folly: added C interface to SingletonVault

Test Plan:
fbconfig folly/experimental/test:singletonvault_c_test && fbmake runtests
buck test folly/experimental/test:singletonvault_c_test

Reviewed By: andrii@fb.com

Subscribers: trunkagent, sdwilsh, folly-diffs@

FB internal diff: D1780054

Signature: t1:1780054:1421187023:b18c1d5575b2864b3d3df001a0024b91eb321c46

folly/experimental/SingletonVault_c.cpp

+/*
+ * Copyright 2015 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 <folly/experimental/SingletonVault_c.h>
+#include <folly/experimental/Singleton.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+SingletonVault_t *SingletonVault_singleton() {
+  return folly::SingletonVault::singleton();
+}
+
+void SingletonVault_registrationComplete(SingletonVault_t *vault) {
+  ((folly::SingletonVault*) vault)->registrationComplete();
+}
+
+void SingletonVault_destroyInstances(SingletonVault_t *vault) {
+  ((folly::SingletonVault*) vault)->destroyInstances();
+}
+
+void SingletonVault_reenableInstances(SingletonVault_t *vault) {
+  ((folly::SingletonVault*) vault)->reenableInstances();
+}
+
+#ifdef __cplusplus
+} // extern "C"
+#endif

folly/experimental/SingletonVault_c.h

+/*
+ * Copyright 2015 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.
+ */
+
+// Plain C interface to SingletonVault. This facilitates combining programs
+// that cannot use C++ (e.g. programs written in C) with libraries that use
+// Singleton, by allowing the program to perform the required SingletonVault
+// lifecycle calls.
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef void SingletonVault_t;
+
+SingletonVault_t *SingletonVault_singleton();
+void SingletonVault_registrationComplete(SingletonVault_t *vault);
+void SingletonVault_destroyInstances(SingletonVault_t *vault);
+void SingletonVault_reenableInstances(SingletonVault_t *vault);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif

folly/experimental/test/SingletonVaultCTest.cpp

+/*
+ * Copyright 2015 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 <folly/experimental/Singleton.h>
+#include <folly/experimental/SingletonVault_c.h>
+
+#include <gtest/gtest.h>
+
+#include <thread>
+
+__thread long instance_counter_instances = 0;
+
+class InstanceCounter {
+ public:
+  InstanceCounter() {
+    instance_counter_instances++;
+  }
+
+  ~InstanceCounter() {
+    instance_counter_instances--;
+  }
+};
+
+TEST(SingletonVault, singletonReturnsSingletonInstance) {
+  SingletonVault_t *c = SingletonVault_singleton();
+  auto *cpp = folly::SingletonVault::singleton();
+  EXPECT_EQ(c, cpp);
+}
+
+TEST(SingletonVault, singletonsAreCreatedAndDestroyed) {
+  auto *vault = new folly::SingletonVault();
+  folly::Singleton<InstanceCounter> counter_singleton(nullptr, nullptr, vault);
+  SingletonVault_registrationComplete((SingletonVault_t*) vault);
+  InstanceCounter *counter = folly::Singleton<InstanceCounter>::get(vault);
+  EXPECT_EQ(instance_counter_instances, 1);
+  delete vault;
+  EXPECT_EQ(instance_counter_instances, 0);
+}