Add Persistent<T>::Reset which disposes the handle and redirects it to point to another object.

test/cctest/test-api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2468 matching lines @@
   {
     v8::HandleScope scope(isolate);
     Local<String> str = v8_str("str");
     global = v8::Persistent<String>::New(isolate, str);
   }
   CHECK_EQ(global->Length(), 3);
   global.Dispose(isolate);
 }
 
 
+THREADED_TEST(ResettingGlobalHandle) {

[Sven Panne, 2013/05/07 09:49:31]

A test for passing an empty handle to reset is missing. Either add this test or
change the API, ASSERTing that it never happens. Don't know the call sites, so I
can't decide...

[marja, 2013/05/07 11:17:17]

Added a test here which says that after resetting to an empty handle, the handle
is empty.

+  v8::Isolate* isolate = v8::Isolate::GetCurrent();
+  v8::internal::GlobalHandles* global_handles = NULL;
+  int initial_handle_count = 0;
+  v8::Persistent<String> global;
+  {
+    v8::HandleScope scope(isolate);
+    Local<String> str = v8_str("str");
+    global_handles =
+        reinterpret_cast<v8::internal::Isolate*>(isolate)->global_handles();
+    initial_handle_count = global_handles->NumberOfGlobalHandles();
+    global = v8::Persistent<String>::New(isolate, str);
+  }
+  CHECK_EQ(global->Length(), 3);
+  CHECK_EQ(global_handles->NumberOfGlobalHandles(), initial_handle_count + 1);
+  {
+    v8::HandleScope scope(isolate);
+    Local<String> str = v8_str("longer");
+    global.Reset(isolate, str);
+  }
+  CHECK_EQ(global->Length(), 6);
+  CHECK_EQ(global_handles->NumberOfGlobalHandles(), initial_handle_count + 1);
+  global.Dispose(isolate);
+  CHECK_EQ(global_handles->NumberOfGlobalHandles(), initial_handle_count);
+}
+
+
 THREADED_TEST(LocalHandle) {
   v8::HandleScope scope(v8::Isolate::GetCurrent());
   v8::Local<String> local = v8::Local<String>::New(v8_str("str"));
   CHECK_EQ(local->Length(), 3);
 
   local = v8::Local<String>::New(v8::Isolate::GetCurrent(), v8_str("str"));
   CHECK_EQ(local->Length(), 3);
 }
 
 
@@ skipping 16394 matching lines @@
   i::Semaphore* sem_;
   volatile int sem_value_;
 };
 
 
 THREADED_TEST(SemaphoreInterruption) {
   ThreadInterruptTest().RunTest();
 }
 
 #endif  // WIN32