Dart

Monitor and Cancel a Running DKIM Operation

Demonstrates the Chilkat Dkim.HeartbeatMs and Dkim.AbortCurrent properties, which monitor and cancel a long-running operation such as a DNS public-key lookup. HeartbeatMs sets how often an AbortCheck event fires, and AbortCurrent requests cancellation.

Background: Most Dkim work is instant, but anything touching DNS can stall on a slow or unresponsive server. HeartbeatMs makes the object emit a periodic AbortCheck callback during such calls so an application stays responsive and can show progress, and AbortCurrent — set from that callback or from another thread — breaks a blocked synchronous call out early. Together they turn an otherwise uninterruptible operation into a cancellable one.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the Dkim properties HeartbeatMs and AbortCurrent, which monitor and cancel a
  // long-running operation such as a DNS public-key lookup.

  final dkim = CkDkim();

  // Fire an AbortCheck event callback every 100 ms during method calls.  In programming languages
  // where Chilkat supports event callbacks, the callback can request cancellation.
  dkim.heartbeatMs = 100;

  // AbortCurrent may be set to true to request cancellation of a running operation.  It is
  // typically set from another thread, or from within an AbortCheck callback.  Setting it false
  // here ensures the operation is not pre-emptively aborted.
  dkim.abortCurrent = false;

  // PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
  // AbortCurrent can cancel.
  try {
    dkim.prefetchPublicKey('myselector', 'example.com');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Public key prefetched.');
}