Implement async file API on top of isolates.

runtime/bin/file_impl.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _FileInputStream implements FileInputStream {
   _FileInputStream(File file) {
     _file = new File(file.name);
     _file.openSync();
   }
 
@@ skipping 72 matching lines @@
     }
   }
 
   void close() {
     _file.closeSync();
   }
 
   File _file;
 }
 
 

[Søren Gjesse, 2011/11/01 13:22:49]

Instead of using a Map for the operations one could consider using:

class FileOperation {
  static int EXISTS = 0;
  static int OPEN = 1;
  ...

  abstract int get type();
  var reply;
}

class FileExitsOperation {
  FileExitsOperation(String this._name);
  int get type() => FileOperation.EXISTS
  String get name() => _name;
  String _name;
}

class FileOpenOperation {
  FileOpenOperation(String this._name);
  int get type() => FileOperation.OPEN
  String get name() => _name;
  String _name;
}

...

[Mads Ager (google), 2011/11/01 14:04:31]

Yes, that would be cleaner. I would like to do that in a separate change.

+class _FileOperationIsolate extends Isolate {
+  static int EXISTS = 0;
+  static int OPEN = 1;
+  static int CLOSE = 2;
+  static int READ_BYTE = 3;
+  static int READ_LIST = 4;
+  static int WRITE_BYTE = 5;
+  static int WRITE_LIST = 6;
+  static int WRITE_STRING = 7;
+  static int POSITION = 8;
+  static int LENGTH = 9;
+  static int FLUSH = 10;
+  static int EXIT = 11;
+
+  _FileOperationIsolate() : super.heavy();
+
+  void handleOperation(Map message, SendPort ignored) {
+    switch (message["type"]) {
+      case EXISTS:
+        message["reply"].send(_File._exists(message["name"]),
+                              port.toSendPort());
+        break;
+      case OPEN:
+        var name = message["name"];
+        var writable = message["writable"];
+        message["reply"].send(_File._open(name, writable),
+                              port.toSendPort());
+        break;
+      case CLOSE:
+        message["reply"].send(_File._close(message["id"]),
+                              port.toSendPort());
+        break;
+      case READ_BYTE:
+        message["reply"].send(_File._readByte(message["id"]),
+                              port.toSendPort());
+        break;
+      case READ_LIST:
+        var replyPort = message["reply"];
+        var bytes = message["bytes"];
+        var offset = message["offset"];
+        var length = message["length"];
+        var id = message["id"];
+        if (bytes == 0) {
+          replyPort.send(0, port.toSendPort());
+          return;
+        }
+        if (offset < 0) {
+          replyPort.send("index out of range in readList: $offset",
+                         port.toSendPort());
+          return;
+        }
+        if (bytes < 0) {
+          replyPort.send("index out of range in readList: $bytes",
+                         port.toSendPort());
+          return;
+        }
+        if ((offset + bytes) > length) {
+          replyPort.send("index out of range in readList: ${offset + bytes}",
+                         port.toSendPort());
+          return;
+        }
+        var buffer = new List(bytes);

[Søren Gjesse, 2011/11/01 13:22:49]

Can't we just call writeByteSync in a try catch block and reply with the
exception if any? Now we are duplicating the arguments checking.

[Mads Ager (google), 2011/11/01 14:04:31]

Unfortunately not. In order to call writeByteSync we would need the file object.
I will extract read/write list parameter checking into a separate function to
share the code.

