null)
                            EraseFilesystemObject(task, fileSystemObjectTarget);
                        else
                            throw new ArgumentException("Unknown erasure target.");
                    }
                    catch (FatalException)
                    {
                        throw;
                    }
                    catch (OperationCanceledException)
                    {
                        throw;
                    }
                    catch (SharingViolationException)
                    {
                    }
                    catch (ThreadAbortException)
                    {
                    }
                    catch (Exception e)
                    {
                        Logger.Log(e.Message, LogLevel.Error);
                        BlackBox.Get().CreateReport(e);
                    }
            }
            catch (FatalException e)
            {
                Logger.Log(e.Message, LogLevel.Fatal);
            }
            catch (OperationCanceledException e)
            {
                Logger.Log(e.Message, LogLevel.Fatal);
            }
            catch (ThreadAbortException)
            {
                //Do nothing. The exception will be rethrown after this block
                //is executed. This is here mainly to ensure that no BlackBox
                //report is created for this exception.
            }
            catch (SharingViolationException)
            {
            }
            catch (Exception e)
            {
                Logger.Log(e.Message, LogLevel.Error);
                BlackBox.Get().CreateReport(e);
            }
            finally
            {
                //Allow the system to sleep again.
                Power.ExecutionState = ExecutionState.Continuous;

                //If the task is a recurring task, reschedule it since we are done.
                if (task.Schedule is RecurringSchedule)
                    ((RecurringSchedule)task.Schedule).Reschedule(DateTime.Now);

                //If the task is an execute on restart task, it is only run
                //once and can now be restored to an immediately executed task
                if (task.Schedule == Schedule.RunOnRestart)
                    task.Schedule = Schedule.RunNow;

                //And the task finished event.
                task.OnTaskFinished();

                //Remove the actively executing task from our instance variable
                currentTask = null;
            }
        }

        /// <summary>
        /// Executes a unused space erase.
        /// </summary>
        /// <param name="task">The task currently being executed</param>
        /// <param name="target">The target of the unused space erase.</param>
        private void EraseUnusedSpace(Task task, UnusedSpaceTarget target)
        {
            //Check for sufficient privileges to run the unused space erasure.
            if (!Security.IsAdministrator())
            {
                if (Environment.OSVersion.Platform == PlatformID.Win32NT &&
                    Environment.OSVersion.Version >= new Version(6, 0))
                {
                    Logger.Log(S._("The program does not have the required permissions to erase " +
                        "the unused space on disk. Run the program as an administrator and retry " +
                        "the operation."), LogLevel.Error);
                }
                else
                {
                    Logger.Log(S._("The program does not have the required permissions to erase " +
                        "the unused space on disk."), LogLevel.Error);
                }

                return;
            }

            //Check whether System Restore has any available checkpoints.
            if (SystemRestore.GetInstances().Count != 0)
            {
                Logger.Log(S._("The drive {0} has System Restore or Volume Shadow Copies " +
                    "enabled. This may allow copies of files stored on the disk to be recovered " +
                    "and pose a security concern.", target.Drive), LogLevel.Warning);
            }
            
            //If the user is under disk quotas, log a warning message
            if (VolumeInfo.FromMountPoint(target.Drive).HasQuota)
                Logger.Log(S._("The drive {0} has disk quotas active. This will prevent the " +
                    "complete erasure of unused space and may pose a security concern.",
                    target.Drive), LogLevel.Warning);

            //Get the erasure method if the user specified he wants the default.
            ErasureMethod method = target.Method;

            //Make a folder to dump our temporary files in
            DirectoryInfo info = new DirectoryInfo(target.Drive);
            VolumeInfo volInfo = VolumeInfo.FromMountPoint(target.Drive);
            FileSystem fsManager = ManagerLibrary.Instance.FileSystemRegistrar[volInfo];

            //Start sampling the speed of the task.
            SteppedProgressManager progress = new SteppedProgressManager();
            target.Progress = progress;
            task.Progress.Steps.Add(new SteppedProgressManagerStep(
                progress, 1.0f / task.Targets.Count));

            //Erase the cluster tips of every file on the drive.
            if (target.EraseClusterTips)
            {
                //Define the callback handlers
                ProgressManager tipSearch = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(tipSearch, 
                    0.0f, S._("Searching for files' cluster tips...")));
                tipSearch.Total = 1;
                ClusterTipsSearchProgress searchProgress = delegate(string path)
                    {
                        if (currentTask.Canceled)
                            throw new OperationCanceledException(S._("The task was cancelled."));

