Use atomic operations to increment/decrement memory usage counts as multiple threads could be alloc…

runtime/vm/atomic_test.cc

 // Copyright (c) 2015, 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.
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/atomic.h"
 #include "vm/globals.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
 UNIT_TEST_CASE(FetchAndIncrement) {
   uintptr_t v = 42;
   EXPECT_EQ(static_cast<uintptr_t>(42),
             AtomicOperations::FetchAndIncrement(&v));
   EXPECT_EQ(static_cast<uintptr_t>(43), v);
 }
 
 
 UNIT_TEST_CASE(FetchAndDecrement) {
   uintptr_t v = 42;
   EXPECT_EQ(static_cast<uintptr_t>(42),
             AtomicOperations::FetchAndDecrement(&v));
   EXPECT_EQ(static_cast<uintptr_t>(41), v);
 }
 
 
+UNIT_TEST_CASE(FetchAndIncrementBy) {
+  intptr_t v = 42;
+  EXPECT_EQ(static_cast<uintptr_t>(42),
+            AtomicOperations::FetchAndIncrementBy(&v, 100));
+  EXPECT_EQ(static_cast<intptr_t>(142), v);
+}
+
+
+UNIT_TEST_CASE(FetchAndDecrementBy) {
+  intptr_t v = 42;
+  EXPECT_EQ(static_cast<uintptr_t>(42),
+            AtomicOperations::FetchAndDecrementBy(&v, 41));
+  EXPECT_EQ(static_cast<intptr_t>(1), v);
+}
+
+
 UNIT_TEST_CASE(LoadRelaxed) {
   uword v = 42;
   EXPECT_EQ(static_cast<uword>(42), AtomicOperations::LoadRelaxed(&v));
 }
 
 
 TEST_CASE(CompareAndSwapWord) {
   uword old_value = 42;
   uword new_value = 100;
   uword result = AtomicOperations::CompareAndSwapWord(
       &old_value, old_value, new_value);
   EXPECT_EQ(static_cast<uword>(42), result);
 }
 
 
 TEST_CASE(CompareAndSwapUint32) {
   uint32_t old_value = 42;
   uint32_t new_value = 100;
   uint32_t result = AtomicOperations::CompareAndSwapUint32(
       &old_value, old_value, new_value);
   EXPECT_EQ(static_cast<uint32_t>(42), result);
 }
 
 }  // namespace dart