Merge 46898854d9 into cc3d361eb2

go.mod

@@ -1,19 +1,22 @@
 module github.com/mailgun/groupcache/v2
 
-go 1.19
+go 1.21
 
 require (
-	github.com/golang/protobuf v1.5.2
+	github.com/golang/protobuf v1.5.3
 	github.com/segmentio/fasthash v1.0.3
 	github.com/sirupsen/logrus v1.9.0
-	github.com/stretchr/testify v1.8.1
+	github.com/stretchr/testify v1.8.4
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/google/go-cmp v0.5.9 // indirect
+	github.com/kr/pretty v0.3.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 // indirect
+	github.com/rogpeppe/go-internal v1.10.0 // indirect
-	golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f // indirect
+	golang.org/x/sys v0.14.0 // indirect
-	google.golang.org/protobuf v1.28.1 // indirect
+	google.golang.org/protobuf v1.31.0 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,37 +1,45 @@
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
-github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
+github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
-github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
-github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
+github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
+github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/segmentio/fasthash v1.0.3 h1:EI9+KE1EwvMLBWwjpRDc+fEM+prwxDYbslddQGtrmhM=
 github.com/segmentio/fasthash v1.0.3/go.mod h1:waKX8l2N8yckOgmSsXJi7x1ZfdKZ4x7KRMzBtS3oedY=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
 github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
-github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
-github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
-github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
-github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 h1:h+EGohizhe9XlX18rfpa8k8RAc5XyaeamM+0VHRd4lc=
+golang.org/x/sys v0.14.0 h1:Vz7Qs629MkJkGyHxUlRHizWJRG2j8fbQKjELVSNhy7Q=
-golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.14.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f h1:uF6paiQQebLeSXkrTqHqz0MXhXXS1KgF41eUdBNvxK0=
-golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f/go.mod h1:K8+ghG5WaK9qNqU5K3HdILfMLy1f3aNYFI/wnl100a8=
 google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
 google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
-google.golang.org/protobuf v1.28.1 h1:d0NfwRgPtno5B1Wa6L2DAG+KivqkdutMf1UhdNx175w=
+google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
-google.golang.org/protobuf v1.28.1/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

groupcache.go

@@ -68,21 +68,32 @@ func (f GetterFunc) Get(ctx context.Context, key string, dest Sink) error {
 	return f(ctx, key, dest)
 }
 
-var (
+// GetGroupWithWorkspace returns the named group previously created with NewGroup, or
-	mu     sync.RWMutex
+// nil if there's no such group.
-	groups = make(map[string]*Group)
+func GetGroupWithWorkspace(ws *workspace, name string) *Group {
-
+	ws.mu.RLock()
-	initPeerServerOnce sync.Once
+	g := ws.groups[name]
-	initPeerServer     func()
+	ws.mu.RUnlock()
-)
+	return g
+}
 
 // GetGroup returns the named group previously created with NewGroup, or
 // nil if there's no such group.
 func GetGroup(name string) *Group {
-	mu.RLock()
+	return GetGroupWithWorkspace(DefaultWorkspace, name)
-	g := groups[name]
+}
-	mu.RUnlock()
+
-	return g
+// NewGroupWithWorkspace creates a coordinated group-aware Getter from a Getter.
+//
+// The returned Getter tries (but does not guarantee) to run only one
+// Get call at once for a given key across an entire set of peer
+// processes. Concurrent callers both in the local process and in
+// other processes receive copies of the answer once the original Get
+// completes.
+//
+// The group name must be unique for each getter.
+func NewGroupWithWorkspace(ws *workspace, name string, cacheBytes int64, getter Getter) *Group {
+	return newGroup(ws, name, cacheBytes, getter, nil)
 }
 
 // NewGroup creates a coordinated group-aware Getter from a Getter.
@@ -95,28 +106,34 @@ func GetGroup(name string) *Group {
 //
 // The group name must be unique for each getter.
 func NewGroup(name string, cacheBytes int64, getter Getter) *Group {
-	return newGroup(name, cacheBytes, getter, nil)
+	return newGroup(DefaultWorkspace, name, cacheBytes, getter, nil)
+}
+
+// DeregisterGroupWithWorkspace removes group from group pool
+func DeregisterGroupWithWorkspace(ws *workspace, name string) {
+	ws.mu.Lock()
+	delete(ws.groups, name)
+	ws.mu.Unlock()
 }
 
