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• Thread Synchronisation 101

  - by taspeotis

  Previously I've written some very simple multithreaded code, and I've always been aware that at any time there could be a context switch right in the middle of what I'm doing, so I've always guarded access the shared variables through a CCriticalSection class that enters the critical section on construction and leaves it on destruction. I know this is fairly aggressive and I enter and leave critical sections quite frequently and sometimes egregiously (e.g. at the start of a function when I could put the CCriticalSection inside a tighter code block) but my code doesn't crash and it runs fast enough. At work my multithreaded code needs to be a tighter, only locking/synchronising at the lowest level needed. At work I was trying to debug some multithreaded code, and I came across this: EnterCriticalSection(&m_Crit4); m_bSomeVariable = true; LeaveCriticalSection(&m_Crit4); Now, m_bSomeVariable is a Win32 BOOL (not volatile), which as far as I know is defined to be an int, and on x86 reading and writing these values is a single instruction, and since context switches occur on an instruction boundary then there's no need for synchronising this operation with a critical section. I did some more research online to see whether this operation did not need synchronisation, and I came up with two scenarios it did: The CPU implements out of order execution or the second thread is running on a different core and the updated value is not written into RAM for the other core to see; and The int is not 4-byte aligned. I believe number 1 can be solved using the "volatile" keyword. In VS2005 and later the C++ compiler surrounds access to this variable using memory barriers, ensuring that the variable is always completely written/read to the main system memory before using it. Number 2 I cannot verify, I don't know why the byte alignment would make a difference. I don't know the x86 instruction set, but does mov need to be given a 4-byte aligned address? If not do you need to use a combination of instructions? That would introduce the problem. So... QUESTION 1: Does using the "volatile" keyword (implicity using memory barriers and hinting to the compiler not to optimise this code) absolve a programmer from the need to synchronise a 4-byte/8-byte on x86/x64 variable between read/write operations? QUESTION 2: Is there the explicit requirement that the variable be 4-byte/8-byte aligned? I did some more digging into our code and the variables defined in the class: class CExample { private: CRITICAL_SECTION m_Crit1; // Protects variable a CRITICAL_SECTION m_Crit2; // Protects variable b CRITICAL_SECTION m_Crit3; // Protects variable c CRITICAL_SECTION m_Crit4; // Protects variable d // ... }; Now, to me this seems excessive. I thought critical sections synchronised threads between a process, so if you've got one you can enter it and no other thread in that process can execute. There is no need for a critical section for each variable you want to protect, if you're in a critical section then nothing else can interrupt you. I think the only thing that can change the variables from outside a critical section is if the process shares a memory page with another process (can you do that?) and the other process starts to change the values. Mutexes would also help here, named mutexes are shared across processes, or only processes of the same name? QUESTION 3: Is my analysis of critical sections correct, and should this code be rewritten to use mutexes? I have had a look at other synchronisation objects (semaphores and spinlocks), are they better suited here? QUESTION 4: Where are critical sections/mutexes/semaphores/spinlocks best suited? That is, which synchronisation problem should they be applied to. Is there a vast performance penalty for choosing one over the other? And while we're on it, I read that spinlocks should not be used in a single-core multithreaded environment, only a multi-core multithreaded environment. So, QUESTION 5: Is this wrong, or if not, why is it right? Thanks in advance for any responses :)

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• C#: Inheritence, Overriding, and Hiding

  - by Rosarch

  I'm having difficulty with an architectural decision for my C# XNA game. The basic entity in the world, such as a tree, zombie, or the player, is represented as a GameObject. Each GameObject is composed of at least a GameObjectController, GameObjectModel, and GameObjectView. These three are enough for simple entities, like inanimate trees or rocks. However, as I try to keep the functionality as factored out as possible, the inheritance begins to feel unwieldy. Syntactically, I'm not even sure how best to accomplish my goals. Here is the GameObjectController: public class GameObjectController { protected GameObjectModel model; protected GameObjectView view; public GameObjectController(GameObjectManager gameObjectManager) { this.gameObjectManager = gameObjectManager; model = new GameObjectModel(this); view = new GameObjectView(this); } public GameObjectManager GameObjectManager { get { return gameObjectManager; } } public virtual GameObjectView View { get { return view; } } public virtual GameObjectModel Model { get { return model; } } public virtual void Update(long tick) { } } I want to specify that each subclass of GameObjectController will have accessible at least a GameObjectView and GameObjectModel. If subclasses are fine using those classes, but perhaps are overriding for a more sophisticated Update() method, I don't want them to have to duplicate the code to produce those dependencies. So, the GameObjectController constructor sets those objects up. However, some objects do want to override the model and view. This is where the trouble comes in. Some objects need to fight, so they are CombatantGameObjects: public class CombatantGameObject : GameObjectController { protected new readonly CombatantGameModel model; public new virtual CombatantGameModel Model { get { return model; } } protected readonly CombatEngine combatEngine; public CombatantGameObject(GameObjectManager gameObjectManager, CombatEngine combatEngine) : base(gameObjectManager) { model = new CombatantGameModel(this); this.combatEngine = combatEngine; } public override void Update(long tick) { if (model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); } base.Update(tick); } } Still pretty simple. Is my use of new to hide instance variables correct? Note that I'm assigning CombatantObjectController.model here, even though GameObjectController.Model was already set. And, combatants don't need any special view functionality, so they leave GameObjectController.View alone. Then I get down to the PlayerController, at which a bug is found. public class PlayerController : CombatantGameObject { private readonly IInputReader inputReader; private new readonly PlayerModel model; public new PlayerModel Model { get { return model; } } private float lastInventoryIndexAt; private float lastThrowAt; public PlayerController(GameObjectManager gameObjectManager, IInputReader inputReader, CombatEngine combatEngine) : base(gameObjectManager, combatEngine) { this.inputReader = inputReader; model = new PlayerModel(this); Model.Health = Constants.PLAYER_HEALTH; } public override void Update(long tick) { if (Model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); for (int i = 0; i < 10; i++) { Debug.WriteLine("YOU DEAD SON!!!"); } return; } UpdateFromInput(tick); // .... } } The first time that this line is executed, I get a null reference exception: model.Body.ApplyImpulse(movementImpulse, model.Position); model.Position looks at model.Body, which is null. This is a function that initializes GameObjects before they are deployed into the world: public void Initialize(GameObjectController controller, IDictionary<string, string> data, WorldState worldState) { controller.View.read(data); controller.View.createSpriteAnimations(data, _assets); controller.Model.read(data); SetUpPhysics(controller, worldState, controller.Model.BoundingCircleRadius, Single.Parse(data["x"]), Single.Parse(data["y"]), bool.Parse(data["isBullet"])); } Every object is passed as a GameObjectController. Does that mean that if the object is really a PlayerController, controller.Model will refer to the base's GameObjectModel and not the PlayerController's overriden PlayerObjectModel?

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• How can I handle parameterized queries in Drupal?

  - by Anthony Gatlin

  We have a client who is currently using Lotus Notes/Domino as their content management system and web server. For many reasons, we are recommending they sunset their Notes/Domino implementation and transition onto a more modern platform--such as Drupal. The client has several web applications which would be a natural fit for Drupal. However, I am unsure of the best way to implement one of the web applications in Drupal. I am running into a knowledge barrier and wondered if any of you could fill in the gaps. Situation The client has a Lotus Domino application which serves as a front-end for querying a large DB2 data store and returning a result set (generally in table form) to a user via the web. The web application provides access to approximately 100 pre-defined queries--50 of which are public and 50 of which are secured. Most of the queries accept some set of user selected parameters as input. The output of the queries is typically returned to users in a list (table) format. A limited number of result sets allow drill-down through the HTML table into detail records. The query parameters often involve database queries themselves. For example, a single query may pull a list of company divisions into a drop-down. Once a division is selected, second drop-down with the departments from that division is populated--but perhaps only departments which meet some special criteria--such as those having taken a loss within a specific time frame. Most queries have 2-4 parameters with the average probably being 3. The application involves no data entry. None of the back-end data is ever modified by the web application. All access is purely based around querying data and viewing results. The queries change relatively infrequently, and the current system has been in place for approximately 10 years. There may be 10-20 query additions, modifications, or other changes in a given year. The client simply desires to change the presentation platform but absolutely does not want to re-do the 100 database queries. Once the project is implemented, the client wants their staff to take over and manage future changes. The client's staff have no background in Drupal or PHP but are somewhat willing to learn as necessary. How would you transition this into Drupal? My major knowledge void relates to how we would manage the query parameters and access the queries themselves. Here are a few specific questions but feel free to chime in on any issue related to this implementation. Would we have to build 100 forms by hand--with each form containing the parameters for a given query? If so, how would we do this? Approximately how long would it take to build/configure each of these forms? Is there a better way than manually building 100 forms? (I understand using CCK to enter data into custom content types but since we aren't adding any nodes, I am a little stuck as to how this might work.) Would it be possible for the internal staff to learn to create these query parameter forms--even if they are unfamiliar with Drupal today? Would they be required to do any PHP programming? How would we take the query parameters from a form and execute a query against DB2? Would this require a custom module? If so, would it require one module total or one module per query? (Note: There is apparently a DB2 driver available for Drupal. See http://groups.drupal.org/node/5511.) Note: I am not looking for CMS recommendations other than Drupal as Drupal nicely fits all of the client's other requirements, and I hope to help them standardize on a single platform. Any assistance you can provide would be helpful. Thank you in advance for your help!

