Source code for torch.distributed.elastic.rendezvous.dynamic_rendezvous
# 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 inspect
import logging
import os
import pickle
import socket
import threading
import time
import weakref
from abc import ABC, abstractmethod
from dataclasses import dataclass
from datetime import datetime, timedelta
from enum import Enum
from typing import Any, Callable, cast, Dict, List, Optional, Set, Tuple
from torch.distributed import PrefixStore, Store
from torch.distributed.elastic.events import construct_and_record_rdzv_event, NodeState
from .api import (
RendezvousClosedError,
RendezvousError,
RendezvousGracefulExitError,
RendezvousHandler,
RendezvousParameters,
RendezvousStateError,
RendezvousTimeoutError,
)
from .utils import _delay, _PeriodicTimer
__all__ = ['RendezvousBackend', 'RendezvousTimeout', 'RendezvousSettings', 'DynamicRendezvousHandler', 'create_handler']
log = logging.getLogger(__name__)
def get_method_name(depth=2):
if len(inspect.stack()) > depth:
return inspect.stack()[depth].function
return "no_method_name"
Token = Any
"""Represent an opaque fencing token used by the rendezvous backend."""
[docs]class RendezvousBackend(ABC):
"""Represent a backend that holds the rendezvous state."""
@property
@abstractmethod
def name(self) -> str:
"""Get the name of the backend."""
[docs] @abstractmethod
def get_state(self) -> Optional[Tuple[bytes, Token]]:
"""Get the rendezvous state.
Returns:
A tuple of the encoded rendezvous state and its fencing token or
``None`` if no state is found in the backend.
Raises:
RendezvousConnectionError:
The connection to the backend has failed.
RendezvousStateError:
The rendezvous state is corrupt.
"""
[docs] @abstractmethod
def set_state(
self, state: bytes, token: Optional[Token] = None
) -> Optional[Tuple[bytes, Token, bool]]:
"""Set the rendezvous state.
The new rendezvous state is set conditionally:
- If the specified ``token`` matches the fencing token stored in the
backend, the state will be updated. The new state will be returned
to the caller along with its fencing token.
- If the specified ``token`` does not match the fencing token stored
in the backend, the state won't be updated; instead the existing
state along with its fencing token will be returned to the caller.
- If the specified ``token`` is ``None``, the new state will be set
only if there is no existing state in the backend. Either the new
state or the existing state along with its fencing token will be
returned to the caller.
Args:
state:
The encoded rendezvous state.
token:
An optional fencing token that was retrieved by a previous call
to :py:meth:`get_state` or ``set_state()``.
Returns:
A tuple of the serialized rendezvous state, its fencing token, and
a boolean value indicating whether our set attempt succeeded.
Raises:
RendezvousConnectionError:
The connection to the backend has failed.
RendezvousStateError:
The rendezvous state is corrupt.
"""
[docs]class RendezvousTimeout:
"""Hold the timeout configuration of a rendezvous.
Args:
join:
The time within which the rendezvous is expected to complete.
last_call:
An additional wait amount before completing the rendezvous once the
rendezvous has the minimum number of required participants.
close:
The time within which the rendezvous is expected to close after a
call to :py:meth:`RendezvousHandler.set_closed` or
:py:meth:`RendezvousHandler.shutdown`.
keep_alive:
The time within which a keep-alive heartbeat is expected to
complete.
"""
_ZERO = timedelta(0)
_DEFAULT_TIMEOUTS = {
"join": timedelta(seconds=600),
"last_call": timedelta(seconds=30),
"close": timedelta(seconds=30),
"heartbeat": timedelta(seconds=5),
}
_join: timedelta
_last_call: timedelta
_close: timedelta
_heartbeat: timedelta
def __init__(
self,
join: Optional[timedelta] = None,
last_call: Optional[timedelta] = None,
close: Optional[timedelta] = None,
heartbeat: Optional[timedelta] = None,
) -> None:
self._set_timeouts(join=join, last_call=last_call, close=close, heartbeat=heartbeat)
@property
def join(self) -> timedelta:
"""Get the join timeout."""
return self._join
@property
def last_call(self) -> timedelta:
"""Get the last call timeout."""
return self._last_call
@property
def close(self) -> timedelta:
"""Get the close timeout."""
return self._close
@property
def heartbeat(self) -> timedelta:
"""Get the keep-alive heartbeat timeout."""
return self._heartbeat
def _set_timeouts(self, **timeouts: Optional[timedelta]):
for name, timeout in timeouts.items():
if timeout is None:
timeout = self._DEFAULT_TIMEOUTS[name]
if timeout <= self._ZERO:
raise ValueError(f"The {name} timeout ({timeout}) must be positive.")
setattr(self, "_" + name, timeout)
@dataclass(repr=False, eq=False, frozen=True)
class RendezvousSettings:
"""Hold the settings of the rendezvous.
