Repository: closeio/redis-hashring Branch: master Commit: 5a64283df5de Files: 10 Total size: 32.6 KB Directory structure: gitextract_e8xbh69s/ ├── .github/ │ └── workflows/ │ └── test.yaml ├── .gitignore ├── LICENSE ├── README.md ├── example.py ├── pyproject.toml ├── redis_hashring/ │ └── __init__.py ├── requirements.txt ├── setup.py └── tests.py ================================================ FILE CONTENTS ================================================ ================================================ FILE: .github/workflows/test.yaml ================================================ name: test-workflow on: [push] permissions: contents: read jobs: lint: runs-on: ubuntu-24.04 steps: - uses: actions/checkout@v4 - name: Set up Python uses: actions/setup-python@v5 with: python-version: "3.13" - name: Install dependencies run: | python -m pip install --upgrade pip pip install -r requirements.txt - name: Format run: | ruff format --check --no-cache - name: Lint run: | ruff check --no-cache test: runs-on: ubuntu-24.04 strategy: fail-fast: false matrix: python-version: ["3.10", "3.11", "3.12", "3.13"] services: redis: image: redis:7.2.4 options: >- --health-cmd "redis-cli ping" --health-interval 10s --health-timeout 5s --health-retries 5 ports: - 6379:6379 steps: - uses: actions/checkout@v4 - name: Set up Python uses: actions/setup-python@v5 with: python-version: ${{ matrix.python-version }} - name: Install dependencies run: | python -m pip install --upgrade pip pip install -r requirements.txt - name: Test run: | pytest ================================================ FILE: .gitignore ================================================ *.pyc venv/ *.egg *.egg-info/ ================================================ FILE: LICENSE ================================================ The MIT License (MIT) Copyright (c) 2015-2024 Elastic Inc. (Close) Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE ================================================ FILE: README.md ================================================ # `redis-hashring` `redis-hashring` is a Python library that implements a consistent hash ring for building distributed applications. The hash ring is stored in Redis. ## The problem Let's assume you're building a distributed application that's responsible for syncing accounts. Accounts are synced continuously, e.g. by keeping a connection open. Given the large amount of accounts, the application can't run in one process and has to be distributed and split up in multiple processes. Also, if one of the processes fails or crashes, other machines need to be able to take over accounts quickly. The load should be balanced equally between the machines. ## The solution A solution to this problem is to use a consistent hash ring: Different Python instances ("nodes") are responsible for a different set of keys. In our account example, the account IDs could be used as keys. A consistent hash ring is a large (integer) space that wraps around to form a circle. Each node picks a few random points ("replicas") on the hash ring when starting. Keys are hashed and looked up on the hash ring: In order to find the node that's responsible for a given key, we move on the hash ring until we find the next smaller point that belongs to a replica. The reason for multiple replicas per node is to ensure better distribution of the keys amongst the nodes. It can also be used to give certain nodes more weight. The ring is automatically rebalanced when a node enters or leaves the ring: If a node crashes or shuts down, its replicas are removed from the ring. ## How it works The ring is stored as a sorted set (ZSET) in Redis. Each replica is a member of the set, scored by it's expiration time. Each node needs to periodically refresh the score of its replicas to stay on the ring. The ring contains 2^32 points, and a replica is created by randomly placing a point on the ring. A replica of a node is responsible for the range of points from its randomly generated starting point until the starting point of the next node or replica. To