runsc: generate exec pidfile after everything is ready.

PiperOrigin-RevId: 221123160
Change-Id: Ia7061d60d114d69f49aba853fe6bae3c733522b5

1 files changed, 9 insertions, 6 deletions

diff --git a/runsc/cmd/exec.go b/runsc/cmd/exec.go
index 9a395e6f1..35aa5499e 100644
--- a/runsc/cmd/exec.go
+++ b/runsc/cmd/exec.go
@@ -146,12 +146,6 @@ func (ex *Exec) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		return ex.execAndWait(waitStatus)
 	}
 
-	if ex.pidFile != "" {
-		if err := ioutil.WriteFile(ex.pidFile, []byte(strconv.Itoa(os.Getpid())), 0644); err != nil {
-			Fatalf("error writing pid file: %v", err)
-		}
-	}
-
 	// Start the new process and get it pid.
 	pid, err := c.Execute(e)
 	if err != nil {
@@ -173,6 +167,15 @@ func (ex *Exec) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		}
 	}
 
+	// Generate the pid file after the internal pid file is generated, so that users
+	// can safely assume that the internal pid file is ready after `runsc exec -d`
+	// returns.
+	if ex.pidFile != "" {
+		if err := ioutil.WriteFile(ex.pidFile, []byte(strconv.Itoa(os.Getpid())), 0644); err != nil {
+			Fatalf("error writing pid file: %v", err)
+		}
+	}
+
 	// Wait for the process to exit.
 	ws, err := c.WaitPID(pid, ex.clearStatus)
 	if err != nil {