[+]优雅关机

client/xclient_test.go

@@ -9,12 +9,44 @@ import (
 	"github.com/smallnest/rpcx/share"
 	"github.com/smallnest/rpcx/protocol"
 	"github.com/smallnest/rpcx/_testutils"
+	"fmt"
 )
 
 
+func TestLoop(t *testing.T) {
+	opt := Option{
+		Retries:        1,
+		RPCPath:        share.DefaultRPCPath,
+		ConnectTimeout: 10 * time.Second,
+		SerializeType:  protocol.Thrift,
+		CompressType:   protocol.None,
+		BackupLatency:  10 * time.Millisecond,
+	}
+
+	d := NewPeer2PeerDiscovery("tcp@127.0.0.1:8995", "desc=a test service")
+	xclient := NewXClient("Arith", Failtry, RandomSelect, d, opt)
+
+	defer xclient.Close()
+
+
+	tick := time.NewTicker(2*time.Second)
+	for ti := range tick.C {
+		fmt.Println(ti)
+		args := testutils.ThriftArgs_{}
+		args.A = 200
+		args.B = 100
+		go func(){
+			reply := testutils.ThriftReply{}
+			err := xclient.Call(context.Background(), "ThriftMul", &args, &reply)
+			fmt.Println(reply.C,err)
+		}()
+	}
+
+}
+
 func TestXClient_Thrift(t *testing.T) {
 	opt := Option{
-		Retries:        3,
+		Retries:        1,
 		RPCPath:        share.DefaultRPCPath,
 		ConnectTimeout: 10 * time.Second,
 		SerializeType:  protocol.Thrift,
@@ -38,6 +70,7 @@ func TestXClient_Thrift(t *testing.T) {
 		t.Fatalf("failed to call: %v", err)
 	}
 
+	fmt.Println(reply.C)
 	if reply.C != 20000 {
 		t.Fatalf("expect 20000 but got %d", reply.C)
 	}

codec/codec.go

@@ -2,7 +2,6 @@ package codec
 
 import (
 	"bytes"
-	"context"
 	"encoding/json"
 	"fmt"
 	"reflect"
@@ -113,7 +112,7 @@ func (c ThriftCodec) Encode(i interface{}) ([]byte, error) {
 		Protocol:  p,
 	}
 	t.Transport.Close()
-	return t.Write(context.Background(), i.(thrift.TStruct))
+	return t.Write( i.(thrift.TStruct))
 }
 
 func (c ThriftCodec) Decode(data []byte, i interface{}) error {

server/common_test.go

@@ -0,0 +1,14 @@
+package server
+
+import (
+	"testing"
+	"fmt"
+)
+
+func TestGo1(t *testing.T) {
+	ch := make(chan struct{},1000)
+	ch<-struct{}{}
+	fmt.Println(len(ch))
+	<-ch
+	fmt.Println(len(ch))
+}

server/server.go

@@ -20,6 +20,9 @@ import (
 	"github.com/smallnest/rpcx/log"
 	"github.com/smallnest/rpcx/protocol"
 	"github.com/smallnest/rpcx/share"
+	"os"
+	"os/signal"
+	"syscall"
 )
 
 // ErrServerClosed is returned by the Server's Serve, ListenAndServe after a call to Shutdown or Close.
@@ -65,7 +68,7 @@ type Server struct {
 	doneChan   chan struct{}
 	seq        uint64
 
-	// inShutdown int32
+	inShutdown int32
 	onShutdown []func()
 
 	// TLSConfig for creating tls tcp connection.
@@ -81,6 +84,10 @@ type Server struct {
 
 	// AuthFunc can be used to auth.
 	AuthFunc func(ctx context.Context, req *protocol.Message, token string) error
+
+	ShutdownFunc func(s *Server)
+
+	HandleMsgChan chan struct{}
 }
 
 // NewServer returns a server.
@@ -90,6 +97,8 @@ func NewServer(options ...OptionFn) *Server {
 		options: make(map[string]interface{}),
 	}
 
+	s.HandleMsgChan = make(chan struct{}, 100000)
+
 	for _, op := range options {
 		op(s)
 	}
@@ -147,9 +156,25 @@ func (s *Server) getDoneChan() <-chan struct{} {
 	return s.doneChan
 }
 
