fix: lock issue reported tekartik/sembast_sqflite#5 and with a good b…

…ackground of information here simolus3/drift#835

The solution from Simon Binder is simple and brilliant

sqflite_common_ffi/lib/src/database_tracker.dart

@@ -0,0 +1,97 @@
+import 'dart:ffi';
+
+import 'package:sqlite3/sqlite3.dart';
+
+/// Copied from moor
+/// This entire file is an elaborate hack to workaround https://github.com/simolus3/moor/issues/835.
+///
+/// Users were running into database deadlocks after (stateless) hot restarts
+/// in Flutter when they use transactions. The problem is that we don't have a
+/// chance to call `sqlite3_close` before a Dart VM restart, the Dart object is
+/// just gone without a trace. This means that we're leaking sqlite3 database
+/// connections on restarts.
+/// Even worse, those connections might have a lock on the database, for
+/// instance if they just started a transaction.
+///
+/// Our solution is to store open sqlite3 database connections in an in-memory
+/// sqlite database which can survive restarts! For now, we keep track of the
+/// pointer of an sqlite3 database handle in that database.
+/// At an early stage of their `main()` method, users can now use
+/// `VmDatabase.closeExistingInstances()` to release those resources.
+DatabaseTracker get tracker => _tracker ??= DatabaseTracker();
+DatabaseTracker _tracker;
+
+var _tableName = 'open_connections';
+var _ptrColName = 'db_pointer';
+
+/// Internal class that we don't export to sqflite users. See [tracker] for why
+/// this is necessary.
+class DatabaseTracker {
+  /// Creates a new tracker with necessary tables.
+  ///
+  /// If the table exists delete any open connection.
+  DatabaseTracker()
+      : _db = sqlite3.open(
+          'file:sqflite_database_tracker?mode=memory&cache=shared',
+          uri: true,
+        ) {
+    try {
+      var tableExists = (_db
+              .select(
+                  'SELECT COUNT(*) FROM sqlite_master WHERE tbl_name = \'$_tableName\'')
+              .first
+              .columnAt(0) as int) >
+          0;
+      if (!tableExists) {
+        _db.execute('''
+CREATE TABLE IF NOT EXISTS $_tableName (
+  $_ptrColName INTEGER NOT NULL PRIMARY KEY
+);
+    ''');
+      } else {
+        _closeExisting();
+      }
+    } catch (e) {
+      print('error $e creating tracker db');
+    }
+  }
+
+  final Database _db;
+
+  /// Tracks the [db]. The [path] argument can be used to track the path
+  /// of that database, if it's bound to a file.
+  void markOpened(Database db) {
+    final ptr = db.handle.address;
+    try {
+      _db.execute('INSERT INTO $_tableName($_ptrColName) VALUES($ptr)');
+    } catch (_) {
+      // Handle when the same pointer is inserted twice
+      // sqlite tends to reuse the same pointer
+    }
+  }
+
+  /// Marks the database [db] as closed.
+  void markClosed(Database db) {
+    final ptr = db.handle.address;
+    _db.execute('DELETE FROM $_tableName WHERE $_ptrColName = $ptr');
+  }
+
+  /// Closes tracked database connections.
+  void _closeExisting() {
+    _db.execute('BEGIN;');
+    try {
+      final results = _db.select('SELECT $_ptrColName FROM $_tableName');
+      for (final row in results) {
+        final ptr = Pointer.fromAddress(row.columnAt(0) as int);
+        try {
+          sqlite3.fromPointer(ptr).dispose();
+        } catch (e) {
+          print('error $e disposing $ptr');
+        }
+      }
+      _db.execute('DELETE FROM $_tableName;');
+    } finally {
+      _db.execute('COMMIT;');
+    }
+  }
+}

sqflite_common_ffi/lib/src/sqflite_ffi_impl.dart

@@ -2,16 +2,17 @@ import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:meta/meta.dart';
-import 'package:sqlite3/sqlite3.dart' as ffi;
 import 'package:path/path.dart';
 import 'package:sqflite_common/sqlite_api.dart';
 import 'package:sqflite_common_ffi/src/constant.dart';
 import 'package:sqflite_common_ffi/src/method_call.dart';
 import 'package:sqflite_common_ffi/src/sqflite_ffi_exception.dart';
 import 'package:sqflite_common_ffi/src/sqflite_import.dart';
+import 'package:sqlite3/sqlite3.dart' as ffi;
 import 'package:synchronized/extension.dart';
 import 'package:synchronized/synchronized.dart';
 
+import 'database_tracker.dart';
 import 'import.dart';
 
 final _debug = false; // devWarning(true); // false
@@ -248,52 +249,6 @@ extension SqfliteFfiMethodCallHandler on FfiMethodCall {
 
       var ffiException = wrapAnyException(e);
       throw ffiException;
-      /*
-      if (e is ffi.SqliteException) {
-        var database = getDatabase();
-        var sql = getSql();
-        var sqlArguments = getSqlArguments();
-        var wrapped = wrapSqlException(e, details: <String, dynamic>{
-          'database': database.toDebugMap(),
-          'sql': sql,
-          'arguments': sqlArguments
-        });
-        // devPrint(wrapped);
-        throw wrapped;
-      }
-      var database = getDatabase();
-      var sql = getSql();
-      var sqlArguments = getSqlArguments();
-      if (_debug) {
-        print('$e in ${database?.toDebugMap()}');
-      }
-      String code;
-      String message;
-      Map<String, dynamic> details;
-      if (e is SqfliteFfiException) {
-        // devPrint('throwing $e');
-        code = e.code;
-        message = e.message;
-        details = e.details;
-      } else {
-        code = anyErrorCode;
-        message = e.toString();
-      }
-      if (_debug) {
-        print('handleError: $e');
-        print('stackTrace : $st');
-      }
-      throw SqfliteFfiException(
-          code: code,
-          message: message,
-          details: <String, dynamic>{
-            if (database != null) 'database': database.toDebugMap(),
-            if (sql != null) 'sql': sql,
-            if (sqlArguments != null) 'arguments': sqlArguments,
-            if (details != null) 'details': details,
-          });
-
-       */
     }
   }
 
@@ -374,6 +329,12 @@ extension SqfliteFfiMethodCallHandler on FfiMethodCall {
         final mode =
             readOnly ? ffi.OpenMode.readOnly : ffi.OpenMode.readWriteCreate;
         ffiDb = ffi.sqlite3.open(path, mode: mode);
+
+        // Handle hot-restart for single instance
+        // The dart code is killed but the native code remains
+        if (singleInstance) {
+          tracker.markOpened(ffiDb);
+        }
       }
     } on ffi.SqliteException catch (e) {
       throw wrapSqlException(e, code: 'open_failed');
@@ -399,6 +360,11 @@ extension SqfliteFfiMethodCallHandler on FfiMethodCall {
     var database = getDatabaseOrThrow();
     if (database.singleInstance ?? false) {
       ffiSingleInstanceDbs.remove(database.path);
+
+      // Handle hot-restart for single instance
+      // The dart code is killed but the native code remains
+      // Remove the database from our cache
+      tracker.markClosed(database._ffiDb);
     }
     database.close();
   }

sqflite_common_ffi/pubspec.yaml

@@ -7,7 +7,7 @@ environment:
   sdk: ">=2.8.0 <3.0.0"
 
 dependencies:
-  sqlite3: '>=0.1.4 <1.0.0'
+  sqlite3: '>=0.1.6 <1.0.0'
   sqflite_common: '>=1.0.1 <3.0.0'
   synchronized: '>=2.0.2 <4.0.0'
   path: '>=1.5.1 <3.0.0'