Split the server mutex into multiple different mutexes that are used in smaller scopes.

fixes #864
Also fixed a data race in the itemdrop manager

src/Inventory.zig

@@ -20,7 +20,7 @@ const Side = enum{client, server};
 pub const Sync = struct { // MARK: Sync
 
 	pub const ClientSide = struct {
-		var mutex: std.Thread.Mutex = .{};
+		pub var mutex: std.Thread.Mutex = .{};
 		var commands: main.utils.CircularBufferQueue(Command) = undefined;
 		var maxId: u32 = 0;
 		var freeIdList: main.List(u32) = undefined;

src/gui/windows/debug_network.zig

@@ -28,7 +28,9 @@ pub fn render() void {
 	var y: f32 = 0;
 	if (main.game.world != null) {
 		if(main.server.world != null) {
-			draw.print("Players Connected: {}", .{main.server.users.items.len}, 0, y, 8, .left);
+			const userList = main.server.getUserListAndIncreaseRefCount(main.stackAllocator);
+			defer main.server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+			draw.print("Players Connected: {}", .{userList.len}, 0, y, 8, .left);
 			y += 8;
 		}
 		const sent = network.Connection.packetsSent.load(.monotonic);

src/gui/windows/debug_network_advanced.zig

@@ -55,9 +55,9 @@ pub fn render() void {
 		renderConnectionData(main.game.world.?.conn, &y);
 	}
 	if(main.server.world != null) {
-		main.server.mutex.lock();
-		defer main.server.mutex.unlock();
-		for(main.server.users.items) |user| {
+		const userList = main.server.getUserListAndIncreaseRefCount(main.stackAllocator);
+		defer main.server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+		for(userList) |user| {
 			draw.print("{s}", .{user.name}, 0, y, 8, .left);
 			y += 8;
 			renderConnectionData(user.conn, &y);

src/gui/windows/manage_players.zig

@@ -28,8 +28,6 @@ fn kick(conn: *main.network.Connection) void {
 pub fn onOpen() void {
 	const list = VerticalList.init(.{padding, 16 + padding}, 300, 16);
 	{
-		main.server.mutex.lock();
-		defer main.server.mutex.unlock();
 		main.server.connectionManager.mutex.lock();
 		defer main.server.connectionManager.mutex.unlock();
 		std.debug.assert(userList.len == 0);
@@ -68,11 +66,9 @@ pub fn onClose() void {
 }
 
 pub fn update() void {
-	main.server.mutex.lock();
 	main.server.connectionManager.mutex.lock();
 	const serverListLen = main.server.connectionManager.connections.items.len;
 	main.server.connectionManager.mutex.unlock();
-	main.server.mutex.unlock();
 	if(userList.len != serverListLen) {
 		std.log.err("{} {}", .{userList.len, serverListLen});
 		onClose();

src/itemdrop.zig

@@ -202,7 +202,9 @@ pub const ItemDropManager = struct { // MARK: ItemDropManager
 	}
 
 	pub fn add(self: *ItemDropManager, pos: Vec3d, vel: Vec3d, rot: Vec3f, itemStack: ItemStack, despawnTime: i32, pickupCooldown: i32) void {
-		if(self.size == maxCapacity) {
+		self.emptyMutex.lock();
+		const i: u16 = @intCast(self.isEmpty.findFirstSet() orelse {
+			self.emptyMutex.unlock();
 			const zon = itemStack.store(main.stackAllocator);
 			defer zon.free(main.stackAllocator);
 			const string = zon.toString(main.stackAllocator);
@@ -212,10 +214,7 @@ pub const ItemDropManager = struct { // MARK: ItemDropManager
 				item.deinit();
 			}
 			return;
-		}
-
-		self.emptyMutex.lock();
-		const i: u16 = @intCast(self.isEmpty.findFirstSet().?);
+		});
 		self.isEmpty.unset(i);
 		self.emptyMutex.unlock();
 		self.changeQueue.enqueue(.{.add = .{i, .{

src/renderer.zig

@@ -810,7 +810,9 @@ pub const MeshSelection = struct { // MARK: MeshSelection
 			var newBlock = block;
 			// TODO: Breaking animation and tools.
 			const relPos: Vec3f = @floatCast(lastPos - @as(Vec3d, @floatFromInt(selectedPos)));
+			main.items.Inventory.Sync.ClientSide.mutex.lock();
 			block.mode().onBlockBreaking(inventory.getStack(slot).item, relPos, lastDir, &newBlock);
+			main.items.Inventory.Sync.ClientSide.mutex.unlock();
 			if(!std.meta.eql(newBlock, block)) {
 				updateBlockAndSendUpdate(inventory, slot, selectedPos[0], selectedPos[1], selectedPos[2], block, newBlock);
 			}