check if a node is responsible for a given key, the key's position on the ring is determined by hashing the key using xxHash (CRC-32 is also supported for backwards-compatibility). For example, let's say there are two nodes, having one replica each. The first node is at 1 000 000 000 (1e9), the second at 2e9. In this case, the first node is responsible for the range [1e9, 2e9-1], the second node is responsible for [2e9, 2^32-1] and [0, 1e9-1], since the ring wraps. To check to which node the key *hello* belongs, we compute its hash, which is 4 211 111 929, and the value is therefore on the second node. Since the node replica points are picked randomly, it is recommended to have multiple replicas of the node on a ring to ensure a more even distribution of the nodes. ## Demo As an example, let's assume you have a process that is responsible for syncing accounts. In this example they are numbered from 0 to 99. Starting node 1 will assign all accounts to node 1, since it's the only node on the ring. We can see this by running the provided example script on node 1: ``` % python example.py INFO:root:PID 80721, 100 keys ([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]) ``` We can print the ring for debugging and see all the nodes and replicas on the ring: ``` % python example.py --print Hash ring "ring" replicas: Start Range Delay Node 706234936 2.97% 0s mbp.local:80721:249d729d 833679955 3.58% 0s mbp.local:80721:aa60d44c 987624694 24.44% 0s mbp.local:80721:aa7d4433 2037338983 3.41% 0s mbp.local:80721:e810d068 2183761853 3.55% 0s mbp.local:80721:3917f572 2336151471 2.82% 0s mbp.local:80721:e42b1b46 2457297989 4.40% 0s mbp.local:80721:e6bd5726 2646391033 4.37% 0s mbp.local:80721:6de2fc22 2834073726 5.30% 0s mbp.local:80721:b6f950b2 3061910569 3.96% 0s mbp.local:80721:d176c9e2 3231812046 5.70% 0s mbp.local:80721:65432143 3476455773 5.71% 0s mbp.local:80721:f2b29682 3721589736 0.65% 0s mbp.local:80721:51d0cb09 3749333446 5.53% 0s mbp.local:80721:3572f718 3986767934 4.39% 0s mbp.local:80721:42147f45 4175523935 19.22% 0s mbp.local:80721:296c9522 Hash ring "ring" nodes: Range Replicas Delay Hostname PID 100.00% 16 0s mbp.local 80721 ``` We can see that the node is responsible for the entire ring (range 100%) and has 16 replicas on the ring. Now let's start another node by running the script again. It will add its replicas to the ring and notify all the remaining nodes. ``` % python example.py INFO:root:PID 80721, 51 keys ([1, 5, 8, 9, 10, 14, 17, 20, 21, 24, 25, 28, 30, 32, 33, 34, 36, 38, 41, 42, 45, 46, 49, 50, 52, 54, 56, 58, 59, 60, 61, 62, 65, 66, 68, 69, 71, 74, 75, 78, 79, 81, 82, 85, 86, 87, 88, 89, 92, 93, 96]) ``` Node 1 will rebalance and is now only responsible for keys not in node 2: ``` INFO:root:PID 80808, 49 keys ([0, 2, 3, 4, 6, 7, 11, 12, 13, 15, 16, 18, 19, 22, 23, 26, 27, 29, 31, 35, 37, 39, 40, 43, 44, 47, 48, 51, 53, 55, 57, 63, 64, 67, 70, 72, 73, 76, 77, 80, 83, 84, 90, 91, 94, 95, 97, 98, 99]) ``` We can inspect the ring: ``` % python example.py --print Hash ring "ring" replicas: Start Range Delay Node 204632062 1.06% 0s mbp.local:80808:f933c33c 250215779 0.36% 0s mbp.local:80808:3b104c45 265648189 1.15% 0s mbp.local:80808:84d71125 315059885 2.77% 0s mbp.local:80808:bab5a03c 434081415 6.34% 0s mbp.local:80808:6eec1b26 706234936 2.97% 0s mbp.local:80721:249d729d 833679955 1.59% 0s mbp.local:80721:aa60d44c 901926411 2.00% 0s mbp.local:80808:bd6f3b27 987624694 2.87% 0s mbp.local:80721:aa7d4433 1110943067 5.42% 0s mbp.local:80808:abfa5d78 1343923832 0.83% 0s mbp.local:80808:5261947f 1379658747 4.70% 0s mbp.local:80808:cb0904de 1581392642 1.06% 0s mbp.local:80808:3050daa3 1627017290 9.55% 0s mbp.local:80808:8e1cef12 2037338983 3.41% 0s mbp.local:80721:e810d068 2183761853 3.55% 0s mbp.local:80721:3917f572 2336151471 2.82% 0s mbp.local:80721:e42b1b46 2457297989 4.40% 0s mbp.local:80721:e6bd5726 2646391033 4.37% 0s mbp.local:80721:6de2fc22 2834073726 2.30% 0s mbp.local:80721:b6f950b2 2932842903 3.01% 0s mbp.local:80808:58f09769 3061910569 3.08% 0s mbp.local:80721:d176c9e2 