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// Copyright 2020 The Pigweed Authors
// 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
// 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.
#pragma once
#include <mutex>
#include "pw_chrono/system_clock.h"
#include "pw_sync/interrupt_spin_lock.h"
namespace pw::chrono {
// A simulated system clock is a concrete virtual SystemClock implementation
// that does not "tick" on its own. Time is advanced by explicit calls to
// AdvanceTime() or SetTime() functions. This can be used as stub for testing
// which can be dependency injected. Be careful when using SetTime() to not
// violate the is_monotonic requirement, in other words avoid going backwards
// unless initializing the clock before consumers have a reference to the clock.
// Example:
// SimulatedSystemClock sim_system_clock;
// SystemClock::time_point now =;
// // now.time_since_epoch.duration() == std::chrono::seconds(0)
// sim_system_clock.AdvanceTime(std::chrono::seconds(42));
// // now.time_since_epoch.duration() == std::chrono::seconds(42)
// This code is thread & IRQ safe.
class SimulatedSystemClock : public VirtualSystemClock {
SimulatedSystemClock(SystemClock::time_point timestamp =
: current_timestamp_(timestamp) {}
void AdvanceTime(SystemClock::duration duration) {
std::lock_guard lock(interrupt_spin_lock_);
current_timestamp_ += duration;
// WARNING: Use of this function may violate the is_monotonic clock attribute.
void SetTime(SystemClock::time_point timestamp) {
std::lock_guard lock(interrupt_spin_lock_);
current_timestamp_ = timestamp;
SystemClock::time_point now() override {
std::lock_guard lock(interrupt_spin_lock_);
return current_timestamp_;
// In theory atomics could be used if 64bit atomics are supported, however
// performance of this test object shouldn't matter.
sync::InterruptSpinLock interrupt_spin_lock_;
SystemClock::time_point current_timestamp_;
} // namespace pw::chrono