From 1ab934ed4db8a13236eb5773b8fd5b7f6ba06973 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Haian=20Huang=28=E6=B7=B1=E5=BA=A6=E7=9C=B8=29?=
 <1286304229@qq.com>
Date: Mon, 8 Nov 2021 20:23:03 +0800
Subject: [PATCH] [Enchance] Set a random seed when the user does not set a
 seed. (#6457)

* fix random seed bug

* add comment

* enchance random seed

* rename

Co-authored-by: Haobo Yuan <yuanhaobo@whu.edu.cn>
---
 mmdet/apis/__init__.py |  5 +++--
 mmdet/apis/train.py    | 36 +++++++++++++++++++++++++++++++++++-
 tools/train.py         | 14 +++++++-------
 3 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/mmdet/apis/__init__.py b/mmdet/apis/__init__.py
index 4a8987d1da8..a865e942afd 100644
--- a/mmdet/apis/__init__.py
+++ b/mmdet/apis/__init__.py
@@ -2,10 +2,11 @@
 from .inference import (async_inference_detector, inference_detector,
                         init_detector, show_result_pyplot)
 from .test import multi_gpu_test, single_gpu_test
-from .train import get_root_logger, set_random_seed, train_detector
+from .train import (get_root_logger, init_random_seed, set_random_seed,
+                    train_detector)
 
 __all__ = [
     'get_root_logger', 'set_random_seed', 'train_detector', 'init_detector',
     'async_inference_detector', 'inference_detector', 'show_result_pyplot',
-    'multi_gpu_test', 'single_gpu_test'
+    'multi_gpu_test', 'single_gpu_test', 'init_random_seed'
 ]
diff --git a/mmdet/apis/train.py b/mmdet/apis/train.py
index b8b6eefc8ab..a7ed2d267eb 100644
--- a/mmdet/apis/train.py
+++ b/mmdet/apis/train.py
@@ -4,10 +4,11 @@
 
 import numpy as np
 import torch
+import torch.distributed as dist
 from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
 from mmcv.runner import (HOOKS, DistSamplerSeedHook, EpochBasedRunner,
                          Fp16OptimizerHook, OptimizerHook, build_optimizer,
-                         build_runner)
+                         build_runner, get_dist_info)
 from mmcv.utils import build_from_cfg
 
 from mmdet.core import DistEvalHook, EvalHook
@@ -16,6 +17,39 @@
 from mmdet.utils import get_root_logger
 
 
+def init_random_seed(seed=None, device='cuda'):
+    """Initialize random seed.
+
+    If the seed is not set, the seed will be automatically randomized,
+    and then broadcast to all processes to prevent some potential bugs.
+
+    Args:
+        seed (int, Optional): The seed. Default to None.
+        device (str): The device where the seed will be put on.
+            Default to 'cuda'.
+
+    Returns:
+        int: Seed to be used.
+    """
+    if seed is not None:
+        return seed
+
+    # Make sure all ranks share the same random seed to prevent
+    # some potential bugs. Please refer to
+    # https://github.com/open-mmlab/mmdetection/issues/6339
+    rank, world_size = get_dist_info()
+    seed = np.random.randint(2**31)
+    if world_size == 1:
+        return seed
+
+    if rank == 0:
+        random_num = torch.tensor(seed, dtype=torch.int32, device=device)
+    else:
+        random_num = torch.tensor(0, dtype=torch.int32, device=device)
+    dist.broadcast(random_num, src=0)
+    return random_num.item()
+
+
 def set_random_seed(seed, deterministic=False):
     """Set random seed.
 
diff --git a/tools/train.py b/tools/train.py
index f59f195332d..45fa03bfad6 100644
--- a/tools/train.py
+++ b/tools/train.py
@@ -13,7 +13,7 @@
 from mmcv.utils import get_git_hash
 
 from mmdet import __version__
-from mmdet.apis import set_random_seed, train_detector
+from mmdet.apis import init_random_seed, set_random_seed, train_detector
 from mmdet.datasets import build_dataset
 from mmdet.models import build_detector
 from mmdet.utils import collect_env, get_root_logger
@@ -148,12 +148,12 @@ def main():
     logger.info(f'Config:\n{cfg.pretty_text}')
 
     # set random seeds
-    if args.seed is not None:
-        logger.info(f'Set random seed to {args.seed}, '
-                    f'deterministic: {args.deterministic}')
-        set_random_seed(args.seed, deterministic=args.deterministic)
-    cfg.seed = args.seed
-    meta['seed'] = args.seed
+    seed = init_random_seed(args.seed)
+    logger.info(f'Set random seed to {seed}, '
+                f'deterministic: {args.deterministic}')
+    set_random_seed(seed, deterministic=args.deterministic)
+    cfg.seed = seed
+    meta['seed'] = seed
     meta['exp_name'] = osp.basename(args.config)
 
     model = build_detector(