Use file pool to handle running out of file descriptors.

pkg/barback/test/too_many_open_files_test.dart

Index: pkg/barback/test/too_many_open_files_test.dart
diff --git a/pkg/barback/test/too_many_open_files_test.dart b/pkg/barback/test/too_many_open_files_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b45af71377690d74613f753e5b1fea884b650ecf
--- /dev/null
+++ b/pkg/barback/test/too_many_open_files_test.dart
@@ -0,0 +1,55 @@
+// 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.test.too_many_open_files_test;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:barback/barback.dart';
+import 'package:path/path.dart' as pathos;
+import 'package:unittest/unittest.dart';
+
+import 'utils.dart';
+
+main() {
+  initConfig();
+
+  test("handles many simultaneous asset read() calls", () {
+    runOnManyFiles((asset) => asset.read().toList());
+  });
+
+  test("handles many simultaneous asset readToString() calls", () {
+    runOnManyFiles((asset) => asset.readAsString());
+  });
+}
+
+runOnManyFiles(Future assetHandler(Asset asset)) {
+  // Make a text file in a temp directory.
+  var tempDir = Directory.systemTemp.createTempSync("barback").path;
+  var filePath = pathos.join(tempDir, "out.txt");
+
+  // Make sure it's large enough to not be read in a single chunk.
+  var contents = new StringBuffer();
+  for (var i = 0; i < 1024; i++) {
+    contents.write(
+        "this is a sixty four character long string that describes itself");
+  }
+
+  new File(filePath).writeAsStringSync(contents.toString());
+
+  var id = new AssetId("myapp", "out.txt");
+
+  // Create a large number of assets, larger than the file descriptor limit
+  // of most machines and start reading from all of them.
+  var futures = [];
+  for (var i = 0; i < 1000; i++) {
+    var asset = new Asset.fromPath(id, filePath);
+    futures.add(assetHandler(asset));
+  }
+
+  expect(Future.wait(futures).whenComplete(() {
+    new Directory(tempDir).delete(recursive: true);
+  }), completes);
+}