RunnerConstructor (#1296)

* runner constructor

* import runner at `__init__`

* fix yapf

* fix

* fix yapf

* better write

* add using example

* add common

* fix lint

* refactor format
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

mmcv/runner/__init__.py

@@ -5,6 +5,7 @@ from .builder import RUNNERS, build_runner
 from .checkpoint import (CheckpointLoader, _load_checkpoint,
                          _load_checkpoint_with_prefix, load_checkpoint,
                          load_state_dict, save_checkpoint, weights_to_cpu)
+from .default_constructor import DefaultRunnerConstructor
 from .dist_utils import (allreduce_grads, allreduce_params, get_dist_info,
                          init_dist, master_only)
 from .epoch_based_runner import EpochBasedRunner, Runner
@@ -42,5 +43,5 @@ __all__ = [
     'allreduce_params', 'LossScaler', 'CheckpointLoader', 'BaseModule',
     '_load_checkpoint_with_prefix', 'EvalHook', 'DistEvalHook', 'Sequential',
     'ModuleList', 'GradientCumulativeOptimizerHook',
-    'GradientCumulativeFp16OptimizerHook'
+    'GradientCumulativeFp16OptimizerHook', 'DefaultRunnerConstructor'
 ]

mmcv/runner/builder.py

 # Copyright (c) OpenMMLab. All rights reserved.
-from ..utils import Registry, build_from_cfg
+import copy
+
+from ..utils import Registry
 
 RUNNERS = Registry('runner')
+RUNNER_BUILDERS = Registry('runner builder')
+
+
+def build_runner_constructor(cfg):
+    return RUNNER_BUILDERS.build(cfg)
 
 
 def build_runner(cfg, default_args=None):
-    return build_from_cfg(cfg, RUNNERS, default_args=default_args)
+    runner_cfg = copy.deepcopy(cfg)
+    constructor_type = runner_cfg.pop('constructor',
+                                      'DefaultRunnerConstructor')
+    runner_constructor = build_runner_constructor(
+        dict(
+            type=constructor_type,
+            runner_cfg=runner_cfg,
+            default_args=default_args))
+    runner = runner_constructor()
+    return runner

mmcv/runner/default_constructor.py

+from .builder import RUNNER_BUILDERS, RUNNERS
+
+
+@RUNNER_BUILDERS.register_module()
+class DefaultRunnerConstructor:
+    """Default constructor for runners.
+
+    Custom existing `Runner` like `EpocBasedRunner` though `RunnerConstructor`.
+    For example, We can inject some new properties and functions for `Runner`.
+
+    Example:
+        >>> from mmcv.runner import RUNNER_BUILDERS, build_runner
+        >>> # Define a new RunnerReconstructor
+        >>> @RUNNER_BUILDERS.register_module()
+        >>> class MyRunnerConstructor:
+        ...     def __init__(self, runner_cfg, default_args=None):
+        ...         if not isinstance(runner_cfg, dict):
+        ...             raise TypeError('runner_cfg should be a dict',
+        ...                             f'but got {type(runner_cfg)}')
+        ...         self.runner_cfg = runner_cfg
+        ...         self.default_args = default_args
+        ...
+        ...     def __call__(self):
+        ...         runner = RUNNERS.build(self.runner_cfg,
+        ...                                default_args=self.default_args)
+        ...         # Add new properties for existing runner
+        ...         runner.my_name = 'my_runner'
+        ...         runner.my_function = lambda self: print(self.my_name)
+        ...         ...
+        >>> # build your runner
+        >>> runner_cfg = dict(type='EpochBasedRunner', max_epochs=40,
+        ...                   constructor='MyRunnerConstructor')
+        >>> runner = build_runner(runner_cfg)
+    """
+
+    def __init__(self, runner_cfg, default_args=None):
+        if not isinstance(runner_cfg, dict):
+            raise TypeError('runner_cfg should be a dict',
+                            f'but got {type(runner_cfg)}')
+        self.runner_cfg = runner_cfg
+        self.default_args = default_args
+
+    def __call__(self):
+        return RUNNERS.build(self.runner_cfg, default_args=self.default_args)