Fix runmqserver error handling

cmd/runmqserver/signals.go

@@ -0,0 +1,79 @@
+/*
+© Copyright IBM Corporation 2017
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package main
+
+import (
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	startReaping = iota
+	reapNow      = iota
+)
+
+func signalHandler(qmgr string) chan int {
+	control := make(chan int)
+	// Use separate channels for the signals, to avoid SIGCHLD signals swamping
+	// the buffer, and preventing other signals.
+	stopSignals := make(chan os.Signal)
+	reapSignals := make(chan os.Signal)
+	signal.Notify(stopSignals, syscall.SIGTERM, syscall.SIGINT)
+	go func() {
+		for {
+			select {
+			case sig := <-stopSignals:
+				log.Printf("Signal received: %v", sig)
+				signal.Stop(reapSignals)
+				signal.Stop(stopSignals)
+				stopQueueManager(qmgr)
+				// One final reap
+				reapZombies()
+				close(control)
+				// End the goroutine
+				return
+			case <-reapSignals:
+				reapZombies()
+			case job := <-control:
+				switch {
+				case job == startReaping:
+					// Add SIGCHLD to the list of signals we're listening to
+					signal.Notify(reapSignals, syscall.SIGCHLD)
+				case job == reapNow:
+					reapZombies()
+				}
+			}
+		}
+	}()
+	return control
+}
+
+// reapZombies reaps any zombie (terminated) processes now.
+// This function should be called before exiting.
+func reapZombies() {
+	for {
+		var ws unix.WaitStatus
+		pid, err := unix.Wait4(-1, &ws, unix.WNOHANG, nil)
+		// If err or pid indicate "no child processes"
+		if pid == 0 || err == unix.ECHILD {
+			return
+		}
+	}
+}