feat: handle graceful shutdown

Trap termination signals in the main program using context.Context.

If a SIGINT or SIGTERM is received, send a SIGTERM to the sub-programs
and wait for them to shutdown gracefully.

If the sub-program is stuck for 5 minutes, force-kill them.

command/cleanup.go

@@ -26,7 +26,7 @@ func CmdCleanup(c *cli.Context) (err error) {
 
 	var toUndeploy []string
 
-	ctx := context.Background()
+	ctx := contextWithHandler()
 	ghCli := githubClient(ctx, c)
 	owner, repo := githubSlug(c)
 
@@ -37,7 +37,7 @@ func CmdCleanup(c *cli.Context) (err error) {
 		// undeploy all closed pull requests
 		var deployed []string
 
-		deployed, err = listDeployedPullRequests(listScript)
+		deployed, err = listDeployedPullRequests(ctx, listScript)
 		if err != nil {
 			return err
 		}
@@ -86,13 +86,36 @@ func CmdCleanup(c *cli.Context) (err error) {
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
 
-		err = cmd.Run()
+		err = cmd.Start()
 		if err != nil {
 			log.Println("undeploy error: ", err)
 
 			lastErr = err
 
-			continue
+			select {
+			case <-ctx.Done():
+				log.Println("undeploy cancelled: ", ctx.Err())
+
+				return lastErr
+			default:
+				continue
+			}
+		}
+
+		err = waitOrStop(ctx, cmd)
+		if err != nil {
+			log.Println("undeploy error: ", err)
+
+			lastErr = err
+
+			select {
+			case <-ctx.Done():
+				log.Println("undeploy cancelled: ", ctx.Err())
+
+				return lastErr
+			default:
+				continue
+			}
 		}
 
 		destroyGitHubDeployments(ctx, ghCli, owner, repo, pullRequestID, ignoreMissing)
@@ -112,13 +135,22 @@ func contains(item string, list []string) bool {
 }
 
 // Get the list of deployed Pull request based on given script.
-func listDeployedPullRequests(listScript string) ([]string, error) {
-	var stdout strings.Builder
+func listDeployedPullRequests(ctx context.Context, listScript string) ([]string, error) {
+	var (
+		stdout strings.Builder
+		err    error
+	)
 
 	cmd := exec.Command(listScript)
 	cmd.Stdout = &stdout
 
-	if err := cmd.Run(); err != nil {
+	err = cmd.Start()
+	if err != nil {
+		return nil, err
+	}
+
+	err = waitOrStop(ctx, cmd)
+	if err != nil {
 		return nil, err
 	}
 

command/please.go

@@ -2,7 +2,6 @@ package command
 
 import (
 	"bytes"
-	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -89,7 +88,7 @@ func CmdPlease(c *cli.Context) (err error) {
 		environment = fmt.Sprintf("pr-%d", pr)
 	}
 
-	ctx := context.Background()
+	ctx := contextWithHandler()
 	ghCli := githubClient(ctx, c)
 
 	log.Println("deploy ref", ref)
@@ -168,7 +167,7 @@ func CmdPlease(c *cli.Context) (err error) {
 	}
 
 	// Wait on the deploy to finish
-	err = cmd.Wait()
+	err = waitOrStop(ctx, cmd)
 	if err != nil {
 		err2 := updateStatus(StateFailure, "")
 		if err2 != nil {

command/utils.go

@@ -3,7 +3,12 @@ package command
 import (
 	"context"
 	"log"
+	"os"
+	"os/exec"
+	"os/signal"
 	"regexp"
+	"syscall"
+	"time"
 
 	"github.com/google/go-github/github"
 	secretvalue "github.com/zimbatm/go-secretvalue"
@@ -61,3 +66,87 @@ func refString(str string) *string {
 func refStringList(l []string) *[]string {
 	return &l
 }
+
+var DefaultKillDelay = 5 * time.Minute
+
+// waitOrStop waits for the already-started command cmd by calling its Wait method.
+//
+// If cmd does not return before ctx is done, waitOrStop sends it the given interrupt signal.
+// waitOrStop waits DefaultKillDelay for Wait to return before sending os.Kill.
+//
+// This function is copied from the one added to x/playground/internal in
+// http://golang.org/cl/228438.
+func waitOrStop(ctx context.Context, cmd *exec.Cmd) error {
+	if cmd.Process == nil {
+		panic("waitOrStop called with a nil cmd.Process — missing Start call?")
+	}
+
+	errc := make(chan error)
+	go func() {
+		select {
+		case errc <- nil:
+			return
+		case <-ctx.Done():
+		}
+
+		err := cmd.Process.Signal(os.Interrupt)
+		if err == nil {
+			err = ctx.Err() // Report ctx.Err() as the reason we interrupted.
+		} else if err.Error() == "os: process already finished" {
+			errc <- nil
+
+			return
+		}
+
+		if DefaultKillDelay > 0 {
+			timer := time.NewTimer(DefaultKillDelay)
+			select {
+			// Report ctx.Err() as the reason we interrupted the process...
+			case errc <- ctx.Err():
+				timer.Stop()
+
+				return
+			// ...but after killDelay has elapsed, fall back to a stronger signal.
+			case <-timer.C:
+			}
+
+			// Wait still hasn't returned.
+			// Kill the process harder to make sure that it exits.
+			//
+			// Ignore any error: if cmd.Process has already terminated, we still
+			// want to send ctx.Err() (or the error from the Interrupt call)
+			// to properly attribute the signal that may have terminated it.
+			_ = cmd.Process.Kill()
+		}
+
+		errc <- err
+	}()
+
+	waitErr := cmd.Wait()
+
+	interruptErr := <-errc
+	if interruptErr != nil {
+		return interruptErr
+	}
+
+	return waitErr
+}
+
+// contextWithHandler returns a context that is canceled when the program receives a SIGINT or SIGTERM.
+//
+// !! Only call this function once per program.
+func contextWithHandler() context.Context {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	signalChan := make(chan os.Signal, 1)
+
+	signal.Notify(signalChan, syscall.SIGINT, syscall.SIGTERM)
+
+	go func() {
+		sig := <-signalChan
+		log.Printf("Received signal %s, stopping", sig)
+		cancel()
+	}()
+
+	return ctx
+}