Add fault tolerance Streaming Dataset 2/n (#19052)

Co-authored-by: thomas <[email protected]>

Author: tchaton

src/lightning/data/streaming/cache.py

@@ -26,7 +26,7 @@
 from lightning.data.streaming.sampler import ChunkedIndex
 from lightning.data.streaming.serializers import Serializer
 from lightning.data.streaming.writer import BinaryWriter
-from lightning.data.utilities.env import _DistributedEnv
+from lightning.data.utilities.env import _DistributedEnv, _WorkerEnv
 from lightning.data.utilities.format import _convert_bytes_to_int
 
 logger = logging.Logger(__name__)
@@ -93,10 +93,15 @@ def __init__(
         )
         self._is_done = False
         self._distributed_env = _DistributedEnv.detect()
+        self._rank: Optional[int] = None
 
     @property
     def rank(self) -> int:
-        return self._reader.rank
+        """Returns the rank of the Cache."""
+        if self._rank is None:
+            self._worker_env = _WorkerEnv.detect()
+            self._rank = self._distributed_env.global_rank * self._worker_env.world_size + self._worker_env.rank
+        return self._rank
 
     @property
     def filled(self) -> bool:
@@ -109,16 +114,16 @@ def filled(self) -> bool:
     @property
     def checkpoint_dir(self) -> str:
         checkpoint_dir = os.path.join(self._cache_dir, "checkpoints")
-        if not os.path.exists(checkpoint_dir):
-            os.makedirs(checkpoint_dir, exist_ok=True)
-        return checkpoint_dir
+        return self._try_create(checkpoint_dir)
 
     @property
     def checkpoint_rank_dir(self) -> str:
-        checkpoint_rank_dir = os.path.join(self.checkpoint_dir, str(self.rank))
-        if not os.path.exists(checkpoint_rank_dir):
-            os.makedirs(checkpoint_rank_dir, exist_ok=True)
-        return checkpoint_rank_dir
+        checkpoint_rank_dir = os.path.join(self._cache_dir, "checkpoints", str(self.rank))
+        return self._try_create(checkpoint_rank_dir)
+
+    def _try_create(self, path: str) -> str:
+        os.makedirs(path, exist_ok=True)
+        return path
 
     def __setitem__(self, index: int, data: Any) -> None:
         """Store an item in the writer."""

src/lightning/data/streaming/dataset.py

@@ -17,15 +17,14 @@
 import shutil
 import sys
 import tempfile
-from copy import deepcopy
 from dataclasses import dataclass
 from datetime import datetime
 from time import time
 from typing import Any, Dict, List, Optional, Union
 
 import numpy as np
 import torch
-from torch.utils.data import IterableDataset
+from torch.utils.data import IterableDataset, get_worker_info
 
 from lightning.data.streaming import Cache
 from lightning.data.streaming.constants import (
@@ -56,7 +55,7 @@ def __init__(
         drop_last: bool = False,
         seed: int = 42,
         serializers: Optional[Dict[str, Serializer]] = None,
-        checkpoint_interval: int = 60 * 5,
+        checkpoint_interval: Optional[int] = None,
     ) -> None:
         """The streaming dataset can be used once your data have been optimised using the DatasetOptimiser class.
 
@@ -93,15 +92,19 @@ def __init__(
         self.worker_intervals: List[List[int]] = []
         self.current_indexes: List[int] = []
         self.chunk_index = 0
+        self.num_chunks: Optional[int] = None
         self.global_index = 0
         self.index = 0
         self.has_triggered_download = False
         self.min_items_per_replica: Optional[int] = None
-        self.current_epoch = 0
+        self.current_epoch = 1
         self.random_state = None
         self.shuffler: Optional[Shuffle] = None
         self.serializers = serializers
-        self.checkpoint_interval = checkpoint_interval
+        if sys.platform == "win32":
+            if checkpoint_interval is not None:
+                raise ValueError("The argument `checkpoint_interval` isn't suported on Windows.")
+        self.checkpoint_interval = checkpoint_interval or 60
         self._state_dict: Optional[Dict[str, Dict[str, Any]]] = None
 
     def _create_cache(self, worker_env: _WorkerEnv) -> Cache:
@@ -170,14 +173,16 @@ def __iter__(self) -> "StreamingDataset":
             self.worker_chunks.append(chunk_index)
             self.worker_intervals.append(chunk_interval)
 
