async_sink: catch back thread exceptions and rethrow on the calling thread on the next logging request

include/spdlog/sinks/async_sink.h

@@ -22,6 +22,14 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
+// async sink:
+// Process logs asynchronously using a back thread.
+//
+// If the internal queue of log messages reaches its max size,
+// then the client call will block until there is more room.
+//
+// If the back thread throws during logging, a spdlog::spdlog_ex exception
+// will be thrown in client's thread when tries to log the next message
 #pragma once
 
 #include <thread>
@@ -68,9 +76,17 @@ private:
     std::atomic<bool> _active;
     q_type _q;
     std::thread _back_thread;
-    //Clear all remaining messages(if any), stop the _back_thread and join it
-    void _join() ;
     std::mutex _mutex;
+    //Last exception thrown from the back thread
+    std::shared_ptr<spdlog_ex> _last_backthread_ex;
+
+
+    //will throw last back thread exception or if backthread no active
+    void _push_sentry();
+
+    //Clear all remaining messages(if any), stop the _back_thread and join it
+    void _join();
+
 };
 }
 }
@@ -80,7 +96,7 @@ private:
 ///////////////////////////////////////////////////////////////////////////////
 inline spdlog::sinks::async_sink::async_sink(const q_type::size_type max_queue_size)
     :_sinks(),
-     _active(true),
+     _active(false),
      _q(max_queue_size),
      _back_thread(&async_sink::_thread_loop, this)
 {}
@@ -92,14 +108,15 @@ inline spdlog::sinks::async_sink::~async_sink()
 
 inline void spdlog::sinks::async_sink::_sink_it(const details::log_msg& msg)
 {
-    if (!_active)
-        return;
+    _push_sentry();
     _q.push(msg);
 }
 
+
 inline void spdlog::sinks::async_sink::_thread_loop()
 {
-    static std::chrono::seconds  pop_timeout { 1 };
+    std::chrono::seconds  pop_timeout { 1 };
+
     while (_active)
     {
         q_type::item_type msg;
@@ -108,9 +125,22 @@ inline void spdlog::sinks::async_sink::_thread_loop()
             if (!_active)
                 return;
             for (auto &s : _sinks)
+            {
+                try
                 {
                     s->log(msg);
                 }
+
+                catch (const std::exception& ex)
+                {
+                    _last_backthread_ex = std::make_shared<spdlog_ex>(ex.what());
+                }
+                catch (...)
+                {
+                    _last_backthread_ex = std::make_shared<spdlog_ex>("Unknown exception");
+                }
+
+            }
         }
     }
 }
@@ -149,10 +179,18 @@ inline void spdlog::sinks::async_sink::shutdown(const std::chrono::milliseconds&
 }
 
 
+inline void spdlog::sinks::async_sink::_push_sentry()
+{
+    std::shared_ptr<spdlog_ex> ex_copy = std::move(_last_backthread_ex);
+    if (ex_copy)
+        throw *ex_copy;
+    if (!_active)
+        throw(spdlog_ex("async_sink not active"));
+}
+
 
 inline void spdlog::sinks::async_sink::_join()
 {
-    std::lock_guard<std::mutex> guard(_mutex);
     _active = false;
     if (_back_thread.joinable())
     {
@@ -160,11 +198,9 @@ inline void spdlog::sinks::async_sink::_join()
         {
             _back_thread.join();
         }
-        catch (const std::system_error&) //Dont crush if thread not joinable
-        {
-        }
+        catch (const std::system_error&) //Dont crash if thread not joinable
+        {}
     }
 
-
 }