[dart:io] Re-limit the number of IO Service ports per Isolate

runtime/bin/io_service_patch.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.
 
 class _IOServicePorts {
-  List<SendPort> _freeServicePorts = <SendPort>[];
-  HashMap<int, SendPort> _usedBy = new HashMap<int, SendPort>();
+  // We limit the number of IO Service ports per isolate so that we don't
+  // spawn too many threads all at once, which can crash the VM on Windows.
+  static const int maxPorts = 32;
+  List<SendPort> _ports = <SendPort>[];
+  List<SendPort> _freePorts = <SendPort>[];
+  HashMap<int, SendPort> _usedPorts = new HashMap<int, SendPort>();
 
   _IOServicePorts();
 
-  SendPort _getFreePort(int forRequestId) {
-    if (_freeServicePorts.isEmpty) {
-      _freeServicePorts.add(_newServicePort());
+  SendPort _getPort(int forRequestId) {
+    if (_freePorts.isEmpty && _usedPorts.length < maxPorts) {
+      final SendPort port = _newServicePort();
+      _ports.add(port);
+      _freePorts.add(port);
     }
-    SendPort freePort = _freeServicePorts.removeLast();
-    assert(!_usedBy.containsKey(forRequestId));
-    _usedBy[forRequestId] = freePort;
-    return freePort;
+    if (!_freePorts.isEmpty) {
+      final SendPort port = _freePorts.removeLast();
+      assert(!_usedPorts.containsKey(forRequestId));
+      _usedPorts[forRequestId] = port;
+      return port;
+    }
+    // We have already allocated the max number of ports. Re-use an
+    // existing one.
+    final SendPort port = _ports[forRequestId % maxPorts];
+    _usedPorts[forRequestId] = port;
+    return port;
   }
 
   void _returnPort(int forRequestId) {
-    _freeServicePorts.add(_usedBy.remove(forRequestId));
+    final SendPort port = _usedPorts.remove(forRequestId);
+    if (!_usedPorts.values.contains(port)) {
+      _freePorts.add(port);
+    }
   }
 
   static SendPort _newServicePort() native "IOService_NewServicePort";
 }
 
 @patch
 class _IOService {
   static _IOServicePorts _servicePorts = new _IOServicePorts();
   static RawReceivePort _receivePort;
   static SendPort _replyToPort;
   static HashMap<int, Completer> _messageMap = new HashMap<int, Completer>();
   static int _id = 0;
 
   @patch
   static Future _dispatch(int request, List data) {
     int id;
     do {
       id = _getNextId();
     } while (_messageMap.containsKey(id));
-    SendPort servicePort = _servicePorts._getFreePort(id);
+    final SendPort servicePort = _servicePorts._getPort(id);
     _ensureInitialize();
-    var completer = new Completer();
+    final Completer completer = new Completer();
     _messageMap[id] = completer;
     try {
       servicePort.send([id, _replyToPort, request, data]);
     } catch (error) {
       _messageMap.remove(id).complete(error);
       if (_messageMap.length == 0) {
         _finalize();
       }
     }
     return completer.future;
@@ skipping 18 matching lines @@
     _id = 0;
     _receivePort.close();
     _receivePort = null;
   }
 
   static int _getNextId() {
     if (_id == 0x7FFFFFFF) _id = 0;
     return _id++;
   }
 }