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| 1 # Copyright 2011 Google Inc. All Rights Reserved. | |
| 2 | |
| 3 """Locked file interface that should work on Unix and Windows pythons. | |
| 4 | |
| 5 This module first tries to use fcntl locking to ensure serialized access | |
| 6 to a file, then falls back on a lock file if that is unavialable. | |
| 7 | |
| 8 Usage: | |
| 9 f = LockedFile('filename', 'r+b', 'rb') | |
| 10 f.open_and_lock() | |
| 11 if f.is_locked(): | |
| 12 print 'Acquired filename with r+b mode' | |
| 13 f.file_handle().write('locked data') | |
| 14 else: | |
| 15 print 'Aquired filename with rb mode' | |
| 16 f.unlock_and_close() | |
| 17 """ | |
| 18 | |
| 19 __author__ = 'cache@google.com (David T McWherter)' | |
| 20 | |
| 21 import errno | |
| 22 import logging | |
| 23 import os | |
| 24 import time | |
| 25 | |
| 26 from oauth2client import util | |
| 27 | |
| 28 logger = logging.getLogger(__name__) | |
| 29 | |
| 30 | |
| 31 class CredentialsFileSymbolicLinkError(Exception): | |
| 32 """Credentials files must not be symbolic links.""" | |
| 33 | |
| 34 | |
| 35 class AlreadyLockedException(Exception): | |
| 36 """Trying to lock a file that has already been locked by the LockedFile.""" | |
| 37 pass | |
| 38 | |
| 39 | |
| 40 def validate_file(filename): | |
| 41 if os.path.islink(filename): | |
| 42 raise CredentialsFileSymbolicLinkError( | |
| 43 'File: %s is a symbolic link.' % filename) | |
| 44 | |
| 45 class _Opener(object): | |
| 46 """Base class for different locking primitives.""" | |
| 47 | |
| 48 def __init__(self, filename, mode, fallback_mode): | |
| 49 """Create an Opener. | |
| 50 | |
| 51 Args: | |
| 52 filename: string, The pathname of the file. | |
| 53 mode: string, The preferred mode to access the file with. | |
| 54 fallback_mode: string, The mode to use if locking fails. | |
| 55 """ | |
| 56 self._locked = False | |
| 57 self._filename = filename | |
| 58 self._mode = mode | |
| 59 self._fallback_mode = fallback_mode | |
| 60 self._fh = None | |
| 61 | |
| 62 def is_locked(self): | |
| 63 """Was the file locked.""" | |
| 64 return self._locked | |
| 65 | |
| 66 def file_handle(self): | |
| 67 """The file handle to the file. Valid only after opened.""" | |
| 68 return self._fh | |
| 69 | |
| 70 def filename(self): | |
| 71 """The filename that is being locked.""" | |
| 72 return self._filename | |
| 73 | |
| 74 def open_and_lock(self, timeout, delay): | |
| 75 """Open the file and lock it. | |
| 76 | |
| 77 Args: | |
| 78 timeout: float, How long to try to lock for. | |
| 79 delay: float, How long to wait between retries. | |
| 80 """ | |
| 81 pass | |
| 82 | |
| 83 def unlock_and_close(self): | |
| 84 """Unlock and close the file.""" | |
| 85 pass | |
| 86 | |
| 87 | |
| 88 class _PosixOpener(_Opener): | |
| 89 """Lock files using Posix advisory lock files.""" | |
| 90 | |
| 91 def open_and_lock(self, timeout, delay): | |
| 92 """Open the file and lock it. | |
| 93 | |
| 94 Tries to create a .lock file next to the file we're trying to open. | |
| 95 | |
| 96 Args: | |
| 97 timeout: float, How long to try to lock for. | |
| 98 delay: float, How long to wait between retries. | |
| 99 | |
| 100 Raises: | |
| 101 AlreadyLockedException: if the lock is already acquired. | |
| 102 IOError: if the open fails. | |
| 103 CredentialsFileSymbolicLinkError if the file is a symbolic link. | |
| 104 """ | |
| 105 if self._locked: | |
| 106 raise AlreadyLockedException('File %s is already locked' % | |
| 107 self._filename) | |
| 108 self._locked = False | |
| 109 | |
| 110 validate_file(self._filename) | |
| 111 try: | |
| 112 self._fh = open(self._filename, self._mode) | |
| 113 except IOError, e: | |
| 114 # If we can't access with _mode, try _fallback_mode and don't lock. | |
| 115 if e.errno == errno.EACCES: | |
| 116 self._fh = open(self._filename, self._fallback_mode) | |
| 117 return | |
| 118 | |
| 119 lock_filename = self._posix_lockfile(self._filename) | |
| 120 start_time = time.time() | |
| 121 while True: | |
| 122 try: | |
| 123 self._lock_fd = os.open(lock_filename, | |
| 124 os.O_CREAT|os.O_EXCL|os.O_RDWR) | |
| 125 self._locked = True | |
| 126 break | |
