Cancelable reads (#120)

This commit implements cancelable reads, which allows Bubble Tea programs to run in succession in a single application. It also makes sure all goroutines terminate before `Program.Start()` returns.

Closes #24.

cancelreader.go

@@ -0,0 +1,72 @@
+package tea
+
+import (
+	"fmt"
+	"io"
+	"sync"
+)
+
+var errCanceled = fmt.Errorf("read cancelled")
+
+// cancelReader is a io.Reader whose Read() calls can be cancelled without data
+// being consumed. The cancelReader has to be closed.
+type cancelReader interface {
+	io.ReadCloser
+
+	// Cancel cancels ongoing and future reads an returns true if it succeeded.
+	Cancel() bool
+}
+
+// fallbackCancelReader implements cancelReader but does not actually support
+// cancelation during an ongoing Read() call. Thus, Cancel() always returns
+// false. However, after calling Cancel(), new Read() calls immediately return
+// errCanceled and don't consume any data anymore.
+type fallbackCancelReader struct {
+	r         io.Reader
+	cancelled bool
+}
+
+// newFallbackCancelReader is a fallback for newCancelReader that cannot
+// actually cancel an ongoing read but will immediately return on future reads
+// if it has been cancelled.
+func newFallbackCancelReader(reader io.Reader) (cancelReader, error) {
+	return &fallbackCancelReader{r: reader}, nil
+}
+
+func (r *fallbackCancelReader) Read(data []byte) (int, error) {
+	if r.cancelled {
+		return 0, errCanceled
+	}
+
+	return r.r.Read(data)
+}
+
+func (r *fallbackCancelReader) Cancel() bool {
+	r.cancelled = true
+
+	return false
+}
+
+func (r *fallbackCancelReader) Close() error {
+	return nil
+}
+
+// cancelMixin represents a goroutine-safe cancelation status.
+type cancelMixin struct {
+	unsafeCancelled bool
+	lock            sync.Mutex
+}
+
+func (c *cancelMixin) isCancelled() bool {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	return c.unsafeCancelled
+}
+
+func (c *cancelMixin) setCancelled() {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	c.unsafeCancelled = true
+}

