Get rid of auto_destoyer

* The destruction order of global static variables is non-deterministic.

include/libnuraft/global_mgr.hxx

@@ -68,9 +68,15 @@ struct nuraft_global_config {
 
 static nuraft_global_config __DEFAULT_NURAFT_GLOBAL_CONFIG;
 
-// Singleton class.
 class nuraft_global_mgr {
 public:
+    nuraft_global_mgr();
+
+    ~nuraft_global_mgr();
+
+    __nocopy__(nuraft_global_mgr);
+public:
+
     /**
      * Initialize the global instance.
      *
@@ -145,12 +151,6 @@ public:
 private:
     struct worker_handle;
 
-    nuraft_global_mgr();
-
-    ~nuraft_global_mgr();
-
-    __nocopy__(nuraft_global_mgr);
-
     /**
      * Initialize thread pool with the given config.
      */
@@ -166,16 +166,6 @@ private:
      */
     void append_worker_loop(ptr<worker_handle> handle);
 
-    /**
-     * Lock for global manager instance.
-     */
-    static std::mutex instance_lock_;
-
-    /**
-     * Global manager instance.
-     */
-    static std::atomic<nuraft_global_mgr*> instance_;
-
     /**
      * Lock for global Asio service instance.
      */

src/global_mgr.cxx

@@ -24,10 +24,44 @@ limitations under the License.
 #include "raft_server.hxx"
 #include "tracer.hxx"
 
+#include <memory>
+
 namespace nuraft {
 
-std::atomic<nuraft_global_mgr*> nuraft_global_mgr::instance_(nullptr);
-std::mutex nuraft_global_mgr::instance_lock_;
+class ngm_singleton {
+public:
+    static ngm_singleton& get_instance() {
+        static ngm_singleton instance;
+        return instance;
+    }
+
+    nuraft_global_mgr* get() {
+        return internal_.get();
+    }
+
+    bool create() {
+        std::lock_guard<std::mutex> l(lock_);
+        if (internal_.get()) {
+            // Already created.
+            return false;
+        }
+        // C++11 doesn't have `make_unique`.
+        internal_ =
+            std::move( std::unique_ptr<nuraft_global_mgr>( new nuraft_global_mgr() ) );
+        return true;
+    }
+
+    void clear() {
+        std::lock_guard<std::mutex> l(lock_);
+        internal_.reset();
+    }
+
+private:
+    ngm_singleton() : internal_(nullptr) {}
+
+    std::unique_ptr<nuraft_global_mgr> internal_;
+    std::mutex lock_;
+};
 
 struct nuraft_global_mgr::worker_handle {
     worker_handle(size_t id = 0)
@@ -84,13 +118,11 @@ nuraft_global_mgr::~nuraft_global_mgr() {
 }
 
 nuraft_global_mgr* nuraft_global_mgr::init(const nuraft_global_config& config) {
-    nuraft_global_mgr* mgr = instance_.load();
+    nuraft_global_mgr* mgr = ngm_singleton::get_instance().get();
     if (!mgr) {
-        std::lock_guard<std::mutex> l(instance_lock_);
-        mgr = instance_.load();
-        if (!mgr) {
-            mgr = new nuraft_global_mgr();
-            instance_.store(mgr);
+        bool created = ngm_singleton::get_instance().create();
+        mgr = ngm_singleton::get_instance().get();
+        if (created) {
             mgr->config_ = config;
             mgr->init_thread_pool();
         }
@@ -99,16 +131,11 @@ nuraft_global_mgr* nuraft_global_mgr::init(const nuraft_global_config& config) {
 }
 
 void nuraft_global_mgr::shutdown() {
-    std::lock_guard<std::mutex> l(instance_lock_);
-    nuraft_global_mgr* mgr = instance_.load();
-    if (mgr) {
-        delete mgr;
-        instance_.store(nullptr);
-    }
+    ngm_singleton::get_instance().clear();
 }
 
 nuraft_global_mgr* nuraft_global_mgr::get_instance() {
-    return instance_.load();
+    return ngm_singleton::get_instance().get();
 }
 
 void nuraft_global_mgr::init_thread_pool() {

src/raft_server.cxx

@@ -44,14 +44,6 @@ const int raft_server::default_snapshot_sync_block_size = 4 * 1024;
 
 raft_server::limits raft_server::raft_limits_;
 
-struct auto_destroyer {
-    ~auto_destroyer() {
-        stat_mgr::destroy();
-        nuraft_global_mgr::shutdown();
-    }
-};
-static auto_destroyer auto_destroyer_;
-
 raft_server::raft_server(context* ctx, const init_options& opt)
     : bg_append_ea_(nullptr)
     , initialized_(false)

src/stat_mgr.cxx

@@ -23,9 +23,6 @@ limitations under the License.
 
 namespace nuraft {
 
-std::atomic<stat_mgr*> stat_mgr::instance_(nullptr);
-std::mutex stat_mgr::instance_lock_;
-
 // === stat_elem ==============================================================
 
 stat_elem::stat_elem(Type _type, const std::string& _name)
@@ -53,43 +50,12 @@ stat_mgr::~stat_mgr() {
     for (auto& entry: stat_map_) {
         delete entry.second;
     }
-}
-
-stat_mgr* stat_mgr::init() {
-    stat_mgr* mgr = instance_.load();
-    if (!mgr) {
-        std::lock_guard<std::mutex> l(instance_lock_);
-        mgr = instance_.load();
-        if (!mgr) {
-            mgr = new stat_mgr();
-            instance_.store(mgr);
-        }
-    }
-    return mgr;
+    stat_map_.clear();
 }
 
 stat_mgr* stat_mgr::get_instance() {
-#ifndef ENABLE_RAFT_STATS
-    static stat_mgr dummy_mgr;
-    return &dummy_mgr;
-#endif
-
-    stat_mgr* mgr = instance_.load();
-    if (!mgr) return init();
-    return mgr;
-}
-
-void stat_mgr::destroy() {
-#ifndef ENABLE_RAFT_STATS
-    return;
-#endif
-
-    std::lock_guard<std::mutex> l(instance_lock_);
-    stat_mgr* mgr = instance_.load();
-    if (mgr) {
-        delete mgr;
-        instance_.store(nullptr);
-    }
+    static stat_mgr mgr_instance;
+    return &mgr_instance;
 }
 
 stat_elem* stat_mgr::get_stat(const std::string& stat_name) {

src/stat_mgr.hxx

@@ -163,12 +163,8 @@ private:
 // Singleton class
 class stat_mgr {
 public:
-    static stat_mgr* init();
-
     static stat_mgr* get_instance();
 
-    static void destroy();
-
     stat_elem* get_stat(const std::string& stat_name);
 
     stat_elem* create_stat(stat_elem::Type type, const std::string& stat_name);
@@ -180,9 +176,6 @@ public:
     void reset_all_stats();
 
 private:
-    static std::mutex instance_lock_;
-    static std::atomic<stat_mgr*> instance_;
-
     stat_mgr();
     ~stat_mgr();