diff lockfile-0.10.2/doc/source/index.rst @ 33:7ceb967147c3

start xena with no gui add library files

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lockfile-0.10.2/doc/source/index.rst	Wed Jul 22 13:24:44 2015 -0700
@@ -0,0 +1,275 @@
+
+:mod:`lockfile` --- Platform-independent file locking
+=====================================================
+
+.. module:: lockfile
+   :synopsis: Platform-independent file locking
+.. moduleauthor:: Skip Montanaro <[e-mail]>
+.. sectionauthor:: Skip Montanaro <[e-mail]>
+
+
+.. note::
+
+   This package is pre-release software.  Between versions 0.8 and 0.9 it
+   was changed from a module to a package.  It is quite possible that the
+   API and implementation will change again in important ways as people test
+   it and provide feedback and bug fixes.  In particular, if the mkdir-based
+   locking scheme is sufficient for both Windows and Unix platforms, the
+   link-based scheme may be deleted so that only a single locking scheme is
+   used, providing cross-platform lockfile cooperation.
+
+.. note::
+
+   The implementation uses the `with` statement, both in the tests and in the
+   main code, so will only work out-of-the-box with Python 2.5 or later.
+   However, the use of the `with` statement is minimal, so if you apply the
+   patch in the included 2.4.diff file you can use it with Python 2.4. It's
+   possible that it will work in Python 2.3 with that patch applied as well,
+   though the doctest code relies on APIs new in 2.4, so will have to be
+   rewritten somewhat to allow testing on 2.3. As they say, patches welcome.
+   ``;-)``
+
+The :mod:`lockfile` package exports a :class:`LockFile` class which provides
+a simple API for locking files.  Unlike the Windows :func:`msvcrt.locking`
+function, the Unix :func:`fcntl.flock`, :func:`fcntl.lockf` and the
+deprecated :mod:`posixfile` module, the API is identical across both Unix
+(including Linux and Mac) and Windows platforms.  The lock mechanism relies
+on the atomic nature of the :func:`link` (on Unix) and :func:`mkdir` (On
+Windows) system calls.  It also contains several lock-method-specific
+modules: :mod:`lockfile.linklockfile`, :mod:`lockfile.mkdirlockfile`, and
+:mod:`lockfile.sqlitelockfile`, each one exporting a single class.  For
+backwards compatibility with versions before 0.9 the :class:`LinkFileLock`,
+:class:`MkdirFileLock` and :class:`SQLiteFileLock` objects are exposed as
+attributes of the top-level lockfile package, though this use was deprecated
+starting with version 0.9 and will be removed in version 1.0.
+
+.. note::
+
+   The current implementation uses :func:`os.link` on Unix, but since that
+   function is unavailable on Windows it uses :func:`os.mkdir` there.  At
+   this point it's not clear that using the :func:`os.mkdir` method would be
+   insufficient on Unix systems.  If it proves to be adequate on Unix then
+   the implementation could be simplified and truly cross-platform locking
+   would be possible.
+
+.. note::
+
+   The current implementation doesn't provide for shared vs. exclusive
+   locks.  It should be possible for multiple reader processes to hold the
+   lock at the same time.
+
+The module defines the following exceptions:
+
+.. exception:: Error
+
+   This is the base class for all exceptions raised by the :class:`LockFile`
+   class.
+
+.. exception:: LockError
+
+   This is the base class for all exceptions raised when attempting to lock
+   a file.
+
+.. exception:: UnlockError
+
+   This is the base class for all exceptions raised when attempting to
+   unlock a file.
+
+.. exception:: LockTimeout
+
+   This exception is raised if the :func:`LockFile.acquire` method is
+   called with a timeout which expires before an existing lock is released.
+
+.. exception:: AlreadyLocked
+
+   This exception is raised if the :func:`LockFile.acquire` detects a
+   file is already locked when in non-blocking mode.
+
+.. exception:: LockFailed
+
+   This exception is raised if the :func:`LockFile.acquire` detects some
+   other condition (such as a non-writable directory) which prevents it from
+   creating its lock file.
+
+.. exception:: NotLocked
+
+   This exception is raised if the file is not locked when
+   :func:`LockFile.release` is called.
+
+.. exception:: NotMyLock
+
+   This exception is raised if the file is locked by another thread or
+   process when :func:`LockFile.release` is called.
+
+The following classes are provided:
+
+.. class:: linklockfile.LinkLockFile(path, threaded=True)
+
+   This class uses the :func:`link(2)` system call as the basic lock
+   mechanism.  *path* is an object in the file system to be locked.  It need
+   not exist, but its directory must exist and be writable at the time the
+   :func:`acquire` and :func:`release` methods are called.  *threaded* is
+   optional, but when set to :const:`True` locks will be distinguished
+   between threads in the same process.
+
+.. class:: symlinklockfile.SymlinkLockFile(path, threaded=True)
+
+   This class uses the :func:`symlink(2)` system call as the basic lock
+   mechanism.  The parameters have the same meaning and constraints as for
+   the :class:`LinkLockFile` class.
+
+.. class:: mkdirlockfile.MkdirLockFile(path, threaded=True)
+
+   This class uses the :func:`mkdir(2)` system call as the basic lock
+   mechanism.  The parameters have the same meaning and constraints as for
+   the :class:`LinkLockFile` class.