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• Using AsyncTask to display data in ListView, but onPostExecute not being called

  - by sumisu

  I made a simple AsyncTask class to display data in ListView with the help of this stackoverflow question. But the AsyncTask onPostExecute is not being called. This is my code: public class Start extends SherlockActivity { // JSON Node names private static final String TAG_ID = "id"; private static final String TAG_NAME = "name"; // category JSONArray JSONArray category = null; private ListView lv; @Override public void onCreate(Bundle savedInstanceState) { setTheme(SampleList.THEME); //Used for theme switching in samples super.onCreate(savedInstanceState); setContentView(R.layout.test); new MyAsyncTask().execute("http://...."); // Launching new screen on Selecting Single ListItem lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // getting values from selected ListItem String name = ((TextView) view.findViewById(R.id.name)).getText().toString(); String cost = ((TextView) view.findViewById(R.id.mail)).getText().toString(); // Starting new intent Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); in.putExtra("categoryname", name); System.out.println(cost); in.putExtra("categoryid", cost); startActivity(in); } }); } public class MyAsyncTask extends AsyncTask<String, Void, ArrayList<HashMap<String, String>> > { // Hashmap for ListView ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>(); @Override protected ArrayList<HashMap<String, String>> doInBackground(String... params) { // Creating JSON Parser instance JSONParser jParser = new JSONParser(); // getting JSON string from URL category = jParser.getJSONArrayFromUrl(params[0]); try { // looping through All Contacts for(int i = 0; i < category.length(); i++){ JSONObject c = category.getJSONObject(i); // Storing each json item in variable String id = c.getString(TAG_ID); String name = c.getString(TAG_NAME); // creating new HashMap HashMap<String, String> map = new HashMap<String, String>(); // adding each child node to HashMap key => value map.put(TAG_ID, id); map.put(TAG_NAME, name); // adding HashList to ArrayList contactList.add(map); } } catch (JSONException e) { Log.e("log_tag", "Error parsing data "+e.toString()); } return contactList; } @Override protected void onPostExecute(ArrayList<HashMap<String, String>> result) { ListAdapter adapter = new SimpleAdapter(Start.this, result , R.layout.list_item, new String[] { TAG_NAME, TAG_ID }, new int[] { R.id.name, R.id.mail }); // selecting single ListView item lv = (ListView) findViewById(R.id.ListView); lv.setAdapter(adapter); } } } Eclipse: 11-25 11:40:31.896: E/AndroidRuntime(917): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.essentials/de.main.Start}: java.lang.NullPointerException

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• Why does vbkeyup produce different results than vbkeydown does in this Code.

  - by Joshua Rhoads

  I have a VB6 app. It consists of a flexgrid. I have code to allow the user to press the up or down arrow key to switch rows in the grid. When the down arrow key is pressed the cursor is placed at the end of the text in the next row, but when the Up arrow key is pressed the cursor is placed in the middle of the text of the previous row. Anybody have any explantion for this. Private Sub Command1_Click() With MSFlexGrid1 .Cols = 4 .Rows = 5 .FixedCols = 1 .FixedRows = 1 MSFlexGrid1.TextMatrix(0, 1) = "FROM" MSFlexGrid1.TextMatrix(0, 2) = "THRU" MSFlexGrid1.TextMatrix(0, 3) = "PAGE" MSFlexGrid1.TextMatrix(1, 1) = "Aa" MSFlexGrid1.TextMatrix(1, 2) = "Az" MSFlexGrid1.TextMatrix(1, 3) = "-" MSFlexGrid1.TextMatrix(2, 1) = "Ba" MSFlexGrid1.TextMatrix(2, 2) = "Bz" MSFlexGrid1.TextMatrix(2, 3) = "-" MSFlexGrid1.TextMatrix(3, 1) = "Ca" MSFlexGrid1.TextMatrix(3, 2) = "Cz" MSFlexGrid1.TextMatrix(3, 3) = "-" MSFlexGrid1.TextMatrix(4, 1) = "Da" MSFlexGrid1.TextMatrix(4, 2) = "Dz" MSFlexGrid1.TextMatrix(4, 3) = "-" End With End Sub Private Sub Command2_Click() End End Sub Private Sub Form_Load() Text1.Visible = False End Sub Private Sub MSFlexGrid1_DblClick() FlexGridEdit Asc(" ") Exit Sub End Sub Private Sub FlexGridEdit(KeyAscii As Integer) Text1.Left = MSFlexGrid1.CellLeft + MSFlexGrid1.Left Text1.Top = MSFlexGrid1.CellTop + MSFlexGrid1.Top Text1.Width = MSFlexGrid1.ColWidth(MSFlexGrid1.Col) - 2 * (MSFlexGrid1.ColWidth (MSFlexGrid1.Col) - MSFlexGrid1.CellWidth) Text1.Height = MSFlexGrid1.RowHeight(MSFlexGrid1.Row) - 2 * (MSFlexGrid1.RowHeight(MSFlexGrid1.Row) - MSFlexGrid1.CellHeight) Text1.MaxLength = 2 Text1.Visible = True Text1.SetFocus Select Case KeyAscii Case 0 To Asc(" ") Text1.Text = MSFlexGrid1.Text Text1.SelStart = Len(Text1.Text) Case Else Text1.Text = Chr$(KeyAscii) Text1.SelStart = 1 End Select Exit Sub End Sub Function ValidateFlexGrid1() As Boolean Dim llCntrRow As Integer Dim llCntrCol As Integer Dim max_len As Single Dim new_len As Single Dim liCntr As Integer Dim lsCheck As String With MSFlexGrid1 If Text1.Visible Then .Text = Text1.Text If .Rows = .FixedRows Then ValidateFlexGrid1 = False End If For llCntrCol = .FixedCols To MSFlexGrid1.Cols - 1 For llCntrRow = .FixedRows To MSFlexGrid1.Rows - 1 If .TextMatrix(llCntrRow, llCntrCol) = "" Then ValidateFlexGrid1 = False Exit Function End If Next llCntrRow Next llCntrCol End With ValidateFlexGrid1 = True Exit Function End Function Private Sub Text1_Keydown(KeyCode As Integer, Shift As Integer) Select Case KeyCode Case vbKeyRight, vbKeyLeft, vbKeyReturn If Text1.Visible = True Then If Text1.Text = "/" Then If MSFlexGrid1.Row > 1 Then Text1.Text = MSFlexGrid1.TextMatrix(MSFlexGrid1.Row - 1, MSFlexGrid1.Col) Text1.SelStart = Len(Text1.Text) End If End If MSFlexGrid1.Text = Text1.Text If KeyCode = vbKeyRight Or KeyCode = vbKeyReturn Then If Text1.SelStart = Len(Text1.Text) Then FlexGridChkPos KeyCode FlexGridEdit Asc(" ") End If Else If Text1.SelStart = 0 Then FlexGridChkPos KeyCode FlexGridEdit Asc(" ") End If End If End If Case vbKeyDown, vbKeyUp If Text1.Visible = True Then MSFlexGrid1.Text = Text1.Text FlexGridChkPos KeyCode FlexGridEdit Asc(" ") End If End Select Exit Sub End Sub Function FlexGridChkPos(KeyCode As Integer) As Boolean Dim llNextRow As Long Dim llNextCol As Long Dim llCurrCol As Long Dim llCurrRow As Long Dim llTotCols As Long Dim llTotRows As Long Dim llBegRow As Long Dim llBegCol As Long Dim llCntrCol As Long Dim lsText As String With MSFlexGrid1 llCurrRow = .Row + 1 llCurrCol = .Col + 1 llTotRows = .Rows llTotCols = .Cols llBegRow = .FixedRows llBegCol = .FixedCols If KeyCode = vbKeyRight Or KeyCode = vbKeyReturn Then llNextCol = llCurrCol + 1 If llNextCol > llTotCols Then llNextRow = llCurrRow + 1 If llNextRow > llTotRows Then .Rows = .Rows + 1 llCurrRow = llCurrRow + 1 llCurrCol = 1 + llBegCol Else llCurrRow = llNextRow llCurrCol = 1 + llBegCol End If Else llCurrCol = llNextCol End If End If If KeyCode = vbKeyLeft Then llNextCol = llCurrCol - 1 If llNextCol = llBegCol Then llNextRow = llCurrRow - 1 If llNextRow = llBegRow Then llCurrRow = llTotRows Else llCurrRow = llNextRow End If llCurrCol = llTotCols Else llCurrCol = llNextCol End If End If If KeyCode = vbKeyUp Then llNextRow = llCurrRow - 1 If llNextRow = llBegRow Then llCurrRow = llTotRows Else llCurrRow = llNextRow End If End If If KeyCode = vbKeyDown Then llNextRow = llCurrRow + 1 If llNextRow > llTotRows Then llCurrRow = llBegRow + 1 Else llCurrRow = llNextRow End If End If .Col = llCurrCol - 1 .Row = llCurrRow - 1 End With Exit Function End Function

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• reuse div container to load images

  - by user295927

  Hi All; What I would like to do: use a single container to load images. As it is now: I have eleven (11) containers in HTML mark-up each with its own div. each container holds 4 images (2 images side by side top and bottom) when link in anchor tag is clicked div with images fades in. /*-- Jquery accordion is used for navigation typical example is below --*/ <li> <a class="head" href="#">commercial/hospitality</a> <ul> <li><a href="#" projectName="project1" projectType="hospitality1" image1="images/testImage1.jpg" image2="images/testImage2.jpg" image3="images/testImage3.jpg" image4="images/testImage4.jpg">hospitality project number 1</a> </li> <li><a href="#" projectName="project2" projectType="hospitality2" image1="images/testImage1.jpg" image2="images/testImage2.jpg" image3="images/testImage3.jpg" image4="images/testImage4.jpg">hospitality project number 2</a> </li> <li><a href="#" projectName="project3" projectType="hospitality3" image1="images/testImage1.jpg" image2="images/testImage2.jpg" image3="images/testImage3.jpg" image4="images/testImage4.jpg">hospitality project number 3</a> </li> </ul> </li> Typical <div> container used for image insertion currently there are 11 of them: <div id="hospitality1" class="current"> <div id="image1"><img src="images/testImage.jpg"/></div> <div id="image2"><img src="images/testImage.jpg"/></div> <div id="image3"><img src="images/testImage.jpg"/></div> <div id="image4"><img src="images/testImage.jpg"/></div> </div> Here is the code I am using at this point, it does work, but is there a better way to do this that will only re-use a single div container for loading the images? $(document).ready(function(){ $('#navigation a').click(function (selected) { var projectType = $(this).attr("projectType"); //projectType var projectName = $(this).attr("projectName"); //projectName var image1 = $(this).attr("image1"); //anchor tag for image number 1 var image2 = $(this).attr("image2"); //anchor tag for image number 2 var image3 = $(this).attr("image3"); //anchor tag for image number 3 var image4 = $(this).attr("image4"); //anchor tag for image number 4 console.log(projectType); //returns type of project console.log(projectName); //returns name of project console.log(image1); //returns 1st image console.log(image2); //returns 2nd image console.log(image3); //returns 3rd image console.log(image4); //returns 4th image $(function() { $(".current").hide(); // hides previous selected image $("#" + projectType ).fadeIn("normal").addClass("current"); }); }); As you can, see the mark up getting quite large. Any help is appreciated. ussteele

