From 232c94c61f6ff4c2745599dc97b821c62e51ef26 Mon Sep 17 00:00:00 2001
From: Pilzinsel64 <pascal.schedel@dr-schneider.com>
Date: Fri, 24 Jan 2025 06:10:43 +0100
Subject: [PATCH] use SemaphoreSlim to limit the amount of parallel http
 requests

---
 Pilz.Net/Api/ApiServer.cs | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/Pilz.Net/Api/ApiServer.cs b/Pilz.Net/Api/ApiServer.cs
index b68d680..ae8dd5d 100644
--- a/Pilz.Net/Api/ApiServer.cs
+++ b/Pilz.Net/Api/ApiServer.cs
@@ -16,6 +16,7 @@ public class ApiServer(string apiUrl) : IApiServer
     protected HttpListener httpListener = new();
     protected int restartAttempts = 0;
     protected DateTime lastRestartAttempt;
+    protected SemaphoreSlim? semaphore;
 
     public event OnCheckAuthenticationEventHandler? OnCheckAuthentication;
     public event OnCheckContextEventHandler? OnCheckContext;
@@ -45,6 +46,8 @@ public class ApiServer(string apiUrl) : IApiServer
 
     public int MaxAutoRestartsPerMinute { get; set; } = 10;
 
+    public int MaxConcurentConnections { get; set; } = 5;
+
     public virtual void Start()
     {
         Log.Info("Starting listener");
@@ -68,6 +71,7 @@ public class ApiServer(string apiUrl) : IApiServer
         Log.Info("Restarting listener");
         Stop();
         httpListener = new();
+        semaphore?.Release(int.MaxValue);
         Start();
         Log.Info("Restarted listener");
     }
@@ -92,6 +96,17 @@ public class ApiServer(string apiUrl) : IApiServer
         return true;
     }
 
+    protected virtual void WaitForSlot()
+    {
+        semaphore ??= new(MaxConcurentConnections);
+        semaphore.Wait();
+    }
+
+    protected virtual void FreeSlot()
+    {
+        semaphore?.Release();
+    }
+
     public virtual void RegisterHandler<T>(T instance) where T : class
     {
         // Get all public instance methods
@@ -166,6 +181,18 @@ public class ApiServer(string apiUrl) : IApiServer
         if (!httpListener.IsListening)
             return;
 
+        // Wait for a free slot
+        try
+        {
+            WaitForSlot();
+        }
+        catch (Exception ex)
+        {
+            Log.Fatal($"Too many concurent connections", ex);
+            Thread.Sleep(1000);
+            return;
+        }
+
         // Get context
         try
         {
@@ -195,7 +222,10 @@ public class ApiServer(string apiUrl) : IApiServer
 
         // Cancel if we don't have a context
         if (context is null)
+        {
+            FreeSlot();
             return;
+        }
 
         // Check context
         Log.Info("Request retrived for " + context.Request.RawUrl);
@@ -215,6 +245,9 @@ public class ApiServer(string apiUrl) : IApiServer
             OnCheckContextCompleted?.Invoke(this, new(context));
         }
 
+        // Release slot
+        FreeSlot();
+
         // Listen for new request
         if (!AllowMultipleRequests)
             Receive();