net: use SetFileCompletionNotificationModes on windows if available

This allows to skip GetQueuedCompletionStatus if an IO operation completes synchronously.
benchmark                    old ns/op    new ns/op    delta
BenchmarkTCP4Persistent          27669        25863   -6.53%
BenchmarkTCP4Persistent-2        18173        15908  -12.46%
BenchmarkTCP4Persistent-4        10390         9766   -6.01%

R=golang-dev, mikioh.mikioh, alex.brainman
CC=golang-dev
https://golang.org/cl/12409044

src/pkg/net/fd_windows.go

@@ -27,7 +27,11 @@ var initErr error
 // package uses CancelIoEx API, if present, otherwise it fallback
 // to CancelIo.
 
-var canCancelIO bool // determines if CancelIoEx API is present
+var (
+	canCancelIO                               bool // determines if CancelIoEx API is present
+	skipSyncNotif                             bool
+	hasLoadSetFileCompletionNotificationModes bool
+)
 
 func sysInit() {
 	var d syscall.WSAData
@@ -40,6 +44,27 @@ func sysInit() {
 		lookupPort = newLookupPort
 		lookupIP = newLookupIP
 	}
+
+	hasLoadSetFileCompletionNotificationModes = syscall.LoadSetFileCompletionNotificationModes() == nil
+	if hasLoadSetFileCompletionNotificationModes {
+		// It's not safe to use FILE_SKIP_COMPLETION_PORT_ON_SUCCESS if non IFS providers are installed:
+		// http://support.microsoft.com/kb/2568167
+		skipSyncNotif = true
+		protos := [2]int32{syscall.IPPROTO_TCP, 0}
+		var buf [32]syscall.WSAProtocolInfo
+		len := uint32(unsafe.Sizeof(buf))
+		n, err := syscall.WSAEnumProtocols(&protos[0], &buf[0], &len)
+		if err != nil {
+			skipSyncNotif = false
+		} else {
+			for i := int32(0); i < n; i++ {
+				if buf[i].ServiceFlags1&syscall.XP1_IFS_HANDLES == 0 {
+					skipSyncNotif = false
+					break
+				}
+			}
+		}
+	}
 }
 
 func closesocket(s syscall.Handle) error {
@@ -148,7 +173,12 @@ func (s *ioSrv) ExecIO(o *operation, name string, submit func(o *operation) erro
 	}
 	switch err {
 	case nil:
-		// IO completed immediately, but we need to get our completion message anyway.
+		// IO completed immediately
+		if o.fd.skipSyncNotif {
+			// No completion message will follow, so return immediately.
+			return int(o.qty), nil
+		}
+		// Need to get our completion message anyway.
 	case syscall.ERROR_IO_PENDING:
 		// IO started, and we have to wait for its completion.
 		err = nil
@@ -222,13 +252,14 @@ type netFD struct {
 	closing bool
 
 	// immutable until Close
-	sysfd       syscall.Handle
-	family      int
-	sotype      int
-	isConnected bool
-	net         string
-	laddr       Addr
-	raddr       Addr
+	sysfd         syscall.Handle
+	family        int
+	sotype        int
+	isConnected   bool
+	skipSyncNotif bool
+	net           string
+	laddr         Addr
+	raddr         Addr
 
 	rop operation // read operation
 	wop operation // write operation
@@ -249,6 +280,19 @@ func (fd *netFD) init() error {
 	if err := fd.pd.Init(fd); err != nil {
 		return err
 	}
+	if hasLoadSetFileCompletionNotificationModes {
+		// We do not use events, so we can skip them always.
+		flags := uint8(syscall.FILE_SKIP_SET_EVENT_ON_HANDLE)
+		// It's not safe to skip completion notifications for UDP:
+		// http://blogs.technet.com/b/winserverperformance/archive/2008/06/26/designing-applications-for-high-performance-part-iii.aspx
+		if skipSyncNotif && fd.net == "tcp" {
+			flags |= syscall.FILE_SKIP_COMPLETION_PORT_ON_SUCCESS
+		}
+		err := syscall.SetFileCompletionNotificationModes(fd.sysfd, flags)
+		if err == nil && flags&syscall.FILE_SKIP_COMPLETION_PORT_ON_SUCCESS != 0 {
+			fd.skipSyncNotif = true
+		}
+	}
 	fd.rop.mode = 'r'
 	fd.wop.mode = 'w'
 	fd.rop.fd = fd

src/pkg/syscall/syscall_windows.go

@@ -508,6 +508,10 @@ func LoadCancelIoEx() error {
 	return procCancelIoEx.Find()
 }
 
