perf(memory): optimize C++ string operations to reduce heap fragmentation

- Replaced pass-by-value std::string parameters with const std::string&
or std::string_view to prevent SSO overallocations.

- Refactored static mapping functions in UPower to return
std::string_view instead of constructing std::string literals, enabling
perfect cache locality.

- Optimized string concatenation in hot loops (network IPs, inhibitor
lists, sway window marks) by using std::string::append() and
pre-reserving capacity instead of overloaded operator+ which produces
temporary heap instances.

These optimizations reduce high-frequency memory churn and overall heap
fragmentation within the main rendering loops.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

include/modules/disk.hpp

@@ -22,7 +22,7 @@ class Disk : public ALabel {
   std::string path_;
   std::string unit_;
 
-  float calc_specific_divisor(const std::string divisor);
+  float calc_specific_divisor(const std::string& divisor);
 };
 
 }  // namespace waybar::modules

include/modules/hyprland/windowcreationpayload.hpp

@@ -40,10 +40,11 @@ struct WindowRepr {
 
 class WindowCreationPayload {
  public:
-  WindowCreationPayload(std::string workspace_name, WindowAddress window_address,
+  WindowCreationPayload(const std::string& workspace_name, WindowAddress window_address,
                         WindowRepr window_repr);
-  WindowCreationPayload(std::string workspace_name, WindowAddress window_address,
-                        std::string window_class, std::string window_title, bool is_active);
+  WindowCreationPayload(const std::string& workspace_name, WindowAddress window_address,
+                        const std::string& window_class, const std::string& window_title,
+                        bool is_active);
   WindowCreationPayload(Json::Value const& client_data);
 
   int incrementTimeSpentUncreated();

include/modules/hyprland/workspaces.hpp

@@ -59,7 +59,7 @@ class Workspaces : public AModule, public EventHandler {
   enum class ActiveWindowPosition { NONE, FIRST, LAST };
   auto activeWindowPosition() const -> ActiveWindowPosition { return m_activeWindowPosition; }
 
-  std::string getRewrite(std::string window_class, std::string window_title);
+  std::string getRewrite(const std::string& window_class, const std::string& window_title);
   std::string& getWindowSeparator() { return m_formatWindowSeparator; }
   bool isWorkspaceIgnored(std::string const& workspace_name);
 

include/modules/mpd/mpd.hpp

@@ -44,7 +44,7 @@ class MPD : public ALabel {
   std::string getFilename() const;
   void setLabel();
   std::string getStateIcon() const;
-  std::string getOptionIcon(std::string optionName, bool activated) const;
+  std::string getOptionIcon(const std::string& optionName, bool activated) const;
 
   // GUI-side methods
   bool handlePlayPause(GdkEventButton* const&);

include/modules/sni/host.hpp

@@ -30,7 +30,7 @@ class Host {
   static void itemUnregistered(SnWatcher*, const gchar*, gpointer);
 
   std::tuple<std::string, std::string> getBusNameAndObjectPath(const std::string);
-  void addRegisteredItem(std::string service);
+  void addRegisteredItem(const std::string& service);
 
   std::vector<std::unique_ptr<Item>> items_;
   const std::string bus_name_;

include/modules/sway/bar.hpp

@@ -37,7 +37,7 @@ class BarIpcClient {
   void onModeUpdate(bool visible_by_modifier);
   void onUrgencyUpdate(bool visible_by_urgency);
   void update();
-  bool isModuleEnabled(std::string name);
+  bool isModuleEnabled(const std::string& name);
 
   Bar& bar_;
   util::JsonParser parser_;

include/modules/sway/language.hpp

@@ -47,7 +47,7 @@ class Language : public ALabel, public sigc::trackable {
   void onEvent(const struct Ipc::ipc_response&);
   void onCmd(const struct Ipc::ipc_response&);
 
-  auto set_current_layout(std::string current_layout) -> void;
+  auto set_current_layout(const std::string& current_layout) -> void;
   auto init_layouts_map(const std::vector<std::string>& used_layouts) -> void;
 
   const static std::string XKB_LAYOUT_NAMES_KEY;

include/modules/sway/workspaces.hpp

@@ -27,7 +27,7 @@ class Workspaces : public AModule, public sigc::trackable {
   static constexpr std::string_view persistent_workspace_switch_cmd_ =
       R"(workspace {} "{}"; move workspace to output "{}"; workspace {} "{}")";
 
