Refactored error handler

include/spdlog/details/default_err_handler.h

@@ -5,6 +5,7 @@
 
 #include <string>
 #include <mutex>
+#include <exception>
 #include "spdlog/common.h"
 
 // by default, prints the error to stderr, thread safe
@@ -13,7 +14,7 @@ namespace details {
 class default_err_handler {
     mutable std::mutex mutex_;
 public:
-    void handle(const std::string& origin, const source_loc& loc, const std::string &err_msg) const;
+    void handle_ex(const std::string& origin, const source_loc& loc, const std::exception& ex) const;
 };
 
 

include/spdlog/logger.h

@@ -3,20 +3,13 @@
 
 #pragma once
 
-// Thread safe logger, Except for the following methods which are not thread-safe:
+// Thread-safe logger, with exceptions for these non-thread-safe methods:
-//   set_pattern()
+//   set_pattern()       - Modifies the log pattern.
-//   set_formatter()
+//   set_formatter()     - Sets a new formatter.
-//   set_error_handler()
+//   set_error_handler() - Assigns a new error handler.
-//   sinks() non const version
+//   sinks() (non-const) - Accesses and potentially modifies the sinks directly.
-// Has name, log level, vector of std::shared sink pointers and formatter
+// By default, the logger does not throw exceptions during logging.
-// Upon each log write the logger:
+// To enable exception throwing for logging errors, set a custom error handler.
-// 1. Checks if its log level is enough to log the message and if yes:
-// 2. Call the underlying sinks to do the job.
-// 3. Each sink use its own private copy of a formatter to format the message
-// and send to its destination.
-//
-// The use of private formatter per sink provides the opportunity to cache some
-// formatted data, and support for different format per sink.
 
 #include <cassert>
 #include <iterator>
@@ -179,12 +172,10 @@ private:
             memory_buf_t buf;
             fmt::vformat_to(std::back_inserter(buf), format_string, fmt::make_format_args(args...));
             sink_it_(details::log_msg(loc, name_, lvl, string_view_t(buf.data(), buf.size())));
-        }
+        } catch (const std::exception &ex) {
-        catch (const std::exception &ex) {                                                                                    \
+            handle_ex_(loc, ex);
-            handle_error_(loc, ex.what());                                                                                           \
+        } catch (...) {
-        }                                                                                                                     \
+            handle_unknown_ex_(loc);
-        catch (...) {                                                                                                         \
-            handle_error_(loc, "Unknown exception");                                                           \
         }
     }
 
@@ -195,12 +186,10 @@ private:
             if (sink->should_log(msg.log_level)) {
                 try {
                     sink->log(msg);
-                }
+                } catch (const std::exception &ex) {
-                catch (const std::exception &ex) {                                                                                    \
+                    handle_ex_(msg.source, ex);
-                    handle_error_(msg.source, ex.what());                                                                                           \
+                } catch (...) {
-                }                                                                                                                     \
+                    handle_unknown_ex_(msg.source);
-                catch (...) {                                                                                                         \
-                    handle_error_(msg.source, "Unknown exception");                                                           \
                 }
             }
         }
@@ -212,7 +201,8 @@ private:
     void flush_();
     [[nodiscard]] bool should_flush_(const details::log_msg &msg) const;
 
-    void handle_error_(const source_loc& loc, const std::string &err_msg) const;
+    void handle_ex_(const source_loc &loc, const std::exception &ex) const;
+    void handle_unknown_ex_(const source_loc &loc) const;
 };
 
