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• How to publish internal data to the internet - as simple as possible

  - by mlarsen

  We have a .net 2-tier application where a desktop program is talking to a database. We support MS SQL Server 2000, 2005, 2008 and Oracle 9, 10 and 11. The application is sold, not as shrink-wrap, but pretty close. It is quite important for us that the installation and configuration is as easy as possible as installation instructions are usually supplied in written form to the customers internal IT-department. Our application is usually not seen as mission critical for the IT-department, so we need to keep their work down to a minimum. Now we are starting to get wishes for a web application build on top of the same data. The web application will be hosted by us and delivered as a SaaS application. Now the challenge is how to move data back and forth between the web application and the customers internal database. as I see it we have some requirements: We must be ready to handle the situation where the customers database is not accessible from the DMZ. I guess the easiest solution is that all communication is initiated from inside the customers lan. As little firewall configuration as possible. The best is if we can run without any special configuration as long as outgoing traffic from the customers lan are not blocked. If we need something changed in the firewall, we must be able to document that the change is secure. It doesn't have to be real time. Moving data in batches every ten minutes or so is OK. Data moves both ways, but not the same tables, so we don't have to support merges. It would be nice if we don't have to roll our own framework completely. Looking forward to hear your suggestions.

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• Thread-safe data structure design

  - by Inso Reiges

  Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of "exists" call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? EDIT: I have a better example. Suppose that element retrieval returns either a reference or a pointer to the stored element and not it's copy. How can a caller be protected to safely use this pointer\reference after the call returns? If you think that not returning copies is a problem, then think about deep copies, i.e. objects that should also copy another objects they point to internally. Thank you.

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• Emacs: Often switching between Emacs and my IDE's editor, how to automatically 'synch' the files?

  - by WizardOfOdds

  I very often need to do some Emacs magic on some files and I need to go back and forth between my IDE (IntelliJ IDEA) and Emacs. When a change is made under Emacs (and after I've saved the file) and I go back to IntelliJ the change appears immediately (if I recall correctly I configured IntelliJ to "always reload file when a modification is detected on disk" or something like that). I don't even need to reload: as soon as IntelliJ IDEA gains focus, it instantly reloads the file (and I hence have immediately access to the modifications I made from Emacs). So far, so very good. However "the other way round", it doesn't work yet. Can I configure Emacs so that everytime a file is changed on disk it reloads it? Or make Emacs, everytime it "gains focus", verify if any file currently opened has been modified on disk? I know I can start modifying the buffer under Emacs and it shall instantly warn that it has been modified, but I'd rather have it do it immediately (for example if I used my IDE to do some big change, when I come back to Emacs what I see may not be at all anymore what the file contains and it's a bit weird).

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• Synchronising scripts / db / files from dev system to web server

  - by Spoonface

  I work as a freelance web dev, and up until now have been ftping my scripts / databases / static files to my web server manually, but I'm finding that is too error prone. So I'm looking for an app to automate uploading new and updated scripts / files / databases / etc. I know a lot of independent devs use WinSCP or Unison, but I don't think those apps can synch databases. Does anyone have any other suggestions? It doesn't need to be anything overly feature rich as I'm not working within a team or across multiple operating systems or anything like that. I can purchase any reasonably priced license if necesary. My work is primarily for PHP / MySQL / Apache on a Windows system, and then uploaded to a Linux / Apache server. thanks for your time!

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• How can I safely raise events in an AsyncCallback?

  - by cyclotis04

  I'm writing a wrapper class around a TcpClient which raises an event when data arrives. I'm using BeginRead and EndRead, but when the parent form handles the event, it's not running on the UI thread. I do I need to use delegates and pass the context into the callback? I thought that callbacks were a way to avoid this... void ReadCallback(IAsyncResult ar) { int length = _tcpClient.GetStream().EndRead(ar); _stringBuilder.Append(ByteArrayToString(_buffer, length)); BeginRead(); OnStringArrival(EventArgs.Empty); }

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• Syncronizing mobile phone contacts with contacts from social networks

  - by Pentium10

  I retrieve a JSON list of contacts from a social network site. It contains firstname, lastname, displayname, data1, data2, etc... What is the efficient way to quickly lookup my local phone contacts database and "match" them based on their name. Since there are firstname, lastname and displayname this can vary. What do you think, how can the best match be achieved? Also how do I make sure I don't parse for each JSON item the whole database I want to avoide having JSON_COUNT x MOBILE COUNT steps.

