Tuesday, December 11, 2007

Scala-style Actors in GWT

Another day, another GWT extension.

Recently, on the Chronoscope mailing list, some users have been asking for the ability to stream in updates to the chart, a typical use case being streaming live stock market data. There are issues in Chronoscope blocking this at the moment that require some extensions, but the greater question of how to do live updates of a GWT application got me thinking about how to appropriately model this in GWT.

RPC? Comet? JSON?

So, ordinarily, in the interest of time, I'd take the road most traveled and simply use GWT RPC, some JSNI Comet integration, or some other simple mechanism to receive poll or push data. However, over the last few months, I've really fallen in love with Scala, and I like Scala's abstraction for message passing: Actors.

I like actors for several reasons. First, they are asynchronous by default, hide the underlying implementation (threads, event queues, in-process calls), and well... I just like em because they're cool.

Actors in Java

Unfortunately, Java doesn't support the elegant syntax of Scala, but with a Generator to implement multiple dispatch, it's not too bad. The approach I've taken is to use overloaded receive methods to implement pattern-matching case classes:

public class Pinger extends Actor {
public void receive(Pong p) {
// pong case
sendTo(sender, new Ping());

public void receive(Stop s) {
GWT.log("Received a stop message!");

public class Ponger extends Actor {
int count = 0;

public void receive(Ping p) {
if(count++ < 100) sendTo(sender, new Pong());
else sendTo(sender, new Stop());

A GWT Generator supplies a compile time dispatch() method which can take dequeued mailbox messages and invoke the appropriate receive() method. Java doesn't have case classes, so you can use Enums or Type-Safe Enum Pattern as messages (as long as they implement org.timepedia.actors.client.Event)

Big deal, Whoop-de-do

What does all this gain us? Well, for one, it abstracts away the RPC mechanism on the client and server. You don't need to deal with RPC interfaces, or AsyncCallback, in fact, RPC can be replaced with Comet for the receive channel if you so desire.

However, the big whoop-de-do is the ability to do peer-to-peer messaging between browsers. Chat? Multiplayer gaming anyone?

Remote Actors

In order to extend actors outside the Javascript environment of your browser, we need to use a server side mailbox server to queue and relay messages between actors in different browsers. In order to publish your actor so that remote actors can retrieve it, all you need to write is:

RemoteActors.register("myId", actor);

and in another peer, you can write:


public .... extends Actor {
public void receive(ActorEndpoint endpoint) { ... }

Wait!? There's no return value? Remote selection is asynchronous (needs to ask mailbox server) so we simply return the result of the select() query as a message using the actor interface!

The returned endpoint represents either a local (in browser), server, or browser peer actor (on someone else's computer).

Chat using Actors

So let's say we want to implement a GTalk chat-like program in GWT, with buddy lists, group chat, and private messages. How would we do this with actors?

public class ChatActor extends Actor {
public void onStart() {
RemoteActors.select("chatLobby", this);

public void receive(ActorEndpoint rae) {
chatLobby = rae.getActor();
sendTo(chatLobby, new JoinLobbyMessage());

public void receive(ChatMessage p) {

public void onChange(Widget sender) {
sendTo(chatLobby, new ChatMessage(((TextBox)sender).getText()));


The above code assumes we are using an HTML Widget to store the chat transcript, and a TextBox to handle user input. We start out by selecting the "chatLobby" actor from the server. We don't know where this Actor really resides, it could be someone's PC, but for my test implementation, it resides in a Servlet.

When someone enters text, we send a "ChatMessage" object to the "chatLobby" actor containing the text. What is chatLobby?

public FooServlet extends HttpServlet ... {
public void init() {
ChatLobbyActor lobbyActor = new ChatLobbyActor();
RemoteActors.register("chatLobby", lobbyActor);

public class ChatLobbyActor extends ReflectionActor {

HashSet<Actor> actors=new HashSet<Actor>;
public void receive(JoinLobbyMessage msg) {
sendTo(sender, new ChatMessage("Welcome to Chat Lobby"));

public void receive(ChatMessage msg) {
for(Actor act : actors)
sendTo(act, msg);

Implementation details

The library isn't ready for release right now, but the mailbox routing servlet uses transient memory arrays to hold per-actor mailboxes (with UUIDs to identify them uniquely). This could be released with transient or persistent JMS queues in some implementations. For communication channels, it uses GWT RPC at the moment. It polls the server periodically for messages, and during the send() operation, it receives all pending messages and sends all pending messages to minimize the number of RPC requests. However, I would like to have a Comet implementation before release that gives you the option of receiving messages pushed on a comet channel.