Attributes:
run_id:
The run id of the rendezvous.
min_nodes:
The minimum number of nodes to admit to the rendezvous.
max_nodes:
The maximum number of nodes to admit to the rendezvous.
timeout:
The timeout configuration of the rendezvous.
keep_alive_interval:
The amount of time a node waits before sending a heartbeat to keep
it alive in the rendezvous.
keep_alive_max_attempt:
The maximum number of failed heartbeat attempts after which a node
is considered dead.
"""
run_id: str
min_nodes: int
max_nodes: int
timeout: RendezvousTimeout
keep_alive_interval: timedelta
keep_alive_max_attempt: int
@dataclass(eq=True, order=True, frozen=True)
class _NodeDesc:
"""Describe a node in the rendezvous.
Attributes:
addr:
The FQDN of the node or user specified local node address.
pid:
The id of the process in which the rendezvous handler runs.
local_id:
A process-wide unique id.
"""
addr: str
pid: int
local_id: int
def __repr__(self) -> str:
return f"{self.addr}_{self.pid}_{self.local_id}"
class _NodeDescGenerator:
"""Generate node descriptors.
A node descriptor is a combination of an FQDN, a process id, and an auto-
incremented integer that uniquely identifies a node in the rendezvous.
"""
_lock: threading.Lock
_local_id: int
def __init__(self) -> None:
self._lock = threading.Lock()
# An integer that is incremented with each call to generate().
self._local_id = 0
def generate(self, local_addr: Optional[str] = None) -> _NodeDesc:
# This method can be called by multiple threads concurrently; therefore,
# we must increment the integer atomically.
with self._lock:
local_id = self._local_id
self._local_id += 1
return _NodeDesc(local_addr or socket.getfqdn(), os.getpid(), local_id)
class _RendezvousState:
"""Hold the state of a rendezvous.
Attributes:
round:
The current round of the rendezvous.
complete:
A boolean value indicating whether the current round of the
rendezvous is complete.
deadline:
The time at which the current round of the rendezvous will be
considered complete if it is still waiting for nodes to join.
closed:
A boolean value indicating whether the rendezvous is closed.
participants:
A dictionary of the participants and their corresponding ranks.
wait_list:
A set of nodes that are waiting to participate in the next round of
the rendezvous.
redundancy_list:
A set of nodes that are redundant in the current round and can join
the next rendezvous without triggering re-rendezvous.
last_heartbeats:
A dictionary containing each node's last heartbeat time.
"""
round: int
complete: bool
deadline: Optional[datetime]
closed: bool
participants: Dict[_NodeDesc, int]
wait_list: Set[_NodeDesc]
redundancy_list: Set[_NodeDesc]
last_heartbeats: Dict[_NodeDesc, datetime]
def __init__(self) -> None:
self.round = 0
self.complete = False
self.deadline = None
self.closed = False
self.participants = {}
self.wait_list = set()
self.redundancy_list = set()
self.last_heartbeats = {}
def _remove_participant_epilogue(state: _RendezvousState, settings: RendezvousSettings) -> None:
if state.complete:
# If we do not have any participants left, move to the next round.
if not state.participants:
msg = "No participants left in the rendezvous, marking rendezvous as incomplete"
log.debug(msg)
state.complete = False
state.round += 1
else:
if len(state.participants) < settings.min_nodes:
msg = (
f"Number of participants {len(state.participants)}) less than"
f"min_nodes {settings.min_nodes}, clearning deadline in state"
)
log.debug(msg)
state.deadline = None
class _RendezvousStateHolder(ABC):
"""Hold the shared rendezvous state synced with other nodes."""
@property
@abstractmethod
def state(self) -> _RendezvousState:
"""Get the local state."""
@abstractmethod
def sync(self) -> Optional[bool]:
"""Read or writes the latest state.
Returns:
A boolean value indicating whether the local state, in case marked
as dirty, was successfully synced with other nodes.
"""
@abstractmethod
def mark_dirty(self) -> None:
"""Mark the local state as dirty."""
class _BackendRendezvousStateHolder(_RendezvousStateHolder):
"""Hold the rendezvous state synced with other nodes via a backend.
