Viewing file:  _fincache.py (2.56 KB) -rw-r--r--
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from weakref import ref
from traceback import print_exc
from twisted.python import log
from axiom import iaxiom
class CacheFault(RuntimeError):
"""
A serious problem has occurred within the cache. This error is internal
and should never really be trapped.
"""
def logErrorNoMatterWhat():
try:
log.msg("Exception in finalizer cannot be propagated")
log.err()
except:
try:
emergLog = file("WEAKREF_EMERGENCY_ERROR.log", 'a')
print_exc(file=emergLog)
emergLog.flush()
emergLog.close()
except:
# Nothing can be done. We can't get an emergency log file to write
# to. Don't bother.
return
def createCacheRemoveCallback(w, k, f):
def remove(self):
# Weakref callbacks cannot raise exceptions or DOOM ensues
try:
f()
except:
logErrorNoMatterWhat()
try:
self = w()
if self is not None:
del self.data[k]
except:
logErrorNoMatterWhat()
return remove
PROFILING = False
class FinalizingCache:
"""Possibly useful for infrastructure? This would be a nice addition (or
perhaps even replacement) for twisted.python.finalize.
"""
def __init__(self):
self.data = {}
if not PROFILING:
# see docstring for 'has'
self.has = self.data.has_key
def cache(self, key, value):
fin = value.__finalizer__()
assert key not in self.data, "Duplicate cache key: %r %r %r" % (key, value, self.data[key])
self.data[key] = ref(value, createCacheRemoveCallback(
ref(self), key, fin))
return value
def uncache(self, key, value):
assert self.get(key) is value
del self.data[key]
def has(self, key):
"""Does the cache have this key?
(This implementation is only used if the system is being profiled, due
to bugs in Python's old profiler and its interaction with weakrefs.
Set the module attribute PROFILING to True at startup for this.)
"""
if key in self.data:
o = self.data[key]()
if o is None:
del self.data[key]
return False
return True
return False
def get(self, key):
o = self.data[key]()
if o is None:
raise CacheFault(
"FinalizingCache has %r but its value is no more." % (key,))
log.msg(interface=iaxiom.IStatEvent, stat_cache_hits=1, key=key)
return o
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