Simplify the event loop code

Also reduce input latency by ignoring repaint_delay when
there is actual pending input.

Gets rid of request_tick_callback(). Now empty events
result in the tick callback being called so there is only a
single mechanism for waking up the main loop and getting
the tick callback called.

glfw/backend_utils.c

@@ -222,19 +222,25 @@ dispatchTimers(EventLoopData *eld) {
 }
 
 static void
-drain_wakeup_fd(int fd, int events UNUSED, void* data UNUSED) {
+drain_wakeup_fd(int fd, EventLoopData* eld) {
     static char drain_buf[64];
+    eld->wakeup_data_read = false;
     while(true) {
         ssize_t ret = read(fd, drain_buf, sizeof(drain_buf));
         if (ret < 0) {
             if (errno == EINTR) continue;
             break;
         }
-        if (ret > 0) continue;
+        if (ret > 0) { eld->wakeup_data_read = true; continue; }
         break;
     }
 }
 
+static void
+mark_wakep_fd_ready(int fd UNUSED, int events UNUSED, void *data) {
+    ((EventLoopData*)(data))->wakeup_fd_ready = true;
+}
+
 bool
 initPollData(EventLoopData *eld, int display_fd) {
     if (!addWatch(eld, "display", display_fd, POLLIN, 1, NULL, NULL)) return false;
@@ -246,10 +252,20 @@ initPollData(EventLoopData *eld, int display_fd) {
     if (pipe2(eld->wakeupFds, O_CLOEXEC | O_NONBLOCK) != 0) return false;
     const int wakeup_fd = eld->wakeupFds[0];
 #endif
-    if (!addWatch(eld, "wakeup", wakeup_fd, POLLIN, 1, drain_wakeup_fd, NULL)) return false;
+    if (!addWatch(eld, "wakeup", wakeup_fd, POLLIN, 1, mark_wakep_fd_ready, eld)) return false;
     return true;
 }
 
+void
+check_for_wakeup_events(EventLoopData *eld) {
+#ifdef HAS_EVENT_FD
+    int fd = eld->wakeupFd;
+#else
+    int fd = eld->wakeupFds[0];
+#endif
+    drain_wakeup_fd(fd, eld);
+}
+
 void
 wakeupEventLoop(EventLoopData *eld) {
 #ifdef HAS_EVENT_FD
@@ -289,6 +305,7 @@ pollForEvents(EventLoopData *eld, double timeout) {
     EVDBG("pollForEvents final timeout: %.3f", timeout);
     int result;
     double end_time = monotonic() + timeout;
+    eld->wakeup_fd_ready = false;
 
     while(1) {
         if (timeout >= 0) {

glfw/backend_utils.h

@@ -66,12 +66,14 @@ typedef struct {
 #else
     int wakeupFds[2];
 #endif
+    bool wakeup_data_read, wakeup_fd_ready;
     nfds_t watches_count, timers_count;
     Watch watches[32];
     Timer timers[128];
 } EventLoopData;
 
 
+void check_for_wakeup_events(EventLoopData *eld);
 id_type addWatch(EventLoopData *eld, const char *name, int fd, int events, int enabled, watch_callback_func cb, void *cb_data);
 void removeWatch(EventLoopData *eld, id_type watch_id);
 void toggleWatch(EventLoopData *eld, id_type watch_id, int enabled);

glfw/cocoa_init.m

@@ -26,6 +26,7 @@
 
 #include "internal.h"
 #include <sys/param.h> // For MAXPATHLEN
+#include <pthread.h>
 
 // Change to our application bundle's resources directory, if present
 //
@@ -471,32 +472,56 @@ const char* _glfwPlatformGetVersionString(void)
 static GLFWtickcallback tick_callback = NULL;
 static void* tick_callback_data = NULL;
 static bool tick_callback_requested = false;
+static pthread_t main_thread;
+static NSLock *tick_lock = NULL;
 
 
 void _glfwDispatchTickCallback() {
-    if (tick_callback) {
+    if (tick_lock && tick_callback) {
+        [tick_lock lock];
+        while(tick_callback_requested) {
             tick_callback_requested = false;
             tick_callback(tick_callback_data);
         }
+        [tick_lock unlock];
+    }
 }
 