+        self.num_chunks = len(self.worker_chunks)
+
         # Handle restart
         if self._state_dict:
             state = self._state_dict[str(self.cache.rank)]
 
             # re-generate indexes
             interval = self.worker_intervals[self.chunk_index]
             current_indexes = np.arange(interval[0], interval[1])
-            current_indexes = self.shuffler(current_indexes, self.current_epoch, self.chunk_index)
+            current_indexes = self.shuffler(current_indexes, self.num_chunks, self.current_epoch, self.chunk_index)
             self.current_indexes = current_indexes[state["index"] :]
 
             # Bump the chunk_index
@@ -210,21 +215,22 @@ def __next__(self) -> Any:
 
         # Lazily re-populate the interval to reduce memory usage.
         if len(self.current_indexes) == 0:
-            if self.chunk_index == len(self.worker_intervals):
+            if self.chunk_index == self.num_chunks:
                 self.current_epoch += 1
                 raise StopIteration
 
             # reset index
             self.index = 0
 
             # Checkpoint when reaching a new chunk
-            self.checkpoint(self.chunk_index)
+            self._checkpoint(self.chunk_index)
 
             interval = self.worker_intervals[self.chunk_index]
             current_indexes = np.arange(interval[0], interval[1])
 
             assert self.shuffler is not None
-            self.current_indexes = self.shuffler(current_indexes, self.current_epoch, self.chunk_index)
+            assert self.num_chunks is not None
+            self.current_indexes = self.shuffler(current_indexes, self.num_chunks, self.current_epoch, self.chunk_index)
 
             self.chunk_index += 1
 
@@ -238,7 +244,7 @@ def __next__(self) -> Any:
                 chunk_index=self.worker_chunks[self.chunk_index - 1],
                 # We provide the chunks indexes only one the first
                 chunk_indexes=None if self.has_triggered_download else self.worker_chunks,
-                last_index=(self.chunk_index - 1) == len(self.worker_intervals) and len(self.current_indexes) == 1,
+                is_last_index=(self.chunk_index - 1) == len(self.worker_intervals) and len(self.current_indexes) == 1,
             )
         )
 
@@ -247,14 +253,16 @@ def __next__(self) -> Any:
         self.index += 1
 
         # Checkpoint based on time
-        if (self.last_time - time()) > self.checkpoint_interval:
-            self.checkpoint(self.chunk_index - 1)
+        if self.checkpoint_interval and (self.last_time - time()) > self.checkpoint_interval:
+            self._checkpoint(self.chunk_index - 1)
 
         return data
 
-    def checkpoint(self, chunk_index: int) -> None:
-        # Checkpointing isn't supported for windows
-        if sys.platform == "win32":
+    def _checkpoint(self, chunk_index: int) -> None:
+        if self.checkpoint_interval is None:
+            return
+
+        if not _is_in_dataloader_worker():
             return
 
         assert self.cache
@@ -284,55 +292,29 @@ def checkpoint(self, chunk_index: int) -> None:
                     f,
                 )
 
-            # 3. Move the file to avoid corrupted read from the main thread.
-            now = datetime.now().strftime(_TIME_FORMAT)
-            checkpoint_path = os.path.join(self.cache.checkpoint_rank_dir, f"checkpoint-{now}.json")
-
             # 4. Move the file to its target position
-            shutil.move(tmp_checkpoint_path, checkpoint_path)
+            shutil.move(tmp_checkpoint_path, os.path.join(self.cache.checkpoint_rank_dir, "checkpoint.json"))
 
         self.last_time = time()
 
     def state_dict(self) -> Dict[str, Any]:
+        if _is_in_dataloader_worker():
+            raise RuntimeError("The method `state_dict` should only be called in the main process.")
+
         if self.cache is None:
             self.worker_env = _WorkerEnv.detect()
             self.cache = self._create_cache(worker_env=self.worker_env)
 
