From cc2784a269a0a1f27cb0472403fa9e81669a8524 Mon Sep 17 00:00:00 2001
From: fluxzy-ci <admin@fluxzy.io>
Date: Sat, 11 Apr 2026 18:44:59 +0200
Subject: [PATCH] Fix concurrent HashSet modification when serializing archive
 meta

UpdateMeta, UpdateTags and Update(ExchangeInfo) all touched
_archiveMetaInformation.Tags but guarded it with two different locks
(one on the path string, another on the meta object itself), so a
thread adding a tag could race a thread serializing the meta file and
trip "Collection was modified" inside JsonSerializer. Route every
access through a single _metaLock and keep UpdateMeta inside the lock.
---
 .../Writers/DirectoryArchiveWriter.cs         | 21 ++++++++++---------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/Fluxzy.Core/Archiving/Writers/DirectoryArchiveWriter.cs b/src/Fluxzy.Core/Archiving/Writers/DirectoryArchiveWriter.cs
index 435565f4..9640693a 100644
--- a/src/Fluxzy.Core/Archiving/Writers/DirectoryArchiveWriter.cs
+++ b/src/Fluxzy.Core/Archiving/Writers/DirectoryArchiveWriter.cs
@@ -17,6 +17,7 @@ namespace Fluxzy.Writers
     public class DirectoryArchiveWriter : RealtimeArchiveWriter
     {
         private readonly ArchiveMetaInformation _archiveMetaInformation = CreateNewCaptureArchiveMetaInformation();
+        private readonly object _metaLock = new object();
 
         private static ArchiveMetaInformation CreateNewCaptureArchiveMetaInformation()
         {
@@ -78,7 +79,7 @@ private void UpdateMeta(bool force)
             if (!force && File.Exists(_archiveMetaInformationPath))
                 return;
 
-            lock (_archiveMetaInformationPath)
+            lock (_metaLock)
             {
                 using var fileStream = File.Create(_archiveMetaInformationPath);
                 JsonSerializer.Serialize(fileStream, _archiveMetaInformation, GlobalArchiveOption.DefaultSerializerOptions);
@@ -87,15 +88,15 @@ private void UpdateMeta(bool force)
 
         public override void UpdateTags(IEnumerable<Tag> tags)
         {
-            lock (_archiveMetaInformationPath)
+            lock (_metaLock)
             {
                 foreach (var tag in tags)
                 {
                     _archiveMetaInformation.Tags.Add(tag);
                 }
-            }
 
-            UpdateMeta(true);
+                UpdateMeta(true);
+            }
         }
 
         protected override bool ExchangeUpdateRequired(Exchange exchange)
@@ -130,18 +131,18 @@ public override bool Update(ExchangeInfo exchangeInfo, CancellationToken cancell
 
             if (exchangeInfo.Tags?.Any() ?? false)
             {
-                var modified = false;
-
-                lock (_archiveMetaInformation) {
+                lock (_metaLock)
+                {
+                    var modified = false;
 
                     foreach (var tag in exchangeInfo.Tags)
                     {
                         modified = _archiveMetaInformation.Tags.Add(tag) || modified;
                     }
-                }
 
-                if (modified)
-                    UpdateMeta(true);
+                    if (modified)
+                        UpdateMeta(true);
+                }
             }
 
             return true;