This document describes the current stable version of Kombu (4.5). For development docs, go here.

Source code for kombu.clocks

"""Logical Clocks and Synchronization."""
from __future__ import absolute_import, unicode_literals

from threading import Lock
from itertools import islice
from operator import itemgetter

from .five import python_2_unicode_compatible, zip

__all__ = ('LamportClock', 'timetuple')

R_CLOCK = '_lamport(clock={0}, timestamp={1}, id={2} {3!r})'


[docs]@python_2_unicode_compatible class timetuple(tuple): """Tuple of event clock information. Can be used as part of a heap to keep events ordered. Arguments: clock (int): Event clock value. timestamp (float): Event UNIX timestamp value. id (str): Event host id (e.g. ``hostname:pid``). obj (Any): Optional obj to associate with this event. """ __slots__ = () def __new__(cls, clock, timestamp, id, obj=None): return tuple.__new__(cls, (clock, timestamp, id, obj)) def __repr__(self): return R_CLOCK.format(*self) def __getnewargs__(self): return tuple(self) def __lt__(self, other): # 0: clock 1: timestamp 3: process id try: A, B = self[0], other[0] # uses logical clock value first if A and B: # use logical clock if available if A == B: # equal clocks use lower process id return self[2] < other[2] return A < B return self[1] < other[1] # ... or use timestamp except IndexError: return NotImplemented def __gt__(self, other): return other < self def __le__(self, other): return not other < self def __ge__(self, other): return not self < other clock = property(itemgetter(0)) timestamp = property(itemgetter(1)) id = property(itemgetter(2)) obj = property(itemgetter(3))
[docs]@python_2_unicode_compatible class LamportClock(object): """Lamport's logical clock. From Wikipedia: A Lamport logical clock is a monotonically incrementing software counter maintained in each process. It follows some simple rules: * A process increments its counter before each event in that process; * When a process sends a message, it includes its counter value with the message; * On receiving a message, the receiver process sets its counter to be greater than the maximum of its own value and the received value before it considers the message received. Conceptually, this logical clock can be thought of as a clock that only has meaning in relation to messages moving between processes. When a process receives a message, it resynchronizes its logical clock with the sender. See Also: * `Lamport timestamps`_ * `Lamports distributed mutex`_ .. _`Lamport Timestamps`: https://en.wikipedia.org/wiki/Lamport_timestamps .. _`Lamports distributed mutex`: https://bit.ly/p99ybE *Usage* When sending a message use :meth:`forward` to increment the clock, when receiving a message use :meth:`adjust` to sync with the time stamp of the incoming message. """ #: The clocks current value. value = 0 def __init__(self, initial_value=0, Lock=Lock): self.value = initial_value self.mutex = Lock()
[docs] def adjust(self, other): with self.mutex: value = self.value = max(self.value, other) + 1 return value
[docs] def forward(self): with self.mutex: self.value += 1 return self.value
[docs] def sort_heap(self, h): """Sort heap of events. List of tuples containing at least two elements, representing an event, where the first element is the event's scalar clock value, and the second element is the id of the process (usually ``"hostname:pid"``): ``sh([(clock, processid, ...?), (...)])`` The list must already be sorted, which is why we refer to it as a heap. The tuple will not be unpacked, so more than two elements can be present. Will return the latest event. """ if h[0][0] == h[1][0]: same = [] for PN in zip(h, islice(h, 1, None)): if PN[0][0] != PN[1][0]: break # Prev and Next's clocks differ same.append(PN[0]) # return first item sorted by process id return sorted(same, key=lambda event: event[1])[0] # clock values unique, return first item return h[0]
def __str__(self): return str(self.value) def __repr__(self): return '<LamportClock: {0.value}>'.format(self)