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• "You have already activated" message even when using bundle exec

  - by juanpastas

  I am installing gems in my Gemfile in shared path as Capistrano does by default, and when I run: bundle exec rake assets:precompile RAILS_ENV=production I get: You have already activated rake 0.9.2.2, but your Gemfile requires rake 10.0.4. Using bundle exec may solve this. See that: cat Gemfile.lock | grep rake returns: rake (>= 0.8.7) rake (10.0.4) This is my gem environment output: - RUBYGEMS VERSION: 1.8.24 - RUBY VERSION: 1.9.3 (2013-06-27 patchlevel 448) [x86_64-linux] - INSTALLATION DIRECTORY: /home/bitnami/my_app/shared/bundle/ruby/1.9.1/ - RUBY EXECUTABLE: /opt/bitnami/ruby/bin/ruby - EXECUTABLE DIRECTORY: /home/bitnami/my_app/shared/bundle/ruby/1.9.1/bin - RUBYGEMS PLATFORMS: - ruby - x86_64-linux - GEM PATHS: - /home/bitnami/my_app/shared/bundle/ruby/1.9.1/ - GEM CONFIGURATION: - :update_sources => true - :verbose => true - :benchmark => false - :backtrace => false - :bulk_threshold => 1000 - "gemhome" => "/home/bitnami/my_app/shared/bundle/ruby/1.9.1/" - "gempath" => ["/home/bitnami/my_app/shared/bundle/ruby/1.9.1/"] - REMOTE SOURCES: - http://rubygems.org/ Update which -a rake /opt/bitnami/rvm/bin/rake /opt/bitnami/ruby/bin/rake Update 2 I tried giving full path to rake, but same problem

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• How to create platform independent 3D video on 3D TV via HDMI 1.4?

  - by artif

  I am writing a real-time, interactive 3D visualization program and at each point in the program, I can compute 2 images (bitmaps) that are meant to look 3D together by means of stereoscopy. How do I get my program to display the image pairs such that they look 3D on a 3D TV? Is there a platform independent way of accomplishing it? (By platform I mean independent of GPU brand, operating system, 3D TV vendor, etc.) If not, which is preferable-- to lock in by GPU, OS, or 3D TV? I suppose I need to be using an HDMI 1.4 cable with the 3D TV? HDMI 1.4 can encode stereoscopy via side-by-side method. But how do I send such an encoded signal to the monitor? What kind of libraries do I use for this sort of thing? Windows DirectShow? If DirectShow is correct, is there a cross platform equivalent available? If anyone asks, yes I have seen this question: http://stackoverflow.com/questions/2811350/generating-3d-tv-stereoscopic-output-programmatically. However, correct me if I am wrong, it does not appear to be what I'm looking for. I do not have an OpenGL or Direct3D program that generates polygons, for which a Nvidia card can do ad-hoc impromptu stereoscopy simply by rendering the scene from 2 slightly offset points of view and then displaying those 2 images on the monitor-- my program already has those image pairs and needs to display them (and they are not the result of rendering polygons). Btw, I have never done any major multimedia programming before and know very little about HDMI, Direct Show, 3D TVs, etc so pardon me if any parts of this question did not make any sense at all.

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• Correct way to generate order numbers in SQL Server

  - by Anton Gogolev

  This question certainly applies to a much broader scope, but here it is. I have a basic ecommerce app, where users can, naturally enough, place orders. Said orders need to have a unique number, which I'm trying to generate right now. Each order is Vendor-specific. Basically, I have an OrderNumberInfo (VendorID, OrderNumber) table. Now whenever a customer places an order I need to increment OrderNumber for a particuar Vendor and return that value. Naturally, I don't want other processes to interfere with me, so I need to exclusively lock this row somehow: begin tranaction declare @n int select @n = OrderNumber from OrderNumberInfo where VendorID = @vendorID update OrderNumberInfo set OrderNumber = @n + 1 where OrderNumber = @n and VendorID = @vendorID commit transaction Now, I've read about select ... with (updlock rowlock), pessimistic locking, etc., but just cannot fit all this in a coherent picture: How do these hints play with SQL Server 2008s' snapshot isolation? Do they perform row-level, page-level or even table-level locks? How does this tolerate multiple users trying to generate numbers for a single Vendor? What isolation levels are appropriate here? And generally - what is the way to do such things?