3194206736 0.88% 0s mbp.local:80808:ce94a1cf 3231812046 5.70% 0s mbp.local:80721:65432143 3476455773 0.21% 0s mbp.local:80721:f2b29682 3485592199 5.49% 0s mbp.local:80808:6fc107a3 3721589736 0.65% 0s mbp.local:80721:51d0cb09 3749333446 0.68% 0s mbp.local:80721:3572f718 3778349273 4.85% 0s mbp.local:80808:e7cc7485 3986767934 1.29% 0s mbp.local:80721:42147f45 4042192844 3.10% 0s mbp.local:80808:001590b5 4175523935 7.55% 0s mbp.local:80721:296c9522 Hash ring "ring" nodes: Range Replicas Delay Hostname PID 47.42% 16 0s mbp.local 80721 52.58% 16 0s mbp.local 80808 ``` ## `gevent` example `redis-hashring` provides a `GeventRingNode` class for `gevent`-based applications. The `GeventRingNode.start()` method spawns a greenlet that initializes the ring and periodically updates the node's replicas. An example app could look as follows: ```python from redis import Redis from redis_hashring import GeventRingNode KEY = "example-ring" redis = Redis() node = GeventRingNode(redis, KEY) node.start() def get_items(): """ Implement this method and return items to be processed. """ raise NotImplementedError() def process_items(items): """ Implement this method and process the given items. """ raise NotImplementedError() try: while True: # Only process items this node is reponsible for. items = [item for item in get_items() if node.contains(item)] process_items(items) except KeyboardInterrupt: pass node.stop() ``` ## Implementation considerations When implementing a distributed application using `redis-hashring`, be aware of the following: - Locking When nodes are added to the ring, multiple nodes might assume they're responsible for the same key until they are notified about the new state of the ring. Depending on the application, locking may be necessary to avoid duplicate processing. For example, in the demo above the node could add a per-account-ID lock if an account should never be synced by multiple nodes at the same time. This can be done using a Redis lock class or any other distributed lock. - Limit It is recommended to add an upper limit to the number of keys a node can process to avoid overloading a node when there are few nodes on the ring or all nodes need to be restarted. For example, in the demo above we could implement a limit of 50 accounts, if we know that a node may not be capable of syncing much more. In this case, multiple nodes would need to be running to sync all the accounts. Also note that the ring is not usually equally balanced, so running 2 nodes wouldn't be enough in this example. ================================================ FILE: example.py ================================================ import argparse import logging import os import sys import time import redis from redis_hashring import RingNode N_KEYS = 100 logging.basicConfig(level=logging.DEBUG) def _parse_arguments(): parser = argparse.ArgumentParser("Hash ring example.", add_help=False) parser.add_argument( "--host", "-h", default="localhost", help="Redis hostname." ) parser.add_argument( "--port", "-p", type=int, default=6379, help="Redis port." ) parser.add_argument( "--print", action="store_true", dest="print", help="Print the hash ring.", ) parser.add_argument( "--help", action="help", default=argparse.SUPPRESS, help="Show this help message and exit.", ) return parser.parse_args() if __name__ == "__main__": args = _parse_arguments() print(f"Attempting to connect to Redis at {args.host}:{args.port}.") r = redis.Redis(args.host, args.port) try: r.ping() except redis.exceptions.ConnectionError: print("Failed to connect to Redis.") sys.exit(1) node = RingNode(r, "ring") if args.print: node.debug_print() sys.exit() pid = os.getpid() node.start() try: while True: keys = [key for key in range(N_KEYS) if node.contains(str(key))] logging.info("PID %d, %d keys (%s)", pid, len(keys), repr(keys)) time.sleep(2) except KeyboardInterrupt: pass node.stop() ================================================ FILE: pyproject.toml ================================================ [tool.ruff] target-version = "py38" line-length = 79 exclude = [ ".git", "venv", ".venv", "__pycache__", ] [tool.ruff.lint] extend-select = ["I"] unfixable = [ # Variable assigned but never used - automatically removing the assignment # is annoying when running autofix on work-in-progress code. "F841", ] [tool.ruff.lint.flake8-tidy-imports] ban-relative-imports = "all" [tool.ruff.lint.flake8-tidy-imports.banned-api] "functools.partial".msg = "Use a lambda or a named function instead. Partials don't type check correctly." "datetime.datetime.utcnow".msg = "Use `datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None)` instead." "datetime.datetime.utcfromtimestamp".msg = "Use `datetime.datetime.fromtimestamp(timestamp, datetime.timezone.utc).replace(tzinfo=None)` instead." [tool.ruff.lint.isort] combine-as-imports = true forced-separate = ["tests"] [tool.ruff.lint.pydocstyle] # https://google.github.io/styleguide/pyguide.html#383-functions-and-methods convention = "google" [tool.ruff.lint.flake8-annotations] ignore-fully-untyped = true [tool.pytest.ini_options] timeout = 180 python_files = "tests.py" testpaths = ["."] xfail_strict = true ================================================ FILE: redis_hashring/__init__.py ================================================ import binascii import collections import enum import operator import os import random import select import socket import threading import time try: import xxhash except ImportError: xxhash = None # Amount of points on the ring. Must not be higher than 2**32. RING_SIZE = 2**32 # Default amount of replicas per node. RING_REPLICAS = 16 class HashAlgorithm(enum.Enum): CRC32 = "crc32" XXHASH = "xxhash" # How often to update a node's heartbeat. POLL_INTERVAL = 10 # After how much time a node is considered to be dead. NODE_TIMEOUT = 60 # How often expired nodes are cleaned up from the ring. CLEANUP_INTERVAL = 120 def _hash_with_xxhash(key): return xxhash.xxh32(key.encode()).intdigest() % RING_SIZE def _hash_with_crc32(key): return binascii.crc32(key.encode()) % RING_SIZE def _decode(data): # Compatibility with different redis-py `decode_responses` settings. if isinstance(data, bytes): return data.decode() else: return data class RingNode(object): """ A node in a Redis hash ring. Each node may have multiple replicas on the ring for more balanced hashing. The ring is stored as follows in Redis: ZSET Represents the ring in Redis. The keys of this ZSET represent "start:replica_name", where start is the start of the range for which the replica is responsible. CHANNEL Represents a pubsub channel in Redis which receives a message every time the ring structure has changed. Simple usage example: ``` node = RingNode(redis, key) node.start() while is_running: # Only process items this node is responsible for. `item` should be an # object that can be encoded to bytes by calling `item.encode()` on it, # like a `str`. items = [item for item in get_items() if node.contains(item)] process_items(items) node.stop() ``` Using CRC-32 (if you need to support hashrings created before xxHash support was introduced): ``` from redis_hashring import RingNode, HashAlgorithm node = RingNode(redis, key, hash_algorithm=HashAlgorithm.CRC32) node.start() ``` As a context manager: ``` with RingNode(redis, key) as node: while is_running: # Only process items this node is responsible for. `item` should be # an object that can be encoded to bytes by calling `item.encode()` # on it, like a `str`. items = [item for item in get_items() if node.contains(item)] process_items(items) ``` """ def __init__( self, conn, key, *, n_replicas=RING_REPLICAS, hash_algorithm=HashAlgorithm.XXHASH, ): """ Initializes a Redis hash ring node. Args: conn: The Redis connection to use. key: A key to use for this node. n_replicas: Number of replicas this node should have on the ring. hash_algorithm: Hash algorithm to use. It is recommended to use `HashAlgorithm.XXHASH` (the default) because it provides better uniform distribution than CRC-32 with faster hashing. If you need to support hashrings created before we introduced support for