runtime: copy netpoll code from Go 1.7 runtime

[official-gcc.git] / libgo / go / runtime / netpoll_solaris.go

// Copyright 2014 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.

package runtime

import "unsafe"

// Solaris runtime-integrated network poller.
//
// Solaris uses event ports for scalable network I/O. Event
// ports are level-triggered, unlike epoll and kqueue which
// can be configured in both level-triggered and edge-triggered
// mode. Level triggering means we have to keep track of a few things
// ourselves. After we receive an event for a file descriptor,
// it's our responsibility to ask again to be notified for future
// events for that descriptor. When doing this we must keep track of
// what kind of events the goroutines are currently interested in,
// for example a fd may be open both for reading and writing.
//
// A description of the high level operation of this code
// follows. Networking code will get a file descriptor by some means
// and will register it with the netpolling mechanism by a code path
// that eventually calls runtime·netpollopen. runtime·netpollopen
// calls port_associate with an empty event set. That means that we
// will not receive any events at this point. The association needs
// to be done at this early point because we need to process the I/O
// readiness notification at some point in the future. If I/O becomes
// ready when nobody is listening, when we finally care about it,
// nobody will tell us anymore.
//
// Beside calling runtime·netpollopen, the networking code paths
// will call runtime·netpollarm each time goroutines are interested
// in doing network I/O. Because now we know what kind of I/O we
// are interested in (reading/writing), we can call port_associate
// passing the correct type of event set (POLLIN/POLLOUT). As we made
// sure to have already associated the file descriptor with the port,
// when we now call port_associate, we will unblock the main poller
// loop (in runtime·netpoll) right away if the socket is actually
// ready for I/O.
//
// The main poller loop runs in its own thread waiting for events
// using port_getn. When an event happens, it will tell the scheduler
// about it using runtime·netpollready. Besides doing this, it must
// also re-associate the events that were not part of this current
// notification with the file descriptor. Failing to do this would
// mean each notification will prevent concurrent code using the
// same file descriptor in parallel.
//
// The logic dealing with re-associations is encapsulated in
// runtime·netpollupdate. This function takes care to associate the
// descriptor only with the subset of events that were previously
// part of the association, except the one that just happened. We
// can't re-associate with that right away, because event ports
// are level triggered so it would cause a busy loop. Instead, that
// association is effected only by the runtime·netpollarm code path,
// when Go code actually asks for I/O.
//
// The open and arming mechanisms are serialized using the lock
// inside PollDesc. This is required because the netpoll loop runs
// asynchronously in respect to other Go code and by the time we get
// to call port_associate to update the association in the loop, the
// file descriptor might have been closed and reopened already. The
// lock allows runtime·netpollupdate to be called synchronously from
// the loop thread while preventing other threads operating to the
// same PollDesc, so once we unblock in the main loop, until we loop
// again we know for sure we are always talking about the same file
// descriptor and can safely access the data we want (the event set).

//extern __go_fcntl_uintptr
func fcntlUintptr(fd, cmd, arg uintptr) (uintptr, uintptr)

func fcntl(fd, cmd int32, arg uintptr) int32 {
        r, _ := fcntlUintptr(uintptr(fd), uintptr(cmd), arg)
        return int32(r)
}

//extern port_create
func port_create() int32

//extern port_associate
func port_associate(port, source int32, object uintptr, events uint32, user uintptr) int32

//extern port_dissociate
func port_dissociate(port, source int32, object uintptr) int32

//extern port_getn
func port_getn(port int32, evs *portevent, max uint32, nget *uint32, timeout *timespec) int32

var portfd int32 = -1

func netpollinit() {
        portfd = port_create()
        if portfd >= 0 {
                fcntl(portfd, _F_SETFD, _FD_CLOEXEC)
                return
        }

        print("netpollinit: failed to create port (", errno(), ")\n")
        throw("netpollinit: failed to create port")
}

func netpollopen(fd uintptr, pd *pollDesc) int32 {
        lock(&pd.lock)
        // We don't register for any specific type of events yet, that's
        // netpollarm's job. We merely ensure we call port_associate before
        // asynchronous connect/accept completes, so when we actually want
        // to do any I/O, the call to port_associate (from netpollarm,
        // with the interested event set) will unblock port_getn right away
        // because of the I/O readiness notification.
        pd.user = 0
        r := port_associate(portfd, _PORT_SOURCE_FD, fd, 0, uintptr(unsafe.Pointer(pd)))
        unlock(&pd.lock)
        if r < 0 {
                return int32(errno())
        }
        return 0
}

func netpollclose(fd uintptr) int32 {
        if port_dissociate(portfd, _PORT_SOURCE_FD, fd) < 0 {
                return int32(errno())
        }
        return 0
}

// Updates the association with a new set of interested events. After
// this call, port_getn will return one and only one event for that
// particular descriptor, so this function needs to be called again.
func netpollupdate(pd *pollDesc, set, clear uint32) {
        if pd.closing {
                return
        }

        old := pd.user
        events := (old & ^clear) | set
        if old == events {
                return
        }

        if events != 0 && port_associate(portfd, _PORT_SOURCE_FD, pd.fd, events, uintptr(unsafe.Pointer(pd))) != 0 {
                print("netpollupdate: failed to associate (", errno(), ")\n")
                throw("netpollupdate: failed to associate")
        }
        pd.user = events
}

// subscribe the fd to the port such that port_getn will return one event.
func netpollarm(pd *pollDesc, mode int) {
        lock(&pd.lock)
        switch mode {
        case 'r':
                netpollupdate(pd, _POLLIN, 0)
        case 'w':
                netpollupdate(pd, _POLLOUT, 0)
        default:
                throw("netpollarm: bad mode")
        }
        unlock(&pd.lock)
}

// polls for ready network connections
// returns list of goroutines that become runnable
func netpoll(block bool) *g {
        if portfd == -1 {
                return nil
        }

        var wait *timespec
        var zero timespec
        if !block {
                wait = &zero
        }

        var events [128]portevent
retry:
        var n uint32 = 1
        if port_getn(portfd, &events[0], uint32(len(events)), &n, wait) < 0 {
                if e := errno(); e != _EINTR {
                        print("runtime: port_getn on fd ", portfd, " failed with ", e, "\n")
                        throw("port_getn failed")
                }
                goto retry
        }

        var gp guintptr
        for i := 0; i < int(n); i++ {
                ev := &events[i]

                if ev.portev_events == 0 {
                        continue
                }
                pd := (*pollDesc)(unsafe.Pointer(ev.portev_user))

                var mode, clear int32
                if (ev.portev_events & (_POLLIN | _POLLHUP | _POLLERR)) != 0 {
                        mode += 'r'
                        clear |= _POLLIN
                }
                if (ev.portev_events & (_POLLOUT | _POLLHUP | _POLLERR)) != 0 {
                        mode += 'w'
                        clear |= _POLLOUT
                }
                // To effect edge-triggered events, we need to be sure to
                // update our association with whatever events were not
                // set with the event. For example if we are registered
                // for POLLIN|POLLOUT, and we get POLLIN, besides waking
                // the goroutine interested in POLLIN we have to not forget
                // about the one interested in POLLOUT.
                if clear != 0 {
                        lock(&pd.lock)
                        netpollupdate(pd, 0, uint32(clear))
                        unlock(&pd.lock)
                }

                if mode != 0 {
                        netpollready(&gp, pd, mode)
                }
        }

        if block && gp == 0 {
                goto retry
        }
        return gp.ptr()
}