 // DeregisterGroup removes group from group pool
 func DeregisterGroup(name string) {
-	mu.Lock()
+	DeregisterGroupWithWorkspace(DefaultWorkspace, name)
-	delete(groups, name)
-	mu.Unlock()
 }
 
 // If peers is nil, the peerPicker is called via a sync.Once to initialize it.
-func newGroup(name string, cacheBytes int64, getter Getter, peers PeerPicker) *Group {
+func newGroup(ws *workspace, name string, cacheBytes int64, getter Getter, peers PeerPicker) *Group {
 	if getter == nil {
 		panic("nil Getter")
 	}
-	mu.Lock()
+	ws.mu.Lock()
-	defer mu.Unlock()
+	defer ws.mu.Unlock()
-	initPeerServerOnce.Do(callInitPeerServer)
+	ws.initPeerServerOnce.Do(func() { callInitPeerServer(ws) })
-	if _, dup := groups[name]; dup {
+	if _, dup := ws.groups[name]; dup {
 		panic("duplicate registration of group " + name)
 	}
 	g := &Group{
+		ws:          ws,
 		name:        name,
 		getter:      getter,
 		peers:       peers,
@@ -125,43 +142,53 @@ func newGroup(name string, cacheBytes int64, getter Getter, peers PeerPicker) *G
 		setGroup:    &singleflight.Group{},
 		removeGroup: &singleflight.Group{},
 	}
-	if fn := newGroupHook; fn != nil {
+	if fn := ws.newGroupHook; fn != nil {
 		fn(g)
 	}
-	groups[name] = g
+	ws.groups[name] = g
 	return g
 }
 
-// newGroupHook, if non-nil, is called right after a new group is created.
+// RegisterNewGroupHookWithWorkspace registers a hook that is run each time
-var newGroupHook func(*Group)
+// a group is created.
+func RegisterNewGroupHookWithWorkspace(ws *workspace, fn func(*Group)) {
+	if ws.newGroupHook != nil {
+		panic("RegisterNewGroupHook called more than once")
+	}
+	ws.newGroupHook = fn
+}
 
 // RegisterNewGroupHook registers a hook that is run each time
 // a group is created.
 func RegisterNewGroupHook(fn func(*Group)) {
-	if newGroupHook != nil {
+	RegisterNewGroupHookWithWorkspace(DefaultWorkspace, fn)
-		panic("RegisterNewGroupHook called more than once")
+}
+
+// RegisterServerStartWithWorkspace registers a hook that is run when the first
+// group is created.
+func RegisterServerStartWithWorkspace(ws *workspace, fn func()) {
+	if ws.initPeerServer != nil {
+		panic("RegisterServerStart called more than once")
 	}
-	newGroupHook = fn
+	ws.initPeerServer = fn
 }
 
 // RegisterServerStart registers a hook that is run when the first
 // group is created.
 func RegisterServerStart(fn func()) {
-	if initPeerServer != nil {
+	RegisterServerStartWithWorkspace(DefaultWorkspace, fn)
-		panic("RegisterServerStart called more than once")
-	}
-	initPeerServer = fn
 }
 
-func callInitPeerServer() {
+func callInitPeerServer(ws *workspace) {
-	if initPeerServer != nil {
+	if ws.initPeerServer != nil {
-		initPeerServer()
+		ws.initPeerServer()
 	}
 }
 
 // A Group is a cache namespace and associated data loaded spread over
 // a group of 1 or more machines.
 type Group struct {
+	ws         *workspace
 	name       string
 	getter     Getter
 	peersOnce  sync.Once
@@ -232,7 +259,7 @@ func (g *Group) Name() string {
 
 func (g *Group) initPeers() {
 	if g.peers == nil {
-		g.peers = getPeers(g.name)
+		g.peers = getPeers(g.ws, g.name)
 	}
 }
 

groupcache_test.go

@@ -310,7 +310,7 @@ func TestPeers(t *testing.T) {
 		localHits++
 		return dest.SetString("got:"+key, time.Time{})
 	}
-	testGroup := newGroup("TestPeers-group", cacheSize, GetterFunc(getter), peerList)
+	testGroup := newGroup(DefaultWorkspace, "TestPeers-group", cacheSize, GetterFunc(getter), peerList)
 	run := func(name string, n int, wantSummary string) {
 		// Reset counters
 		localHits = 0
@@ -438,7 +438,7 @@ func (g *orderedFlightGroup) Lock(fn func()) {
 func TestNoDedup(t *testing.T) {
 	const testkey = "testkey"
 	const testval = "testval"
-	g := newGroup("testgroup", 1024, GetterFunc(func(_ context.Context, key string, dest Sink) error {
+	g := newGroup(DefaultWorkspace, "testgroup", 1024, GetterFunc(func(_ context.Context, key string, dest Sink) error {
 		return dest.SetString(testval, time.Time{})
 	}), nil)
 
