| name | cancellable-loop |
| description | Example skill — demonstrates cooperative cancellation inside a skill script loop using check_cancelled(). Use as a reference when writing long-running domain skills that must respond to notifications/cancelled. Not intended for production use. |
| license | MIT |
| compatibility | Python 3.7+ |
| metadata | {"dcc-mcp":{"dcc":"python","version":"1.0.0","layer":"example","search-hint":"cancellation, cancel, long-running, cooperative, check_cancelled, abort, authoring reference","tags":"example, cancellation, long-running"}} |
Cancellable Loop
A minimal example that shows how to write a skill script that honours
notifications/cancelled from the MCP client.
The pattern is simple: call check_cancelled() at the top of every
iteration of a long-running loop. When the dispatcher installs a
CancelToken and the client cancels the request, check_cancelled()
raises CancelledError and the script unwinds cleanly. Outside of a
request context (REPL, unit tests) check_cancelled() is a no-op, so
the same script remains easy to run in isolation.
Tools
cancellable_loop__count — Iterate iterations times, sleeping
sleep_ms milliseconds per step, checking for cancellation each
iteration.
Example
{"name": "cancellable_loop__count", "arguments": {"iterations": 100, "sleep_ms": 50}}
If the client sends notifications/cancelled while the loop is
running, the next check_cancelled() call raises CancelledError and
the @skill_entry wrapper converts it into a standard error dict.
Related
dcc_mcp_core.check_cancelled — the API this skill demonstrates.- Issue #329 — cooperative cancellation checkpoints.
- Issue #318 — async dispatcher integration (wires the CancelToken).