Args:
backend:
The rendezvous backend to use.
settings:
The rendezvous settings.
cache_duration:
The amount of time, in seconds, to cache the last rendezvous state
before requesting it from the backend again.
"""
_backend: RendezvousBackend
_state: _RendezvousState
_settings: RendezvousSettings
_cache_duration: int
_token: Token
_dirty: bool
_last_sync_time: float
_dead_nodes: List[_NodeDesc]
def __init__(
self,
backend: RendezvousBackend,
settings: RendezvousSettings,
cache_duration: int = 1,
) -> None:
self._backend = backend
self._state = _RendezvousState()
self._settings = settings
self._cache_duration = cache_duration
self._token = None
self._dirty = False
self._last_sync_time = -1
self._dead_nodes = []
def _record(self, message: str, node_state: NodeState = NodeState.RUNNING):
construct_and_record_rdzv_event(
name=f"{self.__class__.__name__}.{get_method_name()}",
run_id=self._settings.run_id,
message=message,
node_state=node_state,
)
@property
def state(self) -> _RendezvousState:
"""See base class."""
return self._state
def sync(self) -> Optional[bool]:
"""See base class."""
state_bits: Optional[bytes] = None
token = None
has_set: Optional[bool]
if self._dirty:
has_set = False
state_bits = pickle.dumps(self._state)
set_response = self._backend.set_state(state_bits, self._token)
if set_response is not None:
state_bits, token, has_set = set_response
else:
has_set = None
if self._cache_duration > 0:
# Avoid overloading the backend if we are asked to retrieve the
# state repeatedly. Try to serve the cached state.
if self._last_sync_time >= max(time.monotonic() - self._cache_duration, 0):
return None
get_response = self._backend.get_state()
if get_response is not None:
state_bits, token = get_response
if state_bits is not None:
try:
self._state = pickle.loads(state_bits)
except pickle.PickleError as exc:
raise RendezvousStateError(
"The rendezvous state is corrupt. See inner exception for details."
) from exc
else:
self._state = _RendezvousState()
if has_set and self._dead_nodes and log.isEnabledFor(logging.DEBUG):
node_list = ", ".join(f"'{dead_node}'" for dead_node in self._dead_nodes)
msg = (
f"As part of the sync operation the node(s) {node_list} have been removed from the "
f"rendezvous '{self._settings.run_id}' since they had no heartbeat."
)
self._record(message=msg)
log.debug(msg)
self._token = token
self._dirty = False
self._last_sync_time = time.monotonic()
self._sanitize()
return has_set
def _sanitize(self) -> None:
state = self._state
expire_time = datetime.utcnow() - (
self._settings.keep_alive_interval * self._settings.keep_alive_max_attempt
)
# Filter out the dead nodes.
self._dead_nodes = [
node
for node, last_heartbeat in state.last_heartbeats.items()
if last_heartbeat < expire_time
]
participant_removed = False
for dead_node in self._dead_nodes:
msg = f"Detected dead node '{dead_node}', removing it from the rendezvous"
log.debug(msg)
del state.last_heartbeats[dead_node]
try:
del state.participants[dead_node]
participant_removed = True
except KeyError:
pass
try:
state.wait_list.remove(dead_node)
except KeyError:
pass
try:
state.redundancy_list.remove(dead_node)
except KeyError:
pass
if participant_removed:
# Common epilogue shared with the _remove_from_participants()
# function of _DistributedRendezvousOpExecutor.
_remove_participant_epilogue(state, self._settings)
def mark_dirty(self) -> None:
"""See base class.
If the local rendezvous state is dirty, the next sync call will try to
write the changes back to the backend. However this attempt might fail
if another node, which had the same state, also made changes and wrote
them before us.
"""
self._dirty = True
class _Action(Enum):
"""Specifies the possible actions based on the state of the rendezvous."""
KEEP_ALIVE = 1
ADD_TO_PARTICIPANTS = 2
ADD_TO_WAIT_LIST = 3
ADD_TO_REDUNDANCY_LIST = 4
REMOVE_FROM_PARTICIPANTS = 5
REMOVE_FROM_WAIT_LIST = 6
REMOVE_FROM_REDUNDANCY_LIST = 7
MARK_RENDEZVOUS_COMPLETE = 8
MARK_RENDEZVOUS_CLOSED = 9
SYNC = 10
ERROR_CLOSED = 11
ERROR_TIMEOUT = 12
FINISH = 13
class _RendezvousContext:
"""Holds the context of the rendezvous.
Attributes:
node:
The node descriptor associated with the current rendezvous handler
instance.
state:
The current state of the rendezvous.
settings:
The rendezvous settings.
