201 lines
6.4 KiB
Python
201 lines
6.4 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2014-2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import contextlib
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import threading
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from collections import deque
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class IdGenerator(object):
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def __init__(self, db_conn, table, column):
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self._lock = threading.Lock()
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self._next_id = _load_current_id(db_conn, table, column)
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def get_next(self):
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with self._lock:
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self._next_id += 1
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return self._next_id
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def _load_current_id(db_conn, table, column, step=1):
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"""
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Args:
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db_conn (object):
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table (str):
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column (str):
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step (int):
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Returns:
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int
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"""
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cur = db_conn.cursor()
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if step == 1:
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cur.execute("SELECT MAX(%s) FROM %s" % (column, table,))
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else:
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cur.execute("SELECT MIN(%s) FROM %s" % (column, table,))
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val, = cur.fetchone()
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cur.close()
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current_id = int(val) if val else step
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return (max if step > 0 else min)(current_id, step)
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class StreamIdGenerator(object):
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"""Used to generate new stream ids when persisting events while keeping
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track of which transactions have been completed.
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This allows us to get the "current" stream id, i.e. the stream id such that
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all ids less than or equal to it have completed. This handles the fact that
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persistence of events can complete out of order.
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Args:
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db_conn(connection): A database connection to use to fetch the
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initial value of the generator from.
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table(str): A database table to read the initial value of the id
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generator from.
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column(str): The column of the database table to read the initial
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value from the id generator from.
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extra_tables(list): List of pairs of database tables and columns to
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use to source the initial value of the generator from. The value
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with the largest magnitude is used.
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step(int): which direction the stream ids grow in. +1 to grow
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upwards, -1 to grow downwards.
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Usage:
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with stream_id_gen.get_next() as stream_id:
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# ... persist event ...
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"""
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def __init__(self, db_conn, table, column, extra_tables=[], step=1):
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assert step != 0
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self._lock = threading.Lock()
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self._step = step
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self._current = _load_current_id(db_conn, table, column, step)
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for table, column in extra_tables:
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self._current = (max if step > 0 else min)(
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self._current,
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_load_current_id(db_conn, table, column, step)
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)
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self._unfinished_ids = deque()
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def get_next(self):
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"""
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Usage:
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with stream_id_gen.get_next() as stream_id:
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# ... persist event ...
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"""
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with self._lock:
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self._current += self._step
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next_id = self._current
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self._unfinished_ids.append(next_id)
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@contextlib.contextmanager
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def manager():
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try:
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yield next_id
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finally:
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with self._lock:
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self._unfinished_ids.remove(next_id)
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return manager()
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def get_next_mult(self, n):
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"""
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Usage:
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with stream_id_gen.get_next(n) as stream_ids:
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# ... persist events ...
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"""
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with self._lock:
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next_ids = range(
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self._current + self._step,
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self._current + self._step * (n + 1),
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self._step
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)
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self._current += n * self._step
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for next_id in next_ids:
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self._unfinished_ids.append(next_id)
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@contextlib.contextmanager
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def manager():
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try:
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yield next_ids
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finally:
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with self._lock:
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for next_id in next_ids:
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self._unfinished_ids.remove(next_id)
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return manager()
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def get_current_token(self):
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"""Returns the maximum stream id such that all stream ids less than or
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equal to it have been successfully persisted.
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Returns:
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int
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"""
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with self._lock:
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if self._unfinished_ids:
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return self._unfinished_ids[0] - self._step
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return self._current
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class ChainedIdGenerator(object):
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"""Used to generate new stream ids where the stream must be kept in sync
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with another stream. It generates pairs of IDs, the first element is an
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integer ID for this stream, the second element is the ID for the stream
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that this stream needs to be kept in sync with."""
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def __init__(self, chained_generator, db_conn, table, column):
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self.chained_generator = chained_generator
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self._lock = threading.Lock()
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self._current_max = _load_current_id(db_conn, table, column)
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self._unfinished_ids = deque()
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def get_next(self):
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"""
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Usage:
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with stream_id_gen.get_next() as (stream_id, chained_id):
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# ... persist event ...
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"""
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with self._lock:
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self._current_max += 1
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next_id = self._current_max
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chained_id = self.chained_generator.get_current_token()
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self._unfinished_ids.append((next_id, chained_id))
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@contextlib.contextmanager
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def manager():
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try:
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yield (next_id, chained_id)
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finally:
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with self._lock:
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self._unfinished_ids.remove((next_id, chained_id))
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return manager()
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def get_current_token(self):
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"""Returns the maximum stream id such that all stream ids less than or
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equal to it have been successfully persisted.
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"""
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with self._lock:
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if self._unfinished_ids:
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stream_id, chained_id = self._unfinished_ids[0]
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return (stream_id - 1, chained_id)
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return (self._current_max, self.chained_generator.get_current_token())
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