Cooperative Tool Cancellation

Cancellation now reaches the tool body that is already running, so a /stop or Ctrl-C aborts a live subprocess within ~100ms instead of waiting for its own timeout.

This is in-flight cancellation. It stops a tool that is already running. To stop the next tool call (deadline or token), see Tool Timeouts & Cancellation.

Quick Start

Just works from an agent

Give the agent an InterruptController, then request a stop from another thread — a running shell tool body is aborted within ~100ms and its result carries interrupted: True.

from praisonaiagents import Agent
from praisonaiagents.agent import InterruptController

controller = InterruptController()

agent = Agent(
    name="Runner",
    instructions="Run shell commands when asked.",
    tools=["shell"],
    interrupt_controller=controller,
)

# From another thread / the CLI /stop / Ctrl-C handler:
controller.request("user_stop")
# A running `shell` tool body is aborted within ~100ms and the
# tool result carries `interrupted: True`.

Custom tool opts into cooperative abort

Read the event inside a custom tool via Injected[AgentState], then poll or wait on it to bail out promptly.

from praisonaiagents import Agent
from praisonaiagents.tools import tool, AgentState, Injected

@tool
def slow_download(url: str, state: Injected[AgentState]) -> str:
    cancel = state.cancel_event
    for chunk in stream(url):                 # your streaming source
        if cancel is not None and cancel.is_set():
            return "interrupted"
        process(chunk)                          # your per-chunk work
    return "done"

agent = Agent(name="Downloader", tools=[slow_download])

How It Works

The controller exposes its underlying Event; the tool-execution loop threads it into AgentState.cancel_event, and the running tool polls it every ~100ms. The event is scoped to the current turn: the controller clears its flag when an interrupted turn ends, so a stale request cannot abort tools launched by the next turn.

Reading the outcome

The built-in shell tool returns a discriminated interrupted payload — distinct from a timeout.

Field	Value	Meaning
`stdout`	`''`	No output captured on abort
`stderr`	`'Command interrupted by user'`	Human-readable reason
`exit_code`	`-1`	Process did not exit normally
`success`	`False`	The call did not complete
`interrupted`	`True`	Aborted by cooperative interrupt (not a timeout)
`execution_time`	`<float>`	Seconds until the abort

A wall-clock timeout instead returns stderr='Command timed out after N seconds' with no interrupted key — check result.get('interrupted') to tell them apart.

Choose your cancellation surface

Pick the surface by what you need to stop.

Stop the next tool → cancel_token / timeout_ms on the executor. See Tool Timeouts & Cancellation.
Stop the tool that is already running → Agent.interrupt_controller + cancel_event (this page).

Streaming honours the same Stop

start(stream=True) and iter_stream() short-circuit a pending tool batch on Stop, just like chat() — the same InterruptController / cancel_token seam covers the streaming path end-to-end.

Coverage	Non-streaming (`chat()`)	Streaming (`start(stream=True)` / `iter_stream()`)
Cancel before model returns tool_calls	✅	✅
Pending tool batch short-circuits on Stop	✅	✅ (since PR #5081)
Follow-up completion request skipped on Stop	✅	✅ (since PR #5081)
Fallback loop (Anthropic / Gemini / Ollama with tools) honours Stop	✅	✅ (since PR #5081)

from praisonaiagents import Agent
from praisonaiagents.agent import InterruptController

controller = InterruptController()

agent = Agent(
    name="Runner",
    instructions="Search, then summarise.",
    tools=["shell", "search"],
    interrupt_controller=controller,
)

# From another thread / a UI Stop button:
# controller.request("user_stop")

for chunk in agent.start("Find the largest file under /var/log and summarise it", stream=True):
    print(chunk, end="", flush=True)
# On Stop mid-turn: pending tools return `error_kind="cancelled"` and the
# stream ends — no further completion request is issued.

Fixed in PraisonAI PR #5081 (issue #5073). Before this PR, cancel_token was dropped at the ToolCallExecutor.execute_batch() boundary on the streaming path — Stop halted the model between iterations but shell / MCP / file tools already dispatched in the current batch ran to completion, and the streaming loop still spent one more completion request on the cancelled turn. Since #5081, the token is forwarded from the public streaming entry point (start(stream=True) / iter_stream()) through get_response_stream into execute_batch, and three additional guards break the streaming and fallback loops the moment the token is signalled.

Custom `InterruptController` implementations

Exposing the event is optional — a controller without it keeps working, giving loop-level cancellation only.

import threading
from praisonaiagents import Agent

class MyController:
    def __init__(self):
        self._flag = threading.Event()

    def request(self, reason: str = "user") -> None:
        self._flag.set()

    def clear(self) -> None:
        self._flag.clear()

    def is_set(self) -> bool:
        return self._flag.is_set()

    @property
    def reason(self):
        return "user" if self._flag.is_set() else None

    def check(self) -> None:
        if self._flag.is_set():
            raise InterruptedError("cancelled")

    @property
    def event(self) -> threading.Event:   # opt in to in-flight abort
        return self._flag

agent = Agent(name="Runner", tools=["shell"], interrupt_controller=MyController())

The runtime probes with getattr(controller, 'event', None), so a controller that omits event is fully backward compatible — it just skips in-flight abort and cancels at the loop boundary.

Best Practices

Check the event exists before using it

A tool may run standalone with no injected state. Guard with if state.cancel_event is not None: before calling .is_set() or .wait().

Prefer wait over busy-polling

Use state.cancel_event.wait(timeout=0.1) for idle waits instead of a tight is_set() loop, so you don’t burn CPU while waiting for work or the signal.

Keep the poll window short

Poll roughly every ~100ms — the same cadence the built-in shell tool uses — so /stop feels instant to the user.

Do not persist the event across turns

The event is scoped to the current turn and cleared when an interrupted turn ends. Read it fresh from state.cancel_event each call; never cache it on a module or instance.

Tool Timeouts

Deadlines and the executor-level cancel token

Tool Progress

Surface progress from the same slow tools

Gateway Abort & Timeout

HTTP-facing abort and deadlines

Run Outcome

Read the discriminated outcome from a run

Getting Started

Install

Core Concepts

Guides

Features

Models

Databases

Observability

Memory

Telemetry & Analytics

Knowledge

RAG

Persistence

Tools

Other Features

Developers

Configuration

Best Practices

Getting Started (No Code)

Cooperative Tool Cancellation

Quick Start

How It Works

Reading the outcome

Choose your cancellation surface

Streaming honours the same Stop

Custom `InterruptController` implementations

Best Practices

Tool Timeouts

Tool Progress

Gateway Abort & Timeout

Run Outcome

​Quick Start

​How It Works

​Reading the outcome

​Choose your cancellation surface

​Streaming honours the same Stop

​Custom InterruptController implementations

​Best Practices

​Related

Tool Timeouts

Tool Progress

Gateway Abort & Timeout

Run Outcome

Quick Start

How It Works

Reading the outcome

Choose your cancellation surface

Streaming honours the same Stop

Custom `InterruptController` implementations

Best Practices

Related