xxHash, use `HashAlgorithm.CRC32`. """ self._polling_thread = None self._stop_polling_fd_r = None self._stop_polling_fd_w = None self._conn = conn self._key = key if hash_algorithm is HashAlgorithm.XXHASH: if xxhash is None: raise ImportError( "xxhash library is required for XXHASH algorithm. " "Install with: pip install redis-hashring[xxhash]" ) self._hash_function = _hash_with_xxhash elif hash_algorithm is HashAlgorithm.CRC32: self._hash_function = _hash_with_crc32 else: raise ValueError("Unexpected hash algorithm requested") host = socket.gethostname() pid = os.getpid() # Create unique identifiers for the replicas. self._replicas = [ ( random.randrange(2**32), "{host}:{pid}:{id_}".format( host=host, pid=pid, id_=binascii.hexlify(os.urandom(4)).decode(), ), ) for _ in range(n_replicas) ] # Number of nodes currently active in the ring. self._node_count = 0 # List of tuples of ranges this node is responsible for, where a tuple # (a, b) includes any N matching a <= N < b. self._ranges = [] self._select = select.select def _fetch_ring(self): """ Fetch the ring from Redis. The fetched ring only includes active nodes. Returns a list of tuples (start, replica) (see _fetch_all docs for more details). """ expiry_time = time.time() - NODE_TIMEOUT data = self._conn.zrangebyscore(self._key, expiry_time, "INF") ring = [] for replica_data in data: start, replica = _decode(replica_data).split(":", 1) ring.append((int(start), replica)) return sorted(ring, key=operator.itemgetter(0)) def _fetch_ring_all(self): """ Fetch the ring from Redis. The fetched ring will include inactive nodes. Returns a list of tuples (start, replica, heartbeat, expired), where: * start: start of the range for which the replica is responsible. * replica: name of the replica. * heartbeat: timestamp of the last heartbeat. * expired: boolean denoting whether this replica is inactive. """ expiry_time = time.time() - NODE_TIMEOUT data = self._conn.zrange(self._key, 0, -1, withscores=True) ring = [] for replica_data, heartbeat in data: start, replica = _decode(replica_data).split(":", 1) ring.append( (int(start), replica, heartbeat, heartbeat < expiry_time) ) return sorted(ring, key=operator.itemgetter(0)) def debug_print(self): """ Prints the ring for debugging purposes. """ ring = self._fetch_ring_all() print('Hash ring "{key}" replicas:'.format(key=self._key)) now = time.time() n_replicas = len(ring) if ring: print( "{:10} {:6} {:7} {}".format("Start", "Range", "Delay", "Node") ) else: print("(no replicas)") nodes = collections.defaultdict(list) for n, (start, replica, heartbeat, expired) in enumerate(ring): hostname, pid, _ = replica.split(":") node = ":".join([hostname, pid]) abs_size = (ring[(n + 1) % n_replicas][0] - ring[n][0]) % RING_SIZE size = 100.0 / RING_SIZE * abs_size delay = int(now - heartbeat) expired_str = "(EXPIRED)" if expired else "" nodes[node].append((hostname, pid, abs_size, delay, expired)) print( f"{start:10} {size:5.2f}% {delay:6}s {replica} {expired_str}" ) print() print('Hash ring "{key}" nodes:'.format(key=self._key)) if nodes: print( "{:8} {:8} {:7} {:20} {:5}".format( "Range", "Replicas", "Delay", "Hostname", "PID" ) ) else: print("(no nodes)") for _, v in nodes.items(): hostname, pid = v[0][0], v[0][1] abs_size = sum(replica[2] for replica in v) size = 100.0 / RING_SIZE * abs_size delay = max(replica[3] for replica in v) expired = any(replica[4] for replica in v) count = len(v) expired_str = "(EXPIRED)" if expired else "" print( f"{size:5.2f}% {count:8} {delay:6}s {hostname:20} {pid:5}" f" {expired_str}" ) def heartbeat(self): """ Add/update the node in Redis. Needs to be called regularly by the node. """ pipeline = self._conn.pipeline() now = time.time() for replica in self._replicas: pipeline.zadd(self._key, {f"{replica[0]}:{replica[1]}": now}) ret = pipeline.execute() # Only notify the other nodes if we're not in the ring yet. if any(ret): self._notify() def remove(self): """ Remove the node from the ring. """ pipeline = self._conn.pipeline() for replica in self._replicas: