implemented async_logger::sync() to solve issue #1696

include/spdlog/async_logger-inl.h

@@ -13,6 +13,8 @@
 #include <memory>
 #include <string>
 
+#include <chrono>
+
 SPDLOG_INLINE spdlog::async_logger::async_logger(
     std::string logger_name, sinks_init_list sinks_list, std::weak_ptr<details::thread_pool> tp, async_overflow_policy overflow_policy)
     : async_logger(std::move(logger_name), sinks_list.begin(), sinks_list.end(), std::move(tp), overflow_policy)

include/spdlog/details/thread_pool-inl.h

@@ -85,6 +85,32 @@ size_t SPDLOG_INLINE thread_pool::queue_size()
     return q_.size();
 }
 
+SPDLOG_INLINE bool thread_pool::sync(int intervalMs, int timeoutMs)
+{
+    using namespace std::chrono;
+
+    auto start=steady_clock::now();
+    bool synced=false;
+    bool indef=(timeoutMs<=0);
+    do
+    {
+        if (!indef && intervalMs>timeoutMs)
+            intervalMs=timeoutMs;  
+
+        std::this_thread::sleep_for(milliseconds(intervalMs));
+        synced=(q_.size()==0);
+
+        if (!indef)
+        {
+            auto now=steady_clock::now();
+            auto passedMs=duration_cast<milliseconds>(now-start);
+            start=now;
+            timeoutMs-=static_cast<int>(passedMs.count());
+        }
+    } while (((!indef && timeoutMs>0) || indef) && !synced);
+    return synced;
+}
+
 void SPDLOG_INLINE thread_pool::post_async_msg_(async_msg &&new_msg, async_overflow_policy overflow_policy)
 {
     if (overflow_policy == async_overflow_policy::block)

include/spdlog/details/thread_pool.h

@@ -100,6 +100,9 @@ class SPDLOG_API thread_pool
     void reset_overrun_counter();
     size_t queue_size();
 
+    // block until all messages in thread pool are processed or the timer goes off.
+    bool sync(int intervalMs=100, int timeoutMs=-1);
+
 private:
     q_type q_;