+func (s *Server)startShutdownListener() {
+	go func(s *Server) {
+		log.Info("server pid:", os.Getpid())
+		c := make(chan os.Signal, 1)
+		signal.Notify(c, syscall.SIGTERM)
+		si := <-c
+		if si.String() == "terminated" {
+			if nil != s.ShutdownFunc {
+				s.ShutdownFunc(s)
+			}
+			os.Exit(0)
+		}
+	}(s)
+}
+
 // Serve starts and listens RPC requests.
 // It is blocked until receiving connectings from clients.
 func (s *Server) Serve(network, address string) (err error) {
+	s.startShutdownListener()
 	var ln net.Listener
 	ln, err = s.makeListener(network, address)
 	if err != nil {
@@ -215,6 +240,7 @@ func (s *Server) serveListener(ln net.Listener) error {
 		if tc, ok := conn.(*net.TCPConn); ok {
 			tc.SetKeepAlive(true)
 			tc.SetKeepAlivePeriod(3 * time.Minute)
+			tc.SetLinger(10)
 		}
 
 		s.mu.Lock()
@@ -278,6 +304,11 @@ func (s *Server) serveConn(conn net.Conn) {
 		s.Plugins.DoPostConnClose(conn)
 	}()
 
+	if isShutdown(s) {
+		closeChannel(s,conn)
+		return
+	}
+
 	if tlsConn, ok := conn.(*tls.Conn); ok {
 		if d := s.readTimeout; d != 0 {
 			conn.SetReadDeadline(time.Now().Add(d))
@@ -292,9 +323,13 @@ func (s *Server) serveConn(conn net.Conn) {
 	}
 
 	r := bufio.NewReaderSize(conn, ReaderBuffsize)
-	//w := bufio.NewWriterSize(conn, WriterBuffsize)
 
 	for {
+		if isShutdown(s) {
+			closeChannel(s,conn)
+			return
+		}
+
 		t0 := time.Now()
 		if s.readTimeout != 0 {
 			conn.SetReadDeadline(t0.Add(s.readTimeout))
@@ -313,6 +348,8 @@ func (s *Server) serveConn(conn net.Conn) {
 			return
 		}
 
+		s.HandleMsgChan <- struct{}{}
+
 		if s.writeTimeout != 0 {
 			conn.SetWriteDeadline(t0.Add(s.writeTimeout))
 		}
@@ -320,7 +357,6 @@ func (s *Server) serveConn(conn net.Conn) {
 		ctx = context.WithValue(ctx, StartRequestContextKey, time.Now().UnixNano())
 		err = s.auth(ctx, req)
 		if err != nil {
-
 			if !req.IsOneway() {
 				res := req.Clone()
 				res.SetMessageType(protocol.Response)
@@ -337,11 +373,14 @@ func (s *Server) serveConn(conn net.Conn) {
 			} else {
 				s.Plugins.DoPreWriteResponse(ctx, req, nil)
 			}
-
+			<-s.HandleMsgChan
 			protocol.FreeMsg(req)
 			continue
 		}
 		go func() {
+			defer func(){
+				<-s.HandleMsgChan
+			}()
 			if req.IsHeartbeat() {
 				req.SetMessageType(protocol.Response)
 				data := req.Encode()
@@ -387,6 +426,17 @@ func (s *Server) serveConn(conn net.Conn) {
 	}
 }
 
+func isShutdown(s *Server) (bool) {
+	return atomic.LoadInt32(&s.inShutdown) == 1
+}
+
+func closeChannel(s *Server,conn net.Conn) {
+	s.mu.Lock()
+	delete(s.activeConn, conn)
+	s.mu.Unlock()
+	conn.Close()
+}
+
 func (s *Server) readRequest(ctx context.Context, r io.Reader) (req *protocol.Message, err error) {
 	err = s.Plugins.DoPreReadRequest(ctx)
 	if err != nil {
@@ -567,14 +617,11 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 
 // Close immediately closes all active net.Listeners.
 func (s *Server) Close() error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
 	s.closeDoneChanLocked()
 	var err error
 	if s.ln != nil {
 		err = s.ln.Close()
 	}
-
 	for c := range s.activeConn {
 		c.Close()
 		delete(s.activeConn, c)
@@ -591,7 +638,7 @@ func (s *Server) RegisterOnShutdown(f func()) {
 	s.mu.Unlock()
 }
 
