feat(main): ignoring SIGTERM when managed by PM2

- there is a race condition during shutting down when go-judge receives SIGTERM from systemd and PM2 dumps a STOPPED status, resulting go-judge not auto-restart after a reboot
- PM2 uses SIGINT for stop signal so that we can distinguish different stop signal sent by different process manager
- So when detected that we are manged by PM2, we ignore the SIGTERM signal from the systemd and wait for PM2's SIGINT to avoid race condition

Unitech/pm2#6036

Author: criyle

cmd/go-judge/main.go

@@ -16,6 +16,7 @@ import (
 	"runtime"
 	"runtime/debug"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/criyle/go-judge/cmd/go-judge/config"
@@ -106,9 +107,21 @@ func main() {
 	newForceGCWorker(conf)
 
 	// Graceful shutdown...
-	signal.Notify(sig, os.Interrupt)
-	<-sig
-	signal.Reset(os.Interrupt)
+	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
+loop:
+	for s := range sig {
+		switch s {
+		case syscall.SIGINT:
+			break loop
+		case syscall.SIGTERM:
+			if isManagedByPM2() {
+				logger.Info("running with PM2, received SIGTERM (from systemd), ignoring")
+			} else {
+				break loop
+			}
+		}
+	}
+	signal.Reset(syscall.SIGINT, syscall.SIGTERM)
 
 	logger.Info("Shutting Down...")
 
@@ -591,3 +604,18 @@ func generateHandleConfig(conf *config.Config, builderParam map[string]any) func
 		})
 	}
 }
+
+func isManagedByPM2() bool {
+	// List of environment variables that pm2 typically sets.
+	pm2EnvVars := []string{
+		"PM2_HOME",
+		"PM2_JSON_PROCESSING",
+		"NODE_APP_INSTANCE",
+	}
+	for _, v := range pm2EnvVars {
+		if os.Getenv(v) != "" {
+			return true
+		}
+	}
+	return false
+}

env/env_cgroup_linux.go

@@ -76,6 +76,7 @@ func startTransientUnit(conn *dbus.Conn, scopeName string, logger *zap.Logger) e
 		dbus.PropWants(scopeName),
 		dbus.PropPids(uint32(os.Getpid())),
 		newSystemdProperty("Delegate", true),
+		newSystemdProperty("KillMode", "process"),
 	}
 	ch := make(chan string, 1)
 	if _, err := conn.StartTransientUnitContext(context.TODO(), scopeName, "replace", properties, ch); err != nil {