Optimize the message queue for many active ports with few messages.

runtime/vm/isolate.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "lib/mirrors.h"
 #include "vm/compiler_stats.h"
@@ skipping 71 matching lines @@
     (*callback)(Api::CastIsolate(isolate_));
   }
 }
 
 
 bool IsolateMessageHandler::HandleMessage(Message* message) {
   StartIsolateScope start_scope(isolate_);
   StackZone zone(isolate_);
   HandleScope handle_scope(isolate_);
 
+  // If the message is in band we lookup the receive port to dispatch to.  If
+  // the receive port is closed, we drop the message without deserializing it.
+  Object& receive_port = Object::Handle();
+  if (!message->IsOOB()) {
+    receive_port = DartLibraryCalls::LookupReceivePort(message->dest_port());
+    if (receive_port.IsError()) {
+      return ProcessUnhandledException(Instance::Handle(),
+                                       Error::Cast(receive_port));
+    }
+    if (receive_port.IsNull()) {
+      delete message;
+      return true;
+    }
+  }
+
   // Parse the message.
   SnapshotReader reader(message->data(), message->len(),
                         Snapshot::kMessage, Isolate::Current());
   const Object& msg_obj = Object::Handle(reader.ReadObject());
   if (msg_obj.IsError()) {
     // An error occurred while reading the message.
     return ProcessUnhandledException(Instance::Handle(), Error::Cast(msg_obj));
   }
   if (!msg_obj.IsNull() && !msg_obj.IsInstance()) {
     // TODO(turnidge): We need to decide what an isolate does with
     // malformed messages.  If they (eventually) come from a remote
     // machine, then it might make sense to drop the message entirely.
     // In the case that the message originated locally, which is
     // always true for now, then this should never occur.
     UNREACHABLE();
   }
 
   Instance& msg = Instance::Handle();
   msg ^= msg_obj.raw();  // Can't use Instance::Cast because may be null.
 
   bool success = true;
   if (message->IsOOB()) {
     // For now the only OOB messages are Mirrors messages.
     HandleMirrorsMessage(isolate_, message->reply_port(), msg);
   } else {
     const Object& result = Object::Handle(
         DartLibraryCalls::HandleMessage(
-            message->dest_port(), message->reply_port(), msg));
+            receive_port, message->reply_port(), msg));
     if (result.IsError()) {
       success = ProcessUnhandledException(msg, Error::Cast(result));
     } else {
       ASSERT(result.IsNull());
     }
   }
   delete message;
   return success;
 }
 
@@ skipping 471 matching lines @@
 
 
 void Isolate::VisitWeakPersistentHandles(HandleVisitor* visitor,
                                          bool visit_prologue_weak_handles) {
   if (api_state() != NULL) {
     api_state()->VisitWeakHandles(visitor, visit_prologue_weak_handles);
   }
 }
 
 }  // namespace dart