Fix data race.

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

Buffer.cc

@@ -292,29 +292,29 @@ Buffer::OpenFromFile(const std::string &path, std::string &err)
 bool
 Buffer::Save(std::string &err) const
 {
-    if (!is_file_backed_ || filename_.empty()) {
-        err = "Buffer is not file-backed; use SaveAs()";
-        return false;
-    }
-    std::ofstream out(filename_, std::ios::out | std::ios::binary | std::ios::trunc);
-    if (!out) {
-        err = "Failed to open for write: " + filename_ + ". Error: " + std::string(std::strerror(errno));
-        return false;
-    }
-    // Stream the content directly from the piece table to avoid relying on
-    // full materialization, which may yield an empty pointer when size > 0.
-    if (content_.Size() > 0) {
-        content_.WriteToStream(out);
-    }
-    // Ensure data hits the OS buffers
-    out.flush();
-    if (!out.good()) {
-        err = "Write error: " + filename_ + ". Error: " + std::string(std::strerror(errno));
-        return false;
-    }
-    // Note: const method cannot change dirty_. Intentionally const to allow UI code
-    // to decide when to flip dirty flag after successful save.
-    return true;
+	if (!is_file_backed_ || filename_.empty()) {
+		err = "Buffer is not file-backed; use SaveAs()";
+		return false;
+	}
+	std::ofstream out(filename_, std::ios::out | std::ios::binary | std::ios::trunc);
+	if (!out) {
+		err = "Failed to open for write: " + filename_ + ". Error: " + std::string(std::strerror(errno));
+		return false;
+	}
+	// Stream the content directly from the piece table to avoid relying on
+	// full materialization, which may yield an empty pointer when size > 0.
+	if (content_.Size() > 0) {
+		content_.WriteToStream(out);
+	}
+	// Ensure data hits the OS buffers
+	out.flush();
+	if (!out.good()) {
+		err = "Write error: " + filename_ + ". Error: " + std::string(std::strerror(errno));
+		return false;
+	}
+	// Note: const method cannot change dirty_. Intentionally const to allow UI code
+	// to decide when to flip dirty flag after successful save.
+	return true;
 }
 
 
@@ -346,16 +346,16 @@ Buffer::SaveAs(const std::string &path, std::string &err)
 		err = "Failed to open for write: " + out_path + ". Error: " + std::string(std::strerror(errno));
 		return false;
 	}
- // Stream content without forcing full materialization
- if (content_.Size() > 0) {
-     content_.WriteToStream(out);
- }
- // Ensure data hits the OS buffers
-    out.flush();
-    if (!out.good()) {
-        err = "Write error: " + out_path + ". Error: " + std::string(std::strerror(errno));
-        return false;
-    }
+	// Stream content without forcing full materialization
+	if (content_.Size() > 0) {
+		content_.WriteToStream(out);
+	}
+	// Ensure data hits the OS buffers
+	out.flush();
+	if (!out.good()) {
+		err = "Write error: " + out_path + ". Error: " + std::string(std::strerror(errno));
+		return false;
+	}
 
 	filename_       = out_path;
 	is_file_backed_ = true;
@@ -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();
@@ -454,8 +455,8 @@ Buffer::delete_text(int row, int col, std::size_t len)
 		const std::size_t L    = line.size();
 		if (c < L) {
 			const std::size_t take = std::min(remaining, L - c);
-			c += take;
-			remaining -= take;
+			c                      += take;
+			remaining              -= take;
 		}
 		if (remaining == 0)
 			break;
@@ -463,8 +464,8 @@ Buffer::delete_text(int row, int col, std::size_t len)
 		if (r + 1 < lc) {
 			if (remaining > 0) {
 				remaining -= 1; // the newline
-				r += 1;
-				c = 0;
+				r         += 1;
+				c         = 0;
 			}
 		} else {
 			// At last line and still remaining: delete to EOF

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

@@ -218,9 +218,9 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 			std::size_t expectStart = last.start + last.len;
 
 			if (expectStart == start) {
-				last.len += len;
+				last.len    += len;
 				total_size_ += len;
-				dirty_ = true;
+				dirty_      = true;
 				version_++;
 				range_cache_ = {};
 				find_cache_  = {};
@@ -231,7 +231,7 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 
 	pieces_.push_back(Piece{src, start, len});
 	total_size_ += len;
-	dirty_ = true;
+	dirty_      = true;
 	InvalidateLineIndex();
 	version_++;
 	range_cache_ = {};
@@ -251,9 +251,9 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 		Piece &first = pieces_.front();
 		if (first.src == src && start + len == first.start) {
 			first.start = start;
-			first.len += len;
+			first.len   += len;
 			total_size_ += len;
-			dirty_ = true;
+			dirty_      = true;
 			version_++;
 			range_cache_ = {};
 			find_cache_  = {};
@@ -262,7 +262,7 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 	}
 	pieces_.insert(pieces_.begin(), Piece{src, start, len});
 	total_size_ += len;
-	dirty_ = true;
+	dirty_      = true;
 	InvalidateLineIndex();
 	version_++;
 	range_cache_ = {};
@@ -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;
 }
 
