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/*
* Copyright (c) 2008-2009 Apple Inc. All rights reserved.
*
* @APPLE_APACHE_LICENSE_HEADER_START@
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* @APPLE_APACHE_LICENSE_HEADER_END@
*/
#include "config/config.h"
#include <dispatch/dispatch.h>
#include <sys/time.h>
#include <math.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include "dispatch_test.h"
//
// Verify that dispatch timers do not drift, that is to say, increasingly
// stray from their intended interval.
//
// The jitter of the event handler is defined to be the amount of time
// difference between the actual and expected timing of the event handler
// invocation. The drift is defined to be the amount that the jitter changes
// over time.
//
// Important: be sure to use the same clock when comparing actual and expected
// values. Skew between different clocks is to be expected.
//
int
main(int argc __attribute__((unused)), char* argv[] __attribute__((unused)))
{
__block uint32_t count = 0;
__block double last_jitter = 0;
// interval is 1/10th of a second
uint64_t interval = NSEC_PER_SEC / 10;
double interval_d = (double)interval / (double)NSEC_PER_SEC;
// for 25 seconds
unsigned int target = 25 / interval_d;
__block double first = 0;
__block double jittersum = 0;
__block double driftsum = 0;
test_start("Timer drift test");
dispatch_source_t timer;
timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
test_ptr_notnull("DISPATCH_SOURCE_TYPE_TIMER", timer);
dispatch_source_set_event_handler(timer, ^{
struct timeval now_tv;
gettimeofday(&now_tv, NULL);
double now = now_tv.tv_sec + ((double)now_tv.tv_usec / (double)USEC_PER_SEC);
if (first == 0) {
first = now;
}
double goal = first + interval_d * count;
double jitter = goal - now;
double drift = jitter - last_jitter;
count += dispatch_source_get_data(timer);
jittersum += jitter;
driftsum += drift;
printf("%4d: jitter %f, drift %f\n", count, jitter, drift);
if (count >= target) {
test_double_less_than("average jitter", fabs(jittersum) / (double)count, 0.0001);
test_double_less_than("average drift", fabs(driftsum) / (double)count, 0.0001);
test_stop();
}
last_jitter = jitter;
});
struct timeval now_tv;
struct timespec now_ts;
gettimeofday(&now_tv, NULL);
now_ts.tv_sec = now_tv.tv_sec;
now_ts.tv_nsec = now_tv.tv_usec * NSEC_PER_USEC;
dispatch_source_set_timer(timer, dispatch_walltime(&now_ts, interval), interval, 0);
dispatch_resume(timer);
dispatch_main();
return 0;
}
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