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Source file src/io/ioutil/tempfile.go

Documentation: io/ioutil

  // Copyright 2010 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.
  
  package ioutil
  
  import (
  	"os"
  	"path/filepath"
  	"strconv"
  	"sync"
  	"time"
  )
  
  // Random number state.
  // We generate random temporary file names so that there's a good
  // chance the file doesn't exist yet - keeps the number of tries in
  // TempFile to a minimum.
  var rand uint32
  var randmu sync.Mutex
  
  func reseed() uint32 {
  	return uint32(time.Now().UnixNano() + int64(os.Getpid()))
  }
  
  func nextSuffix() string {
  	randmu.Lock()
  	r := rand
  	if r == 0 {
  		r = reseed()
  	}
  	r = r*1664525 + 1013904223 // constants from Numerical Recipes
  	rand = r
  	randmu.Unlock()
  	return strconv.Itoa(int(1e9 + r%1e9))[1:]
  }
  
  // TempFile creates a new temporary file in the directory dir
  // with a name beginning with prefix, opens the file for reading
  // and writing, and returns the resulting *os.File.
  // If dir is the empty string, TempFile uses the default directory
  // for temporary files (see os.TempDir).
  // Multiple programs calling TempFile simultaneously
  // will not choose the same file. The caller can use f.Name()
  // to find the pathname of the file. It is the caller's responsibility
  // to remove the file when no longer needed.
  func TempFile(dir, prefix string) (f *os.File, err error) {
  	if dir == "" {
  		dir = os.TempDir()
  	}
  
  	nconflict := 0
  	for i := 0; i < 10000; i++ {
  		name := filepath.Join(dir, prefix+nextSuffix())
  		f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
  		if os.IsExist(err) {
  			if nconflict++; nconflict > 10 {
  				randmu.Lock()
  				rand = reseed()
  				randmu.Unlock()
  			}
  			continue
  		}
  		break
  	}
  	return
  }
  
  // TempDir creates a new temporary directory in the directory dir
  // with a name beginning with prefix and returns the path of the
  // new directory. If dir is the empty string, TempDir uses the
  // default directory for temporary files (see os.TempDir).
  // Multiple programs calling TempDir simultaneously
  // will not choose the same directory. It is the caller's responsibility
  // to remove the directory when no longer needed.
  func TempDir(dir, prefix string) (name string, err error) {
  	if dir == "" {
  		dir = os.TempDir()
  	}
  
  	nconflict := 0
  	for i := 0; i < 10000; i++ {
  		try := filepath.Join(dir, prefix+nextSuffix())
  		err = os.Mkdir(try, 0700)
  		if os.IsExist(err) {
  			if nconflict++; nconflict > 10 {
  				randmu.Lock()
  				rand = reseed()
  				randmu.Unlock()
  			}
  			continue
  		}
  		if os.IsNotExist(err) {
  			if _, err := os.Stat(dir); os.IsNotExist(err) {
  				return "", err
  			}
  		}
  		if err == nil {
  			name = try
  		}
  		break
  	}
  	return
  }
  

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