greenshot/Greenshot/Helpers/ResourceMutex.cs

/*
 * Greenshot - a free and open source screenshot tool
 * Copyright (C) 2007-2021 Thomas Braun, Jens Klingen, Robin Krom
 *
 * For more information see: http://getgreenshot.org/
 * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
 *
 * 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 1 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, see <http://www.gnu.org/licenses/>.
 */

using log4net;
using System;
using System.Security.AccessControl;
using System.Security.Principal;
using System.Threading;

namespace Greenshot.Helpers
{
	/// <summary>
	///     This protects your resources or application from running more than once
	///     Simplifies the usage of the Mutex class, as described here:
	///     https://msdn.microsoft.com/en-us/library/System.Threading.Mutex.aspx
	/// </summary>
	public class ResourceMutex : IDisposable
	{
		private static readonly ILog Log = LogManager.GetLogger(typeof(ResourceMutex));
		private readonly string _mutexId;
		private readonly string _resourceName;
		private Mutex _applicationMutex;

		/// <summary>
		///     Private constructor
		/// </summary>
		/// <param name="mutexId"></param>
		/// <param name="resourceName"></param>
		private ResourceMutex(string mutexId, string resourceName = null)
		{
			_mutexId = mutexId;
			_resourceName = resourceName ?? "some resource";
		}

		/// <summary>
		///     Test if the Mutex was created and locked.
		/// </summary>
		public bool IsLocked { get; set; }

		/// <summary>
		///     Create a ResourceMutex for the specified mutex id and resource-name
		/// </summary>
		/// <param name="mutexId">ID of the mutex, preferably a Guid as string</param>
		/// <param name="resourceName">Name of the resource to lock, e.g your application name, usefull for logs</param>
		/// <param name="global">true to have a global mutex see: https://msdn.microsoft.com/en-us/library/bwe34f1k.aspx </param>
		public static ResourceMutex Create(string mutexId, string resourceName = null, bool global = false)
		{
			var applicationMutex = new ResourceMutex((global ? @"Global\" : @"Local\") + mutexId, resourceName);
			applicationMutex.Lock();
			return applicationMutex;
		}

		/// <summary>
		///     This tries to get the Mutex, which takes care of having multiple instances running
		/// </summary>
		/// <returns>true if it worked, false if another instance is already running or something went wrong</returns>
		public bool Lock()
		{
			Log.DebugFormat("{0} is trying to get Mutex {1}", _resourceName, _mutexId);

			IsLocked = true;
			// check whether there's an local instance running already, but use local so this works in a multi-user environment
			try
			{
				// Added Mutex Security, hopefully this prevents the UnauthorizedAccessException more gracefully
				var sid = new SecurityIdentifier(WellKnownSidType.WorldSid, null);
				var mutexSecurity = new MutexSecurity();
				mutexSecurity.AddAccessRule(new MutexAccessRule(sid, MutexRights.FullControl, AccessControlType.Allow));
				mutexSecurity.AddAccessRule(new MutexAccessRule(sid, MutexRights.ChangePermissions, AccessControlType.Deny));
				mutexSecurity.AddAccessRule(new MutexAccessRule(sid, MutexRights.Delete, AccessControlType.Deny));

                // 1) Create Mutex
				_applicationMutex = new Mutex(true, _mutexId, out var createdNew, mutexSecurity);
				// 2) if the mutex wasn't created new get the right to it, this returns false if it's already locked
				if (!createdNew && !_applicationMutex.WaitOne(100, false))
				{
					Log.InfoFormat("{0} is already in use, mutex {1} is NOT locked for the caller", _resourceName, _mutexId);
					IsLocked = false;
					// Clean up
					_applicationMutex.Close();
					_applicationMutex = null;
				}
				else
				{
					Log.InfoFormat(createdNew ? "{0} has created & claimed the mutex {1}" : "{0} has claimed the mutex {1}", _resourceName, _mutexId);
				}
			}
			catch (AbandonedMutexException e)
			{
				// Another instance didn't cleanup correctly!
				// we can ignore the exception, it happened on the "waitOne" but still the mutex belongs to us
				Log.WarnFormat("{0} didn't cleanup correctly, but we got the mutex {1}.", _resourceName, _mutexId);
				Log.Warn(e);
			}
			catch (UnauthorizedAccessException e)
			{
				Log.ErrorFormat("{0} is most likely already running for a different user in the same session, can't create/get mutex {1} due to error.", _resourceName, _mutexId);
				Log.Error(e);
				IsLocked = false;
			}
			catch (Exception ex)
			{
				Log.ErrorFormat("Problem obtaining the Mutex {1} for {0}, assuming it was already taken!", _resourceName, _mutexId);
				Log.Error(ex);
				IsLocked = false;
			}
			return IsLocked;
		}

        //  To detect redundant Dispose calls
		private bool _disposedValue;

		/// <summary>
		///     The real disposing code
		/// </summary>
		/// <param name="disposing">true if dispose is called, false when the finalizer is called</param>
		protected void Dispose(bool disposing)
		{
			if (_disposedValue) return;
			
			if (_applicationMutex != null)
			{
				try
				{
					_applicationMutex.ReleaseMutex();
					_applicationMutex = null;
					Log.InfoFormat("Released Mutex {0} for {1}", _mutexId, _resourceName);
				}
				catch (Exception ex)
				{
					Log.ErrorFormat("Error releasing Mutex {0} for {1}", _mutexId, _resourceName);
					Log.Error(ex);
				}
			}
			_disposedValue = true;
		}

		/// <summary>
		///     Make sure the ApplicationMutex is disposed when the finalizer is called
		/// </summary>
		~ResourceMutex()
		{
			// Do not change this code. Put cleanup code in Dispose(bool disposing) above.
			Dispose(false);
		}

		/// <summary>
		///     The dispose interface, which calls Dispose(true) to signal that dispose is called.
		/// </summary>
		public void Dispose()
		{
			// Do not change this code. Put cleanup code in Dispose(bool disposing) above.
			Dispose(true);
			GC.SuppressFinalize(this);
		}
    }
}