-// var shutdownPollInterval = 500 * time.Millisecond
+var shutdownPollInterval = 500 * time.Millisecond
 
 // // Shutdown gracefully shuts down the server without interrupting any
 // // active connections. Shutdown works by first closing the
@@ -600,51 +647,35 @@ func (s *Server) RegisterOnShutdown(f func()) {
 // // If the provided context expires before the shutdown is complete,
 // // Shutdown returns the context's error, otherwise it returns any
 // // error returned from closing the Server's underlying Listener.
-// func (s *Server) Shutdown(ctx context.Context) error {
+func (s *Server) Shutdown(ctx context.Context) error {
-// 	atomic.AddInt32(&s.inShutdown, 1)
+	if atomic.CompareAndSwapInt32(&s.inShutdown, 0, 1) {
-// 	defer atomic.AddInt32(&s.inShutdown, -1)
+		log.Info("shutdown begin")
+		ticker := time.NewTicker(shutdownPollInterval)
+		defer ticker.Stop()
+		for {
+			if s.checkProcessMsg() {
+				break
+			}
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-ticker.C:
+			}
+		}
+		s.Close()
+		log.Info("shutdown end")
+	}
+	return nil
+}
 
-// 	s.mu.Lock()
+func (s *Server) checkProcessMsg() (bool) {
-// 	err := s.ln.Close()
+	size := len(s.HandleMsgChan)
-// 	s.closeDoneChanLocked()
+	log.Info("need handle msg size:",size)
-// 	for _, f := range s.onShutdown {
+	if  size == 0 {
-// 		go f()
+		return true
-// 	}
+	}
-// 	s.mu.Unlock()
+	return false
-
+}
-// 	ticker := time.NewTicker(shutdownPollInterval)
-// 	defer ticker.Stop()
-// 	for {
-// 		if s.closeIdleConns() {
-// 			return err
-// 		}
-// 		select {
-// 		case <-ctx.Done():
-// 			return ctx.Err()
-// 		case <-ticker.C:
-// 		}
-// 	}
-// }
-
-// func (s *Server) closeIdleConns() {
-// 	s.mu.Lock()
-// 	defer s.mu.Unlock()
-// 	quiescent := true
-
-// 	for c := range s.activeConn {
-// 		// check whether the conn is idle
-// 		st, ok := c.curState.Load().(ConnState)
-// 		if !ok || st != StateIdle {
-// 			quiescent = false
-// 			continue
-// 		}
-
-// 		s.Close()
-// 		delete(s.activeConn, c)
-// 	}
-
-// 	return quiescent
-// }
 
 func (s *Server) closeDoneChanLocked() {
 	ch := s.getDoneChanLocked()

server/server_test.go

@@ -8,6 +8,8 @@ import (
 	"github.com/smallnest/rpcx/protocol"
 	"github.com/smallnest/rpcx/share"
 	"github.com/smallnest/rpcx/_testutils"
+	"fmt"
+	"time"
 )
 
 type Args struct {
@@ -27,11 +29,11 @@ func (t *Arith) Mul(ctx context.Context, args *Args, reply *Reply) error {
 }
 
 func (t *Arith) ThriftMul(ctx context.Context, args *testutils.ThriftArgs_, reply *testutils.ThriftReply) error {
-	reply.C = args.A * args.B
+	reply.C = args.A * args.B + 11111111
+	time.Sleep(10*time.Second)
 	return nil
 }
 
-
 func TestThrift(t *testing.T) {
 	s := NewServer()
 	s.RegisterName("Arith", new(Arith), "")
@@ -39,7 +41,30 @@ func TestThrift(t *testing.T) {
 	s.Register(new(Arith), "")
 }
 
+func TestGo(t *testing.T) {
+	go func() {
+		ch := make(chan int, 1)
+		time.Sleep(2 * time.Second)
+		ch <- 1
+		<-ch
+		fmt.Println("go")
+	}()
 