src/server/server.zig

@@ -46,6 +46,8 @@ pub const User = struct { // MARK: User
 
 	refCount: Atomic(u32) = .init(1),
 
+	mutex: std.Thread.Mutex = .{},
+
 	pub fn initAndIncreaseRefCount(manager: *ConnectionManager, ipPort: []const u8) !*User {
 		const self = main.globalAllocator.create(User);
 		errdefer main.globalAllocator.destroy(self);
@@ -157,7 +159,8 @@ pub const User = struct { // MARK: User
 	}
 
 	pub fn update(self: *User) void {
-		main.utils.assertLocked(&mutex);
+		self.mutex.lock();
+		defer self.mutex.unlock();
 		var time = @as(i16, @truncate(std.time.milliTimestamp())) -% main.settings.entityLookback;
 		time -%= self.timeDifference.difference.load(.monotonic);
 		self.interpolation.update(time, self.lastTime);
@@ -166,8 +169,8 @@ pub const User = struct { // MARK: User
 	}
 
 	pub fn receiveData(self: *User, data: []const u8) void {
-		mutex.lock();
-		defer mutex.unlock();
+		self.mutex.lock();
+		defer self.mutex.unlock();
 		const position: [3]f64 = .{
 			@bitCast(std.mem.readInt(u64, data[0..8], .big)),
 			@bitCast(std.mem.readInt(u64, data[8..16], .big)),
@@ -198,17 +201,16 @@ pub const updatesPerSec: u32 = 20;
 const updateNanoTime: u32 = 1000000000/20;
 
 pub var world: ?*ServerWorld = null;
-pub var users: main.List(*User) = undefined;
-pub var userDeinitList: main.utils.ConcurrentQueue(*User) = undefined;
-pub var userConnectList: main.utils.ConcurrentQueue(*User) = undefined;
+var userMutex: std.Thread.Mutex = .{};
+var users: main.List(*User) = undefined;
+var userDeinitList: main.utils.ConcurrentQueue(*User) = undefined;
+var userConnectList: main.utils.ConcurrentQueue(*User) = undefined;
 
 pub var connectionManager: *ConnectionManager = undefined;
 
 pub var running: std.atomic.Value(bool) = .init(false);
 var lastTime: i128 = undefined;
 
-pub var mutex: std.Thread.Mutex = .{};
-
 pub var thread: ?std.Thread = null;
 
 fn init(name: []const u8, singlePlayerPort: ?u16) void { // MARK: init()
@@ -267,6 +269,23 @@ fn deinit() void {
 	command.deinit();
 }
 
+pub fn getUserListAndIncreaseRefCount(allocator: utils.NeverFailingAllocator) []*User {
+	userMutex.lock();
+	defer userMutex.unlock();
+	const result = allocator.dupe(*User, users.items);
+	for(result) |user| {
+		user.increaseRefCount();
+	}
+	return result;
+}
+
+pub fn freeUserListAndDecreaseRefCount(allocator: utils.NeverFailingAllocator, list: []*User) void {
+	for(list) |user| {
+		user.decreaseRefCount();
+	}
+	allocator.free(list);
+}
+
 fn sendEntityUpdates(comptime getInitialList: bool, allocator: utils.NeverFailingAllocator) if(getInitialList) []const u8 else void {
 	// Send the entity updates:
 	const updateList = main.ZonElement.initArray(main.stackAllocator);
@@ -297,11 +316,11 @@ fn sendEntityUpdates(comptime getInitialList: bool, allocator: utils.NeverFailin
 		itemDropList.free(main.stackAllocator);
 		initialList = list.toStringEfficient(allocator, &.{});
 	}
-	mutex.lock();
-	for(users.items) |user| {
+	const userList = getUserListAndIncreaseRefCount(main.stackAllocator);
+	defer freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+	for(userList) |user| {
 		main.network.Protocols.entity.send(user.conn, updateData);
 	}
-	mutex.unlock();
 	if(getInitialList) {
 		return initialList;
 	}
@@ -309,27 +328,27 @@ fn sendEntityUpdates(comptime getInitialList: bool, allocator: utils.NeverFailin
 
 fn update() void { // MARK: update()
 	world.?.update();
-	mutex.lock();
-	for(users.items) |user| {
-		user.update();
-	}
-	mutex.unlock();
 
 	while(userConnectList.dequeue()) |user| {
 		connectInternal(user);
 	}
 
+	const userList = getUserListAndIncreaseRefCount(main.stackAllocator);
+	defer freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+	for(userList) |user| {
+		user.update();
+	}
+
 	sendEntityUpdates(false, main.stackAllocator);
 