                        task.OnProgressChanged(target,
                            new ProgressChangedEventArgs(tipSearch,
                                new TaskProgressChangedEventArgs(path, 0, 0)));
                    };

                ProgressManager tipProgress = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(tipProgress, 0.1f,
                    S._("Erasing cluster tips...")));
                ClusterTipsEraseProgress eraseProgress =
                    delegate(int currentFile, int totalFiles, string currentFilePath)
                    {
                        tipSearch.MarkComplete();
                        tipProgress.Total = totalFiles;
                        tipProgress.Completed = currentFile;
                        task.OnProgressChanged(target,
                            new ProgressChangedEventArgs(tipProgress,
                                new TaskProgressChangedEventArgs(currentFilePath, 0, 0)));

                        if (currentTask.Canceled)
                            throw new OperationCanceledException(S._("The task was cancelled."));
                    };

                //Start counting statistics
                fsManager.EraseClusterTips(VolumeInfo.FromMountPoint(target.Drive),
                    method, searchProgress, eraseProgress);
                tipProgress.MarkComplete();
            }

            bool lowDiskSpaceNotifications = Shell.LowDiskSpaceNotificationsEnabled;
            info = info.CreateSubdirectory(Path.GetFileName(
                FileSystem.GenerateRandomFileName(info, 18)));
            try
            {
                //Set the folder's compression flag off since we want to use as much
                //space as possible
                if (info.IsCompressed())
                    info.Uncompress();

                //Disable the low disk space notifications
                Shell.LowDiskSpaceNotificationsEnabled = false;

                ProgressManager mainProgress = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(mainProgress,
                    target.EraseClusterTips ? 0.8f : 0.9f, S._("Erasing unused space...")));

                //Continue creating files while there is free space.
                while (volInfo.AvailableFreeSpace > 0)
                {
                    //Generate a non-existant file name
                    string currFile = FileSystem.GenerateRandomFileName(info, 18);

                    //Create the stream
                    using (FileStream stream = new FileStream(currFile, FileMode.CreateNew,
                        FileAccess.Write, FileShare.None, 8, FileOptions.WriteThrough))
                    {
                        //Set the length of the file to be the amount of free space left
                        //or the maximum size of one of these dumps.
                        mainProgress.Total = mainProgress.Completed +
                            method.CalculateEraseDataSize(null, volInfo.AvailableFreeSpace);
                        long streamLength = Math.Min(ErasureMethod.FreeSpaceFileUnit,
                            mainProgress.Total);

                        //Handle IO exceptions gracefully, because the filesystem
                        //may require more space than demanded by us for file allocation.
                        while (true)
                            try
                            {
                                stream.SetLength(streamLength);
                                break;
                            }
                            catch (IOException)
                            {
                                if (streamLength > volInfo.ClusterSize)
                                    streamLength -= volInfo.ClusterSize;
                                else
                                    throw;
                            }

                        //Then run the erase task
                        method.Erase(stream, long.MaxValue,
                            ManagerLibrary.Instance.PrngRegistrar[ManagerLibrary.Settings.ActivePrng],
                            delegate(long lastWritten, long totalData, int currentPass)
                            {
                                mainProgress.Completed += lastWritten;
                                task.OnProgressChanged(target,
                                    new ProgressChangedEventArgs(mainProgress,
                                        new TaskProgressChangedEventArgs(target.Drive, currentPass, method.Passes)));

                                if (currentTask.Canceled)
                                    throw new OperationCanceledException(S._("The task was cancelled."));
                            }
                        );
                    }
                }

                //Mark the main bulk of the progress as complete
                mainProgress.MarkComplete();

                //Erase old resident file system table files
                ProgressManager residentProgress = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(residentProgress,
                    0.05f, S._("Old resident file system table files")));
                fsManager.EraseOldFileSystemResidentFiles(volInfo, info, method,
                    delegate(int currentFile, int totalFiles)
                    {
                        residentProgress.Completed = currentFile;
                        residentProgress.Total = totalFiles;
                        task.OnProgressChanged(target,
                            new ProgressChangedEventArgs(residentProgress,
                                new TaskProgressChangedEventArgs(string.Empty, 0, 0)));

                        if (currentTask.Canceled)
                            throw new OperationCanceledException(S._("The task was cancelled."));
                    }
                );

                residentProgress.MarkComplete();
            }
            finally
            {
                //Remove the folder holding all our temporary files.
                ProgressManager tempFiles = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(tempFiles,
                    0.0f, S._("Removing temporary files...")));
                task.OnProgressChanged(target, new ProgressChangedEventArgs(tempFiles,
                    new TaskProgressChangedEventArgs(string.Empty, 0, 0)));
                fsManager.DeleteFolder(info);
                tempFiles.Completed = tempFiles.Total;