"""
node: _NodeDesc
state: _RendezvousState
settings: RendezvousSettings
def __init__(
self, node: _NodeDesc, state: _RendezvousState, settings: RendezvousSettings
) -> None:
self.node = node
self.state = state
self.settings = settings
class _RendezvousOpExecutor(ABC):
"""Execute rendezvous operations."""
@abstractmethod
def run(
self,
state_handler: Callable[[_RendezvousContext, float], _Action],
deadline: float,
update_deadline: Optional[Callable[[timedelta], float]] = None,
) -> None:
"""Execute a rendezvous operation.
An operation is run inside a state machine and is expected to transition
the rendezvous from one state to another.
Args:
state_handler:
A callable that is expected to return the next state transition
action based on the current state of the rendezvous.
deadline:
The time, in seconds, at which the operation will be considered
timed-out.
update_deadline:
Function to generate a new operation deadline if the current
node may participate in the next rendezvous.
"""
class _DistributedRendezvousOpExecutor(_RendezvousOpExecutor):
"""Execute rendezvous operations using a shared state.
Args:
node:
The node descriptor associated with the current rendezvous handler
instance.
state_holder:
The ``RendezvousStateHolder`` to use to sync the rendezvous state
with other nodes.
settings:
The rendezvous settings.
"""
_node: _NodeDesc
_state: _RendezvousState
_state_holder: _RendezvousStateHolder
_settings: RendezvousSettings
def __init__(
self,
node: _NodeDesc,
state_holder: _RendezvousStateHolder,
settings: RendezvousSettings,
) -> None:
self._node = node
self._state_holder = state_holder
self._settings = settings
def _record(self, message: str, node_state: NodeState = NodeState.RUNNING) -> None:
construct_and_record_rdzv_event(
name=f"{self.__class__.__name__}.{get_method_name()}",
run_id=self._settings.run_id,
message=message,
node_state=node_state,
hostname=self._node.addr,
pid=self._node.pid,
local_id=self._node.local_id,
)
def run(
self,
state_handler: Callable[[_RendezvousContext, float], _Action],
deadline: float,
update_deadline: Optional[Callable[[timedelta], float]] = None,
) -> None:
"""See base class."""
action = None
while action != _Action.FINISH:
# Reads or writes the latest rendezvous state shared by all nodes in
# the rendezvous. Note that our local changes might get overridden
# by another node if that node synced its changes before us.
has_set = self._state_holder.sync()
if has_set is not None:
if has_set:
msg = (
f"The node '{self._node}' has successfully synced its local changes with "
f"other nodes in the rendezvous '{self._settings.run_id}'."
)
else:
msg = (
f"The node '{self._node}' has a stale state and failed to sync its local "
f"changes with other nodes in the rendezvous '{self._settings.run_id}'."
)
self._record(message=msg)
log.debug(msg)
self._state = self._state_holder.state
ctx = _RendezvousContext(self._node, self._state, self._settings)
# Determine the next action to take based on the current state of
# the rendezvous.
action = state_handler(ctx, deadline)
if action == _Action.FINISH:
continue
if action == _Action.ERROR_CLOSED:
raise RendezvousClosedError()
if action == _Action.ERROR_TIMEOUT:
raise RendezvousTimeoutError()
if action == _Action.SYNC:
# Delay the execution by one second to avoid overloading the
# backend if we are asked to poll for state changes.
_delay(seconds=1)
else:
if action == _Action.KEEP_ALIVE:
self._keep_alive()
elif action == _Action.ADD_TO_PARTICIPANTS:
self._add_to_participants()
elif action == _Action.ADD_TO_WAIT_LIST:
self._add_to_wait_list()
elif action == _Action.ADD_TO_REDUNDANCY_LIST:
self._add_to_redundancy_list()
elif action == _Action.REMOVE_FROM_PARTICIPANTS:
self._remove_from_participants()
elif action == _Action.REMOVE_FROM_WAIT_LIST:
self._remove_from_wait_list()
elif action == _Action.REMOVE_FROM_REDUNDANCY_LIST:
self._remove_from_redundancy_list()
# update deadline since the node may participate in rendezvous process
if update_deadline:
deadline = update_deadline(self._settings.timeout.join)
elif action == _Action.MARK_RENDEZVOUS_COMPLETE:
self._mark_rendezvous_complete()
elif action == _Action.MARK_RENDEZVOUS_CLOSED:
self._mark_rendezvous_closed()
