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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Waiting for FDs via epoll(7).

package net

import (
        "os"
        "syscall"
)

const (
        readFlags  = syscall.EPOLLIN | syscall.EPOLLRDHUP
        writeFlags = syscall.EPOLLOUT
)

type pollster struct {
        epfd int

        // Events we're already waiting for
        // Must hold pollServer lock
        events map[int]uint32

        // An event buffer for EpollWait.
        // Used without a lock, may only be used by WaitFD.
        waitEventBuf [10]syscall.EpollEvent
        waitEvents   []syscall.EpollEvent

        // An event buffer for EpollCtl, to avoid a malloc.
        // Must hold pollServer lock.
        ctlEvent syscall.EpollEvent
}

func newpollster() (p *pollster, err error) {
        p = new(pollster)
        if p.epfd, err = syscall.EpollCreate1(syscall.EPOLL_CLOEXEC); err != nil {
                if err != syscall.ENOSYS {
                        return nil, os.NewSyscallError("epoll_create1", err)
                }
                // The arg to epoll_create is a hint to the kernel
                // about the number of FDs we will care about.
                // We don't know, and since 2.6.8 the kernel ignores it anyhow.
                if p.epfd, err = syscall.EpollCreate(16); err != nil {
                        return nil, os.NewSyscallError("epoll_create", err)
                }
                syscall.CloseOnExec(p.epfd)
        }
        p.events = make(map[int]uint32)
        return p, nil
}

func (p *pollster) AddFD(fd int, mode int, repeat bool) (bool, error) {
        // pollServer is locked.

        var already bool
        p.ctlEvent.Fd = int32(fd)
        p.ctlEvent.Events, already = p.events[fd]
        if !repeat {
                p.ctlEvent.Events |= syscall.EPOLLONESHOT
        }
        if mode == 'r' {
                p.ctlEvent.Events |= readFlags
        } else {
                p.ctlEvent.Events |= writeFlags
        }

        var op int
        if already {
                op = syscall.EPOLL_CTL_MOD
        } else {
                op = syscall.EPOLL_CTL_ADD
        }
        if err := syscall.EpollCtl(p.epfd, op, fd, &p.ctlEvent); err != nil {
                return false, os.NewSyscallError("epoll_ctl", err)
        }
        p.events[fd] = p.ctlEvent.Events
        return false, nil
}

func (p *pollster) StopWaiting(fd int, bits uint) {
        // pollServer is locked.

        events, already := p.events[fd]
        if !already {
                print("Epoll unexpected fd=", fd, "\n")
                return
        }

        // If syscall.EPOLLONESHOT is not set, the wait
        // is a repeating wait, so don't change it.
        if events&syscall.EPOLLONESHOT == 0 {
                return
        }

        // Disable the given bits.
        // If we're still waiting for other events, modify the fd
        // event in the kernel.  Otherwise, delete it.
        events &= ^uint32(bits)
        if int32(events)&^syscall.EPOLLONESHOT != 0 {
                p.ctlEvent.Fd = int32(fd)
                p.ctlEvent.Events = events
                if err := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_MOD, fd, &p.ctlEvent); err != nil {
                        print("Epoll modify fd=", fd, ": ", err.Error(), "\n")
                }
                p.events[fd] = events
        } else {
                if err := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_DEL, fd, nil); err != nil {
                        print("Epoll delete fd=", fd, ": ", err.Error(), "\n")
                }
                delete(p.events, fd)
        }
}

func (p *pollster) DelFD(fd int, mode int) {
        // pollServer is locked.

        if mode == 'r' {
                p.StopWaiting(fd, readFlags)
        } else {
                p.StopWaiting(fd, writeFlags)
        }

        // Discard any queued up events.
        i := 0
        for i < len(p.waitEvents) {
                if fd == int(p.waitEvents[i].Fd) {
                        copy(p.waitEvents[i:], p.waitEvents[i+1:])
                        p.waitEvents = p.waitEvents[:len(p.waitEvents)-1]
                } else {
                        i++
                }
        }
}

func (p *pollster) WaitFD(s *pollServer, nsec int64) (fd int, mode int, err error) {
        for len(p.waitEvents) == 0 {
                var msec int = -1
                if nsec > 0 {
                        msec = int((nsec + 1e6 - 1) / 1e6)
                }

                s.Unlock()
                n, err := syscall.EpollWait(p.epfd, p.waitEventBuf[0:], msec)
                s.Lock()

                if err != nil {
                        if err == syscall.EAGAIN || err == syscall.EINTR {
                                continue
                        }
                        return -1, 0, os.NewSyscallError("epoll_wait", err)
                }
                if n == 0 {
                        return -1, 0, nil
                }
                p.waitEvents = p.waitEventBuf[0:n]
        }

        ev := &p.waitEvents[0]
        p.waitEvents = p.waitEvents[1:]

        fd = int(ev.Fd)

        if ev.Events&writeFlags != 0 {
                p.StopWaiting(fd, writeFlags)
                return fd, 'w', nil
        }
        if ev.Events&readFlags != 0 {
                p.StopWaiting(fd, readFlags)
                return fd, 'r', nil
        }

        // Other events are error conditions - wake whoever is waiting.
        events, _ := p.events[fd]
        if events&writeFlags != 0 {
                p.StopWaiting(fd, writeFlags)
                return fd, 'w', nil
        }
        p.StopWaiting(fd, readFlags)
        return fd, 'r', nil
}

func (p *pollster) Close() error {
        return os.NewSyscallError("close", syscall.Close(p.epfd))
}