Alarm.cc

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#include "Alarm.hh"
#include "Timer.hh"
#include "Semaphore.hh"
#include "MSXException.hh"
#include "StringOp.hh"
#include "stl.hh"
#include <algorithm>
#include <vector>
#include <cassert>
#include <limits>
#include <SDL.h>

namespace openmsx {

class AlarmManager
{
public:
        static AlarmManager& instance();
        void registerAlarm(Alarm& alarm);
        void unregisterAlarm(Alarm& alarm);
        void start(Alarm& alarm, unsigned newPeriod);
        void stop(Alarm& alarm);
        bool isPending(const Alarm& alarm);

private:
        AlarmManager();
        ~AlarmManager();

        static unsigned timerCallback(unsigned interval, void* param);
        unsigned timerCallback2();

        std::vector<Alarm*> alarms;
        int64_t time;
        SDL_TimerID id;
        Semaphore sem;
        static volatile bool enabled;
};


// to minimize (or fix completely?) the race condition on exit
volatile bool AlarmManager::enabled = false;

AlarmManager::AlarmManager()
        : id(nullptr), sem(1)
{
        if (SDL_Init(SDL_INIT_TIMER) < 0) {
                throw FatalError(StringOp::Builder() <<
                        "Couldn't initialize SDL timer subsystem" <<
                        SDL_GetError());
        }
        enabled = true;
}

AlarmManager::~AlarmManager()
{
        assert(alarms.empty());
        enabled = false;
        if (id) {
                SDL_RemoveTimer(id);
        }
}

AlarmManager& AlarmManager::instance()
{
        static AlarmManager oneInstance;
        return oneInstance;
}

void AlarmManager::registerAlarm(Alarm& alarm)
{
        ScopedLock lock(sem);
        assert(!contains(alarms, &alarm));
        alarms.push_back(&alarm);
}

void AlarmManager::unregisterAlarm(Alarm& alarm)
{
        ScopedLock lock(sem);
        alarms.erase(find_unguarded(alarms, &alarm));
}

static int convert(int period)
{
        return std::max(1, period / 1000);
}

void AlarmManager::start(Alarm& alarm, unsigned period)
{
        ScopedLock lock(sem);
        alarm.period = period;
        alarm.time = Timer::getTime() + period;
        alarm.active = true;

        if (id) {
                // there already is a timer
                int64_t diff = time - alarm.time;
                if (diff <= 0) {
                        // but we already have an earlier timer, do nothing
                } else {
                        // new timer is earlier
                        SDL_RemoveTimer(id);
                        time = alarm.time;
                        id = SDL_AddTimer(convert(period), timerCallback, this);
                }
        } else {
                // no timer yet
                time = alarm.time;
                id = SDL_AddTimer(convert(period), timerCallback, this);
        }
}

void AlarmManager::stop(Alarm& alarm)
{
        ScopedLock lock(sem);
        alarm.active = false;
        // No need to remove timer, we can handle spurious callbacks.
        // Maybe in the future remove it as an optimization?
}

bool AlarmManager::isPending(const Alarm& alarm)
{
        ScopedLock lock(sem);
        return alarm.active;
}

unsigned AlarmManager::timerCallback(unsigned /*interval*/, void* param)
{
        // note: runs in a different thread!
        if (!enabled) return 0;
        auto manager = static_cast<AlarmManager*>(param);
        return manager->timerCallback2();
}

unsigned AlarmManager::timerCallback2()
{
        // note: runs in a different thread!
        ScopedLock lock(sem);

        int64_t now = Timer::getTime();
        int64_t earliest = std::numeric_limits<int64_t>::max();
        for (auto& a : alarms) {
                if (a->active) {
                        // timer active
                        // note: don't compare time directly (a->time < now),
                        //       because there is a small chance time will wrap
                        int64_t left = a->time - now;
                        if (left <= 0) {
                                // timer expired
                                if (a->alarm()) {
                                        // repeat
                                        a->time += a->period;
                                        left = a->time - now;
                                        // 'left' can still be negative at this
                                        // point, but that's ok .. convert()
                                        // will return '1' in that case
                                        earliest = std::min(earliest, left);
                                } else {
                                        a->active = false;
                                }
                        } else {
                                // timer active but not yet expired
                                earliest = std::min(earliest, left);
                        }
                }
        }
        if (earliest != std::numeric_limits<int64_t>::max()) {
                time = earliest + now;
                assert(id);
                return convert(int(earliest));
        } else {
                for (auto& a : alarms) {
                        assert(a->active == false); (void)a;
                }
                id = nullptr;
                return 0; // don't repeat
        }
}


// class Alarm

Alarm::Alarm()
        : manager(AlarmManager::instance())
        , active(false)
        , destructing(false)
{
        manager.registerAlarm(*this);
}

Alarm::~Alarm()
{
        assert(destructing); // prepareDelete() must be called in subclass
}

void Alarm::prepareDelete()
{
        assert(!destructing); // not yet called
        manager.unregisterAlarm(*this);
        destructing = true;
}

void Alarm::schedule(unsigned newPeriod)
{
        manager.start(*this, newPeriod);
}

void Alarm::cancel()
{
        manager.stop(*this);
}

bool Alarm::pending() const
{
        return manager.isPending(*this);
}

} // namespace openmsx