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• question about book example - Java Concurrency in Practice, Listing 4.12

  - by mike

  Hi, I am working through an example in Java Concurrency in Practice and am not understanding why a concurrent-safe container is necessary in the following code. I'm not seeing how the container "locations" 's state could be modified after construction; so since it is published through an 'unmodifiableMap' wrapper, it appears to me that an ordinary HashMap would suffice. EG, it is accessed concurrently, but the state of the map is only accessed by readers, no writers. The value fields in the map are syncronized via delegation to the 'SafePoint' class, so while the points are mutable, the keys for the hash, and their associated values (references to SafePoint instances) in the map never change. I think my confusion is based on what precisely the state of the collection is in the problem. Thanks!! -Mike Listing 4.12, Java Concurrency in Practice, (this listing available as .java here, and also in chapter form via google) /////////////begin code @ThreadSafe public class PublishingVehicleTracker { private final Map<String, SafePoint> locations; private final Map<String, SafePoint> unmodifiableMap; public PublishingVehicleTracker( Map<String, SafePoint> locations) { this.locations = new ConcurrentHashMap<String, SafePoint>(locations); this.unmodifiableMap = Collections.unmodifiableMap(this.locations); } public Map<String, SafePoint> getLocations() { return unmodifiableMap; } public SafePoint getLocation(String id) { return locations.get(id); } public void setLocation(String id, int x, int y) { if (!locations.containsKey(id)) throw new IllegalArgumentException( "invalid vehicle name: " + id); locations.get(id).set(x, y); } } // monitor protected helper-class @ThreadSafe public class SafePoint { @GuardedBy("this") private int x, y; private SafePoint(int[] a) { this(a[0], a[1]); } public SafePoint(SafePoint p) { this(p.get()); } public SafePoint(int x, int y) { this.x = x; this.y = y; } public synchronized int[] get() { return new int[] { x, y }; } public synchronized void set(int x, int y) { this.x = x; this.y = y; } } ///////////end code

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• Concurrent threads adding to ArrayList at same time - what happens?

  - by Marcus

  We have multiple threads calling add(obj) on an ArrayList. My theory is that when add is called concurrently by two threads, that only one of the two objects being added is really added to the ArrayList. Is this plausable? If so, how do you get around this? Use a synchronized collection like Vector?

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• Java - when to use notify or notifyAll?

  - by mdma

  Why does java.lang.Object have two notify methods - notify and notifyAll? It seems that notifyAll does at least everything notify does, so why not just use notifyAll all the time? If notifyAll is used instead of notify, is the program still correct, and vice versa? What influences the choice between these two methods?

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• General ORM design question

  - by Calvin

  Suppose you have 2 classes, Person and Rabbit. A person can do a number of things to a rabbit, s/he can either feed it, buy it and become its owner, or give it away. A rabbit can have none or at most 1 owner at a time. And if it is not fed for a while, it may die. Class Person { Void Feed(Rabbit r); Void Buy(Rabbit r); Void Giveaway(Person p, Rabbit r); Rabbit[] rabbits; } Class Rabbit { Bool IsAlive(); Person pwner; } There are a couple of observations from the domain model: Person and Rabbit can have references to each other Any actions on 1 object can also change the state of the other object Even if no explicit actions are invoked, there can still be a change of state in the objects (e.g. Rabbit can be starved to death, and that causes it to be removed from the Person.rabbits array) As DDD is concerned, I think the correct approach is to synchronize all calls that may change the states in the domain model. For instance, if a Person buys a Rabbit, s/he would need to acquire a lock in Person to make a change to the rabbits array AND also another lock in Rabbit to change its owner before releasing the first one. This would prevent a race condition where 2 Persons claim to be the owner of the little Rabbit. The other approach is to let the database to handle all these synchronizations. Who makes the first call wins, but then the DB needs to have some kind of business logics to figure out if it is a valid transaction (e.g. if a Rabbit already has an owner, it cannot change its owner unless the Person gives it away). There are both pros/cons in either approach, and I’d expect the “best” solution would be somewhere in-between. How would you do it in real life? What’s your take and experience? Also, is it a valid concern that there can be another race condition the domain model has committed its change but before it is fully committed in the database? And for the 3rd observation (i.e. state change due to time factor). How will you do it?

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• How do I sync Dreamweaver site definitions across 2 computers?

  - by baritoneuk

  I use Dreamweaver on my laptop and Desktop PC and frequently change between them. I keep all my sites synced using Syncplicity (similar to Dropbox, which indecently I also use) I want my site definitions to be synced across the two computers. If I add a new site on one computer I want it to appear on the other one. I know I can export all sites on one computer and then get Syncplicity to sync the files to the other computer at which point I can import them. However this relies on me remembering to do this each time I add a new site, and it's also quite time consuming. As far as I can tell, Dreamweaver (at least upto CS4- not sure about CS5) stupidly stores the site definitions in the registry. I really don't know why they do this- if they stored it in xml files then I could easily sync the information. Does anyone know if what I am asking is possible?