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• Dynamic model choice field in django formset using multiple select elements

  - by Aryeh Leib Taurog

  I posted this question on the django-users list, but haven't had a reply there yet. I have models that look something like this: class ProductGroup(models.Model): name = models.CharField(max_length=10, primary_key=True) def __unicode__(self): return self.name class ProductRun(models.Model): date = models.DateField(primary_key=True) def __unicode__(self): return self.date.isoformat() class CatalogItem(models.Model): cid = models.CharField(max_length=25, primary_key=True) group = models.ForeignKey(ProductGroup) run = models.ForeignKey(ProductRun) pnumber = models.IntegerField() def __unicode__(self): return self.cid class Meta: unique_together = ('group', 'run', 'pnumber') class Transaction(models.Model): timestamp = models.DateTimeField() user = models.ForeignKey(User) item = models.ForeignKey(CatalogItem) quantity = models.IntegerField() price = models.FloatField() Let's say there are about 10 ProductGroups and 10-20 relevant ProductRuns at any given time. Each group has 20-200 distinct product numbers (pnumber), so there are at least a few thousand CatalogItems. I am working on formsets for the Transaction model. Instead of a single select menu with the several thousand CatalogItems for the ForeignKey field, I want to substitute three drop-down menus, for group, run, and pnumber, which uniquely identify the CatalogItem. I'd also like to limit the choices in the second two drop-downs to those runs and pnumbers which are available for the currently selected product group (I can update them via AJAX if the user changes the product group, but it's important that the initial page load as described without relying on AJAX). What's the best way to do this? As a point of departure, here's what I've tried/considered so far: My first approach was to exclude the item foreign key field from the form, add the substitute dropdowns by overriding the add_fields method of the formset, and then extract the data and populate the fields manually on the model instances before saving them. It's straightforward and pretty simple, but it's not very reusable and I don't think it is the right way to do this. My second approach was to create a new field which inherits both MultiValueField and ModelChoiceField, and a corresponding MultiWidget subclass. This seems like the right approach. As Malcolm Tredinnick put it in a django-users discussion, "the 'smarts' of a field lie in the Field class." The problem I'm having is when/where to fetch the lists of choices from the db. The code I have now does it in the Field's __init__, but that means I have to know which ProductGroup I'm dealing with before I can even define the Form class, since I have to instantiate the Field when I define the form. So I have a factory function which I call at the last minute from my view--after I know what CatalogItems I have and which product group they're in--to create form/formset classes and instantiate them. It works, but I wonder if there's a better way. After all, the field should be able to determine the correct choices much later on, once it knows its current value. Another problem is that my implementation limits the entire formset to transactions relating to (CatalogItems from) a single ProductGroup. A third possibility I'm entertaining is to put it all in the Widget class. Once I have the related model instance, or the cid, or whatever the widget is given, I can get the ProductGroup and construct the drop-downs. This would solve the issues with my second approach, but doesn't seem like the right approach.

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• The maven assembly plugin is not using the finalName for installing with attach=true?

  - by Roland Wiesemann

  I have configured following assembly: <build> <plugins> <plugin> <artifactId>maven-assembly-plugin</artifactId> <version>2.2-beta-5</version> <executions> <execution> <id>${project.name}-test-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> <configuration> <appendAssemblyId>false</appendAssemblyId> <finalName>${project.name}-test</finalName> <filters> <filter>src/assemble/test/distribution.properties</filter> </filters> <descriptors> <descriptor>src/assemble/distribution.xml</descriptor> </descriptors> <attach>true</attach> </configuration> </execution> <execution> <id>${project.name}-prod-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> <configuration> <appendAssemblyId>false</appendAssemblyId> <finalName>${project.name}-prod</finalName> <filters> <filter>src/assemble/prod/distribution.properties</filter> </filters> <descriptors> <descriptor>src/assemble/distribution.xml</descriptor> </descriptors> <attach>true</attach> </configuration> </execution> </executions> </plugin> </plugins> </build> This produced two zip-files: distribution-prod.zip distribution-test.zip My expectation for the property attach=true is, that the two zip-files are installed with the name as given in property finalName. But the result is, only one file is installed (attached) to the artifact. The maven protocol is: distrib-0.1-SNAPSHOT.zip distrib-0.1-SNAPSHOT.zip The plugin is using the artifact-id instead of property finalName! Is this a bug? The last installation is overwriting the first one. What can i do to install this two files with different names? Thanks for your investigation. Roland

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• PHP: How do I loop through every XML file in a directory?

  - by celebritarian

  Hi! I'm building a simple application. It's a user interface to an online order system. Basically, the system is going to work like this: Other companies upload their purchase orders to our FTP server. These orders are simple XML files (containing things like customer data, address information, ordered products and the quantities…) I've built a simple user interface in HTML5, jQuery and CSS — all powered by PHP. PHP reads the content of an order (using the built-in features of SimpleXML) and displays it on the web page. So, it's a web app, supposed to always be running in a browser at the office. The PHP app will display the content of all orders. Every fifteen minutes or so, the app will check for new orders. How do I loop through all XML files in a directory? Right now, my app is able to read the content of a single XML file, and display it in a nice way on the page. My current code looks like this: // pick a random order that I know exists in the Order directory: $xml_file = file_get_contents("Order/6366246.xml",FILE_TEXT); $xml = new SimpleXMLElement($xml_file); // start echo basic order information, like order number: echo $xml->OrderHead->ShopPO; // more information about the order and the customer goes here… echo "<ul>"; // loop through each order line, and echo all quantities and products: foreach ($xml->OrderLines->OrderLine as $orderline) { echo "<tr>\n". "<li>".$orderline->Quantity." st.</li>\n". "<li>".$orderline->SKU."</li>\n"; } echo "</ul>"; // more information about delivery options, address information etc. goes here… So, that's my code. Pretty simple. It only needs to do one thing — print out the content of all order files on the screen — so me and my colleagues can see the order, confirm it and deliver it. That's it. But right now — as you can see — I'm selecting one single order at a time, located in the Order directory. But how do I loop through the entire Order directory, and read aand display the content of each order (like above)? I'm stuck. I don't really know how you get all (xml) files in a directory and then do something with the files (like reading them and echo out the data, like I want to). -- I'd really appreciate some help. I'm not very experienced with PHP/server-side programming, so if you could help me out here I'd be very grateful. Thanks a lot in advance! // Björn (celebritarian at me dot com)

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• Hibernate N+1 from select across multiple tables