cancelreader_bsd.go

@@ -0,0 +1,144 @@
+// +build darwin freebsd netbsd openbsd
+
+// nolint:revive
+package tea
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+// newkqueueCancelReader returns a reader and a cancel function. If the input reader
+// is an *os.File, the cancel function can be used to interrupt a blocking call
+// read call. In this case, the cancel function returns true if the call was
+// cancelled successfully. If the input reader is not a *os.File, the cancel
+// function does nothing and always returns false. The BSD and macOS
+// implementation is based on the kqueue mechanism.
+func newCancelReader(reader io.Reader) (cancelReader, error) {
+	file, ok := reader.(*os.File)
+	if !ok {
+		return newFallbackCancelReader(reader)
+	}
+
+	// kqueue returns instantly when polling /dev/tty so fallback to select
+	if file.Name() == "/dev/tty" {
+		return newSelectCancelReader(reader)
+	}
+
+	kQueue, err := unix.Kqueue()
+	if err != nil {
+		return nil, fmt.Errorf("create kqueue: %w", err)
+	}
+
+	r := &kqueueCancelReader{
+		file:   file,
+		kQueue: kQueue,
+	}
+
+	r.cancelSignalReader, r.cancelSignalWriter, err = os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	unix.SetKevent(&r.kQueueEvents[0], int(file.Fd()), unix.EVFILT_READ, unix.EV_ADD)
+	unix.SetKevent(&r.kQueueEvents[1], int(r.cancelSignalReader.Fd()), unix.EVFILT_READ, unix.EV_ADD)
+
+	return r, nil
+}
+
+type kqueueCancelReader struct {
+	file               *os.File
+	cancelSignalReader *os.File
+	cancelSignalWriter *os.File
+	cancelMixin
+	kQueue       int
+	kQueueEvents [2]unix.Kevent_t
+}
+
+func (r *kqueueCancelReader) Read(data []byte) (int, error) {
+	if r.isCancelled() {
+		return 0, errCanceled
+	}
+
+	err := r.wait()
+	if err != nil {
+		if errors.Is(err, errCanceled) {
+			// remove signal from pipe
+			var b [1]byte
+			_, errRead := r.cancelSignalReader.Read(b[:])
+			if errRead != nil {
+				return 0, fmt.Errorf("reading cancel signal: %w", errRead)
+			}
+		}
+
+		return 0, err
+	}
+
+	return r.file.Read(data)
+}
+
+func (r *kqueueCancelReader) Cancel() bool {
+	r.setCancelled()
+
+	// send cancel signal
+	_, err := r.cancelSignalWriter.Write([]byte{'c'})
+	return err == nil
+}
+
+func (r *kqueueCancelReader) Close() error {
+	var errMsgs []string
+
+	// close kqueue
+	err := unix.Close(r.kQueue)
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing kqueue: %v", err))
+	}
+
+	// close pipe
+	err = r.cancelSignalWriter.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal writer: %v", err))
+	}
+
+	err = r.cancelSignalReader.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal reader: %v", err))
+	}
+
+	if len(errMsgs) > 0 {
+		return fmt.Errorf(strings.Join(errMsgs, ", "))
+	}
+
+	return nil
+}
+
+func (r *kqueueCancelReader) wait() error {
+	events := make([]unix.Kevent_t, 1)
+
+	for {
+		_, err := unix.Kevent(r.kQueue, r.kQueueEvents[:], events, nil)
+		if errors.Is(err, unix.EINTR) {
+			continue // try again if the syscall was interrupted
+		}
+
+		if err != nil {
+			return fmt.Errorf("kevent: %w", err)
+		}
+
+		break
+	}
+
+	switch events[0].Ident {
+	case uint64(r.file.Fd()):
+		return nil
+	case uint64(r.cancelSignalReader.Fd()):
+		return errCanceled
+	}
+
+	return fmt.Errorf("unknown error")
+}

cancelreader_default.go

@@ -0,0 +1,14 @@
+//go:build !darwin && !windows && !linux && !solaris && !freebsd && !netbsd && !openbsd
+// +build !darwin,!windows,!linux,!solaris,!freebsd,!netbsd,!openbsd
+
+package tea
+
+import (
+	"io"
+)
+
+// newCancelReader returns a fallbackCancelReader that satisfies the
+// cancelReader but does not actually support cancelation.
+func newCancelReader(reader io.Reader) (cancelReader, error) {
+	return newFallbackCancelReader(reader)
+}

