Delphi ActiveX

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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var
success: Integer;
dkim: TChilkatDkim;

begin
success := 0;

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

dkim := TChilkatDkim.Create(Self);

//  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 1 to request cancellation of a running operation.  It is
//  typically set from another thread, or from within an AbortCheck callback.  Setting it 0
//  here ensures the operation is not pre-emptively aborted.
dkim.AbortCurrent := 0;

//  PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
//  AbortCurrent can cancel.
success := dkim.PrefetchPublicKey('myselector','example.com');
if (success = 0) then
  begin
    Memo1.Lines.Add(dkim.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add('Public key prefetched.');