Fix data race.

+ Add thread-safety with mutexes in `PieceTable` and `Buffer`
+ Bump version to 1.5.9

Buffer.cc

@@ -412,6 +412,7 @@ Buffer::GetLineView(std::size_t row) const
 void
 Buffer::ensure_rows_cache() const
 {
+	std::lock_guard<std::mutex> lock(buffer_mutex_);
 	if (!rows_cache_dirty_)
 		return;
 	rows_.clear();

Buffer.h

@@ -14,6 +14,7 @@
 #include <cstdint>
 #include "syntax/HighlighterEngine.h"
 #include "Highlight.h"
+#include <mutex>
 
 // Forward declaration for swap journal integration
 namespace kte {
@@ -482,4 +483,6 @@ private:
 	std::unique_ptr<kte::HighlighterEngine> highlighter_;
 	// Non-owning pointer to swap recorder managed by Editor/SwapManager
 	kte::SwapRecorder *swap_rec_ = nullptr;
+
+	mutable std::mutex buffer_mutex_;
 };

CMakeLists.txt

@@ -4,7 +4,7 @@ project(kte)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_STANDARD 20)
-set(KTE_VERSION "1.5.8")
+set(KTE_VERSION "1.5.9")
 
 # Default to terminal-only build to avoid SDL/OpenGL dependency by default.
 # Enable with -DBUILD_GUI=ON when SDL2/OpenGL/Freetype are available.

Frontend.h

@@ -12,7 +12,7 @@ public:
 	virtual ~Frontend() = default;
 
 	// Initialize the frontend (create window/terminal, etc.)
-	virtual bool Init(Editor &ed) = 0;
+	virtual bool Init(int &argc, char **argv, Editor &ed) = 0;
 
 	// Execute one iteration (poll input, dispatch, draw). Set running=false to exit.
 	virtual void Step(Editor &ed, bool &running) = 0;

ImGuiFrontend.cc

@@ -30,8 +30,10 @@
 static auto kGlslVersion = "#version 150"; // GL 3.2 core (macOS compatible)
 
 bool
-GUIFrontend::Init(Editor &ed)
+GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 {
+	(void) argc;
+	(void) argv;
 	// Attach editor to input handler for editor-owned features (e.g., universal argument)
 	input_.Attach(&ed);
 	// editor dimensions will be initialized during the first Step() frame

ImGuiFrontend.h

@@ -17,7 +17,7 @@ public:
 
 	~GUIFrontend() override = default;
 
-	bool Init(Editor &ed) override;
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 

PieceTable.cc

@@ -273,6 +273,7 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 void
 PieceTable::materialize() const
 {
+	std::lock_guard<std::mutex> lock(mutex_);
 	if (!dirty_) {
 		return;
 	}
@@ -348,6 +349,7 @@ PieceTable::coalesceNeighbors(std::size_t index)
 void
 PieceTable::InvalidateLineIndex() const
 {
+	std::lock_guard<std::mutex> lock(mutex_);
 	line_index_dirty_ = true;
 }
 
@@ -355,22 +357,29 @@ PieceTable::InvalidateLineIndex() const
 void
 PieceTable::RebuildLineIndex() const
 {
-	if (!line_index_dirty_)
+	std::lock_guard<std::mutex> lock(mutex_);
+
+	if (!line_index_dirty_) {
 		return;
+	}
 	line_index_.clear();
 	line_index_.push_back(0);
+
 	std::size_t pos = 0;
 	for (const auto &pc: pieces_) {
 		const std::string &src = pc.src == Source::Original ? original_ : add_;
 		const char *base       = src.data() + static_cast<std::ptrdiff_t>(pc.start);
+
 		for (std::size_t j = 0; j < pc.len; ++j) {
 			if (base[j] == '\n') {
 				// next line starts after the newline
 				line_index_.push_back(pos + j + 1);
 			}
 		}
+
 		pos += pc.len;
 	}
+
 	line_index_dirty_ = false;
 }
 
@@ -692,14 +701,18 @@ PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
 		len = total_size_ - byte_offset;
 
 	// Fast path: return cached value if version/offset/len match
+	{
+		std::lock_guard<std::mutex> lock(mutex_);
 		if (range_cache_.valid && range_cache_.version == version_ &&
 		    range_cache_.off == byte_offset && range_cache_.len == len) {
 			return range_cache_.data;
 		}
+	}
 
 	std::string out;
 	out.reserve(len);
 	if (!dirty_) {
+		std::lock_guard<std::mutex> lock(mutex_);
 		// Already materialized; slice directly
 		out.assign(materialized_.data() + static_cast<std::ptrdiff_t>(byte_offset), len);
 	} else {
@@ -723,11 +736,14 @@ PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
 	}
 
 	// Update cache
+	{
+		std::lock_guard<std::mutex> lock(mutex_);
 		range_cache_.valid   = true;
 		range_cache_.version = version_;
 		range_cache_.off     = byte_offset;
 		range_cache_.len     = len;
 		range_cache_.data    = out;
+	}
 	return out;
 }
 