+func LoadSetFileCompletionNotificationModes() error {
+	return procSetFileCompletionNotificationModes.Find()
+}
+
 // net api calls
 
 const socket_error = uintptr(^uint32(0))
@@ -541,6 +545,8 @@ const socket_error = uintptr(^uint32(0))
 //sys	FreeAddrInfoW(addrinfo *AddrinfoW) = ws2_32.FreeAddrInfoW
 //sys	GetIfEntry(pIfRow *MibIfRow) (errcode error) = iphlpapi.GetIfEntry
 //sys	GetAdaptersInfo(ai *IpAdapterInfo, ol *uint32) (errcode error) = iphlpapi.GetAdaptersInfo
+//sys	SetFileCompletionNotificationModes(handle Handle, flags uint8) (err error) = kernel32.SetFileCompletionNotificationModes
+//sys	WSAEnumProtocols(protocols *int32, protocolBuffer *WSAProtocolInfo, bufferLength *uint32) (n int32, err error) [failretval==-1] = ws2_32.WSAEnumProtocolsW
 
 // For testing: clients can set this flag to force
 // creation of IPv6 sockets to return EAFNOSUPPORT.

src/pkg/syscall/ztypes_windows.go

@@ -964,3 +964,69 @@ var WSAID_CONNECTEX = GUID{
 	0x4660,
 	[8]byte{0x8e, 0xe9, 0x76, 0xe5, 0x8c, 0x74, 0x06, 0x3e},
 }
+
+const (
+	FILE_SKIP_COMPLETION_PORT_ON_SUCCESS = 1
+	FILE_SKIP_SET_EVENT_ON_HANDLE        = 2
+)
+
+const (
+	WSAPROTOCOL_LEN    = 255
+	MAX_PROTOCOL_CHAIN = 7
+	BASE_PROTOCOL      = 1
+	LAYERED_PROTOCOL   = 0
+
+	XP1_CONNECTIONLESS           = 0x00000001
+	XP1_GUARANTEED_DELIVERY      = 0x00000002
+	XP1_GUARANTEED_ORDER         = 0x00000004
+	XP1_MESSAGE_ORIENTED         = 0x00000008
+	XP1_PSEUDO_STREAM            = 0x00000010
+	XP1_GRACEFUL_CLOSE           = 0x00000020
+	XP1_EXPEDITED_DATA           = 0x00000040
+	XP1_CONNECT_DATA             = 0x00000080
+	XP1_DISCONNECT_DATA          = 0x00000100
+	XP1_SUPPORT_BROADCAST        = 0x00000200
+	XP1_SUPPORT_MULTIPOINT       = 0x00000400
+	XP1_MULTIPOINT_CONTROL_PLANE = 0x00000800
+	XP1_MULTIPOINT_DATA_PLANE    = 0x00001000
+	XP1_QOS_SUPPORTED            = 0x00002000
+	XP1_UNI_SEND                 = 0x00008000
+	XP1_UNI_RECV                 = 0x00010000
+	XP1_IFS_HANDLES              = 0x00020000
+	XP1_PARTIAL_MESSAGE          = 0x00040000
+	XP1_SAN_SUPPORT_SDP          = 0x00080000
+
+	PFL_MULTIPLE_PROTO_ENTRIES  = 0x00000001
+	PFL_RECOMMENDED_PROTO_ENTRY = 0x00000002
+	PFL_HIDDEN                  = 0x00000004
+	PFL_MATCHES_PROTOCOL_ZERO   = 0x00000008
+	PFL_NETWORKDIRECT_PROVIDER  = 0x00000010
+)
+
+type WSAProtocolInfo struct {
+	ServiceFlags1     uint32
+	ServiceFlags2     uint32
+	ServiceFlags3     uint32
+	ServiceFlags4     uint32
+	ProviderFlags     uint32
+	ProviderId        GUID
+	CatalogEntryId    uint32
+	ProtocolChain     WSAProtocolChain
+	Version           int32
+	AddressFamily     int32
+	MaxSockAddr       int32
+	MinSockAddr       int32
+	SocketType        int32
+	Protocol          int32
+	ProtocolMaxOffset int32
+	NetworkByteOrder  int32
+	SecurityScheme    int32
+	MessageSize       uint32
+	ProviderReserved  uint32
+	ProtocolName      [WSAPROTOCOL_LEN + 1]uint16
+}
+
+type WSAProtocolChain struct {
+	ChainLen     int32
+	ChainEntries [MAX_PROTOCOL_CHAIN]uint32
+}