@@ -522,7 +522,7 @@ func TestContextDeadlineOnPeer(t *testing.T) {
 	getter := func(_ context.Context, key string, dest Sink) error {
 		return dest.SetString("got:"+key, time.Time{})
 	}
-	testGroup := newGroup("TestContextDeadlineOnPeer-group", cacheSize, GetterFunc(getter), peerList)
+	testGroup := newGroup(DefaultWorkspace, "TestContextDeadlineOnPeer-group", cacheSize, GetterFunc(getter), peerList)
 
 	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*300)
 	defer cancel()

http.go

@@ -40,6 +40,8 @@ const defaultReplicas = 50
 
 // HTTPPool implements PeerPicker for a pool of HTTP peers.
 type HTTPPool struct {
+	ws *workspace
+
 	// this peer's base URL, e.g. "https://example.net:8000"
 	self string
 
@@ -76,28 +78,35 @@ type HTTPPoolOptions struct {
 	Context func(*http.Request) context.Context
 }
 
+// NewHTTPPoolWithWorkspace initializes an HTTP pool of peers, and registers itself as a PeerPicker.
+// For convenience, it also registers itself as an http.Handler with http.DefaultServeMux.
+// The self argument should be a valid base URL that points to the current server,
+// for example "http://example.net:8000".
+func NewHTTPPoolWithWorkspace(ws *workspace, self string) *HTTPPool {
+	p := NewHTTPPoolOptsWithWorkspace(ws, self, nil)
+	http.Handle(p.opts.BasePath, p)
+	return p
+}
+
 // NewHTTPPool initializes an HTTP pool of peers, and registers itself as a PeerPicker.
 // For convenience, it also registers itself as an http.Handler with http.DefaultServeMux.
 // The self argument should be a valid base URL that points to the current server,
 // for example "http://example.net:8000".
 func NewHTTPPool(self string) *HTTPPool {
-	p := NewHTTPPoolOpts(self, nil)
+	return NewHTTPPoolWithWorkspace(DefaultWorkspace, self)
-	http.Handle(p.opts.BasePath, p)
-	return p
 }
 
-var httpPoolMade bool
+// NewHTTPPoolOptsWithWorkspace initializes an HTTP pool of peers with the given options.
-
-// NewHTTPPoolOpts initializes an HTTP pool of peers with the given options.
 // Unlike NewHTTPPool, this function does not register the created pool as an HTTP handler.
 // The returned *HTTPPool implements http.Handler and must be registered using http.Handle.
-func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool {
+func NewHTTPPoolOptsWithWorkspace(ws *workspace, self string, o *HTTPPoolOptions) *HTTPPool {
-	if httpPoolMade {
+	if ws.httpPoolMade {
 		panic("groupcache: NewHTTPPool must be called only once")
 	}
-	httpPoolMade = true
+	ws.httpPoolMade = true
 
 	p := &HTTPPool{
+		ws:          ws,
 		self:        self,
 		httpGetters: make(map[string]*httpGetter),
 	}
@@ -112,10 +121,17 @@ func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool {
 	}
 	p.peers = consistenthash.New(p.opts.Replicas, p.opts.HashFn)
 
-	RegisterPeerPicker(func() PeerPicker { return p })
+	RegisterPeerPickerWithWorkspace(ws, func() PeerPicker { return p })
 	return p
 }
 
+// NewHTTPPoolOpts initializes an HTTP pool of peers with the given options.
+// Unlike NewHTTPPool, this function does not register the created pool as an HTTP handler.
+// The returned *HTTPPool implements http.Handler and must be registered using http.Handle.
+func NewHTTPPoolOpts(self string, o *HTTPPoolOptions) *HTTPPool {
+	return NewHTTPPoolOptsWithWorkspace(DefaultWorkspace, self, o)
+}
+
 // Set updates the pool's list of peers.
 // Each peer value should be a valid base URL,
 // for example "http://example.net:8000".
@@ -173,7 +189,7 @@ func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	key := parts[1]
 
