Handle exceptions in async sink

include/spdlog/logger.h

@@ -209,8 +209,7 @@ private:
     void flush_();
     [[nodiscard]] bool should_flush_(const details::log_msg &msg) const;
 
-    // handle errors during logging.
+    // default handler prints the error to stderr
-    // default handler prints the error to stderr at max rate of 1 message/sec.
     void err_handler_(const std::string &msg);
 };
 

include/spdlog/sinks/async_sink.h

@@ -70,9 +70,10 @@ private:
     using queue_t = details::mpmc_blocking_queue<async_log_msg>;
 
     void send_message_(async_log_msg::type msg_type, const details::log_msg &msg) const;
-    void backend_loop_() const;
+    void backend_loop_();
-    void backend_log_(const details::log_msg &msg) const;
+    void backend_log_(const details::log_msg &msg) ;
-    void backend_flush_() const;
+    void backend_flush_();
+    void err_handler_(const std::string &msg);
 
     config config_;
     std::unique_ptr<queue_t> q_;

src/sinks/async_sink.cpp

@@ -82,7 +82,7 @@ void async_sink::send_message_(async_log_msg::type msg_type, const details::log_
     }
 }
 
-void async_sink::backend_loop_() const {
+void async_sink::backend_loop_() {
     details::async_log_msg incoming_msg;
     for (;;) {
         q_->dequeue(incoming_msg);
@@ -101,18 +101,40 @@ void async_sink::backend_loop_() const {
     }
 }
 
-void async_sink::backend_log_(const details::log_msg &msg) const {
+void async_sink::backend_log_(const details::log_msg &msg)  {
     for (const auto &sink : config_.sinks) {
         if (sink->should_log(msg.log_level)) {
+            try {
                 sink->log(msg);
+            } catch (const std::exception &ex) {
+                err_handler_(std::string("async log failed: ") + ex.what());
+            }
         }
     }
 }
 
-void async_sink::backend_flush_() const {
+void async_sink::backend_flush_() {
     for (const auto &sink : config_.sinks) {
+        try {
             sink->flush();
+        } catch (const std::exception &ex) {
+            err_handler_(std::string("async flush failed: ") + ex.what());
+        } catch (...) {
+            err_handler_("Async flush failed with unknown exception");
+        }
+    }
 }
+void async_sink::err_handler_(const std::string &message) {
+    using std::chrono::system_clock;
+    const auto now = system_clock::now();
+    const auto tm_time = details::os::localtime(system_clock::to_time_t(now));
+    char date_buf[64];
+    std::strftime(date_buf, sizeof(date_buf), "%Y-%m-%d %H:%M:%S", &tm_time);
+#if defined(USING_R) && defined(R_R_H)  // if in R environment
+    REprintf("[*** LOG ERROR ***] [%s] [%s] %s\n", date_buf, name().c_str(), message.c_str());
+#else
+    std::fprintf(stderr, "[*** LOG ERROR ***] [%s] %s\n", date_buf, message.c_str());
+#endif
 }
 
 }  // namespace sinks

tests/test_async.cpp

@@ -286,3 +286,12 @@ TEST_CASE("level-off", "[async]") {
     REQUIRE(test_sink->msg_counter() == 0);
     REQUIRE(test_sink->flush_counter() == 0);
 }
+
+TEST_CASE("backend_ex", "[async]") {
+    const auto test_sink = std::make_shared<test_sink_mt>();
+    test_sink->set_exception(std::runtime_error("test backend exception"));
+    constexpr size_t queue_size = 16;
+    auto [logger, async_sink] = creat_async_logger(queue_size, test_sink);
+    REQUIRE_NOTHROW(logger->info("Hello message"));
+    REQUIRE_NOTHROW(logger->flush());
+}

tests/test_sink.h

@@ -8,6 +8,7 @@
 #include <chrono>
 #include <mutex>
 #include <thread>
+#include <exception>
 
 #include "spdlog/details/null_mutex.h"
 #include "spdlog/details/os.h"
@@ -36,6 +37,14 @@ public:
         delay_ = delay;
     }
 
+    void set_exception(const std::runtime_error& ex) {
+        exception_ptr_ = std::make_exception_ptr(ex);
+    }
+
+    void clear_exception() {
+        exception_ptr_ = nullptr;
+    }
+
     // return last output without the eol
     std::vector<std::string> lines() {
         std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
@@ -44,6 +53,9 @@ public:
 
 protected:
     void sink_it_(const details::log_msg &msg) override {
+        if (exception_ptr_) {
+            std::rethrow_exception(exception_ptr_);
+        }
         memory_buf_t formatted;
         base_sink<Mutex>::formatter_->format(msg, formatted);
         // save the line without the eol
@@ -55,12 +67,18 @@ protected:
         std::this_thread::sleep_for(delay_);
     }
 
-    void flush_() override { flush_counter_++; }
+    void flush_() override {
+        if (exception_ptr_) {
+            std::rethrow_exception(exception_ptr_);
+        }
+        flush_counter_++;
+    }
 
     size_t msg_counter_{0};
     size_t flush_counter_{0};
     std::chrono::milliseconds delay_{std::chrono::milliseconds::zero()};
     std::vector<std::string> lines_;
+    std::exception_ptr exception_ptr_; // will be thrown on next log or flush if not null
 };
 
 using test_sink_mt = test_sink<std::mutex>;