75 lines
3.0 KiB
Markdown
75 lines
3.0 KiB
Markdown
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# Global manager (ManagerMixin)
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During the training process, it is inevitable that we need to access some variables globally. Here are some examples:
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- Accessing the [logger](mmengine.logging.MMLogger) in model to print some initialization information
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- Accessing the [Visualizer](mmengine.config.Config) anywhere to visualize the predictions and feature maps.
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- Accessing the scope in [Registry](mmengine.registry.Registry) to get the current scope.
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In order to unify the mechanism to get the global variable built from different classes, MMEngine designs the [ManagerMixin](mmengine.utils.ManagerMixin).
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## Interface introduction
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- get_instance(name='', \*\*kwargs): Create or get the instance by name.
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- get_current_instance(): Get the currently built instance.
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- instance_name: Get the name of the instance.
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## How to use
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1. Define a class inherited from `ManagerMixin`
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```python
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from mmengine.utils import ManagerMixin
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class GlobalClass(ManagerMixin):
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def __init__(self, name, value):
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super().__init__(name)
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self.value = value
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```
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```{note}
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Subclasses of `ManagerMixin` must accept `name` argument in `__init__`. The `name` argument is used to identify the instance, and you can get the instance by `get_instance(name)`.
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```
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2. Instantiate the instance anywhere. let's take the hook as an example:
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```python
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from mmengine import Hook
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class CustomHook(Hook):
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def before_run(self, runner):
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GlobalClass.get_instance('mmengine', value=50)
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GlobalClass.get_instance(runner.experiment_name, value=100)
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```
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`GlobalClass.get_instance({name})` will first check whether the instance with the name `{name}` has been built. If not, it will build a new instance with the name `{name}`, otherwise it will return the existing instance. As the above example shows, when we call `GlobalClass.get_instance('mmengine')` at the first time, it will build a new instance with the name `mmengine`. Then we call `GlobalClass.get_instance(runner.experiment_name)`, it will also build a new instance with a different name.
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Here we build two instances for the convenience of the subsequent introduction of `get_current_instance`.
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3. Accessing the instance anywhere
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```python
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import torch.nn as nn
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class CustomModule(nn.Module):
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def forward(self, x):
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value = GlobalClass.get_current_instance().value
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# Since the name of the latest built instance is
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# `runner.experiment_name`, value will be 100.
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value = GlobalClass.get_instance('mmengine').value
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# The value of instance with the name mmengine is 50.
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value = GlobalClass.get_instance('mmengine', 1000).value
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# `mmengine` instance has been built, an error will be raised
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# if `get_instance` accepts other parameters.
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```
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We can get the instance with the specified name by `get_instance(name)`, or get the currently built instance by `get_current_instance` anywhere.
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```{warning}
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If the instance with the specified name has already been built, `get_instance` will raise an error if it accepts its construct parameters.
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```
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