JUCE/modules/juce_audio_devices/midi_io/juce_ScheduledEventThread.h

/*
  ==============================================================================

   This file is part of the JUCE framework.
   Copyright (c) Raw Material Software Limited

   JUCE is an open source framework subject to commercial or open source
   licensing.

   By downloading, installing, or using the JUCE framework, or combining the
   JUCE framework with any other source code, object code, content or any other
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   framework to you, and you must discontinue the installation or download
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   Or:

   You may also use this code under the terms of the AGPLv3:
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  ==============================================================================
*/

namespace juce
{

/**
    @internal

    Allows events to be queued up, then for each event calls the OutputCallback at the time
    dictated by that event's timestamp.

    Event must have a getTimeStamp() member function that returns the output time of the event.
*/
template <typename Event>
class ScheduledEventThread : private Thread
{
public:
    using OutputCallback = std::function<void (const Event&)>;

    explicit ScheduledEventThread (OutputCallback&& c)
        : Thread (SystemStats::getJUCEVersion() + ": MIDI Out"),
          outputCallback (std::move (c))
    {
        jassert (outputCallback != nullptr);
    }

    ~ScheduledEventThread() override
    {
        stop();
    }

    void clearAllPendingMessages()
    {
        {
            const std::scoped_lock sl (mutex);
            pendingMessages.clear();
        }

        condvar.notify_one();
    }

    void start()
    {
        {
            const std::scoped_lock sl (mutex);
            backgroundThreadRunning = true;
        }

        startThread (Priority::high);
    }

    void stop()
    {
        {
            const std::scoped_lock sl (mutex);
            backgroundThreadRunning = false;
        }

        condvar.notify_one();
        stopThread (-1);
    }

    void addEvent (const Event& event)
    {
        // You've got to call startBackgroundThread() for this to actually work.
        jassert (isThreadRunning());

        {
            const std::scoped_lock sl (mutex);
            pendingMessages.insert (event);
        }

        condvar.notify_one();
    }

    bool isRunning() const
    {
        const std::scoped_lock sl (mutex);
        return backgroundThreadRunning;
    }

private:
    void run() override
    {
        for (;;)
        {
            std::unique_lock lock (mutex);
            condvar.wait (lock, [&]
            {
                return ! pendingMessages.empty() || ! backgroundThreadRunning;
            });

            if (! backgroundThreadRunning)
                return;

            const auto now = Time::getMillisecondCounter();
            const auto event = *pendingMessages.begin();
            pendingMessages.erase (pendingMessages.begin());

            const auto timestamp = event.getTimeStamp();

            if (timestamp > now + 20)
            {
                const auto millis = static_cast<int64_t> (timestamp - (now + 20));
                condvar.wait_for (lock, std::chrono::milliseconds (millis));
                continue;
            }

            if (timestamp > now)
                Time::waitForMillisecondCounter ((uint32) timestamp);

            if (timestamp > now - 200)
                outputCallback (event);
        }
    }

    struct Comparator
    {
        bool operator() (const Event& a, const Event& b) const
        {
            return a.getTimeStamp() < b.getTimeStamp();
        }
    };

    mutable std::mutex mutex;
    std::condition_variable condvar;
    std::multiset<Event, Comparator> pendingMessages;
    OutputCallback outputCallback;
    bool backgroundThreadRunning = false;
};

} // namespace juce