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• Creating a blocking Queue<T> in .NET?

  - by spoon16

  I have a scenario where I have multiple threads adding to a queue and multiple threads reading from the same queue. If the queue reaches a specific size all threads that are filling the queue will be blocked on add until an item is removed from the queue. The solution below is what I am using right now and my question is: How can this be improved? Is there an object that already enables this behavior in the BCL that I should be using? internal class BlockingCollection<T> : CollectionBase, IEnumerable { //todo: might be worth changing this into a proper QUEUE private AutoResetEvent _FullEvent = new AutoResetEvent(false); internal T this[int i] { get { return (T) List[i]; } } private int _MaxSize; internal int MaxSize { get { return _MaxSize; } set { _MaxSize = value; checkSize(); } } internal BlockingCollection(int maxSize) { MaxSize = maxSize; } internal void Add(T item) { Trace.WriteLine(string.Format("BlockingCollection add waiting: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.WaitOne(); List.Add(item); Trace.WriteLine(string.Format("BlockingCollection item added: {0}", Thread.CurrentThread.ManagedThreadId)); checkSize(); } internal void Remove(T item) { lock (List) { List.Remove(item); } Trace.WriteLine(string.Format("BlockingCollection item removed: {0}", Thread.CurrentThread.ManagedThreadId)); } protected override void OnRemoveComplete(int index, object value) { checkSize(); base.OnRemoveComplete(index, value); } internal new IEnumerator GetEnumerator() { return List.GetEnumerator(); } private void checkSize() { if (Count < MaxSize) { Trace.WriteLine(string.Format("BlockingCollection FullEvent set: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.Set(); } else { Trace.WriteLine(string.Format("BlockingCollection FullEvent reset: {0}", Thread.CurrentThread.ManagedThreadId)); _FullEvent.Reset(); } } }

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• Multiple WPFPreviewHandlers in One Window? Can it be done?

  - by Scott

  Here is the scenario. I am building a part of my desktop app up and I have a need to create a preview handler. I found plenty of examples on the web of a WPF Preview handler, but I wanted to go one step more than just that. Lets say we have multiple documents and I wished to compare them. So the ideal scenario would be able to see documents side by side in a collection. Sort of how BING does their image search. But the more documents I select in a list box, the more documents I can compare all at once. The second Ideal solution would be a tabbed interface. One tab for each document. Sort of like how internet browsers are doing it now. Understand? So here is the question that I have been struggling with. I can get one preview to work in a window, but can’t get the second one to show up. This is all WPF code so maybe im doing something wrong, but can you preview more than one document in a window at a time? My thought is no, because the previewhandler needs a window handler to lock onto. I would love small code sample since COM and handlers aren’t my sort of thing, but I can manage if you are just able to point me down the right track. Here is the code I found for the WPF Handler. http://blogs.microsoft.co.il/blogs/tamir/archive/2008/04/18/using-vista-preview-handlers-in-wpf-application.aspx

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• Raising events and object persistence in Django

  - by Mridang Agarwalla

  Hi, I have a tricky Django problem which didn't occur to me when I was developing it. My Django application allows a user to sign up and store his login credentials for a sites. The Django application basically allows the user to search this other site (by scraping content off it) and returns the result to the user. For each query, it does a couple of queries of the other site. This seemed to work fine but sometimes, the other site slaps me with a CAPTCHA. I've written the code to get the CAPTCHA image and I need to return this to the user so he can type it in but I don't know how. My search request (the query, the username and the password) in my Django application gets passed to a view which in turn calls the backend that does the scraping/search. When a CAPTCHA is detected, I'd like to raise a client side event or something on those lines and display the CAPTCHA to the user and wait for the user's input so that I can resume my search. I would somehow need to persist my backend object between calls. I've tried pickling it but it doesn't work because I get the Can't pickle 'lock' object error. I don't know to implement this though. Any help/ideas? Thanks a ton.

