LongDataOperation.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Agni.MDB
{
  /// <summary>
  /// Gets called by various routines that report long-running data operation progress and allow to cancel further processing.
  /// </summary>
  public delegate void LongDataOperationCallback<TResult>(LongDataOperation<TResult> operation);

  /// <summary>
  /// Provides a context for long data operation, such as fetching data from many shards.
  /// Callers may cancel operation and track overall progress via a LongDataOperationCallback.
  /// This is conceptually similar to CancelationToken
  /// </summary>
  public sealed class LongDataOperation<TResult>
  {
    public LongDataOperation()
    {
      m_StartTimeUTC = NFX.App.TimeSource.UTCNow;
    }

    private DateTime m_StartTimeUTC;
    private volatile int m_Total;
    private int m_Current;
    private volatile bool m_Canceled;

    private volatile bool m_HasResult;
    private TResult m_Result;


    /// <summary>
    /// Allows to attach arbitrary object context
    /// </summary>
    public object Context;


    /// <summary>
    /// Returns the UTC timestamp of this operation
    /// </summary>
    public DateTime StartTimeUTC{ get{ return m_StartTimeUTC;} }


    /// <summary>
    /// The total amount of work
    /// </summary>
    public int Total{ get{return m_Total;}}

    /// <summary>
    /// The current progress of work out of Total
    /// </summary>
    public int Current{ get{ return Thread.VolatileRead(ref m_Current);} }

    /// <summary>
    /// True if operation was canceled via Cancel()
    /// </summary>
    public bool Canceled { get{ return m_Canceled;}}

    /// <summary>
    /// True if operation was completed via a call to SetResult()
    /// </summary>
    public bool HasResult { get{ return m_HasResult;}}

    /// <summary>
    /// The final result of operation which is available after completion or cancel
    /// </summary>
    public TResult Result{ get{ return m_Result;}}

    /// <summary>
    /// Sets total amount of work
    /// </summary>
    public void SetTotal(int total){ m_Total = total;}

    /// <summary>
    /// Sets current progress out of total
    /// </summary>
    public void SetCurrent(int current){ m_Current = current;}

    /// <summary>
    /// Sets current progress by +1 via interlocked
    /// </summary>
    public int AdvanceCurrent()
    {
      return Interlocked.Increment(ref m_Current);
    }

    /// <summary>
    /// Call to cancel the further processing
    /// </summary>
    public void Cancel() { m_Canceled = true; }

    /// <summary>
    /// Call to set result
    /// </summary>
    public void SetResult(TResult result)
    {
      m_HasResult = true;
      m_Result = result;
      Thread.MemoryBarrier();
    }
  }
}