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• What are five things you hate about your favorite language?

  - by brian d foy

  There's been a cluster of Perl-hate on Stackoverflow lately, so I thought I'd bring my "Five things you hate about your favorite language" question to StackOverflow. Take your favorite language and tell me five things you hate about it. Those might be things that just annoy you, admitted design flaws, recognized performance problems, or any other category. You just have to hate it, and it has to be your favorite language. Don't compare it to another language, and don't talk about languages that you already hate. Don't talk about the things you like in your favorite language. I just want to hear the things that you hate but tolerate so you can use all of the other stuff, and I want to hear it about the language you wished other people would use. I ask this whenever someone tries to push their favorite language on me, and sometimes as an interview question. If someone can't find five things to hate about his favorite tool, he don't know it well enough to either advocate it or pull in the big dollars using it. He hasn't used it in enough different situations to fully explore it. He's advocating it as a culture or religion, which means that if I don't choose his favorite technology, I'm wrong. I don't care that much which language you use. Don't want to use a particular language? Then don't. You go through due diligence to make an informed choice and still don't use it? Fine. Sometimes the right answer is "You have a strong programming team with good practices and a lot of experience in Bar. Changing to Foo would be stupid." This is a good question for code reviews too. People who really know a codebase will have all sorts of suggestions for it, and those who don't know it so well have non-specific complaints. I ask things like "If you could start over on this project, what would you do differently?" In this fantasy land, users and programmers get to complain about anything and everything they don't like. "I want a better interface", "I want to separate the model from the view", "I'd use this module instead of this other one", "I'd rename this set of methods", or whatever they really don't like about the current situation. That's how I get a handle on how much a particular developer knows about the codebase. It's also a clue about how much of the programmer's ego is tied up in what he's telling me. Hate isn't the only dimension of figuring out how much people know, but I've found it to be a pretty good one. The things that they hate also give me a clue how well they are thinking about the subject.

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• Write binary stream to browser using PHP

  - by Dave Jarvis

  Background Trying to stream a PDF report written using iReport through PHP to the browser. The general problem is: how do you write binary data to the browser using PHP? Working Code The following code does the job, but (for many reasons) it is not as efficient as it should be (the code writes a file then sends the file contents the browser). // Load the MySQL database driver. // java( 'java.lang.Class' )->forName( 'com.mysql.jdbc.Driver' ); // Attempt a database connection. // $conn = java( 'java.sql.DriverManager' )->getConnection( "jdbc:mysql://localhost:3306/climate?user=$user&password=$password" ); // Extract parameters. // $params = new java('java.util.HashMap'); $params->put('DistrictCode', '101'); $params->put('StationCode', '0066'); $params->put('CategoryCode', '010'); // Use the fill manager to produce the report. // $fm = java('net.sf.jasperreports.engine.JasperFillManager'); $pm = $fm->fillReport($report, $params, $conn); header('Cache-Control: no-cache private'); header('Content-Description: File Transfer'); header('Content-Disposition: attachment, filename=climate-report.pdf'); header('Content-Type: application/pdf'); header('Content-Transfer-Encoding: binary'); header('Content-Length: ' . strlen( $result ) ); $path = realpath( "." ) . "/output.pdf"; $em = java('net.sf.jasperreports.engine.JasperExportManager'); $result = $em->exportReportToPdfFile($pm,$path); readfile( $path ); $conn->close(); Non-working Code To remove the slight redundancy (i.e., write directly to the browser), the following code looks like it should work, but it does not: $em = java('net.sf.jasperreports.engine.JasperExportManager'); $result = $em->exportReportToPdf($pm); header('Content-Length: ' . strlen( $result ) ); echo $result; Content is sent to the browser, but the file is corrupt (it begins with the PDF header) and cannot be read by any PDF reader. Question How can I take out the middle step of writing to the file and write directly to the browser so that the PDF is not corrupted? Thank you!

