C++

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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C++

#include <CkDkim.h>

void ChilkatSample(void)
    {
    bool success = false;

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

    CkDkim dkim;

    //  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.put_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.put_AbortCurrent(false);

    //  PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
    //  AbortCurrent can cancel.
    success = dkim.PrefetchPublicKey("myselector","example.com");
    if (success == false) {
        std::cout << dkim.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Public key prefetched." << "\r\n";
    }