1 #

     2 # Copyright (c) 2008-2015 Thierry Florac <tflorac AT ulthar.net>

     3 # All Rights Reserved.

     4 #

     5 # This software is subject to the provisions of the Zope Public License,

     6 # Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.

     7 # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED

     8 # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

     9 # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS

    10 # FOR A PARTICULAR PURPOSE.

    11 #

    12 

    13 __docformat__ = 'restructuredtext'

    14 

    15 

    16 # import standard library

    17 import time

    18 from threading import local

    19 

    20 # import interfaces

    21 

    22 # import packages

    23 from beaker import cache

    24 

    25 

    26 _local = local()

    27 

    28 

    29 def get_locks_cache():

    30     """Get locks shared cache"""

    31     try:

    32         locks_cache = _local.locks_cache

    33     except AttributeError:

    34         manager = cache.CacheManager(**cache.cache_regions['persistent'])

    35         locks_cache = _local.locks_cache = manager.get_cache('PyAMS::locks')

    36     return locks_cache

    37 

    38 

    39 class LockException(Exception):

    40     """Cache lock exception"""

    41 

    42 

    43 class CacheLock(object):

    44     """Beaker based lock"""

    45 

    46     def __init__(self, name, wait=True):

    47         self.key = 'PyAMS_lock::{0}'.format(name)

    48         self.wait = wait

    49         self.has_lock = False

    50 

    51     def __enter__(self):

    52         locks_cache = get_locks_cache()

    53         while True:

    54             test = locks_cache.has_key(self.key)

    55             if test:

    56                 if not self.wait:

    57                     raise LockException()

    58                 else:

    59                     time.sleep(0.1)

    60             else:

    61                 locks_cache.set_value(self.key, 1)

    62                 self.has_lock = True

    63                 return

    64 

    65     def __exit__(self, exc_type, exc_val, exc_tb):

    66         if self.has_lock:

    67             get_locks_cache().remove_value(self.key)

    68         return False

    69 

    70 

    71 def locked(name, wait=True):

    72     """Locked function decorator"""

    73 

    74     def lock_decorator(func):

    75         def wrapper(*args, **kwargs):

    76             with CacheLock(name, wait):

    77                 return func(*args, **kwargs)

    78         return wrapper

    79 

    80     return lock_decorator