Avoid multiple concurrent extractions of the same archive

Kareadita · Apr 27, 2024 · 0d14af0 · 0d14af0
1 parent 5a7fd25
commit 0d14af0
Showing 1 changed file with 16 additions and 4 deletions.
diff --git a/API/Services/CacheService.cs b/API/Services/CacheService.cs
@@ -1,8 +1,10 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using API.Data;
 using API.DTOs.Reader;
@@ -51,6 +53,8 @@ public class CacheService : ICacheService
     private readonly IReadingItemService _readingItemService;
     private readonly IBookmarkService _bookmarkService;
 
+    private static readonly ConcurrentDictionary<int, SemaphoreSlim> ExtractLocks = new();
+
     public CacheService(ILogger<CacheService> logger, IUnitOfWork unitOfWork,
         IDirectoryService directoryService, IReadingItemService readingItemService,
         IBookmarkService bookmarkService)
@@ -166,11 +170,19 @@ public string GetCachedFile(Chapter chapter)
         var chapter = await _unitOfWork.ChapterRepository.GetChapterAsync(chapterId);
         var extractPath = GetCachePath(chapterId);
 
-        if (_directoryService.Exists(extractPath)) return chapter;
-        var files = chapter?.Files.ToList();
-        ExtractChapterFiles(extractPath, files, extractPdfToImages);
+        SemaphoreSlim extractLock = ExtractLocks.GetOrAdd(chapterId, id => new SemaphoreSlim(1,1));
+
+        await extractLock.WaitAsync();
+        try {
+            if(_directoryService.Exists(extractPath)) return chapter;
+
+            var files = chapter?.Files.ToList();
+            ExtractChapterFiles(extractPath, files, extractPdfToImages);
+        } finally {
+            extractLock.Release();
+        }
 
-        return  chapter;
+        return chapter;
     }
 
     /// <summary>