Is file cancellation supported? #3127

braineo · 2021-09-29T10:15:04Z

braineo
Sep 29, 2021

Hi!

For pyright, it seems the client in vscode supports file based cancellation for fast request cancelling. I'm checking lsp-mode but I did not manage to find anything related. It seems only json-rpc is supported?

for file based cancellation, the pyright process needs another argument as discussed. and vscode extension code is here. Maybe need to mimic the behavior as

when vsc extension is activated, cancellationStrategy is instantiated

https://github.com/microsoft/pyright/blob/7bc2bd8ab05fc4967120d1b6b2a0a1834da2b783/packages/vscode-pyright/src/extension.ts#L64

cancellationStrategy = new FileBasedCancellationStrategy();

it pick up a random name, https://github.com/microsoft/pyright/blob/7bc2bd8ab05fc4967120d1b6b2a0a1834da2b783/packages/vscode-pyright/src/cancellationUtils.ts#L77 and tell lsp this is the file for cancellation

export class FileBasedCancellationStrategy implements CancellationStrategy, Disposable {
    constructor() {
        const folderName = randomBytes(21).toString('hex');
        this._sender = new FileCancellationSenderStrategy(folderName);
    }

which is an argument sent to construct the language server process

    getCommandLineArguments(): string[] {
        return [`--cancellationReceive=file:${this._sender.folderName}`];
    }

and this sender sends cancellation by simply writing empty string to this file with name from getCancellationFilePath, typically takes a cancellation id. Assuming we already know from response message format, we know which request to cancel.

class FileCancellationSenderStrategy implements CancellationSenderStrategy {
    sendCancellation(_: MessageConnection, id: CancellationId): void {
        const file = getCancellationFilePath(this.folderName, id);
        tryRun(() => fs.writeFileSync(file, '', { flag: 'w' }));
    }