Add a skia method to perform an atomic add.

Complements sk_atomic_inc for when you want to increase by more than one.

This time, use the correct atomic add function on Windows.

Reviewed at https://codereview.appspot.com/6399050/

Review URL: https://codereview.appspot.com/6407048

git-svn-id: http://skia.googlecode.com/svn/trunk@4623 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/AtomicTest.cpp b/tests/AtomicTest.cpp
new file mode 100644
index 0000000..5275e84
--- /dev/null
+++ b/tests/AtomicTest.cpp
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkThread.h"
+#include "SkThreadUtils.h"
+#include "SkTypes.h"
+#include "Test.h"
+
+struct AddInfo {
+    int32_t valueToAdd;
+    int timesToAdd;
+    unsigned int processorAffinity;
+};
+
+static int32_t base = 0;
+
+static AddInfo gAdds[] = {
+    { 3, 100, 23 },
+    { 2, 200, 2 },
+    { 7, 150, 17 },
+};
+
+static void addABunchOfTimes(void* data) {
+    AddInfo* addInfo = static_cast<AddInfo*>(data);
+    for (int i = 0; i < addInfo->timesToAdd; i++) {
+        sk_atomic_add(&base, addInfo->valueToAdd);
+    }
+}
+
+static void test_atomicAddTests(skiatest::Reporter* reporter) {
+    int32_t total = base;
+    SkThread* threads[SK_ARRAY_COUNT(gAdds)];
+    for (size_t i = 0; i < SK_ARRAY_COUNT(gAdds); i++) {
+        total += gAdds[i].valueToAdd * gAdds[i].timesToAdd;
+    }
+    // Start the threads
+    for (size_t i = 0; i < SK_ARRAY_COUNT(gAdds); i++) {
+        threads[i] = new SkThread(addABunchOfTimes, &gAdds[i]);
+        threads[i]->setProcessorAffinity(gAdds[i].processorAffinity);
+        threads[i]->start();
+    }
+
+    // Now end the threads
+    for (size_t i = 0; i < SK_ARRAY_COUNT(gAdds); i++) {
+        threads[i]->join();
+        delete threads[i];
+    }
+    REPORTER_ASSERT(reporter, total == base);
+    // Ensure that the returned value from sk_atomic_add is correct.
+    int32_t valueToModify = 3;
+    const int32_t originalValue = valueToModify;
+    REPORTER_ASSERT(reporter, originalValue == sk_atomic_add(&valueToModify, 7));
+}
+
+#include "TestClassDef.h"
+DEFINE_TESTCLASS("AtomicAdd", AtomicAddTestClass, test_atomicAddTests)
+