JS synchronous start, better persistent FS sync.

The engine now expects to emscripten FS to be setup and sync-ed before
main is called. This is exposed via `Module["initFS"]` which also allows
to setup multiple persistence paths (internal use only for now).

Additionally, FS syncing is done **once** for every loop if at least one
file in a persistent path was open for writing and closed, and if the FS
is not syncing already.

This should potentially fix issues reported by users where "autosave"
would not work on the web (never calling `syncfs` because of too many
writes).

1 files changed, 26 insertions, 23 deletions

diff --git a/platform/javascript/os_javascript.cpp b/platform/javascript/os_javascript.cpp
index a4fb7dfc6f..cf5751f384 100644
--- a/platform/javascript/os_javascript.cpp
+++ b/platform/javascript/os_javascript.cpp
@@ -72,27 +72,24 @@ MainLoop *OS_JavaScript::get_main_loop() const {
 	return main_loop;
 }
 
-void OS_JavaScript::main_loop_callback() {
-	get_singleton()->main_loop_iterate();
+extern "C" EMSCRIPTEN_KEEPALIVE void _idb_synced() {
+	OS_JavaScript::get_singleton()->idb_is_syncing = false;
 }
 
 bool OS_JavaScript::main_loop_iterate() {
-	if (is_userfs_persistent() && sync_wait_time >= 0) {
-		int64_t current_time = get_ticks_msec();
-		int64_t elapsed_time = current_time - last_sync_check_time;
-		last_sync_check_time = current_time;
-
-		sync_wait_time -= elapsed_time;
-
-		if (sync_wait_time < 0) {
-			/* clang-format off */
-			EM_ASM(
-				FS.syncfs(function(error) {
-					if (error) { err('Failed to save IDB file system: ' + error.message); }
-				});
-			);
-			/* clang-format on */
-		}
+	if (is_userfs_persistent() && idb_needs_sync && !idb_is_syncing) {
+		idb_is_syncing = true;
+		idb_needs_sync = false;
+		/* clang-format off */
+		EM_ASM({
+			FS.syncfs(function(error) {
+				if (error) {
+					err('Failed to save IDB file system: ' + error.message);
+				}
+				ccall("_idb_synced", 'void', [], []);
+			});
+		});
+		/* clang-format on */
 	}
 
 	DisplayServer::get_singleton()->process_events();
@@ -200,11 +197,17 @@ String OS_JavaScript::get_data_path() const {
 }
 
 void OS_JavaScript::file_access_close_callback(const String &p_file, int p_flags) {
-	OS_JavaScript *os = get_singleton();
-	if (os->is_userfs_persistent() && p_file.begins_with("/userfs") && p_flags & FileAccess::WRITE) {
-		os->last_sync_check_time = OS::get_singleton()->get_ticks_msec();
-		// Wait five seconds in case more files are about to be closed.
-		os->sync_wait_time = 5000;
+	OS_JavaScript *os = OS_JavaScript::get_singleton();
+	if (!(os->is_userfs_persistent() && (p_flags & FileAccess::WRITE))) {
+		return; // FS persistence is not working or we are not writing.
+	}
+	bool is_file_persistent = p_file.begins_with("/userfs");
+#ifdef TOOLS_ENABLED
+	// Hack for editor persistence (can we track).
+	is_file_persistent = is_file_persistent || p_file.begins_with("/home/web_user/");
+#endif
+	if (is_file_persistent) {
+		os->idb_needs_sync = true;
 	}
 }