From f3f2456b0451d93a539eac63dac93a748e01317f Mon Sep 17 00:00:00 2001
From: Michael Crosby <michael@crosbymichael.com>
Date: Mon, 13 Jan 2014 16:10:23 -0800
Subject: [PATCH] Simplify chroot wait, address code review issues

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
---
 container.go                |  6 ++++--
 execdriver/chroot/driver.go | 22 +++++-----------------
 execdriver/driver.go        |  5 ++++-
 execdriver/lxc/driver.go    |  7 ++++---
 4 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/container.go b/container.go
index 4e66539c5c..e8277131cf 100644
--- a/container.go
+++ b/container.go
@@ -708,7 +708,7 @@ func (container *Container) Start() (err error) {
 	}
 
 	waitLock := make(chan struct{})
-	f := func(process *execdriver.Process) {
+	callback := func(process *execdriver.Process) {
 		container.State.SetRunning(process.Pid())
 		if process.Tty {
 			// The callback is called after the process Start()
@@ -724,7 +724,9 @@ func (container *Container) Start() (err error) {
 		close(waitLock)
 	}
 
-	go container.monitor(f)
+	// We use a callback here instead of a goroutine and an chan for
+	// syncronization purposes
+	go container.monitor(callback)
 
 	// Start should not return until the process is actually running
 	<-waitLock
diff --git a/execdriver/chroot/driver.go b/execdriver/chroot/driver.go
index eb2525be6d..e5dc69131c 100644
--- a/execdriver/chroot/driver.go
+++ b/execdriver/chroot/driver.go
@@ -9,11 +9,11 @@ import (
 type driver struct {
 }
 
-func NewDriver() (execdriver.Driver, error) {
+func NewDriver() (*driver, error) {
 	return &driver{}, nil
 }
 
-func (d *driver) String() string {
+func (d *driver) Name() string {
 	return "chroot"
 }
 
@@ -23,7 +23,7 @@ func (d *driver) Run(c *execdriver.Process, startCallback execdriver.StartCallba
 		c.Rootfs,
 		"/.dockerinit",
 		"-driver",
-		d.String(),
+		d.Name(),
 	}
 	params = append(params, c.Entrypoint)
 	params = append(params, c.Arguments...)
@@ -43,24 +43,12 @@ func (d *driver) Run(c *execdriver.Process, startCallback execdriver.StartCallba
 		return -1, err
 	}
 
-	var (
-		waitErr  error
-		waitLock = make(chan struct{})
-	)
-	go func() {
-		if err := c.Wait(); err != nil {
-			waitErr = err
-		}
-		close(waitLock)
-	}()
-
 	if startCallback != nil {
 		startCallback(c)
 	}
 
-	<-waitLock
-
-	return c.GetExitCode(), waitErr
+	err = c.Wait()
+	return c.GetExitCode(), err
 }
 
 func (d *driver) Kill(p *execdriver.Process, sig int) error {
diff --git a/execdriver/driver.go b/execdriver/driver.go
index cb9df96e79..fac4e27704 100644
--- a/execdriver/driver.go
+++ b/execdriver/driver.go
@@ -14,7 +14,7 @@ type Driver interface {
 	// TODO: @crosbymichael @creack wait should probably return the exit code
 	Wait(id string, duration time.Duration) error // Wait on an out of process...process - lxc ghosts
 	Version() string
-	String() string
+	Name() string
 }
 
 // Network settings of the container
@@ -43,6 +43,9 @@ type Process struct {
 }
 
 func (c *Process) Pid() int {
+	if c.Process == nil {
+		return -1
+	}
 	return c.Process.Pid
 }
 
diff --git a/execdriver/lxc/driver.go b/execdriver/lxc/driver.go
index b220ff146e..e37e105b5b 100644
--- a/execdriver/lxc/driver.go
+++ b/execdriver/lxc/driver.go
@@ -29,7 +29,7 @@ type driver struct {
 	sharedRoot bool
 }
 
-func NewDriver(root string, apparmor bool) (execdriver.Driver, error) {
+func NewDriver(root string, apparmor bool) (*driver, error) {
 	// setup unconfined symlink
 	if err := linkLxcStart(root); err != nil {
 		return nil, err
@@ -41,7 +41,7 @@ func NewDriver(root string, apparmor bool) (execdriver.Driver, error) {
 	}, nil
 }
 
-func (d *driver) String() string {
+func (d *driver) Name() string {
 	return "lxc"
 }
 
@@ -53,7 +53,7 @@ func (d *driver) Run(c *execdriver.Process, startCallback execdriver.StartCallba
 		"--",
 		c.InitPath,
 		"-driver",
-		d.String(),
+		d.Name(),
 	}
 
 	if c.Network != nil {
@@ -195,6 +195,7 @@ func (d *driver) waitForStart(c *execdriver.Process, waitLock chan struct{}) err
 		select {
 		case <-waitLock:
 			// If the process dies while waiting for it, just return
+			return nil
 			if c.ProcessState != nil && c.ProcessState.Exited() {
 				return nil
 			}