 
 	// Send the entity data:
-	const data = main.stackAllocator.alloc(u8, (4 + 24 + 12 + 24)*users.items.len);
+	const data = main.stackAllocator.alloc(u8, (4 + 24 + 12 + 24)*userList.len);
 	defer main.stackAllocator.free(data);
 	const itemData = world.?.itemDropManager.getPositionAndVelocityData(main.stackAllocator);
 	defer main.stackAllocator.free(itemData);
 	var remaining = data;
-	mutex.lock();
-	for(users.items) |user| {
+	for(userList) |user| {
 		const id = user.id; // TODO
 		std.mem.writeInt(u32, remaining[0..4], id, .big);
 		remaining = remaining[4..];
@@ -345,12 +364,10 @@ fn update() void { // MARK: update()
 		std.mem.writeInt(u64, remaining[16..24], @bitCast(user.player.vel[2]), .big);
 		remaining = remaining[24..];
 	}
-	for(users.items) |user| {
+	for(userList) |user| {
 		main.network.Protocols.entityPosition.send(user.conn, data, itemData);
 	}
 
-	mutex.unlock();
-
 	while(userDeinitList.dequeue()) |user| {
 		user.decreaseRefCount();
 	}
@@ -393,15 +410,16 @@ pub fn removePlayer(user: *User) void { // MARK: removePlayer()
 	if(!user.connected.load(.unordered)) return;
 	const message = std.fmt.allocPrint(main.stackAllocator.allocator, "{s}§#ffff00 left", .{user.name}) catch unreachable;
 	defer main.stackAllocator.free(message);
-	mutex.lock();
-	defer mutex.unlock();
 
+	userMutex.lock();
 	for(users.items, 0..) |other, i| {
 		if(other == user) {
 			_ = users.swapRemove(i);
 			break;
 		}
 	}
+	userMutex.unlock();
+
 	sendMessage(message);
 	// Let the other clients know about that this new one left.
 	const zonArray = main.ZonElement.initArray(main.stackAllocator);
@@ -409,7 +427,9 @@ pub fn removePlayer(user: *User) void { // MARK: removePlayer()
 	zonArray.array.append(.{.int = user.id});
 	const data = zonArray.toStringEfficient(main.stackAllocator, &.{});
 	defer main.stackAllocator.free(data);
-	for(users.items) |other| {
+	const userList = getUserListAndIncreaseRefCount(main.stackAllocator);
+	defer freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+	for(userList) |other| {
 		main.network.Protocols.entity.send(other.conn, data);
 	}
 }
@@ -423,6 +443,8 @@ pub fn connectInternal(user: *User) void {
 	// TODO: addEntity(player);
 	user.id = freeId;
 	freeId += 1;
+	const userList = getUserListAndIncreaseRefCount(main.stackAllocator);
+	defer freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
 	// Let the other clients know about this new one.
 	{
 		const zonArray = main.ZonElement.initArray(main.stackAllocator);
@@ -433,38 +455,33 @@ pub fn connectInternal(user: *User) void {
 		zonArray.array.append(entityZon);
 		const data = zonArray.toStringEfficient(main.stackAllocator, &.{});
 		defer main.stackAllocator.free(data);
-		mutex.lock();
-		defer mutex.unlock();
-		for(users.items) |other| {
+		for(userList) |other| {
 			main.network.Protocols.entity.send(other.conn, data);
 		}
 	}
 	{ // Let this client know about the others:
 		const zonArray = main.ZonElement.initArray(main.stackAllocator);
 		defer zonArray.free(main.stackAllocator);
-		mutex.lock();
-		for(users.items) |other| {
+		for(userList) |other| {
 			const entityZon = main.ZonElement.initObject(main.stackAllocator);
 			entityZon.put("id", other.id);
 			entityZon.put("name", other.name);
 			zonArray.array.append(entityZon);
 		}
-		mutex.unlock();
 		const data = zonArray.toStringEfficient(main.stackAllocator, &.{});
 		defer main.stackAllocator.free(data);
 		if(user.connected.load(.unordered)) main.network.Protocols.entity.send(user.conn, data);
-
 	}
 	const initialList = sendEntityUpdates(true, main.stackAllocator);
 	main.network.Protocols.entity.send(user.conn, initialList);
 	main.stackAllocator.free(initialList);
 	const message = std.fmt.allocPrint(main.stackAllocator.allocator, "{s}§#ffff00 joined", .{user.name}) catch unreachable;
 	defer main.stackAllocator.free(message);
-	mutex.lock();
-	defer mutex.unlock();
 	sendMessage(message);
 
