Mephisto Operations

The contents of the operations folder comprise controllers for launching and monitoring tasks, as well as other classes that either operate on the data model or support the mid level of Mephisto's design. Each has a high level responsibility, detailed below. Within these classes there's something of a heirarchy depending on the amount of underlying infrastructure that a class is built upon.

High-level controller components

This level of components is reserved for modules that operate on the highest level of the Mephisto heirarchy. These should be either directly usable, or easy to bundle into scripts for the client/api.

  • Operator: High-level class responsible for launching and monitoring a TaskRun. Generally initialized using a TaskConfig and the launch_task_run method.

At the moment only the Operator exists in this level, as the module that manages the process of launching and monitoring a complete data collection job. Modules on a similar level of complexity may be written for the review flow, and for packaging data for release.

Mid-level connecting components

These components are responsible for tying some of the underlying data model components to the reality of what they represent. They ensure that tasks remain in sync with what is actually happening, such that the content on Mephisto matches what is present on crowd providers and architects, and to some degree to blueprints.

  • ClientIOHandler: Responsible for processing incoming packets from clients and directing them to the right place. Also ensures that reconnecting workers are directed to the correct agents. The ClientIOHandler acts as the bridge between Architects and Blueprints.
  • WorkerPool: Responsible for following the status of a worker from the point they attempt to accept a Unit until the Unit is either completed or returned. This includes spawning the threads that watch specific Assignment's or Unit's, evaluating onboarding and qualifications.
  • Reponsible for keeping track of instances of all of the Mephisto core abstractions, such that the system is able to refer to them just by name.
  • TaskLauncher: Responsible for moving through an iterator or generator of assignments and units to be created, first creating the local Mephisto state to represent them and then later leveraging the CrowdProvider to launch them. Also ensures certain configuration invariants hold, such as a maximum number of concurrent tasks available.

Low-level Mephisto infra

These modules contain functionality that is used to condense shared behavior from various parts of the Mephisto codebase into standard functionality and utilities.

  • Functions responsible for providing a consistent interface into a user's configuration file for Mephisto, stored at ~/.mephisto/config.yml.
  • Classes and functionality responsible for ensuring that Mephisto operates well using Hydra, including base classes to build Hydra structured configs from (such as the TaskConfig) and methods to simplify interacting with Hydra in the codebase.
  • Helpers to simplify the process of generating unique loggers and logging configuration for various parts of Mephisto. (Much still to be done here).


The Operator is responsible for actually coordinating launching tasks. This is managed using the launch_task_run function. It takes in a Hydra DictConfig of arguments corresponding to the Blueprint, Architect, and CrowdProvider of choice. It can also take a SharedTaskState object to pass information that wouldn't normally be able to be parsed on the command line, or where it can only be extracted at runtime.

One important extra argument is SharedTaskState.qualifications, which allows configuring a task with requirements for workers to be eligibible to work on the task. Functionality for this can be seen in data_model.qualifications, with examples in how operator handles the block_qualification.

The lifecycle of an operator is to launch as many LiveTaskRuns as desired using the launch_task_run function, and then to watch over their progress using the wait_for_runs_then_shutdown function. These methods cover the full requirements for launching and monitoring a job.

If wait_for_runs_then_shutdown is not used, it's always important to call the shutdown methods whenever an operator has been created. While tasks are underway, a user can use get_running_task_runs to see the status of things that are currently running. Once there are no running task runs, the Operator can be told to shut down.


The ClientIOHandler's primary responsiblity is to abstract the remote nature of Mephisto Workers and Agents to allow them to directly act on the local maching. It is the layer that abstracts humans and human work into Workers and Agents that take actions. To that end, it has to set up a socket to connect to the task server, poll status on any agents currently working on tasks, and process incoming agent actions over the socket to put them into the Agent so that a task can use the data.

When provided with details of a LiveTaskRun, the associated Architect tells the ClientIOHandler where the server(s) that agents are communicating with is(/are) running. Then on initialization, Channel can be opened for each of these servers.

