pregel

Utility class for working with channels in the Pregel system. Provides static methods for subscribing to channels and writing to them.

Channels are the communication pathways between nodes in a Pregel graph. They enable message passing and state updates between different parts of the graph.

The Pregel class is the core runtime engine of LangGraph, implementing a message-passing graph computation model inspired by Google's Pregel system. It provides the foundation for building reliable, controllable agent workflows that can evolve state over time.

Key features:

• Message passing between nodes in discrete "supersteps"
• Built-in persistence layer through checkpointers
• First-class streaming support for values, updates, and events
• Human-in-the-loop capabilities via interrupts
• Support for parallel node execution within supersteps

The Pregel class is not intended to be instantiated directly by consumers. Instead, use the following higher-level APIs:

• StateGraph: The main graph class for building agent workflows
  • Compiling a StateGraph will return a CompiledGraph instance, which extends Pregel
• Functional API: A declarative approach using tasks and entrypoints
  • A Pregel instance is returned by the entrypoint function

Configuration options for executing a Pregel graph. These options control how the graph executes, what data is streamed, and how interrupts are handled.