Added support for key removal within a group

groupcache.go

@@ -97,11 +97,12 @@ func newGroup(name string, cacheBytes int64, getter Getter, peers PeerPicker) *G
 		panic("duplicate registration of group " + name)
 	}
 	g := &Group{
-		name:       name,
-		getter:     getter,
-		peers:      peers,
-		cacheBytes: cacheBytes,
-		loadGroup:  &singleflight.Group{},
+		name:        name,
+		getter:      getter,
+		peers:       peers,
+		cacheBytes:  cacheBytes,
+		loadGroup:   &singleflight.Group{},
+		removeGroup: &singleflight.Group{},
 	}
 	if fn := newGroupHook; fn != nil {
 		fn(g)
@@ -167,6 +168,10 @@ type Group struct {
 	// concurrent callers.
 	loadGroup flightGroup
 
+	// removeGroup ensures that each removed key is only removed
+	// remotely once regardless of the number of concurrent callers.
+	removeGroup flightGroup
+
 	_ int32 // force Stats to be 8-byte aligned on 32-bit platforms
 
 	// Stats are statistics on the group.
@@ -177,8 +182,8 @@ type Group struct {
 // satisfies.  We define this so that we may test with an alternate
 // implementation.
 type flightGroup interface {
-	// Done is called when Do is done.
 	Do(key string, fn func() (interface{}, error)) (interface{}, error)
+	Lock(fn func())
 }
 
 // Stats are per-group statistics.
@@ -233,6 +238,53 @@ func (g *Group) Get(ctx Context, key string, dest Sink) error {
 	return setSinkView(dest, value)
 }
 
+// Remove clears the key from our cache then forwards the remove
+// request to all peers.
+func (g *Group) Remove(ctx Context, key string) error {
+	_, err := g.removeGroup.Do(key, func() (interface{}, error) {
+
+		// Remove from key owner first
+		owner, ok := g.peers.PickPeer(key)
+		if ok {
+			if err := g.removeFromPeer(ctx, owner, key); err != nil {
+				return nil, err
+			}
+		}
+		// Remove from our cache first in case we are owner
+		g.localRemove(key)
+		wg := sync.WaitGroup{}
+		errs := make(chan error)
+
+		// Asynchronously clear the key from all hot and main caches of peers
+		for _, peer := range g.peers.GetAll() {
+			// avoid deleting from owner a second time
+			if peer == owner {
+				continue
+			}
+
+			wg.Add(1)
+			go func() {
+				errs <- g.removeFromPeer(ctx, peer, key)
+				wg.Done()
+			}()
+		}
+		go func() {
+			wg.Wait()
+			close(errs)
+		}()
+
+		// TODO(thrawn01): Should we report all errors? Reporting context
+		//  cancelled error for each peer doesn't make much sense.
+		var err error
+		for e := range errs {
+			err = e
+		}
+
+		return nil, err
+	})
+	return err
+}
+
 // load loads key either by invoking the getter locally or by sending it to another machine.
 func (g *Group) load(ctx Context, key string, dest Sink) (value ByteView, destPopulated bool, err error) {
 	g.Stats.Loads.Add(1)
@@ -330,6 +382,14 @@ func (g *Group) getFromPeer(ctx Context, peer ProtoGetter, key string) (ByteView
 	return value, nil
 }
 
+func (g *Group) removeFromPeer(ctx Context, peer ProtoGetter, key string) error {
+	req := &pb.GetRequest{
+		Group: &g.name,
+		Key:   &key,
+	}
+	return peer.Remove(ctx, req)
+}
+
 func (g *Group) lookupCache(key string) (value ByteView, ok bool) {
 	if g.cacheBytes <= 0 {
 		return
@@ -342,6 +402,19 @@ func (g *Group) lookupCache(key string) (value ByteView, ok bool) {
 	return
 }
 
+func (g *Group) localRemove(key string) {
+	// Clear key from our local cache
+	if g.cacheBytes <= 0 {
+		return
+	}
+
+	// Ensure no requests are in flight
+	g.loadGroup.Lock(func() {
+		g.hotCache.remove(key)
+		g.mainCache.remove(key)
+	})
+}
+
 func (g *Group) populateCache(key string, value ByteView, cache *cache) {
 	if g.cacheBytes <= 0 {
 		return
@@ -447,6 +520,15 @@ func (c *cache) get(key string) (value ByteView, ok bool) {
 	return vi.(ByteView), true
 }
 
+func (c *cache) remove(key string) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.lru == nil {
+		return
+	}
+	c.lru.Remove(key)
+}
+
 func (c *cache) removeOldest() {
 	c.mu.Lock()
 	defer c.mu.Unlock()

groupcache_test.go

@@ -263,6 +263,14 @@ func (p *fakePeer) Get(_ Context, in *pb.GetRequest, out *pb.GetResponse) error
 	return nil
 }
 
