Monitor and Cancel a Running DKIM Operation

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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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#include <C_CkDkim.h>

void ChilkatSample(void)
    {
    BOOL success;
    HCkDkim dkim;

    success = FALSE;

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

    dkim = CkDkim_Create();

    //  Fire an AbortCheck event callback every 100 ms during method calls.  In programming languages
    //  where Chilkat supports event callbacks, the callback can request cancellation.
    CkDkim_putHeartbeatMs(dkim,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.
    CkDkim_putAbortCurrent(dkim,FALSE);

    //  PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
    //  AbortCurrent can cancel.
    success = CkDkim_PrefetchPublicKey(dkim,"myselector","example.com");
    if (success == FALSE) {
        printf("%s\n",CkDkim_lastErrorText(dkim));
        CkDkim_Dispose(dkim);
        return;
    }

    printf("Public key prefetched.\n");


    CkDkim_Dispose(dkim);

    }