+
+.. class:: sqlitelockfile.SQLiteLockFile(path, threaded=True)
+
+   This class uses the :mod:`sqlite3` module to implement the lock
+   mechanism.  The parameters have the same meaning as for the
+   :class:`LinkLockFile` class.
+
+.. class:: LockBase(path, threaded=True)
+
+   This is the base class for all concrete implementations and is available
+   at the lockfile package level so programmers can implement other locking
+   schemes.
+
+.. function:: locked(path, timeout=None)
+
+   This function provides a decorator which insures the decorated function
+   is always called with the lock held.
+
+By default, the :const:`LockFile` object refers to the
+:class:`mkdirlockfile.MkdirLockFile` class on Windows.  On all other
+platforms it refers to the :class:`linklockfile.LinkLockFile` class.
+
+When locking a file the :class:`linklockfile.LinkLockFile` class creates a
+uniquely named hard link to an empty lock file.  That hard link contains the
+hostname, process id, and if locks between threads are distinguished, the
+thread identifier.  For example, if you want to lock access to a file named
+"README", the lock file is named "README.lock".  With per-thread locks
+enabled the hard link is named HOSTNAME-THREADID-PID.  With only per-process
+locks enabled the hard link is named HOSTNAME--PID.
+
+When using the :class:`mkdirlockfile.MkdirLockFile` class the lock file is a
+directory.  Referring to the example above, README.lock will be a directory
+and HOSTNAME-THREADID-PID will be an empty file within that directory.
+
+.. seealso::
+
+   Module :mod:`msvcrt`
+      Provides the :func:`locking` function, the standard Windows way of
+      locking (parts of) a file.
+
+   Module :mod:`posixfile`
+      The deprecated (since Python 1.5) way of locking files on Posix systems.
+
+   Module :mod:`fcntl`
+      Provides the current best way to lock files on Unix systems
+      (:func:`lockf` and :func:`flock`).
+
+LockFile Objects
+----------------
+
+:class:`LockFile` objects support the `context manager` protocol used by the
+statement:`with` statement. The timeout option is not supported when used in
+this fashion. While support for timeouts could be implemented, there is no
+support for handling the eventual :exc:`Timeout` exceptions raised by the
+:func:`__enter__` method, so you would have to protect the `with` statement with
+a `try` statement. The resulting construct would not be any simpler than just
+using a `try` statement in the first place.
+
+:class:`LockFile` has the following user-visible methods:
+
+.. method:: LockFile.acquire(timeout=None)
+
+   Lock the file associated with the :class:`LockFile` object.  If the
+   *timeout* is omitted or :const:`None` the caller will block until the
+   file is unlocked by the object currently holding the lock.  If the
+   *timeout* is zero or a negative number the :exc:`AlreadyLocked` exception
+   will be raised if the file is currently locked by another process or
+   thread.  If the *timeout* is positive, the caller will block for that
+   many seconds waiting for the lock to be released.  If the lock is not
+   released within that period the :exc:`LockTimeout` exception will be
+   raised.
+
+.. method:: LockFile.release()
+
+   Unlock the file associated with the :class:`LockFile` object.  If the
+   file is not currently locked, the :exc:`NotLocked` exception is raised.
+   If the file is locked by another thread or process the :exc:`NotMyLock`
+   exception is raised.
+
+.. method:: is_locked()
+
+   Return the status of the lock on the current file.  If any process or
+   thread (including the current one) is locking the file, :const:`True` is
+   returned, otherwise :const:`False` is returned.
+
+.. method:: break_lock()
+
+   If the file is currently locked, break it.
+
+.. method:: i_am_locking()
+
+   Returns true if the caller holds the lock.
+
+Examples
+--------
+
+This example is the "hello world" for the :mod:`lockfile` package::
+
+    from lockfile import LockFile
+    lock = LockFile("/some/file/or/other")
+    with lock:
+        print lock.path, 'is locked.'
+
+To use this with Python 2.4, you can execute::
+
+    from lockfile import LockFile
+    lock = LockFile("/some/file/or/other")
+    lock.acquire()
+    print lock.path, 'is locked.'
+    lock.release()
+
+If you don't want to wait forever, you might try::
+
+    from lockfile import LockFile
+    lock = LockFile("/some/file/or/other")
+    while not lock.i_am_locking():
+	try:
+	    lock.acquire(timeout=60)    # wait up to 60 seconds
+	except LockTimeout:
+	    lock.break_lock()
+	    lock.acquire()
+    print "I locked", lock.path
+    lock.release()
+
+You can also insure that a lock is always held when appropriately decorated
+functions are called::
+
+    from lockfile import locked
+    @locked("/tmp/mylock")
+    def func(a, b):
+        return a + b
+
+Other Libraries
+---------------
+
+The idea of implementing advisory locking with a standard API is not new
+with :mod:`lockfile`.  There are a number of other libraries available:
+
+* locknix - http://pypi.python.org/pypi/locknix - Unix only
+* mx.MiscLockFile - from Marc André Lemburg, part of the mx.Base
+  distribution - cross-platform.
+* Twisted - http://twistedmatrix.com/trac/browser/trunk/twisted/python/lockfile.py
+* zc.lockfile - http://pypi.python.org/pypi/zc.lockfile
+
+
+Contacting the Author
+---------------------
+
+If you encounter any problems with ``lockfile``, would like help or want to
+submit a patch, check http://launchpad.net/pylockfile