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

runtime/vm/atomic_linux.h

 // Copyright (c) 2013, 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_ATOMIC_LINUX_H_
 #define VM_ATOMIC_LINUX_H_
 
 #if !defined VM_ATOMIC_H_
 #error Do not include atomic_linux.h directly. Use atomic.h instead.
 #endif
 
 #if !defined(TARGET_OS_LINUX)
 #error This file should only be included on Linux builds.
 #endif
 
 namespace dart {
 
 
 inline uintptr_t AtomicOperations::FetchAndIncrement(uintptr_t* p) {
   return __sync_fetch_and_add(p, 1);
 }
 
 
+inline intptr_t AtomicOperations::FetchAndAdd(intptr_t* p, intptr_t delta) {
+  return __sync_fetch_and_add(p, delta);
+}
+
+
 #if !defined(USING_SIMULATOR)
 inline uword AtomicOperations::CompareAndSwapWord(uword* ptr,
                                                   uword old_value,
                                                   uword new_value) {
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 }
 #endif  // !defined(USING_SIMULATOR)
 
+
+inline uword AtomicOperations::LoadRelaxed(uword* ptr) {
+#if defined(__ATOMIC_RELAXED)
+  return __atomic_load_n(ptr, __ATOMIC_RELAXED);
+#else
+  // TODO(koda): Consider using C++11 <atomic> to avoid the barrier on more
+  // compilers/platforms.
+  return FetchAndAdd(reinterpret_cast<intptr_t*>(ptr), 0);
+#endif
+}
+
 }  // namespace dart
 
 #endif  // VM_ATOMIC_LINUX_H_