Cap the number of FDs used by barback at 32.

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:collection';
 import 'dart:convert';
 import 'dart:io';
@@ skipping 20 matching lines @@
   /// time a file finishes being read or a new file is opened. If it fires, that
   /// indicates that the caller became deadlocked, likely due to files waiting
   /// for additional files to be read before they could be closed.
   Timer _timer;
 
   /// The number of files currently open in the pool.
   int _openFiles = 0;
 
   /// The maximum number of file descriptors that the pool will allocate.
   ///
-  /// Barback may only use half the available file descriptors.
-  int get _maxOpenFiles => (maxFileDescriptors / 2).floor();
+  /// This is based on empirical tests that indicate that beyond 32, additional
+  /// file reads don't provide substantial additional throughput.
+  final int _maxOpenFiles = 32;

[dgrove, 2013/10/22 20:31:48]

Did you try measuring this on a variety of computers? This number seems pretty
low - if this is the case across powerful machines, can you please file a bug
with dart:io?

 
   /// Opens [file] 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(File file) {
     var reader = new _FileReader(this, file);
     if (_openFiles < _maxOpenFiles) {
       _openFiles++;
@@ skipping 122 matching lines @@
     _onDone();
   }
 
   /// Handles the underlying file stream finishing.
   void _onDone() {
     _subscription = null;
     _controller.close();
     _pool._startPendingListen();
   }
 }