I have created a user interface in java which uses card layout. It basically shows a lot of readings in it which it receives through our company's local network. Now I had to write an OPC server in java so that all the readings my ui receives is stored onto that server. I successfully wrote it. My UI works awesome for almost a day but the next day when i come to office, I find my UI frozen, as in there is no more communication taking place. The UI stops receiving or transmitting numbers. When i run the UI without OPC, it goes on and on forever but its when i add OPC to it, that it freezes/ I have tried all sorts of stuff but I still have not been able to solve it. ANd yes, I have used Jnet Pcap to capture the packets in the UI. There is a huge amount of code in it so if anyone requires any specific code to look at, let me know.
This is really hard to follow. What is the exact problem that you are facing is still unclear.
The openSCADA website that has the free OPC implementation should be your best bet...
http://openscada.org/projects/utgard/
More over you can try the JEasyOPC client which is also free incipiently.
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I have been trying to make multiplayer applications on a website for a while. I wanted to start with a basic chat system. I made one but it is really slow. On the HTML page it send the message through AJAX to a PHP application which saves it to a text file. Then back on the HTML file, it is constantly checking the text file every 3 seconds. This is very slow and unreliable. So i looked up better ways of doing this. I found Node.js and used it along with Socket.io and express to create a faster chat application. But it only works on local host and i have no idea how to implement it on a website. So I kept looking and discovered WebSockets. Which are so confusing and seem to have very little support. I am confused how websites out there have applications that can be real time with so few options. How is this done? Am i missing a way of doing this? If you can help me that would be great.
Socket.io is using websockets under the hood already. Using raw websockets isn't necessary for your chat app.
You're on the right track using socket.io and node.js server-side.
Building a multi-player game in the browser will be a very difficult task for a beginner. But that's why it's good to learn! I suggest using a library for graphics (a quick google gave me this: http://www.pixijs.com/ ).
The over all architecture should be something like:
Users go to your server and receive a web page (.html) which contains the javascript and a canvas they need to play the game. This is the "client-side" because it's all running on each users' web browser on their computer.
The web page runs the javascript which talks to the node.js server using socket.io. This is the "server-side". The job of the server is to coordinate player data (who is who, where are they in the game, who's doing what etc) and keep track of the game state. Basically, this is where the game actually is, kind of like having the Monopoly board on the server, while the client-side is really just responsible for showing the board to the players (drawing it on the HTML5 canvas) and sending player input to the server.
Tutorials:
USE GOOGLE. Try just literally searching for "javascript game tutorial". Try every tutorial that comes up. If something is taking a while to get up and running then ditch it and move to another one.
Do simple little things at first 'till you start to grok what the overall process is like. For example: https://developer.mozilla.org/en-US/docs/Games/Workflows/2D_Breakout_game_pure_JavaScript
Remember playing ultra-simple games like Pong? Try writing games like this first. Your chat system is a great start, by the way, because it covers the basics of how to get a server up and running, how to get a page, how to send data around.
As for getting something up and running on a server where others can connect to it... Check this out: have your buddies come to your house and bring their laptops, start your node.js chat server, tell them what your IP address is, and have them go to "http://YOURIPADDRESS:8000" in their browser-- they'll connect to your node.js server!
Getting it running on a hosting provider is a little more involved and probably not worth the trouble at this stage. You'll learn more about this later just by keeping on the way you're going.
Socket.IO does not only work on localhost. You will need to get a server to run your application on. I highly recommend not worrying about this piece of the puzzle just yet, as it is somewhat complicated if you are brand new at this. Come back to this part when you are ready.
As for the game development, I recommend using Phaser. It has everything you need to get started and great documentation.
http://phaser.io
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I was asked this question once at an interview:
"Suppose you own a website where the server is at some remote location. One day, some user calls/emails you saying the site is abominably slow. How would you identify why the site is slow? Also, when you check the website yourself as any user would (using your browser), the site behaves just fine."
I could think of only one thing (which was shot down):
Check the server logs to analyse incoming traffic. Maybe a DoS attack or exceptionally high traffic. Interviewer told me to assume the server has normal traffic and no DoS.
I was kind of lost because I had never thought of this problem. I have almost no idea how running a server/website works. So if someone could highlight a few approaches, it would be nice.
While googling around, I could find only this relevant, wonderful article. That article is kind of too technical for me now, but I'm slowly breaking it down and understanding it.
Since you already said when you check the site yourself the speed is fine, this means that (at least for the pages you checked) there is nothing wrong with the server and it can serve those pages at a good speed. What you should be figuring out at this point is what the difference is between you and the user that reports your site is slow. It might be a lot of different things:
Is the user using a slow network connection (mobile for example)?
Does the user experience the same problems with other websites hosted at the same webhoster? If so, this could indicate a network problem. Normally this could also indicate a resource problem at the webserver, but in that case the site would also be slow for you.
