#region  --------------- Copyright Dresser Wayne Pignone -------------
/*
 * $Log: /Wrk/WayneLibraries/Wrk/StateEngine/ReentrancyMutex.cs $
 * 
 * 4     07-12-06 11:27 Mattias.larsson
 * 
 * 3     07-10-28 14:47 roger.månsson
 * Added a lock on the mutex object, so we can dispose without exceptions.
 * 
 * 2     07-10-22 16:21 roger.månsson
 * Corrected handling of reentrancy. Must set the owned flag!
 * 
 * 1     07-10-22 11:30 roger.månsson
 * Created
 */
#endregion
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace Wayne.Lib.StateEngine
{
    /// <summary>
    /// A mutex class that protects not only from entering a code section from separate threads, but also 
    /// from reentrancy by the same thread but further up on the call stack.
    /// </summary>
    class ReentrancyMutex : IDisposable
    {
        #region Fields

        bool owned;
        object mutexLock = new object();
        Mutex mutex = new Mutex(false);

        #endregion

        ~ReentrancyMutex()
        {
            Dispose(false);
        }

        public bool TryAquire()
        {
            lock (mutexLock)
            {
                if ((mutex != null) && mutex.WaitOne(0, false)) //First check so this thread can aquire the mutex.
                {
                    if (owned) //Has this thread already the mutex, then we should fail.
                    {
                        mutex.ReleaseMutex();
                        return false;
                    }
                    else
                    {
                        owned = true;
                        return true;
                    }
                }
                else
                {
                    return false;
                }
            }
        }

        public void Release()
        {
            owned = false;
            lock (mutexLock)
            {
                if (mutex != null)
                    mutex.ReleaseMutex();
            }
        }

        internal void Close()
        {
            ((IDisposable)this).Dispose();
        }

        #region IDisposable Members

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                lock (mutexLock)
                {
                    if (mutex != null)
                    {
                        mutex.Close();
                        mutex = null;
                    }
                }
            }
        }

        void IDisposable.Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);

        }

        #endregion
    }
}