stagegate 0.2.0

A small, explicit scheduler for forward-only pipelines with stage-aware task priority.

stagegate

stagegate is a small, explicit, single-process Python library for running many forward-only pipelines with:

• FIFO pipeline scheduling
• stage-aware task priority
• strict head-of-line blocking
• abstract resource quotas

It is aimed at local batch workloads that have grown beyond a plain thread pool but do not justify a full workflow engine.

Why Stagegate

stagegate is built for workloads where:

• many similar pipelines run on one machine
• tasks have heterogeneous CPU / memory / other resource needs
• later-stage work should be preferred over endlessly producing more upstream intermediates
• tasks that spend meaningful time in NumPy, SciPy, Pandas, other C-extension code, or external CLI tools

The scheduler stays intentionally small:

• one Python process
• multiple threads
• no DAG engine
• no persistence layer
• no distributed runtime

Install

pip install stagegate

Quick Example

import stagegate


class ExamplePipeline(stagegate.Pipeline):
    def run(self) -> int:
        a = self.task(step_a, resources={"cpu": 1}).run()
        b = self.task(step_b, resources={"cpu": 1}).run()

        self.wait([a, b], return_when=stagegate.ALL_COMPLETED)
        result_a = a.result()
        result_b = b.result()

        self.stage_forward()

        c = self.task(
            combine,
            resources={"cpu": 4, "mem": 16},
            args=(result_a, result_b),
        ).run()
        return c.result()


with stagegate.Scheduler(
    resources={"cpu": 8, "mem": 32},
    pipeline_parallelism=2,
    task_parallelism=4,
) as scheduler:
    handle = scheduler.run_pipeline(ExamplePipeline())
    print(handle.result())

Cooperative Terminate

For long-running tasks, stagegate supports cooperative terminate:

• TaskHandle.request_terminate()
• stagegate.terminate_requested()
• stagegate.run_subprocess(...)

The scheduler itself does not forcibly stop arbitrary running Python code or running pipelines. Cooperative terminate is opt-in.

stagegate.run_subprocess(...) is currently intended for POSIX platforms such as Linux, macOS, and BSD. stagegate itself may still be usable on Windows if your tasks do not depend on that helper.

Documentation

User's guide, use cases and API reference can be found at http://stagegate.readthedocs.io.