d30ff6cfae
Instead of constantly making these updates, let's just remove the year since things are stored in git anyways, and this is not an actual modern legal risk anymore.
90 lines
2.9 KiB
Go
90 lines
2.9 KiB
Go
// Mgmt
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// Copyright (C) James Shubin and the project contributors
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// Written by James Shubin <james@shubin.ca> and the project contributors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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//
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// Additional permission under GNU GPL version 3 section 7
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//
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// If you modify this program, or any covered work, by linking or combining it
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// with embedded mcl code and modules (and that the embedded mcl code and
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// modules which link with this program, contain a copy of their source code in
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// the authoritative form) containing parts covered by the terms of any other
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// license, the licensors of this program grant you additional permission to
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// convey the resulting work. Furthermore, the licensors of this program grant
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// the original author, James Shubin, additional permission to update this
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// additional permission if he deems it necessary to achieve the goals of this
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// additional permission.
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// Package semaphore contains an implementation of a counting semaphore.
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package semaphore
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import (
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"fmt"
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)
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// Semaphore is a counting semaphore. It must be initialized before use.
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type Semaphore struct {
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C chan struct{}
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closed chan struct{}
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}
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// NewSemaphore creates a new semaphore.
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func NewSemaphore(size int) *Semaphore {
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obj := &Semaphore{}
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obj.Init(size)
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return obj
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}
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// Init initializes the semaphore.
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func (obj *Semaphore) Init(size int) {
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obj.C = make(chan struct{}, size)
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obj.closed = make(chan struct{})
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}
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// Close shuts down the semaphore and releases all the locks.
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func (obj *Semaphore) Close() {
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// TODO: we could return an error if any semaphores were killed, but
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// it's not particularly useful to know that for this application...
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close(obj.closed)
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}
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// P acquires n resources.
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func (obj *Semaphore) P(n int) error {
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for i := 0; i < n; i++ {
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select {
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case obj.C <- struct{}{}: // acquire one
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case <-obj.closed: // exit signal
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return fmt.Errorf("closed")
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}
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}
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return nil
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}
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// V releases n resources.
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func (obj *Semaphore) V(n int) error {
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for i := 0; i < n; i++ {
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select {
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case <-obj.C: // release one
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// TODO: is the closed signal needed if unlocks should always pass?
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case <-obj.closed: // exit signal
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return fmt.Errorf("closed")
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// TODO: is it true you shouldn't call a release before a lock?
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default: // trying to release something that isn't locked
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panic("semaphore: V > P")
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}
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}
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return nil
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}
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