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• Oracle sample data problems

  - by Jay

  So, I have this java based data trasformation / masking tool, which I wanted to test out on Oracle 10g. The good part with Oracle 10g is that you get a load of sample schemas with half a million records in some. The schemas are : SH, OE, HR, IX and etc. So, I installed 10g, found out that the installation scripts are under ORACLE_HOME/demo/scripts. I customized these scripts a bit to run in batch mode. That solves one half of my requirement - to create source data for my testing my data transformation software. The second half of the requirement is that I create the same schemas under different names (TR_HR, TR_OE and so on...) without any data. These schemas would represent my target schemas. So, in short, my software would pick up data from a table in a schema and load it up in to the same table in a different schema. Now, I have two issues in creating my target schema and emptying it. I would like this in a batch job. But the oracle scripts you get, the sample schema names are not configurable. So, I tried creating a script, replacing OE with TR_OE, HR with TR_HR and so on. However, this approach is kind of irritating coz the sample schemas are kind of complicated in the way they are created; Oracle creates synonyms, views, materialized views, data types and lot of weird stuff. I would like the target schemas (TR_HR, TR_OE,...) to be empty. But some of the schemas have circular references, which would not allow me to delete data. The only work around seems to be removing certain foreign keys, deleting data and then adding the constraints back. Is there any easy way to all this, without all this fuss? I would need a complicated data set for my testing (complicated as in tables with triggers, multiple hierarchies.. for instance.. a child table that has children up to 5 levels, a parent table that refers to an IOT table and an IOT table that refers to a non-IOT table etc..). The sample schemas are just about perfect from a data set perspective. The only challenge I see is in automating this whole process of loading up the source schemas, and then creating the target schemas and emptying them. Appreciate your help and suggestions.

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• Cannot populate form with ajax and populate jquery plugin

  - by Azriel_

  I'm trying to populate a form with jquery's populate plugin, but using $.ajax The idea is to retrieve data from my database according to the id in the links (ex of link: get_result_edit.php?id=34), reformulate it to json, return it to my page and fill up the form up with the populate plugin. But somehow i cannot get it to work. Any ideas: here's the code: $('a').click(function(){ $('#updatediv').hide('slow'); $.ajax({ type: "GET", url: "get_result_edit.php", success: function(data) { var $response=$(data); $('#form1').populate($response); } }); $('#updatediv').fadeIn('slow'); return false; whilst the php file states as follow: <?php $conn = new mysqli('localhost', 'XXXX', 'XXXXX', 'XXXXX'); @$query = 'Select * FROM news WHERE id ="'.$_GET['id'].'"'; $stmt = $conn->query($query) or die ($mysql->error()); if ($stmt) { $results = $stmt->fetch_object(); // get database data $json = json_encode($results); // convert to JSON format echo $json; } ?> Now first thing is that the mysql returns a null in this way: is there something wrong with he declaration of the sql statement in the $_GET part? Second is that even if i put a specific record to bring up, populate doesn't populate. Update: I changed the populate library with the one called "PHP jQuery helper functions" and the difference is that finally it says something. finally i get an error saying NO SUCH ELEMENT AS i wen into the library to have a look and up comes the following function function populateFormElement(form, name, value) { // check that the named element exists in the form var name = name; // handle non-php naming var element = form[name]; if(element == undefined) { debug('No such element as ' + name); return false; } // debug options if(options.debug) { _populate.elements.push(element); } } Now looking at it one can see that it should print out also the name, but its not printing it out. so i'm guessing that retrieving the name form the json is not working correctly. Link is at http://www.ocdmonline.org/michael/edit%5Fnews.php with username: Testing and pass:test123 Any ideas?

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• Possible uncommitted transactions causing "System.Data.SqlClient.SqlException: Timeout expired" erro

