I am working on a simple game simulation program in C++, there's a function called update() that updates the current state of the game, it has to be called every 1 second precisely. If I use a loop like this:
while(//some condition) {
update();
Sleep(1000);
}
Then the function will not be called every 1 second, instead, every (1 + execution time of update () ). I read about various solutions like async functions, multithreading, or calculating the function's execution time using std::chrono and subtracting it from the 1000ms parameter to sleep. Some of those were too complicated for my simple case, and others seemed unsafe to use if I don't understand them really well.
Can anyone tell me what would be a suitable solution to my requirement? Thanks in advance.
Instead of sleeping for a duration, you need to sleep until a time point. For example, if your first update is at precisely 2:00:00.000, your future updates should come as closely as possible to 2:00:01.000, 2:00:02.000, etc.
To achieve this you can dedicate a thread to updating, and after the update, goes to sleep until the next time to do a scheduled update. chrono::system_clock::time_point
and this_thread::sleep_until
are your tools to do this.
For example:
#include <atomic>
#include <chrono>
#include <iostream>
#include <thread>
class UpdateManager
{
public:
explicit UpdateManager() = default;
private:
static std::atomic<int> now_;
static std::atomic<bool> stop_;
struct update_thread
: private std::thread
{
~update_thread();
update_thread(update_thread&&) = default;
using std::thread::thread;
};
public:
static update_thread start();
};
void update();
// source
std::atomic<int> UpdateManager::now_{0};
std::atomic<bool> UpdateManager::stop_{false};
UpdateManager::update_thread::~update_thread()
{
if (joinable())
{
stop_ = true;
join();
}
}
UpdateManager::update_thread
UpdateManager::start()
{
return update_thread{[]
{
using namespace std;
using namespace std::chrono;
auto next = system_clock::now() + 1s;
while (!stop_)
{
update();
this_thread::sleep_until(next);
next += 1s;
}
}};
}
#include "date/date.h"
void
update()
{
using namespace date;
using namespace std;
using namespace std::chrono;
cerr << system_clock::now() << '\n';
}
// demo
int
main()
{
auto t = UpdateManager::start();
using namespace std;
this_thread::sleep_for(10s);
}
Just for demo purposes (not necessary for the logic), I'm using Howard Hinnant's, free, open-source date/time library to print the current time (UTC) to microsecond precision in order to illustrate the stability of this technique. A sample output of this program is:
2018-05-02 15:14:25.634809
2018-05-02 15:14:26.637934
2018-05-02 15:14:27.636629
2018-05-02 15:14:28.637947
2018-05-02 15:14:29.638413
2018-05-02 15:14:30.639437
2018-05-02 15:14:31.637217
2018-05-02 15:14:32.637895
2018-05-02 15:14:33.637749
2018-05-02 15:14:34.639084
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