fix issue #85: prepare to handle SIGTERM

Makefile

@@ -68,7 +68,7 @@ research:
 
 .PHONY: test-cmd
 test-cmd:
-	docker run --rm \
+	docker run --rm -it \
 	           -v '$(GOPATH)/src/$(GO_PACKAGE)':'/go/src/$(GO_PACKAGE)' \
 	           -w '/go/src/$(GO_PACKAGE)' \
 	           golang:1.7 \

cmd/semaphore/main.go

@@ -1,13 +1,47 @@
 package main
 
 import (
+	"context"
 	"flag"
 	"fmt"
+	"os"
+	"os/signal"
 	"strings"
 )
 
+/*
+Prototype:
+$ semaphore create 4
+$ semaphore add -- docker build ...
+$ semaphore add -- docker build ...
+...
+$ semaphore wait | semaphore wait --notify
+... show progress (colored output)
+[==>........] 2/10
+
+command `docker build ...`
+output:
+ ...
+
+command...
+*/
 func main() {
+	ctx, cancel := context.WithCancel(context.Background())
+	c := make(chan os.Signal, 1)
+
+	signal.Notify(c, os.Interrupt)
+	defer func() {
+		signal.Stop(c)
+		cancel()
+	}()
+
+	select {
+	case <-c:
+		cancel()
+	case <-ctx.Done():
+	}
+
 	flag.Parse()
 	fmt.Println(strings.Join(flag.Args(), ", "))
-	fmt.Println(commit, date, version)
+	fmt.Println(commit, date, version, os.TempDir())
 }