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• What is the right pattern for a async data fetching method in .net async/await

  - by s093294

  Given a class with a method GetData. A few other clients call GetData, and instead of it fetching data each time, i would like to create a pattern where the first call starts the task to get the data, and the rest of the calls wait for the task to complete. private Task<string> _data; private async Task<string> _getdata() { return "my random data from the net"; //get_data_from_net() } public string GetData() { if(_data==null) _data=_getdata(); _data.wait(); //are there not a problem here. cant wait a task that is already completed ? if(_data.status != rantocompletion) _data.wait() is not any better, it might complete between the check and the _data.wait? return _data.Result; } How would i do the pattern correctly? (Solution) private static object _servertime_lock = new object(); private static Task<string> _servertime; private static async Task<string> servertime() { try { var thetvdb = new HttpClient(); thetvdb.Timeout = TimeSpan.FromSeconds(5); // var st = await thetvdb.GetStreamAsync("http://www.thetvdb.com/api/Updates.php?type=none"); var response = await thetvdb.GetAsync("http://www.thetvdb.com/api/Updates.php?type=none"); response.EnsureSuccessStatusCode(); Stream stream = await response.Content.ReadAsStreamAsync(); XDocument xdoc = XDocument.Load(stream); return xdoc.Descendants("Time").First().Value; } catch { return null; } } public static async Task<string> GetServerTime() { lock (_servertime_lock) { if (_servertime == null) _servertime = servertime(); } var time = await _servertime; if (time == null) _servertime = null; return time; }

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• Core Data: Deleting causes 'NSObjectInaccessibleException' from NSOperation with a reference to a deleted object

  - by Bryan Irace

  My application has NSOperation subclasses that fetch and operate on managed objects. My application also periodically purges rows from the database, which can result in the following race condition: An background operation fetches a bunch of objects (from a thread-specific context). It will iterate over these objects and do something with their properties. A bunch of rows are deleted in the main managed object context. The background operation accesses a property on an object that was deleted from the main context. This results in an 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault' Ideally, the objects that are fetched by the NSOperation can be operated on even if one is deleted in the main context. The best way I can think to achieve this is either to: Call [request setReturnsObjectsAsFaults:NO] to ensure that Core Data won't try to fulfill a fault for an object that no longer exists in the main context. The problem here is I may need to access the object's relationships, which (to my understanding) will still be faulted. Iterate through the managed objects up front and copy the properties I will need into separate non-managed objects. The problem here is that (I think) I will need to synchronize/lock this part, in case an object is deleted in the main context before I can finish copying. Am I missing something obvious? It doesn't seem like what I'm trying to accomplish is too out of the ordinary. Thanks for your help.

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• Thread Safety of C# List<T> for readers

  - by ILIA BROUDNO

  I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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• Hibernate 3.5.0 causes extreme performance problems

  - by user303396

  I've recently updated from hibernate 3.3.1.GA to hibernate 3.5.0 and I'm having a lot of performance issues. As a test, I added around 8000 entities to my DB (which in turn cause other entities to be saved). These entities are saved in batches of 20 so that the transactions aren't too large for performance reasons. When using hibernate 3.3.1.GA all 8000 entities get saved in about 3 minutes. When using hibernate 3.5.0 it starts out slower than with hibernate 3.3.1. But it gets slower and slower. At around 4,000 entities, it sometimes takes 5 minutes just to save a batch of 20. If I then go to a mysql console and manually type in an insert statement from the mysql general query log, half of them run perfect in 0.00 seconds. And half of them take a long time (maybe 40 seconds) or timeout with "ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction" from MySQL. Has something changed in hibernate's transaction management in version 3.5.0 that I should be aware of? The ONLY thing I changed to experience these unusable performance issues is replace the following hibernate 3.3.1.GA jar files: com.springsource.org.hibernate-3.3.1.GA.jar, com.springsource.org.hibernate.annotations-3.4.0.GA.jar, com.springsource.org.hibernate.annotations.common-3.3.0.ga.jar, com.springsource.javassist-3.3.0.ga.jar with the new hibernate 3.5.0 release hibernate3.jar and javassist-3.9.0.GA.jar. Thanks.

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• How can I update a record using a correlated subquery?