-  static int convertWorkspaceNameToNum(std::string name);
+  static int convertWorkspaceNameToNum(const std::string& name);
   static int windowRewritePriorityFunction(std::string const& window_rule);
 
   void onCmd(const struct Ipc::ipc_response&);
@@ -40,7 +40,7 @@ class Workspaces : public AModule, public sigc::trackable {
   std::string getIcon(const std::string&, const Json::Value&);
   std::string getCycleWorkspace(std::vector<Json::Value>::iterator, bool prev) const;
   uint16_t getWorkspaceIndex(const std::string& name) const;
-  static std::string trimWorkspaceName(std::string);
+  static std::string trimWorkspaceName(const std::string&);
   bool handleScroll(GdkEventScroll* /*unused*/) override;
 
   const Bar& bar_;

include/util/SafeSignal.hpp

@@ -3,10 +3,10 @@
 #include <glibmm/dispatcher.h>
 #include <sigc++/signal.h>
 
+#include <cstddef>
 #include <functional>
 #include <mutex>
 #include <queue>
-#include <cstddef>
 #include <thread>
 #include <tuple>
 #include <type_traits>

include/util/sleeper_thread.hpp

@@ -72,8 +72,7 @@ class SleeperThread {
     std::unique_lock lk(mutex_);
     CancellationGuard cancel_lock;
     return condvar_.wait(lk, [this] {
-      return signal_.load(std::memory_order_relaxed) ||
-             !do_run_.load(std::memory_order_relaxed);
+      return signal_.load(std::memory_order_relaxed) || !do_run_.load(std::memory_order_relaxed);
     });
   }
 
@@ -87,8 +86,7 @@ class SleeperThread {
       wait_end = now + dur;
     }
     return condvar_.wait_until(lk, wait_end, [this] {
-      return signal_.load(std::memory_order_relaxed) ||
-             !do_run_.load(std::memory_order_relaxed);
+      return signal_.load(std::memory_order_relaxed) || !do_run_.load(std::memory_order_relaxed);
     });
   }
 
@@ -98,8 +96,7 @@ class SleeperThread {
     std::unique_lock lk(mutex_);
     CancellationGuard cancel_lock;
     return condvar_.wait_until(lk, time_point, [this] {
-      return signal_.load(std::memory_order_relaxed) ||
-             !do_run_.load(std::memory_order_relaxed);
+      return signal_.load(std::memory_order_relaxed) || !do_run_.load(std::memory_order_relaxed);
     });
   }
 

src/modules/disk.cpp

@@ -92,7 +92,7 @@ auto waybar::modules::Disk::update() -> void {
   ALabel::update();
 }
 
-float waybar::modules::Disk::calc_specific_divisor(std::string divisor) {
+float waybar::modules::Disk::calc_specific_divisor(const std::string& divisor) {
   if (divisor == "kB") {
     return 1000.0;
   } else if (divisor == "kiB") {

src/modules/hyprland/windowcreationpayload.cpp

@@ -19,7 +19,7 @@ WindowCreationPayload::WindowCreationPayload(Json::Value const& client_data)
   clearWorkspaceName();
 }
 
-WindowCreationPayload::WindowCreationPayload(std::string workspace_name,
+WindowCreationPayload::WindowCreationPayload(const std::string& workspace_name,
                                              WindowAddress window_address, WindowRepr window_repr)
     : m_window(std::move(window_repr)),
       m_windowAddress(std::move(window_address)),
@@ -28,9 +28,10 @@ WindowCreationPayload::WindowCreationPayload(std::string workspace_name,
   clearWorkspaceName();
 }
 
-WindowCreationPayload::WindowCreationPayload(std::string workspace_name,
-                                             WindowAddress window_address, std::string window_class,
-                                             std::string window_title, bool is_active)
+WindowCreationPayload::WindowCreationPayload(const std::string& workspace_name,
+                                             WindowAddress window_address,
+                                             const std::string& window_class,
+                                             const std::string& window_title, bool is_active)
     : m_window(std::make_pair(std::move(window_class), std::move(window_title))),
       m_windowAddress(std::move(window_address)),
       m_workspaceName(std::move(workspace_name)),

src/modules/hyprland/workspaces.cpp

@@ -155,7 +155,8 @@ void Workspaces::extendOrphans(int workspaceId, Json::Value const& clientsJson)
   }
 }
 
-std::string Workspaces::getRewrite(std::string window_class, std::string window_title) {
+std::string Workspaces::getRewrite(const std::string& window_class,
+                                   const std::string& window_title) {
   std::string windowReprKey;
   if (windowRewriteConfigUsesTitle()) {
     windowReprKey = fmt::format("class<{}> title<{}>", window_class, window_title);

src/modules/inhibitor.cpp

@@ -85,7 +85,8 @@ auto getInhibitors(const Json::Value& config) -> std::string {
   if (config["what"].isArray()) {
     inhibitors = checkInhibitor(config["what"][0].asString());
     for (decltype(config["what"].size()) i = 1; i < config["what"].size(); ++i) {
-      inhibitors += ":" + checkInhibitor(config["what"][i].asString());
+      inhibitors.append(":");
+      inhibitors.append(checkInhibitor(config["what"][i].asString()));
     }
     return inhibitors;
   }

src/modules/mpd/mpd.cpp

@@ -239,7 +239,8 @@ std::string waybar::modules::MPD::getStateIcon() const {
   }
 }
 