pipeline.zrem(self._key, f"{replica[0]}:{replica[1]}") pipeline.execute() # Make sure this node won't contain any items. self._node_count = 0 self._ranges = [] self._notify() def _notify(self): """ Publish an update to the ring's activity channel. """ self._conn.publish(self._key, "*") def cleanup(self): """ Removes expired nodes from the ring. """ expired = time.time() - NODE_TIMEOUT if self._conn.zremrangebyscore(self._key, 0, expired): self._notify() def update(self): """ Fetches the updated ring from Redis and updates the current ranges. """ ring = self._fetch_ring() nodes = set() n_replicas = len(ring) own_replicas = {r[1] for r in self._replicas} self._ranges = [] for n, (start, replica) in enumerate(ring): host, pid, _ = replica.split(":") node = ":".join([host, pid]) nodes.add(node) if replica in own_replicas: end = ring[(n + 1) % n_replicas][0] % RING_SIZE if start < end: self._ranges.append((start, end)) elif end < start: self._ranges.append((start, RING_SIZE)) self._ranges.append((0, end)) else: self._ranges.append((0, RING_SIZE)) self._node_count = len(nodes) def get_ranges(self): """ Return the hash ring ranges that this node owns. """ return self._ranges def get_node_count(self): """ Return the number of active nodes in the ring. """ return self._node_count def contains(self, key): """ Check whether this node is responsible for the item. """ return self._contains_ring_point(self.key_as_ring_point(key)) def key_as_ring_point(self, key): """Turn a key into a point on a hash ring.""" return self._hash_function(key) def _contains_ring_point(self, n): """ Check whether this node is responsible for the ring point. """ for start, end in self._ranges: if start <= n < end: return True return False def poll(self): """ Keep a node in the hash ring. This should be kept running for as long as the node needs to stay in the ring. Can be run in a separate thread or in a greenlet. This takes care of: * Updating the heartbeat. * Checking for ring updates. * Cleaning up expired nodes periodically. """ pubsub = self._conn.pubsub() pubsub.subscribe(self._key) pubsub_fd = pubsub.connection._sock.fileno() last_heartbeat = time.time() self.heartbeat() last_cleanup = time.time() self.cleanup() self._stop_polling_fd_r, self._stop_polling_fd_w = os.pipe() try: while True: # Since Redis' `listen` method blocks, we use `select` to # inspect the underlying socket to see if there is activity. timeout = max( 0.0, POLL_INTERVAL - (time.time() - last_heartbeat) ) r, _, _ = self._select( [self._stop_polling_fd_r, pubsub_fd], [], [], timeout ) if self._stop_polling_fd_r in r: os.close(self._stop_polling_fd_r) os.close(self._stop_polling_fd_w) self._stop_polling_fd_r = None self._stop_polling_fd_w = None break if pubsub_fd in r: while pubsub.get_message(): pass self.update() last_heartbeat = time.time() self.heartbeat() now = time.time() if now - last_cleanup > CLEANUP_INTERVAL: last_cleanup = now self.cleanup() finally: pubsub.close() def start(self): """ Start the node for threads-based applications. """ self._polling_thread = threading.Thread(target=self.poll, daemon=True) self._polling_thread.start() def stop(self): """ Stop the node for threads-based applications. """ if self._polling_thread: while not self._stop_polling_fd_w: # Let's give the thread some time to create the fd. time.sleep(0.1) os.write(self._stop_polling_fd_w, b"1") self._polling_thread.join() self._polling_thread = None self.remove() def __enter__(self): self.start() return self def __exit__(self, *args, **kwargs): self.stop() class GeventRingNode(RingNode): """ A node in a Redis hash ring. This works exactly the same as `RingNode`, except that `start` and `stop` will create a gevent greenlet to maintain the node information up to date with the hash ring. For a usage example, see the documentation for `RingNode`. """ def __init__(self, *args, **kwargs): self._polling_greenlet = None super().