Source code for torch.distributed.elastic.rendezvous.etcd_store
# mypy: allow-untyped-defs
# Copyright (c) Facebook, Inc. and its affiliates.
# All rights reserved.
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.
import datetime
import random
import time
from base64 import b64decode, b64encode
from typing import Optional
import etcd # type: ignore[import]
# pyre-ignore[21]: Could not find name `Store` in `torch.distributed`.
from torch.distributed import Store
# Delay (sleep) for a small random amount to reduce CAS failures.
# This does not affect correctness, but will reduce requests to etcd server.
def cas_delay():
time.sleep(random.uniform(0, 0.1))
# pyre-fixme[11]: Annotation `Store` is not defined as a type.
[docs]class EtcdStore(Store):
"""
Implement a c10 Store interface by piggybacking on the rendezvous etcd instance.
This is the store object returned by ``EtcdRendezvous``.
"""
def __init__(
self,
etcd_client,
etcd_store_prefix,
# Default timeout same as in c10d/Store.hpp
timeout: Optional[datetime.timedelta] = None,
):
super().__init__() # required for pybind trampoline.
self.client = etcd_client
self.prefix = etcd_store_prefix
if timeout is not None:
self.set_timeout(timeout)
if not self.prefix.endswith("/"):
self.prefix += "/"
[docs] def set(self, key, value):
"""
Write a key/value pair into ``EtcdStore``.
Both key and value may be either Python ``str`` or ``bytes``.
"""
self.client.set(key=self.prefix + self._encode(key), value=self._encode(value))
[docs] def get(self, key) -> bytes:
"""
Get a value by key, possibly doing a blocking wait.
If key is not immediately present, will do a blocking wait
for at most ``timeout`` duration or until the key is published.
Returns:
value ``(bytes)``
Raises:
LookupError - If key still not published after timeout
"""
b64_key = self.prefix + self._encode(key)
kvs = self._try_wait_get([b64_key])
if kvs is None:
raise LookupError(f"Key {key} not found in EtcdStore")
return self._decode(kvs[b64_key])
[docs] def add(self, key, num: int) -> int:
"""
Atomically increment a value by an integer amount.
The integer is represented as a string using base 10. If key is not present,
a default value of ``0`` will be assumed.
Returns:
the new (incremented) value
"""
b64_key = self._encode(key)
# c10d Store assumes value is an integer represented as a decimal string
try:
# Assume default value "0", if this key didn't yet:
node = self.client.write(
key=self.prefix + b64_key,
value=self._encode(str(num)), # i.e. 0 + num
prevExist=False,
)
return int(self._decode(node.value))
except etcd.EtcdAlreadyExist:
pass
while True:
# Note: c10d Store does not have a method to delete keys, so we
# can be sure it's still there.
node = self.client.get(key=self.prefix + b64_key)
new_value = self._encode(str(int(self._decode(node.value)) + num))
try:
node = self.client.test_and_set(
key=node.key, value=new_value, prev_value=node.value
)
return int(self._decode(node.value))
except etcd.EtcdCompareFailed:
cas_delay()
[docs] def wait(self, keys, override_timeout: Optional[datetime.timedelta] = None):
"""
Wait until all of the keys are published, or until timeout.
Raises:
LookupError - if timeout occurs
"""
b64_keys = [self.prefix + self._encode(key) for key in keys]
kvs = self._try_wait_get(b64_keys, override_timeout)
if kvs is None:
raise LookupError("Timeout while waiting for keys in EtcdStore")
# No return value on success
[docs] def check(self, keys) -> bool:
"""Check if all of the keys are immediately present (without waiting)."""
b64_keys = [self.prefix + self._encode(key) for key in keys]
kvs = self._try_wait_get(
b64_keys,
override_timeout=datetime.timedelta(microseconds=1), # as if no wait
)
return kvs is not None
#
# Encode key/value data in base64, so we can store arbitrary binary data
# in EtcdStore. Input can be `str` or `bytes`.
# In case of `str`, utf-8 encoding is assumed.
#
def _encode(self, value) -> str:
if type(value) == bytes:
return b64encode(value).decode()
elif type(value) == str:
return b64encode(value.encode()).decode()
raise ValueError("Value must be of type str or bytes")
#
# Decode a base64 string (of type `str` or `bytes`).
# Return type is `bytes`, which is more convenient with the Store interface.
#
def _decode(self, value) -> bytes:
if type(value) == bytes:
return b64decode(value)
elif type(value) == str:
return b64decode(value.encode())
raise ValueError("Value must be of type str or bytes")
#
# Get all of the (base64-encoded) etcd keys at once, or wait until all the keys
# are published or timeout occurs.
# This is a helper method for the public interface methods.
#
# On success, a dictionary of {etcd key -> etcd value} is returned.
# On timeout, None is returned.
#
def _try_wait_get(self, b64_keys, override_timeout=None):
timeout = self.timeout if override_timeout is None else override_timeout # type: ignore[attr-defined]
deadline = time.time() + timeout.total_seconds()
while True:
# Read whole directory (of keys), filter only the ones waited for
all_nodes = self.client.get(key=self.prefix)
req_nodes = {
node.key: node.value
for node in all_nodes.children
if node.key in b64_keys
}
if len(req_nodes) == len(b64_keys):
# All keys are available
return req_nodes
watch_timeout = deadline - time.time()
if watch_timeout <= 0:
return None
try:
self.client.watch(
key=self.prefix,
recursive=True,
timeout=watch_timeout,
index=all_nodes.etcd_index + 1,
)
except etcd.EtcdWatchTimedOut:
if time.time() >= deadline:
return None
else:
continue
except etcd.EtcdEventIndexCleared:
continue