# Attempt to sync our changes back to other nodes.
self._state_holder.mark_dirty()
def _keep_alive(self) -> None:
msg = (
f"The node '{self._node}' updated its keep-alive heartbeat time for the rendezvous "
f"'{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
self._state.last_heartbeats[self._node] = datetime.utcnow()
def _add_to_participants(self) -> None:
msg = (
f"The node '{self._node}' added itself to the participants of round "
f"{self._state.round} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
state = self._state
try:
state.wait_list.remove(self._node)
except KeyError:
pass
# The ranks of the participants will be set once the rendezvous is
# complete.
state.participants[self._node] = 0
self._keep_alive()
if len(state.participants) == self._settings.min_nodes:
state.deadline = datetime.utcnow() + self._settings.timeout.last_call
if len(state.participants) == self._settings.max_nodes:
self._mark_rendezvous_complete()
def _add_to_wait_list(self) -> None:
msg = (
f"The node '{self._node}' added itself to the wait list of round "
f"{self._state.round + 1} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
if self._node in self._state.redundancy_list:
self._state.redundancy_list.remove(self._node)
self._state.wait_list.add(self._node)
self._keep_alive()
def _add_to_redundancy_list(self) -> None:
msg = (
f"The node '{self._node}' added itself to the redundancy list of round "
f"{self._state.round + 1} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
self._state.redundancy_list.add(self._node)
self._keep_alive()
def _remove_from_participants(self) -> None:
msg = (
f"The node '{self._node}' removed itself from the participants of round "
f"{self._state.round} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
state = self._state
del state.participants[self._node]
del state.last_heartbeats[self._node]
# Common epilogue shared with the sanitizer() function of
# _BackendRendezvousStateHolder.
_remove_participant_epilogue(state, self._settings)
def _remove_from_wait_list(self) -> None:
msg = (
f"The node '{self._node}' removed itself from the wait list of round "
f"{self._state.round + 1} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
self._state.wait_list.remove(self._node)
del self._state.last_heartbeats[self._node]
def _remove_from_redundancy_list(self) -> None:
msg = (
f"The node '{self._node}' removed itself from the redunant list of round "
f"{self._state.round + 1} of the rendezvous '{self._settings.run_id}'. Pending sync."
)
self._record(message=msg)
log.debug(msg)
self._state.redundancy_list.remove(self._node)
del self._state.last_heartbeats[self._node]
def _mark_rendezvous_complete(self) -> None:
msg = (
f"The node '{self._node}' marked round {self._state.round} of the rendezvous "
f"'{self._settings.run_id}' as complete. Pending sync."
)
self._record(message=msg, node_state=NodeState.SUCCEEDED)
log.debug(msg)
state = self._state
state.complete = True
state.deadline = None
# Assign the ranks.
for rank, node in enumerate(sorted(state.participants)):
state.participants[node] = rank
def _mark_rendezvous_closed(self) -> None:
msg = (
f"The node '{self._node}' marked the rendezvous '{self._settings.run_id}' as closed. "
"Pending sync."
)
self._record(message=msg, node_state=NodeState.SUCCEEDED)
log.debug(msg)
self._state.closed = True
def _should_keep_alive(ctx: _RendezvousContext) -> bool:
"""Determine whether a keep-alive heartbeat should be sent."""
try:
last_heartbeat = ctx.state.last_heartbeats[ctx.node]
except KeyError:
return False
return last_heartbeat <= datetime.utcnow() - ctx.settings.keep_alive_interval
class _RendezvousExitOp:
"""Represent a rendezvous exit operation."""
def __call__(self, ctx: _RendezvousContext, deadline: float) -> _Action:
if ctx.node in ctx.state.participants:
if time.monotonic() > deadline:
return _Action.ERROR_TIMEOUT
return _Action.REMOVE_FROM_PARTICIPANTS
return _Action.FINISH
class _RendezvousJoinOp:
"""Represent a rendezvous join operation."""
def __call__(self, ctx: _RendezvousContext, deadline: float) -> _Action:
state = ctx.state
# A closed rendezvous means that it no longer accepts new nodes.
if state.closed:
if ctx.node in state.redundancy_list:
msg = f"The rendezvous '{ctx.settings.run_id}' is closed, terminating pending rendezvous."
