Validate files in a thp and add LockFile bundle dep

1 files changed, 189 insertions, 0 deletions

diff --git a/lib/thandy/lockfile/pidlockfile.py b/lib/thandy/lockfile/pidlockfile.py
new file mode 100644
index 0000000..10dcb31
--- /dev/null
+++ b/lib/thandy/lockfile/pidlockfile.py
@@ -0,0 +1,189 @@
+# -*- 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):
+        # pid lockfiles don't support threaded operation, so always force
+        # False as the threaded arg.
+        LockBase.__init__(self, path, False)
+        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.
+        """
+
+        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, 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
+                        else:
+                            raise AlreadyLocked
+                    time.sleep(timeout is not None and timeout/10 or 0.1)
+                else:
+                    raise LockFailed
+            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
+        if not self.i_am_locking():
+            raise NotMyLock
+        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 = 0644
+    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, exc:
+        if exc.errno == errno.ENOENT:
+            pass
+        else:
+            raise