add unit test for Executor::KeepAlive

Summary:
This diff adds a simple unit test, verifying that construction
of a `KeepAlive` object (either from `Executor*` or move construction)
calls `keepAliveAcquire` and `keepAliveRelease` the correct
number of times.

Reviewed By: elsteveogrande

Differential Revision: D8203944

fbshipit-source-id: 297beeaab99c55d7284ca06edd5e6b9023e27619

folly/test/ExecutorTest.cpp

+/*
+ * Copyright 2016-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <atomic>
+
+#include <folly/Executor.h>
+#include <folly/portability/GTest.h>
+
+namespace folly {
+
+class KeepAliveTestExecutor : public Executor {
+ public:
+  void add(Func) override {
+    // this executor does nothing
+  }
+
+  bool keepAliveAcquire() override {
+    ++refCount;
+    return true;
+  }
+
+  void keepAliveRelease() override {
+    --refCount;
+  }
+
+  std::atomic<int> refCount{0};
+};
+
+TEST(ExecutorTest, KeepAliveBasic) {
+  KeepAliveTestExecutor exec;
+
+  {
+    Executor::KeepAlive<KeepAliveTestExecutor>&& ka = getKeepAliveToken(exec);
+    EXPECT_TRUE(ka);
+    EXPECT_EQ(std::addressof(exec), ka.get());
+    EXPECT_EQ(1, exec.refCount);
+  }
+
+  EXPECT_EQ(0, exec.refCount);
+}
+
+TEST(ExecutorTest, KeepAliveMove) {
+  KeepAliveTestExecutor exec;
+
+  {
+    Executor::KeepAlive<KeepAliveTestExecutor>&& ka = getKeepAliveToken(exec);
+    EXPECT_TRUE(ka);
+    EXPECT_EQ(std::addressof(exec), ka.get());
+    EXPECT_EQ(1, exec.refCount);
+
+    Executor::KeepAlive<KeepAliveTestExecutor> ka2{std::move(ka)};
+    EXPECT_FALSE(ka);
+    EXPECT_TRUE(ka2);
+    EXPECT_EQ(std::addressof(exec), ka2.get());
+    EXPECT_EQ(1, exec.refCount);
+  }
+
+  EXPECT_EQ(0, exec.refCount);
+}
+
+TEST(ExecutorTest, KeepAliveConvert) {
+  KeepAliveTestExecutor exec;
+
+  {
+    Executor::KeepAlive<KeepAliveTestExecutor>&& ka = getKeepAliveToken(exec);
+    EXPECT_TRUE(ka);
+    EXPECT_EQ(std::addressof(exec), ka.get());
+    EXPECT_EQ(1, exec.refCount);
+
+    // convert to Executor::KeepAlive<Executor>
+    Executor::KeepAlive<Executor> ka2{std::move(ka)};
+    EXPECT_FALSE(ka);
+    EXPECT_TRUE(ka2);
+    EXPECT_EQ(std::addressof(exec), ka2.get());
+    EXPECT_EQ(1, exec.refCount);
+  }
+
+  EXPECT_EQ(0, exec.refCount);
+}
+
+} // namespace folly