Dart: Merge message pipe query and read into one native call

mojo/public/dart/mojo/lib/src/message_pipe.dart

Index: mojo/public/dart/mojo/lib/src/message_pipe.dart
diff --git a/mojo/public/dart/mojo/lib/src/message_pipe.dart b/mojo/public/dart/mojo/lib/src/message_pipe.dart
index 62c7cb3a88bc6aa7f40bfd9fe09f2b547c2fffd9..faff0375c25467b60f807b3451aba180d63b2d76 100644
--- a/mojo/public/dart/mojo/lib/src/message_pipe.dart
+++ b/mojo/public/dart/mojo/lib/src/message_pipe.dart
@@ -19,11 +19,59 @@ class MojoMessagePipeReadResult {
   }
 }
 
+class MojoMessagePipeQueryAndReadState {
+  static ByteData _data;
+  static Uint32List _rawHandles;
+  static final List _result = new List(5);
+
+  MojoResult _status;
+  List<MojoHandle> _handles;
+  int _dataLength;
+  int _handlesLength;
+
+  MojoResult get status => _status;
+  List<MojoHandle> get handles => _handles;
+  int get dataLength => _dataLength;
+  int get handlesLength => _handlesLength;
+  ByteData get data => _data;
+
+  MojoMessagePipeQueryAndReadState()
+      : _dataLength = 0,
+        _handlesLength = 0;
+
+  void queryAndRead(int handle, int flags) {
+    MojoMessagePipeNatives.MojoQueryAndReadMessage(
+        handle, flags, _data, _rawHandles, _result);
+    _status = new MojoResult(_result[0]);

[Cutch, 2015/11/06 21:59:15]

I wonder if we could just keep _data, etc in the _result list and just pass that
back and forth?

[zra, 2015/11/06 23:35:42]

Done.

+    _data = _result[1];
+    _rawHandles = _result[2];
+    _dataLength = _result[3];
+    _handlesLength = _result[4];
+
+    if (_handlesLength == 0) {
+      _handles = null;
+    } else {
+      _handles = new List(_handlesLength);
+      for (int i = 0; i < _handlesLength; i++) {
+        _handles[i] = new MojoHandle(_rawHandles[i]);
+      }
+    }
+  }
+
+  String toString() {
+    return "MojoMessagePipeQueryAndReadState("
+        "status: $_status, dataLength: $dataLength, "
+        "handlesLength: $handlesLength)";
+  }
+}
+
 class MojoMessagePipeEndpoint {
   static const int WRITE_FLAG_NONE = 0;
   static const int READ_FLAG_NONE = 0;
   static const int READ_FLAG_MAY_DISCARD = 1 << 0;
 
+  static final _queryAndReadState = new MojoMessagePipeQueryAndReadState();
+
   MojoHandle handle;
   MojoResult status;
 
@@ -109,6 +157,19 @@ class MojoMessagePipeEndpoint {
 
   MojoMessagePipeReadResult query() => read(null);
 
+  // Warning: The object returned by this function, and the buffers inside of it
+  // are only valid until the next call to this function by the same isolate.

[Cutch, 2015/11/06 21:59:15]

Make this a doc comment. 

[zra, 2015/11/06 23:35:42]

Done.

+  MojoMessagePipeQueryAndReadState queryAndRead([int flags = 0]) {
+    if (handle == null) {
+      status = MojoResult.INVALID_ARGUMENT;
+      return null;
+    }
+
+    _queryAndReadState.queryAndRead(handle.h, flags);
+    status = _queryAndReadState.status;
+    return _queryAndReadState;
+  }
+
   bool setDescription(String description) {
     assert(MojoHandle._setHandleLeakDescription(handle, description));
     return true;