Use file pool to handle running out of file descriptors.

pkg/barback/test/too_many_open_files_test.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.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();
+
+  runOnManyFiles(Future assetHandler(Asset asset)) {

[nweiz, 2013/10/16 00:16:01]

It feels like this should be defined at the top level or in utils. I find it
confusing to read in main(), where I just expect test cases.

[Bob Nystrom, 2013/10/16 00:51:46]

Done.

+    // 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);
+  }
+
+  test("handles many simultaneous asset read() calls", () {
+    runOnManyFiles((asset) {
+      var completer = new Completer();
+      var stream = asset.read();
+
+      stream.listen((data) {
+        // Do nothing.
+      }, onError: (error) {
+        completer.completeError(error);
+      }, onDone: () {
+        if (!completer.isCompleted) completer.complete();
+      });

[nweiz, 2013/10/16 00:16:01]

It would be cleaner just to return asset.read().toList().

[Bob Nystrom, 2013/10/16 00:51:46]

Indeed! Done.

+
+      return completer.future;
+    });
+  });
+
+  test("handles many simultaneous asset readToString() calls", () {
+    runOnManyFiles((asset) => asset.readAsString());
+  });
+}