syncfile.go RawHistoryFolder

1// Package syncfile waits for Linux sync files (dma-fence fds), such as the
2// GPU fence a frame render returns.
3package syncfile
4
5import (
6	"context"
7	"errors"
8	"fmt"
9	"os"
10
11	"golang.org/x/sys/unix"
12)
13
14// pollSlice bounds one poll so a canceled ctx is seen.
15const pollSlice = 100 // ms
16
17// Wait blocks until f signals or ctx ends. A sync file is signalled when
18// it polls readable; an error or invalid fd is reported, not taken as
19// signalled.
20func Wait(ctx context.Context, f *os.File) error {
21	fds := []unix.PollFd{{Fd: int32(f.Fd()), Events: unix.POLLIN}}
22	for {
23		n, err := unix.Poll(fds, pollSlice)
24		switch {
25		case errors.Is(err, unix.EINTR):
26			continue
27		case err != nil:
28			return fmt.Errorf("poll sync file: %w", err)
29		case n > 0 && fds[0].Revents&unix.POLLIN != 0:
30			return nil
31		case n > 0:
32			return fmt.Errorf("sync file poll events %#x", fds[0].Revents)
33		}
34		if err := ctx.Err(); err != nil {
35			return err
36		}
37	}
38}