WatchdogTimer.m

#import "PLCrashReporterConfig.h"
#import "PLCrashReporter.h"
#import "PLCrashReport.h"
#import "PLCrashReportTextFormatter.h"

- (void)watchdog 
{
    NSTimeInterval pingInterval = 1.0/60.0;
    NSTimeInterval watchdogInterval = 1.0/30.0;

    __block NSTimeInterval lastPing = 0;

    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, pingInterval * NSEC_PER_SEC, 0);
    dispatch_source_set_event_handler(timer, ^{
        lastPing = CFAbsoluteTimeGetCurrent();
    });
    dispatch_resume(timer);

    dispatch_source_t watchdog = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
    dispatch_source_set_timer(watchdog, DISPATCH_TIME_NOW, pingInterval * NSEC_PER_SEC, 0);
    dispatch_source_set_event_handler(watchdog, ^{
        // watchdog event handler gets called before timer event handler
        if(lastPing > 0)
        {
            NSTimeInterval delta = CFAbsoluteTimeGetCurrent() - lastPing;
            if(delta > watchdogInterval) 
            {
                // Reset lastPing to 0
                lastPing = 0;
                NSLog(@"Main thread blocked for %f seconds", delta);
                [self generateStackTraceReport];
            }
        }
    });
    dispatch_resume(watchdog);
}

- (void)generateStackTraceReport
{
    PLCrashReporterConfig *config = [[PLCrashReporterConfig alloc] initWithSignalHandlerType:PLCrashReporterSignalHandlerTypeBSD
                                                                       symbolicationStrategy:PLCrashReporterSymbolicationStrategyNone];
    PLCrashReporter *crashReporter = [[PLCrashReporter alloc] initWithConfiguration:config];
    NSError *err = nil;
    NSData *crashData = [crashReporter generateLiveReportAndReturnError:&err];
    if(!err)
    {
        NSError *crashReportError = nil;
        PLCrashReport *report = [[PLCrashReport alloc] initWithData:crashData error:&crashReportError];
        if(!crashReportError)
        {
            NSString *crashReportText = [PLCrashReportTextFormatter stringValueForCrashReport:report withTextFormat:PLCrashReportTextFormatiOS];
            saveLiveReportForData(crashReportText);
        }
    }
}