94 lines
2.5 KiB
Go
94 lines
2.5 KiB
Go
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build windows darwin
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package robustio
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import (
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"io/ioutil"
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"math/rand"
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"os"
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"syscall"
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"time"
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)
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const arbitraryTimeout = 500 * time.Millisecond
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const ERROR_SHARING_VIOLATION = 32
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// retry retries ephemeral errors from f up to an arbitrary timeout
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// to work around filesystem flakiness on Windows and Darwin.
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func retry(f func() (err error, mayRetry bool)) error {
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var (
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bestErr error
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lowestErrno syscall.Errno
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start time.Time
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nextSleep time.Duration = 1 * time.Millisecond
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)
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for {
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err, mayRetry := f()
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if err == nil || !mayRetry {
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return err
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}
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if errno, ok := err.(syscall.Errno); ok && (lowestErrno == 0 || errno < lowestErrno) {
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bestErr = err
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lowestErrno = errno
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} else if bestErr == nil {
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bestErr = err
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}
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if start.IsZero() {
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start = time.Now()
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} else if d := time.Since(start) + nextSleep; d >= arbitraryTimeout {
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break
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}
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time.Sleep(nextSleep)
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nextSleep += time.Duration(rand.Int63n(int64(nextSleep)))
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}
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return bestErr
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}
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// rename is like os.Rename, but retries ephemeral errors.
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//
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// On windows it wraps os.Rename, which (as of 2019-06-04) uses MoveFileEx with
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// MOVEFILE_REPLACE_EXISTING.
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//
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// Windows also provides a different system call, ReplaceFile,
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// that provides similar semantics, but perhaps preserves more metadata. (The
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// documentation on the differences between the two is very sparse.)
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//
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// Empirical error rates with MoveFileEx are lower under modest concurrency, so
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// for now we're sticking with what the os package already provides.
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func rename(oldpath, newpath string) (err error) {
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return retry(func() (err error, mayRetry bool) {
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err = os.Rename(oldpath, newpath)
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return err, isEphemeralError(err)
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})
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}
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// readFile is like ioutil.ReadFile, but retries ephemeral errors.
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func readFile(filename string) ([]byte, error) {
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var b []byte
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err := retry(func() (err error, mayRetry bool) {
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b, err = ioutil.ReadFile(filename)
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// Unlike in rename, we do not retry errFileNotFound here: it can occur
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// as a spurious error, but the file may also genuinely not exist, so the
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// increase in robustness is probably not worth the extra latency.
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return err, isEphemeralError(err) && err != errFileNotFound
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})
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return b, err
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}
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func removeAll(path string) error {
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return retry(func() (err error, mayRetry bool) {
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err = os.RemoveAll(path)
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return err, isEphemeralError(err)
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})
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}
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