                //Reset the low disk space notifications
                Shell.LowDiskSpaceNotificationsEnabled = lowDiskSpaceNotifications;
            }

            //Then clean the old file system entries
            ProgressManager structureProgress = new ProgressManager();
            progress.Steps.Add(new SteppedProgressManagerStep(structureProgress,
                0.05f, S._("Erasing unused directory structures...")));
            fsManager.EraseDirectoryStructures(volInfo,
                delegate(int currentFile, int totalFiles)
                {
                    if (currentTask.Canceled)
                        throw new OperationCanceledException(S._("The task was cancelled."));

                    //Compute the progress
                    structureProgress.Total = totalFiles;
                    structureProgress.Completed = currentFile;

                    //Set the event parameters, then broadcast the progress event.
                    task.OnProgressChanged(target,
                        new ProgressChangedEventArgs(structureProgress,
                            new TaskProgressChangedEventArgs(string.Empty, 0, 0)));
                }
            );

            structureProgress.MarkComplete();
            target.Progress = null;
        }

        /// <summary>
        /// Erases a file or folder on the volume.
        /// </summary>
        /// <param name="task">The task currently being processed.</param>
        /// <param name="target">The target of the erasure.</param>
        /// <param name="progress">The progress manager for the current task.</param>
        private void EraseFilesystemObject(Task task, FileSystemObjectTarget target)
        {
            //Retrieve the list of files to erase.
            long dataTotal = 0;
            List<string> paths = target.GetPaths(out dataTotal);

            //Get the erasure method if the user specified he wants the default.
            ErasureMethod method = target.Method;
            dataTotal = method.CalculateEraseDataSize(paths, dataTotal);

            //Set the event's current target status.
            SteppedProgressManager progress = new SteppedProgressManager();
            target.Progress = progress;
            task.Progress.Steps.Add(new SteppedProgressManagerStep(progress, 1.0f / task.Targets.Count));

            //Iterate over every path, and erase the path.
            for (int i = 0; i < paths.Count; ++i)
            {
                //Check that the file exists - we do not want to bother erasing nonexistant files
                StreamInfo info = new StreamInfo(paths[i]);
                if (!info.Exists)
                {
                    Logger.Log(S._("The file {0} was not erased as the file does not exist.",
                        paths[i]), LogLevel.Notice);
                    continue;
                }

                //Get the filesystem provider to handle the secure file erasures
                FileSystem fsManager = ManagerLibrary.Instance.FileSystemRegistrar[
                    VolumeInfo.FromMountPoint(info.DirectoryName)];

                bool isReadOnly = false;

                try
                {
                    //Update the task progress
                    ProgressManager step = new ProgressManager();
                    progress.Steps.Add(new SteppedProgressManagerStep(step,
                        info.Length / (float)dataTotal, S._("Erasing files...")));
                    task.OnProgressChanged(target,
                        new ProgressChangedEventArgs(step,
                            new TaskProgressChangedEventArgs(paths[i], 0, method.Passes)));

                    //Remove the read-only flag, if it is set.
                    if (isReadOnly = info.IsReadOnly)
                        info.IsReadOnly = false;

                    //Make sure the file does not have any attributes which may affect
                    //the erasure process
                    if ((info.Attributes & FileAttributes.Compressed) != 0 ||
                        (info.Attributes & FileAttributes.Encrypted) != 0 ||
                        (info.Attributes & FileAttributes.SparseFile) != 0)
                    {
                        //Log the error
                        Logger.Log(S._("The file {0} could not be erased because the file was " +
                            "either compressed, encrypted or a sparse file.", info.FullName),
                            LogLevel.Error);
                        continue;
                    }

                    fsManager.EraseFileSystemObject(info, method,
                        delegate(long lastWritten, long totalData, int currentPass)
                        {
                            if (currentTask.Canceled)
                                throw new OperationCanceledException(S._("The task was cancelled."));

                            step.Total = totalData;
                            step.Completed += lastWritten;
                            task.OnProgressChanged(target,
                                new ProgressChangedEventArgs(step,
                                    new TaskProgressChangedEventArgs(info.FullName, currentPass, method.Passes)));
                        });

