maybeAttach method

@protected bool maybeAttach(CancellationToken? token)

Attaches to the CancellationToken only if it hasn't already been cancelled. If the token has already been cancelled, onCancel is called instead.

Returns true if the token is null or hasn't been cancelled yet, so the async task should continue. Returns false if the token has already been cancelled and the async task should not continue.

Implementation

@protected
bool maybeAttach(CancellationToken? token) {
  if (token?.isCancelled ?? false) {
    // Schedule the cancellation as a microtask to prevent Futures completing
    // before error handlers are registered
    final StackTrace trace = StackTrace.current;
    scheduleMicrotask(() => onCancel(token!.exception, trace));
    return false;
  } else {
    token?.attach(this);
    return true;
  }
}