cancelreader_linux.go

@@ -0,0 +1,152 @@
+//go:build linux
+// +build linux
+
+// nolint:revive
+package tea
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+// newCancelReader returns a reader and a cancel function. If the input reader
+// is an *os.File, the cancel function can be used to interrupt a blocking call
+// read call. In this case, the cancel function returns true if the call was
+// cancelled successfully. If the input reader is not a *os.File, the cancel
+// function does nothing and always returns false. The linux implementation is
+// based on the epoll mechanism.
+func newCancelReader(reader io.Reader) (cancelReader, error) {
+	file, ok := reader.(*os.File)
+	if !ok {
+		return newFallbackCancelReader(reader)
+	}
+
+	epoll, err := unix.EpollCreate1(0)
+	if err != nil {
+		return nil, fmt.Errorf("create epoll: %w", err)
+	}
+
+	r := &epollCancelReader{
+		file:  file,
+		epoll: epoll,
+	}
+
+	r.cancelSignalReader, r.cancelSignalWriter, err = os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	err = unix.EpollCtl(epoll, unix.EPOLL_CTL_ADD, int(file.Fd()), &unix.EpollEvent{
+		Events: unix.EPOLLIN,
+		Fd:     int32(file.Fd()),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("add reader to epoll interrest list")
+	}
+
+	err = unix.EpollCtl(epoll, unix.EPOLL_CTL_ADD, int(r.cancelSignalReader.Fd()), &unix.EpollEvent{
+		Events: unix.EPOLLIN,
+		Fd:     int32(r.cancelSignalReader.Fd()),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("add reader to epoll interrest list")
+	}
+
+	return r, nil
+}
+
+type epollCancelReader struct {
+	file               *os.File
+	cancelSignalReader *os.File
+	cancelSignalWriter *os.File
+	cancelMixin
+	epoll int
+}
+
+func (r *epollCancelReader) Read(data []byte) (int, error) {
+	if r.isCancelled() {
+		return 0, errCanceled
+	}
+
+	err := r.wait()
+	if err != nil {
+		if errors.Is(err, errCanceled) {
+			// remove signal from pipe
+			var b [1]byte
+			_, readErr := r.cancelSignalReader.Read(b[:])
+			if readErr != nil {
+				return 0, fmt.Errorf("reading cancel signal: %w", readErr)
+			}
+		}
+
+		return 0, err
+	}
+
+	return r.file.Read(data)
+}
+
+func (r *epollCancelReader) Cancel() bool {
+	r.setCancelled()
+
+	// send cancel signal
+	_, err := r.cancelSignalWriter.Write([]byte{'c'})
+	return err == nil
+}
+
+func (r *epollCancelReader) Close() error {
+	var errMsgs []string
+
+	// close kqueue
+	err := unix.Close(r.epoll)
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing epoll: %v", err))
+	}
+
+	// close pipe
+	err = r.cancelSignalWriter.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal writer: %v", err))
+	}
+
+	err = r.cancelSignalReader.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal reader: %v", err))
+	}
+
+	if len(errMsgs) > 0 {
+		return fmt.Errorf(strings.Join(errMsgs, ", "))
+	}
+
+	return nil
+}
+
+func (r *epollCancelReader) wait() error {
+	events := make([]unix.EpollEvent, 1)
+
+	for {
+		_, err := unix.EpollWait(r.epoll, events, -1)
+		if errors.Is(err, unix.EINTR) {
+			continue // try again if the syscall was interrupted
+		}
+
+		if err != nil {
+			return fmt.Errorf("kevent: %w", err)
+		}
+
+		break
+	}
+
+	switch events[0].Fd {
+	case int32(r.file.Fd()):
+		return nil
+	case int32(r.cancelSignalReader.Fd()):
+		return errCanceled
+	}
+
+	return fmt.Errorf("unknown error")
+}

