Reorganize barback's source files.

pkg/barback/lib/src/file_pool.dart

-// Copyright (c) 2013, 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.
-
-library barback.file_pool;
-
-import 'dart:async';
-import 'dart:convert';
-import 'dart:io';
-
-import 'package:stack_trace/stack_trace.dart';
-
-import 'pool.dart';
-import 'utils.dart';
-
-/// Manages a pool of files that are opened for reading to cope with maximum
-/// file descriptor limits.
-///
-/// If a file cannot be opened because too many files are already open, this
-/// will defer the open until a previously opened file is closed and then try
-/// again. If this doesn't succeed after a certain amount of time, the open
-/// will fail and the original "too many files" exception will be thrown.
-class FilePool {
-  /// The underlying pool.
-  ///
-  /// The maximum number of allocated descriptors is based on empirical tests
-  /// that indicate that beyond 32, additional file reads don't provide
-  /// substantial additional throughput.
-  final Pool _pool = new Pool(32, timeout: new Duration(seconds: 60));
-
-  /// Opens the file at [path] for reading.
-  ///
-  /// When the returned stream is listened to, if there are too many files
-  /// open, this will wait for a previously opened file to be closed and then
-  /// try again.
-  Stream<List<int>> openRead(String path) {
-    return futureStream(_pool.request().then((resource) {
-      return Chain.track(new File(path).openRead()).transform(
-          new StreamTransformer.fromHandlers(handleDone: (sink) {
-        sink.close();
-        resource.release();
-      }));
-    }));
-  }
-
-  /// Reads [path] as a string using [encoding].
-  ///
-  /// If there are too many files open and the read fails, this will wait for
-  /// a previously opened file to be closed and then try again.
-  Future<String> readAsString(String path, Encoding encoding) {
-    return _readAsBytes(path).then(encoding.decode);
-  }
-
-  /// Reads [path] as a list of bytes, using [openRead] to retry if there are
-  /// failures.
-  Future<List<int>> _readAsBytes(String path) {
-    var completer = new Completer<List<int>>();
-    var builder = new BytesBuilder();
-
-    openRead(path).listen(builder.add, onDone: () {
-      completer.complete(builder.takeBytes());
-    }, onError: completer.completeError, cancelOnError: true);
-
-    return completer.future;
-  }
-}