raise RendezvousGracefulExitError(msg)
return _Action.ERROR_CLOSED
if ctx.node in state.redundancy_list:
msg = f"The node {ctx.node} is in redunancy list"
log.debug(msg)
# don't apply the timeout logic here, since we want to allow the node to rejoin
if len(state.participants) == ctx.settings.max_nodes:
if _should_keep_alive(ctx):
return _Action.KEEP_ALIVE
else:
return _Action.SYNC
else:
# transition to waiting state that will respect timeouts.
msg = f"The node {ctx.node} is removed from redunancy list"
log.debug(msg)
return _Action.REMOVE_FROM_REDUNDANCY_LIST
is_participant = ctx.node in state.participants
# If we are part of the rendezvous and it is already complete there is
# no further action to take.
if state.complete and is_participant:
return _Action.FINISH
now = time.monotonic()
if now > deadline:
rollback_period = 5 # 5 seconds
# If we still have time to rollback (a short period on top of the
# operation deadline), try to remove ourself from the rendezvous.
# It is okay if we can't though as our keep-alive will eventually
# expire.
if now <= deadline + rollback_period:
# If we are part of the rendezvous, it means we couldn't find
# enough participants to complete it on time.
if is_participant:
return _Action.REMOVE_FROM_PARTICIPANTS
# If we are in the wait list, it means we couldn't wait till the
# next round of the rendezvous.
if ctx.node in state.wait_list:
return _Action.REMOVE_FROM_WAIT_LIST
return _Action.ERROR_TIMEOUT
if state.complete:
# If we are here, it means we are not part of the rendezvous. In
# case the rendezvous has capacity for additional participants add
# ourself to the wait list for the next round.
if len(state.participants) < ctx.settings.max_nodes:
if ctx.node not in state.wait_list:
return _Action.ADD_TO_WAIT_LIST
elif len(state.participants) >= ctx.settings.max_nodes:
if ctx.node not in state.redundancy_list and ctx.node not in state.wait_list:
return _Action.ADD_TO_REDUNDANCY_LIST
elif is_participant:
# If the rendezvous has enough number of participants including us,
# check whether we have passed the rendezvous deadline. If yes,
# complete it.
if len(state.participants) >= ctx.settings.min_nodes and \
len(state.participants) <= ctx.settings.max_nodes:
if cast(datetime, state.deadline) < datetime.utcnow():
msg = (
f"The node '{ctx.node}' marking the rendezvous complete, "
f"quorum established within deadline"
)
log.debug(msg)
return _Action.MARK_RENDEZVOUS_COMPLETE
else:
msg = f"The node '{ctx.node}' can't complete rendezvous: deadline reached"
log.debug(msg)
else:
msg = f"The node '{ctx.node}' can't complete rendezvous: not enough participants"
log.debug(msg)
else:
# The rendezvous is not complete yet and we are not part of it. Try
# to join.
return _Action.ADD_TO_PARTICIPANTS
if _should_keep_alive(ctx):
return _Action.KEEP_ALIVE
# At this point either the rendezvous is not complete, but we are part
# of it, which means we have to wait for other participants to join; or
# the rendezvous is complete, but we are not part of it, which means we
# have to wait for the next round.
return _Action.SYNC
class _RendezvousCloseOp:
"""Represent a rendezvous close operation."""
def __call__(self, ctx: _RendezvousContext, deadline: float) -> _Action:
if ctx.state.closed:
return _Action.FINISH
if time.monotonic() > deadline:
return _Action.ERROR_TIMEOUT
return _Action.MARK_RENDEZVOUS_CLOSED
class _RendezvousKeepAliveOp:
"""Represent a rendezvous keep-alive update operation."""
def __call__(self, ctx: _RendezvousContext, deadline: float) -> _Action:
if _should_keep_alive(ctx):
if time.monotonic() > deadline:
return _Action.ERROR_TIMEOUT
return _Action.KEEP_ALIVE
return _Action.FINISH
[docs]class DynamicRendezvousHandler(RendezvousHandler):
"""Represent a handler that sets up a rendezvous among a set of nodes."""
# Static
_node_desc_generator = _NodeDescGenerator()
_this_node: _NodeDesc
_settings: RendezvousSettings
_backend_name: str
_store: Store
_state_holder: _RendezvousStateHolder
_op_executor: _RendezvousOpExecutor
_heartbeat_lock: threading.Lock
_keep_alive_timer: Optional[_PeriodicTimer]
[docs] @classmethod
def from_backend(
cls,
run_id: str,
store: Store,
backend: RendezvousBackend,
min_nodes: int,
max_nodes: int,
local_addr: Optional[str] = None,
timeout: Optional[RendezvousTimeout] = None,
):
"""Create a new :py:class:`DynamicRendezvousHandler`.