-void _glfwPlatformRequestTickCallback() {
+static void
+request_tick_callback() {
     if (!tick_callback_requested) {
         tick_callback_requested = true;
         [NSApp performSelectorOnMainThread:@selector(tick_callback) withObject:nil waitUntilDone:NO];
     }
 }
 
+void _glfwPlatformPostEmptyEvent(void)
+{
+    if (pthread_equal(pthread_self(), main_thread)) {
+        request_tick_callback();
+    } else if (tick_lock) {
+        [tick_lock lock];
+        request_tick_callback();
+        [tick_lock unlock];
+    }
+}
+
+
 void _glfwPlatformStopMainLoop(void) {
-    tick_callback = NULL;
     [NSApp stop:nil];
-    _glfwPlatformPostEmptyEvent();
+    _glfwCocoaPostEmptyEvent();
 }
 
 void _glfwPlatformRunMainLoop(GLFWtickcallback callback, void* data) {
+    main_thread = pthread_self();
     tick_callback = callback;
     tick_callback_data = data;
+    tick_lock = [NSLock new];
     [NSApp run];
+    [tick_lock release];
+    tick_lock = NULL;
+    tick_callback = NULL;
+    tick_callback_data = NULL;
 }
 
 

glfw/cocoa_platform.h

@@ -225,7 +225,7 @@ float _glfwTransformYNS(float y);
 
 void _glfwClearDisplayLinks(void);
 void _glfwRestartDisplayLinks(void);
-void _glfwCocoaPostEmptyEvent(short subtype, long data1, bool at_start);
 void _glfwDispatchTickCallback(void);
 void _glfwDispatchRenderFrame(CGDirectDisplayID);
 void _glfwShutdownCVDisplayLink(unsigned long long, void*);
+void _glfwCocoaPostEmptyEvent(void);

glfw/cocoa_window.m

@@ -579,7 +579,7 @@ static GLFWapplicationshouldhandlereopenfun handle_reopen_callback = NULL;
     [NSApp stop:nil];
 
     CGDisplayRegisterReconfigurationCallback(display_reconfigured, NULL);
-    _glfwPlatformPostEmptyEvent();
+    _glfwCocoaPostEmptyEvent();
 }
 
 - (void)applicationWillTerminate:(NSNotification *)aNotification
@@ -1916,29 +1916,6 @@ _glfwDispatchRenderFrame(CGDirectDisplayID displayID) {
     }
 }
 
-void _glfwCocoaPostEmptyEvent(short subtype, long data1, bool at_start)
-{
-    @autoreleasepool {
-
-    NSEvent* event = [NSEvent otherEventWithType:NSEventTypeApplicationDefined
-                                        location:NSMakePoint(0, 0)
-                                   modifierFlags:0
-                                       timestamp:0
-                                    windowNumber:0
-                                         context:nil
-                                         subtype:subtype
-                                           data1:data1
-                                           data2:0];
-    [NSApp postEvent:event atStart:at_start ? YES : NO];
-
-    } // autoreleasepool
-}
-
-void _glfwPlatformPostEmptyEvent(void)
-{
-    _glfwCocoaPostEmptyEvent(0, 0, true);
-}
-
 void _glfwPlatformGetCursorPos(_GLFWwindow* window, double* xpos, double* ypos)
 {
     const NSRect contentRect = [window->ns.view frame];
@@ -2381,3 +2358,16 @@ float _glfwTransformYNS(float y)
 {
     return CGDisplayBounds(CGMainDisplayID()).size.height - y - 1;
 }
+
+void _glfwCocoaPostEmptyEvent(void) {
+    NSEvent* event = [NSEvent otherEventWithType:NSEventTypeApplicationDefined
+                                        location:NSMakePoint(0, 0)
+                                   modifierFlags:0
+                                       timestamp:0
+                                    windowNumber:0
+                                         context:nil
+                                         subtype:0
+                                           data1:0
+                                           data2:0];
+    [NSApp postEvent:event atStart:YES];
+}

