github.com/graybobo/golang.org-package-offline-cache@v0.0.0-20200626051047-6608995c132f/x/tools/dashboard/builder/filemutex_flock.go (about)

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build darwin dragonfly freebsd linux netbsd openbsd
     6  
     7  package main
     8  
     9  import (
    10  	"sync"
    11  	"syscall"
    12  )
    13  
    14  // FileMutex is similar to sync.RWMutex, but also synchronizes across processes.
    15  // This implementation is based on flock syscall.
    16  type FileMutex struct {
    17  	mu sync.RWMutex
    18  	fd int
    19  }
    20  
    21  func MakeFileMutex(filename string) *FileMutex {
    22  	if filename == "" {
    23  		return &FileMutex{fd: -1}
    24  	}
    25  	fd, err := syscall.Open(filename, syscall.O_CREAT|syscall.O_RDONLY, mkdirPerm)
    26  	if err != nil {
    27  		panic(err)
    28  	}
    29  	return &FileMutex{fd: fd}
    30  }
    31  
    32  func (m *FileMutex) Lock() {
    33  	m.mu.Lock()
    34  	if m.fd != -1 {
    35  		if err := syscall.Flock(m.fd, syscall.LOCK_EX); err != nil {
    36  			panic(err)
    37  		}
    38  	}
    39  }
    40  
    41  func (m *FileMutex) Unlock() {
    42  	if m.fd != -1 {
    43  		if err := syscall.Flock(m.fd, syscall.LOCK_UN); err != nil {
    44  			panic(err)
    45  		}
    46  	}
    47  	m.mu.Unlock()
    48  }
    49  
    50  func (m *FileMutex) RLock() {
    51  	m.mu.RLock()
    52  	if m.fd != -1 {
    53  		if err := syscall.Flock(m.fd, syscall.LOCK_SH); err != nil {
    54  			panic(err)
    55  		}
    56  	}
    57  }
    58  
    59  func (m *FileMutex) RUnlock() {
    60  	if m.fd != -1 {
    61  		if err := syscall.Flock(m.fd, syscall.LOCK_UN); err != nil {
    62  			panic(err)
    63  		}
    64  	}
    65  	m.mu.RUnlock()
    66  }