152 lines
4.4 KiB
Python
152 lines
4.4 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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from twisted.internet import defer
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from collections import deque
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import contextlib
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import threading
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class IdGenerator(object):
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def __init__(self, table, column, store):
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self.table = table
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self.column = column
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self.store = store
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self._lock = threading.Lock()
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self._next_id = None
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@defer.inlineCallbacks
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def get_next(self):
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if self._next_id is None:
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yield self.store.runInteraction(
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"IdGenerator_%s" % (self.table,),
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self.get_next_txn,
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)
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with self._lock:
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i = self._next_id
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self._next_id += 1
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defer.returnValue(i)
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def get_next_txn(self, txn):
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with self._lock:
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if self._next_id:
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i = self._next_id
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self._next_id += 1
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return i
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else:
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txn.execute(
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"SELECT MAX(%s) FROM %s" % (self.column, self.table,)
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)
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val, = txn.fetchone()
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cur = val or 0
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cur += 1
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self._next_id = cur + 1
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return cur
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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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Usage:
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with stream_id_gen.get_next_txn(txn) as stream_id:
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# ... persist event ...
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"""
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def __init__(self, db_conn, table, column):
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self.table = table
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self.column = column
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self._lock = threading.Lock()
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cur = db_conn.cursor()
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self._current_max = self._get_or_compute_current_max(cur)
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cur.close()
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self._unfinished_ids = deque()
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def get_next(self, store):
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"""
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Usage:
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with yield 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_max += 1
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next_id = self._current_max
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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, store, n):
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"""
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Usage:
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with yield stream_id_gen.get_next(store, 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(self._current_max + 1, self._current_max + n + 1)
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self._current_max += n
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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_max_token(self, store):
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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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return self._unfinished_ids[0] - 1
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return self._current_max
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def _get_or_compute_current_max(self, txn):
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with self._lock:
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txn.execute("SELECT MAX(%s) FROM %s" % (self.column, self.table))
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rows = txn.fetchall()
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val, = rows[0]
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self._current_max = int(val) if val else 1
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return self._current_max
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