[heap] Make slot set state and operations atomic.

src/base/atomic-utils.h

 // Copyright 2015 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.
 
 #ifndef V8_ATOMIC_UTILS_H_
 #define V8_ATOMIC_UTILS_H_
 
 #include <limits.h>
 
 #include "src/base/atomicops.h"
@@ skipping 54 matching lines @@
     return cast_helper<T>::to_return_type(base::Acquire_Load(&value_));
   }
 
   V8_INLINE bool TrySetValue(T old_value, T new_value) {
     return base::Release_CompareAndSwap(
                &value_, cast_helper<T>::to_storage_type(old_value),
                cast_helper<T>::to_storage_type(new_value)) ==
            cast_helper<T>::to_storage_type(old_value);
   }
 
+  V8_INLINE void SetBits(T bits, int mask) {

[ulan, 2016/09/20 12:33:02]

mask also should be T

[Hannes Payer (out of office), 2016/09/20 13:51:29]

Done.

+    DCHECK_EQ(bits & ~mask, 0);
+    T old_value;
+    T new_value;
+    do {
+      old_value = Value();
+      new_value = (old_value & ~mask) | bits;
+    } while (!TrySetValue(old_value, new_value));
+  }
+
+  V8_INLINE void SetBit(int bit) { SetBits(1 << bit, 1 << bit); }

[ulan, 2016/09/20 12:33:02]

How about static_cast<T>(1) << bit to avoid potential overflows?

[Hannes Payer (out of office), 2016/09/20 13:51:29]

Done.

+
+  V8_INLINE void ClearBit(int bit) { SetBits(0, 1 << bit); }
+
   V8_INLINE void SetValue(T new_value) {
     base::Release_Store(&value_, cast_helper<T>::to_storage_type(new_value));
   }
 
  private:
   STATIC_ASSERT(sizeof(T) <= sizeof(base::AtomicWord));
 
   template <typename S>
   struct cast_helper {
     static base::AtomicWord to_storage_type(S value) {
@@ skipping 90 matching lines @@
     return static_cast<base::AtomicWord>(1) << element;
   }
 
   base::AtomicWord bits_;
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // #define V8_ATOMIC_UTILS_H_