  - by Marty Pitt

  Given the following hibernate query: String sql = "select distinct changeset " + "from Changeset changeset " + "join fetch changeset.changeEntries as changeEntry " + "join fetch changeEntry.repositoryEntity as repositoryEntity " + "join fetch repositoryEntity.project as project " + "join fetch changeset.author as changesetAuthor " + "where project.id = :projectID "; Why is this resulting in an N+1 problem? I expect this to generate the following single SQL statement (or something similar) select * from Changeset inner join changeEntry on changeset.id = changeEntry.changeset_id inner join repositoryEntity on changeEntry.repositoryentity_id = repositoryentity.id inner join project on repositoryentity.project_id = project.id where project.id = ? Instead, I see many many select statements firing. The data model here looks like this: I would like the full object graph returned from the Select statement in a single trip to the database, which is why I'm explicitly using "fetch" in the hibernate query. The Hibernate log statements are as follows: Hibernate: select distinct changeset0_.id as id2_0_, changeentr1_.id as id1_1_, repository2_.id as id9_2_, project3_.id as id6_3_, user4_.id as id7_4_, changeset0_.author_id as author5_2_0_, changeset0_.createDate as createDate2_0_, changeset0_.message as message2_0_, changeset0_.revision as revision2_0_, changeentr1_.changeType as changeType1_1_, changeentr1_.changeset_id as changeset4_1_1_, changeentr1_.diff as diff1_1_, changeentr1_.repositoryEntity_id as reposito5_1_1_, changeentr1_.repositoryEntityVersion_id as reposito6_1_1_, changeentr1_.sourceChangeEntry_id as sourceCh7_1_1_, changeentr1_.changeset_id as changeset4_0__, changeentr1_.id as id0__, repository2_.project_id as connecti6_9_2_, repository2_.name as name9_2_, repository2_.parent_id as parent7_9_2_, repository2_.path as path9_2_, repository2_.state as state9_2_, repository2_.type as type9_2_, project3_.projectName as connecti2_6_3_, project3_.driverName as driverName6_3_, project3_.isAnonymous as isAnonym4_6_3_, project3_.lastUpdatedRevision as lastUpda5_6_3_, project3_.password as password6_3_, project3_.url as url6_3_, project3_.username as username6_3_, user4_.username as username7_4_, user4_.email as email7_4_, user4_.name as name7_4_, user4_.password as password7_4_, user4_.principles as principles7_4_, user4_.userType as userType7_4_ from Changeset changeset0_ inner join ChangeEntry changeentr1_ on changeset0_.id=changeentr1_.changeset_id inner join RepositoryEntity repository2_ on changeentr1_.repositoryEntity_id=repository2_.id inner join project project3_ on repository2_.project_id=project3_.id inner join users user4_ on changeset0_.author_id=user4_.id where project3_.id=? order by changeset0_.revision desc Hibernate: select repository0_.id as id10_9_, repository0_.changeEntry_id as changeEn2_10_9_, repository0_.repositoryEntity_id as reposito3_10_9_, changeentr1_.id as id1_0_, changeentr1_.changeType as changeType1_0_, changeentr1_.changeset_id as changeset4_1_0_, changeentr1_.diff as diff1_0_, changeentr1_.repositoryEntity_id as reposito5_1_0_, changeentr1_.repositoryEntityVersion_id as reposito6_1_0_, changeentr1_.sourceChangeEntry_id as sourceCh7_1_0_, changeset2_.id as id2_1_, changeset2_.author_id as author5_2_1_, changeset2_.createDate as createDate2_1_, changeset2_.message as message2_1_, changeset2_.revision as revision2_1_, user3_.id as id7_2_, user3_.username as username7_2_, user3_.email as email7_2_, user3_.name as name7_2_, user3_.password as password7_2_, user3_.principles as principles7_2_, user3_.userType as userType7_2_, repository4_.id as id9_3_, repository4_.project_id as connecti6_9_3_, repository4_.name as name9_3_, repository4_.parent_id as parent7_9_3_, repository4_.path as path9_3_, repository4_.state as state9_3_, repository4_.type as type9_3_, project5_.id as id6_4_, project5_.projectName as connecti2_6_4_, project5_.driverName as driverName6_4_, project5_.isAnonymous as isAnonym4_6_4_, project5_.lastUpdatedRevision as lastUpda5_6_4_, project5_.password as password6_4_, project5_.url as url6_4_, project5_.username as username6_4_, repository6_.id as id9_5_, repository6_.project_id as connecti6_9_5_, repository6_.name as name9_5_, repository6_.parent_id as parent7_9_5_, repository6_.path as path9_5_, repository6_.state as state9_5_, repository6_.type as type9_5_, repository7_.id as id10_6_, repository7_.changeEntry_id as changeEn2_10_6_, repository7_.repositoryEntity_id as reposito3_10_6_, repository8_.id as id9_7_, repository8_.project_id as connecti6_9_7_, repository8_.name as name9_7_, repository8_.parent_id as parent7_9_7_, repository8_.path as path9_7_, repository8_.state as state9_7_, repository8_.type as type9_7_, changeentr9_.id as id1_8_, changeentr9_.changeType as changeType1_8_, changeentr9_.changeset_id as changeset4_1_8_, changeentr9_.diff as diff1_8_, changeentr9_.repositoryEntity_id as reposito5_1_8_, changeentr9_.repositoryEntityVersion_id as reposito6_1_8_, changeentr9_.sourceChangeEntry_id as sourceCh7_1_8_ from RepositoryEntityVersion repository0_ left outer join ChangeEntry changeentr1_ on repository0_.changeEntry_id=changeentr1_.id left outer join Changeset changeset2_ on changeentr1_.changeset_id=changeset2_.id left outer join users user3_ on changeset2_.author_id=user3_.id left outer join RepositoryEntity repository4_ on changeentr1_.repositoryEntity_id=repository4_.id left outer join project project5_ on repository4_.project_id=project5_.id left outer join RepositoryEntity repository6_ on repository4_.parent_id=repository6_.id left outer join RepositoryEntityVersion repository7_ on changeentr1_.repositoryEntityVersion_id=repository7_.id left outer join RepositoryEntity repository8_ on repository7_.repositoryEntity_id=repository8_.id left outer join ChangeEntry changeentr9_ on changeentr1_.sourceChangeEntry_id=changeentr9_.id where repository0_.id=? The 2nd one is repeated many times - for a result set of 17 objects, the 2nd statement executed 521 times. I suspect this is as a result of the parent/child relationship in the RepositoryEntity object. For the purposes of this select, I actually only require the parent object fetched. Any suggestions?

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• Hardware/Software inventory open source projects

  - by Dick dastardly

  Dear Stackoverflowers I would like to develop a Network Inventory application that works on any operating system. Reports on every possible resource attacehd to a network. Reports all pertinent details of hardware and software. Thats (and i hate to use the phrase) my "End Game". However I am running before i can crawl here. I have no experience of this type of development, e.g. discovering a computers hardware and software settings. I've spent almost two weeks googling and come up short! :-(. So I am turning to you to ask these questions:- My first step is to find an existing open source project i can incorporate into my own code that extracts the fine grained details i am after, e.g. EVERYTHING there is to know about the hardaware and software on a single machine. Does this project exist? or do i have to develop that first? Have i got to write all this in C? I am guessing getting this information about a computer is going to be easier than for printers, scanners, routers etc... e.g. everything else you would find attached to a network. Once i have access to a single computers details i then need to investigate how i can traverse an entire newtork of printers, scanners, routers, load balancers, switches, firewalls, workstations, servers, storeage devices, laptops, monitors, the list goes on and on One problem i have is i dont have a 1000 machine newtork to play on! Is there any such resource available on theinternet? (is that a silly question?) Anywho, if you dont ask you wont find out! One aspect iam really looking forward to finding out how to travers the entire network, should i be using TCP/IP for this? Whats a good site, blog, usergorup, book for TCP/IP development? How do i go about getting through firewalls? How many questions can i ask in one go? :-) My previous question on this topic ended up with PYTHON being championed as the language/script to go with to develop this application in. Having looked at a few PYTHON examples they all seemed to be related to WINDOWS networks and interrogating Windows Management Instrumentation (WMI). I had the feeling you cant rely on whats in WMI, and even if you can that s no good for UNIX netwrks. Surely there exist common code for extracting hardware and software details from a computer? Why cant i find it on the internet? Pease help? Theres no prizes though :-( Thanks in advance I would like to appologise if i have broken forum rules or not tried hard enough on my own before asking for assistance. I just would like to start moving forward with this as its one of the best projects i have been involved with. I am inspired by the many differnt number of challenges involved and that if i manage to produce a useful application at the end of it it would hopefully be extremely helpful to many people. That sit Thanks in advance DD

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• Dropdown dependent values to be fetch from multiple models using ajax in Yii

  - by newuser

  I searched all the documentation over Yii but not got the answer of it.So I came here finally. I have the following schema Table Schools +------------------+--------------+------+-----+---------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+--------------+------+-----+---------------------+----------------+ | id | int(10) | NO | PRI | NULL | auto_increment | | school_name | varchar(100) | NO | | | | +------------------+--------------+------+-----+---------------------+----------------+ Table Students +------------------+--------------+------+-----+---------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+--------------+------+-----+---------------------+----------------+ | id | int(10) | NO | PRI | NULL | auto_increment | | school_id | int(10) | NO | FK | | | | student_name | varchar(100) | NO | | | | | roll_no | varchar(80) | NO | | | | | class | varchar(20) | NO | | | | | | subjects | varchar(100) | NO | | | | +------------------+--------------+------+-----+---------------------+----------------+ I have made models and CRUD for the both models.In models my relation is like this In Students.php the relation is like public function relations() { // NOTE: you may need to adjust the relation name and the related // class name for the relations automatically generated below. return array( 'School' => array(self::BELONGS_TO,'Schools','school_id'), ); } In Schools.php the relation is like public function relations() { // NOTE: you may need to adjust the relation name and the related // class name for the relations automatically generated below. return array( 'student' => array(self::HAS_MANY, 'Students', 'school_id'), ); } Now I made the two models rendered in a single page so that I can enter all the respective fields in a single form. In the _form.php file of Students I have made some change in student_name like this <div class="row"> <?php echo $form->labelEx($model,'student_name'); ?> <?php echo $form->dropdownList($model,'student_name', CHtml::listData(Students::model()->findAll(), 'id', 'student_name'), array('empty'=>array('Select'=>'--Select One---'))); ?> <?php echo $form->error($model,'student_name'); ?> Now for this piece of code I got all the student name from the Student model. So my problem is when I am getting the student name from the dropdown list and going to select a student it will also fetch all the respective values of the student to be rendered in the _form.php without click on save button.So that user don't have to put it again manually. I think ajax and json encode will work here but don't know how to make them work here. [Update] Here is StudentsController code public function actionDisCoor() { $model = School::model()->findByPk($_POST['Students']['student_id']); $data=CHtml::listData($data,'id','name'); foreach($data as $value=>$name) { echo CHtml::tag('option',array('value'=>$value),CHtml::encode($name),true); } } Here is _form.php code for Students <div class="row"> <?php echo $form->labelEx($model,'student_name'); ?> <?php $List = CHtml::listData(Students::model()->findAll(), 'id', 'student_name'); ?> <?php echo $form->dropdownList($model,'student_name',$List, array('onChange'=>CHtml::ajax(array( 'url' => CController::createUrl('DisCoor'), 'type' => 'POST', 'update'=>'#school_id', )),'style'=>'width:180px;' ) )?> <?php echo $form->error($model,'student_name'); ?> </div> After all that when I saw in firebug I got the error.Here is the screen shot

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• Connecting Android device to multiple Bluetooth serial embedded peers

