fix: drop select atomics in favour of a thread-safe channel

lib/zba-util

@@ -1 +1 @@
-Subproject commit 52ac8d952fe7c722e33a3237e465dcf258076613
+Subproject commit d5e66caf2180324d83ad9be30e887849f5ed74da

src/core/emu.zig

@@ -5,9 +5,9 @@ const config = @import("../config.zig");
 const Scheduler = @import("scheduler.zig").Scheduler;
 const Arm7tdmi = @import("cpu.zig").Arm7tdmi;
 const Tracker = @import("../util.zig").FpsTracker;
+const TwoWayChannel = @import("zba-util").TwoWayChannel;
 
 const Timer = std.time.Timer;
-const Atomic = std.atomic.Atomic;
 
 /// 4 Cycles in 1 dot
 const cycles_per_dot = 4;
@@ -35,29 +35,40 @@ const RunKind = enum {
     LimitedFPS,
 };
 
-pub fn run(quit: *Atomic(bool), pause: *Atomic(bool), cpu: *Arm7tdmi, scheduler: *Scheduler, tracker: *Tracker) void {
+pub fn run(cpu: *Arm7tdmi, scheduler: *Scheduler, tracker: *Tracker, channel: *TwoWayChannel) void {
     const audio_sync = config.config().guest.audio_sync and !config.config().host.mute;
     if (audio_sync) log.info("Audio sync enabled", .{});
 
     if (config.config().guest.video_sync) {
-        inner(.LimitedFPS, audio_sync, quit, pause, cpu, scheduler, tracker);
+        inner(.LimitedFPS, audio_sync, cpu, scheduler, tracker, channel);
     } else {
-        inner(.UnlimitedFPS, audio_sync, quit, pause, cpu, scheduler, tracker);
+        inner(.UnlimitedFPS, audio_sync, cpu, scheduler, tracker, channel);
     }
 }
 
-fn inner(comptime kind: RunKind, audio_sync: bool, quit: *Atomic(bool), pause: *Atomic(bool), cpu: *Arm7tdmi, scheduler: *Scheduler, tracker: ?*Tracker) void {
+fn inner(comptime kind: RunKind, audio_sync: bool, cpu: *Arm7tdmi, scheduler: *Scheduler, tracker: ?*Tracker, channel: *TwoWayChannel) void {
     if (kind == .UnlimitedFPS or kind == .LimitedFPS) {
         std.debug.assert(tracker != null);
         log.info("FPS tracking enabled", .{});
     }
 
+    var paused: bool = false;
+
     switch (kind) {
         .Unlimited, .UnlimitedFPS => {
             log.info("Emulation w/out video sync", .{});
 
-            while (!quit.load(.Monotonic)) {
+            while (true) {
-                if (pause.load(.Monotonic)) continue;
+                if (channel.emu.pop()) |e| switch (e) {
+                    .Quit => break,
+                    .Resume => paused = false,
+                    .Pause => {
+                        paused = true;
+                        channel.gui.push(.Paused);
+                    },
+                };
+
+                if (paused) continue;
 
                 runFrame(scheduler, cpu);
                 audioSync(audio_sync, cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
@@ -70,8 +81,17 @@ fn inner(comptime kind: RunKind, audio_sync: bool, quit: *Atomic(bool), pause: *
             var timer = Timer.start() catch @panic("failed to initalize std.timer.Timer");
             var wake_time: u64 = frame_period;
 
-            while (!quit.load(.Monotonic)) {
+            while (true) {
-                if (pause.load(.Monotonic)) continue;
+                if (channel.emu.pop()) |e| switch (e) {
+                    .Quit => break,
+                    .Resume => paused = false,
+                    .Pause => {
+                        paused = true;
+                        channel.gui.push(.Paused);
+                    },
+                };
+
+                if (paused) continue;
 
                 runFrame(scheduler, cpu);
                 const new_wake_time = videoSync(&timer, wake_time);

src/main.zig

@@ -6,6 +6,7 @@ const clap = @import("clap");
 const config = @import("config.zig");
 const emu = @import("core/emu.zig");
 
+const TwoWayChannel = @import("zba-util").TwoWayChannel;
 const Gui = @import("platform.zig").Gui;
 const Bus = @import("core/Bus.zig");
 const Arm7tdmi = @import("core/cpu.zig").Arm7tdmi;
@@ -13,7 +14,6 @@ const Scheduler = @import("core/scheduler.zig").Scheduler;
 const FilePaths = @import("util.zig").FilePaths;
 const FpsTracker = @import("util.zig").FpsTracker;
 const Allocator = std.mem.Allocator;
-const Atomic = std.atomic.Atomic;
 
 const log = std.log.scoped(.Cli);
 pub const log_level = if (builtin.mode != .Debug) .info else std.log.default_level;
@@ -94,7 +94,10 @@ pub fn main() void {
     var gui = Gui.init(allocator, bus.pak.title, &bus.apu) catch |e| exitln("failed to init gui: {}", .{e});
     defer gui.deinit();
 
