reaper: implement reaper interface

All reaper implementations must override its functions.
This new interface allows the creation of mock reapers that
are useful for unit testing.

Signed-off-by: Julio Montes <julio.montes@intel.com>

agent.go

@@ -69,7 +69,7 @@ type sandbox struct {
 	grpcListener net.Listener
 	sharedPidNs  namespace
 	mounts       []string
-	subreaper    *reaper
+	subreaper    reaper
 }
 
 type namespace struct {
@@ -575,16 +575,17 @@ func main() {
 		os.Exit(exitSuccess)
 	}()
 
+	r := &agentReaper{}
+	r.init()
+
 	// Initialize unique sandbox structure.
 	s := &sandbox{
 		containers: make(map[string]*container),
 		running:    false,
 		// pivot_root won't work for init, see
 		// Documention/filesystem/ramfs-rootfs-initramfs.txt
 		noPivotRoot: os.Getpid() == 1,
-		subreaper: &reaper{
-			exitCodeChans: make(map[int]chan<- int),
-		},
+		subreaper:   r,
 	}
 
 	if err = s.initLogger(); err != nil {

grpc.go

@@ -206,8 +206,8 @@ func (a *agentGRPC) execProcess(ctr *container, proc *process, createContainer b
 	// miss the opportunity to get the exit code, leading WaitProcess() to
 	// wait forever on the new channel.
 	// This lock has to be taken before we run the new process.
-	a.sandbox.subreaper.RLock()
-	defer a.sandbox.subreaper.RUnlock()
+	a.sandbox.subreaper.lock()
+	defer a.sandbox.subreaper.unlock()
 
 	if createContainer {
 		err = ctr.container.Start(&proc.process)

reaper.go

@@ -18,7 +18,19 @@ import (
 	grpcStatus "google.golang.org/grpc/status"
 )
 
-type reaper struct {
+type reaper interface {
+	init()
+	getExitCodeCh(pid int) (chan<- int, error)
+	setExitCodeCh(pid int, exitCodeCh chan<- int)
+	deleteExitCodeCh(pid int)
+	reap() error
+	start(c *exec.Cmd) (<-chan int, error)
+	wait(exitCodeCh <-chan int, proc waitProcess) (int, error)
+	lock()
+	unlock()
+}
+
+type agentReaper struct {
 	sync.RWMutex
 
 	chansLock     sync.RWMutex
@@ -33,7 +45,19 @@ func exitStatus(status unix.WaitStatus) int {
 	return status.ExitStatus()
 }
 
-func (r *reaper) getExitCodeCh(pid int) (chan<- int, error) {
+func (r *agentReaper) init() {
+	r.exitCodeChans = make(map[int]chan<- int)
+}
+
+func (r *agentReaper) lock() {
+	r.RLock()
+}
+
+func (r *agentReaper) unlock() {
+	r.RUnlock()
+}
+
+func (r *agentReaper) getExitCodeCh(pid int) (chan<- int, error) {
 	r.chansLock.RLock()
 	defer r.chansLock.RUnlock()
 
@@ -45,21 +69,21 @@ func (r *reaper) getExitCodeCh(pid int) (chan<- int, error) {
 	return exitCodeCh, nil
 }
 
-func (r *reaper) setExitCodeCh(pid int, exitCodeCh chan<- int) {
+func (r *agentReaper) setExitCodeCh(pid int, exitCodeCh chan<- int) {
 	r.chansLock.Lock()
 	defer r.chansLock.Unlock()
 
 	r.exitCodeChans[pid] = exitCodeCh
 }
 
-func (r *reaper) deleteExitCodeCh(pid int) {
+func (r *agentReaper) deleteExitCodeCh(pid int) {
 	r.chansLock.Lock()
 	defer r.chansLock.Unlock()
 
 	delete(r.exitCodeChans, pid)
 }
 
-func (r *reaper) reap() error {
+func (r *agentReaper) reap() error {
 	var (
 		ws  unix.WaitStatus
 		rus unix.Rusage
@@ -119,7 +143,7 @@ func (r *reaper) reap() error {
 // start starts the exec command and registers the process to the reaper.
 // This function is a helper for exec.Cmd.Start() since this needs to be
 // in sync with exec.Cmd.Wait().
-func (r *reaper) start(c *exec.Cmd) (<-chan int, error) {
+func (r *agentReaper) start(c *exec.Cmd) (<-chan int, error) {
 	// This lock is very important to avoid any race with reaper.reap().
 	// We don't want the reaper to reap a process before we have added
 	// it to the exit code channel list.
@@ -143,7 +167,7 @@ func (r *reaper) start(c *exec.Cmd) (<-chan int, error) {
 // from the subreaper, the exit code is sent through the provided channel.
 // This function is a helper for exec.Cmd.Wait() and os.Process.Wait() since
 // both cannot be used directly, because of the subreaper.
-func (r *reaper) wait(exitCodeCh <-chan int, proc waitProcess) (int, error) {
+func (r *agentReaper) wait(exitCodeCh <-chan int, proc waitProcess) (int, error) {
 	// Wait for the subreaper to receive the SIGCHLD signal. Once it gets
 	// it, this channel will be notified by receiving the exit code of the
 	// corresponding process.