From bc473d354cab3389af93b9f5c2c40a42f0ca5185 Mon Sep 17 00:00:00 2001
From: John Eikenberry <jae@zhar.net>
Date: Wed, 22 Apr 2020 19:01:22 -0700
Subject: [PATCH] fix data race b/w start and kill

Racing over saving and checking ProcessState. It was checking
ProcessState to see if the command had exited. I tweaked exitCh
to have closing it indicate that the command had exited.
---
 child/child.go | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/child/child.go b/child/child.go
index 3c94816f5..1b6742707 100644
--- a/child/child.go
+++ b/child/child.go
@@ -290,14 +290,14 @@ func (c *Child) start() error {
 		// down the exit channel.
 		c.stopLock.RLock()
 		defer c.stopLock.RUnlock()
-		if c.stopped {
-			return
+		if !c.stopped {
+			select {
+			case <-c.stopCh:
+			case exitCh <- code:
+			}
 		}
 
-		select {
-		case <-c.stopCh:
-		case exitCh <- code:
-		}
+		close(exitCh)
 	}()
 
 	c.exitCh = exitCh
@@ -365,16 +365,13 @@ func (c *Child) reload() error {
 	return c.signal(c.reloadSignal)
 }
 
+// kill sends the signal to kill the process using the configured signal
+// if set, else the default system signal
 func (c *Child) kill(immediately bool) {
-	if !c.running() {
-		return
-	}
 
-	exited := false
-	process := c.cmd.Process
-
-	if c.cmd.ProcessState != nil {
+	if !c.running() {
 		log.Printf("[DEBUG] (child) Kill() called but process dead; not waiting for splay.")
+		return
 	} else if immediately {
 		log.Printf("[DEBUG] (child) Kill() called but performing immediate shutdown; not waiting for splay.")
 	} else {
@@ -384,6 +381,9 @@ func (c *Child) kill(immediately bool) {
 		}
 	}
 
+	exited := false
+	process := c.cmd.Process
+
 	if c.killSignal != nil {
 		if err := process.Signal(c.killSignal); err == nil {
 			// Wait a few seconds for it to exit
@@ -410,6 +410,11 @@ func (c *Child) kill(immediately bool) {
 }
 
 func (c *Child) running() bool {
+	select {
+	case <-c.exitCh:
+		return false
+	default:
+	}
 	return c.cmd != nil && c.cmd.Process != nil
 }