Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/utils/file_pool.dart

Index: observatory_pub_packages/barback/src/utils/file_pool.dart
===================================================================
--- observatory_pub_packages/barback/src/utils/file_pool.dart	(revision 0)
+++ observatory_pub_packages/barback/src/utils/file_pool.dart	(working copy)
@@ -0,0 +1,66 @@
+// 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.utils.file_pool;
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:pool/pool.dart';
+import 'package:stack_trace/stack_trace.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;
+  }
+}