+        var result = { "read": _File._readList(id, buffer, 0, bytes),
+                       "buffer": buffer };
+        replyPort.send(result, port.toSendPort());
+        break;
+      case WRITE_BYTE:
+        message["reply"].send(_File._writeByte(message["id"], message["value"]),
+                              port.toSendPort());
+        break;
+      case WRITE_LIST:
+        var replyPort = message["reply"];
+        var buffer = message["buffer"];
+        var bytes = message["bytes"];
+        var offset = message["offset"];
+        var id = message["id"];
+        if (bytes == 0) {
+          replyPort.send(0, port.toSendPort());
+          return;
+        }
+        if (offset < 0) {
+          replyPort.send("index out of range in writeList: $offset",
+                         port.toSendPort());
+          return;
+        }
+        if (bytes < 0) {
+          replyPort.send("index out of range in writeList: $bytes",
+                         port.toSendPort());
+          return;
+        }
+        if ((offset + bytes) > buffer.length) {
+          replyPort.send("index out of range in writeList: ${offset + bytes}",
+                         port.toSendPort());
+          return;
+        }
+        var result = _File._writeList(id, buffer, offset, bytes);
+        replyPort.send(result, port.toSendPort());
+        break;
+      case WRITE_STRING:
+        var id = message["id"];
+        var string = message["string"];
+        message["reply"].send(_File._writeString(id, string),
+                              port.toSendPort());
+        break;
+      case POSITION:
+        message["reply"].send(_File._position(message["id"]),
+                              port.toSendPort());
+        break;
+      case LENGTH:
+        message["reply"].send(_File._length(message["id"]),
+                              port.toSendPort());
+        break;
+      case FLUSH:
+        message["reply"].send(_File._flush(message["id"]),
+                              port.toSendPort());
+        break;
+      case EXIT:
+        port.close();
+        return;
+    }
+    port.receive(handleOperation);
+  }
+
+  void main() {
+    port.receive(handleOperation);
+  }
+}
+
+
+class _FileOperationScheduler {
+  _FileOperationScheduler() : _queue = new Queue();
+
+  void schedule(SendPort port) {
+    assert(_isolate != null);
+    if (_queue.isEmpty()) {
+      port.send({ "type": _FileOperationIsolate.EXIT });
+      _isolate = null;
+    } else {
+      port.send(_queue.removeFirst());
+    }
+  }
+
+  void scheduleWrap(void callback(result, ignored)) {
+    return (result, replyTo) {
+      callback(result, replyTo);
+      schedule(replyTo);
+    };
+  }
+
+  void enqueue(Map params, void callback(result, ignored)) {
+    ReceivePort replyPort = new ReceivePort.singleShot();
+    replyPort.receive(scheduleWrap(callback));
+    params["reply"] = replyPort.toSendPort();
+    _queue.addLast(params);
+    if (_isolate == null) {
+      _isolate = new _FileOperationIsolate();
+      _isolate.spawn().then((port) {
+        schedule(port);
+      });
+    }
+  }
+
+  bool noPendingWrite() {
+    int queuedWrites = 0;
+    _queue.forEach((map) {
+      if (_isWriteOperation(map["type"])) {
+        queuedWrites++;
+      }
+    });
+    return queuedWrites == 0;
+  }
+
+  bool _isWriteOperation(int type) {
+    return (type == _FileOperationIsolate.WRITE_BYTE) ||
+        (type == _FileOperationIsolate.WRITE_LIST) ||
+        (type == _FileOperationIsolate.WRITE_STRING);
+  }
+
+  Queue<Map> _queue;
+  _FileOperationIsolate _isolate;
+}
+
+
 // Class for encapsulating the native implementation of files.
 class _File implements File {
   // Constructor for file.
-  _File(String this._name);
+  _File(String this._name)
+    : _scheduler = new _FileOperationScheduler(),
+      _asyncUsed = false;
+
+  static bool _exists(String name) native "File_Exists";
+  static int _open(String name, bool writable) native "File_Open";
+  static int _close(int id) native "File_Close";
+  static int _readByte(int id) native "File_ReadByte";
+  static int _readList(int id, List<int> buffer, int offset, int bytes)
+      native "File_ReadList";
+  static int _writeByte(int id, int value) native "File_WriteByte";
+  static int _writeList(int id, List<int> buffer, int offset, int bytes)
+      native "File_WriteList";
+  static int _writeString(int id, String string) native "File_WriteString";
+  static int _position(int id) native "File_Position";
+  static int _length(int id) native "File_Length";
+  static int _flush(int id) native "File_Flush";
 
   void exists() {
+    _asyncUsed = true;
+    var handler =
+        (_existsHandler != null) ? _existsHandler : (result) => null;
+    Map params = {
+      "type": _FileOperationIsolate.EXISTS,
+      "name": _name
+    };
+    _scheduler.enqueue(params, (result, ignored) { _existsHandler(result); });
+  }
+
+  bool existsSync() {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");

[Søren Gjesse, 2011/11/01 13:22:49]

Uppercase M in mixed.

