Safe and efficient stack-limit based interrupt checking in C++.

runtime/vm/atomic_win.h

Index: runtime/vm/atomic_win.h
diff --git a/runtime/vm/atomic_win.h b/runtime/vm/atomic_win.h
index 24be3b12c8bc33573215d4fe583a94fa22482974..ccec5278351f366388ad60ec6b1ab0cfad81526a 100644
--- a/runtime/vm/atomic_win.h
+++ b/runtime/vm/atomic_win.h
@@ -28,6 +28,19 @@ inline uintptr_t AtomicOperations::FetchAndIncrement(uintptr_t* p) {
 }
 
 
+inline intptr_t AtomicOperations::FetchAndAdd(intptr_t* p, intptr_t delta) {
+#if defined(TARGET_ARCH_X64)
+  return static_cast<intptr_t>(
+      InterlockedAdd64(reinterpret_cast<LONGLONG*>(p), delta)) - 1;

[Ivan Posva, 2015/08/07 20:55:46]

What does the -1 mean here?

[koda, 2015/08/07 21:05:22]

Fixed to 'delta' (InterlockedAdd returns the value *after*).

+#elif defined(TARGET_ARCH_IA32)
+  return static_cast<intptr_t>(
+      InterlockedAdd(reinterpret_cast<LONG*>(p), delta)) - 1;
+#else
+  UNIMPLEMENTED();
+#endif
+}
+
+
 #if !defined(USING_SIMULATOR)
 inline uword AtomicOperations::CompareAndSwapWord(uword* ptr,
                                                   uword old_value,
@@ -48,6 +61,13 @@ inline uword AtomicOperations::CompareAndSwapWord(uword* ptr,
 }
 #endif  // !defined(USING_SIMULATOR)
 
+
+inline uword AtomicOperations::LoadRelaxed(uword* ptr) {
+  // TODO(koda): Consider using C++11 <atomic> to avoid the barrier on more
+  // compilers/platforms.
+  return FetchAndAdd(reinterpret_cast<intptr_t*>(ptr), 0);
+}
+
 }  // namespace dart
 
 #endif  // VM_ATOMIC_WIN_H_