Args:
run_id:
The run id of the rendezvous.
store:
The C10d store to return as part of the rendezvous.
backend:
The backend to use to hold the rendezvous state.
min_nodes:
The minimum number of nodes to admit to the rendezvous.
max_nodes:
The maximum number of nodes to admit to the rendezvous.
local_addr:
The local node address.
timeout:
The timeout configuration of the rendezvous.
"""
# We associate each handler instance with a unique node descriptor.
node = cls._node_desc_generator.generate(local_addr)
settings = RendezvousSettings(
run_id,
min_nodes,
max_nodes,
timeout or RendezvousTimeout(),
keep_alive_interval=timedelta(seconds=5),
keep_alive_max_attempt=3,
)
state_holder = _BackendRendezvousStateHolder(backend, settings)
return cls(node, settings, backend.name, store, state_holder)
def __init__(
self,
node: _NodeDesc,
settings: RendezvousSettings,
backend_name: str,
store: Store,
state_holder: _RendezvousStateHolder,
) -> None:
if not settings.run_id:
raise ValueError("The run id must be a non-empty string.")
if settings.min_nodes < 1:
raise ValueError(
f"The minimum number of nodes ({settings.min_nodes}) must be greater than zero."
)
if settings.max_nodes < settings.min_nodes:
raise ValueError(
f"The maximum number of nodes ({settings.max_nodes}) must be greater than or equal "
f"to the minimum number of nodes ({settings.min_nodes})."
)
self._this_node = node
self._settings = settings
self._backend_name = backend_name
self._store = store
self._state_holder = state_holder
self._op_executor = _DistributedRendezvousOpExecutor(
self._this_node, self._state_holder, self._settings
)
self._heartbeat_lock = threading.Lock()
self._keep_alive_timer = None
def _record(
self,
message: str,
node_state: NodeState = NodeState.RUNNING,
rank: Optional[int] = None,
) -> None:
construct_and_record_rdzv_event(
name=f"{self.__class__.__name__}.{get_method_name()}",
run_id=self._settings.run_id,
message=message,
node_state=node_state,
hostname=self._this_node.addr,
pid=self._this_node.pid,
local_id=self._this_node.local_id,
rank=rank,
)
@property
def settings(self) -> RendezvousSettings:
"""Get the settings of the rendezvous."""
return self._settings
def get_backend(self) -> str:
"""See base class."""
return self._backend_name
def next_rendezvous(self) -> Tuple[Store, int, int]:
"""See base class."""
msg = (
f"The node '{self._this_node}' attempts to join the next round of the rendezvous "
f"'{self._settings.run_id}'."
)
self._record(message=msg)
log.info(msg)
try:
self._stop_heartbeats()
# Delay the execution for a small random amount of time if this is our
# first run. This will slightly skew the rendezvous attempts across the
# nodes and reduce the load on the backend.
if self._state_holder.state.round == 0:
_delay(seconds=(0, 0.3))
exit_op = _RendezvousExitOp()
join_op = _RendezvousJoinOp()
deadline = self._get_deadline(self._settings.timeout.join)
self._op_executor.run(exit_op, deadline)
self._op_executor.run(
join_op,
deadline,
self._get_deadline)
self._start_heartbeats()
rank, world_size = self._get_world()
store = self._get_store()
except Exception as e:
self._record(
message=f"{type(e).__name__}: {str(e)}",
node_state=NodeState.FAILED,
)
raise
msg = (
f"The node '{self._this_node}' has joined round {self._state_holder.state.round} of "
f"the rendezvous '{self._settings.run_id}' as rank {rank} in a world of size "
f"{world_size}."
)
self._record(message=msg, rank=rank)
log.info(msg)
return store, rank, world_size
def is_closed(self) -> bool:
"""See base class."""
try:
with self._heartbeat_lock:
self._state_holder.sync()
return self._state_holder.state.closed
except Exception as e:
self._record(
message=f"{type(e).__name__}: {str(e)}",
node_state=NodeState.FAILED,
)
raise
def set_closed(self) -> None:
"""See base class."""
try:
with self._heartbeat_lock:
self._close()
except Exception as e:
self._record(
message=f"{type(e).__name__}: {str(e)}",
node_state=NodeState.FAILED,
)
raise
def num_nodes_waiting(self) -> int:
"""See base class."""
try:
with self._heartbeat_lock:
self._state_holder.sync()
return len(self._state_holder.state.wait_list)
except Exception as e:
self._record(
message=f"{type(e).__name__}: {str(e)}",
node_state=NodeState.FAILED,
)
raise
def get_run_id(self) -> str:
"""See base class."""
return self._settings.run_id
def shutdown(self) -> bool:
"""See base class."""
self._stop_heartbeats()
try:
self._close()
return True
except RendezvousError as ex:
msg = (
f"The node '{self._this_node}' has failed to shutdown the rendezvous "
f"'{self._settings.run_id}' due to an error of type {type(ex).__name__}."
