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  • How to communicate between Client and Server in a Client-Server Application?

    - by Sanoj
    I would like to implement an Client-Server Application, where the business-logic, security validations and a database are at the server and the user interface are at the client. I would like to implement clients in different languages i.e. one in WPF/.NET, one Swing/Java , one in Android/Java and maybe one HTML/JavaScript client. The server will be on Internet, so I would like to be able to have encrypted communication. The client will send some lists of items to be added to the database, or update items, and do some transactions. The server will check if the items are already updated by another client, or update the item, add new items or delete items. How do I solve the communication between clients and the server in such a system? I have been thinking about: http/https webserver, and sending messages in JSON or XML and use Web Sockets for bi-directional communication. Use http in a RESTful way, except when WebSockets are needed. But I guess there are better solutions for native desktop applications than http? CORBA - I have just heard about it, and it's old and complex. Not much talk about it these days. XMPP/Jabber - I have just heard about it and I don't know if it fits me at all. EJabberd seams to be a popular implementation. AMQP - I have just heard about it and I don't know if it fits me at all. RabbitMQ seams to be a popular implementation. Windows Communication Foundation, Java RMI, Java Message Service - but are they language independent? I guess some of these alternatives are on different levels, maybe I can have i.e xmpp or amqp in web sockets over https? What technologys are used for this problem in companies today? and what is recommended to use? I have no experience of them other than webservers and http. Please give me some guidance in this jungle. What are the pros and cons of these technologies in my situation?

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  • JMS template credentials default value

    - by Gandalf StormCrow
    Hello everyone I'm trying to work with jboss messaging, does anyone knows the default value for these java.naming.security.principal and java.naming.security.credentials or how can I set them? <bean id="jndiTemplate" class="org.springframework.jndi.JndiTemplate"> <property name="environment"> <props> <prop key="java.naming.factory.initial">org.jnp.interfaces.NamingContextFactory</prop> <prop key="java.naming.provider.url">jnp://localhost:8080</prop> <prop key="java.naming.factory.url.pkgs">org.jboss.naming:org.jnp.interfaces</prop> <prop key="java.naming.security.principal">value</prop> <prop key="java.naming.security.credentials">value</prop> </props> </property> </bean> I'm trying to instansiate the <bean id="connectionFactory" class="org.springframework.jndi.JndiObjectFactoryBean"> I'm guessing that this is the cause why jboss timeouts when starts

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  • How can I implement JMS MessageListener?

    - by newbie
    I tried to implement MessageListener, but it dosen't work, but when I use MessageListner, it doesn't work. So what should I do that MessageListener starts working, I'm using jboss 4.02. recv.receive(); // This works recv.setMessageListener(new ExListener()); // This doesn't work public static class ExListener implements MessageListener { public void onMessage(Message msg) { TextMessage tm = (TextMessage) msg; try { System.out.println("onMessage, recv text="+tm.getText()); } catch(Throwable t) { t.printStackTrace(); } } }

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  • C#: Farm out jobs to worker processes on a multi-processor machine

    - by Andrew White
    Hi there, I have a generic check that needs to be run on ca. 1000 objects. The check takes about 3 seconds. We have a server with 4 processors (and we also have other multi-processor servers in our network) so we would like to create an exe / dll to do the checking and return the results to the "master". Does anyone know of a framework for this, or how would one go about it in C#? Specifically: * What's the best way to transfer data between the master and the worker process? * How would the master ensure that always 4 processes are running at any one time and as soon as a worker process is finished start a new one. * How to register that the worker is finished and append it's results to a list? Hope it's clear enough but happy to clarify. A.

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  • Why does the task name contain "now / 30"?

