Objective-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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Objective-C

#import <CkoDkim.h>

BOOL success = NO;

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

CkoDkim *dkim = [[CkoDkim alloc] init];

//  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 = [NSNumber numberWithInt: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 = NO;

//  PrefetchPublicKey performs a synchronous DNS lookup, which HeartbeatMs monitors and
//  AbortCurrent can cancel.
success = [dkim PrefetchPublicKey: @"myselector" domain: @"example.com"];
if (success == NO) {
    NSLog(@"%@",dkim.LastErrorText);
    return;
}

NSLog(@"%@",@"Public key prefetched.");