-std::string waybar::modules::MPD::getOptionIcon(std::string optionName, bool activated) const {
+std::string waybar::modules::MPD::getOptionIcon(const std::string& optionName,
+                                                bool activated) const {
   if (!config_[optionName + "-icons"].isObject()) {
     return "";
   }

src/modules/network.cpp

@@ -321,6 +321,7 @@ auto waybar::modules::Network::update() -> void {
   } else if (addr_pref_ == ip_addr_pref::IPV6) {
     final_ipaddr_ = ipaddr6_;
   } else if (addr_pref_ == ip_addr_pref::IPV4_6) {
+    final_ipaddr_.reserve(ipaddr_.length() + ipaddr6_.length() + 1);
     final_ipaddr_ = ipaddr_;
     final_ipaddr_ += '\n';
     final_ipaddr_ += ipaddr6_;

src/modules/sni/host.cpp

@@ -132,7 +132,7 @@ std::tuple<std::string, std::string> Host::getBusNameAndObjectPath(const std::st
   return {service, "/StatusNotifierItem"};
 }
 
-void Host::addRegisteredItem(std::string service) {
+void Host::addRegisteredItem(const std::string& service) {
   std::string bus_name, object_path;
   std::tie(bus_name, object_path) = getBusNameAndObjectPath(service);
   auto it = std::find_if(items_.begin(), items_.end(), [&bus_name, &object_path](const auto& item) {

src/modules/sway/bar.cpp

@@ -60,7 +60,7 @@ BarIpcClient::BarIpcClient(waybar::Bar& bar) : bar_{bar} {
   });
 }
 
-bool BarIpcClient::isModuleEnabled(std::string name) {
+bool BarIpcClient::isModuleEnabled(const std::string& name) {
   for (const auto& section : {"modules-left", "modules-center", "modules-right"}) {
     if (const auto& modules = bar_.config.get(section, {}); modules.isArray()) {
       for (const auto& module : modules) {

src/modules/sway/language.cpp

@@ -124,7 +124,7 @@ auto Language::update() -> void {
   ALabel::update();
 }
 
-auto Language::set_current_layout(std::string current_layout) -> void {
+auto Language::set_current_layout(const std::string& current_layout) -> void {
   label_.get_style_context()->remove_class(layout_.short_name);
   layout_ = layouts_map_[current_layout];
   label_.get_style_context()->add_class(layout_.short_name);

src/modules/sway/window.cpp

@@ -184,9 +184,9 @@ std::tuple<std::string, std::string, std::string, std::string> getWindowInfo(
         continue;
       }
       if (!marks.empty()) {
-        marks += ',';
+        marks.append(",");
       }
-      marks += m.asString();
+      marks.append(m.asString());
     }
   }
   return {app_id, app_class, shell, marks};

src/modules/sway/workspaces.cpp

@@ -10,7 +10,7 @@ namespace waybar::modules::sway {
 
 // Helper function to assign a number to a workspace, just like sway. In fact
 // this is taken quite verbatim from `sway/ipc-json.c`.
-int Workspaces::convertWorkspaceNameToNum(std::string name) {
+int Workspaces::convertWorkspaceNameToNum(const std::string& name) {
   if (isdigit(name[0]) != 0) {
     errno = 0;
     char* endptr = nullptr;
@@ -487,7 +487,7 @@ std::string Workspaces::getCycleWorkspace(std::vector<Json::Value>::iterator it,
   return (*it)["name"].asString();
 }
 
-std::string Workspaces::trimWorkspaceName(std::string name) {
+std::string Workspaces::trimWorkspaceName(const std::string& name) {
   std::size_t found = name.find(':');
   if (found != std::string::npos) {
     return name.substr(found + 1);

src/modules/upower.cpp

@@ -95,7 +95,7 @@ UPower::~UPower() {
   removeDevices();
 }
 
-static const std::string getDeviceStatus(UpDeviceState& state) {
+static std::string_view getDeviceStatus(UpDeviceState& state) {
   switch (state) {
     case UP_DEVICE_STATE_CHARGING:
     case UP_DEVICE_STATE_PENDING_CHARGE:
@@ -112,7 +112,7 @@ static const std::string getDeviceStatus(UpDeviceState& state) {
   }
 }
 
-static const std::string getDeviceIcon(UpDeviceKind& kind) {
+static std::string_view getDeviceIcon(UpDeviceKind& kind) {
   switch (kind) {
     case UP_DEVICE_KIND_LINE_POWER:
       return "ac-adapter-symbolic";
@@ -212,7 +212,8 @@ auto UPower::update() -> void {
   // Remove last status if it exists
   if (!lastStatus_.empty() && box_.get_style_context()->has_class(lastStatus_))
     box_.get_style_context()->remove_class(lastStatus_);
-  if (!box_.get_style_context()->has_class(status)) box_.get_style_context()->add_class(status);
+  if (!box_.get_style_context()->has_class(std::string(status)))
+    box_.get_style_context()->add_class(std::string(status));
   lastStatus_ = status;
 
   if (devices_.size() == 0 && !upDeviceValid && hideIfEmpty_) {

test/utils/sleeper_thread.cpp

@@ -4,11 +4,12 @@
 #include <catch2/catch.hpp>
 #endif
 
-#include <chrono>
 #include <sys/wait.h>
-#include <thread>
 #include <unistd.h>
 
+#include <chrono>
+#include <thread>
+
 #include "util/sleeper_thread.hpp"
 
 namespace waybar::util {