refactor: simplify dataset construction (#4437)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced a new function for dataset construction, enhancing data
loading processes.
- Added a method to improve pickling and unpickling capabilities for
path handling classes.

- **Bug Fixes**
- Updated summary printing to prevent redundant output during
distributed training.

- **Refactor**
	- Simplified initialization of the BackgroundConsumer class.
- Streamlined consumer thread and queue handling in the BufferedIterator
class.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Chun Cai <amoycaic@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Han Wang <92130845+wanghan-iapcm@users.noreply.github.com>

deepmd/pt/utils/dataloader.py

@@ -1,11 +1,13 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 import logging
 import os
-import queue
 import time
 from multiprocessing.dummy import (
     Pool,
 )
+from queue import (
+    Queue,
+)
 from threading import (
     Thread,
 )
@@ -204,70 +206,51 @@ def print_summary(
             )
 
 
-_sentinel = object()
-QUEUESIZE = 32
-
-
 class BackgroundConsumer(Thread):
-    def __init__(self, queue, source, max_len) -> None:
-        Thread.__init__(self)
+    def __init__(self, queue, source) -> None:
+        super().__init__()
+        self.daemon = True
         self._queue = queue
         self._source = source  # Main DL iterator
-        self._max_len = max_len  #
 
     def run(self) -> None:
         for item in self._source:
             self._queue.put(item)  # Blocking if the queue is full
 
-        # Signal the consumer we are done.
-        self._queue.put(_sentinel)
+        # Signal the consumer we are done; this should not happen for DataLoader
+        self._queue.put(StopIteration())
+
+
+QUEUESIZE = 32
 
 
 class BufferedIterator:
     def __init__(self, iterable) -> None:
-        self._queue = queue.Queue(QUEUESIZE)
+        self._queue = Queue(QUEUESIZE)
         self._iterable = iterable
-        self._consumer = None
-
-        self.start_time = time.time()
-        self.warning_time = None
-        self.total = len(iterable)
-
-    def _create_consumer(self) -> None:
-        self._consumer = BackgroundConsumer(self._queue, self._iterable, self.total)
-        self._consumer.daemon = True
+        self._consumer = BackgroundConsumer(self._queue, self._iterable)
         self._consumer.start()
+        self.last_warning_time = time.time()
 
     def __iter__(self):
         return self
 
     def __len__(self) -> int:
-        return self.total
+        return len(self._iterable)
 
     def __next__(self):
-        # Create consumer if not created yet
-        if self._consumer is None:
-            self._create_consumer()
-        # Notify the user if there is a data loading bottleneck
-        if self._queue.qsize() < min(2, max(1, self._queue.maxsize // 2)):
-            if time.time() - self.start_time > 5 * 60:
-                if (
-                    self.warning_time is None
-                    or time.time() - self.warning_time > 15 * 60
-                ):
-                    log.warning(
-                        "Data loading buffer is empty or nearly empty. This may "
-                        "indicate a data loading bottleneck, and increasing the "
-                        "number of workers (--num-workers) may help."
-                    )
-                    self.warning_time = time.time()
-
-        # Get next example
+        start_wait = time.time()
         item = self._queue.get()
+        wait_time = time.time() - start_wait
+        if (
+            wait_time > 1.0 and start_wait - self.last_warning_time > 15 * 60
+        ):  # Even for Multi-Task training, each step usually takes < 1s
+            log.warning(
+                f"Data loading is slow, waited {wait_time:.2f} seconds. Ignoring this warning for 15 minutes."
+            )
+            self.last_warning_time = start_wait
         if isinstance(item, Exception):
             raise item
-        if item is _sentinel:
-            raise StopIteration
         return item
 
 

deepmd/utils/path.py

@@ -114,6 +114,10 @@ def is_file(self) -> bool:
     def is_dir(self) -> bool:
         """Check if self is directory."""
 
+    @abstractmethod
+    def __getnewargs__(self):
+        """Return the arguments to be passed to __new__ when unpickling an instance."""
+
     @abstractmethod
     def __truediv__(self, key: str) -> "DPPath":
         """Used for / operator."""
@@ -169,6 +173,9 @@ def __init__(self, path: Union[str, Path], mode: str = "r") -> None:
         self.mode = mode
         self.path = Path(path)
 
+    def __getnewargs__(self):
+        return (self.path, self.mode)
+
     def load_numpy(self) -> np.ndarray:
         """Load NumPy array.
 
@@ -304,6 +311,9 @@ def __init__(self, path: str, mode: str = "r") -> None:
         # h5 path: default is the root path
         self._name = s[1] if len(s) > 1 else "/"
 
+    def __getnewargs__(self):
+        return (self.root_path, self.mode)
+
     @classmethod
     @lru_cache(None)
     def _load_h5py(cls, path: str, mode: str = "r") -> h5py.File: