Nested Task (Submit A Parallel Task Within A Parallel Task)

Nested tasks let tasks submit additional tasks without building a full graph up front.

"""Basic nested submit example (recursive Fibonacci)."""

from scaler import Client
from scaler.cluster.combo import SchedulerClusterCombo


def fibonacci(client: Client, n: int):
    if n == 0:
        return 0
    if n == 1:
        return 1

    a = client.submit(fibonacci, client, n - 1)
    b = client.submit(fibonacci, client, n - 2)
    return a.result() + b.result()


def main():
    cluster = SchedulerClusterCombo(n_workers=1)

    with Client(address=cluster.get_address()) as client:
        result = client.submit(fibonacci, client, 8).result()
        print(result)

    cluster.shutdown()


if __name__ == "__main__":
    main()

What the example does:

• Submits fibonacci as a remote task.

• Inside each task, recursively submits child tasks with submit().

• Waits on child futures and combines their results.

This pattern is useful to demonstrate nested execution, but recursion creates many small tasks and can be expensive.

Nested client scheduler address

When creating a nested Client from inside a task, the address argument is optional. If omitted, the client can detect and use the scheduler address from the worker context. This is useful in environments where external and worker-visible scheduler addresses differ (for example behind NAT/firewalls).

from scaler import Client


def nested_task():
    # Automatically uses worker-visible scheduler address
    with Client() as client:
        result = client.submit(lambda x: x * 2, 5).result()
    return result


client = Client(address="tcp://127.0.0.1:2345")
future = client.submit(nested_task)
print(future.result())  # 10