         state_dict: Dict[str, Any] = {}
-        worker_env = _WorkerEnv.detect()
-        if worker_env.world_size == 1:
-            # 1. Check whether the checkpoint_dir exists
-            if not os.path.exists(self.cache.checkpoint_dir):
-                return state_dict
-
-            # 2. Iterate through the workers and read the latest checkpoint
-            for worker_idx in os.listdir(self.cache.checkpoint_dir):
-                checkpoints = os.listdir(os.path.join(self.cache.checkpoint_dir, str(worker_idx)))
-                checkpoints = sorted(checkpoints, key=_string_to_datetime)
-
-                # Load the latest checkpoint for this worker
-                checkpoint_path = os.path.join(self.cache.checkpoint_dir, str(worker_idx), checkpoints[-1])
-                with open(checkpoint_path) as f:
-                    state_dict[worker_idx] = json.load(f)
-
-            _state_dict = deepcopy(state_dict)
-
-            if self.distributed_env.world_size > 1:
-                # TODO: Move this to fabric.
-                num_devices = torch.cuda.device_count() or 1
-                node_ranks = []
-                for index in range(self.distributed_env.world_size):
-                    node_rank = index // num_devices
-                    if node_rank in node_ranks:
-                        continue
-                    state = {}
-                    obj = [_state_dict]
-                    torch.distributed.broadcast_object_list(obj, index, group=_group.WORLD)
-                    state = obj[0]
-                    state_dict.update(**state)
-                    node_ranks.append(node_rank)
-        else:
-            raise NotImplementedError("The `state_dict` should be called on the main thread.")
+
+        # 1. Check whether the checkpoint_dir exists
+        if not os.path.exists(self.cache.checkpoint_dir):
+            return state_dict
+
+        state_dict = _load_state_dict_from_checkpoint_dir(self.cache.checkpoint_dir)
+
+        if self.distributed_env.world_size > 1:
+            return _collect_distributed_state_dict(state_dict, self.distributed_env.world_size)
         return state_dict
 
     def load_state_dict(self, state_dict: Dict[str, Any]) -> None:
@@ -413,6 +395,42 @@ def _string_to_datetime(item: str) -> datetime:
     return datetime.strptime(item.split("checkpoint-")[1].split(".json")[0], _TIME_FORMAT)
 
 
+def _load_state_dict_from_checkpoint_dir(checkpoint_dir: str) -> Dict[str, Any]:
+    state_dict: Dict[str, Any] = {}
+    if not os.path.exists(checkpoint_dir):
+        return state_dict
+    for worker_idx in os.listdir(checkpoint_dir):
+        checkpoint_filepath = os.path.join(checkpoint_dir, str(worker_idx), "checkpoint.json")
+        if not os.path.exists(checkpoint_filepath):
+            state_dict[worker_idx] = {}
+        else:
+            with open(checkpoint_filepath) as f:
+                state_dict[worker_idx] = json.load(f)
+    return state_dict
+
+
+def _collect_distributed_state_dict(state_dict: Dict[str, Any], world_size: int) -> Dict[str, Any]:
+    state_dict_out: Dict[str, Any] = {}
+    # TODO: Move this to fabric to support all accelerators
+    num_devices = torch.cuda.device_count() or 1
+    node_ranks = []
+    for index in range(world_size):
+        node_rank = index // num_devices
+        if node_rank in node_ranks:
+            continue
+        state = {}
+        obj = [state_dict]
+        torch.distributed.broadcast_object_list(obj, index, group=_group.WORLD)
+        state = obj[0]
+        state_dict_out.update(**state)
+        node_ranks.append(node_rank)
+    return state_dict_out
+
+
+def _is_in_dataloader_worker() -> bool:
+    return get_worker_info() is not None
+
+
 @dataclass
 class RemoteDir:
     """Holds a remote URL to a directory and a cache directory where the data will be downloaded."""

src/lightning/data/streaming/reader.py

@@ -228,7 +228,7 @@ def read(self, index: ChunkedIndex) -> Any:
         chunk_filepath, begin, _ = self.config[index]
         item = self._item_loader.load_item_from_chunk(index.index, index.chunk_index, chunk_filepath, begin)
 
