"""Guard for running certain operations on main process only
Authors:
* Abdel Heba 2020
* Aku Rouhe 2020
* Peter Plantinga 2023
* Adel Moumen 2024
"""
import datetime
import os
from functools import wraps
from typing import Optional
import torch
MAIN_PROC_ONLY: int = 0
NODE_ONCE_ONLY: int = 0
[docs]
def rank_prefixed_message(message: str) -> str:
r"""Prefix a message with the rank of the process.
Arguments
---------
message : str
The message to prefix.
Returns
-------
str
The message prefixed with the rank, if known.
"""
rank = get_rank()
if rank is not None:
return f"[rank: {rank}] {message}"
return message
[docs]
def get_rank() -> Optional[int]:
r"""Get the rank of the current process.
This code is taken from the Pytorch Lightning library:
https://github.com/Lightning-AI/pytorch-lightning/blob/bc3c9c536dc88bfa9a46f63fbce22b382a86a9cb/src/lightning/fabric/utilities/rank_zero.py#L39-L48
Returns
-------
int or None
The rank of the current process, or None if the rank could not be determined.
"""
# SLURM_PROCID can be set even if SLURM is not managing the multiprocessing,
# therefore LOCAL_RANK needs to be checked first
rank_keys = ("RANK", "LOCAL_RANK", "SLURM_PROCID", "JSM_NAMESPACE_RANK")
for key in rank_keys:
rank = os.environ.get(key)
if rank is not None:
return int(rank)
# None to differentiate whether an environment variable was set at all
return None
[docs]
def get_local_rank() -> Optional[int]:
r"""Get the local rank of the current process on the current node.
Returns
-------
int or None
The local rank of the current process, or None if the local rank could not be determined.
"""
rank_keys = ["LOCAL_RANK"]
for key in rank_keys:
rank = os.environ.get(key)
if rank is not None:
return int(rank)
# None to differentiate whether an environment variable was set at all
return None
[docs]
def infer_device() -> str:
"""Make a basic guess about intended running device based on
availability and distributed environment variable 'LOCAL_RANK'"""
if torch.cuda.is_available():
device = "cuda"
local_rank = get_local_rank()
if local_rank is not None:
device += f":{local_rank}"
else:
device = "cpu"
return device
[docs]
def run_on_main(
func,
args=None,
kwargs=None,
post_func=None,
post_args=None,
post_kwargs=None,
run_post_on_main=False,
):
r"""Runs a function with DPP (multi-gpu) support.
The main function is only run on the main process.
A post_function can be specified, to be on non-main processes after the main
func completes. This way whatever the main func produces can be loaded on
the other processes.
Arguments
---------
func : callable
Function to run on the main process.
args : list, None
Positional args to pass to func.
kwargs : dict, None
Keyword args to pass to func.
post_func : callable, None
Function to run after func has finished on main. By default only run on
non-main processes.
post_args : list, None
Positional args to pass to post_func.
post_kwargs : dict, None
Keyword args to pass to post_func.
run_post_on_main : bool
Whether to run post_func on main process as well. (default: False)
Returns
-------
On all processes: the value that func returned, when it ran on the main
process.
"""
# Handle the mutable data types' default args:
if args is None:
args = []
if kwargs is None:
kwargs = {}
if post_args is None:
post_args = []
if post_kwargs is None:
post_kwargs = {}
result = main_process_only(func)(*args, **kwargs)
ddp_barrier()
if post_func is not None:
if run_post_on_main:
# Just run on every process without any barrier.
post_func(*post_args, **post_kwargs)
else:
# Do the opposite of `run_on_main`
if not if_main_process():
post_func(*post_args, **post_kwargs)
ddp_barrier()
return result
[docs]
def run_once_per_node(
func,
args=None,
kwargs=None,
post_func=None,
post_args=None,
post_kwargs=None,
run_post_on_all=False,
):
r"""Runs a function with DPP (multi-gpu) support.
The provided function `func` is only run once on each node, while other processes
block to wait for the function execution to finish. This is useful for things such
as saving a file to the disk on each separate node (i.e. the filesystems are separate).
In addition, a second function can be specified to be run on other processes after the
first function completes, for example, loading a file that was created on each node.
Arguments
---------
func : callable
Function to be run once on each node.
args : list, None
Positional args to pass to func.
kwargs : dict, None
Keyword args to pass to func.
post_func : callable, None
Function to run after `func` has finished. By default, `post_func` is not run
on the process that ran `func`.
post_args : list, None
Positional args to pass to post_func.
post_kwargs : dict, None
Keyword args to pass to post_func.
run_post_on_all : bool
Whether to run post_func on all processes, including the process that ran `func`.
