lspeasy / core/src / CancellationToken

Interface: CancellationToken

Defined in: packages/core/src/utils/cancellation.ts:52

Read-only handle for observing cancellation state.

Remarks

Pass a CancellationToken to long-running request handlers so they can honour client-initiated cancellation ($/cancelRequest notification). The token's isCancellationRequested property changes from false to true exactly once; it never resets.

Use CancellationTokenNone (exported as a constant) when no cancellation support is needed — it is a singleton that is never cancelled.

Use When

You are implementing a RequestHandler that performs async work (file I/O, database queries, tree-sitter parsing) and want to stop early when the client cancels.

Avoid When

The handler is synchronous and returns in less than a few milliseconds. Polling isCancellationRequested in a tight loop has negligible benefit.

Never

NEVER ignore the cancellation token on long-running requests. If a client sends $/cancelRequest and the server does not stop processing, the client times out and receives no usable feedback. Always check token.isCancellationRequested at async yield points.

Example

import { LSPServer } from '@lspeasy/server';

const server = new LSPServer();
server.onRequest('textDocument/hover', async (params, token) => {
  const lines = await readLargeFile(params.textDocument.uri);
  if (token.isCancellationRequested) return null;

  // ... compute hover
  return { contents: { kind: 'plaintext', value: 'info' } };
});

Properties

Property	Modifier	Type	Description	Defined in
isCancellationRequested	readonly	boolean	true once cancellation has been requested; never resets to false.	packages/core/src/utils/cancellation.ts:56

Methods

onCancellationRequested()

onCancellationRequested(callback): Disposable;

Defined in: packages/core/src/utils/cancellation.ts:64

Registers a callback invoked when (or immediately if already) cancelled.

Parameters

Parameter	Type	Description
callback	() => void	Called when cancellation is requested.

Returns

Disposable

A Disposable to unregister the callback.