  - by Michael

  My application requires a user to log in and allows them to edit a list of things. However, it seems that if the same user always logs in and out and edits the list, this user will run into a "System.Data.SqlClient.SqlException: Timeout expired." error. I've read comments about increasing the timeout period but I've also read a comment about it possibly caused by uncommitted transactions. And I do have one going in the application. I'll provide the code I'm working with and there is an IF statement in there that I was a little iffy about but it seemed like a reasonable thing to do. I'll just go over what's going on here, there is a list of objects to update or add into the database. New objects created in the application are given an ID of 0 while existing objects have their own ID's generated from the DB. If the user chooses to delete some objects, their IDs are stored in a separate list of Integers. Once the user is ready to save their changes, the two lists are passed into this method. By use of the IF statement, objects with ID of 0 are added (using the Add stored procedure) and those objects with non-zero IDs are updated (using the Update stored procedure). After all this, a FOR loop goes through all the integers in the "removal" list and uses the Delete stored procedure to remove them. A transaction is used for all this. Public Shared Sub UpdateSomethings(ByVal SomethingList As List(Of Something), ByVal RemovalList As List(Of Integer)) Using DBConnection As New SqlConnection(conn) DBConnection.Open() Dim MyTransaction As SqlTransaction MyTransaction = DBConnection.BeginTransaction() Try For Each SomethingItem As Something In SomethingList Using MyCommand As New SqlCommand() MyCommand.Connection = DBConnection If SomethingItem.ID > 0 Then MyCommand.CommandText = "UpdateSomething" Else MyCommand.CommandText = "AddSomething" End If MyCommand.Transaction = MyTransaction MyCommand.CommandType = CommandType.StoredProcedure With MyCommand.Parameters If MyCommand.CommandText = "UpdateSomething" Then .Add("@id", SqlDbType.Int).Value = SomethingItem.ID End If .Add("@stuff", SqlDbType.Varchar).Value = SomethingItem.Stuff End With MyCommand.ExecuteNonQuery() End Using Next For Each ID As Integer In RemovalList Using MyCommand As New SqlCommand("DeleteSomething", DBConnection) MyCommand.Transaction = MyTransaction MyCommand.CommandType = CommandType.StoredProcedure With MyCommand.Parameters .Add("@id", SqlDbType.Int).Value = ID End With MyCommand.ExecuteNonQuery() End Using Next MyTransaction.Commit() Catch ex As Exception MyTransaction.Rollback() 'Exception handling goes here End Try End Using End Sub There are three stored procedures used here as well as some looping so I can see how something can be holding everything up if the list is large enough. Other users can log in to the system at the same time just fine though. I'm using Visual Studio 2008 to debug and am using SQL Server 2000 for the DB.

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• Are "EXC_BREAKPOINT (SIGTRAP)" exceptions caused by debugging breakpoints?

  - by Dennis

  I have a multithreaded app that is very stable on all my test machines and seems to be stable for almost every one of my users (based on no complaints of crashes). The app crashes frequently for one user, though, who was kind enough to send crash reports. All the crash reports (~10 consecutive reports) look essentially identical: Date/Time: 2010-04-06 11:44:56.106 -0700 OS Version: Mac OS X 10.6.3 (10D573) Report Version: 6 Exception Type: EXC_BREAKPOINT (SIGTRAP) Exception Codes: 0x0000000000000002, 0x0000000000000000 Crashed Thread: 0 Dispatch queue: com.apple.main-thread Thread 0 Crashed: Dispatch queue: com.apple.main-thread 0 com.apple.CoreFoundation 0x90ab98d4 __CFBasicHashRehash + 3348 1 com.apple.CoreFoundation 0x90adf610 CFBasicHashRemoveValue + 1264 2 com.apple.CoreText 0x94e0069c TCFMutableSet::Intersect(__CFSet const*) const + 126 3 com.apple.CoreText 0x94dfe465 TDescriptorSource::CopyMandatoryMatchableRequest(__CFDictionary const*, __CFSet const*) + 115 4 com.apple.CoreText 0x94dfdda6 TDescriptorSource::CopyDescriptorsForRequest(__CFDictionary const*, __CFSet const*, long (*)(void const*, void const*, void*), void*, unsigned long) const + 40 5 com.apple.CoreText 0x94e00377 TDescriptor::CreateMatchingDescriptors(__CFSet const*, unsigned long) const + 135 6 com.apple.AppKit 0x961f5952 __NSFontFactoryWithName + 904 7 com.apple.AppKit 0x961f54f0 +[NSFont fontWithName:size:] + 39 (....more text follows) First, I spent a long time investigating [NSFont fontWithName:size:]. I figured that maybe the user's fonts were screwed up somehow, so that [NSFont fontWithName:size:] was requesting something non-existent and failing for that reason. I added a bunch of code using [[NSFontManager sharedFontManager] availableFontNamesWithTraits:NSItalicFontMask] to check for font availability in advance. Sadly, these changes didn't fix the problem. I've now noticed that I forgot to remove some debugging breakpoints, including _NSLockError, [NSException raise], and objc_exception_throw. However, the app was definitely built using "Release" as the active build configuration. I assume that using the "Release" configuration prevents setting of any breakpoints--but then again I am not sure exactly how breakpoints work or whether the program needs to be run from within gdb for breakpoints to have any effect. My questions are: could my having left the breakpoints set be the cause of the crashes observed by the user? If so, why would the breakpoints cause a problem only for this one user? If not, has anybody else had similar problems with [NSFont fontWithName:size:]? I will probably just try removing the breakpoints and sending back to the user, but I'm not sure how much currency I have left with that user. And I'd like to understand more generally whether leaving the breakpoints set could possibly cause a problem (when the app is built using "Release" configuration).

