Check if Process non-nil before calling Kill

sdboyer · sdboyer · commit e12550c1904b · 2017-04-16T10:32:05.000-04:00
A bad interleaving could (and has - golang#391) cause the context cancellation select branch to run before the normal process termination branch.
diff --git a/cmd.go b/cmd.go
@@ -63,8 +63,10 @@ func (c *monitoredCmd) run(ctx context.Context) error {
 				return &timeoutError{c.timeout}
 			}
 		case <-ctx.Done():
-			if err := c.cmd.Process.Kill(); err != nil {
-				return &killCmdError{err}
+			if c.cmd.Process != nil {
+				if err := c.cmd.Process.Kill(); err != nil {
+					return &killCmdError{err}
+				}
 			}
 			return c.ctx.Err()
 		case err := <-done:

Original file line number	Diff line number	Diff line change
`@@ -63,8 +63,10 @@ func (c *monitoredCmd) run(ctx context.Context) error {`
`63`	`63`	`return &timeoutError{c.timeout}`
`64`	`64`	`}`
`65`	`65`	`case <-ctx.Done():`
`66`		`- if err := c.cmd.Process.Kill(); err != nil {`
`67`		`- return &killCmdError{err}`
	`66`	`+ if c.cmd.Process != nil {`
	`67`	`+ if err := c.cmd.Process.Kill(); err != nil {`
	`68`	`+ return &killCmdError{err}`
	`69`	`+ }`
`68`	`70`	`}`
`69`	`71`	`return c.ctx.Err()`
`70`	`72`	`case err := <-done:`