 	// Fetch the value for this group/key.
-	group := GetGroup(groupName)
+	group := GetGroupWithWorkspace(p.ws, groupName)
 	if group == nil {
 		http.Error(w, "no such group: "+groupName, http.StatusNotFound)
 		return

peers.go

@@ -50,19 +50,35 @@ type NoPeers struct{}
 func (NoPeers) PickPeer(key string) (peer ProtoGetter, ok bool) { return }
 func (NoPeers) GetAll() []ProtoGetter                           { return []ProtoGetter{} }
 
-var (
+// RegisterPeerPickerWithWorkspace registers the peer initialization function.
-	portPicker func(groupName string) PeerPicker
+// It is called once, when the first group is created.
-)
+// Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be
+// called exactly once, but not both.
+func RegisterPeerPickerWithWorkspace(ws *workspace, fn func() PeerPicker) {
+	if ws.portPicker != nil {
+		panic("RegisterPeerPicker called more than once")
+	}
+	ws.portPicker = func(_ string) PeerPicker { return fn() }
+}
 
 // RegisterPeerPicker registers the peer initialization function.
 // It is called once, when the first group is created.
 // Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be
 // called exactly once, but not both.
 func RegisterPeerPicker(fn func() PeerPicker) {
-	if portPicker != nil {
+	RegisterPeerPickerWithWorkspace(DefaultWorkspace, fn)
+}
+
+// RegisterPerGroupPeerPickerWithWorkspace registers the peer initialization function,
+// which takes the groupName, to be used in choosing a PeerPicker.
+// It is called once, when the first group is created.
+// Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be
+// called exactly once, but not both.
+func RegisterPerGroupPeerPickerWithWorkspace(ws *workspace, fn func(groupName string) PeerPicker) {
+	if ws.portPicker != nil {
 		panic("RegisterPeerPicker called more than once")
 	}
-	portPicker = func(_ string) PeerPicker { return fn() }
+	ws.portPicker = fn
 }
 
 // RegisterPerGroupPeerPicker registers the peer initialization function,
@@ -71,17 +87,14 @@ func RegisterPeerPicker(fn func() PeerPicker) {
 // Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be
 // called exactly once, but not both.
 func RegisterPerGroupPeerPicker(fn func(groupName string) PeerPicker) {
-	if portPicker != nil {
+	RegisterPerGroupPeerPickerWithWorkspace(DefaultWorkspace, fn)
-		panic("RegisterPeerPicker called more than once")
-	}
-	portPicker = fn
 }
 
-func getPeers(groupName string) PeerPicker {
+func getPeers(ws *workspace, groupName string) PeerPicker {
-	if portPicker == nil {
+	if ws.portPicker == nil {
 		return NoPeers{}
 	}
-	pk := portPicker(groupName)
+	pk := ws.portPicker(groupName)
 	if pk == nil {
 		pk = NoPeers{}
 	}

workspace.go

@@ -0,0 +1,35 @@
+package groupcache
+
+import "sync"
+
+// workspace holds the "global" state for groupcache.
+type workspace struct {
+	httpPoolMade bool
+	portPicker   func(groupName string) PeerPicker
+
+	mu     sync.RWMutex
+	groups map[string]*Group
+
+	initPeerServerOnce sync.Once
+	initPeerServer     func()
+
+	// newGroupHook, if non-nil, is called right after a new group is created.
+	newGroupHook func(*Group)
+}
+
+// DefaultWorkspace is the default workspace used by non-workspace-aware APIs.
+// If your application does not need to recreate groupcache resources,
+// you should use the non-workspace-aware APIs.
+// This is likely the most common case.
+var DefaultWorkspace = NewWorkspace()
+
+// NewWorkspace creates an explicit workspace for workspace-aware APIs.
+// If your application needs to recreate groupcache resources at some
+// point, you should use the workspace-aware APIs.
+// In order to release current groupcache resources, your application
+// would drop all references to the workspace.
+func NewWorkspace() *workspace {
+	return &workspace{
+		groups: make(map[string]*Group),
+	}
+}