import from UniRx and some modified.

Assets/UniRx.Async/Triggers/AsyncDestroyTrigger.cs

@@ -0,0 +1,93 @@
+#if CSHARP_7_OR_LATER || (UNITY_2018_3_OR_NEWER && (NET_STANDARD_2_0 || NET_4_6))
+#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member
+
+using System.Threading;
+using UniRx.Async.Internal;
+using UnityEngine;
+
+namespace UniRx.Async.Triggers
+{
+    [DisallowMultipleComponent]
+    public class AsyncDestroyTrigger : MonoBehaviour
+    {
+        bool called = false;
+        UniTaskCompletionSource promise;
+        CancellationTokenSource cancellationTokenSource; // main cancellation
+        object canellationTokenSourceOrQueue;            // external from AddCancellationTriggerOnDestory
+
+        public CancellationToken CancellationToken
+        {
+            get
+            {
+                if (cancellationTokenSource == null)
+                {
+                    cancellationTokenSource = new CancellationTokenSource();
+                }
+                return cancellationTokenSource.Token;
+            }
+        }
+
+        /// <summary>This function is called when the MonoBehaviour will be destroyed.</summary>
+        void OnDestroy()
+        {
+            called = true;
+            promise?.TrySetResult();
+            cancellationTokenSource?.Cancel();
+            cancellationTokenSource?.Dispose();
+            if (canellationTokenSourceOrQueue != null)
+            {
+                if (canellationTokenSourceOrQueue is CancellationTokenSource cts)
+                {
+                    cts.Cancel();
+                    cts.Dispose();
+                }
+                else
+                {
+                    var q = (MinimumQueue<CancellationTokenSource>)canellationTokenSourceOrQueue;
+                    while (q.Count != 0)
+                    {
+                        var c = q.Dequeue();
+                        c.Cancel();
+                        c.Dispose();
+                    }
+                }
+                canellationTokenSourceOrQueue = null;
+            }
+        }
+
+        /// <summary>This function is called when the MonoBehaviour will be destroyed.</summary>
+        public UniTask OnDestroyAsync()
+        {
+            if (called) return UniTask.CompletedTask;
+            return new UniTask(promise ?? (promise = new UniTaskCompletionSource()));
+        }
+
+        /// <summary>Add Cancellation Triggers on destroy</summary>
+        public void AddCancellationTriggerOnDestory(CancellationTokenSource cts)
+        {
+            if (called)
+            {
+                cts.Cancel();
+                cts.Dispose();
+            }
+
+            if (canellationTokenSourceOrQueue == null)
+            {
+                canellationTokenSourceOrQueue = cts;
+            }
+            else if (canellationTokenSourceOrQueue is CancellationTokenSource c)
+            {
+                var q = new MinimumQueue<CancellationTokenSource>(4);
+                q.Enqueue(c);
+                q.Enqueue(cts);
+                canellationTokenSourceOrQueue = q;
+            }
+            else
+            {
+                ((MinimumQueue<CancellationTokenSource>)canellationTokenSourceOrQueue).Enqueue(cts);
+            }
+        }
+    }
+}
+
+#endif