VM: Fix race between background compiler and guarded cid update.

runtime/vm/object.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 3107 matching lines @@
   void set_has_initializer(bool has_initializer) const {
     ASSERT(IsOriginal());
     ASSERT(Thread::Current()->IsMutatorThread());
     set_kind_bits(HasInitializerBit::update(has_initializer,
                                             raw_ptr()->kind_bits_));
   }
 
   // Return class id that any non-null value read from this field is guaranteed
   // to have or kDynamicCid if such class id is not known.
   // Stores to this field must update this information hence the name.
-  intptr_t guarded_cid() const { return raw_ptr()->guarded_cid_; }
+  intptr_t guarded_cid() const {
+#if defined(DEGUG)
+    Thread* thread = Thread::Current();
+    ASSERT(!IsOriginal() || thread->IsMutator() || thread->IsAtSafepoint());
+#endif
+    return raw_ptr()->guarded_cid_;
+  }
 
   void set_guarded_cid(intptr_t cid) const {

[Florian Schneider, 2016/05/23 19:26:32]

Add the same assert as for guarded_cid()?

[Vyacheslav Egorov (Google), 2016/05/24 10:57:49]

Done.

-    ASSERT(Thread::Current()->IsMutatorThread());
     StoreNonPointer(&raw_ptr()->guarded_cid_, cid);
   }
   static intptr_t guarded_cid_offset() {
     return OFFSET_OF(RawField, guarded_cid_);
   }
   // Return the list length that any list stored in this field is guaranteed
   // to have. If length is kUnknownFixedLength the length has not
   // been determined. If length is kNoFixedLength this field has multiple
   // list lengths associated with it and cannot be predicted.
   intptr_t guarded_list_length() const;
@@ skipping 5553 matching lines @@
 
 inline void TypeArguments::SetHash(intptr_t value) const {
   // This is only safe because we create a new Smi, which does not cause
   // heap allocation.
   StoreSmi(&raw_ptr()->hash_, Smi::New(value));
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_