76 lines
2.7 KiB
Go
76 lines
2.7 KiB
Go
// Mgmt
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// Copyright (C) 2013-2024+ 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 util
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import (
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"os"
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"syscall"
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)
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// TODO: Consider replacing this with: github.com/gofrs/flock if it's better.
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// NewFlock creates a new flock. Details available in the struct documentation.
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func NewFlock(path string) *Flock {
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return &Flock{
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Path: path,
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}
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}
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// Flock is a structure for building a lock file. This can be used to prevent a
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// binary from running more than one copy at a time on a single machine.
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type Flock struct {
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Path string
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file *os.File
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}
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// TryLock attempts to take the lock. If it errors, it means we couldn't build a
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// lock today. If it returns (nil, nil) it means someone is already locked. If
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// it returns a non-nil function, then you are now locked. Call that function to
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// unlock. Note that it can error if it fails to unlock things.
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func (obj *Flock) TryLock() (func() error, error) {
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var err error
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obj.file, err = os.Create(obj.Path)
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if err != nil {
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return nil, err // actual error, can't continue
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}
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// Exclusive lock in non-blocking mode, we add a shared lock.
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if err := syscall.Flock(int(obj.file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
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return nil, nil // can't lock
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}
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// We're locked!
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return func() error {
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defer obj.file.Close()
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return syscall.Flock(int(obj.file.Fd()), syscall.LOCK_UN)
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}, nil
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}
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