+func (p *fakePeer) Remove(_ Context, in *pb.GetRequest) error {
+	p.hits++
+	if p.fail {
+		return errors.New("simulated error from peer")
+	}
+	return nil
+}
+
 type fakePeers []ProtoGetter
 
 func (p fakePeers) PickPeer(key string) (peer ProtoGetter, ok bool) {
@@ -273,6 +281,10 @@ func (p fakePeers) PickPeer(key string) (peer ProtoGetter, ok bool) {
 	return p[n], p[n] != nil
 }
 
+func (p fakePeers) GetAll() []ProtoGetter {
+	return p
+}
+
 // tests that peers (virtual, in-process) are hit, and how much.
 func TestPeers(t *testing.T) {
 	once.Do(testSetup)
@@ -406,6 +418,10 @@ func (g *orderedFlightGroup) Do(key string, fn func() (interface{}, error)) (int
 	return g.orig.Do(key, fn)
 }
 
+func (g *orderedFlightGroup) Lock(fn func()) {
+	fn()
+}
+
 // TestNoDedup tests invariants on the cache size when singleflight is
 // unable to dedup calls.
 func TestNoDedup(t *testing.T) {

http.go

@@ -126,6 +126,20 @@ func (p *HTTPPool) Set(peers ...string) {
 	}
 }
 
+// GetAll returns all the peers in the pool
+func (p *HTTPPool) GetAll() []ProtoGetter {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	var i int
+	res := make([]ProtoGetter, len(p.httpGetters))
+	for _, v := range p.httpGetters {
+		res[i] = v
+		i++
+	}
+	return res
+}
+
 func (p *HTTPPool) PickPeer(key string) (ProtoGetter, bool) {
 	p.mu.Lock()
 	defer p.mu.Unlock()
@@ -163,6 +177,13 @@ func (p *HTTPPool) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	group.Stats.ServerRequests.Add(1)
+
+	// Delete the key and return 200
+	if r.Method == http.MethodDelete {
+		group.localRemove(key)
+		return
+	}
+
 	var b []byte
 
 	value := AllocatingByteSliceSink(&b)
@@ -201,14 +222,14 @@ var bufferPool = sync.Pool{
 	New: func() interface{} { return new(bytes.Buffer) },
 }
 
-func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error {
+func (h *httpGetter) makeRequest(context Context, method string, in *pb.GetRequest, out *http.Response) error {
 	u := fmt.Sprintf(
 		"%v%v/%v",
 		h.baseURL,
 		url.QueryEscape(in.GetGroup()),
 		url.QueryEscape(in.GetKey()),
 	)
-	req, err := http.NewRequest("GET", u, nil)
+	req, err := http.NewRequest(method, u, nil)
 	if err != nil {
 		return err
 	}
@@ -220,6 +241,15 @@ func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse
 	if err != nil {
 		return err
 	}
+	*out = *res
+	return nil
+}
+
+func (h *httpGetter) Get(ctx Context, in *pb.GetRequest, out *pb.GetResponse) error {
+	var res http.Response
+	if err := h.makeRequest(ctx, http.MethodGet, in, &res); err != nil {
+		return err
+	}
 	defer res.Body.Close()
 	if res.StatusCode != http.StatusOK {
 		return fmt.Errorf("server returned: %v", res.Status)
@@ -227,7 +257,7 @@ func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse
 	b := bufferPool.Get().(*bytes.Buffer)
 	b.Reset()
 	defer bufferPool.Put(b)
-	_, err = io.Copy(b, res.Body)
+	_, err := io.Copy(b, res.Body)
 	if err != nil {
 		return fmt.Errorf("reading response body: %v", err)
 	}
@@ -237,3 +267,15 @@ func (h *httpGetter) Get(context Context, in *pb.GetRequest, out *pb.GetResponse
 	}
 	return nil
 }
+
+func (h *httpGetter) Remove(ctx Context, in *pb.GetRequest) error {
+	var res http.Response
+	if err := h.makeRequest(ctx, http.MethodDelete, in, &res); err != nil {
+		return err
+	}
+	res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return fmt.Errorf("server returned: %v", res.Status)
+	}
+	return nil
+}

http_test.go

@@ -19,9 +19,11 @@ package groupcache
 import (
 	"errors"
 	"flag"
+	"fmt"
 	"log"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"os"
 	"os/exec"
 	"strconv"
@@ -32,14 +34,15 @@ import (
 )
 