glfw/glfw3.h

@@ -1628,7 +1628,6 @@ typedef struct GLFWgamepadstate
 GLFWAPI int glfwInit(void);
 GLFWAPI void glfwRunMainLoop(GLFWtickcallback callback, void *callback_data);
 GLFWAPI void glfwStopMainLoop(void);
-GLFWAPI void glfwRequestTickCallback(void);
 GLFWAPI unsigned long long glfwAddTimer(double interval, bool repeats, GLFWuserdatafun callback, void * callback_data, GLFWuserdatafun free_callback);
 GLFWAPI void glfwUpdateTimer(unsigned long long timer_id, double interval, bool enabled);
 GLFWAPI void glfwRemoveTimer(unsigned long long);

glfw/init.c

@@ -342,10 +342,6 @@ GLFWAPI void glfwRunMainLoop(GLFWtickcallback callback, void *data)
     _glfwPlatformRunMainLoop(callback, data);
 }
 
-GLFWAPI void glfwRequestTickCallback(void) {
-    _glfwPlatformRequestTickCallback();
-}
-
 GLFWAPI void glfwStopMainLoop(void) {
     _GLFW_REQUIRE_INIT();
     _glfwPlatformStopMainLoop();

glfw/internal.h

@@ -822,7 +822,6 @@ const char* _glfwGetVulkanResultString(VkResult result);
 _GLFWwindow* _glfwFocusedWindow(void);
 _GLFWwindow* _glfwWindowForId(GLFWid id);
 void _glfwPlatformRunMainLoop(GLFWtickcallback, void*);
-void _glfwPlatformRequestTickCallback(void);
 void _glfwPlatformStopMainLoop(void);
 unsigned long long _glfwPlatformAddTimer(double interval, bool repeats, GLFWuserdatafun callback, void *callback_data, GLFWuserdatafun free_callback);
 void _glfwPlatformUpdateTimer(unsigned long long timer_id, double interval, bool enabled);

glfw/main_loop.h

@@ -13,36 +13,26 @@
 #define GLFW_LOOP_BACKEND x11
 #endif
 
-static volatile atomic_int keep_going = 0, tick_callback_requested = 0;
+static bool keep_going = false;
 
-void _glfwPlatformRequestTickCallback() {
-    EVDBG("tick_callback requested");
-    tick_callback_requested = 1;
-}
 
 void _glfwPlatformStopMainLoop(void) {
     if (keep_going) {
-        keep_going = 0;
+        keep_going = false;
         _glfwPlatformPostEmptyEvent();
     }
 }
 
-static inline void
-dispatch_tick_callbacks(GLFWtickcallback tick_callback, void *data) {
-    while (tick_callback_requested) {
-        EVDBG("Calling tick callback");
-        tick_callback_requested = 0;
-        tick_callback(data);
-    }
-}
-
 void _glfwPlatformRunMainLoop(GLFWtickcallback tick_callback, void* data) {
     keep_going = 1;
-    tick_callback_requested = 0;
+    EventLoopData *eld = &_glfw.GLFW_LOOP_BACKEND.eventLoopData;
     while(keep_going) {
-        EVDBG("loop tick, tick_callback_requested: %d", tick_callback_requested);
-        dispatch_tick_callbacks(tick_callback, data);
         _glfwPlatformWaitEvents();
+        EVDBG("--------- loop tick, wakeups_happened: %d ----------", eld->wakeup_data_read);
+        if (eld->wakeup_data_read) {
+            eld->wakeup_data_read = false;
+            tick_callback(data);
+        }
     }
     EVDBG("main loop exiting");
 }