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• Synchronisation construct inside pragma for

  - by Sayan Ghosh

  Hi, I have a program block like: for (iIndex1=0; iIndex1 < iSize; iIndex1++) { for (iIndex2=iIndex1+1; iIndex2 < iSize; iIndex2++) { iCount++; fDist =(*this)[iIndex1].distance( (*this)[iIndex2] ); m_oPDF.addPairDistance( fDist ); if ((bShowProgress) && (iCount % 1000000 == 0)) xyz_exception::ui()->progress( iCount, (size()-1)*((size()-1))/2 ); } } } } I have tried parallelising the inner and outer loop and by putting iCount in a critical region. What would be the best approach to parallelise this? If I wrap iCount with omp single or omp atomic then the code gives an error and I figured out that would be invalid inside omp for. I guess I am adding many extraneous stuffs to paralellise this. Need some advice... Thanks, Sayan

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• Java - Multithreading

  - by Mandar

  What is the difference between synchronized methods and synchronized statements ? If possible , please use an example to make it more clear. Thanks.

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• Strophe javascript prevent disconnection on some delay

  - by patrikas

  Hello, I am developing javascript XMPP application which uses Strophe library to connect to Jabber server. I need to engage the thread for about 5-10 seconds when Strophe connects to the server. Thread is engaged by running java applet and after it releases the thread it goes back to handle XMPP events, however at the moment I cannot manage to do that - trying to use a connection after delay gives me 404 HTTP error (this is sent by XMPP-BOSHS service straight after Strophe sends POST request with XMPP message to it). I was trying to 'pause' a connection with Strophe's connection.pause and then resume it - didn't work. Would sending some raw content to the server, maybe if it's possible telling it that client's gonna be unresponsive for a short time work ? Are there any other solutions ? Thanks

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• Synclock a section of code while waiting for ShowDialog to return

  - by clawson

  I'm having trouble working out how to lock my application out of a section of code while it waits for a response from an external program. I've used Synclock on a section of code with the Me object in the expression. In this Synclock I call an overridden ShowDialog method of a dialog box, which has a timeout parameter, but does return the value from the underlying ShowDialog function call ,once the timer is setup. Works like this. SyncLock Me Dim frmDlgWithTimeout As New frmDlgWithTimeout ' dialog box with overridden ShowDialog ' Dim res As DialogResult = frmDlgWithTimeout.ShowDialog(10 * 1000) ' 10 sec timeout ' End SyncLock Now, external programs may raise events that bring my application to this Synclock but it doesn't prevent it from entering it, even though the ShowDialog function hasn't returned a value (and hence what I thought would keep the section of code locked). There is only one instance of the object that is used for lock in the program. Your help is greatly appreciated.

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• What is a good way to sync code files between computer?

  - by erotsppa

  I have a need to code from two computers during the week. What is the best way to sync the two computers (mac)? I've started using source control, like SVN. It works pretty good, except sometimes I check in code that I want to sync but they don't compile and it interferes with other people on the team working on the same project. I don't want to use branch. It wouldn't make sense to branch every night when I head home from office.

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• iPad / iPhone Sync (WLAN or Inet)

  - by tobi

  I have actually one app with a SQLite DB and i port this at the moment to the ipad. My idea is a sync between iPad and iPhone for one table... But the Problem is "Person A" edit/change, create or delete a data record on iphone and "Person B" make the same or delete the edited record from Person A on the same time. Has anybody a idea for this? Or a nice lib for this?

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• Is nested synchronized block necessary?

  - by Dan

  I am writing a multithreaded program and I have a method that has a nested synchronized blocks and I was wondering if I need the inner sync or if just the outer sync is good enough. public class Tester { private BlockingQueue<Ticket> q = new LinkedBlockingQueue<>(); private ArrayList<Long> list = new ArrayList<>(); public void acceptTicket(Ticket p) { try { synchronized (q) { q.put(p); synchronized (list) { if (list.size() < 5) { list.add(p.getSize()); } else { list.remove(0); list.add(p.getSize()); } } } } catch (InterruptedException ex) { Logger.getLogger(Consumer.class.getName()).log(Level.SEVERE, null, ex); } } } EDIT: This isn't a complete class as I am still working on it. But essentially I am trying to emulate a ticket machine. The ticket machine maintains a list of tickets in the BlockingQueue q. Whenever a client adds a ticket to the machine, the machine also keeps track of the price of the last 5 tickets (ArrayList list)

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• local code files synch with server

  - by webdev

  I search for way to synch my local code with server on debain linux. For example i modify some files, then i can run synch command, and only changed files send to server (using ssh for ex). Can you help me with good light solution for this?