Returns
-------
If `post_func` is provided, returns the result on all processes where `post_func` is run.
If `run_post_on_all` is `False` or `post_func` is not provided, returns the result of `func` on the processes where it is run.
If `post_func` is not provided, returns `None` on processes where `func` was not called.
Example
-------
>>> tmpfile = getfixture("tmpdir") / "example.pt"
>>> # Return tensor so we don't have to load it on the saving process
>>> def save_and_return(file, tensor):
... torch.save(tensor, file)
... return tensor
>>> # Load tensor on non-saving processes
>>> def load_tensor(file):
... return torch.load(file)
>>> # Save on node-primary processes, load on others
>>> example_tensor = torch.ones(5)
>>> loaded_tensor = run_once_per_node(
... func=save_and_return,
... args=[tmpfile, example_tensor],
... post_func=load_tensor,
... post_args=[tmpfile],
... run_post_on_all=False,
... )
>>> # We should get the same result on all processes
>>> loaded_tensor
tensor([1., 1., 1., 1., 1.])
"""
# Handle the mutable data types' default args:
args = args or []
kwargs = kwargs or {}
post_args = post_args or []
post_kwargs = post_kwargs or {}
# Call the function exactly once per node, wait on other processes
result = once_per_node(func)(*args, **kwargs)
ddp_barrier()
# Call the post function if provided
if post_func is not None:
if run_post_on_all:
# Just run on every process without any barrier.
result = post_func(*post_args, **post_kwargs)
else:
# Do the opposite of `once_per_node` and await result
if not is_local_rank_zero():
result = post_func(*post_args, **post_kwargs)
ddp_barrier()
return result
[docs]
def is_distributed_initialized() -> bool:
r"Returns whether the current system is distributed."
# `is_initialized` is only defined conditionally
# https://github.com/pytorch/pytorch/blob/v2.1.0/torch/distributed/__init__.py#L25
# this might happen to MacOS builds from source (default) or any build from source that sets `USE_DISTRIBUTED=0`
return (
torch.distributed.is_available() and torch.distributed.is_initialized()
)
[docs]
def if_main_process() -> bool:
r"Returns whether the current process is the main process."
return not is_distributed_initialized() or get_rank() == 0
[docs]
def is_local_rank_zero() -> bool:
r"Returns whether the current process has local rank of 0."
return not is_distributed_initialized() or get_local_rank() == 0
[docs]
class MainProcessContext:
r"""
Context manager to ensure code runs only on the main process.
This is useful to make sure that `MAIN_PROC_ONLY` global variable
is decreased even if there's an exception raised inside of
`main_proc_wrapped_func` fn.
"""
[docs]
def __enter__(self):
r"""Enter the context. Increase the counter."""
global MAIN_PROC_ONLY
MAIN_PROC_ONLY += 1
return self
[docs]
def __exit__(self, exc_type, exc_value, traceback):
r"""Exit the context. Decrease the counter."""
global MAIN_PROC_ONLY
MAIN_PROC_ONLY -= 1
[docs]
class OncePerNodeContext:
r"""
Context manager to ensure code runs only once per node.
This is useful to make sure that `NODE_ONCE_ONLY` global variable
is decreased even if there's an exception raised inside of the
`once_per_node_wrapped_fn` function.
"""
[docs]
def __enter__(self):
r"""Enter the context. Increase the counter."""
global NODE_ONCE_ONLY
NODE_ONCE_ONLY += 1
return self
[docs]
def __exit__(self, exc_type, exc_value, traceback):
r"""Exit the context. Decrease the counter."""
global NODE_ONCE_ONLY
NODE_ONCE_ONLY -= 1
[docs]
def main_process_only(function):
r"""Function decorator to ensure the function runs only on the main process.
This is useful for things like saving to the filesystem or logging
to a web address where you only want it to happen on a single process.
The function will return the result computed on the main process to all
processes.
"""
@wraps(function)
def main_proc_wrapped_func(*args, **kwargs):
"""This decorated function runs only if this is the main process."""
with MainProcessContext():
if if_main_process():
result = function(*args, **kwargs)
else:
result = None
return ddp_broadcast(result)
return main_proc_wrapped_func
[docs]
def once_per_node(function):
r"""Function decorator to ensure the function runs only once per node.
This is useful for things like saving to the filesystem
where you only want it to happen on a single process on each node.
Unlike `main_process_only`, no broadcasting is done. Instead, processes
with local_rank == 0 keep their own result, all other processes
return None.
