kte/syntax/HighlighterEngine.cc

#include "HighlighterEngine.h"
#include "../Buffer.h"
#include "LanguageHighlighter.h"
#include <thread>

namespace kte {
HighlighterEngine::HighlighterEngine() = default;


HighlighterEngine::~HighlighterEngine()
{
	// stop background worker
	if (worker_running_.load()) {
		{
			std::lock_guard<std::mutex> lock(mtx_);
			worker_running_.store(false);
			has_request_ = true; // wake it up to exit
		}
		cv_.notify_one();
		if (worker_.joinable())
			worker_.join();
	}
}


void
HighlighterEngine::SetHighlighter(std::unique_ptr<LanguageHighlighter> hl)
{
	std::lock_guard<std::mutex> lock(mtx_);
	hl_ = std::move(hl);
	cache_.clear();
	state_cache_.clear();
	state_last_contig_.clear();
}


const LineHighlight &
HighlighterEngine::GetLine(const Buffer &buf, int row, std::uint64_t buf_version) const
{
	std::unique_lock<std::mutex> lock(mtx_);
	auto it = cache_.find(row);
	if (it != cache_.end() && it->second.version == buf_version) {
		return it->second;
	}

	// Prepare destination slot to reuse its capacity and avoid allocations
	LineHighlight &slot = cache_[row];
	slot.version        = buf_version;
	slot.spans.clear();

	if (!hl_) {
		return slot;
	}

	// Copy shared_ptr-like raw pointer for use outside critical sections
	LanguageHighlighter *hl_ptr = hl_.get();
	bool is_stateful            = dynamic_cast<StatefulHighlighter *>(hl_ptr) != nullptr;

	if (!is_stateful) {
		// Stateless fast path: we can release the lock while computing to reduce contention
		auto &out = slot.spans;
		lock.unlock();
		hl_ptr->HighlightLine(buf, row, out);
		return cache_.at(row);
	}

	// Stateful path: we need to walk from a known previous state. Keep lock while consulting caches,
	// but release during heavy computation.
	auto *stateful = static_cast<StatefulHighlighter *>(hl_ptr);

	StatefulHighlighter::LineState prev_state;
	int start_row = -1;
	if (!state_cache_.empty()) {
		// linear search over map (unordered), track best candidate
		int best = -1;
		for (const auto &kv: state_cache_) {
			int r = kv.first;
			// Only use cached state if it's for the current version and row still exists
			if (r <= row - 1 && kv.second.version == buf_version) {
				// Validate that the cached row index is still valid in the buffer
				if (r >= 0 && static_cast<std::size_t>(r) < buf.Rows().size()) {
					if (r > best)
						best = r;
				}
			}
		}
		if (best >= 0) {
			start_row  = best;
			prev_state = state_cache_.at(best).state;
		}
	}

	// We'll compute states and the target line's spans without holding the lock for most of the work.
	// Create a local copy of prev_state and iterate rows; we will update caches under lock.
	lock.unlock();
	StatefulHighlighter::LineState cur_state = prev_state;
	for (int r = start_row + 1; r <= row; ++r) {
		std::vector<HighlightSpan> tmp;
		std::vector<HighlightSpan> &out = (r == row) ? slot.spans : tmp;
		auto next_state                 = stateful->HighlightLineStateful(buf, r, cur_state, out);
		// Update state cache for r
		std::lock_guard<std::mutex> gl(mtx_);
		StateEntry se;
		se.version      = buf_version;
		se.state        = next_state;
		state_cache_[r] = se;
		cur_state       = next_state;
	}

	// Return reference under lock to ensure slot's address stability in map
	lock.lock();
	return cache_.at(row);
}


void
HighlighterEngine::InvalidateFrom(int row)
{
	std::lock_guard<std::mutex> lock(mtx_);
	if (cache_.empty())
		return;
	// Simple implementation: erase all rows >= row
	for (auto it = cache_.begin(); it != cache_.end();) {
		if (it->first >= row)
			it = cache_.erase(it);
		else
			++it;
	}
	if (!state_cache_.empty()) {
		for (auto it = state_cache_.begin(); it != state_cache_.end();) {
			if (it->first >= row)
				it = state_cache_.erase(it);
			else
				++it;
		}
	}
}


void
HighlighterEngine::ensure_worker_started() const
{
	if (worker_running_.load())
		return;
	worker_running_.store(true);
	worker_ = std::thread([this]() {
		this->worker_loop();
	});
}


void
HighlighterEngine::worker_loop() const
{
	std::unique_lock<std::mutex> lock(mtx_);
	while (worker_running_.load()) {
		cv_.wait(lock, [this]() {
			return has_request_ || !worker_running_.load();
		});
		if (!worker_running_.load())
			break;
		WarmRequest req = pending_;
		has_request_    = false;
		// Copy locals then release lock while computing
		lock.unlock();
		if (req.buf) {
			int start = std::max(0, req.start_row);
			int end   = std::max(start, req.end_row);
			for (int r = start; r <= end; ++r) {
				// Re-check version staleness quickly by peeking cache version; not strictly necessary
				// Compute line; GetLine is thread-safe
				(void) this->GetLine(*req.buf, r, req.version);
			}
		}
		lock.lock();
	}
}


void
HighlighterEngine::PrefetchViewport(const Buffer &buf, int first_row, int row_count, std::uint64_t buf_version,
                                    int warm_margin) const
{
	if (row_count <= 0)
		return;
	// Synchronously compute visible rows to ensure cache hits during draw
	int start    = std::max(0, first_row);
	int end      = start + row_count - 1;
	int max_rows = static_cast<int>(buf.Nrows());
	if (start >= max_rows)
		return;
	if (end >= max_rows)
		end = max_rows - 1;

	for (int r = start; r <= end; ++r) {
		(void) GetLine(buf, r, buf_version);
	}

	// Enqueue background warm-around
	int warm_start = std::max(0, start - warm_margin);
	int warm_end   = std::min(max_rows - 1, end + warm_margin);
	{
		std::lock_guard<std::mutex> lock(mtx_);
		pending_.buf       = &buf;
		pending_.version   = buf_version;
		pending_.start_row = warm_start;
		pending_.end_row   = warm_end;
		has_request_       = true;
	}
	ensure_worker_started();
	cv_.notify_one();
}
} // namespace kte