cancelreader_select.go

@@ -0,0 +1,137 @@
+//go:build solaris || darwin
+// +build solaris darwin
+
+// nolint:revive
+package tea
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"golang.org/x/sys/unix"
+)
+
+// newSelectCancelReader returns a reader and a cancel function. If the input
+// reader is an *os.File, the cancel function can be used to interrupt a
+// blocking call read call. In this case, the cancel function returns true if
+// the call was cancelled successfully. If the input reader is not a *os.File or
+// the file descriptor is 1024 or larger, the cancel function does nothing and
+// always returns false. The generic unix implementation is based on the posix
+// select syscall.
+func newSelectCancelReader(reader io.Reader) (cancelReader, error) {
+	file, ok := reader.(*os.File)
+	if !ok || file.Fd() >= unix.FD_SETSIZE {
+		return newFallbackCancelReader(reader)
+	}
+	r := &selectCancelReader{file: file}
+
+	var err error
+
+	r.cancelSignalReader, r.cancelSignalWriter, err = os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	return r, nil
+}
+
+type selectCancelReader struct {
+	file               *os.File
+	cancelSignalReader *os.File
+	cancelSignalWriter *os.File
+	cancelMixin
+}
+
+func (r *selectCancelReader) Read(data []byte) (int, error) {
+	if r.isCancelled() {
+		return 0, errCanceled
+	}
+
+	for {
+		err := waitForRead(r.file, r.cancelSignalReader)
+		if err != nil {
+			if errors.Is(err, unix.EINTR) {
+				continue // try again if the syscall was interrupted
+			}
+
+			if errors.Is(err, errCanceled) {
+				// remove signal from pipe
+				var b [1]byte
+				_, readErr := r.cancelSignalReader.Read(b[:])
+				if readErr != nil {
+					return 0, fmt.Errorf("reading cancel signal: %w", readErr)
+				}
+			}
+
+			return 0, err
+		}
+
+		return r.file.Read(data)
+	}
+}
+
+func (r *selectCancelReader) Cancel() bool {
+	r.setCancelled()
+
+	// send cancel signal
+	_, err := r.cancelSignalWriter.Write([]byte{'c'})
+	return err == nil
+}
+
+func (r *selectCancelReader) Close() error {
+	var errMsgs []string
+
+	// close pipe
+	err := r.cancelSignalWriter.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal writer: %v", err))
+	}
+
+	err = r.cancelSignalReader.Close()
+	if err != nil {
+		errMsgs = append(errMsgs, fmt.Sprintf("closing cancel signal reader: %v", err))
+	}
+
+	if len(errMsgs) > 0 {
+		return fmt.Errorf(strings.Join(errMsgs, ", "))
+	}
+
+	return nil
+}
+
+func waitForRead(reader *os.File, abort *os.File) error {
+	readerFd := int(reader.Fd())
+	abortFd := int(abort.Fd())
+
+	maxFd := readerFd
+	if abortFd > maxFd {
+		maxFd = abortFd
+	}
+
+	// this is a limitation of the select syscall
+	if maxFd >= unix.FD_SETSIZE {
+		return fmt.Errorf("cannot select on file descriptor %d which is larger than 1024", maxFd)
+	}
+
+	fdSet := &unix.FdSet{}
+	fdSet.Set(int(reader.Fd()))
+	fdSet.Set(int(abort.Fd()))
+
+	_, err := unix.Select(maxFd+1, fdSet, nil, nil, nil)
+	if err != nil {
+		return fmt.Errorf("select: %w", err)
+	}
+
+	if fdSet.IsSet(abortFd) {
+		return errCanceled
+	}
+
+	if fdSet.IsSet(readerFd) {
+		return nil
+	}
+
+	return fmt.Errorf("select returned without setting a file descriptor")
+}

cancelreader_unix.go

@@ -0,0 +1,20 @@
+//go:build solaris
+// +build solaris
+
+// nolint:revive
+package tea
+
+import (
+	"io"
+)
+
+// newCancelReader returns a reader and a cancel function. If the input reader
+// is an *os.File, the cancel function can be used to interrupt a blocking call
+// read call. In this case, the cancel function returns true if the call was
+// cancelled successfully. If the input reader is not a *os.File or the file
+// descriptor is 1024 or larger, the cancel function does nothing and always
+// returns false. The generic unix implementation is based on the posix select
+// syscall.
+func newCancelReader(reader io.Reader) (cancelReader, error) {
+	return newSelectCancelReader(reader)
+}

