syncthing/lib/model/util.go

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// Copyright (C) 2014 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
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package model
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import (
"fmt"
"path/filepath"
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"sync"
"time"
"github.com/pkg/errors"
"github.com/syncthing/syncthing/lib/fs"
)
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type Holdable interface {
Holders() string
}
func newDeadlockDetector(timeout time.Duration) *deadlockDetector {
return &deadlockDetector{
timeout: timeout,
lockers: make(map[string]sync.Locker),
}
}
type deadlockDetector struct {
timeout time.Duration
lockers map[string]sync.Locker
}
func (d *deadlockDetector) Watch(name string, mut sync.Locker) {
d.lockers[name] = mut
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go func() {
for {
time.Sleep(d.timeout / 4)
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ok := make(chan bool, 2)
go func() {
mut.Lock()
_ = 1 // empty critical section
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mut.Unlock()
ok <- true
}()
go func() {
time.Sleep(d.timeout)
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ok <- false
}()
if r := <-ok; !r {
msg := fmt.Sprintf("deadlock detected at %s", name)
for otherName, otherMut := range d.lockers {
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if otherHolder, ok := otherMut.(Holdable); ok {
msg += "\n===" + otherName + "===\n" + otherHolder.Holders()
}
}
panic(msg)
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}
}
}()
}
// inWritableDir calls fn(path), while making sure that the directory
// containing `path` is writable for the duration of the call.
func inWritableDir(fn func(string) error, targetFs fs.Filesystem, path string, ignorePerms bool) error {
dir := filepath.Dir(path)
info, err := targetFs.Stat(dir)
if err != nil {
return err
}
if !info.IsDir() {
return errors.New("Not a directory: " + path)
}
if info.Mode()&0200 == 0 {
// A non-writeable directory (for this user; we assume that's the
// relevant part). Temporarily change the mode so we can delete the
// file or directory inside it.
if err := targetFs.Chmod(dir, 0755); err == nil {
// Chmod succeeded, we should change the permissions back on the way
// out. If we fail we log the error as we have irrevocably messed up
// at this point. :( (The operation we were called to wrap has
// succeeded or failed on its own so returning an error to the
// caller is inappropriate.)
defer func() {
if err := targetFs.Chmod(dir, info.Mode()&fs.ModePerm); err != nil && !fs.IsNotExist(err) {
logFn := l.Warnln
if ignorePerms {
logFn = l.Debugln
}
logFn("Failed to restore directory permissions after gaining write access:", err)
}
}()
}
}
return fn(path)
}