    - by Jaroslav Záruba
    In the video/PDF from "Data pipelines with Google App Engine" Brett puts "now / 30" into the task name noting that he will explain the reason later, but somehow he never does. :) http://www.youtube.com/watch?v=zSDC_TU7rtc#t=41m35 task_name = '%s-%d-%d' % (sum_name, int(now / 30), index) Do you have any idea about the reason? Does it have anything to do with the 7 day period in which one can't re-use task names? URL to the session page: http://tinyurl.com/3523mej

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  • MySQL primary/foreign key size?

    - by David
    I seem to see a lot of people arbitrarily assigning large sizes to primary/foreign key fields in their MySQL schemas, such as INT(11) and even BIGINT(20) as WordPress uses. Now correct me if I'm wrong, but even an INT(4) would support (unsigned) values up to over 4 billion. Change it to INT(5) and you allow for values up to a quadrillion, which is more than you would ever need, unless possibly you're storing geodata at NASA/Google, which I'm sure most of us aren't. Is there a reason people use such large sizes for their primary keys? Seems like a waste to me...

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  • libpcap read packet size

    - by spicyramen
    I started to write an application which will read RTP/H.264 video packets from an existing .pcap file, I need to read the packet size. I tried to use packet-len or header-len, but it never displays the right number of bytes for packets (I'm using wireshark to verify packet size - under Length column). How to do it? This is part of my code: while (packet = pcap_next(handle,&header)) { u_char *pkt_ptr = (u_char *)packet; struct ip *ip_hdr = (struct ip *)pkt_ptr; //point to an IP header structure struct pcap_pkthdr *pkt_hdr =(struct pcap_pkthdr *)packet; unsigned int packet_length = pkt_hdr->len; unsigned int ip_length = ntohs(ip_hdr->ip_len); printf("Packet # %i IP Header length: %d bytes, Packet length: %d bytes\n",pkt_counter,ip_length,packet_length); Packet # 0 IP Header length: 180 bytes, Packet length: 104857664 bytes Packet # 1 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 2 IP Header length: 100 bytes, Packet length: 104857600 bytes Packet # 3 IP Header length: 100 bytes, Packet length: 104857664 bytes Packet # 4 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 5 IP Header length: 100 bytes, Packet length: 104857600 bytes Another option I tried is to use: pkt_ptr- I get: read_pcapfile.c:67:43: error: request for member ‘len’ in something not a structure or union

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  • Dequeue notification table in Oracle

    - by user171523
    I have implemented below sample. It is working fine. I am planning to integrate with this .net application. As soon i read the entry i would like to dequeue the entry. Can any one tell how i can achive that. http://www.oracle-base.com/articles/10g/dbms_change_notification_10gR2.php Meanwhile i am trying AQ. But it does not have good .net (C#)support

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  • Combining cache methods - memcache/disk based

    - by Industrial
    Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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  • Basic question about request queues in IIS / ASP.Net

    - by larryq
    I have an ASP.Net application running under IIS 6. A simple page has two radio buttons and a submit button. If I select radio button "A" and submit the page, a lengthy PDF file is generated, which takes about a minute to build. If I select radio button "B", a small PDF is generated. (In both cases the PDF is written out to the Response object and it opens in my browser.) If I select radio button "A" and submit, then hit the red X in my browser to stop the current request, then select radio button "B" and resubmit, the page still takes a long time to process my request. No doubt my first request is still being processed on the server, but I was wondering how IIS and/or ASP.Net are queuing my requests so that fair server use is guaranteed among all users. Am I roughly correct in assuming something like this happens, and if so, how is it done?

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  • Is AMQP suitable as both an intra and inter-machine software bus?

    - by Bwooce
    I'm trying to get my head around AMQP. It looks great for inter-machine (cluster, LAN, WAN) communication between applications but I'm not sure if it is suitable (in architectural, and current implementation terms) for use as a software bus within one machine. Would it be worth pulling out a current high performance message passing framework to replace it with AMQP, or is this falling into the same trap as RPC by blurring the distinction between local and non-local communication? I'm also wary of the performance impacts of using a WAN technology for intra-machine communications, although this may be more of an implementation concern than architecture. War stories would be appreciated.

