Make Failure inherit from MaybeObject instead of Object.

src/top.cc

 // Copyright 2006-2008 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 89 matching lines @@
 }
 
 
 void Top::IterateThread(ThreadVisitor* v, char* t) {
   ThreadLocalTop* thread = reinterpret_cast<ThreadLocalTop*>(t);
   v->VisitThread(thread);
 }
 
 
 void Top::Iterate(ObjectVisitor* v, ThreadLocalTop* thread) {
-  v->VisitPointer(&(thread->pending_exception_));
+  // Visit the roots from the top for a given thread.
+  Object *pending;
+  // The pending exception can sometimes be a failure.  We can't show
+  // that to the GC, which only understands objects.
+  if (thread->pending_exception_->ToObject(&pending)) {
+    v->VisitPointer(&pending);
+    thread->pending_exception_ = pending;  // In case GC updated it.
+  }
   v->VisitPointer(&(thread->pending_message_obj_));
   v->VisitPointer(BitCast<Object**>(&(thread->pending_message_script_)));
   v->VisitPointer(BitCast<Object**>(&(thread->context_)));
-  v->VisitPointer(&(thread->scheduled_exception_));
+  Object* scheduled;
+  if (thread->scheduled_exception_->ToObject(&scheduled)) {
+    v->VisitPointer(&scheduled);
+    thread->scheduled_exception_ = scheduled;
+  }
 
   for (v8::TryCatch* block = thread->TryCatchHandler();
        block != NULL;
        block = TRY_CATCH_FROM_ADDRESS(block->next_)) {
     v->VisitPointer(BitCast<Object**>(&(block->exception_)));
     v->VisitPointer(BitCast<Object**>(&(block->message_)));
   }
 
   // Iterate over pointers on native execution stack.
   for (StackFrameIterator it(thread); !it.done(); it.Advance()) {
@@ skipping 556 matching lines @@
   return Failure::Exception();
 }
 
 
 Failure* Top::Throw(Object* exception, MessageLocation* location) {
   DoThrow(exception, location, NULL);
   return Failure::Exception();
 }
 
 
-Failure* Top::ReThrow(Object* exception, MessageLocation* location) {
+Failure* Top::ReThrow(MaybeObject* exception, MessageLocation* location) {
   // Set the exception being re-thrown.
   set_pending_exception(exception);
   return Failure::Exception();
 }
 
 
 Failure* Top::ThrowIllegalOperation() {
   return Throw(Heap::illegal_access_symbol());
 }
 
 
 void Top::ScheduleThrow(Object* exception) {
   // When scheduling a throw we first throw the exception to get the
   // error reporting if it is uncaught before rescheduling it.
   Throw(exception);
   thread_local_.scheduled_exception_ = pending_exception();
   thread_local_.external_caught_exception_ = false;
   clear_pending_exception();
 }
 
 
-Object* Top::PromoteScheduledException() {
-  Object* thrown = scheduled_exception();
+Failure* Top::PromoteScheduledException() {
+  MaybeObject* thrown = scheduled_exception();
   clear_scheduled_exception();
   // Re-throw the exception to avoid getting repeated error reporting.
   return ReThrow(thrown);
 }
 
 
 void Top::PrintCurrentStackTrace(FILE* out) {
   StackTraceFrameIterator it;
   while (!it.done()) {
     HandleScope scope;
@@ skipping 62 matching lines @@
   if (*is_caught_externally) {
     // Only report the exception if the external handler is verbose.
     return thread_local_.TryCatchHandler()->is_verbose_;
   } else {
     // Report the exception if it isn't caught by JavaScript code.
     return handler == NULL;
   }
 }
 
 
-void Top::DoThrow(Object* exception,
+void Top::DoThrow(MaybeObject* exception,
                   MessageLocation* location,
                   const char* message) {
   ASSERT(!has_pending_exception());
 
   HandleScope scope;
-  Handle<Object> exception_handle(exception);
+  Object* exception_object = Smi::FromInt(0);
+  bool is_object = exception->ToObject(&exception_object);
+  Handle<Object> exception_handle(exception_object);
 
