Generator objects can suspend

src/runtime.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 2276 matching lines @@
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
   CONVERT_SMI_ARG_CHECKED(num, 1);
   RUNTIME_ASSERT(num >= 0);
   SetExpectedNofProperties(function, num);
   return isolate->heap()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_CreateJSGeneratorObject) {
   NoHandleAllocation ha(isolate);
   ASSERT(args.length() == 0);

[Michael Starzinger, 2013/04/17 13:43:48]

nit: Let's add an empty newline after the assert and before the frame iterator
is instantiated here.

   JavaScriptFrameIterator it(isolate);
   JavaScriptFrame* frame = it.frame();
   JSFunction* function = JSFunction::cast(frame->function());
   RUNTIME_ASSERT(function->shared()->is_generator());
 
   JSGeneratorObject* generator;
   if (frame->IsConstructor()) {
     generator = JSGeneratorObject::cast(frame->receiver());
   } else {
     MaybeObject* maybe_generator =
         isolate->heap()->AllocateJSGeneratorObject(function);
     if (!maybe_generator->To(&generator)) return maybe_generator;
   }
   generator->set_function(function);
-  generator->set_context(isolate->heap()->undefined_value());
+  generator->set_context(Context::cast(frame->context()));
   generator->set_continuation(0);
   generator->set_operand_stack(isolate->heap()->empty_fixed_array());
 
   return generator;
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_SuspendJSGeneratorObject) {
+  HandleScope scope(isolate);
+  ASSERT(args.length() == 1);
+  CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator_object, 0);
+
+  JavaScriptFrameIterator stack_iterator(isolate);
+  JavaScriptFrame *frame = stack_iterator.frame();
+  Handle<JSFunction> function(JSFunction::cast(frame->function()));

[Michael Starzinger, 2013/04/17 13:43:48]

Let's play it safe for now and add the following here ...

RUNTIME_ASSERT(function->shared()->is_generator());

+
+  intptr_t offset = frame->pc() - function->code()->instruction_start();
+  ASSERT(*function == generator_object->function());
+  ASSERT(offset >= 0 && Smi::IsValid(offset));
+  generator_object->set_continuation(offset);
+
+  // Generator functions force context allocation for locals, so Local0 points
+  // to the bottom of the operand stack.  Assume the stack grows down.
+  intptr_t stack_size_in_bytes =
+      (frame->fp() + JavaScriptFrameConstants::kLocal0Offset) -
+      (frame->sp() - kPointerSize);

[Michael Starzinger, 2013/04/17 13:43:48]

Just for the record: This magic computation needs to be moved into the frames.h
files later. But I agree that for now we should just keep it inline until the
first prototype is up an running and the implementation has stabilized. But
let's add a TODO in that regard.

+  ASSERT(IsAddressAligned(frame->fp(), kPointerSize));
+  ASSERT(IsAligned(stack_size_in_bytes, kPointerSize));
+  ASSERT(stack_size_in_bytes >= 0);
+  ASSERT(Smi::IsValid(stack_size_in_bytes));
+  unsigned stack_size = stack_size_in_bytes >> kPointerSizeLog2;
+
+  // We expect there to be at least two values on the stack: the return value of
+  // the yield expression, and the argument to this runtime call.  Neither of
+  // those should be saved.
+  ASSERT(stack_size >= 2);
+  stack_size -= 2;
+

[Michael Starzinger, 2013/04/17 13:43:48]

IIUC the current implementation relies and the context within the function not
to change. So let's add an assertio checking that. I wouldn't try to fix any
issues with that in this CL, let's just keep the assert around for now.

ASSERT(*generator_object == Context::cast(frame->context()));

[Michael Starzinger, 2013/04/17 13:49:02]

That should have been "generator_object->context()" of course.

+  if (stack_size == 0) {
+    ASSERT(generator_object->operand_stack() ==
+           isolate->heap()->empty_fixed_array());
+    // If there are no operands on the stack, there shouldn't be a handler
+    // active either.  Also, the active context will be the same as the function
+    // itself, so there is no need to save the context.
+    ASSERT_EQ(frame->context(), generator_object->context());
+    ASSERT(!frame->HasHandler());
+  } else {
+    generator_object->set_context(Context::cast(frame->context()));
+    // Saving the operand stack or stack handlers is not currently implemented.

[Michael Starzinger, 2013/04/17 13:43:48]

Let's turn this comment into a TODO.

+    UNIMPLEMENTED();
+  }
+
+  // The return value is the hole for a suspend return, and anything else for a
+  // resume return.
+  return *isolate->factory()->the_hole_value();

[Michael Starzinger, 2013/04/17 13:43:48]

Use "isolate->heap()->the_hole_value()" here instead.

+}
+
+
 MUST_USE_RESULT static MaybeObject* CharFromCode(Isolate* isolate,
                                                  Object* char_code) {
   uint32_t code;
   if (char_code->ToArrayIndex(&code)) {
     if (code <= 0xffff) {
       return isolate->heap()->LookupSingleCharacterStringFromCode(code);
     }
   }
   return isolate->heap()->empty_string();
 }
@@ skipping 10779 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal