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Diffstat (limited to 'external_libs/python/lockfile-0.10.2/lockfile/pidlockfile.py')
| -rw-r--r-- | external_libs/python/lockfile-0.10.2/lockfile/pidlockfile.py | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/external_libs/python/lockfile-0.10.2/lockfile/pidlockfile.py b/external_libs/python/lockfile-0.10.2/lockfile/pidlockfile.py new file mode 100644 index 00000000..e92f9ead --- /dev/null +++ b/external_libs/python/lockfile-0.10.2/lockfile/pidlockfile.py @@ -0,0 +1,193 @@ +# -*- coding: utf-8 -*- + +# pidlockfile.py +# +# Copyright © 2008–2009 Ben Finney <ben+python@benfinney.id.au> +# +# This is free software: you may copy, modify, and/or distribute this work +# under the terms of the Python Software Foundation License, version 2 or +# later as published by the Python Software Foundation. +# No warranty expressed or implied. See the file LICENSE.PSF-2 for details. + +""" Lockfile behaviour implemented via Unix PID files. + """ + +from __future__ import absolute_import + +import os +import sys +import errno +import time + +from . import (LockBase, AlreadyLocked, LockFailed, NotLocked, NotMyLock, + LockTimeout) + + +class PIDLockFile(LockBase): + """ Lockfile implemented as a Unix PID file. + + The lock file is a normal file named by the attribute `path`. + A lock's PID file contains a single line of text, containing + the process ID (PID) of the process that acquired the lock. + + >>> lock = PIDLockFile('somefile') + >>> lock = PIDLockFile('somefile') + """ + + def __init__(self, path, threaded=False, timeout=None): + # pid lockfiles don't support threaded operation, so always force + # False as the threaded arg. + LockBase.__init__(self, path, False, timeout) + dirname = os.path.dirname(self.lock_file) + basename = os.path.split(self.path)[-1] + self.unique_name = self.path + + def read_pid(self): + """ Get the PID from the lock file. + """ + return read_pid_from_pidfile(self.path) + + def is_locked(self): + """ Test if the lock is currently held. + + The lock is held if the PID file for this lock exists. + + """ + return os.path.exists(self.path) + + def i_am_locking(self): + """ Test if the lock is held by the current process. + + Returns ``True`` if the current process ID matches the + number stored in the PID file. + """ + return self.is_locked() and os.getpid() == self.read_pid() + + def acquire(self, timeout=None): + """ Acquire the lock. + + Creates the PID file for this lock, or raises an error if + the lock could not be acquired. + """ + + timeout = timeout is not None and timeout or self.timeout + end_time = time.time() + if timeout is not None and timeout > 0: + end_time += timeout + + while True: + try: + write_pid_to_pidfile(self.path) + except OSError as exc: + if exc.errno == errno.EEXIST: + # The lock creation failed. Maybe sleep a bit. + if timeout is not None and time.time() > end_time: + if timeout > 0: + raise LockTimeout("Timeout waiting to acquire" + " lock for %s" % + self.path) + else: + raise AlreadyLocked("%s is already locked" % + self.path) + time.sleep(timeout is not None and timeout/10 or 0.1) + else: + raise LockFailed("failed to create %s" % self.path) + else: + return + + def release(self): + """ Release the lock. + + Removes the PID file to release the lock, or raises an + error if the current process does not hold the lock. + + """ + if not self.is_locked(): + raise NotLocked("%s is not locked" % self.path) + if not self.i_am_locking(): + raise NotMyLock("%s is locked, but not by me" % self.path) + remove_existing_pidfile(self.path) + + def break_lock(self): + """ Break an existing lock. + + Removes the PID file if it already exists, otherwise does + nothing. + + """ + remove_existing_pidfile(self.path) + +def read_pid_from_pidfile(pidfile_path): + """ Read the PID recorded in the named PID file. + + Read and return the numeric PID recorded as text in the named + PID file. If the PID file cannot be read, or if the content is + not a valid PID, return ``None``. + + """ + pid = None + try: + pidfile = open(pidfile_path, 'r') + except IOError: + pass + else: + # According to the FHS 2.3 section on PID files in /var/run: + # + # The file must consist of the process identifier in + # ASCII-encoded decimal, followed by a newline character. + # + # Programs that read PID files should be somewhat flexible + # in what they accept; i.e., they should ignore extra + # whitespace, leading zeroes, absence of the trailing + # newline, or additional lines in the PID file. + + line = pidfile.readline().strip() + try: + pid = int(line) + except ValueError: + pass + pidfile.close() + + return pid + + +def write_pid_to_pidfile(pidfile_path): + """ Write the PID in the named PID file. + + Get the numeric process ID (“PID”) of the current process + and write it to the named file as a line of text. + + """ + open_flags = (os.O_CREAT | os.O_EXCL | os.O_WRONLY) + open_mode = 0o644 + pidfile_fd = os.open(pidfile_path, open_flags, open_mode) + pidfile = os.fdopen(pidfile_fd, 'w') + + # According to the FHS 2.3 section on PID files in /var/run: + # + # The file must consist of the process identifier in + # ASCII-encoded decimal, followed by a newline character. For + # example, if crond was process number 25, /var/run/crond.pid + # would contain three characters: two, five, and newline. + + pid = os.getpid() + line = "%(pid)d\n" % vars() + pidfile.write(line) + pidfile.close() + + +def remove_existing_pidfile(pidfile_path): + """ Remove the named PID file if it exists. + + Removing a PID file that doesn't already exist puts us in the + desired state, so we ignore the condition if the file does not + exist. + + """ + try: + os.remove(pidfile_path) + except OSError as exc: + if exc.errno == errno.ENOENT: + pass + else: + raise |