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ultralytics/utils/dist.py

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+# Ultralytics 🚀 AGPL-3.0 License - https://ultralytics.com/license
+
+import os
+import shutil
+import sys
+import tempfile
+
+from . import USER_CONFIG_DIR
+from .torch_utils import TORCH_1_9
+
+
+def find_free_network_port() -> int:
+    """
+    Find a free port on localhost.
+
+    It is useful in single-node training when we don't want to connect to a real main node but have to set the
+    `MASTER_PORT` environment variable.
+
+    Returns:
+        (int): The available network port number.
+    """
+    import socket
+
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+        s.bind(("127.0.0.1", 0))
+        return s.getsockname()[1]  # port
+
+
+def generate_ddp_file(trainer):
+    """
+    Generate a DDP (Distributed Data Parallel) file for multi-GPU training.
+
+    This function creates a temporary Python file that enables distributed training across multiple GPUs.
+    The file contains the necessary configuration to initialize the trainer in a distributed environment.
+
+    Args:
+        trainer (ultralytics.engine.trainer.BaseTrainer): The trainer containing training configuration and arguments.
+            Must have args attribute and be a class instance.
+
+    Returns:
+        (str): Path to the generated temporary DDP file.
+
+    Notes:
+        The generated file is saved in the USER_CONFIG_DIR/DDP directory and includes:
+        - Trainer class import
+        - Configuration overrides from the trainer arguments
+        - Model path configuration
+        - Training initialization code
+    """
+    module, name = f"{trainer.__class__.__module__}.{trainer.__class__.__name__}".rsplit(".", 1)
+
+    content = f"""
+# Ultralytics Multi-GPU training temp file (should be automatically deleted after use)
+overrides = {vars(trainer.args)}
+
+if __name__ == "__main__":
+    from {module} import {name}
+    from ultralytics.utils import DEFAULT_CFG_DICT
+
+    cfg = DEFAULT_CFG_DICT.copy()
+    cfg.update(save_dir='')   # handle the extra key 'save_dir'
+    trainer = {name}(cfg=cfg, overrides=overrides)
+    trainer.args.model = "{getattr(trainer.hub_session, "model_url", trainer.args.model)}"
+    results = trainer.train()
+"""
+    (USER_CONFIG_DIR / "DDP").mkdir(exist_ok=True)
+    with tempfile.NamedTemporaryFile(
+        prefix="_temp_",
+        suffix=f"{id(trainer)}.py",
+        mode="w+",
+        encoding="utf-8",
+        dir=USER_CONFIG_DIR / "DDP",
+        delete=False,
+    ) as file:
+        file.write(content)
+    return file.name
+
+
+def generate_ddp_command(trainer):
+    """
+    Generate command for distributed training.
+
+    Args:
+        trainer (ultralytics.engine.trainer.BaseTrainer): The trainer containing configuration for distributed training.
+
+    Returns:
+        cmd (list[str]): The command to execute for distributed training.
+        file (str): Path to the temporary file created for DDP training.
+    """
+    import __main__  # noqa local import to avoid https://github.com/Lightning-AI/pytorch-lightning/issues/15218
+
+    if not trainer.resume:
+        shutil.rmtree(trainer.save_dir)  # remove the save_dir
+    file = generate_ddp_file(trainer)
+    dist_cmd = "torch.distributed.run" if TORCH_1_9 else "torch.distributed.launch"
+    port = find_free_network_port()
+    cmd = [
+        sys.executable,
+        "-m",
+        dist_cmd,
+        "--nproc_per_node",
+        f"{trainer.world_size}",
+        "--master_port",
+        f"{port}",
+        file,
+    ]
+    return cmd, file
+
+
+def ddp_cleanup(trainer, file):
+    """
+    Delete temporary file if created during distributed data parallel (DDP) training.
+
+    This function checks if the provided file contains the trainer's ID in its name, indicating it was created
+    as a temporary file for DDP training, and deletes it if so.
+
+    Args:
+        trainer (ultralytics.engine.trainer.BaseTrainer): The trainer used for distributed training.
+        file (str): Path to the file that might need to be deleted.
+
+    Examples:
+        >>> trainer = YOLOTrainer()
+        >>> file = "/tmp/ddp_temp_123456789.py"
+        >>> ddp_cleanup(trainer, file)
+    """
+    if f"{id(trainer)}.py" in file:  # if temp_file suffix in file
+        os.remove(file)