79 lines
1.6 KiB
Go
79 lines
1.6 KiB
Go
// Copyright (C) 2019 Storj Labs, Inc.
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// See LICENSE for copying information
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package sync2
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import (
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"runtime"
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"sync"
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"sync/atomic"
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)
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// Fence allows to wait for something to happen.
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type Fence struct {
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status uint32
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wait sync.Mutex
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}
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/*
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General flow of the fence:
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init:
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first arriver caller to `init` will setup a lock in `wait`
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Wait callers:
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try to lock/unlock in Wait, this will block until the initial lock will be released
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Release caller:
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first caller will release the initial lock
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*/
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const (
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statusUninitialized = iota
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statusInitializing
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statusBlocked
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statusReleased
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)
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// init sets up the initial lock into wait
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func (fence *Fence) init() {
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// wait for initialization
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for atomic.LoadUint32(&fence.status) <= statusInitializing {
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// first arriver sets up lock
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if atomic.CompareAndSwapUint32(&fence.status, statusUninitialized, statusInitializing) {
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fence.wait.Lock()
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atomic.StoreUint32(&fence.status, statusBlocked)
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} else {
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runtime.Gosched()
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}
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}
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}
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// Wait waits for wait to be unlocked
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func (fence *Fence) Wait() {
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// fast-path
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if fence.Released() {
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return
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}
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fence.init()
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// start waiting on the initial lock to be released
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fence.wait.Lock()
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// intentionally empty critical section to wait for Release
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//nolint
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fence.wait.Unlock()
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}
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// Released returns whether the fence has been released.
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func (fence *Fence) Released() bool {
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return atomic.LoadUint32(&fence.status) >= statusReleased
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}
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// Release releases everyone from Wait
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func (fence *Fence) Release() {
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fence.init()
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// the first one releases the status
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if atomic.CompareAndSwapUint32(&fence.status, statusBlocked, statusReleased) {
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fence.wait.Unlock()
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}
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}
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