If it works, it works everywhere!

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Design

Components

• 👷 Worker, a worker creates a task to run an experiment in background. It periodically sends out transitions between agent and environment, and fetches latest parameter.
• 📢 WorkerProxy, a worker proxy collects messages from/to workers on the same node so that some message data (model params) can be shared across different workers.
• 💿 TrajectoryManager, a trajectory manager is a wrapper around an AbstractTrajectory. It takes in a bulk of transitions and samples a batch of training data in respond to request.
• 💡 Trainer, a trainer is a wrapper around an AbstractPolicy, it does nothing but to update its internal parameters when received a batch of training data and periodically broadcast its latest parameters.
• ⏱️ Orchestrator, an orchestrator is in charge of controlling the start, stop and the speed of communications between the above components.

Note that:

1. We adopt the actor model here. Each instance of the above components is an actor. Only messages are passing between them.
2. A node is a process in Julia. Different nodes can be on one machine or across different machines.
3. Tasks in different workers are initiated with Threads.@spawn. There's no direct communication between them by design.
4. In single node environment (WorkerNode and MainNode are the same one), the WorkerProxy can be removed and workers communicate with Orchestrator directly.

Messages

• 1️⃣ (👷 → 📢) InsertTransitionMsg, contains the local transitions between agent and environment in an experiment.
• 2️⃣ (📢 → ⏱️) InsertTransitionMsg from different workers.
• 3️⃣ (⏱️ → 💿) InsertTransitionMsg and SampleBatchMsg (which contains the address of Trainer).
• 4️⃣ (💿 → 💡) BatchTrainingDataMsg
• 5️⃣ (💡 → 💿) UpdatePriorityMsg, only necessary in prioritized experience replay related algorithms.
• 6️⃣ (💡 → ⏱️) LoadParamsMsg, contains the latest parameters of the policy.
• 7️⃣ (⏱️ → 📢) LoadParamsMsg
• 8️⃣ (📢 → 👷) LoadParamsMsg