src/runtime/netpoll_epoll.go

// Copyright 2013 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.

// +build linux

package runtime

import "unsafe"

func epollcreate(size int32) int32
func epollcreate1(flags int32) int32

//go:noescape
func epollctl(epfd, op, fd int32, ev *epollevent) int32

//go:noescape
func epollwait(epfd int32, ev *epollevent, nev, timeout int32) int32
func closeonexec(fd int32)

var (
	epfd int32 = -1 // epoll descriptor
)

func netpollinit() {
	epfd = epollcreate1(_EPOLL_CLOEXEC)
	if epfd >= 0 {
		return
	}
	epfd = epollcreate(1024)
	if epfd >= 0 {
		closeonexec(epfd)
		return
	}
	println("runtime: epollcreate failed with", -epfd)
	throw("runtime: netpollinit failed")
}

func netpolldescriptor() uintptr {
	return uintptr(epfd)
}

func netpollopen(fd uintptr, pd *pollDesc) int32 {
	var ev epollevent
	ev.events = _EPOLLIN | _EPOLLOUT | _EPOLLRDHUP | _EPOLLET
	*(**pollDesc)(unsafe.Pointer(&ev.data)) = pd
	return -epollctl(epfd, _EPOLL_CTL_ADD, int32(fd), &ev)
}

func netpollclose(fd uintptr) int32 {
	var ev epollevent
	return -epollctl(epfd, _EPOLL_CTL_DEL, int32(fd), &ev)
}

func netpollarm(pd *pollDesc, mode int) {
	throw("runtime: unused")
}

// netpoll checks for ready network connections.
// Returns list of goroutines that become runnable.
// delay < 0: blocks indefinitely
// delay == 0: does not block, just polls
// delay > 0: block for up to that many nanoseconds
func netpoll(delay int64) gList {
	if epfd == -1 {
		return gList{}
	}
	var waitms int32
	if delay < 0 {
		waitms = -1
	} else if delay == 0 {
		waitms = 0
	} else if delay < 1e6 {
		waitms = 1
	} else if delay < 1e15 {
		waitms = int32(delay / 1e6)
	} else {
		// An arbitrary cap on how long to wait for a timer.
		// 1e9 ms == ~11.5 days.
		waitms = 1e9
	}
	var events [128]epollevent
retry:
	n := epollwait(epfd, &events[0], int32(len(events)), waitms)
	if n < 0 {
		if n != -_EINTR {
			println("runtime: epollwait on fd", epfd, "failed with", -n)
			throw("runtime: netpoll failed")
		}
		// If a timed sleep was interrupted, just return to
		// recalculate how long we should sleep now.
		if waitms > 0 {
			return gList{}
		}
		goto retry
	}
	var toRun gList
	for i := int32(0); i < n; i++ {
		ev := &events[i]
		if ev.events == 0 {
			continue
		}
		var mode int32
		if ev.events&(_EPOLLIN|_EPOLLRDHUP|_EPOLLHUP|_EPOLLERR) != 0 {
			mode += 'r'
		}
		if ev.events&(_EPOLLOUT|_EPOLLHUP|_EPOLLERR) != 0 {
			mode += 'w'
		}
		if mode != 0 {
			pd := *(**pollDesc)(unsafe.Pointer(&ev.data))
			pd.everr = false
			if ev.events == _EPOLLERR {
				pd.everr = true
			}
			netpollready(&toRun, pd, mode)
		}
	}
	return toRun
}