// 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.

//go:build (dragonfly || freebsd || linux) && !goexperiment.spinbitmutex

package runtime

import (
	"internal/runtime/atomic"
)

// 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.

type mWaitList struct{}

func lockVerifyMSize() {}

func mutexContended(l *mutex) bool {
	return atomic.Load(key32(&l.key)) > mutex_locked
}

func lock(l *mutex) {
	lockWithRank(l, getLockRank(l))
}

func lock2(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

	timer := &lockTimer{lock: l}
	timer.begin()
	// 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) {
					timer.end()
					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) {
					timer.end()
					return
				}
			}
			osyield()
		}

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

func unlock(l *mutex) {
	unlockWithRank(l)
}

func unlock2(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.mLockProfile.recordUnlock(l)
	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
	}
}