-    var quit = Atomic(bool).init(false);
+    var quit = std.atomic.Atomic(bool).init(false);
+
+    var items: [0x100]u8 = undefined;
+    var channel = TwoWayChannel.init(&items);
 
     if (result.args.gdb) {
         const Server = @import("gdbstub").Server;
@@ -117,21 +120,19 @@ pub fn main() void {
         gui.run(.{
             .cpu = &cpu,
             .scheduler = &scheduler,
-            .quit = &quit,
+            .channel = &channel,
         }) catch |e| exitln("main thread panicked: {}", .{e});
     } else {
         var tracker = FpsTracker.init();
-        var pause = Atomic(bool).init(false);
 
-        const thread = std.Thread.spawn(.{}, emu.run, .{ &quit, &pause, &cpu, &scheduler, &tracker }) catch |e| exitln("emu thread panicked: {}", .{e});
+        const thread = std.Thread.spawn(.{}, emu.run, .{ &cpu, &scheduler, &tracker, &channel }) catch |e| exitln("emu thread panicked: {}", .{e});
         defer thread.join();
 
         gui.run(.{
             .cpu = &cpu,
             .scheduler = &scheduler,
+            .channel = &channel,
             .tracker = &tracker,
-            .quit = &quit,
-            .pause = &pause,
         }) catch |e| exitln("main thread panicked: {}", .{e});
     }
 }

src/platform.zig

@@ -11,7 +11,7 @@ const Apu = @import("core/apu.zig").Apu;
 const Arm7tdmi = @import("core/cpu.zig").Arm7tdmi;
 const Scheduler = @import("core/scheduler.zig").Scheduler;
 const FpsTracker = @import("util.zig").FpsTracker;
-const RingBuffer = @import("util.zig").RingBuffer;
+const TwoWayChannel = @import("zba-util").TwoWayChannel;
 
 const gba_width = @import("core/ppu.zig").width;
 const gba_height = @import("core/ppu.zig").height;
@@ -243,8 +243,7 @@ pub const Gui = struct {
     }
 
     const RunOptions = struct {
-        quit: *std.atomic.Atomic(bool),
+        channel: *TwoWayChannel,
-        pause: ?*std.atomic.Atomic(bool) = null,
         tracker: ?*FpsTracker = null,
         cpu: *Arm7tdmi,
         scheduler: *Scheduler,
@@ -253,8 +252,7 @@ pub const Gui = struct {
     pub fn run(self: *Self, opt: RunOptions) !void {
         const cpu = opt.cpu;
         const tracker = opt.tracker;
-        const quit = opt.quit;
+        const channel = opt.channel;
-        const pause = opt.pause;
 
         const obj_ids = Self.genBufferObjects();
         defer gl.deleteBuffers(3, @as(*const [3]c_uint, &obj_ids));
@@ -269,7 +267,10 @@ pub const Gui = struct {
         emu_loop: while (true) {
             // `quit` from RunOptions may be modified by the GDBSTUB thread,
             // so we want to recognize that it may change to `true` and exit the GUI thread
-            if (quit.load(.Monotonic)) break :emu_loop;
+            if (channel.gui.pop()) |event| switch (event) {
+                .Quit => break :emu_loop,
+                .Paused => @panic("TODO: We want to peek (and then pop if it's .Quit), not always pop"),
+            };
 
             // Outside of `SDL.SDL_QUIT` below, the DearImgui UI might signal that the program
             // should exit, in which case we should also handle this
@@ -325,17 +326,18 @@ pub const Gui = struct {
                 }
             }
 
-            // If `Gui.run` has been passed with a `pause` atomic, we should
-            // pause the emulation thread while we access the data there
             {
-                // TODO: Is there a nicer way to express this?
+                channel.emu.push(.Pause);
-                if (pause) |val| val.store(true, .Monotonic);
+                defer channel.emu.push(.Resume);
-                defer if (pause) |val| val.store(false, .Monotonic);
+
+                // Spin Loop until we know that the emu is paused
+                wait: while (true) switch (channel.gui.pop() orelse continue) {
+                    .Paused => break :wait,
+                    else => |any| std.debug.panic("[Gui/Channel]: Unhandled Event: {}", .{any}),
+                };
 
                 // Add FPS count to the histogram
-                if (tracker) |t| {
+                if (tracker) |t| self.state.fps_hist.push(t.value()) catch {};
-                    self.state.fps_hist.push(t.value()) catch {};
-                }
 
                 // Draw GBA Screen to Texture
                 {
@@ -361,7 +363,7 @@ pub const Gui = struct {
             SDL.SDL_GL_SwapWindow(self.window);
         }
 
-        quit.store(true, .Monotonic); // Signals to emu thread to exit
+        channel.emu.push(.Quit);
     }
 
     fn glGetProcAddress(ctx: SDL.SDL_GLContext, proc: [:0]const u8) ?*anyopaque {