libpod: avoid polling container status

use the inotify backend to be notified on the container exit instead
of polling continuosly the runtime.  Polling the runtime slowns
significantly down the podman execution time for short lived
processes:

$ time bin/podman run --rm -ti fedora true

real	0m0.324s
user	0m0.088s
sys	0m0.064s

from:

$ time podman run --rm -ti fedora true

real	0m4.199s
user	0m5.339s
sys	0m0.344s

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

2 files changed, 23 insertions, 19 deletions

diff --git a/libpod/container_api.go b/libpod/container_api.go
index 9e59104cc..9bf97c5d4 100644
--- a/libpod/container_api.go
+++ b/libpod/container_api.go
@@ -14,7 +14,6 @@ import (
 	"github.com/opentracing/opentracing-go"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
-	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/client-go/tools/remotecommand"
 )
 
@@ -524,24 +523,25 @@ func (c *Container) WaitWithInterval(waitTimeout time.Duration) (int32, error) {
 	if !c.valid {
 		return -1, define.ErrCtrRemoved
 	}
-	err := wait.PollImmediateInfinite(waitTimeout,
-		func() (bool, error) {
-			logrus.Debugf("Checking container %s status...", c.ID())
-			stopped, err := c.isStopped()
-			if err != nil {
-				return false, err
-			}
-			if !stopped {
-				return false, nil
-			}
-			return true, nil
-		},
-	)
-	if err != nil {
-		return 0, err
+
+	exitFile := c.exitFilePath()
+	chWait := make(chan error, 1)
+
+	defer close(chWait)
+
+	for {
+		// ignore errors here, it is only used to avoid waiting
+		// too long.
+		_, _ = WaitForFile(exitFile, chWait, waitTimeout)
+
+		stopped, err := c.isStopped()
+		if err != nil {
+			return -1, err
+		}
+		if stopped {
+			return c.state.ExitCode, nil
+		}
 	}
-	exitCode := c.state.ExitCode
-	return exitCode, nil
 }
 
 // Cleanup unmounts all mount points in container and cleans up container storage
diff --git a/libpod/util.go b/libpod/util.go
index b60575264..164800af4 100644
--- a/libpod/util.go
+++ b/libpod/util.go
@@ -69,7 +69,11 @@ func WaitForFile(path string, chWait chan error, timeout time.Duration) (bool, e
 		defer watcher.Close()
 	}
 
-	timeoutChan := time.After(timeout)
+	var timeoutChan <-chan time.Time
+
+	if timeout != 0 {
+		timeoutChan = time.After(timeout)
+	}
 
 	for {
 		select {