07f542b4d7
Done with: ack '2018+' -l | xargs sed -i -e 's/2018+/2019+/g' Checked manually with: git add -p Hello to future James from 2020, and Happy Hacking!
78 lines
2.2 KiB
Go
78 lines
2.2 KiB
Go
// Mgmt
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// Copyright (C) 2013-2019+ 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 <http://www.gnu.org/licenses/>.
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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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