  - by TacB0sS

  I'm trying to find a solution for this setup: I have a single Android device, which I would like to connect to multiple serial embedded devices... And here is the thing, using the "Normal" way to retrieve the Bluetooth socket, doesn't work on all devices, and while it does, I can connect to multiple devices, and send and receive data to and from multiple devices. public final synchronized void connect() throws ConnectionException { if (socket != null) throw new IllegalStateException("Error socket is not null!!"); connecting = true; lastException = null; lastPacket = null; lastHeartBeatReceivedAt = 0; log.setLength(0); try { socket = fetchBT_Socket_Normal(); connectToSocket(socket); listenForIncomingSPP_Packets(); connecting = false; return; } catch (Exception e) { socket = null; logError(e); } try { socket = fetchBT_Socket_Workaround(); connectToSocket(socket); listenForIncomingSPP_Packets(); connecting = false; return; } catch (Exception e) { socket = null; logError(e); } connecting = false; if (socket == null) throw new ConnectionException("Error creating RFcomm socket for" + this); } private BluetoothSocket fetchBT_Socket_Normal() throws Exception { /* The getType() is a hex 0xXXXX value agreed between peers --- this is the key (in my case) to multiple connections in the "Normal" way */ String uuid = getType() + "1101-0000-1000-8000-00805F9B34FB"; try { logDebug("Fetching BT RFcomm Socket standard for UUID: " + uuid + "..."); socket = btDevice.createRfcommSocketToServiceRecord(UUID.fromString(uuid)); return socket; } catch (Exception e) { logError(e); throw e; } } private BluetoothSocket fetchBT_Socket_Workaround() throws Exception { Method m; int connectionIndex = 1; try { logDebug("Fetching BT RFcomm Socket workaround index " + connectionIndex + "..."); m = btDevice.getClass().getMethod("createRfcommSocket", new Class[]{int.class}); socket = (BluetoothSocket) m.invoke(btDevice, connectionIndex); return socket; } catch (Exception e1) { logError(e1); throw e1; } } private void connectToSocket(BluetoothSocket socket) throws ConnectionException { try { socket.connect(); } catch (IOException e) { try { socket.close(); } catch (IOException e1) { logError("Error while closing socket", e1); } finally { socket = null; } throw new ConnectionException("Error connecting to socket with" + this, e); } } And here is the thing, while on phones which the "Normal" way doesn't work, the "Workaround" way provides a solution for a single connection. I've searched far and wide, but came up with zip. The problem with the workaround is mentioned in the last link, both connection uses the same port, which in my case, causes a block, where both of the embedded devices can actually send data, that is not been processed on the Android, while both embedded devices can receive data sent from the Android. Did anyone handle this before? There is a bit more reference here, UPDATE: Following this (that I posted earlier) I wanted to give the mPort a chance, and perhaps to see other port indices, and how other devices manage them, and I found out the the fields in the BluetoothSocket object are different while it is the same class FQN in both cases: Detils from an HTC Vivid 2.3.4, uses the "workaround" Technic: The Socket class type is: [android.bluetooth.BluetoothSocket] mSocket BluetoothSocket (id=830008629928) EADDRINUSE 98 EBADFD 77 MAX_RFCOMM_CHANNEL 30 TAG "BluetoothSocket" (id=830002722432) TYPE_L2CAP 3 TYPE_RFCOMM 1 TYPE_SCO 2 mAddress "64:9C:8E:DC:56:9A" (id=830008516328) mAuth true mClosed false mClosing AtomicBoolean (id=830007851600) mDevice BluetoothDevice (id=830007854256) mEncrypt true mInputStream BluetoothInputStream (id=830008688856) mLock ReentrantReadWriteLock (id=830008629992) mOutputStream BluetoothOutputStream (id=830008430536) **mPort 1** mSdp null mSocketData 3923880 mType 1 Detils from an LG-P925 2.2.2, uses the "normal" Technic: The Socket class type is: [android.bluetooth.BluetoothSocket] mSocket BluetoothSocket (id=830105532880) EADDRINUSE 98 EBADFD 77 MAX_RFCOMM_CHANNEL 30 TAG "BluetoothSocket" (id=830002668088) TYPE_L2CAP 3 TYPE_RFCOMM 1 TYPE_SCO 2 mAccepted false mAddress "64:9C:8E:B9:3F:77" (id=830105544600) mAuth true mClosed false mConnected ConditionVariable (id=830105533144) mDevice BluetoothDevice (id=830105349488) mEncrypt true mInputStream BluetoothInputStream (id=830105532952) mLock ReentrantReadWriteLock (id=830105532984) mOutputStream BluetoothOutputStream (id=830105532968) mPortName "" (id=830002606256) mSocketData 0 mSppPort BluetoothSppPort (id=830105533160) mType 1 mUuid ParcelUuid (id=830105714176) Anyone have some insight...

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• Two-way databinding of a custom templated control. Eval works, but not Bind.

  - by Jason

  I hate long code snippets and I'm sorry about this one, but it turns out that this asp.net stuff can't get much shorter and it's so specific that I haven't been able to generalize it without a full code listing. I just want simple two-way, declarative databinding to a single instance of an object. Not a list of objects of a type with a bunch of NotImplementedExceptions for Add, Delete, and Select, but just a single view-state persisted object. This is certainly something that can be done but I've struggled with an implementation for years. This newest, closest implementation was inspired by this article from 4-Guys-From-Rolla, http://msdn.microsoft.com/en-us/library/aa478964.aspx. Unfortunately, after implementing, I'm getting the following error and I don't know what I'm missing: System.InvalidOperationException: Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control. If I don't use Bind(), and only use Eval() functionality, it works. In that way, the error is especially confusing. Here's the simplified codeset that still produces the error: using System.ComponentModel; namespace System.Web.UI.WebControls.Special { public class SampleFormData { public string SampleString = "Sample String Data"; public int SampleInt = -1; } [ToolboxItem(false)] public class SampleSpecificFormDataContainer : WebControl, INamingContainer { SampleSpecificEntryForm entryForm; internal SampleSpecificEntryForm EntryForm { get { return entryForm; } } [Bindable(true), Category("Data")] public string SampleString { get { return entryForm.FormData.SampleString; } set { entryForm.FormData.SampleString = value; } } [Bindable(true), Category("Data")] public int SampleInt { get { return entryForm.FormData.SampleInt; } set { entryForm.FormData.SampleInt = value; } } internal SampleSpecificFormDataContainer(SampleSpecificEntryForm entryForm) { this.entryForm = entryForm; } } public class SampleSpecificEntryForm : WebControl, INamingContainer { #region Template private IBindableTemplate formTemplate = null; [Browsable(false), DefaultValue(null), TemplateContainer(typeof(SampleSpecificFormDataContainer), ComponentModel.BindingDirection.TwoWay), PersistenceMode(PersistenceMode.InnerProperty)] public virtual IBindableTemplate FormTemplate { get { return formTemplate; } set { formTemplate = value; } } #endregion #region Viewstate SampleFormData FormDataVS { get { return (ViewState["FormData"] as SampleFormData) ?? new SampleFormData(); } set { ViewState["FormData"] = value; SaveViewState(); } } #endregion public override ControlCollection Controls { get { EnsureChildControls(); return base.Controls; } } private SampleSpecificFormDataContainer formDataContainer = null; [Browsable(false), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)] public SampleSpecificFormDataContainer FormDataContainer { get { EnsureChildControls(); return formDataContainer; } } [Bindable(true), Browsable(false)] public SampleFormData FormData { get { return FormDataVS; } set { FormDataVS = value; } } protected override void CreateChildControls() { if (!this.ChildControlsCreated) { Controls.Clear(); formDataContainer = new SampleSpecificFormDataContainer(this); Controls.Add(formDataContainer); FormTemplate.InstantiateIn(formDataContainer); this.ChildControlsCreated = true; } } public override void DataBind() { CreateChildControls(); base.DataBind(); } } } With an ASP.NET page the following: <%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeBehind="Default2.aspx.cs" Inherits="EntryFormTest._Default2" EnableEventValidation="false" %> <%@ Register Assembly="EntryForm" Namespace="System.Web.UI.WebControls.Special" TagPrefix="cc1" %> <asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent"> </asp:Content> <asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent"> <h2> Welcome to ASP.NET! </h2> <cc1:SampleSpecificEntryForm ID="EntryForm1" runat="server"> <FormTemplate> <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("SampleString") %>'></asp:TextBox><br /> <h3>(<%# Container.SampleString %>)</h3><br /> <asp:Button ID="Button1" runat="server" Text="Button" /> </FormTemplate> </cc1:SampleSpecificEntryForm> </asp:Content> Default2.aspx.cs using System; namespace EntryFormTest { public partial class _Default2 : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { EntryForm1.DataBind(); } } } Thanks for any help!

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• HttpClient multithread performance

  - by pepper

  I have an application which downloads more than 4500 html pages from 62 target hosts using HttpClient (4.1.3 or 4.2-beta). It runs on Windows 7 64-bit. Processor - Core i7 2600K. Network bandwidth - 54 Mb/s. At this moment it uses such parameters: DefaultHttpClient and PoolingClientConnectionManager; Also it hasIdleConnectionMonitorThread from http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html; Maximum total connections = 80; Default maximum connections per route = 5; For thread management it uses ForkJoinPool with the parallelism level = 5 (Do I understand correctly that it is a number of working threads?) In this case my network usage (in Windows task manager) does not rise above 2.5%. To download 4500 pages it takes 70 minutes. And in HttpClient logs I have such things: DEBUG ForkJoinPool-2-worker-1 [org.apache.http.impl.conn.PoolingClientConnectionManager]: Connection released: [id: 209][route: {}-http://stackoverflow.com][total kept alive: 6; route allocated: 1 of 5; total allocated: 10 of 80] Total allocated connections do not raise above 10-12, in spite of that I've set it up to 80 connections. If I'll try to rise parallelism level to 20 or 80, network usage remains the same but a lot connection time-outs will be generated. I've read tutorials on hc.apache.org (HttpClient Performance Optimization Guide and HttpClient Threading Guide) but they does not help. Task's code looks like this: public class ContentDownloader extends RecursiveAction { private final HttpClient httpClient; private final HttpContext context; private List<Entry> entries; public ContentDownloader(HttpClient httpClient, List<Entry> entries){ this.httpClient = httpClient; context = new BasicHttpContext(); this.entries = entries; } private void computeDirectly(Entry entry){ final HttpGet get = new HttpGet(entry.getLink()); try { HttpResponse response = httpClient.execute(get, context); int statusCode = response.getStatusLine().getStatusCode(); if ( (statusCode >= 400) && (statusCode <= 600) ) { logger.error("Couldn't get content from " + get.getURI().toString() + "\n" + response.toString()); } else { HttpEntity entity = response.getEntity(); if (entity != null) { String htmlContent = EntityUtils.toString(entity).trim(); entry.setHtml(htmlContent); EntityUtils.consumeQuietly(entity); } } } catch (Exception e) { } finally { get.releaseConnection(); } } @Override protected void compute() { if (entries.size() <= 1){ computeDirectly(entries.get(0)); return; } int split = entries.size() / 2; invokeAll(new ContentDownloader(httpClient, entries.subList(0, split)), new ContentDownloader(httpClient, entries.subList(split, entries.size()))); } } And the question is - what is the best practice to use multi threaded HttpClient, may be there is a some rules for setting up ConnectionManager and HttpClient? How can I use all of 80 connections and raise network usage? If necessary, I will provide more code.

