event dispatcher

apps/LoopThroughWithOpenGLCompositing/runtime/events/RuntimeEventCoalescingQueue.h

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+#pragma once
+
+#include "RuntimeEvent.h"
+
+#include <chrono>
+#include <cstddef>
+#include <deque>
+#include <functional>
+#include <map>
+#include <mutex>
+#include <string>
+#include <utility>
+#include <vector>
+
+struct RuntimeEventCoalescingQueueMetrics
+{
+	std::size_t depth = 0;
+	std::size_t capacity = 0;
+	std::size_t droppedCount = 0;
+	std::size_t coalescedCount = 0;
+	double oldestEventAgeMilliseconds = 0.0;
+};
+
+inline std::string RuntimeEventDefaultCoalescingKey(const RuntimeEvent& event)
+{
+	if (const auto* payload = std::get_if<OscValueReceivedEvent>(&event.payload))
+		return std::string(RuntimeEventTypeName(event.type)) + ":" + payload->routeKey;
+	if (const auto* payload = std::get_if<OscCommitRequestedEvent>(&event.payload))
+		return std::string(RuntimeEventTypeName(event.type)) + ":" + payload->routeKey;
+	if (const auto* payload = std::get_if<FileChangeDetectedEvent>(&event.payload))
+		return std::string(RuntimeEventTypeName(event.type)) + ":" + payload->path;
+	if (const auto* payload = std::get_if<QueueDepthChangedEvent>(&event.payload))
+		return std::string(RuntimeEventTypeName(event.type)) + ":" + payload->queueName;
+
+	return std::string(RuntimeEventTypeName(event.type));
+}
+
+class RuntimeEventCoalescingQueue
+{
+public:
+	using KeySelector = std::function<std::string(const RuntimeEvent&)>;
+
+	explicit RuntimeEventCoalescingQueue(std::size_t capacity = 256, KeySelector keySelector = RuntimeEventDefaultCoalescingKey) :
+		mCapacity(capacity),
+		mKeySelector(std::move(keySelector))
+	{
+	}
+
+	bool Push(RuntimeEvent event)
+	{
+		const std::string key = mKeySelector(event);
+		if (key.empty())
+			return false;
+
+		std::lock_guard<std::mutex> lock(mMutex);
+		auto found = mEntries.find(key);
+		if (found != mEntries.end())
+		{
+			const auto firstCreatedAt = found->second.event.createdAt;
+			found->second.event = std::move(event);
+			found->second.event.createdAt = firstCreatedAt;
+			++found->second.coalescedCount;
+			++mCoalescedCount;
+			return true;
+		}
+
+		if (mEntries.size() >= mCapacity)
+		{
+			++mDroppedCount;
+			return false;
+		}
+
+		mOrder.push_back(key);
+		Entry entry;
+		entry.event = std::move(event);
+		mEntries.emplace(key, std::move(entry));
+		return true;
+	}
+
+	std::vector<RuntimeEvent> Drain(std::size_t maxEvents = 0)
+	{
+		std::vector<RuntimeEvent> events;
+
+		std::lock_guard<std::mutex> lock(mMutex);
+		const std::size_t count = maxEvents == 0 || maxEvents > mOrder.size() ? mOrder.size() : maxEvents;
+		events.reserve(count);
+
+		for (std::size_t index = 0; index < count; ++index)
+		{
+			const std::string key = std::move(mOrder.front());
+			mOrder.pop_front();
+
+			auto found = mEntries.find(key);
+			if (found == mEntries.end())
+				continue;
+
+			events.push_back(std::move(found->second.event));
+			mEntries.erase(found);
+		}
+
+		return events;
+	}
+
+	RuntimeEventCoalescingQueueMetrics GetMetrics(std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now()) const
+	{
+		std::lock_guard<std::mutex> lock(mMutex);
+
+		RuntimeEventCoalescingQueueMetrics metrics;
+		metrics.depth = mEntries.size();
+		metrics.capacity = mCapacity;
+		metrics.droppedCount = mDroppedCount;
+		metrics.coalescedCount = mCoalescedCount;
+
+		if (!mOrder.empty())
+		{
+			const auto found = mEntries.find(mOrder.front());
+			if (found != mEntries.end())
+			{
+				const auto age = now - found->second.event.createdAt;
+				metrics.oldestEventAgeMilliseconds = std::chrono::duration<double, std::milli>(age).count();
+			}
+		}
+
+		return metrics;
+	}
+
+	std::size_t Depth() const
+	{
+		std::lock_guard<std::mutex> lock(mMutex);
+		return mEntries.size();
+	}
+
+private:
+	struct Entry
+	{
+		RuntimeEvent event;
+		std::size_t coalescedCount = 0;
+	};
+
+	mutable std::mutex mMutex;
+	std::size_t mCapacity = 0;
+	KeySelector mKeySelector;
+	std::deque<std::string> mOrder;
+	std::map<std::string, Entry> mEntries;
+	std::size_t mDroppedCount = 0;
+	std::size_t mCoalescedCount = 0;
+};