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Source file src/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		"path/filepath"
    10		"strconv"
    11		"sync"
    12		"time"
    13	)
    14	
    15	// Random number state.
    16	// We generate random temporary file names so that there's a good
    17	// chance the file doesn't exist yet - keeps the number of tries in
    18	// TempFile to a minimum.
    19	var rand uint32
    20	var randmu sync.Mutex
    21	
    22	func reseed() uint32 {
    23		return uint32(time.Now().UnixNano() + int64(os.Getpid()))
    24	}
    25	
    26	func nextSuffix() string {
    27		randmu.Lock()
    28		r := rand
    29		if r == 0 {
    30			r = reseed()
    31		}
    32		r = r*1664525 + 1013904223 // constants from Numerical Recipes
    33		rand = r
    34		randmu.Unlock()
    35		return strconv.Itoa(int(1e9 + r%1e9))[1:]
    36	}
    37	
    38	// TempFile creates a new temporary file in the directory dir
    39	// with a name beginning with prefix, opens the file for reading
    40	// and writing, and returns the resulting *os.File.
    41	// If dir is the empty string, TempFile uses the default directory
    42	// for temporary files (see os.TempDir).
    43	// Multiple programs calling TempFile simultaneously
    44	// will not choose the same file. The caller can use f.Name()
    45	// to find the pathname of the file. It is the caller's responsibility
    46	// to remove the file when no longer needed.
    47	func TempFile(dir, prefix string) (f *os.File, err error) {
    48		if dir == "" {
    49			dir = os.TempDir()
    50		}
    51	
    52		nconflict := 0
    53		for i := 0; i < 10000; i++ {
    54			name := filepath.Join(dir, prefix+nextSuffix())
    55			f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
    56			if os.IsExist(err) {
    57				if nconflict++; nconflict > 10 {
    58					randmu.Lock()
    59					rand = reseed()
    60					randmu.Unlock()
    61				}
    62				continue
    63			}
    64			break
    65		}
    66		return
    67	}
    68	
    69	// TempDir creates a new temporary directory in the directory dir
    70	// with a name beginning with prefix and returns the path of the
    71	// new directory. If dir is the empty string, TempDir uses the
    72	// default directory for temporary files (see os.TempDir).
    73	// Multiple programs calling TempDir simultaneously
    74	// will not choose the same directory. It is the caller's responsibility
    75	// to remove the directory when no longer needed.
    76	func TempDir(dir, prefix string) (name string, err error) {
    77		if dir == "" {
    78			dir = os.TempDir()
    79		}
    80	
    81		nconflict := 0
    82		for i := 0; i < 10000; i++ {
    83			try := filepath.Join(dir, prefix+nextSuffix())
    84			err = os.Mkdir(try, 0700)
    85			if os.IsExist(err) {
    86				if nconflict++; nconflict > 10 {
    87					randmu.Lock()
    88					rand = reseed()
    89					randmu.Unlock()
    90				}
    91				continue
    92			}
    93			if os.IsNotExist(err) {
    94				if _, err := os.Stat(dir); os.IsNotExist(err) {
    95					return "", err
    96				}
    97			}
    98			if err == nil {
    99				name = try
   100			}
   101			break
   102		}
   103		return
   104	}
   105	

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