1 files changed, 66 insertions, 0 deletions
diff --git a/xpcom/tests/gtest/TestAutoRefCnt.cpp b/xpcom/tests/gtest/TestAutoRefCnt.cpp
new file mode 100644
index 0000000000..92cc0d2538
--- /dev/null
+++ b/xpcom/tests/gtest/TestAutoRefCnt.cpp
@@ -0,0 +1,66 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupportsImpl.h"
+
+#include "mozilla/Atomics.h"
+#include "nsIThread.h"
+#include "nsThreadUtils.h"
+
+#include "gtest/gtest.h"
+#include "mozilla/gtest/MozAssertions.h"
+
+using namespace mozilla;
+
+class nsThreadSafeAutoRefCntRunner final : public Runnable {
+ public:
+  NS_IMETHOD Run() final {
+    for (int i = 0; i < 10000; i++) {
+      if (++sRefCnt == 1) {
+        sIncToOne++;
+      }
+      if (--sRefCnt == 0) {
+        sDecToZero++;
+      }
+    }
+    return NS_OK;
+  }
+
+  static ThreadSafeAutoRefCnt sRefCnt;
+  static Atomic<uint32_t, Relaxed> sIncToOne;
+  static Atomic<uint32_t, Relaxed> sDecToZero;
+
+  nsThreadSafeAutoRefCntRunner() : Runnable("nsThreadSafeAutoRefCntRunner") {}
+
+ private:
+  ~nsThreadSafeAutoRefCntRunner() = default;
+};
+
+ThreadSafeAutoRefCnt nsThreadSafeAutoRefCntRunner::sRefCnt;
+Atomic<uint32_t, Relaxed> nsThreadSafeAutoRefCntRunner::sIncToOne(0);
+Atomic<uint32_t, Relaxed> nsThreadSafeAutoRefCntRunner::sDecToZero(0);
+
+// When a refcounted object is actually owned by a cache, we may not
+// want to release the object after last reference gets released. In
+// this pattern, the cache may rely on the balance of increment to one
+// and decrement to zero, so that it can maintain a counter for GC.
+TEST(AutoRefCnt, ThreadSafeAutoRefCntBalance)
+{
+  static const size_t kThreadCount = 4;
+  nsCOMPtr<nsIThread> threads[kThreadCount];
+  for (size_t i = 0; i < kThreadCount; i++) {
+    nsresult rv =
+        NS_NewNamedThread("AutoRefCnt Test", getter_AddRefs(threads[i]),
+                          new nsThreadSafeAutoRefCntRunner);
+    EXPECT_NS_SUCCEEDED(rv);
+  }
+  for (size_t i = 0; i < kThreadCount; i++) {
+    threads[i]->Shutdown();
+  }
+  EXPECT_EQ(nsThreadSafeAutoRefCntRunner::sRefCnt, nsrefcnt(0));
+  EXPECT_EQ(nsThreadSafeAutoRefCntRunner::sIncToOne,
+            nsThreadSafeAutoRefCntRunner::sDecToZero);
+}