 var (
-	peerAddrs = flag.String("test_peer_addrs", "", "Comma-separated list of peer addresses; used by TestHTTPPool")
-	peerIndex = flag.Int("test_peer_index", -1, "Index of which peer this child is; used by TestHTTPPool")
-	peerChild = flag.Bool("test_peer_child", false, "True if running as a child process; used by TestHTTPPool")
+	peerAddrs  = flag.String("test_peer_addrs", "", "Comma-separated list of peer addresses; used by TestHTTPPool")
+	peerIndex  = flag.Int("test_peer_index", -1, "Index of which peer this child is; used by TestHTTPPool")
+	peerChild  = flag.Bool("test_peer_child", false, "True if running as a child process; used by TestHTTPPool")
+	serverAddr = flag.String("test_server_addr", "", "Address of the server Child Getters will hit ; used by TestHTTPPool")
 )
 
 func TestHTTPPool(t *testing.T) {
 	if *peerChild {
-		beChildForTestHTTPPool()
+		beChildForTestHTTPPool(t)
 		os.Exit(0)
 	}
 
@@ -48,6 +51,13 @@ func TestHTTPPool(t *testing.T) {
 		nGets  = 100
 	)
 
+	var serverHits int
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, "Hello")
+		serverHits++
+	}))
+	defer ts.Close()
+
 	var childAddr []string
 	for i := 0; i < nChild; i++ {
 		childAddr = append(childAddr, pickFreeAddr(t))
@@ -61,6 +71,7 @@ func TestHTTPPool(t *testing.T) {
 			"--test_peer_child",
 			"--test_peer_addrs="+strings.Join(childAddr, ","),
 			"--test_peer_index="+strconv.Itoa(i),
+			"--test_server_addr="+ts.URL,
 		)
 		cmds = append(cmds, cmd)
 		wg.Add(1)
@@ -100,6 +111,41 @@ func TestHTTPPool(t *testing.T) {
 		}
 		t.Logf("Get key=%q, value=%q (peer:key)", key, value)
 	}
+
+	if serverHits != nGets {
+		t.Error("expected serverHits to equal nGets")
+	}
+	serverHits = 0
+
+	var value string
+	var key = "removeTestKey"
+
+	// Multiple gets on the same key
+	for i := 0; i < 2; i++ {
+		if err := g.Get(nil, key, StringSink(&value)); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// Should result in only 1 server get
+	if serverHits != 1 {
+		t.Error("expected serverHits to be '1'")
+	}
+
+	// Remove the key from the cache and we should see another server hit
+	if err := g.Remove(nil, key); err != nil {
+		t.Fatal(err)
+	}
+
+	// Get the key again
+	if err := g.Get(nil, key, StringSink(&value)); err != nil {
+		t.Fatal(err)
+	}
+
+	// Should register another server get
+	if serverHits != 2 {
+		t.Error("expected serverHits to be '2'")
+	}
 }
 
 func testKeys(n int) (keys []string) {
@@ -110,13 +156,17 @@ func testKeys(n int) (keys []string) {
 	return
 }
 
-func beChildForTestHTTPPool() {
+func beChildForTestHTTPPool(t *testing.T) {
 	addrs := strings.Split(*peerAddrs, ",")
 
 	p := NewHTTPPool("http://" + addrs[*peerIndex])
 	p.Set(addrToURL(addrs)...)
 
 	getter := GetterFunc(func(ctx Context, key string, dest Sink) error {
+		if _, err := http.Get(*serverAddr); err != nil {
+			t.Logf("HTTP request from getter failed with '%s'", err)
+		}
+
 		dest.SetString(strconv.Itoa(*peerIndex)+":"+key, time.Time{})
 		return nil
 	})

peers.go

@@ -30,6 +30,7 @@ type Context interface{}
 // ProtoGetter is the interface that must be implemented by a peer.
 type ProtoGetter interface {
 	Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error
+	Remove(context Context, in *pb.GetRequest) error
 }
 
 // PeerPicker is the interface that must be implemented to locate
@@ -39,12 +40,14 @@ type PeerPicker interface {
 	// and true to indicate that a remote peer was nominated.
 	// It returns nil, false if the key owner is the current peer.
 	PickPeer(key string) (peer ProtoGetter, ok bool)
+	GetAll() []ProtoGetter
 }
 
 // NoPeers is an implementation of PeerPicker that never finds a peer.
 type NoPeers struct{}
 
 func (NoPeers) PickPeer(key string) (peer ProtoGetter, ok bool) { return }
+func (NoPeers) GetAll() []ProtoGetter                           { return []ProtoGetter{} }
 
 var (
 	portPicker func(groupName string) PeerPicker

singleflight/singleflight.go

@@ -62,3 +62,12 @@ func (g *Group) Do(key string, fn func() (interface{}, error)) (interface{}, err
 
 	return c.val, c.err
 }
+
+// Lock prevents single flights from occurring for the duration
+// of the provided function. This allows users to clear caches
+// or preform some operation in between running flights.
+func (g *Group) Lock(fn func()) {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	fn()
+}