Document bullshit

src/common/database.c

@@ -4614,7 +4614,7 @@ gchar *dt_database_get_most_recent_snap(const char* db_filename)
 //       transaction routines. And it has been done to help further implementation for
 //       proper threading and nested transaction support.
 //
-void dt_database_start_transaction(const struct dt_database_t *db)
+void dt_database_start_transaction_debug(const struct dt_database_t *db)
 {
   const int trxid = dt_atomic_add_int(&_trxid, 1);
 
@@ -4625,6 +4625,8 @@ void dt_database_start_transaction(const struct dt_database_t *db)
   {
     // In theads application it may be safer to use an IMMEDIATE transaction:
     // "BEGIN IMMEDIATE TRANSACTION"
+    // This implies "BEGIN DEFERRED TRANSACTION", which means
+    // no write event is dispatched to DB until the first "COMMIT"
     DT_DEBUG_SQLITE3_EXEC(dt_database_get(db), "BEGIN TRANSACTION", NULL, NULL, NULL);
   }
 #ifdef USE_NESTED_TRANSACTIONS
@@ -4640,7 +4642,7 @@ void dt_database_start_transaction(const struct dt_database_t *db)
     fprintf(stderr, "[dt_database_start_transaction] more than %d nested transaction\n", MAX_NESTED_TRANSACTIONS);
 }
 
-void dt_database_release_transaction(const struct dt_database_t *db)
+void dt_database_release_transaction_debug(const struct dt_database_t *db)
 {
   const int trxid = dt_atomic_sub_int(&_trxid, 1);
 

src/common/database.h

@@ -52,14 +52,16 @@ gchar *dt_database_get_most_recent_snap(const char* db_filename);
 
 
 // nested transactions support
-
-void dt_database_start_transaction(const struct dt_database_t *db);
-void dt_database_release_transaction(const struct dt_database_t *db);
+void dt_database_start_transaction_debug(const struct dt_database_t *db);
+void dt_database_release_transaction_debug(const struct dt_database_t *db);
 void dt_database_rollback_transaction(const struct dt_database_t *db);
 
+#define dt_database_start_transaction(db) DT_DEBUG_TRACE_WRAPPER(DT_DEBUG_SQL, dt_database_start_transaction_debug, (db))
+#define dt_database_release_transaction(db) DT_DEBUG_TRACE_WRAPPER(DT_DEBUG_SQL, dt_database_release_transaction_debug, (db))
+
+
 // clang-format off
 // modelines: These editor modelines have been set for all relevant files by tools/update_modelines.py
 // vim: shiftwidth=2 expandtab tabstop=2 cindent
 // kate: tab-indents: off; indent-width 2; replace-tabs on; indent-mode cstyle; remove-trailing-spaces modified;
 // clang-format on
-

src/develop/dev_history.c

@@ -1448,6 +1448,35 @@ static inline void _dt_dev_load_pipeline_defaults(dt_develop_t *dev)
 }
 
 
+/**
+ * TODO: this is a big pile of bullshit
+ *
+ * We insert modules into a temporary history SQL table in memory.history
+ * Then perform all kinds of silly SQL operations.
+ * Then merge into where we keep the real histories, aka main.history in dev_merge_history function.
+ *
+ * First of all, that merge_history function needs to re-index all entries sequentially through C
+ * because SQLite doesn't do it.
+ *
+ * Then, when loading large numbers of small files (PNG, JPEG) for the first time in lighttable,
+ * sooner or later, we get the error:
+ * `function dt_database_start_transaction_debug(), query "BEGIN": cannot start a transaction within a transaction`,
+ * coming from _merge_history. When using a DEBUG build, which checks asserts, that makes the app crash.
+ * Otherwise, the app doesn't crash and there is no telling what's going on in histories.
+ *
+ * But then, I couldn't find where we nest transactions here.
+ *
+ * Or perhaps, due to DEBUG builds being slow due to -O0 optimization, the race condition shows, and doesn't otherwise.
+ *
+ * So, anyway… history init should be done in C, so modules are inserted with defaults params inited
+ * and sanitized directly with a pipe order. Then, we save to history or keep building the pipeline,
+ * because anyway, read_history_ext() init defaults only if it's the first time we open the image,
+ * and then reloads everything from main.history table from database.
+ *
+ * None of that is thread-safe.
+ *
+ **/
+
 static void _init_default_history(dt_develop_t *dev, const int imgid, gboolean *first_run, gboolean *auto_apply_modules)
 {
   // cleanup DB