@@ -739,15 +755,21 @@ PieceTable::Find(const std::string &needle, std::size_t start) const
 		return start <= total_size_ ? start : std::numeric_limits<std::size_t>::max();
 	if (start > total_size_)
 		return std::numeric_limits<std::size_t>::max();
+	{
+		std::lock_guard<std::mutex> lock(mutex_);
 		if (find_cache_.valid &&
 		    find_cache_.version == version_ &&
 		    find_cache_.needle == needle &&
 		    find_cache_.start == start) {
 			return find_cache_.result;
 		}
+	}
 
 	materialize();
-	auto pos = materialized_.find(needle, start);
+	std::size_t pos;
+	{
+		std::lock_guard<std::mutex> lock(mutex_);
+		pos = materialized_.find(needle, start);
 		if (pos == std::string::npos)
 			pos = std::numeric_limits<std::size_t>::max();
 		// Update cache
@@ -756,6 +778,7 @@ PieceTable::Find(const std::string &needle, std::size_t start) const
 		find_cache_.needle  = needle;
 		find_cache_.start   = start;
 		find_cache_.result  = pos;
+	}
 	return pos;
 }
 
@@ -764,7 +787,10 @@ void
 PieceTable::WriteToStream(std::ostream &out) const
 {
 	// Stream the content piece-by-piece without forcing full materialization
-    for (const auto &p : pieces_) {
+	// No lock needed for original_ and add_ if they are not being modified.
+	// Since this is a const method and kte's piece table isn't modified by multiple threads
+	// (only queried), we just iterate pieces_.
+	for (const auto &p: pieces_) {
 		if (p.len == 0)
 			continue;
 		const std::string &src = (p.src == Source::Original) ? original_ : add_;

PieceTable.h

@@ -8,6 +8,7 @@
 #include <ostream>
 #include <vector>
 #include <limits>
+#include <mutex>
 
 
 class PieceTable {
@@ -181,4 +182,6 @@ private:
 
 	mutable RangeCache range_cache_;
 	mutable FindCache find_cache_;
+
+	mutable std::mutex mutex_;
 };

QtFrontend.cc

@@ -658,10 +658,8 @@ private:
 } // namespace
 
 bool
-GUIFrontend::Init(Editor &ed)
+GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 {
-	int argc    = 0;
-	char **argv = nullptr;
 	app_ = new QApplication(argc, argv);
 
 	window_ = new MainWindow(input_);

QtFrontend.h

@@ -18,7 +18,7 @@ public:
 
 	~GUIFrontend() override = default;
 
-	bool Init(Editor &ed) override;
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 

TerminalFrontend.cc

@@ -8,8 +8,10 @@
 
 
 bool
-TerminalFrontend::Init(Editor &ed)
+TerminalFrontend::Init(int &argc, char **argv, Editor &ed)
 {
+	(void) argc;
+	(void) argv;
 	// Ensure Control keys reach the app: disable XON/XOFF and dsusp/susp bindings (e.g., ^S/^Q, ^Y on macOS)
 	{
 		struct termios tio{};

TerminalFrontend.h

@@ -21,7 +21,7 @@ public:
 	// Adjust if your terminal needs a different threshold.
 	static constexpr int kEscDelayMs = 50;
 
-	bool Init(Editor &ed) override;
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 

TestFrontend.cc

@@ -4,8 +4,10 @@
 
 
 bool
-TestFrontend::Init(Editor &ed)
+TestFrontend::Init(int &argc, char **argv, Editor &ed)
 {
+	(void) argc;
+	(void) argv;
 	ed.SetDimensions(24, 80);
 	return true;
 }

TestFrontend.h

@@ -13,7 +13,7 @@ public:
 
 	~TestFrontend() override = default;
 
-	bool Init(Editor &ed) override;
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 

main.cc

@@ -112,7 +112,7 @@ RunStressHighlighter(unsigned seconds)
 
 
 int
-main(int argc, const char *argv[])
+main(int argc, char *argv[])
 {
 	std::setlocale(LC_ALL, "");
 
@@ -136,7 +136,7 @@ main(int argc, const char *argv[])
 	int opt;
 	int long_index          = 0;
 	unsigned stress_seconds = 0;
-	while ((opt = getopt_long(argc, const_cast<char *const *>(argv), "gthV", long_opts, &long_index)) != -1) {
+	while ((opt = getopt_long(argc, argv, "gthV", long_opts, &long_index)) != -1) {
 		switch (opt) {
 		case 'g':
 			req_gui = true;
@@ -303,7 +303,7 @@ main(int argc, const char *argv[])
 	}
 #endif
 
-	if (!fe->Init(editor)) {
+	if (!fe->Init(argc, argv, editor)) {
 		std::cerr << "kte: failed to initialize frontend" << std::endl;
 		return 1;
 	}