cancelreader_windows.go

@@ -0,0 +1,239 @@
+//go:build windows
+// +build windows
+
+package tea
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"syscall"
+	"time"
+	"unicode/utf16"
+
+	"golang.org/x/sys/windows"
+)
+
+var fileShareValidFlags uint32 = 0x00000007
+
+// newCancelReader returns a reader and a cancel function. If the input reader
+// is an *os.File with the same file descriptor as os.Stdin, the cancel function
+// can be used to interrupt a blocking call read call. In this case, the cancel
+// function returns true if the call was cancelled successfully. If the input
+// reader is not a *os.File with the same file descriptor as os.Stdin, the
+// cancel function does nothing and always returns false. The Windows
+// implementation is based on WaitForMultipleObject with overlapping reads from
+// CONIN$.
+func newCancelReader(reader io.Reader) (cancelReader, error) {
+	if f, ok := reader.(*os.File); !ok || f.Fd() != os.Stdin.Fd() {
+		return newFallbackCancelReader(reader)
+	}
+
+	// it is neccessary to open CONIN$ (NOT windows.STD_INPUT_HANDLE) in
+	// overlapped mode to be able to use it with WaitForMultipleObjects.
+	conin, err := windows.CreateFile(
+		&(utf16.Encode([]rune("CONIN$\x00"))[0]), windows.GENERIC_READ|windows.GENERIC_WRITE,
+		fileShareValidFlags, nil, windows.OPEN_EXISTING, windows.FILE_FLAG_OVERLAPPED, 0)
+	if err != nil {
+		return nil, fmt.Errorf("open CONIN$ in overlapping mode: %w", err)
+	}
+
+	resetConsole, err := prepareConsole(conin)
+	if err != nil {
+		return nil, fmt.Errorf("prepare console: %w", err)
+	}
+
+	// flush input, otherwise it can contain events which trigger
+	// WaitForMultipleObjects but which ReadFile cannot read, resulting in an
+	// un-cancelable read
+	err = flushConsoleInputBuffer(conin)
+	if err != nil {
+		return nil, fmt.Errorf("flush console input buffer: %w", err)
+	}
+
+	cancelEvent, err := windows.CreateEvent(nil, 0, 0, nil)
+	if err != nil {
+		return nil, fmt.Errorf("create stop event: %w", err)
+	}
+
+	return &winCancelReader{
+		conin:              conin,
+		cancelEvent:        cancelEvent,
+		resetConsole:       resetConsole,
+		blockingReadSignal: make(chan struct{}, 1),
+	}, nil
+}
+
+type winCancelReader struct {
+	conin       windows.Handle
+	cancelEvent windows.Handle
+	cancelMixin
+
+	resetConsole       func() error
+	blockingReadSignal chan struct{}
+}
+
+func (r *winCancelReader) Read(data []byte) (int, error) {
+	if r.isCancelled() {
+		return 0, errCanceled
+	}
+
+	err := r.wait()
+	if err != nil {
+		return 0, err
+	}
+
+	if r.isCancelled() {
+		return 0, errCanceled
+	}
+
+	// windows.Read does not work on overlapping windows.Handles
+	return r.readAsync(data)
+}
+
+// Cancel cancels ongoing and future Read() calls and returns true if the
+// cancelation of the ongoing Read() was successful. On Windows Terminal,
+// WaitForMultipleObjects sometimes immediately returns without input being
+// available. In this case, graceful cancelation is not possible and Cancel()
+// returns false.
+func (r *winCancelReader) Cancel() bool {
+	r.setCancelled()
+
+	select {
+	case r.blockingReadSignal <- struct{}{}:
+		err := windows.SetEvent(r.cancelEvent)
+		if err != nil {
+			return false
+		}
+		<-r.blockingReadSignal
+	case <-time.After(100 * time.Millisecond):
+		// Read() hangs in a GetOverlappedResult which is likely due to
