From b9fd20501e2cff8831832f00d7ca9fcfc0d9e801 Mon Sep 17 00:00:00 2001
From: Andrey Kleshchev <117672381+akleshchev@users.noreply.github.com>
Date: Thu, 12 Feb 2026 00:37:46 +0200
Subject: #5356 Fix fast texture cache's mutex stall #2

---
 indra/newview/llmeshrepository.cpp    |  5 +++++
 indra/newview/lltexturecache.cpp      |  6 ++++--
 indra/newview/lltexturecache.h        |  4 ++--
 indra/newview/llviewertexturelist.cpp | 20 ++++++++++++--------
 4 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/indra/newview/llmeshrepository.cpp b/indra/newview/llmeshrepository.cpp
index ed342935ad..20bda5039d 100644
--- a/indra/newview/llmeshrepository.cpp
+++ b/indra/newview/llmeshrepository.cpp
@@ -3331,6 +3331,8 @@ void LLMeshRepoThread::notifyLoadedMeshes()
             loaded_queue.swap(mLoadedQ);
             mLoadedMutex->unlock();
 
+            LL_PROFILE_ZONE_NAMED("notify loaded meshes");
+
             update_metrics = true;
 
             // Process the elements free of the lock
@@ -3362,6 +3364,8 @@ void LLMeshRepoThread::notifyLoadedMeshes()
             unavil_queue.swap(mUnavailableQ);
             mLoadedMutex->unlock();
 
+            LL_PROFILE_ZONE_NAMED("notify unavail meshes");
+
             update_metrics = true;
 
             // Process the elements free of the lock
@@ -3380,6 +3384,7 @@ void LLMeshRepoThread::notifyLoadedMeshes()
     {
         if (mLoadedMutex->trylock())
         {
+            LL_PROFILE_ZONE_NAMED("notify misc meshes");
             std::deque<LLPointer<LLMeshSkinInfo>> skin_info_q;
             std::deque<UUIDBasedRequest> skin_info_unavail_q;
             std::list<LLModel::Decomposition*> decomp_q;
diff --git a/indra/newview/lltexturecache.cpp b/indra/newview/lltexturecache.cpp
index 2e7f353e03..8c8734b52f 100644
--- a/indra/newview/lltexturecache.cpp
+++ b/indra/newview/lltexturecache.cpp
@@ -2048,7 +2048,7 @@ LLPointer<LLImageRaw> LLTextureCache::readFromFastCache(const LLUUID& id, S32& d
         LL_PROFILE_ZONE_NAMED("Read fast cache");
         LLMutexLock lock(&mFastCacheMutex);
 
-        openFastCache();
+        openFastCache(); // only reopens if needed, lasts 10 seconds
 
         mFastCachep->seek(APR_SET, offset);
 
@@ -2079,7 +2079,9 @@ LLPointer<LLImageRaw> LLTextureCache::readFromFastCache(const LLUUID& id, S32& d
 
         closeFastCache();
     }
-    LLPointer<LLImageRaw> raw = new LLImageRaw(data, head[0], head[1], head[2], true);
+
+    // directly construct image from new buffer.
+    LLPointer<LLImageRaw> raw = new LLImageRaw(data, head[0], head[1], head[2], true /*take ownership*/);
 
     return raw;
 }
diff --git a/indra/newview/lltexturecache.h b/indra/newview/lltexturecache.h
index 42894383fd..a09bcc1572 100644
--- a/indra/newview/lltexturecache.h
+++ b/indra/newview/lltexturecache.h
@@ -148,7 +148,7 @@ public:
     U32 getMaxEntries() { return sCacheMaxEntries; };
     bool isInCache(const LLUUID& id) ;
     bool isInLocal(const LLUUID& id) ; //not thread safe at the moment
-
+    LLMutex* getFastCacheMutex() { return &mFastCacheMutex; }
 protected:
     // Accessed by LLTextureCacheWorker
     std::string getLocalFileName(const LLUUID& id);
@@ -194,7 +194,7 @@ private:
     // Internal
     LLMutex mWorkersMutex;
     LLMutex mHeaderMutex;
-    LLMutex mHeaderIDMapMutex;
+    LLMutex mHeaderIDMapMutex; // To avoid deadlocks, never lock mFastCacheMutex after mHeaderIDMapMutex.
     LLMutex mListMutex;
     LLMutex mFastCacheMutex;
     LLAPRFile* mHeaderAPRFile;
diff --git a/indra/newview/llviewertexturelist.cpp b/indra/newview/llviewertexturelist.cpp
index 11ca3098fd..96962bbeae 100644
--- a/indra/newview/llviewertexturelist.cpp
+++ b/indra/newview/llviewertexturelist.cpp
@@ -1191,15 +1191,19 @@ F32 LLViewerTextureList::updateImagesLoadingFastCache(F32 max_time)
 
     LLTimer timer;
     image_list_t::iterator enditer = mFastCacheList.begin();
-    for (image_list_t::iterator iter = mFastCacheList.begin();
-         iter != mFastCacheList.end();)
     {
-        image_list_t::iterator curiter = iter++;
-        enditer = iter;
-        LLViewerFetchedTexture *imagep = *curiter;
-        imagep->loadFromFastCache();
-        if (timer.getElapsedTimeF32() > max_time)
-            break;
+        // prelock fast cache mutex to avoid waiting multiple times.
+        LLMutexLock cache_lock(LLAppViewer::getTextureCache()->getFastCacheMutex());
+        for (image_list_t::iterator iter = mFastCacheList.begin();
+            iter != mFastCacheList.end();)
+        {
+            image_list_t::iterator curiter = iter++;
+            enditer = iter;
+            LLViewerFetchedTexture* imagep = *curiter;
+            imagep->loadFromFastCache();
+            if (timer.getElapsedTimeF32() > max_time)
+                break;
+        }
     }
     mFastCacheList.erase(mFastCacheList.begin(), enditer);
     return timer.getElapsedTimeF32();
-- 
cgit v1.3