Added periodic flusher support, and fixed some registry issues

include/spdlog/details/periodic_worker.h

@@ -0,0 +1,80 @@
+
+//
+// Copyright(c) 2018 Gabi Melman.
+// Distributed under the MIT License (http://opensource.org/licenses/MIT)
+//
+
+#pragma once
+
+// periodic worker thread - peridically executes the given callback function.
+//
+// RAII over the owned thread:
+//    creates the thread on construction.
+//    stops and joins the thread on destruction.
+
+#include <mutex>
+#include <atomic>
+#include <condition_variable>
+#include <chrono>
+#include <functional>
+
+namespace spdlog
+{
+namespace details {
+
+class periodic_worker
+{
+public:
+    periodic_worker(std::function<void()> callback_fun, std::chrono::seconds interval)
+    {
+
+        if (interval == std::chrono::seconds::zero())
+        {
+            active_ = false;
+            return;
+        }
+        active_ = true;
+        flusher_thread_ = std::thread([callback_fun, interval, this]()
+        {
+            using std::chrono::steady_clock;
+
+            auto last_flush_tp = steady_clock::now();
+            for (;;)
+            {
+                std::unique_lock<std::mutex> lock(this->mutex_);
+                this->cv_.wait_for(lock, interval, [callback_fun, interval, last_flush_tp, this]
+                {
+                    return !this->active_ || (steady_clock::now() - last_flush_tp) >= interval;
+                });
+                if (!this->active_)
+                {
+                    break;
+                }
+                callback_fun();
+                last_flush_tp = steady_clock::now();
+            }
+        });
+    }
+
+    periodic_worker(const periodic_worker&) = delete;
+    periodic_worker &operator=(const periodic_worker &) = delete;
+
+    // stop the back thread and join it
+    ~periodic_worker()
+    {
+        if (active_)
+        {
+            active_ = false;
+            cv_.notify_one();
+            flusher_thread_.join();
+        }
+    }
+
+private:
+    std::atomic<bool> active_;
+    std::thread flusher_thread_;
+    std::mutex mutex_;
+    std::condition_variable cv_;
+};
+}
+}