[Mads Ager (google), 2011/11/01 14:04:31]

Thanks, done throughout the file.

+    }
+    return _exists(_name);
+  }
+
+  void create() {
+    _asyncUsed = true;
     throw "Unimplemented";
   }
 
-  bool existsSync() {
-    return _fileExists(_name);
-  }
-
-  bool _fileExists(String name) native "File_Exists";
-
-  void create() {
+  void createSync() {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
     throw "Unimplemented";
   }
 
-  void createSync() {
-    throw "Unimplemented";
-  }
-
   void open([bool writable = false]) {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handler = (_openHandler != null) ? _openHandler : () => null;
+    var handleOpenResult = (result, ignored) {
+      if (result != 0) {
+        _id = result;
+        handler();
+      } else if (_errorHandler != null) {
+        _errorHandler("Cannot open file: $_name");
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.OPEN,
+      "name": _name,
+      "writable": writable
+    };
+    _scheduler.enqueue(params, handleOpenResult);
   }
 
   void openSync([bool writable = false]) {
-    if (!_openFile(_name, writable)) {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    _id = _open(_name, writable);
+    if (_id == 0) {
       throw new FileIOException("Cannot open file: $_name");
     }
   }
 
-  bool _openFile(String name, bool writable) native "File_OpenFile";
-
   void close() {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handler = (_closeHandler != null) ? _closeHandler : () => null;
+    var handleOpenResult = (result, ignored) {
+      if (result != -1) {
+        _id = result;
+        handler();
+      } else if (_errorHandler != null) {
+        _errorHandler("Cannot open file: $_name");
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.CLOSE,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleOpenResult);
   }
 
   void closeSync() {
-    _close();
-  }
-
-  int _close() native "File_Close";
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    _id = _close(_id);
+    if (_id == -1) {
+      throw new FileIOException("Cannot close file: $_name");
+    }
+  }
 
   void readByte() {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handler =
+        (_readByteHandler != null) ? _readByteHandler : (byte) => null;
+    var handleReadByteResult = (result, ignored) {
+      if (result != -1) {
+        handler(result);
+      } else if (_errorHandler != null) {
+        _errorHandler("readByte failed");
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.READ_BYTE,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleReadByteResult);
   }
 
   int readByteSync() {
-    int result = _readByte();
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _readByte(_id);
     if (result == -1) {
-      throw new FileIOException("Error: readByte failed");
+      throw new FileIOException("readByte failed");
     }
     return result;
   }
 
-  int _readByte() native "File_ReadByte";
-
   void readList(List<int> buffer, int offset, int bytes) {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handler =
+        (_readListHandler != null) ? _readListHandler : (result) => null;
+    var errorHandler =

[Søren Gjesse, 2011/11/01 13:22:49]

is "var errorHandler" actually used?

[Mads Ager (google), 2011/11/01 14:04:31]

Done.