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  • Ideas on frameworks in .NET that can be used for job processing and notifications

    - by Rajat Mehta
    Scenario: We have one instance of WCF windows service which exposes contracts like: AddNewJob(Job job), GetJobs(JobQuery query) etc. This service is consumed by 70-100 instances of client which is Windows Form based .NET app. Typically the service has 50-100 inward calls/minute to add or query jobs that are stored in a table on Sql Server. The same service is also responsible for processing these jobs in real time. It queries database every 5 seconds picks up the queued jobs and starts processing them. A job has 6 states. Queued, Pre-processing, Processing, Post-processing, Completed, Failed, Locked. Another responsibility on this service is to update all clients on every state change of every job. This means almost 200+ callbacks to clients per second. Question: This whole implementation is done using WCF Duplex bindings and works perfectly fine on small number of parallel jobs. Problem arises when we scale it up to 1000 jobs at a time. The notifications don't work as expected, it leads to memory overflow etc. Is there any standard framework that can provide a clean infrastructure for handling this scenario?? Apologies for the long explanation!

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  • Any way to have delayed_job execute some run-once code at startup and use across all jobs?

    - by Rob Cameron
    So I've got a delayed_job task that pushes some info to an XMPP server. Ideally you create a connection to XMPP once and then constantly push data to it, rather than creating a new connection every time you have some data to send. Is there any kind of facility in delayed_job for running a sort of 'setup' method when a worker starts, have it set some instance variables (like the XMPP connection object) that can then be used by all the jobs that come up? It's okay if each worker runs its own setup method. I just don't want every job (thousands per day) connecting to the XMPP server from scratch every time. Thanks for any help!

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  • How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

    - by Stu Thompson
    Prelude: I'm a code-monkey that's increasingly taken on SysAdmin duties for my small company. My code is our product, and increasingly we provide the same app as SaaS. About 18 months ago I moved our servers from a premium hosting centric vendor to a barebones rack pusher in a tier IV data center. (Literally across the street.) This ment doing much more ourselves--things like networking, storage and monitoring. As part the big move, to replace our leased direct attached storage from the hosting company, I built a 9TB two-node NAS based on SuperMicro chassises, 3ware RAID cards, Ubuntu 10.04, two dozen SATA disks, DRBD and . It's all lovingly documented in three blog posts: Building up & testing a new 9TB SATA RAID10 NFSv4 NAS: Part I, Part II and Part III. We also setup a Cacit monitoring system. Recently we've been adding more and more data points, like SMART values. I could not have done all this without the awesome boffins at ServerFault. It's been a fun and educational experience. My boss is happy (we saved bucket loads of $$$), our customers are happy (storage costs are down), I'm happy (fun, fun, fun). Until yesterday. Outage & Recovery: Some time after lunch we started getting reports of sluggish performance from our application, an on-demand streaming media CMS. About the same time our Cacti monitoring system sent a blizzard of emails. One of the more telling alerts was a graph of iostat await. Performance became so degraded that Pingdom began sending "server down" notifications. The overall load was moderate, there was not traffic spike. After logging onto the application servers, NFS clients of the NAS, I confirmed that just about everything was experiencing highly intermittent and insanely long IO wait times. And once I hopped onto the primary NAS node itself, the same delays were evident when trying to navigate the problem array's file system. Time to fail over, that went well. Within 20 minuts everything was confirmed to be back up and running perfectly. Post-Mortem: After any and all system failures I perform a post-mortem to determine the cause of the failure. First thing I did was ssh back into the box and start reviewing logs. It was offline, completely. Time for a trip to the data center. Hardware reset, backup an and running. In /var/syslog I found this scary looking entry: Nov 15 06:49:44 umbilo smartd[2827]: Device: /dev/twa0 [3ware_disk_00], 6 Currently unreadable (pending) sectors Nov 15 06:49:44 umbilo smartd[2827]: Device: /dev/twa0 [3ware_disk_07], SMART Prefailure Attribute: 1 Raw_Read_Error_Rate changed from 171 to 170 Nov 15 06:49:45 umbilo smartd[2827]: Device: /dev/twa0 [3ware_disk_10], 16 Currently unreadable (pending) sectors Nov 15 06:49:45 umbilo smartd[2827]: Device: /dev/twa0 [3ware_disk_10], 4 Offline uncorrectable sectors Nov 15 06:49:45 umbilo smartd[2827]: Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error Nov 15 06:49:45 umbilo smartd[2827]: # 1 Short offline Completed: read failure 90% 6576 3421766910 Nov 15 06:49:45 umbilo smartd[2827]: # 2 Short offline Completed: read failure 90% 6087 3421766910 Nov 15 06:49:45 umbilo smartd[2827]: # 3 Short offline Completed: read failure 10% 5901 656821791 Nov 15 06:49:45 umbilo smartd[2827]: # 4 Short offline Completed: read failure 90% 5818 651637856 Nov 15 06:49:45 umbilo smartd[2827]: So I went to check the Cacti graphs for the disks in the array. Here we see that, yes, disk 7 is slipping away just like syslog says it is. But we also see that disk 8's SMART Read Erros are fluctuating. There are no messages about disk 8 in syslog. More interesting is that the fluctuating values for disk 8 directly correlate to the high IO wait times! My interpretation is that: Disk 8 is experiencing an odd hardware fault that results in intermittent long operation times. Somehow this fault condition on the disk is locking up the entire array Maybe there is a more accurate or correct description, but the net result has been that the one disk is impacting the performance of the whole array. The Question(s) How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt? Am I being naïve to think that the RAID card should have dealt with this? How can I prevent a single misbehaving disk from impacting the entire array? Am I missing something?

