libgo: update to Go 1.11

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

// Copyright 2011 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 dragonfly freebsd linux

package runtime

import (
        "runtime/internal/atomic"
        "unsafe"
)

// For gccgo, while we still have C runtime code, use go:linkname to
// rename some functions to themselves, so that the compiler will
// export them.
//
//go:linkname lock runtime.lock
//go:linkname unlock runtime.unlock
//go:linkname noteclear runtime.noteclear
//go:linkname notewakeup runtime.notewakeup
//go:linkname notesleep runtime.notesleep
//go:linkname notetsleep runtime.notetsleep
//go:linkname notetsleepg runtime.notetsleepg

// This implementation depends on OS-specific implementations of
//
//      futexsleep(addr *uint32, val uint32, ns int64)
//              Atomically,
//                      if *addr == val { sleep }
//              Might be woken up spuriously; that's allowed.
//              Don't sleep longer than ns; ns < 0 means forever.
//
//      futexwakeup(addr *uint32, cnt uint32)
//              If any procs are sleeping on addr, wake up at most cnt.

const (
        mutex_unlocked = 0
        mutex_locked   = 1
        mutex_sleeping = 2

        active_spin     = 4
        active_spin_cnt = 30
        passive_spin    = 1
)

// Possible lock states are mutex_unlocked, mutex_locked and mutex_sleeping.
// mutex_sleeping means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.

// We use the uintptr mutex.key and note.key as a uint32.
//go:nosplit
func key32(p *uintptr) *uint32 {
        return (*uint32)(unsafe.Pointer(p))
}

func lock(l *mutex) {
        gp := getg()

        if gp.m.locks < 0 {
                throw("runtime·lock: lock count")
        }
        gp.m.locks++

        // Speculative grab for lock.
        v := atomic.Xchg(key32(&l.key), mutex_locked)
        if v == mutex_unlocked {
                return
        }

        // wait is either MUTEX_LOCKED or MUTEX_SLEEPING
        // depending on whether there is a thread sleeping
        // on this mutex. If we ever change l->key from
        // MUTEX_SLEEPING to some other value, we must be
        // careful to change it back to MUTEX_SLEEPING before
        // returning, to ensure that the sleeping thread gets
        // its wakeup call.
        wait := v

        // On uniprocessors, no point spinning.
        // On multiprocessors, spin for ACTIVE_SPIN attempts.
        spin := 0
        if ncpu > 1 {
                spin = active_spin
        }
        for {
                // Try for lock, spinning.
                for i := 0; i < spin; i++ {
                        for l.key == mutex_unlocked {
                                if atomic.Cas(key32(&l.key), mutex_unlocked, wait) {
                                        return
                                }
                        }
                        procyield(active_spin_cnt)
                }

                // Try for lock, rescheduling.
                for i := 0; i < passive_spin; i++ {
                        for l.key == mutex_unlocked {
                                if atomic.Cas(key32(&l.key), mutex_unlocked, wait) {
                                        return
                                }
                        }
                        osyield()
                }

                // Sleep.
                v = atomic.Xchg(key32(&l.key), mutex_sleeping)
                if v == mutex_unlocked {
                        return
                }
                wait = mutex_sleeping
                futexsleep(key32(&l.key), mutex_sleeping, -1)
        }
}

func unlock(l *mutex) {
        v := atomic.Xchg(key32(&l.key), mutex_unlocked)
        if v == mutex_unlocked {
                throw("unlock of unlocked lock")
        }
        if v == mutex_sleeping {
                futexwakeup(key32(&l.key), 1)
        }

        gp := getg()
        gp.m.locks--
        if gp.m.locks < 0 {
                throw("runtime·unlock: lock count")
        }
        // if gp.m.locks == 0 && gp.preempt { // restore the preemption request in case we've cleared it in newstack
        //      gp.stackguard0 = stackPreempt
        // }
}

// One-time notifications.
func noteclear(n *note) {
        n.key = 0
}

func notewakeup(n *note) {
        old := atomic.Xchg(key32(&n.key), 1)
        if old != 0 {
                print("notewakeup - double wakeup (", old, ")\n")
                throw("notewakeup - double wakeup")
        }
        futexwakeup(key32(&n.key), 1)
}

func notesleep(n *note) {
        gp := getg()
        if gp != gp.m.g0 {
                throw("notesleep not on g0")
        }
        ns := int64(-1)
        if *cgo_yield != nil {
                // Sleep for an arbitrary-but-moderate interval to poll libc interceptors.
                ns = 10e6
        }
        for atomic.Load(key32(&n.key)) == 0 {
                gp.m.blocked = true
                futexsleep(key32(&n.key), 0, ns)
                if *cgo_yield != nil {
                        asmcgocall(*cgo_yield, nil)
                }
                gp.m.blocked = false
        }
}

// May run with m.p==nil if called from notetsleep, so write barriers
// are not allowed.
//
//go:nosplit
//go:nowritebarrier
func notetsleep_internal(n *note, ns int64) bool {
        gp := getg()

        if ns < 0 {
                if *cgo_yield != nil {
                        // Sleep for an arbitrary-but-moderate interval to poll libc interceptors.
                        ns = 10e6
                }
                for atomic.Load(key32(&n.key)) == 0 {
                        gp.m.blocked = true
                        futexsleep(key32(&n.key), 0, ns)
                        if *cgo_yield != nil {
                                asmcgocall(*cgo_yield, nil)
                        }
                        gp.m.blocked = false
                }
                return true
        }

        if atomic.Load(key32(&n.key)) != 0 {
                return true
        }

        deadline := nanotime() + ns
        for {
                if *cgo_yield != nil && ns > 10e6 {
                        ns = 10e6
                }
                gp.m.blocked = true
                futexsleep(key32(&n.key), 0, ns)
                if *cgo_yield != nil {
                        asmcgocall(*cgo_yield, nil)
                }
                gp.m.blocked = false
                if atomic.Load(key32(&n.key)) != 0 {
                        break
                }
                now := nanotime()
                if now >= deadline {
                        break
                }
                ns = deadline - now
        }
        return atomic.Load(key32(&n.key)) != 0
}

func notetsleep(n *note, ns int64) bool {
        gp := getg()
        if gp != gp.m.g0 && gp.m.preemptoff != "" {
                throw("notetsleep not on g0")
        }

        return notetsleep_internal(n, ns)
}

// same as runtime·notetsleep, but called on user g (not g0)
// calls only nosplit functions between entersyscallblock/exitsyscall
func notetsleepg(n *note, ns int64) bool {
        gp := getg()
        if gp == gp.m.g0 {
                throw("notetsleepg on g0")
        }

        entersyscallblock()
        ok := notetsleep_internal(n, ns)
        exitsyscall()
        return ok
}

func pauseSchedulerUntilCallback() bool {
        return false
}

func checkTimeouts() {}