dotcloud/docker

package trap // import "github.com/docker/docker/cmd/dockerd/trap"

import (
    "context"
    "os"
    "os/signal"
    "syscall"

    "github.com/containerd/log"
)

const (
    // Immediately terminate the process when this many SIGINT or SIGTERM
    // signals are received.
    forceQuitCount = 3
)

// 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).
//
// The first time a SIGINT or SIGTERM signal is received, `cleanup` is called in
// a new goroutine.
//
// If SIGINT or SIGTERM are received 3 times, the process is terminated
// immediately with an exit code of 128 + the signal number.
func Trap(cleanup func()) {
    c := make(chan os.Signal, forceQuitCount)
    signal.Notify(c, os.Interrupt, syscall.SIGTERM)
    go func() {
        var interruptCount int
        for sig := range c {
            log.G(context.TODO()).Infof("Processing signal '%v'", sig)
            if interruptCount < forceQuitCount {
                interruptCount++
                // Initiate the cleanup only once
                if interruptCount == 1 {
                    go cleanup()
                }
                continue
            }

            log.G(context.TODO()).Info("Forcing docker daemon shutdown without cleanup; 3 interrupts received")
            os.Exit(128 + int(sig.(syscall.Signal)))
        }
    }()
}