Merge pull request #80 from nanomsg/norace2

fixes #67 DialPipe problem with multiple calls / waiting for busy pipe

Author: jstarks

pipe.go

@@ -15,7 +15,6 @@ import (
 //sys connectNamedPipe(pipe syscall.Handle, o *syscall.Overlapped) (err error) = ConnectNamedPipe
 //sys createNamedPipe(name string, flags uint32, pipeMode uint32, maxInstances uint32, outSize uint32, inSize uint32, defaultTimeout uint32, sa *syscall.SecurityAttributes) (handle syscall.Handle, err error)  [failretval==syscall.InvalidHandle] = CreateNamedPipeW
 //sys createFile(name string, access uint32, mode uint32, sa *syscall.SecurityAttributes, createmode uint32, attrs uint32, templatefile syscall.Handle) (handle syscall.Handle, err error) [failretval==syscall.InvalidHandle] = CreateFileW
-//sys waitNamedPipe(name string, timeout uint32) (err error) = WaitNamedPipeW
 //sys getNamedPipeInfo(pipe syscall.Handle, flags *uint32, outSize *uint32, inSize *uint32, maxInstances *uint32) (err error) = GetNamedPipeInfo
 //sys getNamedPipeHandleState(pipe syscall.Handle, state *uint32, curInstances *uint32, maxCollectionCount *uint32, collectDataTimeout *uint32, userName *uint16, maxUserNameSize uint32) (err error) = GetNamedPipeHandleStateW
 //sys localAlloc(uFlags uint32, length uint32) (ptr uintptr) = LocalAlloc
@@ -139,12 +138,14 @@ func (s pipeAddress) String() string {
 }
 
 // DialPipe connects to a named pipe by path, timing out if the connection
-// takes longer than the specified duration. If timeout is nil, then the timeout
-// is the default timeout established by the pipe server.
+// takes longer than the specified duration. If timeout is nil, then we use
+// a default timeout of 5 seconds.  (We do not use WaitNamedPipe.)
 func DialPipe(path string, timeout *time.Duration) (net.Conn, error) {
 	var absTimeout time.Time
 	if timeout != nil {
 		absTimeout = time.Now().Add(*timeout)
+	} else {
+		absTimeout = time.Now().Add(time.Second * 2)
 	}
 	var err error
 	var h syscall.Handle
@@ -153,22 +154,13 @@ func DialPipe(path string, timeout *time.Duration) (net.Conn, error) {
 		if err != cERROR_PIPE_BUSY {
 			break
 		}
-		now := time.Now()
-		var ms uint32
-		if absTimeout.IsZero() {
-			ms = cNMPWAIT_USE_DEFAULT_WAIT
-		} else if now.After(absTimeout) {
-			ms = cNMPWAIT_NOWAIT
-		} else {
-			ms = uint32(absTimeout.Sub(now).Nanoseconds() / 1000 / 1000)
-		}
-		err = waitNamedPipe(path, ms)
-		if err != nil {
-			if err == cERROR_SEM_TIMEOUT {
-				return nil, ErrTimeout
-			}
-			break
+		if time.Now().After(absTimeout) {
+			return nil, ErrTimeout
 		}
+
+		// Wait 10 msec and try again. This is a rather simplistic
+		// view, as we always try each 10 milliseconds.
+		time.Sleep(time.Millisecond * 10)
 	}
 	if err != nil {
 		return nil, &os.PathError{Op: "open", Path: path, Err: err}
@@ -349,13 +341,23 @@ func ListenPipe(path string, c *PipeConfig) (net.Listener, error) {
 	if err != nil {
 		return nil, err
 	}
-	// Immediately open and then close a client handle so that the named pipe is
-	// created but not currently accepting connections.
+	// Create a client handle and connect it.  This results in the pipe
+	// instance always existing, so that clients see ERROR_PIPE_BUSY
+	// rather than ERROR_FILE_NOT_FOUND.  This ties the first instance
+	// up so that no other instances can be used.  This would have been
+	// cleaner if the Win32 API matched CreateFile with ConnectNamedPipe
+	// instead of CreateNamedPipe.  (Apparently created named pipes are
+	// considered to be in listening state regardless of whether any
+	// active calls to ConnectNamedPipe are outstanding.)
 	h2, err := createFile(path, 0, 0, nil, syscall.OPEN_EXISTING, cSECURITY_SQOS_PRESENT|cSECURITY_ANONYMOUS, 0)
 	if err != nil {
 		syscall.Close(h)
 		return nil, err
 	}
+	// Close the client handle. The server side of the instance will
+	// still be busy, leading to ERROR_PIPE_BUSY instead of
+	// ERROR_NOT_FOUND, as long as we don't close the server handle,
+	// or disconnect the client with DisconnectNamedPipe.
 	syscall.Close(h2)
 	l := &win32PipeListener{
 		firstHandle:        h,