add empty getter function to tracer

include/spdlog/details/backtracer-inl.h

@@ -54,6 +54,12 @@ SPDLOG_INLINE void backtracer::push_back(const log_msg &msg)
     messages_.push_back(log_msg_buffer{msg});
 }
 
+SPDLOG_INLINE bool backtracer::empty() const
+{
+    std::lock_guard<std::mutex> lock{mutex_};
+    return messages_.empty();
+}
+
 // pop all items in the q and apply the given fun on each of them.
 SPDLOG_INLINE void backtracer::foreach_pop(std::function<void(const details::log_msg &)> fun)
 {

include/spdlog/details/backtracer.h

@@ -32,6 +32,7 @@ public:
     void disable();
     bool enabled() const;
     void push_back(const log_msg &msg);
+    bool empty() const;
 
     // pop all items in the q and apply the given fun on each of them.
     void foreach_pop(std::function<void(const details::log_msg &)> fun);

include/spdlog/logger-inl.h

@@ -210,7 +210,7 @@ SPDLOG_INLINE void logger::flush_()
 SPDLOG_INLINE void logger::dump_backtrace_()
 {
     using details::log_msg;
-    if (tracer_.enabled())
+    if (tracer_.enabled() && !tracer_.empty())
     {
         sink_it_(log_msg{name(), level::info, "****************** Backtrace Start ******************"});
         tracer_.foreach_pop([this](const log_msg &msg) { this->sink_it_(msg); });