# Parallel Execution

> Foundry V2 introduces a Task Dependency Graph (DAG) and a Parallel Worker Pool, allowing independent tasks to run concurrently.

Source: https://bifrost5.com/foundry/docs/parallel-execution/

# Parallel Execution (V2)

Information

Start building in parallel from a ready-made starter kit that you can white-label and own the source of.

[See editions](/foundry/docs/editions)

Foundry V2 introduces a **Task Dependency Graph (DAG)** and a **Parallel Worker Pool**, allowing independent tasks to run concurrently.

## How It Works

The monolithic control loop splits into two components:

### The Scheduler (The Brain)

Runs on every "Task Completed" event:

- **Update Graph**: Mark completed task.

- **Check Dependents**: Find all tasks depending on the completed one.

- **Promote**: If all dependencies are met, atomically move task from Waiting → Ready.

### The Worker Pool (The Muscles)

A configurable set of workers (default: 3):

- **Poll**: Take the next task from the ready queue.

- **Lock**: Acquire execution lock for the task.

- **Execute**: Spawn isolated agent context in a **git worktree**.

- **Report**: Write result to state. Emit task completed event.

## Dual-Queue System

| Queue | Contains | Behavior |
| --- | --- | --- |
| **Ready** (`queue:ready`) | Tasks with all dependencies met | Active: polled by Worker Pool |
| **Waiting** (`queue:waiting`) | Tasks with unmet dependencies | Passive: checked on task completion |

## Concurrency Control

- **File Locking**: Tasks declare `affects_files`. The scheduler uses file-level locking with exponential backoff so no two tasks edit the same file.

- **Git Worktree Isolation**: Each worker operates in its own worktree, preventing file system conflicts between concurrent tasks.

- **Task Recovery**: On scheduler crash, interrupted tasks are re-enqueued automatically.

## Task Fields for Parallel Mode

- `affects_files` (required): Files this task modifies: used for file-level locking.

- `depends_on` (optional): Task IDs that must complete first: auto-promoted when deps met.