Add %N pattern formatter for logging the thread name using pthreads

This commit adds the SPDLOG_NO_PTHREAD_ID CMake option for enabling
saving of the pthread handle. This can be used in conjunction with the
%N pattern formatter for logging the name of the thread. This can be
really useful if you have a large application with many threads that are
hard to differentiate.

The option is disabled by default as I'm sure this won't work on
windows.

This patch also adds a test for testing the new flag.

CMakeLists.txt

@@ -105,6 +105,7 @@ endif()
 
 option(SPDLOG_PREVENT_CHILD_FD "Prevent from child processes to inherit log file descriptors" OFF)
 option(SPDLOG_NO_THREAD_ID "prevent spdlog from querying the thread id on each log call if thread id is not needed" OFF)
+option(SPDLOG_NO_PTHREAD_ID "prevent spdlog from querying the pthread id on each log call if pthread id is not needed (required for %N)" ON)
 option(SPDLOG_NO_TLS "prevent spdlog from using thread local storage" OFF)
 option(
     SPDLOG_NO_ATOMIC_LEVELS
@@ -220,6 +221,7 @@ foreach(
     SPDLOG_CLOCK_COARSE
     SPDLOG_PREVENT_CHILD_FD
     SPDLOG_NO_THREAD_ID
+    SPDLOG_NO_PTHREAD_ID
     SPDLOG_NO_TLS
     SPDLOG_NO_ATOMIC_LEVELS
     SPDLOG_DISABLE_DEFAULT_LOGGER)

include/spdlog/details/log_msg-inl.h

@@ -19,6 +19,9 @@ SPDLOG_INLINE log_msg::log_msg(spdlog::log_clock::time_point log_time, spdlog::s
     , time(log_time)
 #ifndef SPDLOG_NO_THREAD_ID
     , thread_id(os::thread_id())
+#endif
+#ifndef SPDLOG_NO_PTHREAD_ID
+    , pthread_id(pthread_self())
 #endif
     , source(loc)
     , payload(msg)

include/spdlog/details/log_msg.h

@@ -22,6 +22,10 @@ struct SPDLOG_API log_msg
     log_clock::time_point time;
     size_t thread_id{0};
 
+#ifndef SPDLOG_NO_PTHREAD_ID
+    pthread_t pthread_id{0};
+#endif
+
     // wrapping the formatted text with color (updated by pattern_formatter).
     mutable size_t color_range_start{0};
     mutable size_t color_range_end{0};

include/spdlog/pattern_formatter-inl.h

@@ -658,6 +658,29 @@ public:
     }
 };
 
+// Thread name
+template<typename ScopedPadder>
+class N_formatter final : public flag_formatter
+{
+public:
+    explicit N_formatter(padding_info padinfo)
+        : flag_formatter(padinfo)
+    {}
+
+    void format(const details::log_msg &msg, const std::tm &, memory_buf_t &dest) override
+    {
+        char threadNameBuffer[16] = { 0 };
+#ifndef SPDLOG_NO_PTHREAD_ID
+        pthread_getname_np(msg.pthread_id, threadNameBuffer, 16);
+#endif
+        threadName_ = threadNameBuffer;
+        ScopedPadder p(threadName_.size(), padinfo_, dest);
+        fmt_helper::append_string_view(threadName_, dest);
+    }
+private:
+    std::string threadName_;
+};
+
 // Current pid
 template<typename ScopedPadder>
 class pid_formatter final : public flag_formatter
@@ -1115,6 +1138,10 @@ SPDLOG_INLINE void pattern_formatter::handle_flag_(char flag, details::padding_i
         formatters_.push_back(details::make_unique<details::t_formatter<Padder>>(padding));
         break;
 
+    case ('N'): // thread name
+        formatters_.push_back(details::make_unique<details::N_formatter<Padder>>(padding));
+        break;
+
     case ('v'): // the message text
         formatters_.push_back(details::make_unique<details::v_formatter<Padder>>(padding));
         break;

tests/test_pattern_formatter.cpp

@@ -59,6 +59,23 @@ TEST_CASE("date MM/DD/YY ", "[pattern_formatter]")
     REQUIRE(log_to_str("Some message", "%D %v", spdlog::pattern_time_type::local, "\n") == oss.str());
 }
 
+
+#ifndef SPDLOG_NO_PTHREAD_ID
+TEST_CASE("thread name formatter", "[pattern_formatter]")
+{
+    char originalName[16] = { 0 };
+    pthread_getname_np(pthread_self(), originalName, 16);
+    std::string expected = "[";
+    expected += originalName;
+    expected += "] Some message\n";
+    REQUIRE(log_to_str("Some message", "[%N] %v", spdlog::pattern_time_type::local, "\n") == expected);
+    pthread_setname_np(pthread_self(), "Testname");
+    REQUIRE(log_to_str("Some message", "[%N] %v", spdlog::pattern_time_type::local, "\n") == "[Testname] Some message\n");
+    pthread_setname_np(pthread_self(), originalName);
+}
+
+#endif
+
 TEST_CASE("color range test1", "[pattern_formatter]")
 {
     auto formatter = std::make_shared<spdlog::pattern_formatter>("%^%v%$", spdlog::pattern_time_type::local, "\n");