feature: add process renice functionality

This adds the ability to change the nice value of a process from within
btop. A new menu is introduced, accessible by pressing 'N', which allows
the user to input a new nice value for the selected process.

Fixes #1245

src/btop_draw.cpp

@@ -1662,11 +1662,14 @@ namespace Proc {
 				}
 				out += title_left + hi_color + Fx::b + (vim_keys ? 'K' : 'k') + t_color + "ill" + Fx::ub + title_right
 					+ title_left + hi_color + Fx::b + 's' + t_color + "ignals" + Fx::ub + title_right
+					+ title_left + hi_color + Fx::b + 'N' + t_color + "ice" + Fx::ub + title_right
 					+ Mv::to(d_y, d_x + d_width - 10) + title_left + t_color + Fx::b + hide + Symbols::enter + Fx::ub + title_right;
 				if (alive and selected == 0) {
 					Input::mouse_mappings["k"] = {d_y, mouse_x, 1, 4};
 					mouse_x += 6;
 					Input::mouse_mappings["s"] = {d_y, mouse_x, 1, 7};
+				    mouse_x += 9;
+					Input::mouse_mappings["N"] = {d_y, mouse_x, 1, 5};
 				}
 				if (selected == 0) Input::mouse_mappings["enter"] = {d_y, d_x + d_width - 9, 1, 6};
 
@@ -1760,6 +1763,9 @@ namespace Proc {
 			}
 			out += title_left_down + Fx::b + hi_color + 's' + t_color + "ignals" + Fx::ub + title_right_down;
 			if (selected > 0) Input::mouse_mappings["s"] = {y + height - 1, mouse_x, 1, 7};
+		    mouse_x += 9;
+		    out += title_left_down + Fx::b + hi_color + 'N' + t_color + "ice" + Fx::ub + title_right_down;
+		    if (selected > 0) Input::mouse_mappings["N"] = {y + height -1, mouse_x, 1, 5};
 
 			//? Labels for fields in list
 			if (not proc_tree)

src/btop_input.cpp

@@ -421,6 +421,12 @@ namespace Input {
 					Menu::show(Menu::Menus::SignalChoose);
 					return;
 				}
+			    else if (key == "N" and (Config::getB("show_detailed") or Config::getI("selected_pid") > 0)) {
+					atomic_wait(Runner::active);
+				    if (Config::getB("show_detailed") and Config::getI("proc_selected") == 0 and Proc::detailed.status == "Dead") return;
+				    Menu::show(Menu::Menus::Renice);
+				    return;
+			    }
 				else if (is_in(key, "up", "down", "page_up", "page_down", "home", "end") or (vim_keys and is_in(key, "j", "k", "g", "G"))) {
 					proc_mouse_scroll:
 					redraw = false;

src/btop_menu.cpp

@@ -203,6 +203,7 @@ namespace Menu {
 		{"Selected t", "Terminate selected process with SIGTERM - 15."},
 		{"Selected k", "Kill selected process with SIGKILL - 9."},
 		{"Selected s", "Select or enter signal to send to process."},
+		{"Selected N", "Select new nice value for selected process."},
 		{"", " "},
 		{"", "For bug reporting and project updates, visit:"},
 		{"", "https://github.com/aristocratos/btop"},
@@ -1595,6 +1596,94 @@ static int optionsMenu(const string& key) {
 		return (redraw ? Changed : retval);
 	}
 