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• Implementing a robust async stream reader

  - by Jon

  I recently provided an answer to this question: C# - Realtime console output redirection. As often happens, explaining stuff (here "stuff" was how I tackled a similar problem) leads you to greater understanding and/or, as is the case here, "oops" moments. I realized that my solution, as implemented, has a bug. The bug has little practical importance, but it has an extremely large importance to me as a developer: I can't rest easy knowing that my code has the potential to blow up. Squashing the bug is the purpose of this question. I apologize for the long intro, so let's get dirty. I wanted to build a class that allows me to receive input from a Stream in an event-based manner. The stream, in my scenario, is guaranteed to be a FileStream and there is also an associated StreamReader already present to leverage. The public interface of the class is this: public class MyStreamManager { public event EventHandler<ConsoleOutputReadEventArgs> StandardOutputRead; public void StartSendingEvents(); public void StopSendingEvents(); } Obviously this specific scenario has to do with a console's standard output, but that is a detail and does not play an important role. StartSendingEvents and StopSendingEvents do what they advertise; for the purposes of this discussion, we can assume that events are always being sent without loss of generality. The class uses these two fields internally: protected readonly StringBuilder inputAccumulator = new StringBuilder(); protected readonly byte[] buffer = new byte[256]; The functionality of the class is implemented in the methods below. To get the ball rolling: public void StartSendingEvents(); { this.stopAutomation = false; this.BeginReadAsync(); } To read data out of the Stream without blocking, and also without requiring a carriage return char, BeginRead is called: protected void BeginReadAsync() { if (!this.stopAutomation) { this.StandardOutput.BaseStream.BeginRead( this.buffer, 0, this.buffer.Length, this.ReadHappened, null); } } The challenging part: BeginRead requires using a buffer. This means that when reading from the stream, it is possible that the bytes available to read ("incoming chunk") are larger than the buffer. Since we are only handing off data from the stream to a consumer, and that consumer may well have inside knowledge about the size and/or format of these chunks, I want to call event subscribers exactly once for each chunk. Otherwise the abstraction breaks down and the subscribers have to buffer the incoming data and reconstruct the chunks themselves using said knowledge. This is much less convenient to the calling code, and detracts from the usefulness of my class. To this end, if the buffer is full after EndRead, we don't send its contents to subscribers immediately but instead append them to a StringBuilder. The contents of the StringBuilder are only sent back whenever there is no more to read from the stream (thus preserving the chunks). private void ReadHappened(IAsyncResult asyncResult) { var bytesRead = this.StandardOutput.BaseStream.EndRead(asyncResult); if (bytesRead == 0) { this.OnAutomationStopped(); return; } var input = this.StandardOutput.CurrentEncoding.GetString( this.buffer, 0, bytesRead); this.inputAccumulator.Append(input); if (bytesRead < this.buffer.Length) { this.OnInputRead(); // only send back if we 're sure we got it all } this.BeginReadAsync(); // continue "looping" with BeginRead } After any read which is not enough to fill the buffer, all accumulated data is sent to the subscribers: private void OnInputRead() { var handler = this.StandardOutputRead; if (handler == null) { return; } handler(this, new ConsoleOutputReadEventArgs(this.inputAccumulator.ToString())); this.inputAccumulator.Clear(); } (I know that as long as there are no subscribers the data gets accumulated forever. This is a deliberate decision). The good This scheme works almost perfectly: Async functionality without spawning any threads Very convenient to the calling code (just subscribe to an event) Maintains the "chunkiness" of the data; this allows the calling code to use inside knowledge of the data without doing any extra work Is almost agnostic to the buffer size (it will work correctly with any size buffer irrespective of the data being read) The bad That last almost is a very big one. Consider what happens when there is an incoming chunk with length exactly equal to the size of the buffer. The chunk will be read and buffered, but the event will not be triggered. This will be followed up by a BeginRead that expects to find more data belonging to the current chunk in order to send it back all in one piece, but... there will be no more data in the stream. In fact, as long as data is put into the stream in chunks with length exactly equal to the buffer size, the data will be buffered and the event will never be triggered. This scenario may be highly unlikely to occur in practice, especially since we can pick any number for the buffer size, but the problem is there. Solution? Unfortunately, after checking the available methods on FileStream and StreamReader, I can't find anything which lets me peek into the stream while also allowing async methods to be used on it. One "solution" would be to have a thread wait on a ManualResetEvent after the "buffer filled" condition is detected. If the event is not signaled (by the async callback) in a small amount of time, then more data from the stream will not be forthcoming and the data accumulated so far should be sent to subscribers. However, this introduces the need for another thread, requires thread synchronization, and is plain inelegant. Specifying a timeout for BeginRead would also suffice (call back into my code every now and then so I can check if there's data to be sent back; most of the time there will not be anything to do, so I expect the performance hit to be negligible). But it looks like timeouts are not supported in FileStream. Since I imagine that async calls with timeouts are an option in bare Win32, another approach might be to PInvoke the hell out of the problem. But this is also undesirable as it will introduce complexity and simply be a pain to code. Is there an elegant way to get around the problem? Thanks for being patient enough to read all of this.

