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1# Copyright 2020, Google LLC
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7# https://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
15import collections
16import logging
17import typing
18from typing import Any, Callable, Iterable, Optional
20if typing.TYPE_CHECKING: # pragma: NO COVER
21 from google.cloud.pubsub_v1 import subscriber
24_LOGGER = logging.getLogger(__name__)
27class MessagesOnHold(object):
28 """Tracks messages on hold by ordering key. Not thread-safe."""
30 def __init__(self):
31 self._size = 0
33 # A FIFO queue for the messages that have been received from the server,
34 # but not yet sent to the user callback.
35 # Both ordered and unordered messages may be in this queue. Ordered
36 # message state tracked in _pending_ordered_messages once ordered
37 # messages are taken off this queue.
38 # The tail of the queue is to the right side of the deque; the head is
39 # to the left side.
40 self._messages_on_hold = collections.deque()
42 # Dict of ordering_key -> queue of ordered messages that have not been
43 # delivered to the user.
44 # All ordering keys in this collection have a message in flight. Once
45 # that one is acked or nacked, the next message in the queue for that
46 # ordering key will be sent.
47 # If the queue is empty, it means there's a message for that key in
48 # flight, but there are no pending messages.
49 self._pending_ordered_messages = {}
51 @property
52 def size(self) -> int:
53 """Return the number of messages on hold across ordered and unordered messages.
55 Note that this object may still store information about ordered messages
56 in flight even if size is zero.
58 Returns:
59 The size value.
60 """
61 return self._size
63 def get(self) -> Optional["subscriber.message.Message"]:
64 """Gets a message from the on-hold queue. A message with an ordering
65 key wont be returned if there's another message with the same key in
66 flight.
68 Returns:
69 A message that hasn't been sent to the user yet or ``None`` if there are no
70 messages available.
71 """
72 while self._messages_on_hold:
73 msg = self._messages_on_hold.popleft()
75 if msg.ordering_key:
76 pending_queue = self._pending_ordered_messages.get(msg.ordering_key)
77 if pending_queue is None:
78 # Create empty queue to indicate a message with the
79 # ordering key is in flight.
80 self._pending_ordered_messages[
81 msg.ordering_key
82 ] = collections.deque()
83 self._size = self._size - 1
84 return msg
85 else:
86 # Another message is in flight so add message to end of
87 # queue for this ordering key.
88 pending_queue.append(msg)
89 else:
90 # Unordered messages can be returned without any
91 # restrictions.
92 self._size = self._size - 1
93 return msg
95 return None
97 def put(self, message: "subscriber.message.Message") -> None:
98 """Put a message on hold.
100 Args:
101 message: The message to put on hold.
102 """
103 if message.opentelemetry_data:
104 message.opentelemetry_data.start_subscribe_scheduler_span()
105 self._messages_on_hold.append(message)
106 self._size = self._size + 1
108 def activate_ordering_keys(
109 self,
110 ordering_keys: Iterable[str],
111 schedule_message_callback: Callable[["subscriber.message.Message"], Any],
112 ) -> None:
113 """Send the next message in the queue for each of the passed-in
114 ordering keys, if they exist. Clean up state for keys that no longer
115 have any queued messages.
117 See comment at streaming_pull_manager.activate_ordering_keys() for more
118 detail about the impact of this method on load.
120 Args:
121 ordering_keys:
122 The ordering keys to activate. May be empty, or contain duplicates.
123 schedule_message_callback:
124 The callback to call to schedule a message to be sent to the user.
125 """
126 for key in ordering_keys:
127 pending_ordered_messages = self._pending_ordered_messages.get(key)
128 if pending_ordered_messages is None:
129 _LOGGER.warning(
130 "No message queue exists for message ordering key: %s.", key
131 )
132 continue
133 next_msg = self._get_next_for_ordering_key(key)
134 if next_msg:
135 # Schedule the next message because the previous was dropped.
136 # Note that this may overload the user's `max_bytes` limit, but
137 # not their `max_messages` limit.
138 schedule_message_callback(next_msg)
139 else:
140 # No more messages for this ordering key, so do clean-up.
141 self._clean_up_ordering_key(key)
143 def _get_next_for_ordering_key(
144 self, ordering_key: str
145 ) -> Optional["subscriber.message.Message"]:
146 """Get next message for ordering key.
148 The client should call clean_up_ordering_key() if this method returns
149 None.
151 Args:
152 ordering_key: Ordering key for which to get the next message.
154 Returns:
155 The next message for this ordering key or None if there aren't any.
156 """
157 queue_for_key = self._pending_ordered_messages.get(ordering_key)
158 if queue_for_key:
159 self._size = self._size - 1
160 return queue_for_key.popleft()
161 return None
163 def _clean_up_ordering_key(self, ordering_key: str) -> None:
164 """Clean up state for an ordering key with no pending messages.
166 Args
167 ordering_key: The ordering key to clean up.
168 """
169 message_queue = self._pending_ordered_messages.get(ordering_key)
170 if message_queue is None:
171 _LOGGER.warning(
172 "Tried to clean up ordering key that does not exist: %s", ordering_key
173 )
174 return
175 if len(message_queue) > 0:
176 _LOGGER.warning(
177 "Tried to clean up ordering key: %s with %d messages remaining.",
178 ordering_key,
179 len(message_queue),
180 )
181 return
182 del self._pending_ordered_messages[ordering_key]