+	static int reniceMenu(const string& key) {
+		auto s_pid = (Config::getB("show_detailed") and Config::getI("selected_pid") == 0 ? Config::getI("detailed_pid") : Config::getI("selected_pid"));
+		static int x{};
+		static int y{};
+		static int selected_nice = 0;
+		static string nice_edit;
+
+		if (bg.empty()) {
+			selected_nice = 0;
+			nice_edit.clear();
+		}
+		auto& out = Global::overlay;
+		int retval = Changed;
+
+		if (redraw) {
+			x = Term::width/2 - 25;
+			y = Term::height/2 - 6;
+			bg = Draw::createBox(x + 2, y, 50, 13, Theme::c("hi_fg"), true, "renice");
+			bg += Mv::to(y+2, x+3) + Theme::c("title") + Fx::b + cjust("Renice PID " + to_string(s_pid) + " ("
+				+ uresize((s_pid == Config::getI("detailed_pid") ? Proc::detailed.entry.name : Config::getS("selected_name")), 15) + ")", 48);
+		}
+		else if (is_in(key, "escape", "q")) {
+			return Closed;
+		}
+		else if (is_in(key, "enter", "space")) {
+			if (s_pid > 0) {
+				if (not nice_edit.empty()) {
+					try {
+						selected_nice = stoi(nice_edit);
+					}
+					catch (...) { selected_nice = 0; }
+				}
+				if (not Proc::set_priority(s_pid, selected_nice)) {
+					// TODO: show error message
+				}
+			}
+			return Closed;
+		}
+		else if (key.size() == 1 and (isdigit(key.at(0)) or (key.at(0) == '-' and nice_edit.empty()))) {
+			nice_edit += key;
+		}
+		else if (key == "backspace" and not nice_edit.empty()) {
+			nice_edit.pop_back();
+		}
+		else if (is_in(key, "up", "k")) {
+			if (++selected_nice > 19) selected_nice = -20;
+			nice_edit.clear();
+		}
+		else if (is_in(key, "down", "j")) {
+			if (--selected_nice < -20) selected_nice = 19;
+			nice_edit.clear();
+		}
+		else if (is_in(key, "left", "h")) {
+			if ((selected_nice -= 5) < -20) selected_nice += 40;
+			nice_edit.clear();
+		}
+		else if (is_in(key, "right", "l")) {
+			if ((selected_nice += 5) > 19) selected_nice -= 40;
+			nice_edit.clear();
+		}
+		else {
+			retval = NoChange;
+		}
+
+		if (retval == Changed) {
+			int cy = y+4;
+			if (not nice_edit.empty()) {
+				try {
+					selected_nice = stoi(nice_edit);
+				}
+				catch (...) { selected_nice = 0; }
+			}
+			out = bg + Mv::to(cy++, x+3) + Theme::c("main_fg") + Fx::ub
+				+ rjust("Enter nice value: ", 30) + Theme::c("hi_fg") + (nice_edit.empty() ? to_string(selected_nice) : nice_edit) + Theme::c("main_fg") + Fx::bl + "█" + Fx::ubl;
+
+			cy++;
+			out += Mv::to(++cy, x+3) + Fx::b + Theme::c("hi_fg") + rjust( "↑ ↓", 20, true) + Theme::c("main_fg") + Fx::ub + " | To change value.";
+			out += Mv::to(++cy, x+3) + Fx::b + Theme::c("hi_fg") + rjust( "← →", 20, true) + Theme::c("main_fg") + Fx::ub + " | To change value by 5.";
+			out += Mv::to(++cy, x+3) + Fx::b + Theme::c("hi_fg") + rjust("0-9", 20) + Theme::c("main_fg") + Fx::ub + " | Enter manually.";
+			out += Mv::to(++cy, x+3) + Fx::b + Theme::c("hi_fg") + rjust("ENTER", 20) + Theme::c("main_fg") + Fx::ub + " | To set nice value.";
+			out += Mv::to(++cy, x+3) + Fx::b + Theme::c("hi_fg") + rjust("ESC or 'q'", 20) + Theme::c("main_fg") + Fx::ub + " | To abort.";
+
+			out += Fx::reset;
+		}
+
+		return (redraw ? Changed : retval);
+	}
+
 	//* Add menus here and update enum Menus in header
 	const auto menuFunc = vector{
 		ref(sizeError),
@@ -1603,6 +1692,7 @@ static int optionsMenu(const string& key) {
 		ref(signalReturn),
 		ref(optionsMenu),
 		ref(helpMenu),
+		ref(reniceMenu),
 		ref(mainMenu),
 	};
 	bitset<8> menuMask;

src/btop_menu.hpp

@@ -72,6 +72,8 @@ namespace Menu {
 
 		//? Clears content vector and private strings
 		void clear();
+        int getX() const { return x; }
+        int getY() const { return y; }
 	};
 
 	extern bitset<8> menuMask;
@@ -84,6 +86,7 @@ namespace Menu {
 		SignalReturn,
 		Options,
 		Help,
+	    Renice,
 		Main
 	};
 

src/btop_shared.cpp

@@ -16,6 +16,7 @@ indent = tab
 tab-size = 4
 */
 
+#include <sys/resource.h>
 #include <ranges>
 #include <regex>
 #include <string>
@@ -87,6 +88,13 @@ namespace Gpu {
 #endif
 
 namespace Proc {
+bool set_priority(pid_t pid, int priority) {
+  if (setpriority(PRIO_PROCESS, pid, priority) == 0) {
+    return true;
+  }
+  return false;
+}
+
 	void proc_sorter(vector<proc_info>& proc_vec, const string& sorting, bool reverse, bool tree) {
 		if (reverse) {
 			switch (v_index(sort_vector, sorting)) {

src/btop_shared.hpp

@@ -431,6 +431,9 @@ namespace Proc {
 		vector<tree_proc> children;
 	};
 
+	//* Change priority (nice) of pid, returns true on success otherwise false
+	bool set_priority(pid_t pid, int priority);
+
 	//* Sort vector of proc_info's
 	void proc_sorter(vector<proc_info>& proc_vec, const string& sorting, bool reverse, bool tree = false);