Dart: Performance improvements to Dart's handle watcher.

mojo/public/dart/mojo/sdk_ext/src/wait_many_state.dart

Index: mojo/public/dart/mojo/sdk_ext/src/wait_many_state.dart
diff --git a/mojo/public/dart/mojo/sdk_ext/src/wait_many_state.dart b/mojo/public/dart/mojo/sdk_ext/src/wait_many_state.dart
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index 0000000000000000000000000000000000000000..ea388e5a142bba9972a30e789cc5578ae019eeff
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+++ b/mojo/public/dart/mojo/sdk_ext/src/wait_many_state.dart
@@ -0,0 +1,138 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+part of internal;
+
+class WaitManyState {
+  static const int _GROWTH_SIZE = 100;
+  Uint32List _handles;
+  Uint32List _signals;
+  Uint32List _outIndex;
+  Uint64List _outSignals;
+
+  // A port for each handle on which to send events back to the isolate that
+  // owns the handle.
+  List<SendPort> _ports;
+
+  // A mapping from Mojo handles to their indices in _handles.
+  Map<int, int> _handleIndices;
+
+  int _occupied;
+
+  WaitManyState() {
+    _ports = [];
+    _handleIndices = new Map<int, int>();
+    _occupied = 0;
+    _grow();
+  }
+
+  int get length => _occupied;
+  Uint32List get handles => _handles;
+  Uint32List get signals => _signals;
+  List<SendPort> get ports => _ports;
+  Map<int, int> get handleIndices => _handleIndices;
+
+  // Output of calls to waitMany.
+  int mojoResult;
+  int get outIndex => _outIndex[0];
+  int outSignals(int idx) =>
+      _outSignals[idx] & MojoHandleWatcher.kMojoSignalsAll;
+
+  void waitMany(int deadline) {
+    mojoResult = MojoHandleWatcherNatives.waitMany(_occupied, deadline);
+  }
+
+  // The control handle lives at entry zero. So we add new entries at
+  // index 1, shifting the existing entries down by 1. The idea here is that
+  // more active handles will tend to be at the front of the list.
+  void addFront(int handle, int signals, SendPort port) {
+    if (_occupied == 0) {
+      add(handle, signals, port);
+      return;
+    }
+
+    // Grow if needed.
+    if (_occupied == _handles.length) {
+      _grow();
+    }
+
+    // Shift existing entries down by one.
+    for (int i = _occupied - 1; i >= 1; i--) {
+      int h = _handles[i];
+      _handleIndices[h] = i + 1;
+      _handles[i + 1] = h;
+      _signals[i + 1] = _signals[i];
+      _ports[i + 1] = _ports[i];
+    }
+
+    // Insert new entry.
+    _handleIndices[handle] = 1;
+    _handles[1] = handle;
+    _signals[1] = signals;
+    _ports[1] = port;
+    _occupied++;
+  }
+
+  void add(int handle, int signals, SendPort port) {
+    if (_occupied == _handles.length) {
+      _grow();
+    }
+    _handleIndices[handle] = _occupied;
+    _handles[_occupied] = handle;
+    _signals[_occupied] = signals;
+    _ports[_occupied] = port;
+    _occupied++;
+  }
+
+  void removeLast() {
+    int handle = _handles[_occupied - 1];
+    _handleIndices[handle] = null;
+    _handles[_occupied - 1] = 0;
+    _signals[_occupied - 1] = 0;
+    _ports[_occupied - 1] = null;
+    _occupied--;
+  }
+
+  void remove(int idx) {
+    if (idx == (_occupied - 1)) {
+      removeLast();
+      return;
+    }
+    // Copy the last element over the one being removed.
+    int last = _occupied - 1;
+    _handleIndices.remove(_handles[idx]);
+    _handles[idx] = _handles[last];
+    _signals[idx] = _signals[last];
+    _ports[idx] = _ports[last];
+
+    // Remove the old copy.
+    removeLast();
+    _handleIndices[_handles[idx]] = idx;
+  }
+
+  void _grow() {
+    int newSize = _occupied + _GROWTH_SIZE;
+    List newArrays =
+        MojoHandleWatcherNatives.growStateArrays(_occupied + _GROWTH_SIZE);
+    _handles = newArrays[0];
+    _signals = newArrays[1];
+    _outIndex = newArrays[2];
+    _outSignals = newArrays[3];
+    _ports.length = _handles.length;
+  }
+
+  String toString() {
+    String hands = "";
+    String sigs = "";
+    for (int i = 0; i < _occupied; i++) {
+      hands = "$hands ${_handles[i]}";
+      sigs = "$sigs ${_outSignals[i] & _signals[i]}";
+    }
+    return "length: $_occupied\n"
+        "status: $result\n"
+        "index: $index\n"
+        "handles: $hands\n"
+        "signals: $sigs\n";
+  }
+}