Holy Grail

I have an itch, a real bad, unproductive itch, to implement a multiplayer graphics game in GWT using Chronoscope's Canvas, Fred Sauer's GWT-Sound library, and this GWT Actors library. And I'm not talking turn based action, but real, predictive physics simulation, such as a 2D space spacewar/omega-race style shooter.

But if I start messing around with this, I'll never finish this blog series, nor fix the Chronoscope bugs, nor launch Timepedia. Argh!

In an upcoming article, I'll talk more about the implementation under the hood, and hopefully release the code.



Robert Hanson said...

> I have an itch, a real bad,
> unproductive itch, to implement
> a multiplayer graphics game in GWT
> using Chronoscope's Canvas, Fred
> Sauer's GWT-Sound library, and this
> GWT Actors library.

Maybe you should wait for Fred to release his game engine. I haven't seen it yet, but if it is like his other works it won't be shabby. He used it to build the Hornet Blast game.

zproxy said...

Looking forward for the game :)

Jonathan said...

Re actors architecture for Java (and Squeak and Lisp), you might want to take a look at E. Lots of good ideas - if you can't use the code you may still be able to learn from what they've done. It has both a scripting language (which you could choose to ignore) and an API (which could be used from Java). Unfortunately I don't believe there's a Javascript binding.

Raoul Duke said...
This comment has been removed by the author.
Raoul Duke said...

[argh, formatting woes]

(a) pretty please release your gwt-actors stuff; it would be pretty cool to see that snowball start rolling!

(b) re: E-lang, there is Caja which is E-in-Javascript.

sexy said...




色情A片,A片下載,色情遊戲,色情影片,色情聊天室,情色電影,免費視訊,免費視訊聊天,免費視訊聊天室,一葉情貼圖片區,情色視訊,免費成人影片,視訊交友,視訊聊天,言情小說,愛情小說,AV片,A漫,av dvd,情色論壇,視訊美女,AV成人網,情色文學,成人交友,成人電影,成人貼圖,成人小說,成人文章,成人圖片區,成人遊戲,愛情公寓,情色貼圖,成人論壇,色情








一夜情聊天室,一夜情,情色聊天室,情色,美女交友,交友,AIO交友愛情館,AIO,成人交友,愛情公寓,做愛影片,做愛,性愛,微風成人區,微風成人,嘟嘟成人網,成人影片,成人,成人貼圖,18成人,成人圖片區,成人圖片,成人影城,成人小說,成人文章,成人網站,成人論壇,情色貼圖,色情貼圖,色情A片,A片,色情小說,情色小說,情色文學,寄情築園小遊戲, 情色A片,色情影片,AV女優,AV,A漫,免費A片,A片下載

信次 said...

