Pool future creation to ensure no more than 10 ops are in flight

pkg/barback/lib/src/phase.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.phase;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset_cascade.dart';
@@ skipping 255 matching lines @@
         if (_inputOrigins.contains(asset.origin)) {
           _forwarders[asset.id].addIntermediateAsset(asset);
           continue;
         }
 
         outputIds.add(asset.id);
         _addOutput(asset);
       }
     }
 
-    var outputFutures = [];
-    outputFutures.addAll(_inputs.values.map((input) {
-      if (!input.isDirty) return new Future.value(new Set());
-      return input.process().then(_handleOutputs);
-    }));
-    outputFutures.addAll(_groups.values.map((input) {
-      if (!input.isDirty) return new Future.value(new Set());
-      return input.process().then(_handleOutputs);
-    }));
+    var outputs = new List.from(_inputs.values);
+    outputs.addAll(_groups.values);
 
     // TODO(nweiz): handle pass-through.
 
-    return Future.wait(outputFutures).then((_) {
+    return forEachPooledFuture(outputs, (input) {
+      if (!input.isDirty) return null;
+      return input.process().then(_handleOutputs);
+    }).then((_) {
       // Report collisions in a deterministic order.
       outputIds = outputIds.toList();
       outputIds.sort((a, b) => a.compareTo(b));
       for (var id in outputIds) {
         // It's possible the output was removed before other transforms in this
         // phase finished.
         if (!_outputs.containsKey(id)) continue;
         var exception = _outputs[id].collisionException;
         if (exception != null) cascade.reportError(exception);
       }
     });
   }
 
   /// Add [asset] as an output of this phase.
   void _addOutput(AssetNode asset) {
     if (_outputs.containsKey(asset.id)) {
       _outputs[asset.id].add(asset);
     } else {
       _outputs[asset.id] = new PhaseOutput(this, asset);
       _outputs[asset.id].output.whenRemoved.then((_) {
         _outputs.remove(asset.id);
       });
       if (_next != null) _next.addInput(_outputs[asset.id].output);
     }
   }
 }