From f06a89b42b95efdedfd2d7af6f821dc59c223296 Mon Sep 17 00:00:00 2001
From: Mikal Stordal <mikalstordal@gmail.com>
Date: Wed, 30 Oct 2024 16:58:43 +0100
Subject: [PATCH] fix: non-blocking rate-limit for anidb commands

Switch from using a monitor and thread sleep (both sync) while rate limiting to using a semaphore slim and thread delay (both async) to not block the thread while we wait for the delay to elapse.
---
 .../Providers/AniDB/AniDBRateLimiter.cs        | 18 ++++++++----------
 .../AniDB/HTTP/AniDBHttpConnectionHandler.cs   |  8 +++++---
 .../AniDB/UDP/AniDBUDPConnectionHandler.cs     |  2 +-
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/Shoko.Server/Providers/AniDB/AniDBRateLimiter.cs b/Shoko.Server/Providers/AniDB/AniDBRateLimiter.cs
index 2cb103cbe..870825fa9 100644
--- a/Shoko.Server/Providers/AniDB/AniDBRateLimiter.cs
+++ b/Shoko.Server/Providers/AniDB/AniDBRateLimiter.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics;
 using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.Extensions.Logging;
 
 namespace Shoko.Server.Providers.AniDB;
@@ -8,7 +9,7 @@ namespace Shoko.Server.Providers.AniDB;
 public abstract class AniDBRateLimiter
 {
     private readonly ILogger _logger;
-    private readonly object _lock = new();
+    private readonly SemaphoreSlim _lock = new(1, 1);
     private readonly Stopwatch _requestWatch = new();
     private readonly Stopwatch _activeTimeWatch = new();
 
@@ -42,14 +43,11 @@ private void ResetRate()
         _logger.LogTrace("Rate is reset. Active time was {Time} ms", elapsedTime);
     }
 
-    public T EnsureRate<T>(Func<T> action)
+    public async Task<T> EnsureRateAsync<T>(Func<Task<T>> action)
     {
+        await _lock.WaitAsync();
         try
         {
-            var entered = false;
-            Monitor.Enter(_lock, ref entered);
-            if (!entered) throw new SynchronizationLockException();
-
             var delay = _requestWatch.ElapsedMilliseconds;
             if (delay > ResetPeriod) ResetRate();
             var currentDelay = _activeTimeWatch.ElapsedMilliseconds > ShortPeriod ? LongDelay : ShortDelay;
@@ -58,22 +56,22 @@ public T EnsureRate<T>(Func<T> action)
             {
                 _logger.LogTrace("Time since last request is {Delay} ms, not throttling", delay);
                 _logger.LogTrace("Sending AniDB command");
-                return action();
+                return await action();
             }
 
             // add 50ms for good measure
             var waitTime = currentDelay - (int)delay + 50;
 
             _logger.LogTrace("Time since last request is {Delay} ms, throttling for {Time}", delay, waitTime);
-            Thread.Sleep(waitTime);
+            await Task.Delay(waitTime);
 
             _logger.LogTrace("Sending AniDB command");
-            return action();
+            return await action();
         }
         finally
         {
             _requestWatch.Restart();
-            Monitor.Exit(_lock);
+            _lock.Release();
         }
     }
 }
diff --git a/Shoko.Server/Providers/AniDB/HTTP/AniDBHttpConnectionHandler.cs b/Shoko.Server/Providers/AniDB/HTTP/AniDBHttpConnectionHandler.cs
index 8c8036063..3c22cf2a6 100644
--- a/Shoko.Server/Providers/AniDB/HTTP/AniDBHttpConnectionHandler.cs
+++ b/Shoko.Server/Providers/AniDB/HTTP/AniDBHttpConnectionHandler.cs
@@ -48,11 +48,12 @@ public async Task<HttpResponse<string>> GetHttpDirectly(string url)
         {
             throw new AniDBBannedException
             {
-                BanType = UpdateType.HTTPBan, BanExpires = BanTime?.AddHours(BanTimerResetLength)
+                BanType = UpdateType.HTTPBan,
+                BanExpires = BanTime?.AddHours(BanTimerResetLength),
             };
         }
 
-        var response = await RateLimiter.EnsureRate(async () =>
+        var response = await RateLimiter.EnsureRateAsync(async () =>
         {
             using var response = await _httpClient.GetAsync(url);
             response.EnsureSuccessStatusCode();
@@ -63,7 +64,8 @@ public async Task<HttpResponse<string>> GetHttpDirectly(string url)
             {
                 throw new AniDBBannedException
                 {
-                    BanType = UpdateType.HTTPBan, BanExpires = BanTime?.AddHours(BanTimerResetLength)
+                    BanType = UpdateType.HTTPBan,
+                    BanExpires = BanTime?.AddHours(BanTimerResetLength),
                 };
             }
 
diff --git a/Shoko.Server/Providers/AniDB/UDP/AniDBUDPConnectionHandler.cs b/Shoko.Server/Providers/AniDB/UDP/AniDBUDPConnectionHandler.cs
index f943681b1..6b68b6183 100644
--- a/Shoko.Server/Providers/AniDB/UDP/AniDBUDPConnectionHandler.cs
+++ b/Shoko.Server/Providers/AniDB/UDP/AniDBUDPConnectionHandler.cs
@@ -280,7 +280,7 @@ private async Task<string> SendInternal(string command, bool needsUnicode = true
                 Logger.LogWarning("AniDB request timed out. Checking Network and trying again");
                 await _connectivityService.CheckAvailability();
             });
-        var result = await timeoutPolicy.ExecuteAndCaptureAsync(async () => await RateLimiter.EnsureRate(async () =>
+        var result = await timeoutPolicy.ExecuteAndCaptureAsync(async () => await RateLimiter.EnsureRateAsync(async () =>
         {
             if (_connectivityService.NetworkAvailability < NetworkAvailability.PartialInternet)
             {