Small clean up of externalizing strings.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/allocation-site-scopes.h"
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 1034 matching lines @@
   if (FLAG_enable_slow_asserts) {
     // Assert that the resource and the string are equivalent.
     DCHECK(static_cast<size_t>(this->length()) == resource->length());
     ScopedVector<uc16> smart_chars(this->length());
     String::WriteToFlat(this, smart_chars.start(), 0, this->length());
     DCHECK(memcmp(smart_chars.start(),
                   resource->data(),
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
 #endif  // DEBUG
+  int size = this->Size();  // Byte size of the original string.
+  // Abort if size does not allow in-place conversion.
+  if (size < ExternalString::kShortSize) return false;
   Heap* heap = GetHeap();
-  int size = this->Size();  // Byte size of the original string.
-  if (size < ExternalString::kShortSize) {
-    return false;
-  }
   bool is_ascii = this->IsOneByteRepresentation();
   bool is_internalized = this->IsInternalizedString();
 
   // Morph the string to an external string by replacing the map and
   // reinitializing the fields.  This won't work if
   // - the space the existing string occupies is too small for a regular
   //   external string.
   // - the existing string is in old pointer space and the backing store of
   //   the external string is not aligned.  The GC cannot deal with a field
   //   containing a possibly unaligned address to outside of V8's heap.
@@ skipping 32 matching lines @@
   ExternalTwoByteString* self = ExternalTwoByteString::cast(this);
   self->set_resource(resource);
   if (is_internalized) self->Hash();  // Force regeneration of the hash value.
 
   heap->AdjustLiveBytes(this->address(), new_size - size, Heap::FROM_MUTATOR);
   return true;
 }
 
 
 bool String::MakeExternal(v8::String::ExternalAsciiStringResource* resource) {
+  // Externalizing twice leaks the external resource, so it's
+  // prohibited by the API.
+  DCHECK(!this->IsExternalString());
 #ifdef ENABLE_SLOW_DCHECKS
   if (FLAG_enable_slow_asserts) {
     // Assert that the resource and the string are equivalent.
     DCHECK(static_cast<size_t>(this->length()) == resource->length());
     if (this->IsTwoByteRepresentation()) {
       ScopedVector<uint16_t> smart_chars(this->length());
       String::WriteToFlat(this, smart_chars.start(), 0, this->length());
       DCHECK(String::IsOneByte(smart_chars.start(), this->length()));
     }
     ScopedVector<char> smart_chars(this->length());
     String::WriteToFlat(this, smart_chars.start(), 0, this->length());
     DCHECK(memcmp(smart_chars.start(),
                   resource->data(),
                   resource->length() * sizeof(smart_chars[0])) == 0);
   }
 #endif  // DEBUG
+  int size = this->Size();  // Byte size of the original string.
+  // Abort if size does not allow in-place conversion.
+  if (size < ExternalString::kShortSize) return false;
   Heap* heap = GetHeap();
-  int size = this->Size();  // Byte size of the original string.
-  if (size < ExternalString::kShortSize) {
-    return false;
-  }
   bool is_internalized = this->IsInternalizedString();
 
   // Morph the string to an external string by replacing the map and
   // reinitializing the fields.  This won't work if
   // - the space the existing string occupies is too small for a regular
   //   external string.
   // - the existing string is in old pointer space and the backing store of
   //   the external string is not aligned.  The GC cannot deal with a field
   //   containing a possibly unaligned address to outside of V8's heap.
   // In either case we resort to a short external string instead, omitting
@@ skipping 15755 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal