BUG-230673: Add warning that LLDiskCache::purge() is also called from outside the main thread

indra/llfilesystem/lldiskcache.cpp

@@ -51,6 +51,8 @@ LLDiskCache::LLDiskCache(const std::string cache_dir,
     LLFile::mkdir(cache_dir);
 }
 
+// WARNING: purge() is called by LLPurgeDiskCacheThread. As such it must
+// NOT touch any LLDiskCache data without introducing and locking a mutex!
 void LLDiskCache::purge()
 {
     if (mEnableCacheDebugInfo)

indra/llfilesystem/lldiskcache.h

@@ -118,6 +118,9 @@ class LLDiskCache :
         /**
          * Purge the oldest items in the cache so that the combined size of all files
          * is no bigger than mMaxSizeBytes.
+         *
+         * WARNING: purge() is called by LLPurgeDiskCacheThread. As such it must
+         * NOT touch any LLDiskCache data without introducing and locking a mutex!
          */
         void purge();