If neither of the above leads to an answer, you could assume that the connection to the server and the server itself are fine. This means the problem must be in the users device. Find out which browser/OS he uses and try to replicate the problem. If that fails find out if he uses any antivirus or similar software that might cause problems.
This is a great tool to find the speed of web pages and tells you what makes it slow: https://developers.google.com/speed/pagespeed/insights
I think one of the important thing that is missing from above answers is the server location, which can play a vital in web performance.
When someone is saying that it is taking a longer time to open a web page that means high latency. High latency can be caused due to server location.
Let's assume as you are the owner of the web page then the server and client are co-located, so it will have a low latency.
But, now if client is across the border, then latency time will increase drastically. And hence a slow perfomance.
Another factor is caching which drastically affects the latency time.
Taking the example of facebook, they have server all over the world to reduce the latency time (and also to provide several other advantages) and they use huge caching system to cache their hot data (trending topics) whereas cold data (old data) are stored in hard disk so it takes a longer time to load an older photo or post.
So, a user might would have complained about this as they were trying load up some cold data.
I can think of these few reasons (first two are already mentioned above):
High Latency due to location of client
Server memory might need to be increased
Number of service calls from the page.
If a service could be down at the time of complaint, it could prevent page from loading.
The server load might be too high at the time of the poor experience. The server might need to increase the resources (e.g. adding another server/web server to the cluster).
Check if there was any background job running on the server at that time.
It is important to check the logs and schedules of the batch jobs to determine what all was running at that time.
Hope this help.
Normally the user takes the page loading time as a measure to find out that the site is slow. But if you really want to know that what is taking the maximum time the you can open the browser debugger by pressing f12. if your browser is chrome the click on network and see what calls your application is making and which are taking maximum time. If you are using Firefox the you need to install firebug. If you have that, then again press f12 and click on Net.
One reason could be the role of the user is different of your role. You might be having suppose an administrator privilege (some thing like super user role) and the code might be just allowing everything for such role that means it does not really do much of conditional checking to see what is allowed or not. Some times, it's a considerable over ahead to get all the privileges of the user and have the conditions checking, how course depends how how the authorization is implemented. That means, the page might be really slow for specific roles. Hence, you should find out the roles of the user and see if that is a reason.
Obviously an issue with the connection of the person connecting to your site OR it's possible it was a temporary issue and by the time you checked your site, everything was dandy. You could check your logs or ask your host if there was an issue at the time the slow down occured.
This is usually a memory issue and it can be resolved by increasing the Heap Size of the Web Server hosting the application. In case the application is running on Weblogic Server. Heap size can be increased in "setEnv" file located in Application Home.
Goodluck!
Michael Orebe
Though your question is quite clear, web site optimisation is a very extensive subject.
The majority of the popular web developing frameworks are for some reason, extremely processor inefficient.
The old fashioned way of developing n-tier web applications is still very relevant and is still considered to be best practice according the W3C. If you take a little time to read the source code structure of the most popular web developing frameworks you will see that they run much more code at the server than is necessary.
This may seem a bit of a simple answer but, the less code you run at the server and the more code you run at the client the faster your servers will work.
Sometimes contrasting framework code against the old fashioned way is the best way to get an understanding of this. Here is a link to a fully working mini web application which represents W3C best practices and runs the minimum amount of code at the server and the maximum amount of code at the client: http://developersfound.com/W3C_MVC_EX.zip this codebases is also MVC compliant.
This codebase comes with a MySQL database dump, php and client side code. To see this code in action you will need to restore the SQL dump to a MySQL instance (sql dump came from MySQL 8 Community) and add the user and schema permissions that are found in the php file (conn_include.php); setting the user to have execute permissions on the schema.
If you contrast this code base against all of the most popular web frameworks, it will really open your eyes to just how inefficient these frameworks are. The popular PHP frameworks that claim to be MVC frameworks aren’t actually MVC compliant at all. This is because they rely on embedding PHP tags inside HTML tags or visa-versa (considered very bad practice according the W3C). Also most popular node frameworks run way more code at the server than is necessary. Embedded tags also stop asynchronous calls from working properly unless the framework supports AJAX dumps such as Yii 2.
Two of the most important rules to follow with MVC compliance is: never embed server side tags (such as PHP tags) in HTML tags or visa-versa (unless there is a very good excuse such as SEO) and religiously never write code to run at the server if it can be run at the client. Also true MVC is based on tier separation, where as the MVC frameworks are based on code separation. True MVC compliance is very processor efficient. Don’t get me wrong MVC frameworks are very useful for a lot of things, but if you’re developing a site that is going to get millions of hits, they are quite useless, or at least they will drive your cloud bills so high that it will really eat into your company’s profits.
In summary frameworks don’t give much control over what code runs at the client or server and are very inefficient but you can get prototypes up and running quicker with less code.
