Use SemaphoreSlim instead of lock()

UnityMainThreadDispatcher.cs

@@ -18,102 +18,129 @@ limitations under the License.
 using System.Collections;
 using System.Collections.Generic;
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 
 /// Author: Pim de Witte (pimdewitte.com) and contributors, https://github.com/PimDeWitte/UnityMainThreadDispatcher
 /// <summary>
 /// A thread-safe class which holds a queue with actions to execute on the next Update() method. It can be used to make calls to the main thread for
 /// things such as UI Manipulation in Unity. It was developed for use in combination with the Firebase Unity plugin, which uses separate threads for event handling
 /// </summary>
-public class UnityMainThreadDispatcher : MonoBehaviour {
-
-	private static readonly Queue<Action> _executionQueue = new Queue<Action>();
-
-	public void Update() {
-		lock(_executionQueue) {
-			while (_executionQueue.Count > 0) {
-				_executionQueue.Dequeue().Invoke();
-			}
-		}
-	}
-
-	/// <summary>
-	/// Locks the queue and adds the IEnumerator to the queue
-	/// </summary>
-	/// <param name="action">IEnumerator function that will be executed from the main thread.</param>
-	public void Enqueue(IEnumerator action) {
-		lock (_executionQueue) {
-			_executionQueue.Enqueue (() => {
-				StartCoroutine (action);
-			});
-		}
-	}
-
-        /// <summary>
-        /// Locks the queue and adds the Action to the queue
-	/// </summary>
-	/// <param name="action">function that will be executed from the main thread.</param>
-	public void Enqueue(Action action)
-	{
-		Enqueue(ActionWrapper(action));
-	}
-
-	/// <summary>
-	/// Locks the queue and adds the Action to the queue, returning a Task which is completed when the action completes
-	/// </summary>
-	/// <param name="action">function that will be executed from the main thread.</param>
-	/// <returns>A Task that can be awaited until the action completes</returns>
-	public Task EnqueueAsync(Action action)
-	{
-		var tcs = new TaskCompletionSource<bool>();
-
-		void WrappedAction() {
-			try 
-			{
-				action();
-				tcs.TrySetResult(true);
-			} catch (Exception ex) 
-			{
-				tcs.TrySetException(ex);
-			}
-		}
-
-		Enqueue(ActionWrapper(WrappedAction));
-		return tcs.Task;
-	}
-
-
-	IEnumerator ActionWrapper(Action a)
-	{
-		a();
-		yield return null;
-	}
-
-
-	private static UnityMainThreadDispatcher _instance = null;
-
-	public static bool Exists() {
-		return _instance != null;
-	}
-
-	public static UnityMainThreadDispatcher Instance() {
-		if (!Exists ()) {
-			throw new Exception ("UnityMainThreadDispatcher could not find the UnityMainThreadDispatcher object. Please ensure you have added the MainThreadExecutor Prefab to your scene.");
-		}
-		return _instance;
-	}
-
-
-	void Awake() {
-		if (_instance == null) {
-			_instance = this;
-			DontDestroyOnLoad(this.gameObject);
-		}
-	}
-
-	void OnDestroy() {
-			_instance = null;
-	}
+public class UnityMainThreadDispatcher : MonoBehaviour
+{
+
+    private static readonly Queue<Action> _executionQueue = new Queue<Action>();
+    private static SemaphoreSlim _executionQueueLock = new SemaphoreSlim(1, 1);
+
+    public void Update()
+    {
+        _executionQueueLock.Wait();
+        try
+        {
+            while (_executionQueue.Count > 0)
+            {
+                _executionQueue.Dequeue().Invoke();
+            }
+        }
+        finally
+        {
+            _executionQueueLock.Release();
+        }
+    }
+
+    /// <summary>
+    /// Locks the queue and adds the IEnumerator to the queue
+    /// </summary>
+    /// <param name="action">IEnumerator function that will be executed from the main thread.</param>
+    public void Enqueue(IEnumerator action)
+    {
+        _executionQueueLock.Wait();
+        try
+        {
+            _executionQueue.Enqueue(() =>
+            {
+                StartCoroutine(action);
+            });
+        }
+        finally
+        {
+            _executionQueueLock.Release();
+        }
+    }
+
+    /// <summary>
+    /// Locks the queue and adds the Action to the queue
+    /// </summary>
+    /// <param name="action">function that will be executed from the main thread.</param>
+    public void Enqueue(Action action)
+    {
+        Enqueue(ActionWrapper(action));
+    }
+
+    /// <summary>
+    /// Locks the queue and adds the Action to the queue, returning a Task which is completed when the action completes
+    /// </summary>
+    /// <param name="action">function that will be executed from the main thread.</param>
+    /// <returns>A Task that can be awaited until the action completes</returns>
+    public Task EnqueueAsync(Action action)
+    {
+        var tcs = new TaskCompletionSource<bool>();
+
+        void WrappedAction()
+        {
+            try
+            {
+                action();
+                tcs.TrySetResult(true);
+            }
+            catch (Exception ex)
+            {
+                tcs.TrySetException(ex);
+            }
+        }
+
+        Enqueue(ActionWrapper(WrappedAction));
+        return tcs.Task;
+    }
+
+
+    IEnumerator ActionWrapper(Action a)
+    {
+        a();
+        yield return null;
+    }
+
+
+    private static UnityMainThreadDispatcher _instance = null;
+
+    public static bool Exists()
+    {
+        return _instance != null;
+    }
+
+    public static UnityMainThreadDispatcher Instance()
+    {
+        if (!Exists())
+        {
+            throw new Exception("UnityMainThreadDispatcher could not find the UnityMainThreadDispatcher object. Please ensure you have added the MainThreadExecutor Prefab to your scene.");
+        }
+        return _instance;
+    }
+
+
+    void Awake()
+    {
+        if (_instance == null)
+        {
+            _instance = this;
+            DontDestroyOnLoad(this.gameObject);
+        }
+    }
+
+    void OnDestroy()
+    {
+        _instance = null;
+    }
 
 
 }