ergo/irc/utils/semaphores.go

// Copyright (c) 2018 Shivaram Lingamneni

package utils

import (
	"log"
	"runtime/debug"
)

// Semaphore is a counting semaphore. Note that a capacity of n requires O(n) storage.
// A semaphore of capacity 1 can be used as a trylock.
type Semaphore (chan bool)

// Initialize initializes a semaphore to a given capacity.
func (semaphore *Semaphore) Initialize(capacity int) {
	*semaphore = make(chan bool, capacity)
	for i := 0; i < capacity; i++ {
		(*semaphore) <- true
	}
}

// Acquire acquires a semaphore, blocking if necessary.
func (semaphore *Semaphore) Acquire() {
	<-(*semaphore)
}

// TryAcquire tries to acquire a semaphore, returning whether the acquire was
// successful. It never blocks.
func (semaphore *Semaphore) TryAcquire() (acquired bool) {
	select {
	case <-(*semaphore):
		return true
	default:
		return false
	}
}

// Release releases a semaphore. It never blocks. (This is not a license
// to program spurious releases.)
func (semaphore *Semaphore) Release() {
	select {
	case (*semaphore) <- true:
		// good
	default:
		// spurious release
		log.Printf("spurious semaphore release (full to capacity %d)", cap(*semaphore))
		debug.PrintStack()
	}
}