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|
package state
import (
"encoding/gob"
"errors"
"io/fs"
"os"
"path"
"strconv"
"sync"
"syscall"
)
// file-based locking
type simpleStore struct {
path []string
// created/opened by prepare
lockfile *os.File
// enforce prepare method
init sync.Once
// error returned by prepare
initErr error
lock sync.Mutex
}
func (s *simpleStore) Do(f func(b Backend)) (bool, error) {
s.init.Do(s.prepare)
if s.initErr != nil {
return false, s.initErr
}
s.lock.Lock()
defer s.lock.Unlock()
// lock store
if err := s.lockFile(); err != nil {
return false, err
}
// initialise new backend for caller
b := new(simpleBackend)
b.path = path.Join(s.path...)
f(b)
// disable backend
b.lock.Lock()
// unlock store
return true, s.unlockFile()
}
func (s *simpleStore) lockFileAct(lt int) (err error) {
op := "LockAct"
switch lt {
case syscall.LOCK_EX:
op = "Lock"
case syscall.LOCK_UN:
op = "Unlock"
}
for {
err = syscall.Flock(int(s.lockfile.Fd()), lt)
if !errors.Is(err, syscall.EINTR) {
break
}
}
if err != nil {
return &fs.PathError{
Op: op,
Path: s.lockfile.Name(),
Err: err,
}
}
return nil
}
func (s *simpleStore) lockFile() error {
return s.lockFileAct(syscall.LOCK_EX)
}
func (s *simpleStore) unlockFile() error {
return s.lockFileAct(syscall.LOCK_UN)
}
func (s *simpleStore) prepare() {
s.initErr = func() error {
prefix := path.Join(s.path...)
// ensure directory
if err := os.MkdirAll(prefix, 0700); err != nil && !errors.Is(err, fs.ErrExist) {
return err
}
// open locker file
if f, err := os.OpenFile(prefix+".lock", os.O_RDWR|os.O_CREATE, 0600); err != nil {
return err
} else {
s.lockfile = f
}
return nil
}()
}
func (s *simpleStore) Close() error {
s.lock.Lock()
defer s.lock.Unlock()
err := s.lockfile.Close()
if err == nil || errors.Is(err, os.ErrInvalid) || errors.Is(err, os.ErrClosed) {
return nil
}
return err
}
type simpleBackend struct {
path string
lock sync.RWMutex
}
func (b *simpleBackend) filename(pid int) string {
return path.Join(b.path, strconv.Itoa(pid))
}
// reads all launchers in simpleBackend
// file contents are ignored if decode is false
func (b *simpleBackend) load(decode bool) ([]*State, error) {
b.lock.RLock()
defer b.lock.RUnlock()
var (
r []*State
f *os.File
)
// read directory contents, should only contain files named after PIDs
if pl, err := os.ReadDir(b.path); err != nil {
return nil, err
} else {
for _, e := range pl {
// run in a function to better handle file closing
if err = func() error {
// open state file for reading
if f, err = os.Open(path.Join(b.path, e.Name())); err != nil {
return err
} else {
defer func() {
if f.Close() != nil {
// unreachable
panic("foreign state file closed prematurely")
}
}()
var s State
r = append(r, &s)
// append regardless, but only parse if required, used to implement Len
if decode {
return gob.NewDecoder(f).Decode(&s)
} else {
return nil
}
}
}(); err != nil {
return nil, err
}
}
}
return r, nil
}
// Save writes process state to filesystem
func (b *simpleBackend) Save(state *State) error {
b.lock.Lock()
defer b.lock.Unlock()
if state.Config == nil {
return errors.New("state does not contain config")
}
statePath := b.filename(state.PID)
// create and open state data file
if f, err := os.OpenFile(statePath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600); err != nil {
return err
} else {
defer func() {
if f.Close() != nil {
// unreachable
panic("state file closed prematurely")
}
}()
// encode into state file
return gob.NewEncoder(f).Encode(state)
}
}
func (b *simpleBackend) Destroy(pid int) error {
b.lock.Lock()
defer b.lock.Unlock()
return os.Remove(b.filename(pid))
}
func (b *simpleBackend) Load() ([]*State, error) {
return b.load(true)
}
func (b *simpleBackend) Len() (int, error) {
// rn consists of only nil entries but has the correct length
rn, err := b.load(false)
return len(rn), err
}
// NewSimple returns an instance of a file-based store.
func NewSimple(runDir string, prefix ...string) Store {
b := new(simpleStore)
b.path = append([]string{runDir, "state"}, prefix...)
return b
}
|