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• Break a class in twain, or impose an interface for restricted access?

  - by bedwyr

  What's the best way of partitioning a class when its functionality needs to be externally accessed in different ways by different classes? Hopefully the following example will make the question clear :) I have a Java class which accesses a single location in a directory allowing external classes to perform read/write operations to it. Read operations return usage stats on the directory (e.g. available disk space, number of writes, etc.); write operations, obviously, allow external classes to write data to the disk. These methods always work on the same location, and receive their configuration (e.g. which directory to use, min disk space, etc.) from an external source (passed to the constructor). This class looks something like this: public class DiskHandler { public DiskHandler(String dir, int minSpace) { ... } public void writeToDisk(String contents, String filename) { int space = getAvailableSpace(); ... } public void getAvailableSpace() { ... } } There's quite a bit more going on, but this will do to suffice. This class needs to be accessed differently by two external classes. One class needs access to the read operations; the other needs access to both read and write operations. public class DiskWriter { DiskHandler diskHandler; public DiskWriter() { diskHandler = new DiskHandler(...); } public void doSomething() { diskHandler.writeToDisk(...); } } public class DiskReader { DiskHandler diskHandler; public DiskReader() { diskHandler = new DiskHandler(...); } public void doSomething() { int space = diskHandler.getAvailableSpace(...); } } At this point, both classes share the same class, but the class which should only read has access to the write methods. Solution 1 I could break this class into two. One class would handle read operations, and the other would handle writes: // NEW "UTILITY" CLASSES public class WriterUtil { private ReaderUtil diskReader; public WriterUtil(String dir, int minSpace) { ... diskReader = new ReaderUtil(dir, minSpace); } public void writeToDisk(String contents, String filename) { int = diskReader.getAvailableSpace(); ... } } public class ReaderUtil { public ReaderUtil(String dir, int minSpace) { ... } public void getAvailableSpace() { ... } } // MODIFIED EXTERNALLY-ACCESSING CLASSES public class DiskWriter { WriterUtil diskWriter; public DiskWriter() { diskWriter = new WriterUtil(...); } public void doSomething() { diskWriter.writeToDisk(...); } } public class DiskReader { ReaderUtil diskReader; public DiskReader() { diskReader = new ReaderUtil(...); } public void doSomething() { int space = diskReader.getAvailableSpace(...); } } This solution prevents classes from having access to methods they should not, but it also breaks encapsulation. The original DiskHandler class was completely self-contained and only needed config parameters via a single constructor. By breaking apart the functionality into read/write classes, they both are concerned with the directory and both need to be instantiated with their respective values. In essence, I don't really care to duplicate the concerns. Solution 2 I could implement an interface which only provisions read operations, and use this when a class only needs access to those methods. The interface might look something like this: public interface Readable { int getAvailableSpace(); } The Reader class would instantiate the object like this: Readable diskReader; public DiskReader() { diskReader = new DiskHandler(...); } This solution seems brittle, and prone to confusion in the future. It doesn't guarantee developers will use the correct interface in the future. Any changes to the implementation of the DiskHandler could also need to update the interface as well as the accessing classes. I like it better than the previous solution, but not by much. Frankly, neither of these solutions seems perfect, but I'm not sure if one should be preferred over the other. I really don't want to break the original class up, but I also don't know if the interface buys me much in the long run. Are there other solutions I'm missing?

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• How to design a C / C++ library to be usable in many client languages?

  - by Brian Schimmel

  I'm planning to code a library that should be usable by a large number of people in on a wide spectrum of platforms. What do I have to consider to design it right? To make this questions more specific, there are four "subquestions" at the end. Choice of language Considering all the known requirements and details, I concluded that a library written in C or C++ was the way to go. I think the primary usage of my library will be in programs written in C, C++ and Java SE, but I can also think of reasons to use it from Java ME, PHP, .NET, Objective C, Python, Ruby, bash scrips, etc... Maybe I cannot target all of them, but if it's possible, I'll do it. Requirements It would be to much to describe the full purpose of my library here, but there are some aspects that might be important to this question: The library itself will start out small, but definitely will grow to enormous complexity, so it is not an option to maintain several versions in parallel. Most of the complexity will be hidden inside the library, though The library will construct an object graph that is used heavily inside. Some clients of the library will only be interested in specific attributes of specific objects, while other clients must traverse the object graph in some way Clients may change the objects, and the library must be notified thereof The library may change the objects, and the client must be notified thereof, if it already has a handle to that object The library must be multi-threaded, because it will maintain network connections to several other hosts While some requests to the library may be handled synchronously, many of them will take too long and must be processed in the background, and notify the client on success (or failure) Of course, answers are welcome no matter if they address my specific requirements, or if they answer the question in a general way that matters to a wider audience! My assumptions, so far So here are some of my assumptions and conclusions, which I gathered in the past months: Internally I can use whatever I want, e.g. C++ with operator overloading, multiple inheritance, template meta programming... as long as there is a portable compiler which handles it (think of gcc / g++) But my interface has to be a clean C interface that does not involve name mangling Also, I think my interface should only consist of functions, with basic/primitive data types (and maybe pointers) passed as parameters and return values If I use pointers, I think I should only use them to pass them back to the library, not to operate directly on the referenced memory For usage in a C++ application, I might also offer an object oriented interface (Which is also prone to name mangling, so the App must either use the same compiler, or include the library in source form) Is this also true for usage in C# ? For usage in Java SE / Java EE, the Java native interface (JNI) applies. I have some basic knowledge about it, but I should definitely double check it. Not all client languages handle multithreading well, so there should be a single thread talking to the client For usage on Java ME, there is no such thing as JNI, but I might go with Nested VM For usage in Bash scripts, there must be an executable with a command line interface For the other client languages, I have no idea For most client languages, it would be nice to have kind of an adapter interface written in that language. I think there are tools to automatically generate this for Java and some others For object oriented languages, it might be possible to create an object oriented adapter which hides the fact that the interface to the library is function based - but I don't know if its worth the effort Possible subquestions is this possible with manageable effort, or is it just too much portability? are there any good books / websites about this kind of design criteria? are any of my assumptions wrong? which open source libraries are worth studying to learn from their design / interface / souce? meta: This question is rather long, do you see any way to split it into several smaller ones? (If you reply to this, do it as a comment, not as an answer)

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• How to find minimum weight with maximum cost in 0-1 Knapsack algorithm?

  - by Nitin9791

  I am trying to solve a spoj problem Party Schedule the problem statement is- You just received another bill which you cannot pay because you lack the money. Unfortunately, this is not the first time to happen, and now you decide to investigate the cause of your constant monetary shortness. The reason is quite obvious: the lion's share of your money routinely disappears at the entrance of party localities. You make up your mind to solve the problem where it arises, namely at the parties themselves. You introduce a limit for your party budget and try to have the most possible fun with regard to this limit. You inquire beforehand about the entrance fee to each party and estimate how much fun you might have there. The list is readily compiled, but how do you actually pick the parties that give you the most fun and do not exceed your budget? Write a program which finds this optimal set of parties that offer the most fun. Keep in mind that your budget need not necessarily be reached exactly. Achieve the highest possible fun level, and do not spend more money than is absolutely necessary. Input The first line of the input specifies your party budget and the number n of parties. The following n lines contain two numbers each. The first number indicates the entrance fee of each party. Parties cost between 5 and 25 francs. The second number indicates the amount of fun of each party, given as an integer number ranging from 0 to 10. The budget will not exceed 500 and there will be at most 100 parties. All numbers are separated by a single space. There are many test cases. Input ends with 0 0. Output For each test case your program must output the sum of the entrance fees and the sum of all fun values of an optimal solution. Both numbers must be separated by a single space. Example Sample input: 50 10 12 3 15 8 16 9 16 6 10 2 21 9 18 4 12 4 17 8 18 9 50 10 13 8 19 10 16 8 12 9 10 2 12 8 13 5 15 5 11 7 16 2 0 0 Sample output: 49 26 48 32 now I know that it is an advance version of 0/1 knapsack problem where along with maximum cost we also have to find minimum weight that is less than a a given weight and have maximum cost. so I have used dp to solve this problem but still get a wrong awnser on submission while it is perfectly fine with given test cases. My code is typedef vector<int> vi; #define pb push_back #define FOR(i,n) for(int i=0;i<n;i++) int main() { //freopen("input.txt","r",stdin); while(1) { int W,n; cin>>W>>n; if(W==0 && n==0) break; int K[n+1][W+1]; vi val,wt; FOR(i,n) { int x,y; cin>>x>>y; wt.pb(x); val.pb(y); } FOR(i,n+1) { FOR(w,W+1) { if(i==0 || w==0) { K[i][w]=0; } else if (wt[i-1] <= w) { if(val[i-1] + K[i-1][w-wt[i-1]]>=K[i-1][w]) { K[i][w]=val[i-1] + K[i-1][w-wt[i-1]]; } else { K[i][w]=K[i-1][w]; } } else { K[i][w] = K[i-1][w]; } } } int a1=K[n][W],a2; for(int j=0;j<W;j++) { if(K[n][j]==a1) { a2=j; break; } } cout<<a2<<" "<<a1<<"\n"; } return 0; } Could anyone suggest what am I missing??