glfw/wl_window.c

@@ -783,6 +783,7 @@ handleEvents(double timeout)
     }
     glfw_ibus_dispatch(&_glfw.wl.xkb.ibus);
     glfw_dbus_session_bus_dispatch();
+    if (_glfw.wl.eventLoopData.wakeup_fd_ready) check_for_wakeup_events(&_glfw.wl.eventLoopData);
 }
 
 static struct wl_cursor*

glfw/x11_window.c

@@ -71,6 +71,7 @@ handleEvents(double timeout) {
     glfw_ibus_dispatch(&_glfw.x11.xkb.ibus);
     glfw_dbus_session_bus_dispatch();
     EVDBG("other dispatch done");
+    if (_glfw.x11.eventLoopData.wakeup_fd_ready) check_for_wakeup_events(&_glfw.x11.eventLoopData);
 }
 
 static bool

kitty/child-monitor.c

@@ -295,13 +295,15 @@ shutdown_monitor(ChildMonitor *self, PyObject *a UNUSED) {
     Py_RETURN_NONE;
 }
 
-static inline void
+static inline bool
 do_parse(ChildMonitor *self, Screen *screen, double now) {
+    bool input_read = false;
     screen_mutex(lock, read);
     if (screen->read_buf_sz || screen->pending_mode.used) {
         double time_since_new_input = now - screen->new_input_at;
         if (time_since_new_input >= OPT(input_delay)) {
             bool read_buf_full = screen->read_buf_sz >= READ_BUF_SZ;
+            input_read = true;
             parse_func(screen, self->dump_callback, now);
             if (read_buf_full) wakeup_io_loop(self, false);  // Ensure the read fd has POLLIN set
             screen->new_input_at = 0;
@@ -312,12 +314,14 @@ do_parse(ChildMonitor *self, Screen *screen, double now) {
         } else set_maximum_wait(OPT(input_delay) - time_since_new_input);
     }
     screen_mutex(unlock, read);
+    return input_read;
 }
 
-static void
+static bool
 parse_input(ChildMonitor *self) {
     // Parse all available input that was read in the I/O thread.
     size_t count = 0, remove_count = 0;
+    bool input_read = false;
     double now = monotonic();
     PyObject *msg = NULL;
     children_mutex(lock);
@@ -372,10 +376,11 @@ parse_input(ChildMonitor *self) {
 
     for (size_t i = 0; i < count; i++) {
         if (!scratch[i].needs_removal) {
-            do_parse(self, scratch[i].screen, now);
+            if (do_parse(self, scratch[i].screen, now)) input_read = true;
         }
         DECREF_CHILD(scratch[i]);
     }
+    return input_read;
 }
 
 static inline void
@@ -634,10 +639,11 @@ no_render_frame_received_recently(OSWindow *w, double now, double max_wait) {
 }
 
 static inline void
-render(double now) {
+render(double now, bool input_read) {
+    EVDBG("input_read: %d", input_read);
     static double last_render_at = -DBL_MAX;
     double time_since_last_render = now - last_render_at;
-    if (time_since_last_render < OPT(repaint_delay)) {
+    if (!input_read && time_since_last_render < OPT(repaint_delay)) {
         set_maximum_wait(OPT(repaint_delay) - time_since_last_render);
         return;
     }
@@ -905,7 +911,8 @@ process_global_state(void *data) {
 
     double now = monotonic();
     if (global_state.has_pending_resizes) process_pending_resizes(now);
-    render(now);
+    bool input_read = parse_input(self);
+    render(now, input_read);
 #ifdef __APPLE__
         if (cocoa_pending_actions) {
             if (cocoa_pending_actions & PREFERENCES_WINDOW) { call_boss(edit_config_file, NULL); }
@@ -919,7 +926,6 @@ process_global_state(void *data) {
             cocoa_pending_actions = 0;
         }
 #endif
-    parse_input(self);
     if (global_state.terminate) {
         global_state.terminate = false;
         close_all_windows();