+		// WaitForMultipleObjects returning without input being available
+		// so we cannot cancel this ongoing read.
+		return false
+	}
+
+	return true
+}
+
+func (r *winCancelReader) Close() error {
+	err := windows.CloseHandle(r.cancelEvent)
+	if err != nil {
+		return fmt.Errorf("closing cancel event handle: %w", err)
+	}
+
+	err = r.resetConsole()
+	if err != nil {
+		return err
+	}
+
+	err = windows.Close(r.conin)
+	if err != nil {
+		return fmt.Errorf("closing CONIN$")
+	}
+
+	return nil
+}
+
+func (r *winCancelReader) wait() error {
+	event, err := windows.WaitForMultipleObjects([]windows.Handle{r.conin, r.cancelEvent}, false, windows.INFINITE)
+	switch {
+	case windows.WAIT_OBJECT_0 <= event && event < windows.WAIT_OBJECT_0+2:
+		if event == windows.WAIT_OBJECT_0+1 {
+			return errCanceled
+		}
+
+		if event == windows.WAIT_OBJECT_0 {
+			return nil
+		}
+
+		return fmt.Errorf("unexpected wait object is ready: %d", event-windows.WAIT_OBJECT_0)
+	case windows.WAIT_ABANDONED <= event && event < windows.WAIT_ABANDONED+2:
+		return fmt.Errorf("abandoned")
+	case event == uint32(windows.WAIT_TIMEOUT):
+		return fmt.Errorf("timeout")
+	case event == windows.WAIT_FAILED:
+		return fmt.Errorf("failed")
+	default:
+		return fmt.Errorf("unexpected error: %w", error(err))
+	}
+}
+
+// readAsync is neccessary to read from a windows.Handle in overlapping mode.
+func (r *winCancelReader) readAsync(data []byte) (int, error) {
+	hevent, err := windows.CreateEvent(nil, 0, 0, nil)
+	if err != nil {
+		return 0, fmt.Errorf("create event: %w", err)
+	}
+
+	overlapped := windows.Overlapped{
+		HEvent: hevent,
+	}
+
+	var n uint32
+
+	err = windows.ReadFile(r.conin, data, &n, &overlapped)
+	if err != nil && err != windows.ERROR_IO_PENDING {
+		return int(n), err
+	}
+
+	r.blockingReadSignal <- struct{}{}
+	err = windows.GetOverlappedResult(r.conin, &overlapped, &n, true)
+	if err != nil {
+		return int(n), nil
+	}
+	<-r.blockingReadSignal
+
+	return int(n), nil
+}
+
+func prepareConsole(input windows.Handle) (reset func() error, err error) {
+	var originalMode uint32
+
+	err = windows.GetConsoleMode(input, &originalMode)
+	if err != nil {
+		return nil, fmt.Errorf("get console mode: %w", err)
+	}
+
+	var newMode uint32
+	newMode &^= windows.ENABLE_ECHO_INPUT
+	newMode &^= windows.ENABLE_LINE_INPUT
+	newMode &^= windows.ENABLE_MOUSE_INPUT
+	newMode &^= windows.ENABLE_WINDOW_INPUT
+	newMode &^= windows.ENABLE_PROCESSED_INPUT
+
+	newMode |= windows.ENABLE_EXTENDED_FLAGS
+	newMode |= windows.ENABLE_INSERT_MODE
+	newMode |= windows.ENABLE_QUICK_EDIT_MODE
+
+	newMode &^= windows.ENABLE_VIRTUAL_TERMINAL_INPUT
+
+	err = windows.SetConsoleMode(input, newMode)
+	if err != nil {
+		return nil, fmt.Errorf("set console mode: %w", err)
+	}
+
+	return func() error {
+		err := windows.SetConsoleMode(input, originalMode)
+		if err != nil {
+			return fmt.Errorf("reset console mode: %w", err)
+		}
+
+		return nil
+	}, nil
+}
+
+var (
+	modkernel32                 = windows.NewLazySystemDLL("kernel32.dll")
+	procFlushConsoleInputBuffer = modkernel32.NewProc("FlushConsoleInputBuffer")
+)
+
+func flushConsoleInputBuffer(consoleInput windows.Handle) error {
+	r, _, e := syscall.Syscall(procFlushConsoleInputBuffer.Addr(), 1,
+		uintptr(consoleInput), 0, 0)
+	if r == 0 {
+		return error(e)
+	}
+
+	return nil
+}

