From 7dbcc456b98046ffc734d38aba7ee926389ceb8f Mon Sep 17 00:00:00 2001
From: Spirtix <michal.prazak1@gmail.com>
Date: Mon, 30 Jun 2025 19:33:49 +0200
Subject: [PATCH] async locking for VikingSession

---
 src/Attributes/VikingSession.cs | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/src/Attributes/VikingSession.cs b/src/Attributes/VikingSession.cs
index e93eb2b..044adaf 100644
--- a/src/Attributes/VikingSession.cs
+++ b/src/Attributes/VikingSession.cs
@@ -1,5 +1,6 @@
 using Microsoft.AspNetCore.Mvc.Filters;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
 using sodoff.Model;
 
 namespace sodoff.Attributes;
@@ -12,6 +13,9 @@ public class VikingSession : Attribute, IAsyncActionFilter {
     public Modes Mode { get; set; } = Modes.VIKING;
     public bool  UseLock = false;
 
+    private static Dictionary<string, SemaphoreSlim> semaphores = new();
+    private static SemaphoreSlim dictSemaphore = new(1, 1);
+
     public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next) {
         DBContext ctx = context.HttpContext.RequestServices.GetService(typeof(DBContext)) as DBContext;
 
@@ -22,7 +26,7 @@ public class VikingSession : Attribute, IAsyncActionFilter {
             return;
         }
 
-        Session? session = ctx.Sessions.FirstOrDefault(x => x.ApiToken == Guid.Parse(context.HttpContext.Request.Form[ApiToken].ToString()));
+        Session? session = await ctx.Sessions.FirstOrDefaultAsync(x => x.ApiToken == Guid.Parse(context.HttpContext.Request.Form[ApiToken].ToString()));
 
         // get viking / user id from session
 
@@ -44,15 +48,16 @@ public class VikingSession : Attribute, IAsyncActionFilter {
             // NOTE: we can't refer to session.User / session.Viking here,
             //       because it may cause to ignore modifications from the threads we are waiting for
             //       we can use its only after vikingMutex.WaitOne()
-
-            Mutex vikingMutex = new Mutex(false, "SoDOffViking:" + userVikingId);
+            string semKey = "SoDOffViking:" + userVikingId;
+            SemaphoreSlim semaphore = await GetSemaphore(semKey);
             try {
-                vikingMutex.WaitOne();
+                await semaphore.WaitAsync();
                 context.ActionArguments["user"] = session.User;
                 context.ActionArguments["viking"] = session.Viking;
                 await next();
             } finally {
-                vikingMutex.ReleaseMutex();
+                semaphore.Release();
+                await RemoveSemaphore(semKey, semaphore);
             }
         } else {
             context.ActionArguments["user"] = session.User;
@@ -60,4 +65,22 @@ public class VikingSession : Attribute, IAsyncActionFilter {
             await next();
         }
     }
+
+    private static async Task<SemaphoreSlim> GetSemaphore(string key) {
+        await dictSemaphore.WaitAsync();
+        if (!semaphores.TryGetValue(key, out SemaphoreSlim semaphore)) {
+            semaphore = new SemaphoreSlim(1, 1);
+            semaphores.Add(key, semaphore);
+        }
+        dictSemaphore.Release();
+        return semaphore;
+    }
+
+    private static async Task RemoveSemaphore(string key, SemaphoreSlim sem) {
+        await dictSemaphore.WaitAsync();
+        if (sem.CurrentCount == 1) {
+            semaphores.Remove(key);
+        }
+        dictSemaphore.Release();
+    }
 }