In contrast the old fashioned way takes a bit more elbow grease but you have complete control over what runs at the server and what runs at the client.
As an additional bit of advice for optimisation avoid using pass-through queries and triggers and instead opt for stored procedures. Historically stored procedures weren’t invented at the time MVC was present as a paradigm but it definitely increases separation of concerns between the tiers and is much more processor efficient.
Hope this advice helps.
I will try first to explain my web application goal.
It is dedicated to an intranet and the architecture will consist in a server connected to the web and less than 10 clients.
The application will be used to give aeronautical information. This will be achieved by retrieving with cURL requests (php scripts) launched every X minutes (CRON jobs) on remote sites (meteorology,airways and airport information) and saved in an XML file or a DB. The information gathered is then presented on a web page(a kind of well-organised synthesis) to air trafic controllers to enhance their situation awareness.
As data gathered must reach the client in real-time, I cannot rely on browser interaction : if an airport is closing due to bad weather,that piece of information has to be displayed as soon as possible without any user interaction.
The number of airport monitored will be around 30 (thus giving you an idea of the server load, knowing that meteorology reports are stored on the X website, airport data on the Y website etc..) .
After reading a lot on Reverse Ajax (Server-Push), I really need a professional experience to help me choose the best approach to develop this application.
The Server-Push technologies I discovered on the net are:
1) APE (Ajax Push Engine) -> This one makes me feel like trying to open a door with a bazooka (can handle thousands of connections).
2) Long polling (Comet) -> I fear this one could put to much stress on the server load.
3) Web sockets -> I must first wait for it to get mature and supported by firefox 6 (no more security issues)
As I am completely new to server-push, I hope you will help me find the appropriate way to achieve displaying these data in a close to real-time manner. It would certainly be a pity if I ended up setting "refresh" buttons to update the air pressure at the location of airport "A" using Ajax.
Thanks for reading.
If you speak C, there is an example of how to do pushing here. This 3-calls API is much simpler than others so it might match your relatively simple needs.
I have to use scanner on Internet site web page. As far as I know not Flash nor Silverlight is capable to communicate with such hardware nowadays. It looks like there is no alternative to Active-X at present for such operation (correct me if I'm wrong).
After image is scanned I have to send it to server via HTTPS and wait for processing result.
I have some alternatives here:
Start ajax polling with regular interval
Put polling functionality straight into active-x component
What approach would you personally preffer?
Is it possible to establish event mechanism for Active-X approach (when server pushes result back to a web-page?). Will events work for javascript/ajax approach?
Thank you in advance!
Have the client scan and upload a file. That's how it's done these days. Scanning software is a part of OS - at least, in Windows and MacOS it is.
With an ActiveX object, it will become a support nightmare. Also, think of all the Firefox/Chrome/Opera/Non-Windows users out there.
Also, I vaguely recall scanner support will be added in HTML5.
I am currently working on a project that embeds a flash game, that uses Smartfoxserver for the flash communication. That communication is mostly just synchronizing the cursor and object movements between the two players.
Since I am not a flash guy, but a ruby programmer, I got curious: What kind of communication options does flash offer for this kind of time sensitive data exchange? I was thinking of writing a ruby-eventmachine based communication server to minimize the dependencies on external programs. Would that even be feasible?
Although I don't have a complete answer for you, because I'm not done myself, I have found myself in almost the exact same position as you.
My current approach is for my ruby server to essentially just be a socket server that handles all of the communication between clients, however I personally intend on keeping any of the logic outside of the server ( unless I run across a reason to change that idea).
If you haven't done any socket programming in ruby, I recommend the following as a jumping point. This is an IBM document on Ruby Socket programming and discusses an approach for asynchronous data:
Ruby Sockets - IBM
I think what it ultimately comes down to as well will be performance. I currently use a version of my ruby server in my daily work, but the data doesn't have to be updated in a time sensitive manner.
You can create a server in (almost?) any language that supports sockets and manage your clients with that.
From a flash perspective you could use ruby, but I don't know how fitted ruby would be for the task...I mean, you can make a PHP socket server but it would not handle much stress.
An alternative to SmartFoxServer could be open sourced Red5, written in Java.
If you want to know about flash built in capabilities in handling p2p:
Flash p2p: Everett Church
In Flash Player 10 adobe added Live media (RTMFP) support- Media was always sourced from the publishing peer. In Flash Player 10.1 beta they introduced groups and application-level multicast.
However, you would still need a server (Stratus) to handle introductions and manage active connections. ( Also, I regard it as geared towards flash video, Stratus does not support shared objects or scripting. So with Stratus, your applications will be clients communicating directly with each other.)
Edit:
After re-reading your question and the answer provided by Beanish, I think the first time I got your question wrong. So I just re-wrote my answer...