Adds a special case for sending an int over a port with the native API.

runtime/vm/message.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_MESSAGE_H_
 #define VM_MESSAGE_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 19 matching lines @@
   // Values defining the type of OOB messages. OOB messages can only be
   // fixed length arrays where the first element is a Smi with one of the
   // valid values below.
   typedef enum {
     kIllegalOOB = 0,
     kServiceOOBMsg = 1,
     kIsolateLibOOBMsg = 2,
     kDelayedIsolateLibOOBMsg = 3,
   } OOBMsgTag;
 
+  typedef enum {
+    kDataType = 0,
+    kIntegerType = 1,
+    kNumTypes = 2,
+  } MessageType;
+
   // A port number which is never used.
   static const Dart_Port kIllegalPort = 0;
 
   // A new message to be sent between two isolates. The data handed to this
   // message will be disposed by calling free() once the message object is
   // being destructed (after delivery or when the receiving port is closed).
   Message(Dart_Port dest_port,
           uint8_t* data,
           intptr_t len,
           Priority priority,
           Dart_Port delivery_failure_port = kIllegalPort)
       : next_(NULL),
         dest_port_(dest_port),
         delivery_failure_port_(delivery_failure_port),
-        data_(data),
-        len_(len),
-        priority_(priority) {
+        priority_(priority),
+        type_(kDataType) {
     ASSERT((priority == kNormalPriority) ||
            (delivery_failure_port == kIllegalPort));
+    data_.buffer.data = data;
+    data_.buffer.len = len;
+  }
+  Message(Dart_Port dest_port,
+          intptr_t data,
+          Priority priority,
+          Dart_Port delivery_failure_port = kIllegalPort)
+      : next_(NULL),
+        dest_port_(dest_port),
+        delivery_failure_port_(delivery_failure_port),
+        priority_(priority),
+        type_(kIntegerType) {
+    ASSERT((priority == kNormalPriority) ||
+           (delivery_failure_port == kIllegalPort));
+    data_.integer = data;
   }
   ~Message() {
     ASSERT(delivery_failure_port_ == kIllegalPort);
-    free(data_);
+    if (type_ == kDataType) {
+      free(data_.buffer.data);
+    }
   }
 
   Dart_Port dest_port() const { return dest_port_; }
-  uint8_t* data() const { return data_; }
-  intptr_t len() const { return len_; }
+  MessageType type() const { return type_; }
+  uint8_t* data() const {
+    ASSERT(type_ == kDataType);
+    return data_.buffer.data;
+  }
+  intptr_t len() const {
+    ASSERT(type_ == kDataType);
+    return data_.buffer.len;
+  }
+  intptr_t integer() const {
+    ASSERT(type_ == kIntegerType);
+    return data_.integer;
+  }
   Priority priority() const { return priority_; }
 
   bool IsOOB() const { return priority_ == Message::kOOBPriority; }
 
   bool RedirectToDeliveryFailurePort();
 
   intptr_t Id() const;
 
   static const char* PriorityAsString(Priority priority);
 
  private:
   friend class MessageQueue;
 
   Message* next_;
   Dart_Port dest_port_;
   Dart_Port delivery_failure_port_;
-  uint8_t* data_;
-  intptr_t len_;
+  union {
+    struct {
+      uint8_t* data;
+      intptr_t len;
+    } buffer;  // Avtive when type_ == kDataType.
+    intptr_t integer;  // Active when type_ == kIntegerType.

[Ivan Posva, 2015/12/08 08:25:55]

Let's discuss this change in person to figure out whether there are more ways of
optimizing this.

+  } data_;
   Priority priority_;
+  MessageType type_;
 
   DISALLOW_COPY_AND_ASSIGN(Message);
 };
 
 // There is a message queue per isolate.
 class MessageQueue {
  public:
   MessageQueue();
   ~MessageQueue();
 
@@ skipping 36 matching lines @@
  private:
   Message* head_;
   Message* tail_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageQueue);
 };
 
 }  // namespace dart
 
 #endif  // VM_MESSAGE_H_