Workers

A Worker is a process-isolated wrapper around a reinforcement learning library or framework. Workers are the execution layer of the platform. These workers are the main decision makers, they run the actual training, evaluation, custom scripts and so on. Whereas MOSAIC handles orchestration, telemetry, and visualization.

Some workers are designed to facilitate training reinforcement learning algorithms. These workers often bundle training scripts, evaluation scripts, and benchmark files. While other Workers are designed for evaluation only, such as LLM related benchmarks. The common thread is that they all implement the same simple interface, which allows the GUI to interact with them in a consistent way.

        graph TB
    subgraph "MOSAIC Core"
        GUI["Qt6 GUI<br/>(Main Process)"]
        Daemon["Trainer Daemon<br/>(AsyncIO)"]
    end

    subgraph "Worker Sub-Processes"
        W1["CleanRL Worker<br/>PPO · DQN · SAC"]
        W2["XuanCe Worker<br/>MAPPO · QMIX"]
        W3["RLlib Worker<br/>PPO · IMPALA"]
        W4["BALROG Worker<br/>Single-Agent LLM"]
        W5["MOSAIC LLM Worker<br/>Multi-Agent LLM"]
    end

    GUI -- "gRPC" --> Daemon
    Daemon -- "spawn + JSONL" --> W1
    Daemon -- "spawn + JSONL" --> W2
    Daemon -- "spawn + JSONL" --> W3
    Daemon -- "spawn + JSONL" --> W4
    Daemon -- "spawn + JSONL" --> W5

    style GUI fill:#4a90d9,stroke:#2e5a87,color:#fff
    style Daemon fill:#50c878,stroke:#2e8b57,color:#fff
    style W1 fill:#ff7f50,stroke:#cc5500,color:#fff
    style W2 fill:#ff7f50,stroke:#cc5500,color:#fff
    style W3 fill:#ff7f50,stroke:#cc5500,color:#fff
    style W4 fill:#ff7f50,stroke:#cc5500,color:#fff
    style W5 fill:#ff7f50,stroke:#cc5500,color:#fff
    

Key Principles

Process Isolation	Each worker runs as a separate OS process. A worker crash never takes down the GUI or other workers.
Zero Modification	Upstream libraries (CleanRL, Ray, XuanCe) are never modified. A thin “shim” layer translates between MOSAIC and the library.
JSONL Telemetry	Workers emit structured JSON lines to stdout. This is the simplest possible output mechanism. No gRPC client code required inside the worker itself.
Automatic Discovery	Workers register via Python entry points ([project.entry-points."mosaic.workers"]). The GUI discovers them at startup.
Protocol-Based	Workers implement Python Protocol classes instead of inheriting from base classes.

Available Workers

Worker	Paradigm	Algorithms	Use Case
CleanRL	Single-Agent	PPO, DQN, SAC, TD3, DDPG, C51	Simple single-file RL training
XuanCe	Multi-Agent	MAPPO, QMIX, MADDPG, VDN, COMA	Multi-agent RL research
RLlib	Multi-Agent	PPO, IMPALA, APPO, SAC, DQN	Distributed training at scale
BALROG	Evaluation	GPT-4, Claude, Llama (single-agent)	Single-agent LLM benchmarking (MiniGrid, BabyAI)
MOSAIC LLM	Evaluation	GPT-4, Claude, Llama (multi-agent)	Multi-agent LLM with coordination strategies and Theory of Mind

Tip

Install a specific worker with pip install -e ".[<worker>]". For example: pip install -e ".[cleanrl]" or pip install -e ".[xuance]".