Merge pull request #9774 from pwaller/cancellation

Add basic build cancellation

engine/engine.go

@@ -124,6 +124,8 @@ func (eng *Engine) Job(name string, args ...string) *Job {
 		Stderr:  NewOutput(),
 		env:     &Env{},
 		closeIO: true,
+
+		cancelled: make(chan struct{}),
 	}
 	if eng.Logging {
 		job.Stderr.Add(ioutils.NopWriteCloser(eng.Stderr))

engine/job.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"sync"
 	"time"
 
 	log "github.com/Sirupsen/logrus"
@@ -34,6 +35,12 @@ type Job struct {
 	status  Status
 	end     time.Time
 	closeIO bool
+
+	// When closed, the job has been cancelled.
+	// Note: not all jobs implement cancellation.
+	// See Job.Cancel() and Job.WaitCancelled()
+	cancelled  chan struct{}
+	cancelOnce sync.Once
 }
 
 type Status int
@@ -248,3 +255,15 @@ func (job *Job) StatusCode() int {
 func (job *Job) SetCloseIO(val bool) {
 	job.closeIO = val
 }
+
+// When called, causes the Job.WaitCancelled channel to unblock.
+func (job *Job) Cancel() {
+	job.cancelOnce.Do(func() {
+		close(job.cancelled)
+	})
+}
+
+// Returns a channel which is closed ("never blocks") when the job is cancelled.
+func (job *Job) WaitCancelled() <-chan struct{} {
+	return job.cancelled
+}