initial commit

Plugins/BTCPayServer.Plugins.Wabisabi/Extensions.cs

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+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Plugins.Wabisabi;
+
+public static class Extensions
+{
+    /// <summary>
+    /// Returns an existing task from the concurrent dictionary, or adds a new task
+    /// using the specified asynchronous factory method. Concurrent invocations for
+    /// the same key are prevented, unless the task is removed before the completion
+    /// of the delegate. Failed tasks are evicted from the concurrent dictionary.
+    /// </summary>
+    public static Task<TValue> GetOrAddAsync<TKey, TValue>(
+        this ConcurrentDictionary<TKey, Task<TValue>> source, TKey key,
+        Func<TKey, Task<TValue>> valueFactory)
+    {
+        if (!source.TryGetValue(key, out var currentTask))
+        {
+            Task<TValue> newTask = null;
+            var newTaskTask = new Task<Task<TValue>>(async () =>
+            {
+                try { return await valueFactory(key).ConfigureAwait(false); }
+                catch
+                {
+                    source.TryRemove(KeyValuePair.Create(key, newTask));
+                    throw;
+                }
+            });
+            newTask = newTaskTask.Unwrap();
+            currentTask = source.GetOrAdd(key, newTask);
+            if (currentTask == newTask) newTaskTask.Start(TaskScheduler.Default);
+        }
+        return currentTask;
+    }
+}