-        if index.last_index and self._prepare_thread:
+        if index.is_last_index and self._prepare_thread:
             self._prepare_thread.stop()
             self._prepare_thread = None
 

src/lightning/data/streaming/sampler.py

@@ -25,7 +25,7 @@ class ChunkedIndex:
     index: int
     chunk_index: int
     chunk_indexes: Optional[List[int]] = None
-    last_index: bool = False
+    is_last_index: bool = False
 
 
 class CacheBatchSampler:

src/lightning/data/streaming/serializers.py

@@ -149,10 +149,10 @@ class TensorSerializer(Serializer):
 
     def __init__(self) -> None:
         super().__init__()
-        self._dtype_to_indice = {v: k for k, v in _TORCH_DTYPES_MAPPING.items()}
+        self._dtype_to_indices = {v: k for k, v in _TORCH_DTYPES_MAPPING.items()}
 
     def serialize(self, item: torch.Tensor) -> Tuple[bytes, Optional[str]]:
-        dtype_indice = self._dtype_to_indice[item.dtype]
+        dtype_indice = self._dtype_to_indices[item.dtype]
         data = [np.uint32(dtype_indice).tobytes()]
         data.append(np.uint32(len(item.shape)).tobytes())
         for dim in item.shape:
@@ -182,14 +182,14 @@ class NoHeaderTensorSerializer(Serializer):
 
     def __init__(self) -> None:
         super().__init__()
-        self._dtype_to_indice = {v: k for k, v in _TORCH_DTYPES_MAPPING.items()}
+        self._dtype_to_indices = {v: k for k, v in _TORCH_DTYPES_MAPPING.items()}
         self._dtype: Optional[torch.dtype] = None
 
     def setup(self, data_format: str) -> None:
         self._dtype = _TORCH_DTYPES_MAPPING[int(data_format.split(":")[1])]
 
     def serialize(self, item: torch.Tensor) -> Tuple[bytes, Optional[str]]:
-        dtype_indice = self._dtype_to_indice[item.dtype]
+        dtype_indice = self._dtype_to_indices[item.dtype]
         return item.numpy().tobytes(order="C"), f"no_header_tensor:{dtype_indice}"
 
     def deserialize(self, data: bytes) -> torch.Tensor:
@@ -205,10 +205,10 @@ class NumpySerializer(Serializer):
 
     def __init__(self) -> None:
         super().__init__()
-        self._dtype_to_indice = {v: k for k, v in _NUMPY_DTYPES_MAPPING.items()}
+        self._dtype_to_indices = {v: k for k, v in _NUMPY_DTYPES_MAPPING.items()}
 
     def serialize(self, item: np.ndarray) -> Tuple[bytes, Optional[str]]:
-        dtype_indice = self._dtype_to_indice[item.dtype]
+        dtype_indice = self._dtype_to_indices[item.dtype]
         data = [np.uint32(dtype_indice).tobytes()]
         data.append(np.uint32(len(item.shape)).tobytes())
         for dim in item.shape:
@@ -221,8 +221,12 @@ def deserialize(self, data: bytes) -> np.ndarray:
         dtype = _NUMPY_DTYPES_MAPPING[dtype_indice]
         shape_size = np.frombuffer(data[4:8], np.uint32).item()
         shape = []
+        # deserialize the shape header
+        # Note: The start position of the shape value: 8 (dtype + shape length) + 4 * shape_idx
         for shape_idx in range(shape_size):
             shape.append(np.frombuffer(data[8 + 4 * shape_idx : 8 + 4 * (shape_idx + 1)], np.uint32).item())
+
+        # deserialize the numpy array bytes
         tensor = np.frombuffer(data[8 + 4 * (shape_idx + 1) : len(data)], dtype=dtype)
         if tensor.shape == shape:
             return tensor
@@ -237,14 +241,14 @@ class NoHeaderNumpySerializer(Serializer):
 
     def __init__(self) -> None:
         super().__init__()
-        self._dtype_to_indice = {v: k for k, v in _NUMPY_DTYPES_MAPPING.items()}
+        self._dtype_to_indices = {v: k for k, v in _NUMPY_DTYPES_MAPPING.items()}
         self._dtype: Optional[np.dtype] = None
 
     def setup(self, data_format: str) -> None:
         self._dtype = _NUMPY_DTYPES_MAPPING[int(data_format.split(":")[1])]
 
     def serialize(self, item: np.ndarray) -> Tuple[bytes, Optional[str]]:
-        dtype_indice: int = self._dtype_to_indice[item.dtype]
+        dtype_indice: int = self._dtype_to_indices[item.dtype]
         return item.tobytes(order="C"), f"no_header_numpy:{dtype_indice}"
 
     def deserialize(self, data: bytes) -> np.ndarray: