Linux: Only process global state when something interesting happens

This matches behavior on macOS. Had initially set the code to process
on every loop tick in an attmept to workaround the issue of the event
loop freezing on X11 until an X event is delivered. However, in light
of #1782 that workaround was incorrect anyway. Better to have similar
behavior across platforms. This also has the advantage of reducing CPU
consumption.

Also add a simple program to test event loop wakeups.

glfw/main_loop.h

@@ -12,9 +12,11 @@
 #define GLFW_LOOP_BACKEND x11
 #endif
 
-static bool keep_going = false;
+static bool keep_going = false, tick_callback_requested = false;
 
 void _glfwPlatformRequestTickCallback() {
+    EVDBG("tick_callback requested");
+    tick_callback_requested = true;
 }
 
 void _glfwPlatformStopMainLoop(void) {
@@ -24,15 +26,26 @@ void _glfwPlatformStopMainLoop(void) {
     }
 }
 
-void _glfwPlatformRunMainLoop(GLFWtickcallback tick_callback, void* data) {
-    keep_going = true;
-    while(keep_going) {
-        _glfwPlatformWaitEvents();
-        EVDBG("loop tick");
+static inline void
+dispatch_tick_callbacks(GLFWtickcallback tick_callback, void *data) {
+    while (tick_callback_requested) {
+        EVDBG("Calling tick callback");
+        tick_callback_requested = false;
         tick_callback(data);
     }
 }
 
+void _glfwPlatformRunMainLoop(GLFWtickcallback tick_callback, void* data) {
+    keep_going = true;
+    tick_callback_requested = false;
+    while(keep_going) {
+        EVDBG("loop tick, tick_callback_requested: %d", tick_callback_requested);
+        dispatch_tick_callbacks(tick_callback, data);
+        _glfwPlatformWaitEvents();
+    }
+    EVDBG("main loop exiting");
+}
+
 unsigned long long _glfwPlatformAddTimer(double interval, bool repeats, GLFWuserdatafreefun callback, void *callback_data, GLFWuserdatafreefun free_callback) {
     return addTimer(&_glfw.GLFW_LOOP_BACKEND.eventLoopData, "user timer", interval, 1, repeats, callback, callback_data, free_callback);
 }

kitty/child-monitor.c

@@ -889,14 +889,9 @@ set_cocoa_pending_action(CocoaPendingAction action, const char *wd) {
 static void process_global_state(void *data);
 
 static void
-do_state_check(id_type timer_id UNUSED, void *data UNUSED) {
+do_state_check(id_type timer_id UNUSED, void *data) {
     EVDBG("State check timer fired");
-#ifdef __APPLE__
     process_global_state(data);
-#endif
-    // We don't actually do anything here as process_global_state
-    // will be called when the loop ticks on Linux
-
 }
 
 static id_type state_check_timer = 0;
@@ -937,7 +932,8 @@ process_global_state(void *data) {
     if (global_state.has_pending_closes) has_open_windows = process_pending_closes(self);
     if (has_open_windows) {
         if (maximum_wait >= 0) {
-            state_check_timer_enabled = true;
+            if (maximum_wait == 0) request_tick_callback();
+            else state_check_timer_enabled = true;
         }
     } else {
         stop_main_loop();

kitty/glfw.c

@@ -5,6 +5,7 @@
  */
 
 #include "state.h"
+#include "glfw_tests.h"
 #include "fonts.h"
 #include <structmember.h>
 #include "glfw-wrapper.h"
@@ -27,11 +28,9 @@ static GLFWcursor *standard_cursor = NULL, *click_cursor = NULL, *arrow_cursor =
 static void set_os_window_dpi(OSWindow *w);
 
 
-static void
+void
 request_tick_callback(void) {
-#ifdef __APPLE__
     glfwRequestTickCallback();
-#endif
 }
 
 static int min_width = 100, min_height = 100;
@@ -1150,6 +1149,18 @@ stop_main_loop(void) {
     glfwStopMainLoop();
 }
 
+
+static PyObject*
+test_empty_event(PYNOARG) {
+
+    int ret = empty_main();
+    if (ret != EXIT_SUCCESS) {
+        PyErr_Format(PyExc_RuntimeError, "Empty test returned failure code: %d", ret);
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 // Boilerplate {{{
 
 static PyMethodDef module_methods[] = {
@@ -1178,6 +1189,7 @@ static PyMethodDef module_methods[] = {
     {"glfw_get_key_name", (PyCFunction)glfw_get_key_name, METH_VARARGS, ""},
     {"glfw_primary_monitor_size", (PyCFunction)primary_monitor_size, METH_NOARGS, ""},
     {"glfw_primary_monitor_content_scale", (PyCFunction)primary_monitor_content_scale, METH_NOARGS, ""},
+    {"glfw_test_empty_event", (PyCFunction)test_empty_event, METH_NOARGS, ""},
     {NULL, NULL, 0, NULL}        /* Sentinel */
 };
 

kitty/glfw_tests.c

@@ -0,0 +1,112 @@
+/*
+ * glfw_tests.c
+ * Copyright (C) 2019 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#include "glfw_tests.h"
+
+
+#include "glfw-wrapper.h"
+#include "gl.h"
+
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+static volatile bool running = true;
+
+static void* empty_thread_main(void* data UNUSED)
+{
+    struct timespec time = { .tv_sec = 1 };
+
+    while (running)
+    {
+        nanosleep(&time, NULL);
+        glfwRequestTickCallback();
+        glfwPostEmptyEvent();
+    }
+
+    return 0;
+}
+
+static void key_callback(GLFWwindow *w UNUSED, int key, int scancode UNUSED, int action, int mods UNUSED, const char* text UNUSED, int state UNUSED)
+{
+    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) {
+        glfwSetWindowShouldClose(w, true);
+        wakeup_main_loop();
+    }
+}
+
+static void
+window_close_callback(GLFWwindow* window) {
+    glfwSetWindowShouldClose(window, true);
+    glfwRequestTickCallback();
+    wakeup_main_loop();
+}
+
+
+static float nrand(void)
+{
+    return (float) rand() / (float) RAND_MAX;
+}
+
+static void
+empty_main_tick(void *data) {
+    GLFWwindow *window = data;
+    if (glfwWindowShouldClose(window)) {
+        running = false;
+        glfwStopMainLoop();
+        return;
+    }
+    int width, height;
+    float r = nrand(), g = nrand(), b = nrand();
+    float l = (float) sqrt(r * r + g * g + b * b);
+
+    glfwGetFramebufferSize(window, &width, &height);
+
+    glViewport(0, 0, width, height);
+    glClearColor(r / l, g / l, b / l, 1.f);
+    glClear(GL_COLOR_BUFFER_BIT);
+    glfwSwapBuffers(window);
+}
+
+int empty_main(void)
+{
+    pthread_t thread;
+    GLFWwindow* window;
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, OPENGL_REQUIRED_VERSION_MAJOR);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, OPENGL_REQUIRED_VERSION_MINOR);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
+    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, true);
+
+
+    srand((unsigned int) time(NULL));
+
+    window = glfwCreateWindow(640, 480, "Empty Event Test", NULL, NULL);
+    if (!window)
+    {
+        return (EXIT_FAILURE);
+    }
+
+    glfwMakeContextCurrent(window);
+    gl_init();
+    glfwSetKeyboardCallback(window, key_callback);
+    glfwSetWindowCloseCallback(window, window_close_callback);
+
+    if (pthread_create(&thread, NULL, empty_thread_main, NULL) != 0)
+    {
+        fprintf(stderr, "Failed to create secondary thread\n");
+        return (EXIT_FAILURE);
+    }
+
+    glfwRunMainLoop(empty_main_tick, window);
+
+    glfwHideWindow(window);
+    pthread_join(thread, NULL);
+    glfwDestroyWindow(window);
+
+    return (EXIT_SUCCESS);
+}

kitty/glfw_tests.h

@@ -0,0 +1,11 @@
+/*
+ * Copyright (C) 2019 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#pragma once
+
+#include "state.h"
+
+int empty_main(void);

kitty/state.h

@@ -234,6 +234,7 @@ bool application_quit_requested(void);
 void request_application_quit(void);
 #endif
 void request_frame_render(OSWindow *w);
+void request_tick_callback(void);
 typedef void (* timer_callback_fun)(id_type, void*);
 typedef void (* tick_callback_fun)(void*);
 id_type add_main_loop_timer(double interval, bool repeats, timer_callback_fun callback, void *callback_data, timer_callback_fun free_callback);