  - by froadie

  I have a function that accepts one parameter and returns a table/resultset. I want to set a field in a table to the first result of that recordset, passing in one of the table's other fields as the parameter. If that's too complicated in words, the query looks something like this: UPDATE myTable SET myField = (SELECT TOP 1 myFunctionField FROM fn_doSomething(myOtherField) WHERE someCondition = 'something') WHERE someOtherCondition = 'somethingElse' In this example, myField and myOtherField are fields in myTable, and myFunctionField is a field return by fn_doSomething. This seems logical to me, but I'm getting the following strange error: 'myOtherField' is not a recognized OPTIMIZER LOCK HINTS option. Any idea what I'm doing wrong, and how I can accomplish this? *UPDATE: * Based on Anil Soman's answer, I realized that the function is expecting a string parameter and the field being passed is an integer. I'm not sure if this should be a problem as an explicit call to the function using an integer value works - e.g. fn_doSomething(12345) seems to automatically cast the number to an string. However, I tried to do an explicit cast: UPDATE myTable SET myField = (SELECT TOP 1 myFunctionField FROM fn_doSomething(CAST(myOtherField AS varchar(1000))) WHERE someCondition = 'something') WHERE someOtherCondition = 'somethingElse' Now I'm getting the following error: Line 5: Incorrect syntax near '('.

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• "database already closed" is shown using a custom cursor adapter

