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|
package main
import (
"errors"
"fmt"
"runtime"
"syscall"
"time"
"unsafe"
"golang.org/x/sys/unix"
)
func pollingEpoll() error {
epfd, err := unix.EpollCreate1(unix.EPOLL_CLOEXEC)
if err != nil {
return fmt.Errorf("epoll_create1: %w", err)
}
defer syscall.Close(epfd) //nolint:errcheck
var pipefd [2]int
if err := syscall.Pipe(pipefd[:]); err != nil {
return fmt.Errorf("pipe: %w", err)
}
defer syscall.Close(pipefd[0]) //nolint:errcheck
defer syscall.Close(pipefd[1]) //nolint:errcheck
event := unix.EpollEvent{Events: unix.EPOLLIN, Fd: int32(pipefd[0])}
if err := unix.EpollCtl(epfd, unix.EPOLL_CTL_ADD, pipefd[0], &event); err != nil {
return fmt.Errorf("epoll_ctl add: %w", err)
}
pwait2Supported := true
deadline := time.Now().Add(5 * time.Second)
for time.Now().Before(deadline) {
if err := waitAndDrain(epfd, pipefd, callEpollWait); err != nil {
return err
}
if err := waitAndDrain(epfd, pipefd, callEpollPwait); err != nil {
return err
}
if pwait2Supported {
if err := waitAndDrain(epfd, pipefd, callEpollPwait2); err != nil {
if !isUnsupportedEpollPwait2Err(err) {
return err
}
if drainErr := drainWakeByte(pipefd[0]); drainErr != nil {
return drainErr
}
pwait2Supported = false
}
}
if err := waitAndDrainReadiness(pipefd, callPoll); err != nil {
return err
}
if err := waitAndDrainReadiness(pipefd, callPpoll); err != nil {
return err
}
if err := waitAndDrainReadiness(pipefd, callSelect); err != nil {
return err
}
if err := waitAndDrainReadiness(pipefd, callPselect6); err != nil {
return err
}
time.Sleep(2 * time.Millisecond)
}
return nil
}
type readinessWaitFn func(pipefd [2]int) (int, error)
func waitAndDrainReadiness(pipefd [2]int, waitFn readinessWaitFn) error {
if _, err := syscall.Write(pipefd[1], []byte{1}); err != nil {
return fmt.Errorf("write wake byte: %w", err)
}
ready, err := waitFn(pipefd)
if err != nil {
return err
}
if ready < 1 {
return fmt.Errorf("polling wait returned %d ready events", ready)
}
return drainWakeByte(pipefd[0])
}
func waitAndDrain(epfd int, pipefd [2]int, waitFn func(int, []unix.EpollEvent) (int, error)) error {
if _, err := syscall.Write(pipefd[1], []byte{1}); err != nil {
return fmt.Errorf("write wake byte: %w", err)
}
events := make([]unix.EpollEvent, 4)
ready, err := waitFn(epfd, events)
if err != nil {
return err
}
if ready < 1 {
return fmt.Errorf("epoll wait returned %d ready events", ready)
}
return drainWakeByte(pipefd[0])
}
func drainWakeByte(readFD int) error {
var buf [1]byte
if _, err := syscall.Read(readFD, buf[:]); err != nil {
return fmt.Errorf("drain wake byte: %w", err)
}
return nil
}
func callEpollWait(epfd int, events []unix.EpollEvent) (int, error) {
eventPtr := unsafe.Pointer(&events[0])
r1, _, errno := syscall.RawSyscall6(
syscall.SYS_EPOLL_WAIT,
uintptr(epfd),
uintptr(eventPtr),
uintptr(len(events)),
uintptr(100),
0,
0,
)
runtime.KeepAlive(events)
if errno != 0 {
return 0, fmt.Errorf("epoll_wait: %w", errno)
}
return int(r1), nil
}
func callEpollPwait(epfd int, events []unix.EpollEvent) (int, error) {
eventPtr := unsafe.Pointer(&events[0])
r1, _, errno := syscall.RawSyscall6(
syscall.SYS_EPOLL_PWAIT,
uintptr(epfd),
uintptr(eventPtr),
uintptr(len(events)),
uintptr(100),
0,
0,
)
runtime.KeepAlive(events)
