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diff --git a/scripts/external_libs/lockfile-0.10.2/doc/source/index.rst b/scripts/external_libs/lockfile-0.10.2/doc/source/index.rst new file mode 100644 index 00000000..f76173dc --- /dev/null +++ b/scripts/external_libs/lockfile-0.10.2/doc/source/index.rst @@ -0,0 +1,275 @@ + +:mod:`lockfile` --- Platform-independent file locking +===================================================== + +.. module:: lockfile + :synopsis: Platform-independent file locking +.. moduleauthor:: Skip Montanaro <skip@pobox.com> +.. sectionauthor:: Skip Montanaro <skip@pobox.com> + + +.. 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 |