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• Can Windows Mobile Synch Services use a business layer

  - by Andy Kakembo

  We're building a Win Mobile 6 warehouse app which needs to update our server based corporate DB. We've got a C# business layer that sits on our app server and we'd really like our warehouse app to go through this. We also like MS Synch Services. Is there a way to combine the two ie can we use sync services but get them to go through our business layer ? Has anyone done this and got an example I can follow ? Is there a best practice for this kind of scenario ? Thanks, Andy

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• Syncing magento database froms development to production

  - by ringerce

  I use git for version control. I have a development, staging and production environment. When I finish in development I push to staging for review by the client. When approved, I push changes from staging to production. That works fine as long as there is no database changes. What happens if I install modules via Magento connect on local development and it makes database modifications. How would I push those changes up to the production server since the production server is always changing? Edit: I wrote two shell scripts. One that pulls the production database down to my development server, replaces base url with develpment url and updates my development db accordingly. It also leaves the production sql dump behind to be added to my git repo. I'm not really sure if it's beneficial to keep the raw dumps in source control but I'm going to try it out. The second scripts moves the development database up to staging and essentially performs the same operations as the first. Now when it comes time to move to production I pull the updated production repo into the production server and allow magento to do it's thing. I also started using SQLYog recently and it has a database comparison wizard which will give me the differences in my development and production databases and allow me to merge the changes in selectively. It always creates a migration script that I added to source control as well. If anything goes wrong I can run the comparison to see if anything was missed. Does this sounds like a decent workflow to you guys?

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• Linked list example using threads

  - by Carl_1789

  I have read the following code of using CRITICAL_SECTION when working with multiple threads to grow a linked list. what would be the main() part which uses two threads to add to linked list? #include <windows.h> typedef struct _Node { struct _Node *next; int data; } Node; typedef struct _List { Node *head; CRITICAL_SECTION critical_sec; } List; List *CreateList() { List *pList = (List*)malloc(sizeof(pList)); pList->head = NULL; InitializeCriticalSection(&pList->critical_sec); return pList; } void AddHead(List *pList, Node *node) { EnterCriticalSection(&pList->critical_sec); node->next = pList->head; pList->head = node; LeaveCriticalSection(&pList->critical_sec); } void Insert(List *pList, Node *afterNode, Node *newNode) { EnterCriticalSection(&pList->critical_sec); if (afterNode == NULL) { AddHead(pList, newNode); } else { newNode->next = afterNode->next; afterNode->next = newNode; } LeaveCriticalSection(&pList->critical_sec); } Node *Next(List *pList, Node *node) { Node* next; EnterCriticalSection(&pList->critical_sec); next = node->next; LeaveCriticalSection(&pList->critical_sec); return next; }

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• ruby thread programming , ruby equivalent of java wait/notify/notifyAll

  - by Geo

  I would like to know what are ruby's alternatives to the Java methods : wait notify notifyAll Could you please post a small snippet or some links ?

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• Synchronizing DataGridView (DataTable) with the DB

  - by Ezekiel Rage

  Hi! I have the following situation: there is a table in the DB that is queried when the form loads and the retrieved data is filled into a DataGridView via the DataTable underneath. After the data is loaded the user is free to modify the data (add / delete rows, modify entries). The form has 2 buttons: Apply and Refresh. The first one sends the changes to the database, the second one re-reads the data from the DB and erases any changes that have been made by the user. My question is: is this the best way to keep a DataGridView synchronized with the DB (from a users point of view)? For now these are the downsides: the user must keep track of what he is doing and must press the button every while the modifications are lost if the form is closed / app crash / ... I tried sending the changes to the DB on CellEndEdit event but then the user also needs some Undo/Redo functionality and that is ... well ... a different story. So, any suggestions?

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• How do I make my ArrayList Thread-Safe? Another approach to problem in Java?

  - by thechiman

  I have an ArrayList that I want to use to hold RaceCar objects that extend the Thread class as soon as they are finished executing. A class, called Race, handles this ArrayList using a callback method that the RaceCar object calls when it is finished executing. The callback method, addFinisher(RaceCar finisher), adds the RaceCar object to the ArrayList. This is supposed to give the order in which the Threads finish executing. I know that ArrayList isn't synchronized and thus isn't thread-safe. I tried using the Collections.synchronizedCollection(c Collection) method by passing in a new ArrayList and assigning the returned Collection to an ArrayList. However, this gives me a compiler error: Race.java:41: incompatible types found : java.util.Collection required: java.util.ArrayList finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); Here is the relevant code: public class Race implements RaceListener { private Thread[] racers; private ArrayList finishingOrder; //Make an ArrayList to hold RaceCar objects to determine winners finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racers[i] = new RaceCar(laps, inputs[i]); //Add this as a RaceListener to each RaceCar ((RaceCar) racers[i]).addRaceListener(this); } //Implement the one method in the RaceListener interface public void addFinisher(RaceCar finisher) { finishingOrder.add(finisher); } What I need to know is, am I using a correct approach and if not, what should I use to make my code thread-safe? Thanks for the help!

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