From d17faf6bcbc15ea0a3c3ea13f100c5aaf5f0384c Mon Sep 17 00:00:00 2001
From: Shivaram Lingamneni <slingamn@cs.stanford.edu>
Date: Sun, 11 Dec 2022 00:53:12 -0500
Subject: [PATCH] fix #1975

Provide a nondestructive stack trace dump option even when the http pprof
listener is disabled
---
 irc/server.go              | 26 +++++++++++++++++++++-----
 irc/utils/signals.go       |  4 ++++
 irc/utils/signals_plan9.go |  3 +++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/irc/server.go b/irc/server.go
index 5800f5a4..1a7e1abd 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -12,6 +12,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"os/signal"
+	"runtime/pprof"
 	"strconv"
 	"strings"
 	"sync"
@@ -83,6 +84,7 @@ type Server struct {
 	rehashSignal      chan os.Signal
 	pprofServer       *http.Server
 	exitSignals       chan os.Signal
+	tracebackSignal   chan os.Signal
 	snomasks          SnoManager
 	store             *buntdb.DB
 	historyDB         mysql.MySQL
@@ -98,11 +100,12 @@ type Server struct {
 func NewServer(config *Config, logger *logger.Manager) (*Server, error) {
 	// initialize data structures
 	server := &Server{
-		ctime:        time.Now().UTC(),
-		listeners:    make(map[string]IRCListener),
-		logger:       logger,
-		rehashSignal: make(chan os.Signal, 1),
-		exitSignals:  make(chan os.Signal, len(utils.ServerExitSignals)),
+		ctime:           time.Now().UTC(),
+		listeners:       make(map[string]IRCListener),
+		logger:          logger,
+		rehashSignal:    make(chan os.Signal, 1),
+		exitSignals:     make(chan os.Signal, len(utils.ServerExitSignals)),
+		tracebackSignal: make(chan os.Signal, len(utils.ServerTracebackSignals)),
 	}
 	server.defcon.Store(5)
 
@@ -120,6 +123,9 @@ func NewServer(config *Config, logger *logger.Manager) (*Server, error) {
 	// Attempt to clean up when receiving these signals.
 	signal.Notify(server.exitSignals, utils.ServerExitSignals...)
 	signal.Notify(server.rehashSignal, syscall.SIGHUP)
+	if len(utils.ServerTracebackSignals) != 0 {
+		signal.Notify(server.tracebackSignal, utils.ServerTracebackSignals...)
+	}
 
 	time.AfterFunc(alwaysOnMaintenanceInterval, server.periodicAlwaysOnMaintenance)
 
@@ -158,6 +164,8 @@ func (server *Server) Run() {
 		case <-server.rehashSignal:
 			server.logger.Info("server", "Rehashing due to SIGHUP")
 			go server.rehash()
+		case <-server.tracebackSignal:
+			go server.dumpStacks()
 		}
 	}
 }
@@ -1128,3 +1136,11 @@ var (
     Edmund Huber,           edmund-huber
 `, "\n")
 )
+
+func (server *Server) dumpStacks() {
+	if gprof := pprof.Lookup("goroutine"); gprof != nil {
+		gprof.WriteTo(os.Stderr, 2)
+	} else {
+		server.logger.Error("internal", "unable to dump goroutine stacks")
+	}
+}
diff --git a/irc/utils/signals.go b/irc/utils/signals.go
index e381ab6d..20f45301 100644
--- a/irc/utils/signals.go
+++ b/irc/utils/signals.go
@@ -18,4 +18,8 @@ var (
 		syscall.SIGTERM,
 		syscall.SIGQUIT,
 	}
+
+	ServerTracebackSignals = []os.Signal{
+		syscall.SIGUSR1,
+	}
 )
diff --git a/irc/utils/signals_plan9.go b/irc/utils/signals_plan9.go
index 318a0552..9e1968e9 100644
--- a/irc/utils/signals_plan9.go
+++ b/irc/utils/signals_plan9.go
@@ -18,4 +18,7 @@ var (
 		syscall.SIGINT,
 		syscall.SIGTERM,
 	}
+
+	// no SIGUSR1 on plan9
+	ServerTracebackSignals []os.Signal
 )