)
self._record(message=msg, node_state=NodeState.FAILED)
log.warning(msg)
return False
except Exception as e:
self._record(
message=f"{type(e).__name__}: {str(e)}",
node_state=NodeState.FAILED,
)
raise
def _close(self) -> None:
op = _RendezvousCloseOp()
deadline = self._get_deadline(self._settings.timeout.close)
self._op_executor.run(op, deadline)
msg = f"The node '{self._this_node}' has closed the rendezvous '{self._settings.run_id}'."
self._record(message=msg, node_state=NodeState.SUCCEEDED)
log.info(msg)
@staticmethod
def _keep_alive_weak(weak_self) -> None:
self = weak_self()
if self is not None:
self._keep_alive()
def _keep_alive(self) -> None:
self._heartbeat_lock.acquire()
op = _RendezvousKeepAliveOp()
deadline = self._get_deadline(self._settings.timeout.heartbeat)
try:
self._op_executor.run(op, deadline)
msg = (
f"The node '{self._this_node}' has sent a keep-alive heartbeat to the rendezvous "
f"'{self._settings.run_id}'."
)
self._record(message=msg)
log.debug(msg)
except RendezvousError as ex:
msg = (
f"The node '{self._this_node}' has failed to send a keep-alive heartbeat to the "
f"rendezvous '{self._settings.run_id}' due to an error of type {type(ex).__name__}."
)
self._record(message=msg, node_state=NodeState.FAILED)
log.warning(msg)
finally:
self._heartbeat_lock.release()
def _start_heartbeats(self) -> None:
self._keep_alive_timer = _PeriodicTimer(
self._settings.keep_alive_interval, self._keep_alive_weak, weakref.ref(self)
)
self._keep_alive_timer.set_name(f"RendezvousKeepAliveTimer_{self._this_node.local_id}")
self._keep_alive_timer.start()
def _stop_heartbeats(self) -> None:
if self._keep_alive_timer is None:
return
self._keep_alive_timer.cancel()
def _get_world(self) -> Tuple[int, int]:
state = self._state_holder.state
return state.participants[self._this_node], len(state.participants)
def _get_store(self) -> Store:
key_prefix = f"torch.rendezvous.{self._settings.run_id}.{self._state_holder.state.round}"
return PrefixStore(key_prefix, self._store)
def _get_deadline(self, timeout: timedelta) -> float:
return time.monotonic() + timeout.total_seconds()
def _get_timeout(params: RendezvousParameters, key: str) -> Optional[timedelta]:
timeout = params.get_as_int(key + "_timeout")
if timeout is None:
return None
return timedelta(seconds=timeout)
[docs]def create_handler(
store: Store, backend: RendezvousBackend, params: RendezvousParameters
) -> DynamicRendezvousHandler:
"""Create a new :py:class:`DynamicRendezvousHandler` from the specified parameters.
Args:
store:
The C10d store to return as part of the rendezvous.
backend:
The backend to use to hold the rendezvous state.
+-------------------+------------------------------------------------------+
| Parameter | Description |
+===================+======================================================+
| join_timeout | The total time, in seconds, within which the |
| | rendezvous is expected to complete. Defaults to 600 |
| | seconds. |
+-------------------+------------------------------------------------------+
| last_call_timeout | An additional wait amount, in seconds, before |
| | completing the rendezvous once the minimum number of |
| | nodes has been reached. Defaults to 30 seconds. |
+-------------------+------------------------------------------------------+
| close_timeout | The time, in seconds, within which the rendezvous is |
| | expected to close after a call to |
| | :py:meth:`RendezvousHandler.set_closed` or |
| | :py:meth:`RendezvousHandler.shutdown`. Defaults to |
| | 30 seconds. |
+-------------------+------------------------------------------------------+
"""
try:
timeout = RendezvousTimeout(
_get_timeout(params, "join"),
_get_timeout(params, "last_call"),
_get_timeout(params, "close"),
)
return DynamicRendezvousHandler.from_backend(
params.run_id,
store,
backend,
params.min_nodes,
params.max_nodes,
params.local_addr,
timeout,
)
except Exception as e:
construct_and_record_rdzv_event(
message=f"{type(e).__name__}: {str(e)}",
run_id=params.run_id,
node_state=NodeState.FAILED,
)
raise