+        (_errorHandler != null) ? _errorHandler : (error) => null;
+    var handleReadListResult = (result, ignored) {
+      if (result is Map && result["read"] != -1) {
+        var read = result["read"];
+        buffer.setRange(offset, read, result["buffer"]);
+        handler(read);
+        return;
+      }
+      if (_errorHandler != null) {
+        _errorHandler(result is String ? result : "readList failed");
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.READ_LIST,
+      "length": buffer.length,
+      "offset": offset,
+      "bytes": bytes,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleReadListResult);
   }
 
   int readListSync(List<int> buffer, int offset, int bytes) {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
     if (bytes == 0) {
       return 0;
     }
     if (offset < 0) {
       throw new IndexOutOfRangeException(offset);
     }
     if (bytes < 0) {
       throw new IndexOutOfRangeException(bytes);
     }
     if ((offset + bytes) > buffer.length) {
       throw new IndexOutOfRangeException(offset + bytes);
     }
-    int result = _readList(buffer, offset, bytes);
+    int result = _readList(_id, buffer, offset, bytes);
     if (result == -1) {
-      throw new FileIOException("Error: readList failed");
+      throw new FileIOException("readList failed");
     }
     return result;
   }
 
-  int _readList(List<int> buffer, int offset, int bytes) native "File_ReadList";
+  void _checkPendingWrites() {
+    if (_scheduler.noPendingWrite() && _noPendingWriteHandler != null) {
+      _noPendingWriteHandler();
+    }
+  }
 
   void writeByte(int value) {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handleReadByteResult = (result, ignored) {
+      if (result == -1 &&_errorHandler != null) {
+        _errorHandler("writeByte failed");
+        return;
+      }
+      _checkPendingWrites();
+    };
+    Map params = {
+      "type": _FileOperationIsolate.WRITE_BYTE,
+      "value": value,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleReadByteResult);
   }
 
   int writeByteSync(int value) {
-    int result = _writeByte(value);
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _writeByte(_id, value);
     if (result == -1) {
-      throw new FileIOException("Error: writeByte failed");
+      throw new FileIOException("writeByte failed");
     }
     return result;
   }
 
-  int _writeByte(int value) native "File_WriteByte";
-
-  int writeList(List<int> buffer, int offset, int bytes) {
-    throw "Unimplemented";
+  void writeList(List<int> buffer, int offset, int bytes) {
+    _asyncUsed = true;
+    var errorHandler =

[Søren Gjesse, 2011/11/01 13:22:49]

var errorHandler used?

[Mads Ager (google), 2011/11/01 14:04:31]

Done.

+        (_errorHandler != null) ? _errorHandler : (error) => null;
+    var handleWriteListResult = (result, ignored) {
+      if (result is !String && result != -1) {
+        if (result < bytes) {
+          writeList(buffer, offset + result, bytes - result);
+        } else {
+          _checkPendingWrites();
+        }
+        return;
+      }
+      if (_errorHandler != null) {
+        _errorHandler(result is String ? result : "writeList failed");
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.WRITE_LIST,
+      "buffer": buffer,
+      "offset": offset,
+      "bytes": bytes,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleWriteListResult);
   }
 
   int writeListSync(List<int> buffer, int offset, int bytes) {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
     if (bytes == 0) {
       return 0;
     }
     if (offset < 0) {
       throw new IndexOutOfRangeException(offset);
     }
     if (bytes < 0) {
       throw new IndexOutOfRangeException(bytes);
     }
     if ((offset + bytes) > buffer.length) {
       throw new IndexOutOfRangeException(offset + bytes);
     }
-    int result = _writeList(buffer, offset, bytes);
+    int result = _writeList(_id, buffer, offset, bytes);
     if (result == -1) {
-      throw new FileIOException("Error: writeList failed");
+      throw new FileIOException("writeList failed");
     }
     return result;
   }
 
-  int _writeList(List<int> buffer, int offset, int bytes)
-      native "File_WriteList";
-
-  int writeString(String string) {
-    throw "Unimplemented";
+  void writeString(String string) {
+    _asyncUsed = true;
+    var handleWriteStringResult = (result, ignored) {
+      if (result == -1 &&_errorHandler != null) {
+        _errorHandler("writeString failed");
+        return;
+      }
+      if (result < string.length) {
+        writeString(string.substring(result));
+      } else {
+        _checkPendingWrites();
+      }
+    };
+    Map params = {
+      "type": _FileOperationIsolate.WRITE_STRING,
+      "string": string,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleWriteStringResult);
   }
 
   int writeStringSync(String string) {
-    int result = _writeString(string);
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _writeString(_id, string);
     if (result == -1) {
       throw new FileIOException("Error: writeString failed");
     }
     return result;
   }
 