@@ -391,7 +400,7 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 	if (pieces_.empty()) {
 		pieces_.push_back(Piece{Source::Add, add_start, len});
 		total_size_ += len;
-		dirty_ = true;
+		dirty_      = true;
 		InvalidateLineIndex();
 		maybeConsolidate();
 		version_++;
@@ -405,7 +414,7 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 		// insert at end
 		pieces_.push_back(Piece{Source::Add, add_start, len});
 		total_size_ += len;
-		dirty_ = true;
+		dirty_      = true;
 		InvalidateLineIndex();
 		coalesceNeighbors(pieces_.size() - 1);
 		maybeConsolidate();
@@ -433,7 +442,7 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 	pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(idx), repl.begin(), repl.end());
 
 	total_size_ += len;
-	dirty_ = true;
+	dirty_      = true;
 	InvalidateLineIndex();
 	// Try coalescing around the inserted position (the inserted piece is at idx + (inner>0 ? 1 : 0))
 	std::size_t ins_index = idx + (inner > 0 ? 1 : 0);
@@ -488,13 +497,13 @@ PieceTable::Delete(std::size_t byte_offset, std::size_t len)
 			// entire piece removed
 			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(idx));
 			// stay at same idx for next piece
-			inner = 0;
+			inner     = 0;
 			remaining -= take;
 			continue;
 		}
 
 		// After modifying current idx, next deletion continues at beginning of the next logical region
-		inner = 0;
+		inner     = 0;
 		remaining -= take;
 		if (remaining == 0)
 			break;
@@ -503,7 +512,7 @@ PieceTable::Delete(std::size_t byte_offset, std::size_t len)
 	}
 
 	total_size_ -= len;
-	dirty_ = true;
+	dirty_      = true;
 	InvalidateLineIndex();
 	if (idx < pieces_.size())
 		coalesceNeighbors(idx);
@@ -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
-	if (range_cache_.valid && range_cache_.version == version_ &&
-	    range_cache_.off == byte_offset && range_cache_.len == len) {
-		return range_cache_.data;
+	{
+		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 {
@@ -714,8 +727,8 @@ PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
 				const char *base = src.data() + static_cast<std::ptrdiff_t>(p.start + inner);
 				out.append(base, take);
 				remaining -= take;
-				inner = 0;
-				idx += 1;
+				inner     = 0;
+				idx       += 1;
 			} else {
 				break;
 			}
@@ -723,11 +736,14 @@ PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
 	}
 
 	// Update cache
-	range_cache_.valid   = true;
-	range_cache_.version = version_;
-	range_cache_.off     = byte_offset;
-	range_cache_.len     = len;
-	range_cache_.data    = out;
+	{
+		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;
 }
 
@@ -739,23 +755,30 @@ 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();
-	if (find_cache_.valid &&
-	    find_cache_.version == version_ &&
-	    find_cache_.needle == needle &&
-	    find_cache_.start == start) {
-		return find_cache_.result;
+	{
+		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);
-	if (pos == std::string::npos)
-		pos = std::numeric_limits<std::size_t>::max();
-	// Update cache
-	find_cache_.valid   = true;
-	find_cache_.version = version_;
-	find_cache_.needle  = needle;
-	find_cache_.start   = start;
-	find_cache_.result  = pos;
+	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
+		find_cache_.valid   = true;
+		find_cache_.version = version_;
+		find_cache_.needle  = needle;
+		find_cache_.start   = start;
+		find_cache_.result  = pos;
+	}
 	return pos;
 }
 
@@ -763,12 +786,15 @@ PieceTable::Find(const std::string &needle, std::size_t start) const
 void
 PieceTable::WriteToStream(std::ostream &out) const
 {
-    // Stream the content piece-by-piece without forcing full materialization
-    for (const auto &p : pieces_) {
-        if (p.len == 0)
-            continue;
-        const std::string &src = (p.src == Source::Original) ? original_ : add_;
-        const char *base       = src.data() + static_cast<std::ptrdiff_t>(p.start);
-        out.write(base, static_cast<std::streamsize>(p.len));
-    }
+	// Stream the content piece-by-piece without forcing full materialization
+	// 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_;
+		const char *base       = src.data() + static_cast<std::ptrdiff_t>(p.start);
+		out.write(base, static_cast<std::streamsize>(p.len));
+	}
 }

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

@@ -658,11 +658,9 @@ 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);
+	app_ = new QApplication(argc, argv);
 
 	window_ = new MainWindow(input_);
 	window_->show();

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;
 	}