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"""Scheduling Utilities."""
from __future__ import annotations
from itertools import count
from .imports import symbol_by_name
__all__ = (
'FairCycle', 'priority_cycle', 'round_robin_cycle', 'sorted_cycle',
)
CYCLE_ALIASES = {
'priority': 'kombu.utils.scheduling:priority_cycle',
'round_robin': 'kombu.utils.scheduling:round_robin_cycle',
'sorted': 'kombu.utils.scheduling:sorted_cycle',
}
class FairCycle:
"""Cycle between resources.
Consume from a set of resources, where each resource gets
an equal chance to be consumed from.
Arguments:
---------
fun (Callable): Callback to call.
resources (Sequence[Any]): List of resources.
predicate (type): Exception predicate.
"""
def __init__(self, fun, resources, predicate=Exception):
self.fun = fun
self.resources = resources
self.predicate = predicate
self.pos = 0
def _next(self):
while 1:
try:
resource = self.resources[self.pos]
self.pos += 1
return resource
except IndexError:
self.pos = 0
if not self.resources:
raise self.predicate()
def get(self, callback, **kwargs):
"""Get from next resource."""
for tried in count(0): # for infinity
resource = self._next()
try:
return self.fun(resource, callback, **kwargs)
except self.predicate:
# reraise when retries exchausted.
if tried >= len(self.resources) - 1:
raise
def close(self):
"""Close cycle."""
def __repr__(self):
"""``repr(cycle)``."""
return '<FairCycle: {self.pos}/{size} {self.resources}>'.format(
self=self, size=len(self.resources))
class round_robin_cycle:
"""Iterator that cycles between items in round-robin."""
def __init__(self, it=None):
self.items = it if it is not None else []
def update(self, it):
"""Update items from iterable."""
self.items[:] = it
def consume(self, n):
"""Consume n items."""
return self.items[:n]
def rotate(self, last_used):
"""Move most recently used item to end of list."""
items = self.items
try:
items.append(items.pop(items.index(last_used)))
except ValueError:
pass
return last_used
class priority_cycle(round_robin_cycle):
"""Cycle that repeats items in order."""
def rotate(self, last_used):
"""Unused in this implementation."""
class sorted_cycle(priority_cycle):
"""Cycle in sorted order."""
def consume(self, n):
"""Consume n items."""
return sorted(self.items[:n])
def cycle_by_name(name):
"""Get cycle class by name."""
return symbol_by_name(name, CYCLE_ALIASES)
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