-  int _writeString(String string) native "File_WriteString";
-
-  int position() {
-    throw "Unimplemented";
+  void position() {
+    _asyncUsed = true;
+    var handler = (_positionHandler != null) ? _positionHandler : (pos) => null;
+    var handlePositionResult = (result, ignored) {
+      if (result == -1 && _errorHandler != null) {
+        _errorHandler("position failed");
+        return;
+      }
+      handler(result);
+    };
+    Map params = {
+      "type": _FileOperationIsolate.POSITION,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handlePositionResult);
   }
 
   int positionSync() {
-    int result = _position;
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _position(_id);
     if (result == -1) {
-      throw new FileIOException("Error: get position failed");
+      throw new FileIOException("position failed");
     }
     return result;
   }
 
-  int get _position() native "File_Position";
-
-  int length() {
-    throw "Unimplemented";
+  void length() {
+    _asyncUsed = true;
+    var handler = (_lengthHandler != null) ? _lengthHandler : (pos) => null;
+    var handleLengthResult = (result, ignored) {
+      if (result == -1 && _errorHandler != null) {
+        _errorHandler("length failed");
+        return;
+      }
+      handler(result);
+    };
+    Map params = {
+      "type": _FileOperationIsolate.LENGTH,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleLengthResult);
   }
 
   int lengthSync() {
-    int result = _length;
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _length(_id);
     if (result == -1) {
-      throw new FileIOException("Error: get length failed");
+      throw new FileIOException("length failed");
     }
     return result;
   }
 
-  int get _length() native "File_Length";
-
   void flush() {
-    throw "Unimplemented";
+    _asyncUsed = true;
+    var handler = (_flushHandler != null) ? _flushHandler : (pos) => null;
+    var handleFlushResult = (result, ignored) {
+      if (result == -1 && _errorHandler != null) {
+        _errorHandler("flush failed");
+        return;
+      }
+      handler();
+    };
+    Map params = {
+      "type": _FileOperationIsolate.FLUSH,
+      "id": _id
+    };
+    _scheduler.enqueue(params, handleFlushResult);
   }
 
   void flushSync() {
-    int result = _flush();
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "mixed use of synchronous and asynchronous API");
+    }
+    int result = _flush(_id);
     if (result == -1) {
-      throw new FileIOException("Error: flush failed");
+      throw new FileIOException("flush failed");
     }
   }
 
-  int _flush() native "File_Flush";
-
   InputStream openInputStream() {
     return new _FileInputStream(this);
   }
 
   OutputStream openOutputStream() {
     return new _FileOutputStream(this);
   }
 
   String get name() {
     return _name;
@@ skipping 20 matching lines @@
   }
 
   void set readListHandler(void handler(int read)) {
     _readListHandler = handler;
   }
 
   void set noPendingWriteHandler(void handler()) {
     _noPendingWriteHandler = handler;
   }
 
+  void set positionHandler(void handler(int pos)) {
+    _positionHandler = handler;
+  }
+
+  void set lengthHandler(void handler(int length)) {
+    _lengthHandler = handler;
+  }
+
+  void set flushHandler(void handler()) {
+    _flushHandler = handler;
+  }
+
   void set errorHandler(void handler(String error)) {
     _errorHandler = handler;
   }
 
   String _name;
   int _id;
+  bool _asyncUsed;
+
+  _FileOperationScheduler _scheduler;
 
   var _existsHandler;
   var _createHandler;
   var _openHandler;
   var _closeHandler;
   var _readByteHandler;
   var _readListHandler;
   var _noPendingWriteHandler;
+  var _positionHandler;
+  var _lengthHandler;
+  var _flushHandler;
   var _errorHandler;
 }