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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Waiting for FDs via epoll(7).
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readFlags = syscall.EPOLLIN | syscall.EPOLLRDHUP
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writeFlags = syscall.EPOLLOUT
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type pollster struct {
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// Events we're already waiting for
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// Must hold pollServer lock
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// An event buffer for EpollWait.
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// Used without a lock, may only be used by WaitFD.
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waitEventBuf [10]syscall.EpollEvent
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waitEvents []syscall.EpollEvent
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// An event buffer for EpollCtl, to avoid a malloc.
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// Must hold pollServer lock.
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ctlEvent syscall.EpollEvent
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func newpollster() (p *pollster, err error) {
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if p.epfd, err = syscall.EpollCreate1(syscall.EPOLL_CLOEXEC); err != nil {
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if err != syscall.ENOSYS {
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return nil, os.NewSyscallError("epoll_create1", err)
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// The arg to epoll_create is a hint to the kernel
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// about the number of FDs we will care about.
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// We don't know, and since 2.6.8 the kernel ignores it anyhow.
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if p.epfd, err = syscall.EpollCreate(16); err != nil {
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return nil, os.NewSyscallError("epoll_create", err)
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syscall.CloseOnExec(p.epfd)
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p.events = make(map[int]uint32)
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func (p *pollster) AddFD(fd int, mode int, repeat bool) (bool, error) {
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// pollServer is locked.
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p.ctlEvent.Fd = int32(fd)
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p.ctlEvent.Events, already = p.events[fd]
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p.ctlEvent.Events |= syscall.EPOLLONESHOT
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p.ctlEvent.Events |= readFlags
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p.ctlEvent.Events |= writeFlags
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op = syscall.EPOLL_CTL_MOD
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op = syscall.EPOLL_CTL_ADD
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if err := syscall.EpollCtl(p.epfd, op, fd, &p.ctlEvent); err != nil {
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return false, os.NewSyscallError("epoll_ctl", err)
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p.events[fd] = p.ctlEvent.Events
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func (p *pollster) StopWaiting(fd int, bits uint) {
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// pollServer is locked.
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events, already := p.events[fd]
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// The fd returned by the kernel may have been
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// cancelled already; return silently.
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// If syscall.EPOLLONESHOT is not set, the wait
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// is a repeating wait, so don't change it.
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if events&syscall.EPOLLONESHOT == 0 {
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// Disable the given bits.
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// If we're still waiting for other events, modify the fd
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// event in the kernel. Otherwise, delete it.
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events &= ^uint32(bits)
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if int32(events)&^syscall.EPOLLONESHOT != 0 {
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p.ctlEvent.Fd = int32(fd)
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p.ctlEvent.Events = events
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if err := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_MOD, fd, &p.ctlEvent); err != nil {
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print("Epoll modify fd=", fd, ": ", err.Error(), "\n")
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p.events[fd] = events
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if err := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_DEL, fd, nil); err != nil {
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print("Epoll delete fd=", fd, ": ", err.Error(), "\n")
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func (p *pollster) DelFD(fd int, mode int) {
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// pollServer is locked.
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p.StopWaiting(fd, readFlags)
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p.StopWaiting(fd, writeFlags)
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// Discard any queued up events.
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for i < len(p.waitEvents) {
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if fd == int(p.waitEvents[i].Fd) {
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copy(p.waitEvents[i:], p.waitEvents[i+1:])
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p.waitEvents = p.waitEvents[:len(p.waitEvents)-1]
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func (p *pollster) WaitFD(s *pollServer, nsec int64) (fd int, mode int, err error) {
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for len(p.waitEvents) == 0 {
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msec = int((nsec + 1e6 - 1) / 1e6)
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n, err := syscall.EpollWait(p.epfd, p.waitEventBuf[0:], msec)
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if err == syscall.EAGAIN || err == syscall.EINTR {
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return -1, 0, os.NewSyscallError("epoll_wait", err)
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p.waitEvents = p.waitEventBuf[0:n]
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ev := &p.waitEvents[0]
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p.waitEvents = p.waitEvents[1:]
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if ev.Events&writeFlags != 0 {
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p.StopWaiting(fd, writeFlags)
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if ev.Events&readFlags != 0 {
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p.StopWaiting(fd, readFlags)
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// Other events are error conditions - wake whoever is waiting.
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events, _ := p.events[fd]
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if events&writeFlags != 0 {
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p.StopWaiting(fd, writeFlags)
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p.StopWaiting(fd, readFlags)
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func (p *pollster) Close() error {
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return os.NewSyscallError("close", syscall.Close(p.epfd))