fix #1975

Provide a nondestructive stack trace dump option even when the http pprof
listener is disabled

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
@@ -103,6 +105,7 @@ func NewServer(config *Config, logger *logger.Manager) (*Server, error) {
 		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")
+	}
+}

irc/utils/signals.go

@@ -18,4 +18,8 @@ var (
 		syscall.SIGTERM,
 		syscall.SIGQUIT,
 	}
+
+	ServerTracebackSignals = []os.Signal{
+		syscall.SIGUSR1,
+	}
 )

irc/utils/signals_plan9.go

@@ -18,4 +18,7 @@ var (
 		syscall.SIGINT,
 		syscall.SIGTERM,
 	}
+
+	// no SIGUSR1 on plan9
+	ServerTracebackSignals []os.Signal
 )