| 127 | |
| 128 except OSError, e: | |
| 129 if e.errno != errno.EEXIST: | |
| 130 raise | |
| 131 if (time.time() - start_time) >= timeout: | |
| 132 logger.warn('Could not acquire lock %s in %s seconds' % ( | |
| 133 lock_filename, timeout)) | |
| 134 # Close the file and open in fallback_mode. | |
| 135 if self._fh: | |
| 136 self._fh.close() | |
| 137 self._fh = open(self._filename, self._fallback_mode) | |
| 138 return | |
| 139 time.sleep(delay) | |
| 140 | |
| 141 def unlock_and_close(self): | |
| 142 """Unlock a file by removing the .lock file, and close the handle.""" | |
| 143 if self._locked: | |
| 144 lock_filename = self._posix_lockfile(self._filename) | |
| 145 os.close(self._lock_fd) | |
| 146 os.unlink(lock_filename) | |
| 147 self._locked = False | |
| 148 self._lock_fd = None | |
| 149 if self._fh: | |
| 150 self._fh.close() | |
| 151 | |
| 152 def _posix_lockfile(self, filename): | |
| 153 """The name of the lock file to use for posix locking.""" | |
| 154 return '%s.lock' % filename | |
| 155 | |
| 156 | |
| 157 try: | |
| 158 import fcntl | |
| 159 | |
| 160 class _FcntlOpener(_Opener): | |
| 161 """Open, lock, and unlock a file using fcntl.lockf.""" | |
| 162 | |
| 163 def open_and_lock(self, timeout, delay): | |
| 164 """Open the file and lock it. | |
| 165 | |
| 166 Args: | |
| 167 timeout: float, How long to try to lock for. | |
| 168 delay: float, How long to wait between retries | |
| 169 | |
| 170 Raises: | |
| 171 AlreadyLockedException: if the lock is already acquired. | |
| 172 IOError: if the open fails. | |
| 173 CredentialsFileSymbolicLinkError if the file is a symbolic link. | |
| 174 """ | |
| 175 if self._locked: | |
| 176 raise AlreadyLockedException('File %s is already locked' % | |
| 177 self._filename) | |
| 178 start_time = time.time() | |
| 179 | |
| 180 validate_file(self._filename) | |
| 181 try: | |
| 182 self._fh = open(self._filename, self._mode) | |
| 183 except IOError, e: | |
| 184 # If we can't access with _mode, try _fallback_mode and don't lock. | |
| 185 if e.errno == errno.EACCES: | |
| 186 self._fh = open(self._filename, self._fallback_mode) | |
| 187 return | |
| 188 | |
| 189 # We opened in _mode, try to lock the file. | |
| 190 while True: | |
| 191 try: | |
| 192 fcntl.lockf(self._fh.fileno(), fcntl.LOCK_EX) | |
| 193 self._locked = True | |
| 194 return | |
| 195 except IOError, e: | |
| 196 # If not retrying, then just pass on the error. | |
| 197 if timeout == 0: | |
| 198 raise e | |
| 199 if e.errno != errno.EACCES: | |
| 200 raise e | |
| 201 # We could not acquire the lock. Try again. | |
| 202 if (time.time() - start_time) >= timeout: | |
| 203 logger.warn('Could not lock %s in %s seconds' % ( | |
| 204 self._filename, timeout)) | |
| 205 if self._fh: | |
| 206 self._fh.close() | |
| 207 self._fh = open(self._filename, self._fallback_mode) | |
| 208 return | |
| 209 time.sleep(delay) | |
| 210 | |
| 211 def unlock_and_close(self): | |
| 212 """Close and unlock the file using the fcntl.lockf primitive.""" | |
| 213 if self._locked: | |
| 214 fcntl.lockf(self._fh.fileno(), fcntl.LOCK_UN) | |
| 215 self._locked = False | |
| 216 if self._fh: | |
| 217 self._fh.close() | |
| 218 except ImportError: | |
| 219 _FcntlOpener = None | |
| 220 | |
| 221 | |
| 222 try: | |
| 223 import pywintypes | |
| 224 import win32con | |
| 225 import win32file | |
| 226 | |
| 227 class _Win32Opener(_Opener): | |
| 228 """Open, lock, and unlock a file using windows primitives.""" | |
| 229 | |
| 230 # Error #33: | |
| 231 # 'The process cannot access the file because another process' | |
| 232 FILE_IN_USE_ERROR = 33 | |
| 233 | |
| 234 # Error #158: | |
| 235 # 'The segment is already unlocked.' | |
| 236 FILE_ALREADY_UNLOCKED_ERROR = 158 | |
| 237 | |
| 238 def open_and_lock(self, timeout, delay): | |
| 239 """Open the file and lock it. | |
| 240 | |
| 241 Args: | |
| 242 timeout: float, How long to try to lock for. | |
| 243 delay: float, How long to wait between retries | |
| 244 | |
| 245 Raises: | |
| 246 AlreadyLockedException: if the lock is already acquired. | |
| 247 IOError: if the open fails. | |
| 248 CredentialsFileSymbolicLinkError if the file is a symbolic link. | |