  - by kiduxa

  I'm using a cursor with a custom adapter that extends SimpleCursorAdapter: public class ListWordAdapter extends SimpleCursorAdapter { private LayoutInflater inflater; private Cursor mCursor; private int mLayout; private String[] from; private int[] to; public ListWordAdapter(Context context, int layout, Cursor c, String[] from, int[] to, int flags) { super(context, layout, c, from, to, flags); this.mCursor = c; this.inflater = LayoutInflater.from(context); this.mLayout = layout; this.from = from; this.to = to; } private static class ViewHolder { //public ImageView img; public TextView name; public TextView type; public TextView translate; } @Override public View getView(int position, View convertView, ViewGroup parent) { if (mCursor.moveToPosition(position)) { ViewHolder holder; if (convertView == null) { convertView = inflater.inflate(mLayout, null); holder = new ViewHolder(); // holder.img = (ImageView) convertView.findViewById(R.id.img_row); holder.name = (TextView) convertView.findViewById(to[0]); holder.type = (TextView) convertView.findViewById(to[1]); holder.translate = (TextView) convertView.findViewById(to[2]); convertView.setTag(holder); } else { holder = (ViewHolder) convertView.getTag(); } holder.name.setText(mCursor.getString(mCursor.getColumnIndex(from[0]))); holder.type.setText(mCursor.getString(mCursor.getColumnIndex(from[1]))); holder.translate.setText(mCursor.getString(mCursor.getColumnIndex(from[2]))); // holder.img.setImageResource(img_resource); } return convertView; } } And in the main activity I call it as: adapter = new ListWordAdapter(getSherlockActivity(), R.layout.row_list_words, mCursorWords, from, to, 0); When a modification in the list is made, I call this method: public void onWordSaved() { WordDAO wordsDao = new WordSqliteDAO(); Cursor mCursorWords = wordsDao.list(getSherlockActivity()); adapter.changeCursor(mCursorWords); } The thing here is that this produces me this exception: 10-29 11:14:33.810: E/AndroidRuntime(18659): java.lang.IllegalStateException: database /data/data/com.example.palabrasdeldia/databases/palabrasDelDia (conn# 0) already closed Complete stack trace: 10-29 11:14:33.810: E/AndroidRuntime(18659): FATAL EXCEPTION: main 10-29 11:14:33.810: E/AndroidRuntime(18659): java.lang.IllegalStateException: database /data/data/com.example.palabrasdeldia/databases/palabrasDelDia (conn# 0) already closed 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteDatabase.verifyDbIsOpen(SQLiteDatabase.java:2123) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteDatabase.lock(SQLiteDatabase.java:398) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteDatabase.lock(SQLiteDatabase.java:390) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:74) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:311) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.sqlite.SQLiteCursor.onMove(SQLiteCursor.java:283) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.database.AbstractCursor.moveToPosition(AbstractCursor.java:173) 10-29 11:14:33.810: E/AndroidRuntime(18659): at com.example.palabrasdeldia.adapters.ListWordAdapter.getView(ListWordAdapter.java:42) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.AbsListView.obtainView(AbsListView.java:2128) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.ListView.makeAndAddView(ListView.java:1817) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.ListView.fillSpecific(ListView.java:1361) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.ListView.layoutChildren(ListView.java:1646) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.AbsListView.onLayout(AbsListView.java:1979) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1542) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1527) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.onLayout(LinearLayout.java:1316) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.FrameLayout.onLayout(FrameLayout.java:400) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1589) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.FrameLayout.onLayout(FrameLayout.java:400) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1542) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1403) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.onLayout(LinearLayout.java:1314) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.FrameLayout.onLayout(FrameLayout.java:400) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1542) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1403) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.LinearLayout.onLayout(LinearLayout.java:1314) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.FrameLayout.onLayout(FrameLayout.java:400) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.widget.FrameLayout.onLayout(FrameLayout.java:400) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.View.layout(View.java:9593) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewGroup.layout(ViewGroup.java:3877) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewRoot.performTraversals(ViewRoot.java:1253) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.view.ViewRoot.handleMessage(ViewRoot.java:2017) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.os.Handler.dispatchMessage(Handler.java:99) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.os.Looper.loop(Looper.java:132) 10-29 11:14:33.810: E/AndroidRuntime(18659): at android.app.ActivityThread.main(ActivityThread.java:4028) 10-29 11:14:33.810: E/AndroidRuntime(18659): at java.lang.reflect.Method.invokeNative(Native Method) 10-29 11:14:33.810: E/AndroidRuntime(18659): at java.lang.reflect.Method.invoke(Method.java:491) 10-29 11:14:33.810: E/AndroidRuntime(18659): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:844) 10-29 11:14:33.810: E/AndroidRuntime(18659): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602) 10-29 11:14:33.810: E/AndroidRuntime(18659): at dalvik.system.NativeStart.main(Native Method) If I use SimpleCursorAdapter directly instead of ListWordAdapter, it works fine. What's wrong with my custom adapter implementation? The line in bold in the stack trace corresponds with: if (mCursor.moveToPosition(position)) inside getView method. EDIT: I have created a custom class to manage DB operations as open and close: public class ConexionBD { private Context context; private SQLiteDatabase database; private DataBaseHelper dbHelper; public ConexionBD(Context context) { this.context = context; } public ConexionBD open() throws SQLException { this.dbHelper = DataBaseHelper.getInstance(context); this.database = dbHelper.getWritableDatabase(); database.execSQL("PRAGMA foreign_keys=ON"); return this; } public void close() { if (database.isOpen() && database != null) { dbHelper.close(); } } /*Getters y setters*/ public SQLiteDatabase getDatabase() { return database; } public void setDatabase(SQLiteDatabase database) { this.database = database; } } And this is my DataBaseHelper: public class DataBaseHelper extends SQLiteOpenHelper { private static final String DATABASE_NAME = "myDb"; private static final int DATABASE_VERSION = 1; private static DataBaseHelper sInstance = null; public static DataBaseHelper getInstance(Context context) { // Use the application context, which will ensure that you // don't accidentally leak an Activity's context. // See this article for more information: http://bit.ly/6LRzfx if (sInstance == null) { sInstance = new DataBaseHelper(context.getApplicationContext()); } return sInstance; } @Override public void onCreate(SQLiteDatabase database) { ... } .... And this is an example of how I manage a query: public Cursor list(Context context) { ConexionBD conexion = new ConexionBD(context); Cursor mCursor = null; try{ conexion.open(); mCursor = conexion.getDatabase().query(DataBaseHelper.TABLE_WORD , null , null, null, null, null, Word.NAME); if (mCursor != null) { mCursor.moveToFirst(); } }finally{ conexion.close(); } return mCursor; } For every connection to the DB I open it and close it.

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• NHibernate correct way to reattach cached entity to different session

  - by Chris Marisic

  I'm using NHibernate to query a list of objects from my database. After I get the list of objects over them I iterate over the list of objects and apply a distance approximation algorithm to find the nearest object. I consider this function of getting the list of objects and apply the algorithm over them to be a heavy operation so I cache the object which I find from the algorithm in HttpRuntime.Cache. After this point whenever I'm given the supplied input again I can just directly pull the object from Cache instead of having to hit the database and traverse the list. My object is a complex object that has collections attached to it, inside the query where I return the full list of objects I don't bring back any of the sub collections eagerly so when I read my cached object I need lazy loading to work correctly to be able to display the object fully. Originally I tried using this to re-associate my cached object back to a new session _session.Lock(obj, LockMode.None); However when accessing the page concurrently from another instance I get the error Illegal attempt to associate a collection with two open sessions I then tried something different with _session.Merge(obj); However watching the output of this in NHProf shows that it is deleting and re-associating my object's contained collections with my object, which is not what I want although it seems to work fine. What is the correct way to do this? Neither of these seem to be right.

