[heap] Make slot set state and operations atomic.

src/base/atomic-utils.h

Index: src/base/atomic-utils.h
diff --git a/src/base/atomic-utils.h b/src/base/atomic-utils.h
index e19385dcb15742909517cb208f048d10dfee9ea7..bb55ea890042079b7bc88e0968731caa14294419 100644
--- a/src/base/atomic-utils.h
+++ b/src/base/atomic-utils.h
@@ -72,6 +72,20 @@ class AtomicValue {
            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));
   }