| 249 """ | |
| 250 if self._locked: | |
| 251 raise AlreadyLockedException('File %s is already locked' % | |
| 252 self._filename) | |
| 253 start_time = time.time() | |
| 254 | |
| 255 validate_file(self._filename) | |
| 256 try: | |
| 257 self._fh = open(self._filename, self._mode) | |
| 258 except IOError, e: | |
| 259 # If we can't access with _mode, try _fallback_mode and don't lock. | |
| 260 if e.errno == errno.EACCES: | |
| 261 self._fh = open(self._filename, self._fallback_mode) | |
| 262 return | |
| 263 | |
| 264 # We opened in _mode, try to lock the file. | |
| 265 while True: | |
| 266 try: | |
| 267 hfile = win32file._get_osfhandle(self._fh.fileno()) | |
| 268 win32file.LockFileEx( | |
| 269 hfile, | |
| 270 (win32con.LOCKFILE_FAIL_IMMEDIATELY| | |
| 271 win32con.LOCKFILE_EXCLUSIVE_LOCK), 0, -0x10000, | |
| 272 pywintypes.OVERLAPPED()) | |
| 273 self._locked = True | |
| 274 return | |
| 275 except pywintypes.error, e: | |
| 276 if timeout == 0: | |
| 277 raise e | |
| 278 | |
| 279 # If the error is not that the file is already in use, raise. | |
| 280 if e[0] != _Win32Opener.FILE_IN_USE_ERROR: | |
| 281 raise | |
| 282 | |
| 283 # We could not acquire the lock. Try again. | |
| 284 if (time.time() - start_time) >= timeout: | |
| 285 logger.warn('Could not lock %s in %s seconds' % ( | |
| 286 self._filename, timeout)) | |
| 287 if self._fh: | |
| 288 self._fh.close() | |
| 289 self._fh = open(self._filename, self._fallback_mode) | |
| 290 return | |
| 291 time.sleep(delay) | |
| 292 | |
| 293 def unlock_and_close(self): | |
| 294 """Close and unlock the file using the win32 primitive.""" | |
| 295 if self._locked: | |
| 296 try: | |
| 297 hfile = win32file._get_osfhandle(self._fh.fileno()) | |
| 298 win32file.UnlockFileEx(hfile, 0, -0x10000, pywintypes.OVERLAPPED()) | |
| 299 except pywintypes.error, e: | |
| 300 if e[0] != _Win32Opener.FILE_ALREADY_UNLOCKED_ERROR: | |
| 301 raise | |
| 302 self._locked = False | |
| 303 if self._fh: | |
| 304 self._fh.close() | |
| 305 except ImportError: | |
| 306 _Win32Opener = None | |
| 307 | |
| 308 | |
| 309 class LockedFile(object): | |
| 310 """Represent a file that has exclusive access.""" | |
| 311 | |
| 312 @util.positional(4) | |
| 313 def __init__(self, filename, mode, fallback_mode, use_native_locking=True): | |
| 314 """Construct a LockedFile. | |
| 315 | |
| 316 Args: | |
| 317 filename: string, The path of the file to open. | |
| 318 mode: string, The mode to try to open the file with. | |
| 319 fallback_mode: string, The mode to use if locking fails. | |
| 320 use_native_locking: bool, Whether or not fcntl/win32 locking is used. | |
| 321 """ | |
| 322 opener = None | |
| 323 if not opener and use_native_locking: | |
| 324 if _Win32Opener: | |
| 325 opener = _Win32Opener(filename, mode, fallback_mode) | |
| 326 if _FcntlOpener: | |
| 327 opener = _FcntlOpener(filename, mode, fallback_mode) | |
| 328 | |
| 329 if not opener: | |
| 330 opener = _PosixOpener(filename, mode, fallback_mode) | |
| 331 | |
| 332 self._opener = opener | |
| 333 | |
| 334 def filename(self): | |
| 335 """Return the filename we were constructed with.""" | |
| 336 return self._opener._filename | |
| 337 | |
| 338 def file_handle(self): | |
| 339 """Return the file_handle to the opened file.""" | |
| 340 return self._opener.file_handle() | |
| 341 | |
| 342 def is_locked(self): | |
| 343 """Return whether we successfully locked the file.""" | |
| 344 return self._opener.is_locked() | |
| 345 | |
| 346 def open_and_lock(self, timeout=0, delay=0.05): | |
| 347 """Open the file, trying to lock it. | |
| 348 | |
| 349 Args: | |
| 350 timeout: float, The number of seconds to try to acquire the lock. | |
| 351 delay: float, The number of seconds to wait between retry attempts. | |
| 352 | |
| 353 Raises: | |
| 354 AlreadyLockedException: if the lock is already acquired. | |
| 355 IOError: if the open fails. | |
| 356 """ | |
| 357 self._opener.open_and_lock(timeout, delay) | |
| 358 | |
| 359 def unlock_and_close(self): | |
| 360 """Unlock and close a file.""" | |
| 361 self._opener.unlock_and_close() | |
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