From ef91bc3550e5f0cdfbf2ec005ea4e2f3b1b5d631 Mon Sep 17 00:00:00 2001
From: Vince Prignano <vincepri@vmware.com>
Date: Tue, 27 Jul 2021 12:07:46 -0700
Subject: [PATCH] :bug: Use non blocking file locking for flock library

Signed-off-by: Vince Prignano <vincepri@vmware.com>
---
 go.mod                               |  1 +
 pkg/internal/flock/flock_unix.go     | 17 ++++++++++++++---
 pkg/internal/testing/addr/manager.go | 20 ++++++++++----------
 3 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/go.mod b/go.mod
index 0ce3b6c132..8e8e3f0d5f 100644
--- a/go.mod
+++ b/go.mod
@@ -12,6 +12,7 @@ require (
 	github.com/imdario/mergo v0.3.12 // indirect
 	github.com/onsi/ginkgo v1.16.4
 	github.com/onsi/gomega v1.13.0
+	github.com/pkg/errors v0.9.1
 	github.com/prometheus/client_golang v1.11.0
 	github.com/prometheus/client_model v0.2.0
 	go.uber.org/goleak v1.1.10
diff --git a/pkg/internal/flock/flock_unix.go b/pkg/internal/flock/flock_unix.go
index 3dae621b73..c33a95cb7e 100644
--- a/pkg/internal/flock/flock_unix.go
+++ b/pkg/internal/flock/flock_unix.go
@@ -18,7 +18,15 @@ limitations under the License.
 
 package flock
 
-import "golang.org/x/sys/unix"
+import (
+	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
+)
+
+var (
+	// ErrAlreadyLocked is returned when the file is already locked.
+	ErrAlreadyLocked = errors.New("the file is already locked")
+)
 
 // Acquire acquires a lock on a file for the duration of the process. This method
 // is reentrant.
@@ -30,6 +38,9 @@ func Acquire(path string) error {
 
 	// We don't need to close the fd since we should hold
 	// it until the process exits.
-
-	return unix.Flock(fd, unix.LOCK_EX)
+	err = unix.Flock(fd, unix.LOCK_NB|unix.LOCK_EX)
+	if errors.Is(err, unix.EWOULDBLOCK) { // This condition requires LOCK_NB.
+		return errors.Wrapf(ErrAlreadyLocked, "cannot lock file %q", path)
+	}
+	return err
 }
diff --git a/pkg/internal/testing/addr/manager.go b/pkg/internal/testing/addr/manager.go
index 2326af1569..9dcbaa437f 100644
--- a/pkg/internal/testing/addr/manager.go
+++ b/pkg/internal/testing/addr/manager.go
@@ -17,6 +17,7 @@ limitations under the License.
 package addr
 
 import (
+	"errors"
 	"fmt"
 	"io/fs"
 	"net"
@@ -31,7 +32,7 @@ import (
 // TODO(directxman12): interface / release functionality for external port managers
 
 const (
-	portReserveTime   = 10 * time.Minute
+	portReserveTime   = 2 * time.Minute
 	portConflictRetry = 100
 	portFilePrefix    = "port-"
 )
@@ -76,7 +77,8 @@ func (c *portCache) add(port int) (bool, error) {
 		return false, err
 	}
 	// Try allocating new port, by acquiring a file.
-	if err := flock.Acquire(fmt.Sprintf("%s/%s%d", cacheDir, portFilePrefix, port)); os.IsExist(err) {
+	path := fmt.Sprintf("%s/%s%d", cacheDir, portFilePrefix, port)
+	if err := flock.Acquire(path); errors.Is(err, os.ErrExist) || errors.Is(err, flock.ErrAlreadyLocked) {
 		return false, nil
 	} else if err != nil {
 		return false, err
@@ -86,22 +88,19 @@ func (c *portCache) add(port int) (bool, error) {
 
 var cache = &portCache{}
 
-func suggest(listenHost string) (int, string, error) {
+func suggest(listenHost string) (*net.TCPListener, int, string, error) {
 	if listenHost == "" {
 		listenHost = "localhost"
 	}
 	addr, err := net.ResolveTCPAddr("tcp", net.JoinHostPort(listenHost, "0"))
 	if err != nil {
-		return -1, "", err
+		return nil, -1, "", err
 	}
 	l, err := net.ListenTCP("tcp", addr)
 	if err != nil {
-		return -1, "", err
+		return nil, -1, "", err
 	}
-	if err := l.Close(); err != nil {
-		return -1, "", err
-	}
-	return l.Addr().(*net.TCPAddr).Port,
+	return l, l.Addr().(*net.TCPAddr).Port,
 		addr.IP.String(),
 		nil
 }
@@ -112,10 +111,11 @@ func suggest(listenHost string) (int, string, error) {
 // allocated within 1 minute.
 func Suggest(listenHost string) (int, string, error) {
 	for i := 0; i < portConflictRetry; i++ {
-		port, resolvedHost, err := suggest(listenHost)
+		listener, port, resolvedHost, err := suggest(listenHost)
 		if err != nil {
 			return -1, "", err
 		}
+		defer listener.Close()
 		if ok, err := cache.add(port); ok {
 			return port, resolvedHost, nil
 		} else if err != nil {