Unnecessary backtrace begin/end logs (#2568)

* add empty getter function to tracer

* add unit test to check empty tracer

Co-authored-by: Gyorgy Katona <gykatona@logmein.com>

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); });

tests/test_backtrace.cpp

@@ -31,6 +31,19 @@ TEST_CASE("bactrace1", "[bactrace]")
     REQUIRE(test_sink->lines()[7] == "****************** Backtrace End ********************");
 }
 
+TEST_CASE("bactrace-empty", "[bactrace]")
+{
+    using spdlog::sinks::test_sink_st;
+    auto test_sink = std::make_shared<test_sink_st>();
+    size_t backtrace_size = 5;
+
+    spdlog::logger logger("test-backtrace", test_sink);
+    logger.set_pattern("%v");
+    logger.enable_backtrace(backtrace_size);
+    logger.dump_backtrace();
+    REQUIRE(test_sink->lines().size() == 0);
+}
+
 TEST_CASE("bactrace-async", "[bactrace]")
 {
     using spdlog::sinks::test_sink_mt;