signals_unix.go

@@ -4,6 +4,7 @@
 package tea
 
 import (
+	"context"
 	"os"
 	"os/signal"
 	"syscall"
@@ -14,15 +15,31 @@ import (
 // listenForResize sends messages (or errors) when the terminal resizes.
 // Argument output should be the file descriptor for the terminal; usually
 // os.Stdout.
-func listenForResize(output *os.File, msgs chan Msg, errs chan error) {
+func listenForResize(ctx context.Context, output *os.File, msgs chan Msg, errs chan error, done chan struct{}) {
 	sig := make(chan os.Signal, 1)
 	signal.Notify(sig, syscall.SIGWINCH)
+
+	defer func() {
+		signal.Stop(sig)
+		close(done)
+	}()
+
 	for {
-		<-sig
+		select {
+		case <-ctx.Done():
+			return
+		case <-sig:
+		}
+
 		w, h, err := term.GetSize(int(output.Fd()))
 		if err != nil {
 			errs <- err
 		}
-		msgs <- WindowSizeMsg{w, h}
+
+		select {
+		case <-ctx.Done():
+			return
+		case msgs <- WindowSizeMsg{w, h}:
+		}
 	}
 }

signals_windows.go

@@ -2,8 +2,14 @@
 
 package tea
 
-import "os"
+import (
+	"context"
+	"os"
+)
 
 // listenForResize is not available on windows because windows does not
 // implement syscall.SIGWINCH.
-func listenForResize(_ *os.File, _ chan Msg, _ chan error) {}
+func listenForResize(ctx context.Context, output *os.File, msgs chan Msg,
+	errs chan error, done chan struct{}) {
+	close(done)
+}

tea.go

@@ -11,6 +11,7 @@ package tea
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -18,6 +19,7 @@ import (
 	"runtime/debug"
 	"sync"
 	"syscall"
+	"time"
 
 	"github.com/containerd/console"
 	isatty "github.com/mattn/go-isatty"
@@ -79,7 +81,6 @@ type Program struct {
 	startupOptions startupOptions
 
 	mtx *sync.Mutex
-	done chan struct{}
 
 	msgs chan Msg
 
@@ -250,15 +251,39 @@ func NewProgram(model Model, opts ...ProgramOption) *Program {
 // Start initializes the program.
 func (p *Program) Start() error {
 	p.msgs = make(chan Msg)
-	p.done = make(chan struct{})
 
 	var (
 		cmds = make(chan Cmd)
 		errs = make(chan error)
 	)
 
-	ctx, cancel := context.WithCancel(context.Background())
+	// channels for managing goroutine lifecycles
-	defer cancel()
+	var (
+		readLoopDone   = make(chan struct{})
+		sigintLoopDone = make(chan struct{})
+		cmdLoopDone    = make(chan struct{})
+		resizeLoopDone = make(chan struct{})
+		initSignalDone = make(chan struct{})
+
+		waitForGoroutines = func(withReadLoop bool) {
+			if withReadLoop {
+				select {
+				case <-readLoopDone:
+				case <-time.After(500 * time.Millisecond):
+					// the read loop hangs, which means the input cancelReader's
+					// cancel function has returned true even though it was not
+					// able to cancel the read
+				}
+			}
+			<-cmdLoopDone
+			<-resizeLoopDone
+			<-sigintLoopDone
+			<-initSignalDone
+		}
+	)
+
+	ctx, cancelContext := context.WithCancel(context.Background())
+	defer cancelContext()
 
 	switch {
 	case p.startupOptions.has(withInputTTY):
@@ -267,6 +292,9 @@ func (p *Program) Start() error {
 		if err != nil {
 			return err
 		}
+
+		defer f.Close() // nolint:errcheck
+
 		p.input = f
 
 	case !p.startupOptions.has(withCustomInput):
@@ -287,6 +315,9 @@ func (p *Program) Start() error {
 		if err != nil {
 			return err
 		}
+
+		defer f.Close() // nolint:errcheck
+
 		p.input = f
 	}
 