+	ch2 := make(chan struct{}, 1)
+	<-ch2
+	fmt.Println("over")
+}
+
+func TestShutdownHook(t *testing.T) {
+	s := NewServer()
+	s.ShutdownFunc = func(s *Server) {
+		ctx, _ := context.WithTimeout(context.Background(), 155*time.Second)
+		s.Shutdown(ctx)
+	}
+	s.RegisterName("Arith", new(Arith), "")
+	s.Serve("tcp", ":8995")
+	s.Register(new(Arith), "")
+}
 
 func TestHandleRequest(t *testing.T) {
 	//use jsoncodec

sync/map.go

@@ -0,0 +1,376 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package sync
+
+import (
+	"sync/atomic"
+	"unsafe"
+	"sync"
+)
+
+// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
+// It is safe for multiple goroutines to call a Map's methods concurrently.
+//
+// It is optimized for use in concurrent loops with keys that are
+// stable over time, and either few steady-state stores, or stores
+// localized to one goroutine per key.
+//
+// For use cases that do not share these attributes, it will likely have
+// comparable or worse performance and worse type safety than an ordinary
+// map paired with a read-write mutex.
+//
+// The zero Map is valid and empty.
+//
+// A Map must not be copied after first use.
+type Map struct {
+	mu sync.Mutex
+
+	// read contains the portion of the map's contents that are safe for
+	// concurrent access (with or without mu held).
+	//
+	// The read field itself is always safe to load, but must only be stored with
+	// mu held.
+	//
+	// Entries stored in read may be updated concurrently without mu, but updating
+	// a previously-expunged entry requires that the entry be copied to the dirty
+	// map and unexpunged with mu held.
+	read atomic.Value // readOnly
+
+	// dirty contains the portion of the map's contents that require mu to be
+	// held. To ensure that the dirty map can be promoted to the read map quickly,
+	// it also includes all of the non-expunged entries in the read map.
+	//
+	// Expunged entries are not stored in the dirty map. An expunged entry in the
+	// clean map must be unexpunged and added to the dirty map before a new value
+	// can be stored to it.
+	//
+	// If the dirty map is nil, the next write to the map will initialize it by
+	// making a shallow copy of the clean map, omitting stale entries.
+	dirty map[interface{}]*entry
+
+	// misses counts the number of loads since the read map was last updated that
+	// needed to lock mu to determine whether the key was present.
+	//
+	// Once enough misses have occurred to cover the cost of copying the dirty
+	// map, the dirty map will be promoted to the read map (in the unamended
+	// state) and the next store to the map will make a new dirty copy.
+	misses int
+}
+
+// readOnly is an immutable struct stored atomically in the Map.read field.
+type readOnly struct {
+	m       map[interface{}]*entry
+	amended bool // true if the dirty map contains some key not in m.
+}
+
+// expunged is an arbitrary pointer that marks entries which have been deleted
+// from the dirty map.
+var expunged = unsafe.Pointer(new(interface{}))
+
+// An entry is a slot in the map corresponding to a particular key.
+type entry struct {
+	// p points to the interface{} value stored for the entry.
+	//
+	// If p == nil, the entry has been deleted and m.dirty == nil.
+	//
+	// If p == expunged, the entry has been deleted, m.dirty != nil, and the entry
+	// is missing from m.dirty.
+	//
+	// Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty
+	// != nil, in m.dirty[key].
+	//
+	// An entry can be deleted by atomic replacement with nil: when m.dirty is
+	// next created, it will atomically replace nil with expunged and leave
+	// m.dirty[key] unset.
+	//
+	// An entry's associated value can be updated by atomic replacement, provided
+	// p != expunged. If p == expunged, an entry's associated value can be updated
+	// only after first setting m.dirty[key] = e so that lookups using the dirty