+	userMutex.lock();
 	users.append(user);
+	userMutex.unlock();
 }
 
 pub fn messageFrom(msg: []const u8, source: *User) void { // MARK: message
@@ -474,16 +491,18 @@ pub fn messageFrom(msg: []const u8, source: *User) void { // MARK: message
 	} else {
 		const newMessage = std.fmt.allocPrint(main.stackAllocator.allocator, "[{s}§#ffffff] {s}", .{source.name, msg}) catch unreachable;
 		defer main.stackAllocator.free(newMessage);
-		main.server.mutex.lock();
-		defer main.server.mutex.unlock();
 		main.server.sendMessage(newMessage);
 	}
 }
 
+var chatMutex: std.Thread.Mutex = .{};
 pub fn sendMessage(msg: []const u8) void {
-	main.utils.assertLocked(&mutex);
+	chatMutex.lock();
+	defer chatMutex.unlock();
 	std.log.info("Chat: {s}", .{msg}); // TODO use color \033[0;32m
-	for(users.items) |user| {
+	const userList = getUserListAndIncreaseRefCount(main.stackAllocator);
+	defer freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+	for(userList) |user| {
 		user.sendMessage(msg);
 	}
 }

src/server/world.zig

@@ -229,9 +229,9 @@ const ChunkManager = struct { // MARK: ChunkManager
 			if(self.source) |source| {
 				if(source.connected.load(.unordered)) main.network.Protocols.lightMapTransmission.sendLightMap(source.conn, map);
 			} else {
-				server.mutex.lock();
-				defer server.mutex.unlock();
-				for(server.users.items) |user| {
+				const userList = server.getUserListAndIncreaseRefCount(main.stackAllocator);
+				defer server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+				for(userList) |user| {
 					main.network.Protocols.lightMapTransmission.sendLightMap(user.conn, map);
 				}
 			}
@@ -815,9 +815,9 @@ pub const ServerWorld = struct { // MARK: ServerWorld
 		}
 		if(self.lastUnimportantDataSent + 2000 < newTime) {// Send unimportant data every ~2s.
 			self.lastUnimportantDataSent = newTime;
-			server.mutex.lock();
-			defer server.mutex.unlock();
-			for(server.users.items) |user| {
+			const userList = server.getUserListAndIncreaseRefCount(main.stackAllocator);
+			defer server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+			for(userList) |user| {
 				main.network.Protocols.genericUpdate.sendTimeAndBiome(user.conn, self);
 			}
 		}
@@ -826,9 +826,9 @@ pub const ServerWorld = struct { // MARK: ServerWorld
 		// Item Entities
 		self.itemDropManager.update(deltaTime);
 		{ // Collect item entities:
-			server.mutex.lock();
-			defer server.mutex.unlock();
-			for(server.users.items) |user| {
+			const userList = server.getUserListAndIncreaseRefCount(main.stackAllocator);
+			defer server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+			for(userList) |user| {
 				self.itemDropManager.checkEntity(user);
 			}
 		}
@@ -945,9 +945,9 @@ pub const ServerWorld = struct { // MARK: ServerWorld
 		baseChunk.mutex.lock();
 		defer baseChunk.mutex.unlock();
 		baseChunk.updateBlockAndSetChanged(x, y, z, newBlock);
-		server.mutex.lock();
-		defer server.mutex.unlock();
-		for(main.server.users.items) |user| {
+		const userList = server.getUserListAndIncreaseRefCount(main.stackAllocator);
+		defer server.freeUserListAndDecreaseRefCount(main.stackAllocator, userList);
+		for(userList) |user| {
 			main.network.Protocols.blockUpdate.send(user.conn, wx, wy, wz, _newBlock);
 		}
 		return null;