Current File : //usr/lib/python3/dist-packages/duplicity/dup_threading.py
# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4; encoding:utf-8 -*-
#
# Copyright 2002 Ben Escoto <ben@emerose.org>
# Copyright 2007 Kenneth Loafman <kenneth@loafman.com>
#
# This file is part of duplicity.
#
# Duplicity is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2 of the License, or (at your
# option) any later version.
#
# Duplicity is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with duplicity; if not, write to the Free Software Foundation,
# Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""
Duplicity specific but otherwise generic threading interfaces and
utilities.
(Not called "threading" because we do not want to conflict with
the standard threading module.)
"""
import _thread
import sys
import threading
from duplicity import errors
def with_lock(lock, fn):
"""
Call fn with lock acquired. Guarantee that lock is released upon
the return of fn.
Returns the value returned by fn, or raises the exception raised
by fn.
(Lock can actually be anything responding to acquire() and
release().)
"""
lock.acquire()
try:
return fn()
finally:
lock.release()
def interruptably_wait(cv, waitFor):
"""
cv - The threading.Condition instance to wait on
test - Callable returning a boolean to indicate whether
the criteria being waited on has been satisfied.
Perform a wait on a condition such that it is keyboard
interruptable when done in the main thread. Due to Python
limitations as of <= 2.5, lock acquisition and conditions waits
are not interruptable when performed in the main thread.
Currently, this comes at a cost additional CPU use, compared to a
normal wait. Future implementations may be more efficient if the
underlying python supports it.
The condition must be acquired.
This function should only be used on conditions that are never
expected to be acquired for extended periods of time, or the
lock-acquire of the underlying condition could cause an
uninterruptable state despite the efforts of this function.
There is no equivalent for acquireing a lock, as that cannot be
done efficiently.
Example:
Instead of:
cv.acquire()
while not thing_done:
cv.wait(someTimeout)
cv.release()
do:
cv.acquire()
interruptable_condwait(cv, lambda: thing_done)
cv.release()
"""
# We can either poll at some interval, or wait with a short enough
# timeout to be practical (i.e., such that it interactively seems
# to response semi-immediately to an interrupt).
#
# Both approaches waste CPU, but the latter approach does not
# imply a latency penalty in the common case of a
# notify.
while not waitFor():
cv.wait(0.1)
def async_split(fn):
"""
Splits the act of calling the given function into one front-end
part for waiting on the result, and a back-end part for performing
the work in another thread.
Returns (waiter, caller) where waiter is a function to be called
in order to wait for the results of an asynchronous invokation of
fn to complete, returning fn's result or propagating it's
exception.
Caller is the function to call in a background thread in order to
execute fn asynchronously. Caller will return (success, waiter)
where success is a boolean indicating whether the function
suceeded (did NOT raise an exception), and waiter is the waiter
that was originally returned by the call to async_split().
"""
# Implementation notes:
#
# We use a dictionary to track the state of the asynchronous call,
# rather than local variables. This is to get around the way
# closures work with respect to local variables in Python. We do
# not care about hash lookup overhead since this is intended to be
# used for significant amounts of work.
cv = threading.Condition()
state = {"done": False, "error": None, "trace": None, "value": None}
def waiter():
cv.acquire()
try:
interruptably_wait(cv, lambda: state["done"])
if state["error"] is None:
return state["value"]
else:
raise state["error"].with_traceback(state["trace"])
finally:
cv.release()
def caller():
try:
value = fn()
cv.acquire()
state["done"] = True
state["value"] = value
cv.notify()
cv.release()
return True, waiter
except Exception as e:
cv.acquire()
state["done"] = True
state["error"] = e
state["trace"] = sys.exc_info()[2]
cv.notify()
cv.release()
return False, waiter
return waiter, caller
class Value(object):
"""
A thread-safe container of a reference to an object (but not the
object itself).
In particular this means it is safe to:
value.set(1)
But unsafe to:
value.get()['key'] = value
Where the latter must be done using something like:
def _setprop():
value.get()['key'] = value
with_lock(value, _setprop)
Operations such as increments are best done as:
value.transform(lambda val: val + 1)
"""
def __init__(self, value=None):
"""
Initialuze with the given value.
"""
self.__value = value
self.__cv = threading.Condition()
def get(self):
"""
Returns the value protected by this Value.
"""
return with_lock(self.__cv, lambda: self.__value)
def set(self, value):
"""
Resets the value protected by this Value.
"""
def _set():
self.__value = value
with_lock(self.__cv, _set)
def transform(self, fn):
"""
Call fn with the current value as the parameter, and reset the
value to the return value of fn.
During the execution of fn, all other access to this Value is
prevented.
If fn raised an exception, the value is not reset.
Returns the value returned by fn, or raises the exception
raised by fn.
"""
def _transform():
self.__value = fn(self.__value)
return self.__value
return with_lock(self.cv, _transform)
def acquire(self):
"""
Acquire this Value for mutually exclusive access. Only ever
needed when calling code must perform operations that cannot
be done with get(), set() or transform().
"""
self.__cv.acquire()
def release(self):
"""
Release this Value for mutually exclusive access.
"""
self.__cv.release()
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