Improve name generation on concurrent requests

Fixes #2586

This fixes a few races where the name generator asks if a name is free
but another container takes the name before it can be reserved.  This
solves this by generating the name and setting it.  If the set fails
with a non unique error then we try again.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

daemon/daemon.go

@@ -29,6 +29,7 @@ import (
 	"github.com/dotcloud/docker/pkg/graphdb"
 	"github.com/dotcloud/docker/pkg/label"
 	"github.com/dotcloud/docker/pkg/mount"
+	"github.com/dotcloud/docker/pkg/namesgenerator"
 	"github.com/dotcloud/docker/pkg/networkfs/resolvconf"
 	"github.com/dotcloud/docker/pkg/selinux"
 	"github.com/dotcloud/docker/pkg/sysinfo"
@@ -250,20 +251,15 @@ func (daemon *Daemon) register(container *Container, updateSuffixarray bool) err
 
 func (daemon *Daemon) ensureName(container *Container) error {
 	if container.Name == "" {
-		name, err := generateRandomName(daemon)
+		name, err := daemon.generateNewName(container.ID)
 		if err != nil {
-			name = utils.TruncateID(container.ID)
+			return err
 		}
 		container.Name = name
 
 		if err := container.ToDisk(); err != nil {
 			utils.Debugf("Error saving container name %s", err)
 		}
-		if !daemon.containerGraph.Exists(name) {
-			if _, err := daemon.containerGraph.Set(name, container.ID); err != nil {
-				utils.Debugf("Setting default id - %s", err)
-			}
-		}
 	}
 	return nil
 }
@@ -370,12 +366,8 @@ func (daemon *Daemon) restore() error {
 	// Any containers that are left over do not exist in the graph
 	for _, container := range containers {
 		// Try to set the default name for a container if it exists prior to links
-		container.Name, err = generateRandomName(daemon)
+		container.Name, err = daemon.generateNewName(container.ID)
 		if err != nil {
-			container.Name = utils.TruncateID(container.ID)
-		}
-
-		if _, err := daemon.containerGraph.Set(container.Name, container.ID); err != nil {
 			utils.Debugf("Setting default id - %s", err)
 		}
 		registerContainer(container)
@@ -470,42 +462,75 @@ func (daemon *Daemon) generateIdAndName(name string) (string, string, error) {
 	)
 
 	if name == "" {
-		name, err = generateRandomName(daemon)
-		if err != nil {
-			name = utils.TruncateID(id)
-		}
-	} else {
-		if !validContainerNamePattern.MatchString(name) {
-			return "", "", fmt.Errorf("Invalid container name (%s), only %s are allowed", name, validContainerNameChars)
+		if name, err = daemon.generateNewName(id); err != nil {
+			return "", "", err
 		}
+		return id, name, nil
 	}
+
+	if name, err = daemon.reserveName(id, name); err != nil {
+		return "", "", err
+	}
+
+	return id, name, nil
+}
+
+func (daemon *Daemon) reserveName(id, name string) (string, error) {
+	if !validContainerNamePattern.MatchString(name) {
+		return "", fmt.Errorf("Invalid container name (%s), only %s are allowed", name, validContainerNameChars)
+	}
+
 	if name[0] != '/' {
 		name = "/" + name
 	}
-	// Set the enitity in the graph using the default name specified
+
 	if _, err := daemon.containerGraph.Set(name, id); err != nil {
 		if !graphdb.IsNonUniqueNameError(err) {
-			return "", "", err
+			return "", err
 		}
 
 		conflictingContainer, err := daemon.GetByName(name)
 		if err != nil {
 			if strings.Contains(err.Error(), "Could not find entity") {
-				return "", "", err
+				return "", err
 			}
 
 			// Remove name and continue starting the container
 			if err := daemon.containerGraph.Delete(name); err != nil {
-				return "", "", err
+				return "", err
 			}
 		} else {
 			nameAsKnownByUser := strings.TrimPrefix(name, "/")
-			return "", "", fmt.Errorf(
+			return "", fmt.Errorf(
 				"Conflict, The name %s is already assigned to %s. You have to delete (or rename) that container to be able to assign %s to a container again.", nameAsKnownByUser,
 				utils.TruncateID(conflictingContainer.ID), nameAsKnownByUser)
 		}
 	}
-	return id, name, nil
+	return name, nil
+}
+
+func (daemon *Daemon) generateNewName(id string) (string, error) {
+	var name string
+	for i := 1; i < 6; i++ {
+		name = namesgenerator.GetRandomName(i)
+		if name[0] != '/' {
+			name = "/" + name
+		}
+
+		if _, err := daemon.containerGraph.Set(name, id); err != nil {
+			if !graphdb.IsNonUniqueNameError(err) {
+				return "", err
+			}
+			continue
+		}
+		return name, nil
+	}
+
+	name = "/" + utils.TruncateID(id)
+	if _, err := daemon.containerGraph.Set(name, id); err != nil {
+		return "", err
+	}
+	return name, nil
 }
 