if errno != 0 {
return 0, fmt.Errorf("epoll_pwait: %w", errno)
}
return int(r1), nil
}
func callEpollPwait2(epfd int, events []unix.EpollEvent) (int, error) {
eventPtr := unsafe.Pointer(&events[0])
timeout := unix.Timespec{Sec: 0, Nsec: 100 * 1_000_000}
r1, _, errno := syscall.RawSyscall6(
unix.SYS_EPOLL_PWAIT2,
uintptr(epfd),
uintptr(eventPtr),
uintptr(len(events)),
uintptr(unsafe.Pointer(&timeout)),
0,
0,
)
runtime.KeepAlive(events)
runtime.KeepAlive(timeout)
if errno != 0 {
return 0, fmt.Errorf("epoll_pwait2: %w", errno)
}
return int(r1), nil
}
func callPoll(pipefd [2]int) (int, error) {
fds := []unix.PollFd{{Fd: int32(pipefd[0]), Events: unix.POLLIN}}
r1, _, errno := syscall.RawSyscall(
syscall.SYS_POLL,
uintptr(unsafe.Pointer(&fds[0])),
uintptr(len(fds)),
uintptr(100),
)
runtime.KeepAlive(fds)
if errno != 0 {
return 0, fmt.Errorf("poll: %w", errno)
}
return int(r1), nil
}
func callPpoll(pipefd [2]int) (int, error) {
fds := []unix.PollFd{{Fd: int32(pipefd[0]), Events: unix.POLLIN}}
timeout := unix.Timespec{Sec: 0, Nsec: 100 * 1_000_000}
r1, _, errno := syscall.RawSyscall6(
unix.SYS_PPOLL,
uintptr(unsafe.Pointer(&fds[0])),
uintptr(len(fds)),
uintptr(unsafe.Pointer(&timeout)),
0,
0,
0,
)
runtime.KeepAlive(fds)
runtime.KeepAlive(timeout)
if errno != 0 {
return 0, fmt.Errorf("ppoll: %w", errno)
}
return int(r1), nil
}
// fdSetBits is the maximum number of file descriptors an fdSet can represent.
// This matches the Linux FD_SETSIZE constant (1024).
const fdSetBits = 16 * 64
// errFDOutOfRange is returned when a file descriptor is too large for the
// fixed-size fd_set used by select/pselect6 (>= 1024).
var errFDOutOfRange = fmt.Errorf("fd >= %d: too large for select fd_set", fdSetBits)
type fdSet [16]uint64
// set marks fd in the bitset. It returns errFDOutOfRange when fd falls
// outside the fixed 1024-bit array, preventing an index-out-of-bounds panic.
func (s *fdSet) set(fd int) error {
if fd < 0 || fd >= fdSetBits {
return errFDOutOfRange
}
idx := fd / 64
bit := uint(fd % 64)
s[idx] |= 1 << bit
return nil
}
func callSelect(pipefd [2]int) (int, error) {
var readSet fdSet
if err := readSet.set(pipefd[0]); err != nil {
return 0, fmt.Errorf("select: %w", err)
}
timeout := syscall.Timeval{Sec: 0, Usec: 100000}
r1, _, errno := syscall.RawSyscall6(
syscall.SYS_SELECT,
uintptr(pipefd[0]+1),
uintptr(unsafe.Pointer(&readSet)),
0,
0,
uintptr(unsafe.Pointer(&timeout)),
0,
)
runtime.KeepAlive(readSet)
runtime.KeepAlive(timeout)
if errno != 0 {
return 0, fmt.Errorf("select: %w", errno)
}
return int(r1), nil
}
func callPselect6(pipefd [2]int) (int, error) {
var readSet fdSet
if err := readSet.set(pipefd[0]); err != nil {
return 0, fmt.Errorf("pselect6: %w", err)
}
timeout := unix.Timespec{Sec: 0, Nsec: 100 * 1_000_000}
r1, _, errno := syscall.RawSyscall6(
unix.SYS_PSELECT6,
uintptr(pipefd[0]+1),
uintptr(unsafe.Pointer(&readSet)),
0,
0,
uintptr(unsafe.Pointer(&timeout)),
0,
)
runtime.KeepAlive(readSet)
runtime.KeepAlive(timeout)
if errno != 0 {
return 0, fmt.Errorf("pselect6: %w", errno)
}
return int(r1), nil
}
func isUnsupportedEpollPwait2Err(err error) bool {
if err == nil {
return false
}
var errno syscall.Errno
if !errors.As(err, &errno) {
return false
}
return errno == syscall.ENOSYS || errno == syscall.ENOTSUP
}
|