 }  // namespace spdlog

src/details/default_err_handler.cpp

@@ -8,17 +8,18 @@
 namespace spdlog {
 namespace details {
 
-void default_err_handler::handle(const std::string &origin, const source_loc &loc, const std::string &err_msg) const {
+// print error to stderr with source location if present
+void default_err_handler::handle_ex(const std::string &origin, const source_loc &loc, const std::exception &ex) const {
     std::lock_guard lk{mutex_};
     const auto tm_time = os::localtime();
     char date_buf[128];
     std::strftime(date_buf, sizeof(date_buf), "%Y-%m-%d %H:%M:%S", &tm_time);
     std::string msg;
     if (loc.empty()) {
-        msg = fmt_lib::format("[*** LOGGING ERROR ***] [{}] [{}] {}\n", date_buf, origin, err_msg);
+        msg = fmt_lib::format("[*** LOGGING ERROR ***] [{}] [{}] {}\n", date_buf, origin, ex.what());
-    }
+    } else {
-    else {
+        msg = fmt_lib::format("[*** LOGGING ERROR ***] [{}({})] [{}] [{}] {}\n", loc.filename, loc.line, date_buf, origin,
-        msg = fmt_lib::format("[*** LOGGING ERROR ***] [{}({})] [{}] [{}] {}\n", loc.filename, loc.line, date_buf, origin, err_msg);
+                              ex.what());
     }
     std::fputs(msg.c_str(), stderr);
 }

src/logger.cpp

@@ -60,9 +60,7 @@ const std::vector<sink_ptr> &logger::sinks() const { return sinks_; }
 std::vector<sink_ptr> &logger::sinks() { return sinks_; }
 
 // custom error handler
-void logger::set_error_handler(err_handler handler) {
+void logger::set_error_handler(err_handler handler) { custom_err_handler_ = std::move(handler); }
-    custom_err_handler_ = std::move(handler);
-}
 
 // create new logger with same sinks and configuration.
 std::shared_ptr<logger> logger::clone(std::string logger_name) {
@@ -76,12 +74,10 @@ void logger::flush_() {
     for (auto &sink : sinks_) {
         try {
             sink->flush();
-        }
+        } catch (const std::exception &ex) {
-        catch (const std::exception &ex) {                                                                                    \
+            handle_ex_(source_loc{}, ex);
-            handle_error_(source_loc{}, ex.what());                                                                                           \
+        } catch (...) {
-        }                                                                                                                     \
+            handle_unknown_ex_(source_loc{});
-        catch (...) {                                                                                                         \
-            handle_error_(source_loc{}, "Unknown exception");                                                           \
         }
     }
 }
@@ -91,12 +87,20 @@ bool logger::should_flush_(const details::log_msg &msg) const {
     return (msg.log_level >= flush_level) && (msg.log_level != level::off);
 }
 
-void logger::handle_error_(const source_loc &loc, const std::string &err_msg) const {
+void logger::handle_ex_(const source_loc &loc, const std::exception &ex) const {
     if (custom_err_handler_) {
-        custom_err_handler_(err_msg);
+        custom_err_handler_(ex.what());
         return;
     }
-    default_err_handler_.handle(name_, loc, err_msg);
+    default_err_handler_.handle_ex(name_, loc, ex);
+}
+
+void logger::handle_unknown_ex_(const source_loc &loc) const {
+    if (custom_err_handler_) {
+        custom_err_handler_("unknown exception");
+        return;
+    }
+    default_err_handler_.handle_ex(name_, loc, std::runtime_error("Unknown exception"));
 }
 
 }  // namespace spdlog

src/sinks/async_sink.cpp

@@ -107,7 +107,7 @@ void async_sink::backend_log_(const details::log_msg &msg)  {
             try {
                 sink->log(msg);
             } catch (const std::exception &ex) {
-                err_handler_.handle("async", msg.source, std::string("async log failed: ") + ex.what());
+                err_handler_.handle_ex("async log", msg.source, ex);
             }
         }
     }
@@ -118,9 +118,9 @@ void async_sink::backend_flush_() {
         try {
             sink->flush();
         } catch (const std::exception &ex) {
-            err_handler_.handle("async", source_loc{}, std::string("async flush failed: ") + ex.what());
+            err_handler_.handle_ex("async flush", source_loc{}, ex);
         } catch (...) {
-            err_handler_.handle("async", source_loc{}, "Async flush failed with unknown exception");
+            err_handler_.handle_ex("async flush", source_loc{}, std::runtime_error("Unknown exception during flush"));
         }
     }
 }