/*
  KeePass Password Safe - The Open-Source Password Manager
  Copyright (C) 2003-2019 Dominik Reichl <dominik.reichl@t-online.de>

  This program 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 2 of the License, or
  (at your option) any later version.

  This program 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.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text;
using System.Threading;

namespace KeePass.Util
{
	/// <summary>
	/// Mechanism to synchronize access to an object.
	/// In addition to a usual critical section (which locks an object
	/// to a single thread), <c>CriticalSectionEx</c> also prevents
	/// subsequent accesses from the same thread.
	/// </summary>
	public sealed class CriticalSectionEx
	{
		private int m_iLock = 0;

#if (DEBUG && !KeePassUAP)
		private int m_iThreadId = -1;
#endif

		public CriticalSectionEx() { }

#if DEBUG
		~CriticalSectionEx()
		{
			// The object should be unlocked when the lock is disposed
			Debug.Assert(Interlocked.CompareExchange(ref m_iLock, 0, 2) == 0);
		}
#endif

		public bool TryEnter()
		{
			bool b = (Interlocked.Exchange(ref m_iLock, 1) == 0);

#if (DEBUG && !KeePassUAP)
			if(b) m_iThreadId = Thread.CurrentThread.ManagedThreadId;
#endif

			return b;
		}

		public void Exit()
		{
			if(Interlocked.Exchange(ref m_iLock, 0) != 1)
			{
				Debug.Assert(false);
			}
#if (DEBUG && !KeePassUAP)
			else
			{
				// Lock should be released by the original thread
				Debug.Assert(Thread.CurrentThread.ManagedThreadId == m_iThreadId);
				m_iThreadId = -1;
			}
#endif
		}
	}
}
