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Telegram/ThirdParty/dispatch/tests/dispatch_drift.c

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+/*
+ * 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>
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
+#include <sys/time.h>
+#include <unistd.h>
+#endif
+#include <stdio.h>
+#include <stdlib.h>
+#ifdef __APPLE__
+#include <TargetConditionals.h>
+#endif
+#include <bsdtests.h>
+#include "dispatch_test.h"
+
+#if LENIENT_DEADLINES
+#define ACCEPTABLE_DRIFT 0.1
+#else
+#define ACCEPTABLE_DRIFT 0.001
+#endif
+
+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;
+#if defined(_WIN32)
+	// 25 times a second (Windows timer resolution is poor)
+	uint64_t interval = 1000000000 / 25;
+#else
+	// 100 times a second
+	uint64_t interval = 1000000000 / 100;
+#endif
+	double interval_d = interval / 1000000000.0;
+	// for 25 seconds
+	unsigned int target = (unsigned int)(25.0 / 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, (int64_t)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;
+}