Hiroyuki Yamanaka

Golang Standard library (io.ioutil TempDir)

• https://golang.org/pkg/io/ioutil/#TempDir

TempDir

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
}

nextSuffix

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:]
}

randmu.Lock

Because values are bad as they conflict, they are locking

var randmu sync.Mutex

os.Mkdir

• https://golang.org/pkg/os/#Mkdir

func Mkdir(name string, perm FileMode) error {
	e := syscall.Mkdir(fixLongPath(name), syscallMode(perm))

	if e != nil {
		return &PathError{"mkdir", name, e}
	}

	// mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
	if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
		Chmod(name, perm)
	}

	return nil
}

syscall.Mkdir

• https://golang.org/pkg/syscall/#Mkdir

func Mkdir(path string, mode uint32) (err error) {
	return Mkdirat(_AT_FDCWD, path, mode)
}

syscall.Mkdirat

// mksyscall.pl -tags linux,amd64 syscall_linux.go syscall_linux_amd64.go // MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT // +build linux,amd64

// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT

func Mkdirat(dirfd int, path string, mode uint32) (err error) {
	var _p0 *byte
	_p0, err = BytePtrFromString(path)
	if err != nil {
		return
	}
	_, _, e1 := Syscall(SYS_MKDIRAT, uintptr(dirfd), uintptr(unsafe.Pointer(_p0)), uintptr(mode))
	if e1 != 0 {
		err = errnoErr(e1)
	}
	return
}

Syscall

• https://golang.org/pkg/syscall/#Syscall

func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)