Handle collected objects and expired handles more gracefully.

runtime/vm/service.cc

 // 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.
 
 #include "vm/service.h"
 
 #include "include/dart_api.h"
 
 #include "vm/compiler.h"
 #include "vm/coverage.h"
@@ skipping 839 matching lines @@
   CHECK_COLLECTION_ID_BOUNDS("libraries", libs.Length(), js->GetArgument(1),
                              id, js);
   Library& lib = Library::Handle();
   lib ^= libs.At(id);
   ASSERT(!lib.IsNull());
   lib.PrintToJSONStream(js, false);
   return true;
 }
 
 
+static void PrintPseudoNull(JSONStream* js,
+                            const char* id,
+                            const char* preview) {
+  JSONObject jsobj(js);
+  jsobj.AddProperty("type", "Null");
+  jsobj.AddProperty("id", id);
+  jsobj.AddProperty("preview", preview);
+}
+
+
 static bool HandleObjects(Isolate* isolate, JSONStream* js) {
   REQUIRE_COLLECTION_ID("objects");
   ASSERT(js->num_arguments() >= 2);
   const char* arg = js->GetArgument(1);
 
   // TODO(turnidge): Handle <optimized out> the same way as other
   // special nulls.
-  if (strcmp(arg, "null") == 0 ||
-      strcmp(arg, "not-initialized") == 0 ||
-      strcmp(arg, "being-initialized") == 0 ||
-      strcmp(arg, "optimized-out") == 0) {
+  if (strcmp(arg, "null") == 0) {
     Object::null_object().PrintToJSONStream(js, false);
     return true;
 
+  } else if (strcmp(arg, "not-initialized") == 0) {
+    Object::sentinel().PrintToJSONStream(js, false);
+    return true;
+
+  } else if (strcmp(arg, "being-initialized") == 0) {
+    Object::transition_sentinel().PrintToJSONStream(js, false);
+    return true;
+
+  } else if (strcmp(arg, "optimized-out") == 0) {
+    Symbols::OptimizedOut().PrintToJSONStream(js, false);
+    return true;
+
+  } else if (strcmp(arg, "collected") == 0) {
+    PrintPseudoNull(js, "objects/collected", "<collected>");
+    return true;
+
+  } else if (strcmp(arg, "expired") == 0) {
+    PrintPseudoNull(js, "objects/expired", "<expired>");
+    return true;
+
   } else if (strcmp(arg, "int") == 0) {
     if (js->num_arguments() < 3) {
       PrintError(js, "expected 3 arguments but found %" Pd "\n",
                  js->num_arguments());
       return true;
     }
     int64_t value = 0;
     if (!OS::StringToInt64(js->GetArgument(2), &value) ||
         !Smi::IsValid64(value)) {
       PrintError(js, "integer value too large\n",
@@ skipping 26 matching lines @@
   }
 
   ObjectIdRing* ring = isolate->object_id_ring();
   ASSERT(ring != NULL);
   intptr_t id = -1;
   if (!GetIntegerId(arg, &id)) {
     Object::null_object().PrintToJSONStream(js, false);
     return true;
   }
   Object& obj = Object::Handle(ring->GetObjectForId(id));
+  if (obj.IsNull()) {
+    // The object has been collected by the gc.
+    PrintPseudoNull(js, "objects/collected", "<collected>");
+    return true;
+  } else if (obj.raw() == Object::sentinel().raw()) {
+    // The object id has expired.
+    PrintPseudoNull(js, "objects/expired", "<expired>");
+    return true;
+  }
   obj.PrintToJSONStream(js, false);
   return true;
 }
 
 
 
 static bool HandleScriptsEnumerate(Isolate* isolate, JSONStream* js) {
   JSONObject jsobj(js);
   jsobj.AddProperty("type", "ScriptList");
   JSONArray members(&jsobj, "members");
@@ skipping 430 matching lines @@
   while (current != NULL) {
     if (strcmp(name, current->name()) == 0) {
       return current;
     }
     current = current->next();
   }
   return NULL;
 }
 
 }  // namespace dart