Move signal handling code to pkg/signal.Trap

Signed-off-by: Solomon Hykes <solomon@docker.com>

signal/trap.go

@@ -0,0 +1,53 @@
+package signal
+
+import (
+	"log"
+	"os"
+	gosignal "os/signal"
+	"sync/atomic"
+	"syscall"
+)
+
+// Trap sets up a simplified signal "trap", appropriate for common
+// behavior expected from a vanilla unix command-line tool in general
+// (and the Docker engine in particular).
+//
+// * If SIGINT or SIGTERM are received, `cleanup` is called, then the process is terminated.
+// * If SIGINT or SIGTERM are repeated 3 times before cleanup is complete, then cleanup is
+// skipped and the process terminated directly.
+// * If "DEBUG" is set in the environment, SIGQUIT causes an exit without cleanup.
+//
+func Trap(cleanup func()) {
+	c := make(chan os.Signal, 1)
+	signals := []os.Signal{os.Interrupt, syscall.SIGTERM}
+	if os.Getenv("DEBUG") == "" {
+		signals = append(signals, syscall.SIGQUIT)
+	}
+	gosignal.Notify(c, signals...)
+	go func() {
+		interruptCount := uint32(0)
+		for sig := range c {
+			go func(sig os.Signal) {
+				log.Printf("Received signal '%v', starting shutdown of docker...\n", sig)
+				switch sig {
+				case os.Interrupt, syscall.SIGTERM:
+					// If the user really wants to interrupt, let him do so.
+					if atomic.LoadUint32(&interruptCount) < 3 {
+						atomic.AddUint32(&interruptCount, 1)
+						// Initiate the cleanup only once
+						if atomic.LoadUint32(&interruptCount) == 1 {
+							// Call cleanup handler
+							cleanup()
+						} else {
+							return
+						}
+					} else {
+						log.Printf("Force shutdown of docker, interrupting cleanup\n")
+					}
+				case syscall.SIGQUIT:
+				}
+				os.Exit(128 + int(sig.(syscall.Signal)))
+			}(sig)
+		}
+	}()
+}