Move the render to a timer that slows down under load

src/App.zig

@@ -85,31 +85,12 @@ pub fn run(self: App) !void {
     }).callback);
 
     while (!self.window.shouldClose()) {
-        // Mark this so we're in a totally different "frame"
-        tracy.frameMark();
-
-        // Track the render part of the frame separately.
-        {
-            const frame = tracy.frame("render");
-            defer frame.end();
-            try self.window.run();
-        }
-
         // Block for any glfw events. This may also be an "empty" event
         // posted by the libuv watcher so that we trigger a libuv loop tick.
         try glfw.waitEvents();
 
-        // If the window wants the event loop to wakeup, then we "kick" the
-        // embed thread to wake up. I'm not sure why we have to do this in a
-        // loop, this is surely a lacking in my understanding of libuv. But
-        // this works.
-        if (self.window.wakeup) {
-            self.window.wakeup = false;
-            while (embed.sleeping.load(.SeqCst) and embed.terminate.load(.SeqCst) == false) {
-                try async_h.send();
-                try embed.loopRun();
-            }
-        }
+        // Mark this so we're in a totally different "frame"
+        tracy.frameMark();
 
         // Run the libuv loop
         const frame = tracy.frame("libuv");

src/Window.zig

@@ -17,7 +17,11 @@ const Pty = @import("Pty.zig");
 const Command = @import("Command.zig");
 const Terminal = @import("terminal/Terminal.zig");
 const SegmentedPool = @import("segmented_pool.zig").SegmentedPool;
+const frame = @import("tracy/tracy.zig").frame;
 const trace = @import("tracy/tracy.zig").trace;
+const max_timer = @import("max_timer.zig");
+
+const RenderTimer = max_timer.MaxTimer(renderTimerCallback);
 
 const log = std.log.scoped(.window);
 
@@ -49,6 +53,9 @@ terminal: Terminal,
 /// Timer that blinks the cursor.
 cursor_timer: libuv.Timer,
 
+/// Render at least 60fps.
+render_timer: RenderTimer,
+
 /// The reader/writer stream for the pty.
 pty_stream: libuv.Tty,
 
@@ -180,6 +187,7 @@ pub fn create(alloc: Allocator, loop: libuv.Loop) !*Window {
         .command = cmd,
         .terminal = term,
         .cursor_timer = timer,
+        .render_timer = try RenderTimer.init(loop, self, 16, 64),
         .pty_stream = stream,
     };
 
@@ -211,6 +219,8 @@ pub fn destroy(self: *Window) void {
         }
     }).callback);
 
+    self.render_timer.deinit();
+
     // We have to dealloc our window in the close callback because
     // we can't free some of the memory associated with the window
     // until the stream is closed.
@@ -231,21 +241,6 @@ pub fn shouldClose(self: Window) bool {
     return self.window.shouldClose();
 }
 
-pub fn run(self: Window) !void {
-    const tracy = trace(@src());
-    defer tracy.end();
-
-    // Set our background
-    gl.clearColor(0.2, 0.3, 0.3, 1.0);
-    gl.clear(gl.c.GL_COLOR_BUFFER_BIT);
-
-    // Render the grid
-    try self.grid.render();
-
-    // Swap
-    try self.window.swapBuffers();
-}
-
 fn sizeCallback(window: glfw.Window, width: i32, height: i32) void {
     const tracy = trace(@src());
     defer tracy.end();
@@ -281,8 +276,7 @@ fn sizeCallback(window: glfw.Window, width: i32, height: i32) void {
         log.err("error updating OpenGL viewport err={}", .{err});
 
     // Draw
-    win.run() catch |err|
-        log.err("error redrawing window during resize err={}", .{err});
+    win.render_timer.schedule() catch unreachable;
 }
 
 fn charCallback(window: glfw.Window, codepoint: u21) void {
@@ -369,6 +363,7 @@ fn focusCallback(window: glfw.Window, focused: bool) void {
     defer tracy.end();
 
     const win = window.getUserPointer(Window) orelse return;
+    win.render_timer.schedule() catch unreachable;
     if (focused) {
         win.wakeup = true;
         win.cursor_timer.start(cursorTimerCallback, 0, win.cursor_timer.getRepeat()) catch unreachable;
@@ -389,6 +384,7 @@ fn cursorTimerCallback(t: *libuv.Timer) void {
     const win = t.getData(Window) orelse return;
     win.grid.cursor_visible = !win.grid.cursor_visible;
     win.grid.updateCells(win.terminal) catch unreachable;
+    win.render_timer.schedule() catch unreachable;
 }
 
 fn ttyReadAlloc(t: *libuv.Tty, size: usize) ?[]u8 {
@@ -434,6 +430,9 @@ fn ttyRead(t: *libuv.Tty, n: isize, buf: []const u8) void {
 
