Global manager (ManagerMixin)

During the training process, it is inevitable that we need to access some variables globally. Here are some examples:

  • Accessing the logger in model to print some initialization information

  • Accessing the Visualizer anywhere to visualize the predictions and feature maps.

  • Accessing the scope in Registry to get the current scope.

In order to unify the mechanism to get the global variable built from different classes, MMEngine designs the ManagerMixin.

Interface introduction

  • get_instance(name=’’, **kwargs): Create or get the instance by name.

  • get_current_instance(): Get the currently built instance.

  • instance_name: Get the name of the instance.

How to use

  1. Define a class inherited from ManagerMixin

from mmengine.utils import ManagerMixin

class GlobalClass(ManagerMixin):
    def __init__(self, name, value):
        self.value = value


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).

  1. Instantiate the instance anywhere. let’s take the hook as an example:

from mmengine import Hook

class CustomHook(Hook):
    def before_run(self, runner):
        GlobalClass.get_instance('mmengine', value=50)
        GlobalClass.get_instance(runner.experiment_name, value=100)

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.

Here we build two instances for the convenience of the subsequent introduction of get_current_instance.

  1. Accessing the instance anywhere

import torch.nn as nn

class CustomModule(nn.Module):
    def forward(self, x):
        value = GlobalClass.get_current_instance().value
        # Since the name of the latest built instance is
        # `runner.experiment_name`, value will be 100.

        value = GlobalClass.get_instance('mmengine').value
        # The value of instance with the name mmengine is 50.

        value = GlobalClass.get_instance('mmengine', 1000).value
        # `mmengine` instance has been built, an error will be raised
        # if `get_instance` accepts other parameters.

We can get the instance with the specified name by get_instance(name), or get the currently built instance by get_current_instance anywhere.


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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