__init__(*args, **kwargs) def start(self): """ Start the node for gevent-based applications. """ import gevent import gevent.select self._select = gevent.select.select self._polling_greenlet = gevent.spawn(self.poll) # Even though `self.poll` will run `self.heartbeat` and `self.update` # immediately as it starts, this is gevent and `self.poll` may take a # while to run, depending on how long the greenlet that creates the # node takes to yield. So we'll run these functions here to make sure # the node is up to date immediately. self.heartbeat() self.update() def stop(self): """ Stop the node for gevent-based applications. """ if self._polling_greenlet: while not self._stop_polling_fd_w: # Let's give the greenlet some time to create the fd. time.sleep(0.1) os.write(self._stop_polling_fd_w, b"1") self._polling_greenlet.join() self._polling_greenlet = None self.remove() self._select = select.select ================================================ FILE: requirements.txt ================================================ pytest==7.2.2 redis==4.6.0 ruff==0.4.3 xxhash==3.5.0 ================================================ FILE: setup.py ================================================ from setuptools import setup setup( name="redis-hashring", version="0.6.0", author="Close Engineering", author_email="engineering@close.com", url="https://github.com/closeio/redis-hashring", license="MIT", description=( "Python library for distributed applications using a Redis hash ring" ), install_requires=["redis>=3"], extras_require={ "xxhash": ["xxhash>=3.5.0"], }, platforms="any", classifiers=[ "Intended Audience :: Developers", "License :: OSI Approved :: MIT License", "Operating System :: OS Independent", "Topic :: Software Development :: Libraries :: Python Modules", "Programming Language :: Python", "Programming Language :: Python :: 3", "Programming Language :: Python :: 3 :: Only", "Programming Language :: Python :: 3.10", "Programming Language :: Python :: 3.11", "Programming Language :: Python :: 3.12", "Programming Language :: Python :: 3.13", ], packages=["redis_hashring"], ) ================================================ FILE: tests.py ================================================ import socket from unittest.mock import patch import pytest from redis import Redis from redis_hashring import HashAlgorithm, RingNode TEST_KEY = "hashring-test" @pytest.fixture def redis(): redis = Redis() yield redis redis.delete(TEST_KEY) def get_node(redis, n_replicas, total_replicas, hash_algorithm): node = RingNode( redis, TEST_KEY, n_replicas=n_replicas, hash_algorithm=hash_algorithm ) assert len(node._replicas) == n_replicas assert redis.zcard(TEST_KEY) == total_replicas - n_replicas node.heartbeat() assert redis.zcard(TEST_KEY) == total_replicas assert len(node.get_ranges()) == 0 return node def test_node(redis): with patch.object(socket, "gethostname", return_value="host1"): node1 = get_node(redis, 1, 1, HashAlgorithm.XXHASH) node1.update() assert len(node1.get_ranges()) == 1 assert node1.get_node_count() == 1 with patch.object(socket, "gethostname", return_value="host2"): node2 = get_node(redis, 1, 2, HashAlgorithm.XXHASH) node1.update() node2.update() assert len(node1.get_ranges()) + len(node2.get_ranges()) == 3 assert node1.get_node_count() == 2 assert node2.get_node_count() == 2 with patch.object(socket, "gethostname", return_value="host3"): node3 = get_node(redis, 2, 4, HashAlgorithm.XXHASH) node1.update() node2.update() node3.update() assert ( len(node1.get_ranges()) + len(node2.get_ranges()) + len(node3.get_ranges()) == 5 ) assert node1.get_node_count() == 3 assert node2.get_node_count() == 3 assert node3.get_node_count() == 3 node1.remove() node2.update() node3.update() assert len(node1.get_ranges()) == 0 assert node1.get_node_count() == 0 assert len(node2.get_ranges()) + len(node3.get_ranges()) == 4 assert node2.get_node_count() == 2 assert node3.get_node_count() == 2 @pytest.mark.parametrize( "hash_algorithm", [HashAlgorithm.CRC32, HashAlgorithm.XXHASH] ) def test_contains(redis, hash_algorithm): node1 = get_node(redis, 1, 1, hash_algorithm=hash_algorithm) node1.update() assert node1.contains("item") is True node1.remove() assert node1.contains("item") is False