     // Update the cells for drawing
     win.grid.updateCells(win.terminal) catch unreachable;
+
+    // Schedule a render
+    win.render_timer.schedule() catch unreachable;
 }
 
 fn ttyWrite(req: *libuv.WriteReq, status: i32) void {
@@ -450,3 +449,29 @@ fn ttyWrite(req: *libuv.WriteReq, status: i32) void {
 
     //log.info("WROTE: {d}", .{status});
 }
+
+fn renderTimerCallback(t: *libuv.Timer) void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    const win = t.getData(Window).?;
+
+    // Set our background
+    gl.clearColor(0.2, 0.3, 0.3, 1.0);
+    gl.clear(gl.c.GL_COLOR_BUFFER_BIT);
+
+    // Render the grid
+    win.grid.render() catch |err| {
+        log.err("error rendering grid: {}", .{err});
+        return;
+    };
+
+    // Swap
+    win.window.swapBuffers() catch |err| {
+        log.err("error swapping buffers: {}", .{err});
+        return;
+    };
+
+    // Record our run
+    win.render_timer.tick();
+}

src/max_timer.zig

@@ -0,0 +1,88 @@
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const libuv = @import("libuv/main.zig");
+
+/// A coalescing timer that forces a run after a certain maximum time
+/// since the last run. This is used for example by the renderer to try
+/// to render at a high FPS but gracefully fall back under high IO load so
+/// that we can process more data and increase throughput.
+pub fn MaxTimer(comptime cb: fn (*libuv.Timer) void) type {
+    return struct {
+        const Self = @This();
+
+        /// The underlying libuv timer.
+        timer: libuv.Timer,
+
+        /// The maximum time between timer calls. This is best effort based on
+        /// event loop load. If the event loop is busy, the timer will be run on
+        /// the next available tick.
+        max: u64,
+
+        /// The fastest the timer will ever run.
+        min: u64,
+
+        /// The last time this timer ran.
+        last: u64 = 0,
+
+        pub fn init(
+            loop: libuv.Loop,
+            data: ?*anyopaque,
+            min: u64,
+            max: u64,
+        ) !Self {
+            const alloc = loop.getData(Allocator).?.*;
+            var timer = try libuv.Timer.init(alloc, loop);
+            timer.setData(data);
+
+            // The maximum time can't be less than the interval otherwise this
+            // will just constantly fire.
+            if (max < min) return error.MaxShorterThanTimer;
+            return Self{
+                .timer = timer,
+                .min = min,
+                .max = max,
+            };
+        }
+
+        pub fn deinit(self: *Self) void {
+            self.timer.close((struct {
+                fn callback(t: *libuv.Timer) void {
+                    const alloc = t.loop().getData(Allocator).?.*;
+                    t.deinit(alloc);
+                }
+            }).callback);
+            self.* = undefined;
+        }
+
+        /// This should be called from the callback to update the last called time.
+        pub fn tick(self: *Self) void {
+            self.timer.loop().updateTime();
+            self.last = self.timer.loop().now();
+            self.timer.stop() catch unreachable;
+        }
+
+        /// Schedule the timer to run. If the timer is not started, it'll
+        /// run on the next min tick. If the timer is started, this will
+        /// delay the timer up to max time since the last run.
+        pub fn schedule(self: *Self) !void {
+            // If the timer hasn't been started, start it now and schedule
+            // a tick as soon as possible.
+            if (!try self.timer.isActive()) {
+                try self.timer.start(cb, self.min, self.min);
+                return;
+            }
+
+            // If we are past the max time, we run the timer now.
+            try self.timer.stop();
+            self.timer.loop().updateTime();
+            if (self.timer.loop().now() - self.last > self.max) {
+                @call(.{ .modifier = .always_inline }, cb, .{&self.timer});
+                return;
+            }
+
+            // We still have time, restart the timer so that it is min time away.
+            try self.timer.start(cb, self.min, 0);
+        }
+    };
+}