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  • How Long Can Same-Page Anchor Links (#) Be?

    - by Volomike
    What is the maximum number of characters that a same-page anchor tag link can be on all mainstream platform browsers released from IE6 on up? For instance, a link like: http://example.com/#a789c4d8ecb0ec2201444bfa64b04696aa2bbaa41eb331535d1dd6d219558a02968d5af97ae74359973163337ef9b09c65dd70d40c3c79a4169355ea92db45e21fe30550dce4987987237652a347b97759f2753b412ee50d4121d0f6382580b5a62d1e02921c39c252c5e4731e38fc295ad6abcb22613513c4fd7599ab10d3f9c970b9eb3ddf5b2cf233af25005298590ce798b28092cecdc6756c8205e9a0650826e42a184267d0bfb5e3d7b3d1c25e324fe6329cf7681ffae7c01c86d4a70 Note the # symbol above. Note I'm using XHTML transitional, if that matters any.

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  • Android: Quitting the Looper?

    - by stormin986
    I have a thread I use to periodically update the data in my Activity. I create the thread and start a looper for using a handler with postDelay(). In onDestroy() for my activity, I call removeCallbacks() on my handler. Should I then call handler.getLooper().quit()? Or not worry about it and let the OS deal with it? Or would it just run forever then, consuming CPU cycles?

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  • Referencing file on disk from NSManagedObject

    - by Kamchatka
    Hello, What would be the best way to name a file associated to a NSManagedObject. The NSManagedObject will hold the URL to this file. But I need to create a unique filename for my file. Is there some kind of autoincrement id that I could use? Should I use mktemp (but it's not a temporary file) or try to convert the NSManagedObjectId to a filename? but I fear there will be special characters which might cause problem. What would you suggest?

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  • Java - PriorityQueue vs sorted LinkedList

    - by msr
    Hello, Which implementation is less "heavy": PriorityQueue or a sorted LinkedList (using a Comparator)? I want to have all the items sorted. The insertion will be very frequent and ocasionally I will have to run all the list to make some operations. Thank you!