情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣用品,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,情趣,美國aneros,rudeboy,英國rudeboy,英國Rocksoff,德國Fun Factory,Fun Factory,英國甜筒造型按摩座,甜筒造型按摩座,英國Rock Chic ,瑞典 Lelo ,英國Emotional Bliss,英國 E.B,荷蘭 Natural Contours,荷蘭 N C,美國 OhMiBod,美國 OMB,Naughti Nano ,音樂按摩棒,ipod按摩棒,美國 The Screaming O,美國TSO,美國TOPCO,美國Doc Johnson,美國CA Exotic,美國CEN,美國Nasstoy,美國Tonguejoy,英國Je Joue,美國Pipe Dream,美國California Exotic,美國NassToys,美國Vibropod,美國Penthouse,仿真按摩棒,矽膠按摩棒,猛男倒模,真人倒模,仿真倒模,PJUR,Zestra,適趣液,穿戴套具,日本NPG,雙頭龍,FANCARNAL,日本NIPPORI,日本GEL,日本Aqua Style,美國WET,費洛蒙,費洛蒙香水,仿真名器,av女優,打炮,做愛,性愛,口交,吹喇叭,肛交,魔女訓練大師,無線跳蛋,有線跳蛋,震動棒,震動保險套,震動套,TOY-情趣用品,情趣用品網,情趣購物網,成人用品網,情趣用品討論,成人購物網,鎖精套,鎖精環,持久環,持久套,拉珠,逼真按摩棒,名器,超名器,逼真老二,電動自慰,自慰,打手槍,仿真女郎,SM道具,SM,性感內褲,仿真按摩棒,pornograph,hunter系列,h動畫,成人動畫,成人卡通,情色動畫,情色卡通,色情動畫,色情卡通,無修正,禁斷,人妻,極悪調教,姦淫,近親相姦,顏射,盜攝,偷拍,本土自拍,素人自拍,公園露出,街道露出,野外露出,誘姦,迷姦,輪姦,凌辱,痴漢,痴女,素人娘,中出,巨乳,調教,潮吹,av,a片,成人影片,成人影音,線上影片,成人光碟,成人無碼,成人dvd,情色影音,情色影片,情色dvd,情色光碟,航空版,薄碼,色情dvd,色情影音,色情光碟,線上A片,免費A片,A片下載,成人電影,色情電影,TOKYO HOT,SKY ANGEL,一本道,SOD,S1,ALICE JAPAN,皇冠系列,老虎系列,東京熱,亞熱,武士系列,新潮館,情趣用品,情趣,情趣商品,情趣網站,跳蛋,按摩棒,充氣娃娃,自慰套,G點,性感內衣,情趣內衣,角色扮演,生日禮物,生日精品,自慰,打手槍,潮吹,高潮,後庭,情色論譠,影片下載,遊戲下載,手機鈴聲,音樂下載,開獎號碼,統一發票號碼,夜市,統一發票對獎,保險套,做愛,減肥,美容,瘦身,當舖,軟體下載,汽車,機車,手機,來電答鈴,週年慶,美食,徵信社,網頁設計,網站設計,室內設計,靈異照片,同志,聊天室,運動彩券,大樂透,威力彩,搬家公司,除蟲,偷拍,自拍,無名破解,av女優,小說,民宿,大樂透開獎號碼,大樂透中獎號碼,威力彩開獎號碼,討論區,痴漢,懷孕,美女交友,交友,日本av,日本,機票,香水,股市,股市行情, 股市分析,租房子,成人影片,免費影片,醫學美容,免費算命,算命,姓名配對,姓名學,姓名學免費,遊戲,好玩遊戲,好玩遊戲區,線上遊戲,新遊戲,漫畫,線上漫畫,動畫,成人圖片,桌布,桌布下載,電視節目表,線上電視,線上a片,線上掃毒,線上翻譯,購物車,身分證製造機,身分證產生器,手機,二手車,中古車,法拍屋,歌詞,音樂,音樂網,火車,房屋,情趣用品,情趣,情趣商品,情趣網站,跳蛋,按摩棒,充氣娃娃,自慰套, G點,性感內衣,情趣內衣,角色扮演,生日禮物,精品,禮品,自慰,打手槍,潮吹,高潮,後庭,情色論譠,影片下載,遊戲下載,手機鈴聲,音樂下載,開獎號碼,統一發票,夜市,保險套,做愛,減肥,美容,瘦身,當舖,軟體下載,汽車,機車,手機,來電答鈴,週年慶,美食,徵信社,網頁設計,網站設計,室內設計,靈異照片,同志,聊天室,運動彩券,,大樂透,威力彩,搬家公司,除蟲,偷拍,自拍,無名破解, av女優,小說,民宿,大樂透開獎號碼,大樂透中獎號碼,威力彩開獎號碼,討論區,痴漢,懷孕,美女交友,交友,日本av ,日本,機票,香水,股市,股市行情,股市分析,租房子,成人影片,免費影片,醫學美容,免費算命,算命,姓名配對,姓名學,姓名學免費,遊戲,好玩遊戲,好玩遊戲區,線上遊戲,新遊戲,漫畫,線上漫畫,動畫,成人圖片,桌布,桌布下載,電視節目表,線上電視,線上a片,線上a片,線上翻譯,購物車,身分證製造機,身分證產生器,手機,二手車,中古車,法拍屋,歌詞,音樂,音樂網,借錢,房屋,街頭籃球,找工作,旅行社,六合彩,整型,整型,珠海,雷射溶脂,婚紗,網頁設計,水噹噹,台中隆鼻,果凍隆乳,改運整型,自體脂肪移植,新娘造型,婚禮顧問,下川島,常平,常平,珠海,澳門機票,香港機票,貸款,貸款,信用貸款,宜蘭民宿,花蓮民宿,未婚聯誼,網路購物,婚友,婚友社,未婚聯誼,交友,婚友,婚友社,單身聯誼,未婚聯誼,未婚聯誼, 婚友社,婚友,婚友社,單身聯誼,婚友,未婚聯誼,婚友社,未婚聯誼,單身聯誼,單身聯誼,白蟻,白蟻,除蟲,老鼠,減肥,減肥,在家工作,在家工作,婚友,單身聯誼,未婚聯誼,婚友,交友,交友,婚友社,婚友社,婚友社,大陸新娘,大陸新娘,越南新娘,越南新娘,外籍新娘,外籍新娘,台中坐月子中心,搬家公司,搬家公司,中和搬家,台北搬家,板橋搬家,新店搬家,線上客服,網頁設計,線上客服,網頁設計,植牙,關鍵字,關鍵字,seo,seo,網路排名,自然排序,網路排名軟體,交友,越南新娘,婚友社,外籍新娘,大陸新娘,越南新娘,交友,外籍新娘,視訊聊天,大陸新娘,婚友社,婚友,越南新娘,大陸新娘,越南新娘,視訊交友,外籍新娘,網路排名,網路排名軟體,網站排名優化大師,關鍵字排名大師,網站排名seo大師,關鍵字行銷專家,關鍵字,seo,關鍵字行銷,網頁排序,網頁排名,關鍵字大師,seo大,自然排名,網站排序,網路行銷創業,汽車借款,汽車借錢,汽車貸款,汽車貸款,拉皮,抽脂,近視雷射,隆乳,隆鼻,變性,雙眼皮,眼袋,牙齒,下巴,植牙,人工植牙,植髮,雷射美容,膠原蛋白,皮膚科,醫學美容,玻尿酸,肉毒桿菌,微晶瓷,電波拉皮,脈衝光,關鍵字,關鍵字,seo,seo,網路排名,自然排序,網路排名軟體,汽車借款,汽車借款,汽車借款,汽車貸款,汽車貸款,借錢,借貸,當舖,借款,借貸,借錢,週轉,學英文,英文社團,英語俱樂部,學習英文,英語會話,英文演講,English Club,學英語,學英文,美語社團,英語社團,英文讀書會,Toastmasters,Toastmaster,英語讀書會,拍樂得批發,拍樂得飾品,拍樂得化妝品批發,