Once this connection is established:

  • Incoming messages from the server (which represent actions taken by human agents) are passed to the pending_actions queue of the Agent that corresponds with that human agent. Future calls to Agent.get_live_update() will pop off from this queue.
  • Calls to Agent.observe() will push the message through to the appropriate Channel's sending queue immediately.
  • The ClientIOHandler should also be querying for Agent's status and pushing responses to the WorkerPool to handle updates.


The WorkerPool is responsible for placing workers into appropriate Agents after finding Units they are eligible for, and passing off task execution to a Blueprint's TaskRunner. It also monitors changes to agent status.

In order to properly determine eligibility and launch tasks, the WorkerPool relies on the Blueprint and CrowdProvider for the registered LiveTaskRun:

  • The Blueprint contains details about the relevant task run, and is used for properly registering a new Agent the correct Unit. For this, in _register_agent it gets all Units that a worker is eligible for, reserves one, and then handles creating a new Agent out of the given Worker-Unit pair.
  • The CrowdProvider is also used during the registration process. In the first part it ensures that upon a first connect by a new person, a corresponding Worker is created to keep records for that worker (_register_worker). Later it is used during _register_agent to ensure that the Agent class used is associated with the correct CrowdProvider and has its relevant abstractions.

From this point, all interactions are handled from the perspective of pure Mephisto Agents, and the remaining responsibilities of the WorkerPool are to ensure that, from the perspective of a Blueprint's TaskRunner, the Agents local python state is entirely representative of the actual state of the human worker in the task.


The file contains functions required for establishing a registry of abstraction modules for Mephisto to refer to. This allows Mephisto to properly re-initialize classes and get information for data stored in the MephistoDB without needing to store pickled modules, or information beyond the registration key.

The file exposes the register_mephisto_abstraction class decorator, which ensures that on import a specific module will be added to the given registry. The fill_registries function automatically populates the registry dicts with all of the relevant modules in Mephisto, though this should likely be expanded to allow users or repositories to mark or register their own Mephisto implementations.

Mephisto classes can then use the get_<abstraction>_from_type methods from the file to retrieve the specific modules to be initialized for the given abstraction type string.


The TaskLauncher class is a fairly lightweight class responsible for handling the process of launching units. A TaskLauncher is created for a specific TaskRun, and provided with assignment_data for that full task run. It creates Assignments and Units for the TaskRun, and packages the expected data into the Assignment. When a task is ready to go live, one calls launch_units(url) with the url that the task should be pointed to. If units need to be expired (such as during a shutdown), expire_units handles this for all units created for the given TaskRun.

TaskLaunchers will parse the TaskRun's TaskRunArgs to know what parameters to set. This info should be used to initialize the assignments and the units as specified. The TaskLauncher can also be used to limit the number of currently available tasks using the max_num_concurrent_units argument, which prevents too many tasks from running at the same time, potentially overrunning the TaskRunner that the Blueprint has provided.

The methods in this module standardize how Mephisto interacts with the user configurations options for the whole system. These are stored in "~/.mephisto/config.yml" at the moment. The structure of the config file is such that it subdivides values to store into sections containing keys. Those keys can contain any value, but writing and reading data is done by referring to the section and the key for the data being written or read.

The following methods are defined:

  • get_config: loads all of the contents of the mephisto config file.
  • write_config: Writes an entirely new config to file
  • init_config: Tries to create an initial configuration file if none exists
  • add_config_arg: Sets the value for just one configuration arg in the whole set.
  • get_config_arg: Returns a specific argument value from a section of the config.

The hydra config module contains a number of classes and methods to make interfacing with hydra a little more convenient for Mephisto and its users. It defines common structured config types, currently the MephistoConfig and the TaskConfig, for use in user code. It also defines methods for handling registering those structured configs under the expected names, which the registry relies on. Lastly, it provides the register_script_config method, which lets a user define a structured config for use in their scripts without needing to initialize a hydra ConfigStore.

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