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  • Thread loses Message after wait() and notify()

    - by fugu2.0
    Hey Guys! I have a problem handling messages in a Thread. My run-method looks like this public void run() { Looper.prepareLooper(); parserHandler = new Handler { public void handleMessage(Message msg) { Log.i("","id from message: "+msg.getData.getString("id")); // handle message this.wait(); } } } I have several Activities sending messages to this thread, like this: Message parserMessage = new Message(); Bundle data = new Bundle(); data.putString("id", realId); data.putString("callingClass", "CategoryList"); parserMessage.setData(data); parserMessage.what = PARSE_CATEGORIES_OR_PRODUCTS; parserHandler = parser.getParserHandler(); synchronized (parserHandler) { parserHandler.notify(); Log.i("","message ID: " + parserMessage.getData().getString("id")); } parserHandler.sendMessage(parserMessage); The problem is that the run-method logs "id from message: null" though "message ID" has a value in the Log-statement. Why does the message "lose" it's data when being send to the thread? Has it something to do with the notify? Thanks for your help

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  • While saving a PNG image using NSData writetofile saves corrupted data on the iphone disk

    - by jAmi
    I have a number of images (PNG,GIF and JPG) in my Application Resource Bundle. I want some images to be saved in my Documents Directory so i use : imgPath=[documentsDirectoryPath stringByAppendingPathComponent:@"myImage.png"]; if (![fileMgr fileExistsAtPath:imgPath]) { [[fileMgr contentsAtPath:[[NSBundle mainBundle] pathForResource:@"myImage"ofType:@"png"]] writeToFile:imgPath atomically:NO]; } This saves an Image file on my desired Path but this file has an Extra 300 bytes (of maybe junk data) in it which results in a corrupted image... Am i doing something wrong here? This works in the simulator but on the real device the image has some extra 300 bytes. Also a GIF image gets copied nicely and works but this problem occurs for PNG image.

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  • In which domains are message oriented middleware like AMQP useful?

    - by cocotwo
    What problem do MOM (Message Oriented Middleware) solve? Scalability? Integration? In which domain are they typically used and in which domains are they typically not used? For example, say, is Google using such solution for it's main search engine or to power GMail? What about big websites like Walmart, eBay, FedEx (pretty much a Java shop) and buy.com (pretty much an MS shop)? Does MOM solve a need there? Does it make any sense when you're writing a Webapp where you control the server-side and have an homogenous environment (say tens of Amazon EC2 instances all running Linux + Java JVMs) there and where the clients are, well, Web browsers? Does it make sense for desktop apps that need to communicate with a server? Or is it 'only' for big enterprise stuff where you typically have a happy mix of countless of different systems that needs to communicate in a way or another? I'm a bit confused as to what they're useful for and I think that with example of where they're appropriate and where they're not appropriate I could better understand their use.

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  • How do I make custom functions chain-able with jQuery's?

    - by sergio
    I need a "callfront" or "precall" (the opposite of "callback" ¿?) to add in MANY places before an animation occurs in an existing plugin, To be used like e.g. $(some_unpredictable_obj).preFunct().animate(… The problem is, as I said they are MANY places, and all of them are different animations, on different objects. I can TELL where all of them occur, but I don't want to add over and over the same code. I actually have to add both a function before and after those animations, but I think I can use the callback for all of them. In a perfect world, I'd like to replace every animate(property, duration) by preFunct().animate(property,duration).postFunct() preFunct and postFunct don't need parameters, since they are always the same action, on the same object. This could be an amazing addition to "jQuery" (an easy way to jQuerize custom functions to be added to the normal chain (without messing with queues) I found this example but it will act on the applied element, and I don't want that because, as I said above, all the original animations to be added to are on different elements. I also found jQuery.timing, but it looks cooler the chain-able function :) Thanks.

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