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• Advanced Regex: Smart auto detect and replace URLs with anchor tags

  - by Robert Koritnik

  I've written a regular expression that automatically detects URLs in free text that users enter. This is not such a simple task as it may seem at first. Jeff Atwood writes about it in his post. His regular expression works, but needs extra code after detection is done. I've managed to write a regular expression that does everything in a single go. This is how it looks like (I've broken it down into separate lines to make it more understandable what it does): 1 (?<outer>\()? 2 (?<scheme>http(?<secure>s)?://)? 3 (?<url> 4 (?(scheme) 5 (?:www\.)? 6 | 7 www\. 8 ) 9 [a-z0-9] 10 (?(outer) 11 [-a-z0-9/+&@#/%?=~_()|!:,.;cšžcd]+(?=\)) 12 | 13 [-a-z0-9/+&@#/%?=~_()|!:,.;cšžcd]+ 14 ) 15 ) 16 (?<ending>(?(outer)\))) As you may see, I'm using named capture groups (used later in Regex.Replace()) and I've also included some local characters (cšžcd), that allow our localised URLs to be parsed as well. You can easily omit them if you'd like. Anyway. Here's what it does (referring to line numbers): 1 - detects if URL starts with open braces (is contained inside braces) and stores it in "outer" named capture group 2 - checks if it starts with URL scheme also detecting whether scheme is SSL or not 3 - start parsing URL itself (will store it in "url" named capture group) 4-8 - if statement that says: if "sheme" was present then www. part is optional, otherwise mandatory for a string to be a link (so this regular expression detects all strings that start with either http or www) 9 - first character after http:// or www. should be either a letter or a number (this can be extended if you'd like to cover even more links, but I've decided not to because I can't think of a link that would start with some obscure character) 10-14 - if statement that says: if "outer" (braces) was present capture everything up to the last closing braces otherwise capture all 15 - closes the named capture group for URL 16 - if open braces were present, capture closing braces as well and store it in "ending" named capture group First and last line used to have \s* in them as well, so user could also write open braces and put a space inside before pasting link. Anyway. My code that does link replacement with actual anchor HTML elements looks exactly like this: value = Regex.Replace( value, @"(?<outer>\()?(?<scheme>http(?<secure>s)?://)?(?<url>(?(scheme)(?:www\.)?|www\.)[a-z0-9](?(outer)[-a-z0-9/+&@#/%?=~_()|!:,.;cšžcd]+(?=\))|[-a-z0-9/+&@#/%?=~_()|!:,.;cšžcd]+))(?<ending>(?(outer)\)))", "${outer}<a href=\"http${secure}://${url}\">http${secure}://${url}</a>${ending}", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase); As you can see I'm using named capture groups to replace link with an Anchor tag: "${outer}<a href=\"http${secure}://${url}\">http${secure}://${url}</a>${ending}" I could as well omit the http(s) part in anchor display to make links look friendlier, but for now I decided not to. Question I would like my links to be replaced with shortenings as well. So when user copies a very long link (for instance if they would copy a link from google maps that usually generates long links) I would like to shorten the visible part of the anchor tag. Link would work, but visible part of an anchor tag would be shortened to some number of characters. I could as well append ellipsis at the end of at all possible (and make things even more perfect). Does Regex.Replace() method support replacement notations so that I can still use a single call? Something similar as string.Format() method does when you'd like to format values in string format (decimals, dates etc...).

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• FMOD surround sound openframeworks

  - by user1449425

  Ok, I hope I don't mess this up, I have had a look for some answers but can't find anything. I am trying to make a simple sampler in openframeworks using the FMOD sound player in 3D mode. I can make a single instance work fine (recording a new file using libsndfilerecorder and then playing it back and moving it in surround. However I want to have 8 layers of looping audio that I can record and replace one layer at a time in a live show. I get a lot of problems as soon as I have more than 1 layer. The first part of my question relates to the FMOD 3D modes, it is listener relative, so I have to define the position of my listener for every sound (I would prefer to have head relative mode but I cannot make this work at all. Again this works fine when I am using a single player but with multiple players only the last listener I update actually works. The main problem I have is that when I use multiple players I get distortion, and often a mix of other currently playing sounds (even when the microphone cannot hear them) in my new recordings. Is there an incompatability with libsndfilerecorder and FMOD? Here I initialise the players for (int i=0; i<CHANNEL_COUNT; i++) { lvelocity[i].set(1, 1, 1); lup[i].set(0, 1, 0); lforward[i].set(0, 0, 1); lposition[i].set(0, 0, 0); sposition[i].set(3, 3, 2); svelocity[i].set(1, 1, 1); //player[1].initializeFmod(); //player[i].loadSound( "1.wav" ); player[i].setVolume(0.75); player[i].setMultiPlay(true); player[i].play(); setupHold[i]==false; recording[i]=false; channelHasFile[i]=false; settingOsc[i]=false; } When I am recording I unload the file and make sure the positions of the player that is not loaded are not updating. void fmodApp::recordingStart( int recordingId ){ if (recording[recordingId]==false) { setupHold[recordingId]=true; //this stops the position updating cout<<"Start recording Channel " + ofToString(recordingId+1)+" setup hold is true \n"; pt=getDateName() +".wav"; player[recordingId].stop(); player[recordingId].unloadSound(); audioRecorder.setup(pt); audioRecorder.setFormat(SF_FORMAT_WAV | SF_FORMAT_PCM_16); recording[recordingId]=true; //this starts the libSndFIleRecorder } else { cout<<"Channel" + ofToString(recordingId+1)+" is already recording \n"; } } And I stop the recording like this. void fmodApp::recordingEnd( int recordingId ){ if (recording[recordingId]=true) { recording[recordingId]=false; cout<<"Stop recording" + ofToString(recordingId+1)+" \n"; audioRecorder.finalize(); audioRecorder.close(); player[recordingId].loadSound(pt); setupHold[recordingId]=false; channelHasFile[recordingId]=true; cout<< "File recorded channel " + ofToString(recordingId+1) + " file is called " + pt + "\n"; } else { cout << "Sorry track" + ofToString(recordingId+1) + "is not recording"; } } I am careful not to interrupt the updating process but I cannot see where I am going wrong. Many Thanks

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• NetworkOnMainThread exception occuring

  - by Akshat

  I got a code from Android Hive to parse JSON data from url. Then I am trying to implement the same code on Rotten Tomatoes Upcoming Movies Api. I have implemented the same code with almost modifying all the xml files according to my needs. But the problem is when I am trying to run the code, its showing NetworkOnMainThread Exception. This is my code.. public class Upcoming extends ListActivity { String url = "http://api.rottentomatoes.com/api/public/v1.0/lists/movies/upcoming.json?apikey=yvvgsv722gy2zkey3ebkda5t"; final String TAG_MOVIES = "movies"; final String TAG_ID = "id"; final String TAG_TITLE = "title"; final String TAG_YEAR = "year"; final String TAG_MPAA_RATING = "mpaa_rating"; final String TAG_RUNTIME = "runtime"; final String TAG_RELEASE_DATES = "release_dates"; final String TAG_RATINGS = "ratings"; final String TAG_CRITIC_RATING = "critics_ratings"; final String TAG_AUDIENCE_RATING = "audience_ratings"; final String TAG_SYNOPSIS = "synopsis"; final String TAG_POSTERS = "posters"; JSONArray upcomings = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_upcoming_list); ArrayList<HashMap<String, String>> UpcomingList = new ArrayList<HashMap<String, String>>(); // Creating JSON Parser instance JSONParser jParser = new JSONParser(); // getting JSON string from URL JSONObject json = jParser.getJSONFromUrl(url); try { // Getting Array of Contacts upcomings = json.getJSONArray(TAG_MOVIES); // looping through All Contacts for(int i = 0; i < upcomings.length(); i++){ JSONObject c = upcomings.getJSONObject(i); // Storing each json item in variable String id = c.getString(TAG_ID); String title = c.getString(TAG_TITLE); String year = c.getString(TAG_YEAR); String mpaa_rating = c.getString(TAG_MPAA_RATING); String runtime = c.getString(TAG_RUNTIME); JSONObject release_dates = c.getJSONObject(TAG_RELEASE_DATES); JSONObject ratings = c.getJSONObject(TAG_RATINGS); String critic_rating = c.getString(TAG_CRITIC_RATING); String audience_rating = c.getString(TAG_AUDIENCE_RATING); String synopsis = c.getString(TAG_SYNOPSIS); JSONObject posters = c.getJSONObject(TAG_POSTERS); HashMap<String, String> map = new HashMap<String, String>(); map.put(TAG_TITLE, title); map.put(TAG_YEAR, year); map.put(TAG_CRITIC_RATING, critic_rating); map.put(TAG_AUDIENCE_RATING, audience_rating); UpcomingList.add(map); } } catch (JSONException e) { e.printStackTrace(); } ListAdapter adapter = new SimpleAdapter(this, UpcomingList, R.layout.activity_upcoming, new String[] { TAG_TITLE, TAG_YEAR, TAG_CRITIC_RATING, TAG_AUDIENCE_RATING }, new int[] { R.id.title, R.id.year, R.id.critic_rating, R.id.audience_rating }); setListAdapter(adapter); // selecting single ListView item ListView lv = getListView(); // Launching new screen on Selecting Single ListItem lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // getting values from selected ListItem String name = ((TextView) view.findViewById(R.id.title)).getText().toString(); String cost = ((TextView) view.findViewById(R.id.year)).getText().toString(); String critic_rating = ((TextView) view.findViewById(R.id.critic_rating)).getText().toString(); String audience_rating = ((TextView) view.findViewById(R.id.audience_rating)).getText().toString(); // Starting new intent Intent in = new Intent(getApplicationContext(), Upcoming.class); in.putExtra(TAG_TITLE, name); in.putExtra(TAG_YEAR, cost); in.putExtra(TAG_CRITIC_RATING, critic_rating); in.putExtra(TAG_AUDIENCE_RATING, audience_rating); startActivity(in); } }); } } Can anyone please help me with anything I am missing.? I am totally blind on it now. Thanx in advance.

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• How to convert an ORM to its subclass using Hibernate ?

