Don't externalize fresh strings.

test/cctest/test-api.cc

 // Copyright 2007-2009 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 376 matching lines @@
 }
 
 
 THREADED_TEST(ScriptMakingExternalString) {
   TestResource::dispose_count = 0;
   uint16_t* two_byte_source = AsciiToTwoByteString("1 + 2 * 3");
   {
     v8::HandleScope scope;
     LocalContext env;
     Local<String> source = String::New(two_byte_source);
+    // Trigger GCs so that the newly allocated string moves to old gen.
+    i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in survivor space now
+    i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in old gen now
     bool success = source->MakeExternal(new TestResource(two_byte_source));
     CHECK(success);
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     v8::internal::Heap::CollectAllGarbage(false);
     CHECK_EQ(0, TestResource::dispose_count);
   }
   v8::internal::CompilationCache::Clear();
   v8::internal::Heap::CollectAllGarbage(false);
   CHECK_EQ(1, TestResource::dispose_count);
 }
 
 
 THREADED_TEST(ScriptMakingExternalAsciiString) {
   TestAsciiResource::dispose_count = 0;
   const char* c_source = "1 + 2 * 3";
   {
     v8::HandleScope scope;
     LocalContext env;
     Local<String> source = v8_str(c_source);
+    // Trigger GCs so that the newly allocated string moves to old gen.
+    i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in survivor space now
+    i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in old gen now
     bool success = source->MakeExternal(
         new TestAsciiResource(i::StrDup(c_source)));
     CHECK(success);
     Local<Script> script = Script::Compile(source);
     Local<Value> value = script->Run();
     CHECK(value->IsNumber());
     CHECK_EQ(7, value->Int32Value());
     v8::internal::Heap::CollectAllGarbage(false);
     CHECK_EQ(0, TestAsciiResource::dispose_count);
   }
   v8::internal::CompilationCache::Clear();
   v8::internal::Heap::CollectAllGarbage(false);
   CHECK_EQ(1, TestAsciiResource::dispose_count);
 }
 
 
+TEST(MakingExternalStringConditions) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  // Free some space in the new space so that we can check freshness.
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);
+
+  Local<String> small_string = String::New(AsciiToTwoByteString("small"));
+  // We should refuse to externalize newly created small string.
+  CHECK(!small_string->CanMakeExternal());
+  // Trigger GCs so that the newly allocated string moves to old gen.
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in survivor space now
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in old gen now
+  // Old space strings should be accepted.
+  CHECK(small_string->CanMakeExternal());
+
+  small_string = String::New(AsciiToTwoByteString("small 2"));
+  // We should refuse externalizing newly created small string.
+  CHECK(!small_string->CanMakeExternal());
+  for (int i = 0; i < 100; i++) {
+    String::Value value(small_string);
+  }
+  // Frequently used strings should be accepted.
+  CHECK(small_string->CanMakeExternal());
+
+  const int buf_size = 10 * 1024;
+  char* buf = i::NewArray<char>(buf_size);
+  memset(buf, 'a', buf_size);
+  buf[buf_size - 1] = '\0';
+  Local<String> large_string = String::New(AsciiToTwoByteString(buf));
+  i::DeleteArray(buf);
+  // Large strings should be immediately accepted.
+  CHECK(small_string->CanMakeExternal());

[Mads Ager (chromium), 2010/02/16 08:16:19]

small_ -> large_

[Vitaly Repeshko, 2010/02/16 18:56:42]

Oops. Done.

+}
+
+
+TEST(MakingExternalAsciiStringConditions) {
+  v8::HandleScope scope;
+  LocalContext env;
+
+  // Free some space in the new space so that we can check freshness.
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);
+
+  Local<String> small_string = String::New("small");
+  // We should refuse to externalize newly created small string.
+  CHECK(!small_string->CanMakeExternal());
+  // Trigger GCs so that the newly allocated string moves to old gen.
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in survivor space now
+  i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in old gen now
+  // Old space strings should be accepted.
+  CHECK(small_string->CanMakeExternal());
+
+  small_string = String::New("small 2");
+  // We should refuse externalizing newly created small string.
+  CHECK(!small_string->CanMakeExternal());
+  for (int i = 0; i < 100; i++) {
+    String::Value value(small_string);
+  }
+  // Frequently used strings should be accepted.
+  CHECK(small_string->CanMakeExternal());
+
+  const int buf_size = 10 * 1024;
+  char* buf = i::NewArray<char>(buf_size);
+  memset(buf, 'a', buf_size);
+  buf[buf_size - 1] = '\0';
+  Local<String> large_string = String::New(buf);
+  i::DeleteArray(buf);
+  // Large strings should be immediately accepted.
+  CHECK(small_string->CanMakeExternal());

[Mads Ager (chromium), 2010/02/16 08:16:19]

small_ -> large_

[Vitaly Repeshko, 2010/02/16 18:56:42]

Ditto.

+}
+
+
 THREADED_TEST(UsingExternalString) {
   {
     v8::HandleScope scope;
     uint16_t* two_byte_string = AsciiToTwoByteString("test string");
     Local<String> string =
         String::NewExternal(new TestResource(two_byte_string));
     i::Handle<i::String> istring = v8::Utils::OpenHandle(*string);
     // Trigger GCs so that the newly allocated string moves to old gen.
     i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in survivor space now
     i::Heap::CollectGarbage(0, i::NEW_SPACE);  // in old gen now
@@ skipping 9029 matching lines @@
     CompileRun(source_exception);
     other_context->Exit();
     v8::internal::Heap::CollectAllGarbage(false);
     if (GetGlobalObjectsCount() == 1) break;
   }
   CHECK_GE(2, gc_count);
   CHECK_EQ(1, GetGlobalObjectsCount());
 
   other_context.Dispose();
 }