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127 lines
3.3 KiB
Go
127 lines
3.3 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package syncs contains additional sync types and functionality.
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package syncs
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import (
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"context"
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"sync/atomic"
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)
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// ClosedChan returns a channel that's already closed.
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func ClosedChan() <-chan struct{} { return closedChan }
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var closedChan = initClosedChan()
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func initClosedChan() <-chan struct{} {
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ch := make(chan struct{})
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close(ch)
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return ch
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}
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// WaitGroupChan is like a sync.WaitGroup, but has a chan that closes
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// on completion that you can wait on. (This, you can only use the
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// value once)
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// Also, its zero value is not usable. Use the constructor.
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type WaitGroupChan struct {
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n int64 // atomic
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done chan struct{} // closed on transition to zero
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}
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// NewWaitGroupChan returns a new single-use WaitGroupChan.
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func NewWaitGroupChan() *WaitGroupChan {
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return &WaitGroupChan{done: make(chan struct{})}
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}
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// DoneChan returns a channel that's closed on completion.
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func (wg *WaitGroupChan) DoneChan() <-chan struct{} { return wg.done }
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// Add adds delta, which may be negative, to the WaitGroupChan
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// counter. If the counter becomes zero, all goroutines blocked on
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// Wait or the Done chan are released. If the counter goes negative,
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// Add panics.
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//
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// Note that calls with a positive delta that occur when the counter
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// is zero must happen before a Wait. Calls with a negative delta, or
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// calls with a positive delta that start when the counter is greater
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// than zero, may happen at any time. Typically this means the calls
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// to Add should execute before the statement creating the goroutine
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// or other event to be waited for.
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func (wg *WaitGroupChan) Add(delta int) {
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n := atomic.AddInt64(&wg.n, int64(delta))
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if n == 0 {
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close(wg.done)
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}
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}
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// Decr decrements the WaitGroup counter by one.
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//
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// (It is like sync.WaitGroup's Done method, but we don't use Done in
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// this type, because it's ambiguous between Context.Done and
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// WaitGroup.Done. So we use DoneChan and Decr instead.)
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func (wg *WaitGroupChan) Decr() {
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wg.Add(-1)
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}
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// Wait blocks until the WaitGroupChan counter is zero.
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func (wg *WaitGroupChan) Wait() { <-wg.done }
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// AtomicBool is an atomic boolean.
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type AtomicBool int32
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func (b *AtomicBool) Set(v bool) {
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var n int32
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if v {
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n = 1
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}
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atomic.StoreInt32((*int32)(b), n)
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}
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func (b *AtomicBool) Get() bool {
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return atomic.LoadInt32((*int32)(b)) != 0
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}
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// Semaphore is a counting semaphore.
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//
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// Use NewSemaphore to create one.
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type Semaphore struct {
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c chan struct{}
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}
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// NewSemaphore returns a semaphore with resource count n.
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func NewSemaphore(n int) Semaphore {
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return Semaphore{c: make(chan struct{}, n)}
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}
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// Acquire blocks until a resource is acquired.
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func (s Semaphore) Acquire() {
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s.c <- struct{}{}
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}
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// AcquireContext reports whether the resource was acquired before the ctx was done.
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func (s Semaphore) AcquireContext(ctx context.Context) bool {
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select {
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case s.c <- struct{}{}:
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return true
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case <-ctx.Done():
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return false
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}
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}
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// TryAcquire reports, without blocking, whether the resource was acquired.
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func (s Semaphore) TryAcquire() bool {
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select {
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case s.c <- struct{}{}:
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return true
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default:
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return false
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}
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}
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// Release releases a resource.
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func (s Semaphore) Release() {
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<-s.c
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}
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