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• Does cout need to be terminated with a semicolon ?

  - by Philippe Harewood

  I am reading Bjarne Stroustrup's Programming : Principles and Practice Using C++ In the drill section for Chapter 2 it talks about various ways to look at typing errors when compiling the hello_world program #include "std_lib_facilities.h" int main() //C++ programs start by executing the function main { cout << "Hello, World!\n", // output "Hello, World!" keep_window_open(); // wait for a character to be entered return 0; } In particular this section asks: Think of at least five more errors you might have made typing in your program (e.g. forget keep_window_open(), leave the Caps Lock key on while typing a word, or type a comma instead of a semicolon) and try each to see what happens when you try to compile and run those versions. For the cout line, you can see that there is a comma instead of a semicolon. This compiles and runs (for me). Is it making an assumption ( like in the javascript question: Why use semicolon? ) that the statement has been terminated ? Because when I try for keep_terminal_open(); the compiler informs me of the semicolon exclusion.

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• Create new or update existing entity at one go with JPA

  - by Alex R

  A have a JPA entity that has timestamp field and is distinguished by a complex identifier field. What I need is to update timestamp in an entity that has already been stored, otherwise create and store new entity with the current timestamp. As it turns out the task is not as simple as it seems from the first sight. The problem is that in concurrent environment I get nasty "Unique index or primary key violation" exception. Here's my code: // Load existing entity, if any. Entity e = entityManager.find(Entity.class, id); if (e == null) { // Could not find entity with the specified id in the database, so create new one. e = entityManager.merge(new Entity(id)); } // Set current time... e.setTimestamp(new Date()); // ...and finally save entity. entityManager.flush(); Please note that in this example entity identifier is not generated on insert, it is known in advance. When two or more of threads run this block of code in parallel, they may simultaneously get null from entityManager.find(Entity.class, id) method call, so they will attempt to save two or more entities at the same time, with the same identifier resulting in error. I think that there are few solutions to the problem. Sure I could synchronize this code block with a global lock to prevent concurrent access to the database, but would it be the most efficient way? Some databases support very handy MERGE statement that updates existing or creates new row if none exists. But I doubt that OpenJPA (JPA implementation of my choice) supports it. Event if JPA does not support SQL MERGE, I can always fall back to plain old JDBC and do whatever I want with the database. But I don't want to leave comfortable API and mess with hairy JDBC+SQL combination. There is a magic trick to fix it using standard JPA API only, but I don't know it yet. Please help.

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• sqlite3 'database is locked' won't go away with retries

  - by Azarias

  I have a sqlite3 database that is accessed by a few threads (3-4). I am aware of the general limitations of sqlite3 with regards to concurrency as stated http://www.sqlite.org/faq.html#q6 , but I am convinced that is not the problem. All of the threads both read and write from this database. Whenever I do a write, I have the following construct: try: Cursor.execute(q, params) Connection.commit() except sqlite3.IntegrityError: Notify except sqlite3.OperationalError: print sys.exc_info() print("DATABASE LOCKED; sleeping for 3 seconds and trying again") time.sleep(3) Retry On some runs, I won't even hit this block, but when I do, it never comes out of it (keeps retrying, but I keep getting the 'database is locked' error from exc_info. If I understand the reader/writer lock usage correctly, some amount of waiting should help with the contention. What this sounds like is deadlock, but I do not use any transactions in my code, and every SELECT or INSERT is simply a one off. Some threads, however, keep the same connection when they do their operation (which includes a mix of SELECTS and INSERTS and other modifiers). I would appericiate it if you could shade a light on this, and also ways around fixing it (besides using a different database engine.)