                    //Remove the file.
                    FileInfo fileInfo = info.File;
                    if (fileInfo != null)
                        fsManager.DeleteFile(fileInfo);
                    step.MarkComplete();
                }
                catch (UnauthorizedAccessException)
                {
                    Logger.Log(S._("The file {0} could not be erased because the file's " +
                        "permissions prevent access to the file.", info.FullName), LogLevel.Error);
                }
                catch (SharingViolationException)
                {
                    if (!ManagerLibrary.Settings.ForceUnlockLockedFiles)
                        throw;

                    List<System.Diagnostics.Process> processes =
                        new List<System.Diagnostics.Process>();
                    foreach (OpenHandle handle in OpenHandle.Items)
                        if (handle.Path == paths[i])
                            processes.Add(System.Diagnostics.Process.GetProcessById(handle.ProcessId));

                    string lockedBy = null;
                    if (processes.Count > 0)
                    {
                        StringBuilder processStr = new StringBuilder();
                        foreach (System.Diagnostics.Process process in processes)
                        {
                            try
                            {
                                processStr.AppendFormat(System.Globalization.CultureInfo.InvariantCulture,
                                    "{0}, ", process.MainModule.FileName);
                            }
                            catch (System.ComponentModel.Win32Exception)
                            {
                            }
                        }

                        lockedBy = S._("(locked by {0})", processStr.ToString().Remove(processStr.Length - 2));
                    }

                    Logger.Log(S._("Could not force closure of file \"{0}\" {1}", paths[i],
                        lockedBy == null ? string.Empty : lockedBy).Trim(), LogLevel.Error);
                }
                finally
                {
                    //Re-set the read-only flag if the file exists (i.e. there was an error)
                    if (isReadOnly && info.Exists && !info.IsReadOnly)
                        info.IsReadOnly = isReadOnly;
                }
            }

            //If the user requested a folder removal, do it.
            if ((target is FolderTarget) && Directory.Exists(target.Path))
            {
                ProgressManager step = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(step,
                    0.0f, S._("Removing folders...")));
                
                //Remove all subfolders which are empty.
                FolderTarget fldr = (FolderTarget)target;
                FileSystem fsManager = ManagerLibrary.Instance.FileSystemRegistrar[VolumeInfo.FromMountPoint(fldr.Path)];
                Action<DirectoryInfo> eraseEmptySubFolders = null;
                eraseEmptySubFolders = delegate(DirectoryInfo info)
                {
                     foreach (DirectoryInfo subDir in info.GetDirectories())
                         eraseEmptySubFolders(subDir);
                     task.OnProgressChanged(target,
                         new ProgressChangedEventArgs(step,
                             new TaskProgressChangedEventArgs(info.FullName, 0, 0)));

                     FileSystemInfo[] files = info.GetFileSystemInfos();
                     if (files.Length == 0)
                         fsManager.DeleteFolder(info);
                };

                DirectoryInfo directory = new DirectoryInfo(fldr.Path);
                foreach (DirectoryInfo subDir in directory.GetDirectories())
                    eraseEmptySubFolders(subDir);

                if (fldr.DeleteIfEmpty)
                {
                    //See if this is the root of a volume.
                    bool isVolumeRoot = directory.Parent == null;
                    foreach (VolumeInfo volume in VolumeInfo.Volumes)
                        foreach (string mountPoint in volume.MountPoints)
                            if (directory.FullName == mountPoint)
                                isVolumeRoot = true;

                    //If the folder is a mount point, then don't delete it. If it isn't,
                    //search for files under the folder to see if it is empty.
                    if (!isVolumeRoot && directory.Exists &&
                        directory.GetFiles("*", SearchOption.AllDirectories).Length == 0)
                    {
                        fsManager.DeleteFolder(directory);
                    }
                }
            }

            //If the user was erasing the recycle bin, clear the bin.
            if (target is RecycleBinTarget)
            {
                ProgressManager step = new ProgressManager();
                progress.Steps.Add(new SteppedProgressManagerStep(step,
                    0.0f, S._("Emptying recycle bin...")));
                task.OnProgressChanged(target,
                    new ProgressChangedEventArgs(step,
                        new TaskProgressChangedEventArgs(string.Empty, 0, 0)));

                RecycleBin.Empty(EmptyRecycleBinOptions.NoConfirmation |
                    EmptyRecycleBinOptions.NoProgressUI | EmptyRecycleBinOptions.NoSound);
            }

            target.Progress = null;
        }

        /// <summary>
        /// The thread object.
        /// </summary>
        private Thread thread;

        /// <summary>
        /// The lock preventing concurrent access for the tasks list and the
        /// tasks queue.
        /// </summary>
        private object tasksLock = new object();

