RaspberryIO/Unosquare.Swan.Lite/Abstractions/RunnerBase.cs

#if !NETSTANDARD1_3 
using System;
using System.Collections.Generic;
using System.Threading;
namespace Unosquare.Swan.Abstractions {
  /// <summary>
  /// Represents an background worker abstraction with a life cycle and running at a independent thread.
  /// </summary>
  public abstract class RunnerBase {
    private Thread _worker;
    private CancellationTokenSource _cancelTokenSource;
    private ManualResetEvent _workFinished;

    /// <summary>
    /// Initializes a new instance of the <see cref="RunnerBase"/> class.
    /// </summary>
    /// <param name="isEnabled">if set to <c>true</c> [is enabled].</param>
    protected RunnerBase(Boolean isEnabled) {
      this.Name = this.GetType().Name;
      this.IsEnabled = isEnabled;
    }

    /// <summary>
    /// Gets the error messages.
    /// </summary>
    /// <value>
    /// The error messages.
    /// </value>
    public List<String> ErrorMessages { get; } = new List<String>();

    /// <summary>
    /// Gets the name.
    /// </summary>
    /// <value>
    /// The name.
    /// </value>
    public String Name {
      get;
    }

    /// <summary>
    /// Gets a value indicating whether this instance is running.
    /// </summary>
    /// <value>
    ///   <c>true</c> if this instance is running; otherwise, <c>false</c>.
    /// </value>
    public Boolean IsRunning {
      get; private set;
    }

    /// <summary>
    /// Gets a value indicating whether this instance is enabled.
    /// </summary>
    /// <value>
    ///   <c>true</c> if this instance is enabled; otherwise, <c>false</c>.
    /// </value>
    public Boolean IsEnabled {
      get;
    }

    /// <summary>
    /// Starts this instance.
    /// </summary>
    public virtual void Start() {
      if(this.IsEnabled == false) {
        return;
      }

      $"Start Requested".Debug(this.Name);
      this._cancelTokenSource = new CancellationTokenSource();
      this._workFinished = new ManualResetEvent(false);

      this._worker = new Thread(() => {
        _ = this._workFinished.Reset();
        this.IsRunning = true;
        try {
          this.Setup();
          this.DoBackgroundWork(this._cancelTokenSource.Token);
        } catch(ThreadAbortException) {
          $"{nameof(ThreadAbortException)} caught.".Warn(this.Name);
        } catch(Exception ex) {
          $"{ex.GetType()}: {ex.Message}\r\n{ex.StackTrace}".Error(this.Name);
        } finally {
          this.Cleanup();
          _ = this._workFinished?.Set();
          this.IsRunning = false;
          "Stopped Completely".Debug(this.Name);
        }
      }) {
        IsBackground = true,
        Name = $"{this.Name}Thread",
      };

      this._worker.Start();
    }

    /// <summary>
    /// Stops this instance.
    /// </summary>
    public virtual void Stop() {
      if(this.IsEnabled == false || this.IsRunning == false) {
        return;
      }

      $"Stop Requested".Debug(this.Name);
      this._cancelTokenSource.Cancel();
      Int32 waitRetries = 5;
      while(waitRetries >= 1) {
        if(this._workFinished.WaitOne(250)) {
          waitRetries = -1;
          break;
        }

        waitRetries--;
      }

      if(waitRetries < 0) {
        "Workbench stopped gracefully".Debug(this.Name);
      } else {
        "Did not respond to stop request. Aborting thread and waiting . . .".Warn(this.Name);
        this._worker.Abort();

        if(this._workFinished.WaitOne(5000) == false) {
          "Waited and no response. Worker might have been left in an inconsistent state.".Error(this.Name);
        } else {
          "Waited for worker and it finally responded (OK).".Debug(this.Name);
        }
      }

      this._workFinished.Dispose();
      this._workFinished = null;
    }

    /// <summary>
    /// Setups this instance.
    /// </summary>
    protected virtual void Setup() {
      // empty
    }

    /// <summary>
    /// Cleanups this instance.
    /// </summary>
    protected virtual void Cleanup() {
      // empty
    }

    /// <summary>
    /// Does the background work.
    /// </summary>
    /// <param name="ct">The ct.</param>
    protected abstract void DoBackgroundWork(CancellationToken ct);
  }
}
#endif