libgo/go/io/ioutil/tempfile.go

   1 // Copyright 2010 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 package ioutil
   6
   7 import (
   8         "os"
   9         "strconv"
  10 )
  11
  12 // Random number state, accessed without lock; racy but harmless.
  13 // We generate random temporary file names so that there's a good
  14 // chance the file doesn't exist yet - keeps the number of tries in
  15 // TempFile to a minimum.
  16 var rand uint32
  17
  18 func reseed() uint32 {
  19         sec, nsec, _ := os.Time()
  20         return uint32(sec*1e9 + nsec + int64(os.Getpid()))
  21 }
  22
  23 func nextSuffix() string {
  24         r := rand
  25         if r == 0 {
  26                 r = reseed()
  27         }
  28         r = r*1664525 + 1013904223 // constants from Numerical Recipes
  29         rand = r
  30         return strconv.Itoa(int(1e9 + r%1e9))[1:]
  31 }
  32
  33 // TempFile creates a new temporary file in the directory dir
  34 // with a name beginning with prefix, opens the file for reading
  35 // and writing, and returns the resulting *os.File.
  36 // If dir is the empty string, TempFile uses the default directory
  37 // for temporary files (see os.TempDir).
  38 // Multiple programs calling TempFile simultaneously
  39 // will not choose the same file.  The caller can use f.Name()
  40 // to find the name of the file.  It is the caller's responsibility to
  41 // remove the file when no longer needed.
  42 func TempFile(dir, prefix string) (f *os.File, err os.Error) {
  43         if dir == "" {
  44                 dir = os.TempDir()
  45         }
  46
  47         nconflict := 0
  48         for i := 0; i < 10000; i++ {
  49                 name := dir + "/" + prefix + nextSuffix()
  50                 f, err = os.Open(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
  51                 if pe, ok := err.(*os.PathError); ok && pe.Error == os.EEXIST {
  52                         if nconflict++; nconflict > 10 {
  53                                 rand = reseed()
  54                         }
  55                         continue
  56                 }
  57                 break
  58         }
  59         return
  60 }