   // Determine reporting and whether the exception is caught externally.
   bool is_caught_externally = false;
   bool is_out_of_memory = exception == Failure::OutOfMemoryException();
   bool is_termination_exception = exception == Heap::termination_exception();
   bool catchable_by_javascript = !is_termination_exception && !is_out_of_memory;
+  // Only real objects can be caught by JS.
+  ASSERT(!catchable_by_javascript || is_object);
   bool should_return_exception =
       ShouldReturnException(&is_caught_externally, catchable_by_javascript);
   bool report_exception = catchable_by_javascript && should_return_exception;
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // Notify debugger of exception.
   if (catchable_by_javascript) {
     Debugger::OnException(exception_handle, report_exception);
   }
 #endif
@@ skipping 15 matching lines @@
       // traces while the bootstrapper is active since the infrastructure
       // may not have been properly initialized.
       Handle<String> stack_trace;
       if (FLAG_trace_exception) stack_trace = StackTraceString();
       Handle<JSArray> stack_trace_object;
       if (report_exception && capture_stack_trace_for_uncaught_exceptions) {
           stack_trace_object = Top::CaptureCurrentStackTrace(
               stack_trace_for_uncaught_exceptions_frame_limit,
               stack_trace_for_uncaught_exceptions_options);
       }
+      ASSERT(is_object);  // Can't use the handle unless there's a real object.
       message_obj = MessageHandler::MakeMessageObject("uncaught_exception",
           location, HandleVector<Object>(&exception_handle, 1), stack_trace,
           stack_trace_object);
     }
   }
 
   // Save the message for reporting if the the exception remains uncaught.
   thread_local_.has_pending_message_ = report_exception;
   thread_local_.pending_message_ = message;
   if (!message_obj.is_null()) {
     thread_local_.pending_message_obj_ = *message_obj;
     if (location != NULL) {
       thread_local_.pending_message_script_ = *location->script();
       thread_local_.pending_message_start_pos_ = location->start_pos();
       thread_local_.pending_message_end_pos_ = location->end_pos();
     }
   }
 
   if (is_caught_externally) {
     thread_local_.catcher_ = thread_local_.TryCatchHandler();
   }
 
   // NOTE: Notifying the debugger or generating the message
   // may have caused new exceptions. For now, we just ignore
   // that and set the pending exception to the original one.
-  set_pending_exception(*exception_handle);
+  if (is_object) {
+    set_pending_exception(*exception_handle);
+  } else {
+    // Failures are not on the heap so they neither need nor work with handles.
+    ASSERT(exception_handle->IsFailure());
+    set_pending_exception(exception);
+  }
 }
 
 
 void Top::ReportPendingMessages() {
   ASSERT(has_pending_exception());
   setup_external_caught();
   // If the pending exception is OutOfMemoryException set out_of_memory in
   // the global context.  Note: We have to mark the global context here
   // since the GenerateThrowOutOfMemory stub cannot make a RuntimeCall to
   // set it.
   bool external_caught = thread_local_.external_caught_exception_;
   HandleScope scope;
   if (thread_local_.pending_exception_ == Failure::OutOfMemoryException()) {
     context()->mark_out_of_memory();
   } else if (thread_local_.pending_exception_ ==
              Heap::termination_exception()) {
     if (external_caught) {
       thread_local_.TryCatchHandler()->can_continue_ = false;
       thread_local_.TryCatchHandler()->exception_ = Heap::null_value();
     }
   } else {
-    Handle<Object> exception(pending_exception());
+    // At this point all non-object (failure) exceptions have
+    // been dealt with so this shouldn't fail.
+    Object* pending_exception_object = pending_exception()->ToObjectUnchecked();
+    Handle<Object> exception(pending_exception_object);
     thread_local_.external_caught_exception_ = false;
     if (external_caught) {
       thread_local_.TryCatchHandler()->can_continue_ = true;
       thread_local_.TryCatchHandler()->exception_ =
         thread_local_.pending_exception_;
       if (!thread_local_.pending_message_obj_->IsTheHole()) {
         try_catch_handler()->message_ = thread_local_.pending_message_obj_;
       }
     }
     if (thread_local_.has_pending_message_) {
@@ skipping 73 matching lines @@
       int frame_limit,
       StackTrace::StackTraceOptions options) {
   capture_stack_trace_for_uncaught_exceptions = capture;
   stack_trace_for_uncaught_exceptions_frame_limit = frame_limit;
   stack_trace_for_uncaught_exceptions_options = options;
 }
 
 
 bool Top::is_out_of_memory() {
   if (has_pending_exception()) {
-    Object* e = pending_exception();
+    MaybeObject* e = pending_exception();
     if (e->IsFailure() && Failure::cast(e)->IsOutOfMemoryException()) {
       return true;
     }
   }
   if (has_scheduled_exception()) {
-    Object* e = scheduled_exception();
+    MaybeObject* e = scheduled_exception();
     if (e->IsFailure() && Failure::cast(e)->IsOutOfMemoryException()) {
       return true;
     }
   }
   return false;
 }
 
 
 Handle<Context> Top::global_context() {
   GlobalObject* global = thread_local_.context_->global();
@@ skipping 40 matching lines @@
   Top::break_access_->Lock();
 }
 
 
 ExecutionAccess::~ExecutionAccess() {
   Top::break_access_->Unlock();
 }
 
 
 } }  // namespace v8::internal