Redundant process spawning when watching

[BHznJNs]

Description

I tried to use task to watch my FastAPI project.

The task script is like (since this project can not automatically kill the process, I used cleanup_port.py to do that):

  dev:
    deps: [install-dev]
    watch: true
    sources:
      - src/**
      - entry.py
    cmds:
      - uv run python scripts/cleanup_port.py 1460
      - uv run python entry.py

My entry.py points to my main.py, and this is how it look like:

# main.py
import argparse
import uvicorn
from loguru import logger
from .api import app

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--port", type=int, default=1460)
    args = parser.parse_args()

    logger.info("Starting server on port {}", args.port)
    uvicorn.run(app, host="127.0.0.1", port=args.port) # no hot reload here

And here is the logs:

> task dev
task: Started watching for tasks: dev
task: Task "install-dev" is up to date
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-02 23:54:38.913 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [dev] uv run python entry.py
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-02 23:54:42.953 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [19260]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:1460 (Press CTRL+C to quit) # I changed file here
task: Failed to run task "dev": exit status 1
task: Task "install-dev" is up to date
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-02 23:55:02.488 | WARNING  | __main__:try_kill_process:11 - Killing process 19260 (python.exe)...
2026-02-02 23:55:02.514 | SUCCESS  | __main__:kill_port_process:43 - Process 19260 killed successfully
task: [dev] uv run python entry.py
task: Failed to run task "dev": exit status 1
task: Task "install-dev" is up to date
task: Task "install-dev" is up to date
task: [dev] uv run python scripts/cleanup_port.py 1460
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-02 23:55:05.070 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
2026-02-02 23:55:05.104 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [dev] uv run python entry.py
task: [dev] uv run python entry.py
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-02 23:55:07.277 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [16408]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:1460 (Press CTRL+C to quit)
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-02 23:55:11.145 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [20536]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
ERROR:    [Errno 10048] error while attempting to bind on address ('127.0.0.1', 1460): [winerror 10048] only one usage of each socket address (protocol/network address/port) is normally permitted
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-02 23:55:11.688 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [25608]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
ERROR:    [Errno 10048] error while attempting to bind on address ('127.0.0.1', 1460): [winerror 10048] only one usage of each socket address (protocol/network address/port) is normally permitted
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
task: Failed to run task "dev": exit status 1
task: Failed to run task "dev": exit status 1
task: Signal received: "interrupt"

Version

3.48.0

Operating system

Windows 11 25H2

Experiments Enabled

No response

Example Taskfile

version: '3'

tasks:
  install-dev:
    sources:
      - pyproject.toml
    generates:
      - .venv/**
    cmds:
      - uv sync --group dev

  dev:
    deps: [install-dev]
    watch: true
    sources:
      - src/**
      - entry.py
    cmds:
      - uv run python scripts/cleanup_port.py 1460
      - uv run python entry.py

[trulede]

It looks a bit odd. Perhaps add a sleep 5 as the first command, and a second between the commands, to see if that calms things down a bit. And make sure these commands really are executing in discrete steps, or perhaps interacting between restarts, which creates the odd behaviour.

[BHznJNs]

I added sleeps and removed deps like this:

  dev:
    watch: true
    sources:
      - src/**
      - entry.py
    cmds:
      - sleep 5
      - uv run python scripts/cleanup_port.py 1460
      - sleep 5
      - uv run python entry.py

And in the logs:

> task dev
task: Started watching for tasks: dev
task: [dev] sleep 5
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-03 10:57:50.498 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [dev] sleep 5
task: [dev] uv run python entry.py
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-03 10:57:59.595 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [21520]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:1460 (Press CTRL+C to quit)
task: Failed to run task "dev": exit status 1
task: [dev] sleep 5
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-03 10:58:14.308 | WARNING  | __main__:try_kill_process:11 - Killing process 21520 (python.exe)...
2026-02-03 10:58:14.331 | SUCCESS  | __main__:kill_port_process:43 - Process 21520 killed successfully
task: [dev] sleep 5
task: [dev] uv run python entry.py
task: Failed to run task "dev": exit status 1
task: [dev] sleep 5
task: [dev] sleep 5
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-03 10:58:23.551 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [24780]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:1460 (Press CTRL+C to quit)
task: [dev] uv run python scripts/cleanup_port.py 1460
task: [dev] uv run python scripts/cleanup_port.py 1460
2026-02-03 10:58:25.052 | WARNING  | __main__:try_kill_process:11 - Killing process 24780 (python.exe)...
2026-02-03 10:58:25.072 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
2026-02-03 10:58:25.075 | SUCCESS  | __main__:kill_port_process:43 - Process 24780 killed successfully
task: [dev] sleep 5
task: [dev] sleep 5
task: [dev] uv run python entry.py
task: [dev] uv run python entry.py
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-03 10:58:34.209 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [13444]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:1460 (Press CTRL+C to quit)
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
2026-02-03 10:58:35.197 | INFO     | src.main:main:13 - Starting server on port 1460
INFO:     Started server process [26164]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
ERROR:    [Errno 10048] error while attempting to bind on address ('127.0.0.1', 1460): [winerror 10048] only one usage of each socket address (protocol/network address/port) is normally permitted
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
task: Failed to run task "dev": exit status 1

We can see that even the sleep command also be executed double.

What's more wired, I tested another temp testing command:

  test_script:
    watch: true
    sources:
      - src/**
      - test.py
    cmds:
      - uv run python scripts/cleanup_port.py 1460
      - uv run python test.py

# test.py
print("test script")

And it just works fine:

> task test_script
task: Started watching for tasks: test_script
task: [test_script] uv run python scripts/cleanup_port.py 1460
2026-02-03 11:02:08.845 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [test_script] uv run python test.py
test script
task: task "test_script" finished running
task: Task "test_script" is up to date # saved file without modification
task: task "test_script" finished running
task: Task "test_script" is up to date
task: task "test_script" finished running
task: Task "test_script" is up to date
task: task "test_script" finished running
task: Task "test_script" is up to date
task: task "test_script" finished running
task: Task "test_script" is up to date
task: task "test_script" finished running
task: [test_script] uv run python scripts/cleanup_port.py 1460 # saved file with modification
2026-02-03 11:03:09.765 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [test_script] uv run python test.py
test script
task: task "test_script" finished running
task: [test_script] uv run python scripts/cleanup_port.py 1460
2026-02-03 11:03:14.462 | INFO     | __main__:kill_port_process:48 - Port 1460 is free, no need to clean
task: [test_script] uv run python test.py
test script
task: task "test_script" finished running