| /* |
| * Copyright (c) 2008-2011 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@ |
| */ |
| |
| #ifdef __APPLE__ |
| #include <mach/mach_time.h> |
| #endif |
| #include <dispatch/dispatch.h> |
| #include <sys/time.h> |
| #include <unistd.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #ifdef __APPLE__ |
| #include <TargetConditionals.h> |
| #endif |
| #include <bsdtests.h> |
| #include "dispatch_test.h" |
| |
| #define ACCEPTABLE_DRIFT 0.001 |
| |
| int |
| main(int argc __attribute__((unused)), char* argv[] __attribute__((unused))) |
| { |
| __block uint32_t count = 0; |
| __block double last_jitter = 0; |
| __block double drift_sum = 0; |
| // 100 times a second |
| uint64_t interval = 1000000000 / 100; |
| double interval_d = interval / 1000000000.0; |
| // for 25 seconds |
| unsigned int target = 25 / interval_d; |
| |
| dispatch_test_start("Dispatch Timer Drift"); |
| |
| dispatch_source_t t = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue()); |
| test_ptr_notnull("dispatch_source_create", t); |
| |
| dispatch_source_set_timer(t, dispatch_time(DISPATCH_TIME_NOW, interval), interval, 0); |
| |
| dispatch_source_set_event_handler(t, ^{ |
| struct timeval now_tv; |
| static double first = 0; |
| gettimeofday(&now_tv, NULL); |
| double now = now_tv.tv_sec + now_tv.tv_usec / 1000000.0; |
| |
| if (count == 0) { |
| // Because this is taken at 1st timer fire, |
| // later jitter values may be negitave. |
| // This doesn't effect the drift calculation. |
| first = now; |
| } |
| double goal = first + interval_d * count; |
| double jitter = goal - now; |
| double drift = jitter - last_jitter; |
| drift_sum += drift; |
| |
| printf("%4d: jitter %f, drift %f\n", count, jitter, drift); |
| |
| if (target <= ++count) { |
| drift_sum /= count - 1; |
| if (drift_sum < 0) { |
| drift_sum = -drift_sum; |
| } |
| double acceptable_drift = ACCEPTABLE_DRIFT; |
| test_double_less_than("drift", drift_sum, acceptable_drift); |
| test_stop(); |
| } |
| last_jitter = jitter; |
| }); |
| |
| dispatch_resume(t); |
| |
| dispatch_main(); |
| return 0; |
| } |