Get all Sqlite connections in the pool

packages/sqlite_async/lib/src/common/sqlite_database.dart

@@ -39,6 +39,14 @@ mixin SqliteDatabaseMixin implements SqliteConnection, SqliteQueries {
   ///
   /// Use this to access the database in background isolates.
   IsolateConnectionFactory isolateConnectionFactory();
+
+  /// Locks all underlying connections making up this database, and gives [block] access to all of them at once.
+  /// This can be useful to run the same statement on all connections. For instance,
+  /// ATTACHing a database, that is expected to be available in all connections.
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block);
 }
 
 /// A SQLite database instance.

packages/sqlite_async/lib/src/impl/single_connection_database.dart

@@ -57,4 +57,12 @@ final class SingleConnectionDatabase
     return connection.writeLock(callback,
         lockTimeout: lockTimeout, debugContext: debugContext);
   }
+
+  @override
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) {
+    return writeLock((_) => block(connection, []));
+  }
 }

packages/sqlite_async/lib/src/impl/stub_sqlite_database.dart

@@ -64,4 +64,12 @@ class SqliteDatabaseImpl
   Future<bool> getAutoCommit() {
     throw UnimplementedError();
   }
+
+  @override
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) {
+    throw UnimplementedError();
+  }
 }

packages/sqlite_async/lib/src/native/database/connection_pool.dart

@@ -31,6 +31,8 @@ class SqliteConnectionPool with SqliteQueries implements SqliteConnection {
 
   final MutexImpl mutex;
 
+  int _runningWithAllConnectionsCount = 0;
+
   @override
   bool closed = false;
 
@@ -88,6 +90,14 @@ class SqliteConnectionPool with SqliteQueries implements SqliteConnection {
       return;
     }
 
+    if (_availableReadConnections.isEmpty &&
+        _runningWithAllConnectionsCount > 0) {
+      // Wait until [withAllConnections] is done. Otherwise we could spawn a new
+      // reader while the user is configuring all the connections,
+      // e.g. a global open factory configuration shared across all connections.
+      return;
+    }
+
     var nextItem = _queue.removeFirst();
     while (nextItem.completer.isCompleted) {
       // This item already timed out - try the next one if available
@@ -232,6 +242,66 @@ class SqliteConnectionPool with SqliteQueries implements SqliteConnection {
       await connection.refreshSchema();
     }
   }
+
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) async {
+    try {
+      _runningWithAllConnectionsCount++;
+
+      final blockCompleter = Completer<T>();
+      final (write, reads) = await _lockAllConns<T>(blockCompleter);
+
+      try {
+        final res = await block(write, reads);
+        blockCompleter.complete(res);
+        return res;
+      } catch (e, st) {
+        blockCompleter.completeError(e, st);
+        rethrow;
+      }
+    } finally {
+      _runningWithAllConnectionsCount--;
+
+      // Continue processing any pending read requests that may have been queued while
+      // the block was running.
+      Timer.run(_nextRead);
+    }
+  }
+
+  /// Locks all connections, returning the acquired contexts.
+  /// We pass a completer that would be called after the locks are taken.
+  Future<(SqliteWriteContext, List<SqliteReadContext>)> _lockAllConns<T>(
+      Completer<T> lockCompleter) async {
+    final List<Completer<SqliteReadContext>> readLockedCompleters = [];
+    final Completer<SqliteWriteContext> writeLockedCompleter = Completer();
+
+    // Take the write lock
+    writeLock((ctx) {
+      writeLockedCompleter.complete(ctx);
+      return lockCompleter.future;
+    });
+
+    // Take all the read locks
+    for (final readConn in _allReadConnections) {
+      final completer = Completer<SqliteReadContext>();
+      readLockedCompleters.add(completer);
+
+      readConn.readLock((ctx) {
+        completer.complete(ctx);
+        return lockCompleter.future;
+      });
+    }
+
+    // Wait after all locks are taken
+    final [writer as SqliteWriteContext, ...readers] = await Future.wait([
+      writeLockedCompleter.future,
+      ...readLockedCompleters.map((e) => e.future)
+    ]);
+
+    return (writer, readers);
+  }
 }
 
 typedef ReadCallback<T> = Future<T> Function(SqliteReadContext tx);

packages/sqlite_async/lib/src/native/database/native_sqlite_database.dart

@@ -171,4 +171,12 @@ class SqliteDatabaseImpl
   Future<void> refreshSchema() {
     return _pool.refreshSchema();
   }
+
+  @override
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) {
+    return _pool.withAllConnections(block);
+  }
 }

packages/sqlite_async/lib/src/web/database.dart

@@ -171,6 +171,14 @@ class WebDatabase
     await isInitialized;
     return _database.fileSystem.flush();
   }
+
+  @override
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) {
+    return writeLock((_) => block(this, []));
+  }
 }
 
 final class _UnscopedContext extends UnscopedContext {

packages/sqlite_async/lib/src/web/database/web_sqlite_database.dart

@@ -178,4 +178,12 @@ class SqliteDatabaseImpl
   Future<WebDatabaseEndpoint> exposeEndpoint() async {
     return await _connection.exposeEndpoint();
   }
+
+  @override
+  Future<T> withAllConnections<T>(
+      Future<T> Function(
+              SqliteWriteContext writer, List<SqliteReadContext> readers)
+          block) {
+    return writeLock((_) => block(_connection, []));
+  }
 }

packages/sqlite_async/test/basic_test.dart

@@ -7,6 +7,7 @@ import 'utils/test_utils_impl.dart';
 
 final testUtils = TestUtils();
 const _isDart2Wasm = bool.fromEnvironment('dart.tool.dart2wasm');
+const _isWeb = identical(0, 0.0) || _isDart2Wasm;
 
 void main() {
   group('Shared Basic Tests', () {
@@ -301,6 +302,49 @@ void main() {
         'Web locks are managed with a shared worker, which does not support timeouts',
       )
     });
+
+    test('with all connections', () async {
+      final maxReaders = _isWeb ? 0 : 3;
+
+      final db = SqliteDatabase.withFactory(
+        await testUtils.testFactory(path: path),
+        maxReaders: maxReaders,
+      );
+      await db.initialize();
+      await createTables(db);
+
+      // Warm up to spawn the max readers
+      await Future.wait([for (var i = 0; i < 10; i++) db.get('SELECT $i')]);
+
+      bool finishedWithAllConns = false;
+
+      late Future<void> readsCalledWhileWithAllConnsRunning;
+
+      final parentZone = Zone.current;
+      await db.withAllConnections((writer, readers) async {
+        expect(readers.length, maxReaders);
+
+        // Run some reads during the block that they should run after the block finishes and releases
+        // all locks
+        // Need a root zone here to avoid recursive lock errors.
+        readsCalledWhileWithAllConnsRunning =
+            Future(parentZone.bindCallback(() async {
+          await Future.wait(
+            [1, 2, 3, 4, 5, 6, 7, 8].map((i) async {
+              await db.readLock((c) async {
+                expect(finishedWithAllConns, isTrue);
+                await Future.delayed(const Duration(milliseconds: 100));
+              });
+            }),
+          );
+        }));
+
+        await Future.delayed(const Duration(milliseconds: 200));
+        finishedWithAllConns = true;
+      });
+
+      await readsCalledWhileWithAllConnsRunning;
+    });
   });
 }