threads: prefix log messages with thread names

Introduce a new flag (`-logthreadnames`) which allows toggling
of this behavior.

4 files changed, 26 insertions, 10 deletions

diff --git a/doc/release-notes-15849.md b/doc/release-notes-15849.md
new file mode 100644
index 0000000000..a1df31f250
--- /dev/null
+++ b/doc/release-notes-15849.md
@@ -0,0 +1,6 @@
+Thread names in logs
+--------------------
+
+On platforms supporting `thread_local`, log lines can be prefixed with the name
+of the thread that caused the log. To enable this behavior, use
+`-logthreadnames=1`.
diff --git a/src/init.cpp b/src/init.cpp
index 408a133e4e..84fb313e96 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -508,6 +508,7 @@ void SetupServerArgs()
     gArgs.AddArg("-debugexclude=<category>", strprintf("Exclude debugging information for a category. Can be used in conjunction with -debug=1 to output debug logs for all categories except one or more specified categories."), false, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-logips", strprintf("Include IP addresses in debug output (default: %u)", DEFAULT_LOGIPS), false, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-logtimestamps", strprintf("Prepend debug output with timestamp (default: %u)", DEFAULT_LOGTIMESTAMPS), false, OptionsCategory::DEBUG_TEST);
+    gArgs.AddArg("-logthreadnames", strprintf("Prepend debug output with name of the originating thread (only available on platforms supporting thread_local) (default: %u)", DEFAULT_LOGTHREADNAMES), false, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-logtimemicros", strprintf("Add microsecond precision to debug timestamps (default: %u)", DEFAULT_LOGTIMEMICROS), true, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-mocktime=<n>", "Replace actual time with <n> seconds since epoch (default: 0)", true, OptionsCategory::DEBUG_TEST);
     gArgs.AddArg("-maxsigcachesize=<n>", strprintf("Limit sum of signature cache and script execution cache sizes to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE), true, OptionsCategory::DEBUG_TEST);
@@ -866,6 +867,7 @@ void InitLogging()
     LogInstance().m_print_to_console = gArgs.GetBoolArg("-printtoconsole", !gArgs.GetBoolArg("-daemon", false));
     LogInstance().m_log_timestamps = gArgs.GetBoolArg("-logtimestamps", DEFAULT_LOGTIMESTAMPS);
     LogInstance().m_log_time_micros = gArgs.GetBoolArg("-logtimemicros", DEFAULT_LOGTIMEMICROS);
+    LogInstance().m_log_threadnames = gArgs.GetBoolArg("-logthreadnames", DEFAULT_LOGTHREADNAMES);
 
     fLogIPs = gArgs.GetBoolArg("-logips", DEFAULT_LOGIPS);
 
diff --git a/src/logging.cpp b/src/logging.cpp
index 36cad6573a..3eda4995db 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -4,8 +4,11 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <logging.h>
+#include <util/threadnames.h>
 #include <util/time.h>
 
+#include <mutex>
+
 const char * const DEFAULT_DEBUGLOGFILE = "debug.log";
 
 BCLog::Logger& LogInstance()
@@ -174,7 +177,7 @@ std::vector<CLogCategoryActive> ListActiveLogCategories()
     return ret;
 }
 
-std::string BCLog::Logger::LogTimestampStr(const std::string &str)
+std::string BCLog::Logger::LogTimestampStr(const std::string& str)
 {
     std::string strStamped;
 
@@ -196,21 +199,24 @@ std::string BCLog::Logger::LogTimestampStr(const std::string &str)
     } else
         strStamped = str;
 
-    if (!str.empty() && str[str.size()-1] == '\n')
-        m_started_new_line = true;
-    else
-        m_started_new_line = false;
-
     return strStamped;
 }
 
 void BCLog::Logger::LogPrintStr(const std::string &str)
 {
-    std::string strTimestamped = LogTimestampStr(str);
+    std::string str_prefixed = str;
+
+    if (m_log_threadnames && m_started_new_line) {
+        str_prefixed.insert(0, "[" + util::ThreadGetInternalName() + "] ");
+    }
+
+    str_prefixed = LogTimestampStr(str_prefixed);
+
+    m_started_new_line = !str.empty() && str[str.size()-1] == '\n';
 
     if (m_print_to_console) {
         // print to console
-        fwrite(strTimestamped.data(), 1, strTimestamped.size(), stdout);
+        fwrite(str_prefixed.data(), 1, str_prefixed.size(), stdout);
         fflush(stdout);
     }
     if (m_print_to_file) {
@@ -218,7 +224,7 @@ void BCLog::Logger::LogPrintStr(const std::string &str)
 
         // buffer if we haven't opened the log yet
         if (m_fileout == nullptr) {
-            m_msgs_before_open.push_back(strTimestamped);
+            m_msgs_before_open.push_back(str_prefixed);
         }
         else
         {
@@ -232,7 +238,7 @@ void BCLog::Logger::LogPrintStr(const std::string &str)
                     m_fileout = new_fileout;
                 }
             }
-            FileWriteStr(strTimestamped, m_fileout);
+            FileWriteStr(str_prefixed, m_fileout);
         }
     }
 }
diff --git a/src/logging.h b/src/logging.h
index ac9d0dc0c7..e399d4c307 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -19,6 +19,7 @@
 static const bool DEFAULT_LOGTIMEMICROS = false;
 static const bool DEFAULT_LOGIPS        = false;
 static const bool DEFAULT_LOGTIMESTAMPS = true;
+static const bool DEFAULT_LOGTHREADNAMES = false;
 extern const char * const DEFAULT_DEBUGLOGFILE;
 
 extern bool fLogIPs;
@@ -81,6 +82,7 @@ namespace BCLog {
 
         bool m_log_timestamps = DEFAULT_LOGTIMESTAMPS;
         bool m_log_time_micros = DEFAULT_LOGTIMEMICROS;
+        bool m_log_threadnames = DEFAULT_LOGTHREADNAMES;
 
         fs::path m_file_path;
         std::atomic<bool> m_reopen_file{false};