Increased mutex safety.

Don't even query the size() without having at least a shared_lock.

*May* prevent KICAD-4S, but seems unlikely.

eeschema/dialogs/panel_sym_lib_table.cpp

@@ -932,7 +932,7 @@ bool PANEL_SYM_LIB_TABLE::TransferDataFromWindow()
         m_globalTable->Clear();
         m_globalTable->m_rows.transfer( m_globalTable->m_rows.end(), global_model()->m_rows.begin(),
                                       global_model()->m_rows.end(), global_model()->m_rows );
-        m_globalTable->reindex( true );
+        m_globalTable->reindex();
     }
 
     if( project_model() && *project_model() != *m_projectTable )
@@ -942,7 +942,7 @@ bool PANEL_SYM_LIB_TABLE::TransferDataFromWindow()
         m_projectTable->Clear();
         m_projectTable->m_rows.transfer( m_projectTable->m_rows.end(), project_model()->m_rows.begin(),
                                        project_model()->m_rows.end(), project_model()->m_rows );
-        m_projectTable->reindex( true );
+        m_projectTable->reindex();
     }
 
     return true;

include/lib_table_base.h

@@ -462,7 +462,7 @@ public:
             if( *iter == *aRow )
             {
                 m_rows.erase( iter, iter + 1 );
-                reindex( true );
+                reindex();
                 return true;
             }
         }
@@ -528,6 +528,18 @@ public:
         return m_version;
     }
 
+    /**
+     * While this is an encapsulation leak, calling it before threaded loads *may* prevent
+     * some Sentry crashes we're seeing (KICAD-4S).
+     */
+    void EnsureIndex()
+    {
+        ensureIndex();
+
+        if( m_fallBack )
+            m_fallBack->EnsureIndex();
+    }
+
 protected:
     /**
      * Return a #LIB_TABLE_ROW if \a aNickname is found in this table or in any chained
@@ -553,16 +565,10 @@ protected:
      * @param aForce is to avoid rebuilding the index multiple times because multiple threads hit ensureIndex
      * at the same time
      */
-    void reindex( bool aForce )
+    void reindex()
     {
         std::lock_guard<std::shared_mutex> lock( m_nickIndexMutex );
 
-        if( !aForce )
-        {
-            if( m_nickIndex.size() )
-                return;
-        }
-
         m_nickIndex.clear();
 
         for( LIB_TABLE_ROWS_ITER it = m_rows.begin(); it != m_rows.end(); ++it )
@@ -574,8 +580,14 @@ protected:
         // The dialog lib table editor may not maintain the nickIndex.
         // Lazy indexing may be required.  To handle lazy indexing, we must enforce
         // that "nickIndex" is either empty or accurate, but never inaccurate.
-        if( !m_nickIndex.size() )
+        {
-            reindex( false );
+            std::shared_lock<std::shared_mutex> lock( m_nickIndexMutex );
+
+            if( m_nickIndex.size() )
+                return;
+        }
+
+        reindex();
     }
 
 private:

pcbnew/dialogs/panel_fp_lib_table.cpp

@@ -971,7 +971,7 @@ bool PANEL_FP_LIB_TABLE::TransferDataFromWindow()
             m_global->Clear();
             m_global->m_rows.transfer( m_global->m_rows.end(), global_model()->m_rows.begin(),
                                      global_model()->m_rows.end(), global_model()->m_rows );
-            m_global->reindex( true );
+            m_global->reindex();
         }
 
         if( project_model() && *project_model() != *m_project )
@@ -981,7 +981,7 @@ bool PANEL_FP_LIB_TABLE::TransferDataFromWindow()
             m_project->Clear();
             m_project->m_rows.transfer( m_project->m_rows.end(), project_model()->m_rows.begin(),
                                       project_model()->m_rows.end(), project_model()->m_rows );
-            m_project->reindex( true );
+            m_project->reindex();
         }
 
         return true;

pcbnew/footprint_info_impl.cpp

@@ -268,6 +268,12 @@ void FOOTPRINT_LIST_IMPL::loadFootprints()
                 return 1;
             };
 
+    // While the private ensureIndex() is supposedly thread-safe, and having a public call is
+    // a bit of an encapsulation leak, we have at least one non-reproducible Sentry issue
+    // (KICAD-4S) that *might* be prevented by doing the EnsureIndex() before spooling up the
+    // multi-threaded part.
+    m_lib_table->EnsureIndex();
+
     for( size_t ii = 0; ii < num_elements; ++ii )
         returns[ii] = tp.submit( fp_thread );