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