"""
@wraps(function)
def once_per_node_wrapped_fn(*args, **kwargs):
"""This decorated function runs only if this is the main process."""
with OncePerNodeContext():
if is_local_rank_zero():
return function(*args, **kwargs)
else:
return None
return once_per_node_wrapped_fn
[docs]
def ddp_prevent_block():
r"Prevent blocking because only one or partial threads running."
return (
MAIN_PROC_ONLY >= 1
or NODE_ONCE_ONLY >= 1
or not is_distributed_initialized()
)
[docs]
def ddp_barrier():
r"""
Synchronize all processes in distributed data parallel (DDP) mode.
This function blocks the execution of the current process until all
processes in the distributed group have reached the same point. It ensures
that no process moves ahead until every other process has also reached this
barrier. If DDP is not being used (i.e., only one process is running),
this function has no effect and immediately returns.
Returns
-------
None
Example
-------
>>> ddp_barrier()
>>> print("hello world")
hello world
"""
if ddp_prevent_block():
return
if torch.distributed.get_backend() == torch.distributed.Backend.NCCL:
torch.distributed.barrier(device_ids=[torch.cuda.current_device()])
else:
torch.distributed.barrier()
[docs]
def ddp_broadcast(communication_object, src=0):
r"""In DDP mode, this function will broadcast an object to all
processes.
Arguments
---------
communication_object: Any
The object to be communicated to all processes. Must be picklable.
See docs for ``torch.distributed.broadcast_object_list()``
src: int
The rank which holds the object to be communicated.
Returns
-------
The communication_object passed on rank src.
"""
if ddp_prevent_block():
return communication_object
# Wrapping object in a list is required for preventing
# a copy of the object, maintaining a pointer instead
communication_list = [communication_object]
torch.distributed.broadcast_object_list(communication_list, src=src)
return communication_list[0]
[docs]
def ddp_all_reduce(communication_object, reduce_op):
r"""In DDP mode, this function will perform an all_reduce operation with the
specified torch operator.
See: https://pytorch.org/docs/stable/distributed.html#torch.distributed.all_reduce
Arguments
---------
communication_object: Any
The object to be reduced across processes.
reduce_op: torch.distributed.ReduceOp
The operation to perform. E.g. include torch.distributed.ReduceOp.AVG or
torch.distributed.ReduceOp.SUM. See the Torch documentation for more.
Returns
-------
The communication_object once reduced (or itself if DDP not initialised)
"""
# If DDP not initialised or executed with a main process barrier
if ddp_prevent_block():
return communication_object
torch.distributed.all_reduce(communication_object, op=reduce_op)
return communication_object
[docs]
def ddp_init_group(run_opts):
r"""This function will initialize the ddp group if
distributed_launch bool is given in the python command line.
The ddp group will use distributed_backend arg for setting the
DDP communication protocol. `RANK` Unix variable will be used for
registering the subprocess to the ddp group.
Arguments
---------
run_opts: list
A list of arguments to parse, most often from `sys.argv[1:]`.
Returns
-------
None
"""
rank = get_rank()
local_rank = get_local_rank()
if local_rank is None or rank is None:
return
if not run_opts["distributed_backend"] == "gloo":
if local_rank + 1 > torch.cuda.device_count():
raise ValueError(
"Killing process " + "" + "\nNot enough GPUs available!"
)
rank = int(rank)
if run_opts["distributed_backend"] == "nccl":
if not torch.distributed.is_nccl_available():
raise ValueError("NCCL is not supported in your machine.")
elif run_opts["distributed_backend"] == "gloo":
if not torch.distributed.is_gloo_available():
raise ValueError("GLOO is not supported in your machine.")
elif run_opts["distributed_backend"] == "mpi":
if not torch.distributed.is_mpi_available():
raise ValueError("MPI is not supported in your machine.")
else:
raise ValueError(
run_opts["distributed_backend"]
+ " communication protocol doesn't exist."
)
if run_opts["distributed_backend"] == "nccl":
device = torch.device(f"cuda:{local_rank}")
torch.cuda.set_device(device)
# rank arg is used to set the right rank of the current process for ddp.
# if you have 2 servers with 2 gpu:
# server1:
# GPU0: local_rank=device=0, rank=0
# GPU1: local_rank=device=1, rank=1
# server2:
# GPU0: local_rank=device=0, rank=2
# GPU1: local_rank=device=1, rank=3
torch.distributed.init_process_group(
backend=run_opts["distributed_backend"],
rank=rank,
timeout=datetime.timedelta(seconds=7200),
)