清朝美女 said...

(法新社倫敦四日電) 英國情色大亨芮孟a片的公司昨天說,芮孟av日前成人影片av女優世,享壽八十二歲;這位身價上億的房地產日本av開發商,部落格a片經在倫成人av推出第一場脫衣舞表演。






kevio said...







平平 said...

^^ nice blog!! ^@^

徵信, 徵信網, 徵信社, 徵信社, 徵信社, 徵信社, 感情挽回, 婚姻挽回, 挽回婚姻, 挽回感情, 徵信, 徵信社, 徵信, 徵信, 捉姦, 徵信公司, 通姦, 通姦罪, 抓姦, 抓猴, 捉猴, 捉姦, 監聽, 調查跟蹤, 反跟蹤, 外遇問題, 徵信, 捉姦, 女人徵信, 女子徵信, 外遇問題, 女子徵信, 徵信社, 外遇, 徵信公司, 徵信網, 外遇蒐證, 抓姦, 抓猴, 捉猴, 調查跟蹤, 反跟蹤, 感情挽回, 挽回感情, 婚姻挽回, 挽回婚姻, 外遇沖開, 抓姦, 女子徵信, 外遇蒐證, 外遇, 通姦, 通姦罪, 贍養費, 徵信, 徵信社, 抓姦, 徵信社, 徵信, 徵信公司, 徵信社, 徵信, 徵信公司, 徵信社, 徵信公司, 女人徵信, 外遇

徵信, 徵信網, 徵信社, 徵信網, 外遇, 徵信, 徵信社, 抓姦, 徵信, 女人徵信, 徵信社, 女人徵信社, 外遇, 抓姦, 徵信公司, 徵信社, 徵信社, 徵信社, 徵信社, 徵信社, 徵信社, 女人徵信社, 徵信社, 徵信, 徵信社, 徵信, 女子徵信社, 女子徵信社, 女子徵信社, 女子徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信社,

徵信, 徵信社,徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 外遇, 抓姦, 離婚, 外遇,離婚,

徵信, 外遇, 離婚, 徵信社, 徵信, 外遇, 抓姦, 徵信社, 徵信, 徵信社, 徵信, 外遇, 徵信社, 徵信, 外遇, 抓姦, 徵信社, 征信, 征信, 徵信, 徵信社, 徵信, 徵信社, 征信, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信, 徵信社, 徵信社, 徵信社, 徵信, 外遇, 抓姦, 徵信, 徵信社, 徵信, 徵信社, 徵信,