+	// map find the entry.
+	p unsafe.Pointer // *interface{}
+}
+
+func newEntry(i interface{}) *entry {
+	return &entry{p: unsafe.Pointer(&i)}
+}
+
+// Load returns the value stored in the map for a key, or nil if no
+// value is present.
+// The ok result indicates whether value was found in the map.
+func (m *Map) Load(key interface{}) (value interface{}, ok bool) {
+	read, _ := m.read.Load().(readOnly)
+	e, ok := read.m[key]
+	if !ok && read.amended {
+		m.mu.Lock()
+		// Avoid reporting a spurious miss if m.dirty got promoted while we were
+		// blocked on m.mu. (If further loads of the same key will not miss, it's
+		// not worth copying the dirty map for this key.)
+		read, _ = m.read.Load().(readOnly)
+		e, ok = read.m[key]
+		if !ok && read.amended {
+			e, ok = m.dirty[key]
+			// Regardless of whether the entry was present, record a miss: this key
+			// will take the slow path until the dirty map is promoted to the read
+			// map.
+			m.missLocked()
+		}
+		m.mu.Unlock()
+	}
+	if !ok {
+		return nil, false
+	}
+	return e.load()
+}
+
+func (e *entry) load() (value interface{}, ok bool) {
+	p := atomic.LoadPointer(&e.p)
+	if p == nil || p == expunged {
+		return nil, false
+	}
+	return *(*interface{})(p), true
+}
+
+// Store sets the value for a key.
+func (m *Map) Store(key, value interface{}) {
+	read, _ := m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok && e.tryStore(&value) {
+		return
+	}
+
+	m.mu.Lock()
+	read, _ = m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		if e.unexpungeLocked() {
+			// The entry was previously expunged, which implies that there is a
+			// non-nil dirty map and this entry is not in it.
+			m.dirty[key] = e
+		}
+		e.storeLocked(&value)
+	} else if e, ok := m.dirty[key]; ok {
+		e.storeLocked(&value)
+	} else {
+		if !read.amended {
+			// We're adding the first new key to the dirty map.
+			// Make sure it is allocated and mark the read-only map as incomplete.
+			m.dirtyLocked()
+			m.read.Store(readOnly{m: read.m, amended: true})
+		}
+		m.dirty[key] = newEntry(value)
+	}
+	m.mu.Unlock()
+}
+
+// tryStore stores a value if the entry has not been expunged.
+//
+// If the entry is expunged, tryStore returns false and leaves the entry
+// unchanged.
+func (e *entry) tryStore(i *interface{}) bool {
+	p := atomic.LoadPointer(&e.p)
+	if p == expunged {
+		return false
+	}
+	for {
+		if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) {
+			return true
+		}
+		p = atomic.LoadPointer(&e.p)
+		if p == expunged {
+			return false
+		}
+	}
+}
+
+// unexpungeLocked ensures that the entry is not marked as expunged.
+//
+// If the entry was previously expunged, it must be added to the dirty map
+// before m.mu is unlocked.
+func (e *entry) unexpungeLocked() (wasExpunged bool) {
+	return atomic.CompareAndSwapPointer(&e.p, expunged, nil)
+}
+
+// storeLocked unconditionally stores a value to the entry.
+//
+// The entry must be known not to be expunged.
+func (e *entry) storeLocked(i *interface{}) {
+	atomic.StorePointer(&e.p, unsafe.Pointer(i))
+}
+
+// LoadOrStore returns the existing value for the key if present.
+// Otherwise, it stores and returns the given value.
+// The loaded result is true if the value was loaded, false if stored.
+func (m *Map) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) {
+	// Avoid locking if it's a clean hit.
+	read, _ := m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		actual, loaded, ok := e.tryLoadOrStore(value)
+		if ok {
+			return actual, loaded
+		}
+	}
+
+	m.mu.Lock()
+	read, _ = m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		if e.unexpungeLocked() {
+			m.dirty[key] = e
+		}
+		actual, loaded, _ = e.tryLoadOrStore(value)
+	} else if e, ok := m.dirty[key]; ok {
+		actual, loaded, _ = e.tryLoadOrStore(value)
+		m.missLocked()
+	} else {
+		if !read.amended {
+			// We're adding the first new key to the dirty map.
