From 7886c2df7abae474733620ef73b80a938fe7821e Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 7 Jul 2022 10:48:42 -0400
Subject: [PATCH] Start experimenting with a more event-based approach to
 timing.

---
 Concurrency/AsyncUpdater.hpp                  | 77 +++++++++++++++++++
 .../Clock Signal.xcodeproj/project.pbxproj    |  2 +
 .../Mac/Clock Signal/Machine/CSMachine.mm     |  9 +++
 3 files changed, 88 insertions(+)
 create mode 100644 Concurrency/AsyncUpdater.hpp

diff --git a/Concurrency/AsyncUpdater.hpp b/Concurrency/AsyncUpdater.hpp
new file mode 100644
index 000000000..5596a1dcd
--- /dev/null
+++ b/Concurrency/AsyncUpdater.hpp
@@ -0,0 +1,77 @@
+//
+//  AsyncUpdater.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 06/07/2022.
+//  Copyright © 2022 Thomas Harte. All rights reserved.
+//
+
+#ifndef AsyncUpdater_hpp
+#define AsyncUpdater_hpp
+
+#include <atomic>
+#include <condition_variable>
+#include <mutex>
+
+#include "../ClockReceiver/TimeTypes.hpp"
+
+namespace Concurrency {
+
+template <typename Performer> class AsyncUpdater {
+	public:
+		template <typename... Args> AsyncUpdater(Args&&... args)
+			: performer_(std::forward<Args>(args)...),
+			performer_thread_{
+				[this] {
+					Time::Nanos last_fired = Time::nanos_now();
+
+					while(!should_quit) {
+						// Wait for a new action to be signalled, and grab it.
+						std::unique_lock lock(condition_mutex_);
+						while(actions_.empty()) {
+							condition_.wait(lock);
+						}
+						auto action = actions_.pop_back();
+						lock.unlock();
+
+						// Update to now.
+						auto time_now = Time::nanos_now();
+						performer_.perform(time_now - last_fired);
+						last_fired = time_now;
+
+						// Perform the action.
+						action();
+					}
+				}
+			} {}
+
+		/// Run the performer up to 'now' and then perform @c post_action.
+		///
+		/// @c post_action will be performed asynchronously, on the same
+		/// thread as the performer.
+		void update(const std::function<void(void)> &post_action) {
+			std::lock_guard guard(condition_mutex_);
+			actions_.push_back(post_action);
+			condition_.notify_all();
+		}
+
+		~AsyncUpdater() {
+			should_quit = true;
+			update([] {});
+			performer_thread_.join();
+		}
+
+	private:
+		Performer performer_;
+
+		std::thread performer_thread_;
+		std::mutex condition_mutex_;
+		std::condition_variable condition_;
+		std::vector<std::function<void(void)>> actions_;
+		std::atomic<bool> should_quit = false;
+};
+
+
+}
+
+#endif /* AsyncUpdater_hpp */
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 3311a4686..87026c868 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -2138,6 +2138,7 @@
 		4BDCC5F81FB27A5E001220C5 /* ROMMachine.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ROMMachine.hpp; sourceTree = "<group>"; };
 		4BDDBA981EF3451200347E61 /* Z80MachineCycleTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Z80MachineCycleTests.swift; sourceTree = "<group>"; };
 		4BE0151C286A8C8E00EA42E9 /* MemorySwitches.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = MemorySwitches.hpp; sourceTree = "<group>"; };
+		4BE0151E28766ECF00EA42E9 /* AsyncUpdater.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = AsyncUpdater.hpp; sourceTree = "<group>"; };
 		4BE0A3EC237BB170002AB46F /* ST.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = ST.cpp; sourceTree = "<group>"; };
 		4BE0A3ED237BB170002AB46F /* ST.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = ST.hpp; sourceTree = "<group>"; };
 		4BE211DD253E4E4800435408 /* 65C02_no_Rockwell_test.bin */ = {isa = PBXFileReference; lastKnownFileType = archive.macbinary; name = 65C02_no_Rockwell_test.bin; path = "Klaus Dormann/65C02_no_Rockwell_test.bin"; sourceTree = "<group>"; };
@@ -2754,6 +2755,7 @@
 			children = (
 				4B3940E51DA83C8300427841 /* AsyncTaskQueue.cpp */,
 				4B3940E61DA83C8300427841 /* AsyncTaskQueue.hpp */,
+				4BE0151E28766ECF00EA42E9 /* AsyncUpdater.hpp */,
 			);
 			name = Concurrency;
 			path = ../../Concurrency;
diff --git a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm
index 61206bd56..214aa280c 100644
--- a/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
+++ b/OSBindings/Mac/Clock Signal/Machine/CSMachine.mm	
@@ -24,6 +24,7 @@
 
 #include "../../../../ClockReceiver/TimeTypes.hpp"
 #include "../../../../ClockReceiver/ScanSynchroniser.hpp"
+#include "../../../../Concurrency/AsyncUpdater.hpp"
 
 #import "CSStaticAnalyser+TargetVector.h"
 #import "NSBundle+DataResource.h"
@@ -34,6 +35,14 @@
 #include <codecvt>
 #include <locale>
 
+namespace {
+
+struct Updater {};
+
+Concurrency::AsyncUpdater<Updater> updater();
+
+}
+
 @interface CSMachine() <CSScanTargetViewDisplayLinkDelegate>
 - (void)speaker:(Outputs::Speaker::Speaker *)speaker didCompleteSamples:(const int16_t *)samples length:(int)length;
 - (void)speakerDidChangeInputClock:(Outputs::Speaker::Speaker *)speaker;