  - by Gaaston

  Hi everybody, For example, I have two classes : Person and Employee (Employee is a subclass of Person). Person : has a lastname and a firstname. Employee : has also a salary. On the client-side, I have a single HTML form where i can fill the person informations (like lastname and firstname). I also have a "switch" between "Person" and "Employee", and if the switch is on Employee I can fill the salary field. On the server-side, Servlets receive informations from the client and use the Hibernate framework to create/update data to/from the database. The mapping i'm using is a single table for persons and employee, with a discriminator. I don't know how to convert a Person in an Employee. I firstly tried to : load the Person p from the database create an empty Employee e object copy values from p into e set the salary value save e into the database But i couldn't, as I also copy the ID, and so Hibernate told me they where two instanciated ORM with the same id. And I can't cast a Person into an Employee directly, as Person is Employee's superclass. There seems to be a dirty way : delete the person, and create an employee with the same informations, but I don't really like it.. So I'd appreciate any help on that :) Some precisions : The person class : public class Person { protected int id; protected String firstName; protected String lastName; // usual getters and setters } The employee class : public class Employee extends Person { // string for now protected String salary; // usual getters and setters } And in the servlet : // type is the "switch" if(request.getParameter("type").equals("Employee")) { Employee employee = daoPerson.getEmployee(Integer.valueOf(request.getParameter("ID"))); modifyPerson(employee, request); employee.setSalary(request.getParameter("salary")); daoPerson.save(employee ); } else { Person person = daoPerson.getPerson(Integer.valueOf(request.getParameter("ID"))); modifyPerson(employee, request); daoPerson.save(person); } And finally, the loading (in the dao) : public Contact getPerson(int ID){ Session session = HibernateSessionFactory.getSession(); Person p = (Person) session.load(Person.class, new Integer(ID)); return p; } public Contact getEmployee(int ID){ Session session = HibernateSessionFactory.getSession(); Employee = (Employee) session.load(Employee.class, new Integer(ID)); return p; } With this, i'm getting a ClassCastException when trying to load a Person using getEmployee. XML Hibernate mapping : <class name="domain.Person" table="PERSON" discriminator-value="P"> <id name="id" type="int"> <column name="ID" /> <generator class="native" /> </id> <discriminator column="type" type="character"/> <property name="firstName" type="java.lang.String"> <column name="FIRSTNAME" /> </property> <property name="lastName" type="java.lang.String"> <column name="LASTNAME" /> </property> <subclass name="domain.Employee" discriminator-value="E"> <property name="salary" column="SALARY" type="java.lang.String" /> </subclass> </class> Is it clear enough ? :-/

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• What's the best way to refactor this Rails controller?

  - by Robert DiNicolas

  I'd like some advice on how to best refactor this controller. The controller builds a page of zones and modules. Page has_many zones, zone has_many modules. So zones are just a cluster of modules wrapped in a container. The problem I'm having is that some modules may have some specific queries that I don't want executed on every page, so I've had to add conditions. The conditions just test if the module is on the page, if it is the query is executed. One of the problems with this is if I add a hundred special module queries, the controller has to iterate through each one. I think I would like to see these module condition moved out of the controller as well as all the additional custom actions. I can keep everything in this one controller, but I plan to have many apps using this controller so it could get messy. class PagesController < ApplicationController # GET /pages/1 # GET /pages/1.xml # Show is the main page rendering action, page routes are aliased in routes.rb def show #-+-+-+-+-Core Page Queries-+-+-+-+- @page = Page.find(params[:id]) @zones = @page.zones.find(:all, :order => 'zones.list_order ASC') @mods = @page.mods.find(:all) @columns = Page.columns # restful params to influence page rendering, see routes.rb @fragment = params[:fragment] # render single module @cluster = params[:cluster] # render single zone @head = params[:head] # render html, body and head #-+-+-+-+-Page Level Json Conversions-+-+-+-+- @metas = @page.metas ? ActiveSupport::JSON.decode(@page.metas) : nil @javascripts = @page.javascripts ? ActiveSupport::JSON.decode(@page.javascripts) : nil #-+-+-+-+-Module Specific Queries-+-+-+-+- # would like to refactor this process @mods.each do |mod| # Reps Module Custom Queries if mod.name == "reps" @reps = User.find(:all, :joins => :roles, :conditions => { :roles => { :name => 'rep' } }) end # Listing-poc Module Custom Queries if mod.name == "listing-poc" limit = params[:limit].to_i < 1 ? 10 : params[:limit] PropertyEntry.update_from_listing(mod.service_url) @properties = PropertyEntry.all(:limit => limit, :order => "city desc") end # Talents-index Module Custom Queries if mod.name == "talents-index" @talent = params[:type] @reps = User.find(:all, :joins => :talents, :conditions => { :talents => { :name => @talent } }) end end respond_to do |format| format.html # show.html.erb format.xml { render :xml => @page.to_xml( :include => { :zones => { :include => :mods } } ) } format.json { render :json => @page.to_json } format.css # show.css.erb, CSS dependency manager template end end # for property listing ajax request def update_properties limit = params[:limit].to_i < 1 ? 10 : params[:limit] offset = params[:offset] @properties = PropertyEntry.all(:limit => limit, :offset => offset, :order => "city desc") #render :nothing => true end end So imagine a site with a hundred modules and scores of additional controller actions. I think most would agree that it would be much cleaner if I could move that code out and refactor it to behave more like a configuration.

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• Lockless queue implementation ends up having a loop under stress

  - by Fozi

  I have lockless queues written in C in form of a linked list that contains requests from several threads posted to and handled in a single thread. After a few hours of stress I end up having the last request's next pointer pointing to itself, which creates an endless loop and locks up the handling thread. The application runs (and fails) on both Linux and Windows. I'm debugging on Windows, where my COMPARE_EXCHANGE_PTR maps to InterlockedCompareExchangePointer. This is the code that pushes a request to the head of the list, and is called from several threads: void push_request(struct request * volatile * root, struct request * request) { assert(request); do { request->next = *root; } while(COMPARE_EXCHANGE_PTR(root, request, request->next) != request->next); } This is the code that gets a request from the end of the list, and is only called by a single thread that is handling them: struct request * pop_request(struct request * volatile * root) { struct request * volatile * p; struct request * request; do { p = root; while(*p && (*p)->next) p = &(*p)->next; // <- loops here request = *p; } while(COMPARE_EXCHANGE_PTR(p, NULL, request) != request); assert(request->next == NULL); return request; } Note that I'm not using a tail pointer because I wanted to avoid the complication of having to deal with the tail pointer in push_request. However I suspect that the problem might be in the way I find the end of the list. There are several places that push a request into the queue, but they all look generaly like this: // device->requests is defined as struct request * volatile requests; struct request * request = malloc(sizeof(struct request)); if(request) { // fill out request fields push_request(&device->requests, request); sem_post(device->request_sem); } The code that handles the request is doing more than that, but in essence does this in a loop: if(sem_wait_timeout(device->request_sem, timeout) == sem_success) { struct request * request = pop_request(&device->requests); // handle request free(request); } I also just added a function that is checking the list for duplicates before and after each operation, but I'm afraid that this check will change the timing so that I will never encounter the point where it fails. (I'm waiting for it to break as I'm writing this.) When I break the hanging program the handler thread loops in pop_request at the marked position. I have a valid list of one or more requests and the last one's next pointer points to itself. The request queues are usually short, I've never seen more then 10, and only 1 and 3 the two times I could take a look at this failure in the debugger. I thought this through as much as I could and I came to the conclusion that I should never be able to end up with a loop in my list unless I push the same request twice. I'm quite sure that this never happens. I'm also fairly sure (although not completely) that it's not the ABA problem. I know that I might pop more than one request at the same time, but I believe this is irrelevant here, and I've never seen it happening. (I'll fix this as well) I thought long and hard about how I can break my function, but I don't see a way to end up with a loop. So the question is: Can someone see a way how this can break? Can someone prove that this can not? Eventually I will solve this (maybe by using a tail pointer or some other solution - locking would be a problem because the threads that post should not be locked, I do have a RW lock at hand though) but I would like to make sure that changing the list actually solves my problem (as opposed to makes it just less likely because of different timing).

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• algorithm q: Fuzzy matching of structured data

  - by user86432

  I have a fairly small corpus of structured records sitting in a database. Given a tiny fraction of the information contained in a single record, submitted via a web form (so structured in the same way as the table schema), (let us call it the test record) I need to quickly draw up a list of the records that are the most likely matches for the test record, as well as provide a confidence estimate of how closely the search terms match a record. The primary purpose of this search is to discover whether someone is attempting to input a record that is duplicate to one in the corpus. There is a reasonable chance that the test record will be a dupe, and a reasonable chance the test record will not be a dupe. The records are about 12000 bytes wide and the total count of records is about 150,000. There are 110 columns in the table schema and 95% of searches will be on the top 5% most commonly searched columns. The data is stuff like names, addresses, telephone numbers, and other industry specific numbers. In both the corpus and the test record it is entered by hand and is semistructured within an individual field. You might at first blush say "weight the columns by hand and match word tokens within them", but it's not so easy. I thought so too: if I get a telephone number I thought that would indicate a perfect match. The problem is that there isn't a single field in the form whose token frequency does not vary by orders of magnitude. A telephone number might appear 100 times in the corpus or 1 time in the corpus. The same goes for any other field. This makes weighting at the field level impractical. I need a more fine-grained approach to get decent matching. My initial plan was to create a hash of hashes, top level being the fieldname. Then I would select all of the information from the corpus for a given field, attempt to clean up the data contained in it, and tokenize the sanitized data, hashing the tokens at the second level, with the tokens as keys and frequency as value. I would use the frequency count as a weight: the higher the frequency of a token in the reference corpus, the less weight I attach to that token if it is found in the test record. My first question is for the statisticians in the room: how would I use the frequency as a weight? Is there a precise mathematical relationship between n, the number of records, f(t), the frequency with which a token t appeared in the corpus, the probability o that a record is an original and not a duplicate, and the probability p that the test record is really a record x given the test and x contain the same t in the same field? How about the relationship for multiple token matches across multiple fields? Since I sincerely doubt that there is, is there anything that gets me close but is better than a completely arbitrary hack full of magic factors? Barring that, has anyone got a way to do this? I'm especially keen on other suggestions that do not involve maintaining another table in the database, such as a token frequency lookup table :). This is my first post on StackOverflow, thanks in advance for any replies you may see fit to give.

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