Add SemaphoreCache

ArcaneLibs/Collections/ObservableDictionary.cs

@@ -61,7 +61,7 @@ public void Clear() {
 
     public TValue this[TKey key] {
         get {
-            Console.WriteLine($"Getting value {key}");
+            // Console.WriteLine($"Getting value {key}");
             return _dictionary[key];
         }
         set {

ArcaneLibs/Collections/SemaphoreCache.cs

@@ -0,0 +1,53 @@
+using System.Collections.Concurrent;
+
+namespace ArcaneLibs.Collections;
+
+public class SemaphoreCache<T> where T : class {
+
+    private readonly ConcurrentDictionary<string, T> _values = new();
+    private readonly ConcurrentDictionary<string, SemaphoreSlim> _semaphores = new();
+
+    public async Task<T> GetOrAdd(string key, Func<Task<T>> factory) {
+        ArgumentNullException.ThrowIfNull(key);
+        _semaphores.TryAdd(key, new SemaphoreSlim(1, 1));
+        await _semaphores[key].WaitAsync();
+        if (_values.TryGetValue(key, out var value)) {
+            _semaphores[key].Release();
+            return value;
+        }
+
+        var val = await factory();
+        _values.TryAdd(key, val);
+        _semaphores[key].Release();
+        return val;
+    }
+}
+
+public class ExiringSemaphoreCache<T> where T : class {
+
+    private readonly ConcurrentDictionary<string, T> _values = new();
+    private readonly ConcurrentDictionary<string, SemaphoreSlim> _semaphores = new();
+
+    public async Task<T> GetOrAdd(string key, Func<Task<T>> factory, TimeSpan expiry) {
+        ArgumentNullException.ThrowIfNull(key);
+        _semaphores.TryAdd(key, new SemaphoreSlim(1, 1));
+        await _semaphores[key].WaitAsync();
+        if (_values.TryGetValue(key, out var value)) {
+            _semaphores[key].Release();
+            return value;
+        }
+
+        var val = await factory();
+        _values.TryAdd(key, val);
+        _semaphores[key].Release();
+
+#pragma warning disable CS4014 // We intentionally do not await this task - this handles cache expiry
+        Task.Delay(expiry).ContinueWith(__ => {
+            _values.TryRemove(key, out var _);
+            _semaphores.TryRemove(key, out var _);
+        });
+#pragma warning restore CS4014
+
+        return val;
+    }
+}