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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The working directory in Plan 9 is effectively per P, so different
// goroutines and even the same goroutine as it's rescheduled on
// different Ps can see different working directories.
//
// Instead, track a Go process-wide intent of the current working directory,
// and switch to it at important points.
package syscall
import (
"runtime"
"sync"
)
var (
wdmu sync.Mutex // guards following
wdSet bool
wdStr string
)
// Ensure current working directory seen by this goroutine matches
// the most recent [Chdir] called in any goroutine. It's called internally
// before executing any syscall which uses a relative pathname. Must
// be called with the goroutine locked to the OS thread, to prevent
// rescheduling on a different thread (potentially with a different
// working directory) before the syscall is executed.
func Fixwd() {
wdmu.Lock()
defer wdmu.Unlock()
fixwdLocked()
}
func fixwdLocked() {
if !wdSet {
return
}
// always call chdir when getwd returns an error
wd, _ := getwd()
if wd == wdStr {
return
}
if err := chdir(wdStr); err != nil {
return
}
}
// If any of the paths is relative, call Fixwd and return true
// (locked to OS thread). Otherwise return false.
func fixwd(paths ...string) bool {
for _, path := range paths {
if path != "" && path[0] != '/' && path[0] != '#' {
runtime.LockOSThread()
Fixwd()
return true
}
}
return false
}
// goroutine-specific getwd
func getwd() (wd string, err error) {
fd, err := open(".", O_RDONLY)
if err != nil {
return "", err
}
defer Close(fd)
return Fd2path(fd)
}
func Getwd() (wd string, err error) {
wdmu.Lock()
defer wdmu.Unlock()
if wdSet {
return wdStr, nil
}
wd, err = getwd()
if err != nil {
return
}
wdSet = true
wdStr = wd
return wd, nil
}
func Chdir(path string) error {
// If Chdir is to a relative path, sync working dir first
if fixwd(path) {
defer runtime.UnlockOSThread()
}
wdmu.Lock()
defer wdmu.Unlock()
runtime.LockOSThread()
defer runtime.UnlockOSThread()
if err := chdir(path); err != nil {
return err
}
wd, err := getwd()
if err != nil {
return err
}
wdSet = true
wdStr = wd
return nil
}
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