kitty/config_data.py

@@ -481,7 +481,8 @@ Delay (in milliseconds) between screen updates. Decreasing it, increases
 frames-per-second (FPS) at the cost of more CPU usage. The default value
 yields ~100 FPS which is more than sufficient for most uses. Note that to
 actually achieve 100 FPS you have to either set :opt:`sync_to_monitor` to no
-or use a monitor with a high refresh rate.'''))
+or use a monitor with a high refresh rate. Also, to minimize latency
+when there is pending input to be processed, repaint_delay is ignored.'''))
 
 o('input_delay', 3, option_type=positive_int, long_text=_('''
 Delay (in milliseconds) before input from the program running in the terminal

kitty/glfw-wrapper.c

@@ -23,9 +23,6 @@ load_glfw(const char* path) {
     *(void **) (&glfwStopMainLoop_impl) = dlsym(handle, "glfwStopMainLoop");
     if (glfwStopMainLoop_impl == NULL) fail("Failed to load glfw function glfwStopMainLoop with error: %s", dlerror());
 
-    *(void **) (&glfwRequestTickCallback_impl) = dlsym(handle, "glfwRequestTickCallback");
-    if (glfwRequestTickCallback_impl == NULL) fail("Failed to load glfw function glfwRequestTickCallback with error: %s", dlerror());
-
     *(void **) (&glfwAddTimer_impl) = dlsym(handle, "glfwAddTimer");
     if (glfwAddTimer_impl == NULL) fail("Failed to load glfw function glfwAddTimer with error: %s", dlerror());
 

kitty/glfw-wrapper.h

@@ -1403,10 +1403,6 @@ typedef void (*glfwStopMainLoop_func)(void);
 glfwStopMainLoop_func glfwStopMainLoop_impl;
 #define glfwStopMainLoop glfwStopMainLoop_impl
 
-typedef void (*glfwRequestTickCallback_func)(void);
-glfwRequestTickCallback_func glfwRequestTickCallback_impl;
-#define glfwRequestTickCallback glfwRequestTickCallback_impl
-
 typedef unsigned long long (*glfwAddTimer_func)(double, bool, GLFWuserdatafun, void *, GLFWuserdatafun);
 glfwAddTimer_func glfwAddTimer_impl;
 #define glfwAddTimer glfwAddTimer_impl

kitty/glfw.c

@@ -30,7 +30,7 @@ static void set_os_window_dpi(OSWindow *w);
 
 void
 request_tick_callback(void) {
-    glfwRequestTickCallback();
+    glfwPostEmptyEvent();
 }
 
 static int min_width = 100, min_height = 100;
@@ -934,12 +934,7 @@ swap_window_buffers(OSWindow *os_window) {
 
 void
 wakeup_main_loop() {
-    request_tick_callback();
-#ifndef __APPLE__
-    // On Cocoa request_tick_callback() uses performSelectorOnMainLoop which
-    // wakes up the main loop anyway
     glfwPostEmptyEvent();
-#endif
 }
 
 void

kitty/glfw_tests.c

@@ -25,8 +25,7 @@ static void* empty_thread_main(void* data UNUSED)
     while (running)
     {
         nanosleep(&time, NULL);
-        glfwRequestTickCallback();
+        wakeup_main_loop();
-        glfwPostEmptyEvent();
     }
 
     return 0;
@@ -43,7 +42,6 @@ static void key_callback(GLFWwindow *w UNUSED, int key, int scancode UNUSED, int
 static void
 window_close_callback(GLFWwindow* window) {
     glfwSetWindowShouldClose(window, true);
-    glfwRequestTickCallback();
     wakeup_main_loop();
 }