@@ -297,7 +328,10 @@ func (p *Program) Start() error {
 	go func() {
 		sig := make(chan os.Signal, 1)
 		signal.Notify(sig, syscall.SIGINT)
-		defer signal.Stop(sig)
+		defer func() {
+			signal.Stop(sig)
+			close(sigintLoopDone)
+		}()
 
 		select {
 		case <-ctx.Done():
@@ -342,8 +376,14 @@ func (p *Program) Start() error {
 	model := p.initialModel
 	if initCmd := model.Init(); initCmd != nil {
 		go func() {
-			cmds <- initCmd
+			defer close(initSignalDone)
+			select {
+			case cmds <- initCmd:
+			case <-ctx.Done():
+			}
 		}()
+	} else {
+		close(initSignalDone)
 	}
 
 	// Start renderer
@@ -353,21 +393,37 @@ func (p *Program) Start() error {
 	// Render initial view
 	p.renderer.write(model.View())
 
+	cancelReader, err := newCancelReader(p.input)
+	if err != nil {
+		return err
+	}
+
+	defer cancelReader.Close() // nolint:errcheck
+
 	// Subscribe to user input
 	if p.input != nil {
 		go func() {
+			defer close(readLoopDone)
+
 			for {
-				msg, err := readInput(p.input)
+				if ctx.Err() != nil {
-				if err != nil {
+					return
-					// If we get EOF just stop listening for input
-					if err == io.EOF {
-						break
 				}
+
+				msg, err := readInput(cancelReader)
+				if err != nil {
+					if !errors.Is(err, io.EOF) && !errors.Is(err, errCanceled) {
 						errs <- err
 					}
+
+					return
+				}
+
 				p.msgs <- msg
 			}
 		}()
+	} else {
+		defer close(readLoopDone)
 	}
 
 	if f, ok := p.output.(*os.File); ok {
@@ -377,25 +433,44 @@ func (p *Program) Start() error {
 			if err != nil {
 				errs <- err
 			}
-			p.msgs <- WindowSizeMsg{w, h}
+
+			select {
+			case <-ctx.Done():
+			case p.msgs <- WindowSizeMsg{w, h}:
+			}
 		}()
 
 		// Listen for window resizes
-		go listenForResize(f, p.msgs, errs)
+		go listenForResize(ctx, f, p.msgs, errs, resizeLoopDone)
+	} else {
+		close(resizeLoopDone)
 	}
 
 	// Process commands
 	go func() {
+		defer close(cmdLoopDone)
+
 		for {
 			select {
-			case <-p.done:
+			case <-ctx.Done():
+
 				return
 			case cmd := <-cmds:
-				if cmd != nil {
+				if cmd == nil {
-					go func() {
+					continue
-						p.msgs <- cmd()
-					}()
 				}
+
+				// Don't wait on these goroutines, otherwise the shutdown
+				// latency would get too large as a Cmd can run for some time
+				// (e.g. tick commands that sleep for half a second). It's not
+				// possible to cancel them so we'll have to leak the goroutine
+				// until Cmd returns.
+				go func() {
+					select {
+					case p.msgs <- cmd():
+					case <-ctx.Done():
+					}
+				}()
 			}
 		}
 	}()
@@ -404,13 +479,18 @@ func (p *Program) Start() error {
 	for {
 		select {
 		case err := <-errs:
+			cancelContext()
+			waitForGoroutines(cancelReader.Cancel())
 			p.shutdown(false)
+
 			return err
 		case msg := <-p.msgs:
 
 			// Handle special internal messages
 			switch msg := msg.(type) {
 			case quitMsg:
+				cancelContext()
+				waitForGoroutines(cancelReader.Cancel())
 				p.shutdown(false)
 				return nil
 
@@ -479,7 +559,6 @@ func (p *Program) shutdown(kill bool) {
 	} else {
 		p.renderer.stop()
 	}
-	close(p.done)
 	p.ExitAltScreen()
 	p.DisableMouseCellMotion()
 	p.DisableMouseAllMotion()

tty_unix.go

@@ -28,7 +28,7 @@ func (p *Program) initInput() error {
 // program exits.
 func (p *Program) restoreInput() error {
 	if p.console != nil {
-		return p.console.Close()
+		return p.console.Reset()
 	}
 	return nil
 }