/*
 * P2PFaaS - A framework for FaaS Load Balancing
 * Copyright (c) 2019 - 2022. Gabriele Proietti Mattia <pm.gabriele@outlook.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package utils

/*
 * From http://www.golangpatterns.info/concurrency/semaphores
 */

type empty struct{}
type Semaphore chan empty

// P acquires n resources
func (s Semaphore) P(n int) {
	e := empty{}
	for i := 0; i < n; i++ {
		s <- e
	}
}

// V releases n resources
func (s Semaphore) V(n int) {
	for i := 0; i < n; i++ {
		<-s
	}
}

/* mutexes */

func (s Semaphore) Lock() {
	s.P(1)
}

func (s Semaphore) Unlock() {
	s.V(1)
}

/* signal-wait */

func (s Semaphore) Signal() {
	s.V(1)
}

func (s Semaphore) Wait(n int) {
	s.P(n)
}