packer/plugin: Count number of interrupts atomically

packer/plugin/plugin.go

@@ -19,8 +19,14 @@ import (
 	"os/signal"
 	"runtime"
 	"strconv"
+	"sync/atomic"
 )
 
+// This is a count of the number of interrupts the process has received.
+// This is updated with sync/atomic whenever a SIGINT is received and can
+// be checked by the plugin safely to take action.
+var Interrupts int32 = 0
+
 const MagicCookieKey = "PACKER_PLUGIN_MAGIC_COOKIE"
 const MagicCookieValue = "d602bf8f470bc67ca7faa0386276bbdd4330efaf76d1a219cb4d6991ca9872b2"
 
@@ -86,17 +92,18 @@ func serve(server *rpc.Server) (err error) {
 	return
 }
 
-// Registers a signal handler to "swallow" interrupts so that the
+// Registers a signal handler to swallow and count interrupts so that the
 // plugin isn't killed. The main host Packer process is responsible
 // for killing the plugins when interrupted.
-func swallowInterrupts() {
+func countInterrupts() {
 	ch := make(chan os.Signal, 1)
 	signal.Notify(ch, os.Interrupt)
 
 	go func() {
 		for {
 			<-ch
-			log.Println("Received interrupt signal. Ignoring.")
+			newCount := atomic.AddInt32(&Interrupts, 1)
+			log.Printf("Received interrupt signal (count: %d). Ignoring.", newCount)
 		}
 	}()
 }
@@ -108,7 +115,7 @@ func ServeBuilder(builder packer.Builder) {
 	server := rpc.NewServer()
 	packrpc.RegisterBuilder(server, builder)
 
-	swallowInterrupts()
+	countInterrupts()
 	if err := serve(server); err != nil {
 		log.Printf("ERROR: %s", err)
 		os.Exit(1)
@@ -122,7 +129,7 @@ func ServeCommand(command packer.Command) {
 	server := rpc.NewServer()
 	packrpc.RegisterCommand(server, command)
 
-	swallowInterrupts()
+	countInterrupts()
 	if err := serve(server); err != nil {
 		log.Printf("ERROR: %s", err)
 		os.Exit(1)
@@ -136,7 +143,7 @@ func ServeHook(hook packer.Hook) {
 	server := rpc.NewServer()
 	packrpc.RegisterHook(server, hook)
 
-	swallowInterrupts()
+	countInterrupts()
 	if err := serve(server); err != nil {
 		log.Printf("ERROR: %s", err)
 		os.Exit(1)
@@ -150,7 +157,7 @@ func ServePostProcessor(p packer.PostProcessor) {
 	server := rpc.NewServer()
 	packrpc.RegisterPostProcessor(server, p)
 
-	swallowInterrupts()
+	countInterrupts()
 	if err := serve(server); err != nil {
 		log.Printf("ERROR: %s", err)
 		os.Exit(1)
@@ -164,7 +171,7 @@ func ServeProvisioner(p packer.Provisioner) {
 	server := rpc.NewServer()
 	packrpc.RegisterProvisioner(server, p)
 
-	swallowInterrupts()
+	countInterrupts()
 	if err := serve(server); err != nil {
 		log.Printf("ERROR: %s", err)
 		os.Exit(1)