 func (daemon *Daemon) generateHostname(id string, config *runconfig.Config) {

daemon/utils.go

@@ -2,10 +2,10 @@ package daemon
 
 import (
 	"fmt"
+	"strings"
+
 	"github.com/dotcloud/docker/nat"
-	"github.com/dotcloud/docker/pkg/namesgenerator"
 	"github.com/dotcloud/docker/runconfig"
-	"strings"
 )
 
 func migratePortMappings(config *runconfig.Config, hostConfig *runconfig.HostConfig) error {
@@ -49,16 +49,3 @@ func mergeLxcConfIntoOptions(hostConfig *runconfig.HostConfig, driverConfig map[
 		driverConfig["lxc"] = lxc
 	}
 }
-
-type checker struct {
-	daemon *Daemon
-}
-
-func (c *checker) Exists(name string) bool {
-	return c.daemon.containerGraph.Exists("/" + name)
-}
-
-// Generate a random and unique name
-func generateRandomName(daemon *Daemon) (string, error) {
-	return namesgenerator.GenerateRandomName(&checker{daemon})
-}

pkg/namesgenerator/names-generator.go

@@ -6,10 +6,6 @@ import (
 	"time"
 )
 
-type NameChecker interface {
-	Exists(name string) bool
-}
-
 var (
 	left = [...]string{"happy", "jolly", "dreamy", "sad", "angry", "pensive", "focused", "sleepy", "grave", "distracted", "determined", "stoic", "stupefied", "sharp", "agitated", "cocky", "tender", "goofy", "furious", "desperate", "hopeful", "compassionate", "silly", "lonely", "condescending", "naughty", "kickass", "drunk", "boring", "nostalgic", "ecstatic", "insane", "cranky", "mad", "jovial", "sick", "hungry", "thirsty", "elegant", "backstabbing", "clever", "trusting", "loving", "suspicious", "berserk", "high", "romantic", "prickly", "evil"}
 	// Docker 0.7.x generates names from notable scientists and hackers.
@@ -79,16 +75,17 @@ var (
 	right = [...]string{"lovelace", "franklin", "tesla", "einstein", "bohr", "davinci", "pasteur", "nobel", "curie", "darwin", "turing", "ritchie", "torvalds", "pike", "thompson", "wozniak", "galileo", "euclid", "newton", "fermat", "archimedes", "poincare", "heisenberg", "feynman", "hawking", "fermi", "pare", "mccarthy", "engelbart", "babbage", "albattani", "ptolemy", "bell", "wright", "lumiere", "morse", "mclean", "brown", "bardeen", "brattain", "shockley", "goldstine", "hoover", "hopper", "bartik", "sammet", "jones", "perlman", "wilson", "kowalevski", "hypatia", "goodall", "mayer", "elion", "blackwell", "lalande", "kirch", "ardinghelli", "colden", "almeida", "leakey", "meitner", "mestorf", "rosalind", "sinoussi", "carson", "mcclintock", "yonath"}
 )
 
-func GenerateRandomName(checker NameChecker) (string, error) {
-	retry := 5
+func GetRandomName(retry int) string {
 	rand.Seed(time.Now().UnixNano())
+
+begin:
 	name := fmt.Sprintf("%s_%s", left[rand.Intn(len(left))], right[rand.Intn(len(right))])
-	for checker != nil && checker.Exists(name) && retry > 0 || name == "boring_wozniak" /* Steve Wozniak is not boring */ {
-		name = fmt.Sprintf("%s%d", name, rand.Intn(10))
-		retry = retry - 1
+	if name == "boring_wozniak" /* Steve Wozniak is not boring */ {
+		goto begin
 	}
-	if retry == 0 {
-		return name, fmt.Errorf("Error generating random name")
+
+	if retry > 0 {
+		name = fmt.Sprintf("%s%d", name, rand.Intn(10))
 	}
-	return name, nil
+	return name
 }

pkg/namesgenerator/names-generator_test.go

@@ -4,35 +4,9 @@ import (
 	"testing"
 )
 
-type FalseChecker struct{}
-
-func (n *FalseChecker) Exists(name string) bool {
-	return false
-}
-
-type TrueChecker struct{}
-
-func (n *TrueChecker) Exists(name string) bool {
-	return true
-}
-
-func TestGenerateRandomName(t *testing.T) {
-	if _, err := GenerateRandomName(&FalseChecker{}); err != nil {
-		t.Error(err)
-	}
-
-	if _, err := GenerateRandomName(&TrueChecker{}); err == nil {
-		t.Error("An error was expected")
-	}
-
-}
-
 // Make sure the generated names are awesome
 func TestGenerateAwesomeNames(t *testing.T) {
-	name, err := GenerateRandomName(&FalseChecker{})
-	if err != nil {
-		t.Error(err)
-	}
+	name := GetRandomName(0)
 	if !isAwesome(name) {
 		t.Fatalf("Generated name '%s' is not awesome.", name)
 	}