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• Coupling an MFC CListCtrl and CTreeCtrl to get a view of the whole tree, not just one node at a time

  - by omatai

  Consider Windows Explorer (or regedit or similar). To the left side, there is a tree view, and to the right, a list view. In all cases I know of, the contents of the right view reflect the attributes of the selected node from the left pane. This is all well and good... but just not what I want. The nodes of the tree I want to display have a very few attributes (2-3) associated with each node - a reasonable amount to display horizontally as a row in a table. Rather than waste all that list view space on a single node with very few properties, I would like to have my list view display a table of the whole tree's properties (as the part of the tree currently expanded). So the nth line in the left view (tree) will correspond directly to the nth line in the right view (list/table), and I will get a decent overview of the properties of my tree. Does anyone know of code that does this? I am guessing that slaving a CListCtrl to a CTreeCtrl would be the way to go, and somehow overriding the vertical scrolling functions so that they are locked together. I'm just not sure that it is possible to lock the scrolls together like this... among other things! All advice gratefully welcomed :-)

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• How would you code an efficient Circular Buffer in Java or C#

  - by Cheeso

  I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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• SQL Server log backups "stalling"

  - by MattK

  I have interited a box running SQL Server 2008 and Windows 2003, and have had a few events where largeish (35GB) log backups "stall", both before and after the installation of SQL 2008 SP1. The server log ships to a standby, so regular log backups are taken at 15 minute intervals. However, after an index reorg causes the log to grow to about 35GB (on a DB with about 17GB of data), the next log backup runs to ~95% completion, then seems to stop. The process shows as suspended, with a wait state of BACKUPIO. CPU, read, and write activity on the SPID also does not change, and the process stays in this state for hours, when normally a backup of this size should complete in about 20 minutes. This server has a single RAID-1 volume, thus the source database files and destination backup files are on the same volume. However, I cannot determine if another process is blocking the backup. The backup SPID cannot be killed, and the only way to terminate the log backup and clear the lock on the backup file is to cycle the SQL Server service. There was one event where the backup terminated completely, with an error that another process had locked the backup file, but no details about what that process was. Can anyone suggest a cause or diagnostic process to this situation?

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• How to avoid user keep trying login using Ruby on Rails?

  - by Tattat

  I want to create a login page, it can easy implement using Ruby on Rails. But the login is very simple, but I want more security. I want to stop the user keep trying the password. So, I have some ideas on that. First, stop login feature if the user keep trying the password for 15 mins. After the user login fail 5 times in 15 mins, the system should not allow the user login again in next 15 mins, ever his/her password is correct. Second, I want to add a human verification, after the user tried 5 times. After the user wait for 15 mins to login, I want to add an addition verification to the user. I want the user click the password, and the CAPTCHA image. If one of them is failed, they still can't login the system. He/She have 5 times to try, if he / she failed again, he/she need to want another 15 mins. Third, After the user tried 15 times, and still can't get into the system. I want to lock the user account, the user will receive an email, with a link to assign the password again. So, the question is "Is there any library to implement such authorization easily?" I know it can be implemented using code, but using library is much convenient. Also, I want to ask is there any security suggestion for that? thank u.

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• Problem in Application_Error in Global.asax

  - by mmtemporary

  my problem is User.Identity.Name or Request.Url.AbsoluteUri in exception handling is empty when exception email to me. this is Application_Code: void Application_Error(object sender, EventArgs e) { Server.Transfer("~/errors/default.aspx"); } and this is default.aspx code: protected void Page_Load(object sender, EventArgs e) { if (Server.GetLastError() == null) return; Exception ex = Server.GetLastError().GetBaseException(); if (ex == null) return; string message = string.Format("User: ", User.Identity.Name); message += Environment.NewLine; message += string.Format("AbsoluteUri: ", Request.Url.AbsoluteUri); message += Environment.NewLine; message += string.Format("Form: ", Request.Form.ToString()); message += Environment.NewLine; message += string.Format("QueryString: ", Request.QueryString.ToString()); message += Environment.NewLine; HttpBrowserCapabilities browser = Request.Browser; string s = "Browser Capabilities:\n" + "Type = " + browser.Type + "\n" + "Name = " + browser.Browser + "\n" + "Version = " + browser.Version + "\n" + "Platform = " + browser.Platform + "\n" + "Is Crawler = " + browser.Crawler + "\n" + "Supports Cookies = " + browser.Cookies + "\n" + "Supports JavaScript = " + browser.EcmaScriptVersion.ToString() + "\n" + "\n"; message += s; message += Environment.NewLine; message += ex.ToString(); Exception lastException = (Exception)Application["LastException"]; if (lastException == null || lastException.Message != ex.Message) { Application.Lock(); Application["LastException"] = ex; Application.UnLock(); SiteHelper.SendEmail(SiteHelper.AdministratorEMail, "Error!!!", message, false); } Server.ClearError(); } but i receive email like this (this is header without full exception content): User: AbsoluteUri: Form: QueryString: Browser Capabilities: Type = IE8 Name = IE Version = 8.0 Platform = WinXP Is Crawler = False Supports Cookies = True Supports JavaScript = 1.2 why username and request url is emty? this problem is exist when i replace transfer with redirect or i don't use both. tanx