+			// Make sure it is allocated and mark the read-only map as incomplete.
+			m.dirtyLocked()
+			m.read.Store(readOnly{m: read.m, amended: true})
+		}
+		m.dirty[key] = newEntry(value)
+		actual, loaded = value, false
+	}
+	m.mu.Unlock()
+
+	return actual, loaded
+}
+
+// tryLoadOrStore atomically loads or stores a value if the entry is not
+// expunged.
+//
+// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and
+// returns with ok==false.
+func (e *entry) tryLoadOrStore(i interface{}) (actual interface{}, loaded, ok bool) {
+	p := atomic.LoadPointer(&e.p)
+	if p == expunged {
+		return nil, false, false
+	}
+	if p != nil {
+		return *(*interface{})(p), true, true
+	}
+
+	// Copy the interface after the first load to make this method more amenable
+	// to escape analysis: if we hit the "load" path or the entry is expunged, we
+	// shouldn't bother heap-allocating.
+	ic := i
+	for {
+		if atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) {
+			return i, false, true
+		}
+		p = atomic.LoadPointer(&e.p)
+		if p == expunged {
+			return nil, false, false
+		}
+		if p != nil {
+			return *(*interface{})(p), true, true
+		}
+	}
+}
+
+// Delete deletes the value for a key.
+func (m *Map) Delete(key interface{}) {
+	read, _ := m.read.Load().(readOnly)
+	e, ok := read.m[key]
+	if !ok && read.amended {
+		m.mu.Lock()
+		read, _ = m.read.Load().(readOnly)
+		e, ok = read.m[key]
+		if !ok && read.amended {
+			delete(m.dirty, key)
+		}
+		m.mu.Unlock()
+	}
+	if ok {
+		e.delete()
+	}
+}
+
+func (e *entry) delete() (hadValue bool) {
+	for {
+		p := atomic.LoadPointer(&e.p)
+		if p == nil || p == expunged {
+			return false
+		}
+		if atomic.CompareAndSwapPointer(&e.p, p, nil) {
+			return true
+		}
+	}
+}
+
+// Range calls f sequentially for each key and value present in the map.
+// If f returns false, range stops the iteration.
+//
+// Range does not necessarily correspond to any consistent snapshot of the Map's
+// contents: no key will be visited more than once, but if the value for any key
+// is stored or deleted concurrently, Range may reflect any mapping for that key
+// from any point during the Range call.
+//
+// Range may be O(N) with the number of elements in the map even if f returns
+// false after a constant number of calls.
+func (m *Map) Range(f func(key, value interface{}) bool) {
+	// We need to be able to iterate over all of the keys that were already
+	// present at the start of the call to Range.
+	// If read.amended is false, then read.m satisfies that property without
+	// requiring us to hold m.mu for a long time.
+	read, _ := m.read.Load().(readOnly)
+	if read.amended {
+		// m.dirty contains keys not in read.m. Fortunately, Range is already O(N)
+		// (assuming the caller does not break out early), so a call to Range
+		// amortizes an entire copy of the map: we can promote the dirty copy
+		// immediately!
+		m.mu.Lock()
+		read, _ = m.read.Load().(readOnly)
+		if read.amended {
+			read = readOnly{m: m.dirty}
+			m.read.Store(read)
+			m.dirty = nil
+			m.misses = 0
+		}
+		m.mu.Unlock()
+	}
+
+	for k, e := range read.m {
+		v, ok := e.load()
+		if !ok {
+			continue
+		}
+		if !f(k, v) {
+			break
+		}
+	}
+}
+
+func (m *Map) missLocked() {
+	m.misses++
+	if m.misses < len(m.dirty) {
+		return
+	}
+	m.read.Store(readOnly{m: m.dirty})
+	m.dirty = nil
+	m.misses = 0
+}
+
+func (m *Map) dirtyLocked() {
+	if m.dirty != nil {
+		return
+	}
+
+	read, _ := m.read.Load().(readOnly)
+	m.dirty = make(map[interface{}]*entry, len(read.m))
+	for k, e := range read.m {
+		if !e.tryExpungeLocked() {
+			m.dirty[k] = e
+		}
+	}
+}
+
+func (e *entry) tryExpungeLocked() (isExpunged bool) {
+	p := atomic.LoadPointer(&e.p)
+	for p == nil {
+		if atomic.CompareAndSwapPointer(&e.p, nil, expunged) {
+			return true
+		}
+		p = atomic.LoadPointer(&e.p)
+	}
+	return p == expunged
+}