        /// <summary>
        /// The queue of tasks. This queue is executed when the first element's
        /// timestamp (the key) has been past. This list assumes that all tasks
        /// are sorted by timestamp, smallest one first.
        /// </summary>
        private SortedList<DateTime, List<Task>> scheduledTasks =
            new SortedList<DateTime, List<Task>>();

        /// <summary>
        /// The task list associated with this executor instance.
        /// </summary>
        private DirectExecutorTasksCollection tasks;

        /// <summary>
        /// The currently executing task.
        /// </summary>
        Task currentTask;

        /// <summary>
        /// An automatically reset event allowing the addition of new tasks to
        /// interrupt the thread's sleeping state waiting for the next recurring
        /// task to be due.
        /// </summary>
        AutoResetEvent schedulerInterrupt = new AutoResetEvent(true);

        private class DirectExecutorTasksCollection : ExecutorTasksCollection
        {
            /// <summary>
            /// Constructor.
            /// </summary>
            /// <param name="executor">The <see cref="DirectExecutor"/> object owning
            /// this list.</param>
            public DirectExecutorTasksCollection(DirectExecutor executor)
                : base(executor)
            {
            }

            #region IList<Task> Members
            public override int IndexOf(Task item)
            {
                return list.IndexOf(item);
            }

            public override void Insert(int index, Task item)
            {
                item.Executor = Owner;
                lock (list)
                    list.Insert(index, item);

                //Call all the event handlers who registered to be notified of tasks
                //being added.
                Owner.OnTaskAdded(new TaskEventArgs(item));

                //If the task is scheduled to run now, break the waiting thread and
                //run it immediately
                if (item.Schedule == Schedule.RunNow)
                {
                    Owner.QueueTask(item);
                }
                //If the task is scheduled, add the next execution time to the list
                //of schduled tasks.
                else if (item.Schedule != Schedule.RunOnRestart)
                {
                    Owner.ScheduleTask(item);
                }
            }

            public override void RemoveAt(int index)
            {
                lock (list)
                {
                    Task task = list[index];
                    task.Cancel();
                    task.Executor = null;
                    list.RemoveAt(index);

                    //Call all event handlers registered to be notified of task deletions.
                    Owner.OnTaskDeleted(new TaskEventArgs(task));
                }
            }

            public override Task this[int index]
            {
                get
                {
                    lock (list)
                        return list[index];
                }
                set
                {
                    lock (list)
                        list[index] = value;
                }
            }
            #endregion

            #region ICollection<Task> Members
            public override void Add(Task item)
            {
                Insert(Count, item);
            }

            public override void Clear()
            {
                foreach (Task task in list)
                    Remove(task);
            }

            public override bool Contains(Task item)
            {
                lock (list)
                    return list.Contains(item);
            }

            public override void CopyTo(Task[] array, int arrayIndex)
            {
                lock (list)
                    list.CopyTo(array, arrayIndex);
            }

            public override int Count
            {
                get
                {
                    lock (list)
                        return list.Count;
                }
            }

            public override bool Remove(Task item)
            {
                lock (list)
                {
                    int index = list.IndexOf(item);
                    if (index < 0)
                        return false;

                    RemoveAt(index);
                }

                return true;
            }
            #endregion

            #region IEnumerable<Task> Members
            public override IEnumerator<Task> GetEnumerator()
            {
                return list.GetEnumerator();
            }
            #endregion

            public override void SaveToStream(Stream stream)
            {
                lock (list)
                    new BinaryFormatter().Serialize(stream, list);
            }

            public override void LoadFromStream(Stream stream)
            {
                //Load the list into the dictionary
                StreamingContext context = new StreamingContext(
                    StreamingContextStates.All, Owner);
                BinaryFormatter formatter = new BinaryFormatter(null, context);

                try
                {
                    List<Task> deserialised = (List<Task>)formatter.Deserialize(stream);
                    list.AddRange(deserialised);

                    foreach (Task task in deserialised)
                    {
                        Owner.OnTaskAdded(new TaskEventArgs(task));
                        if (task.Schedule is RecurringSchedule)
                            Owner.ScheduleTask(task);
                    }
                }
                catch (FileLoadException e)
                {
                    throw new InvalidDataException(e.Message, e);
                }
                catch (SerializationException e)
                {
                    throw new InvalidDataException(e.Message, e);
                }
            }

            /// <summary>
            /// The data store for this object.
            /// </summary>
            private List<Task> list = new List<Task>();
        }
    }
}