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• JSF: Showing/Calling a dialog programatically

  - by Sway

  has anybody an idea to show/call a dialog programatically and add this to stage(actual browser window) ?! I am running in circles and cannot find a solution :/ More background what I want to do: I want to trigger a database update every 2 hours. This I have done with a TimerTask... This works fine for me, the Timertask gets all the data I want from the database... Before this TimerTask is triggered I want to "lock" the screen for some seconds that no user(session scoped) can access the database(this I also know how this will work) ... My problem is that I don't know/ cannot find a way/ i am to stupid to call a dialog programatically ... Any tips, hints would be very cool :) Thanks a lot ! UPDATE: I want to set this primefaces dialog: Dialog dialog = new Dialog(); dialog.setAppendToBody(true); dialog.setModal(true); dialog.setVisible(true); dialog.setWidgetVar("generatedDialog"); dialog.setId("fancyDialog"); dialog.setClosable(false); dialog.setHeader("Getting latest information from the database"); dialog.setDynamic(true); dialog.setResizable(false); dialog.setDraggable(false); How can I do that ? :/ How do I display it to my browser ? :o Regards

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• Testing approach for multi-threaded software

  - by Shane MacLaughlin

  I have a piece of mature geospatial software that has recently had areas rewritten to take better advantage of the multiple processors available in modern PCs. Specifically, display, GUI, spatial searching, and main processing have all been hived off to seperate threads. The software has a pretty sizeable GUI automation suite for functional regression, and another smaller one for performance regression. While all automated tests are passing, I'm not convinced that they provide nearly enough coverage in terms of finding bugs relating race conditions, deadlocks, and other nasties associated with multi-threading. What techniques would you use to see if such bugs exist? What techniques would you advocate for rooting them out, assuming there are some in there to root out? What I'm doing so far is running the GUI functional automation on the app running under a debugger, such that I can break out of deadlocks and catch crashes, and plan to make a bounds checker build and repeat the tests against that version. I've also carried out a static analysis of the source via PC-Lint with the hope of locating potential dead locks, but not had any worthwhile results. The application is C++, MFC, mulitple document/view, with a number of threads per doc. The locking mechanism I'm using is based on an object that includes a pointer to a CMutex, which is locked in the ctor and freed in the dtor. I use local variables of this object to lock various bits of code as required, and my mutex has a time out that fires my a warning if the timeout is reached. I avoid locking where possible, using resource copies where possible instead. What other tests would you carry out?

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• Iterating through Event Log Entry Collection, IndexOutOutOfBoundsException

  - by fjdumont

  Hello, in a service application I am iterating through the Windows application event log to parse Events in order react depanding on the entry message. In the case that the event log is full (Windows usually makes sure there is enough space by deleting old entries - this is configurable in the eventvwr.exe settings), the service always runs into an IndexOutOfBoundsException while iterating through the EventLog.Entries collection. No matter how I iterate (for-loop, using the collections enumerator, copying the collection into an array, ...), I can't seem to get rid of this ´bug´. Currently, I ensure that the log is not full in order to keep the service running by regularly deleting the last few item by parsing the event log file and deleting the last few nodes (Don't beat me up, I couldn't find a better alternative...). How can I iterate through the collection without trying to access already deleted entries? Is there probably a more elegant method? I am only trying to acces the logs written during the last x seconds (even LINQ failed to select those when the log is full - same exception), could this help? Thanks for any advice and hints Frank Edit: I forgot to mention that my assumption is the loops are accessing entries which are being deleted during iteration by Windows. Basically that is why I tried to clone the collection. Is there perhaps a way to lock the collection for a small amount of time for just my application?

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