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• Historical / auditable database

  - by Mark

  Hi all, This question is related to the schema that can be found in one of my other questions here. Basically in my database I store users, locations, sensors amongst other things. All of these things are editable in the system by users, and deletable. However - when an item is edited or deleted I need to store the old data; I need to be able to see what the data was before the change. There are also non-editable items in the database, such as "readings". They are more of a log really. Readings are logged against sensors, because its the reading for a particular sensor. If I generate a report of readings, I need to be able to see what the attributes for a location or sensor was at the time of the reading. Basically I should be able to reconstruct the data for any point in time. Now, I've done this before and got it working well by adding the following columns to each editable table: valid_from valid_to edited_by If valid_to = 9999-12-31 23:59:59 then that's the current record. If valid_to equals valid_from, then the record is deleted. However, I was never happy with the triggers I needed to use to enforce foreign key consistency. I can possibly avoid triggers by using the extension to the "PostgreSQL" database. This provides a column type called "period" which allows you to store a period of time between two dates, and then allows you to do CHECK constraints to prevent overlapping periods. That might be an answer. I am wondering though if there is another way. I've seen people mention using special historical tables, but I don't really like the thought of maintainling 2 tables for almost every 1 table (though it still might be a possibility). Maybe I could cut down my initial implementation to not bother checking the consistency of records that aren't "current" - i.e. only bother to check constraints on records where the valid_to is 9999-12-31 23:59:59. Afterall, the people who use historical tables do not seem to have constraint checks on those tables (for the same reason, you'd need triggers). Does anyone have any thoughts about this? PS - the title also mentions auditable database. In the previous system I mentioned, there is always the edited_by field. This allowed all changes to be tracked so we could always see who changed a record. Not sure how much difference that might make. Thanks.

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• WCF timeout exception detailed investigation

  - by Jason Kealey

  We have an application that has a WCF service (*.svc) running on IIS7 and various clients querying the service. The server is running Win 2008 Server. The clients are running either Windows 2008 Server or Windows 2003 server. I am getting the following exception, which I have seen can in fact be related to a large number of potential WCF issues. System.TimeoutException: The request channel timed out while waiting for a reply after 00:00:59.9320000. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout. ---> System.TimeoutException: The HTTP request to 'http://www.domain.com/WebServices/myservice.svc/gzip' has exceeded the allotted timeout of 00:01:00. The time allotted to this operation may have been a portion of a longer timeout. I have increased the timeout to 30min and the error still occurred. This tells me that something else is at play, because the quantity of data could never take 30min to upload or download. The error comes and goes. At the moment, it is more frequent. It does not seem to matter if I have 3 clients running simultaneously or 100, it still occurs once in a while. Most of the time, there are no timeouts but I still get a few per hour. The error comes from any of the methods that are invoked. One of these methods does not have parameters and returns a bit of data. Another takes in lots of data as a parameter but executes asynchronously. The errors always originate from the client and never reference any code on the server in the stack trace. It always ends with: at System.Net.HttpWebRequest.GetResponse() at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) On the server: I've tried (and currently have) the following binding settings: maxBufferSize="2147483647" maxReceivedMessageSize="2147483647" maxBufferPoolSize="2147483647" It does not seem to have an impact. I've tried (and currently have) the following throttling settings: <serviceThrottling maxConcurrentCalls="1500" maxConcurrentInstances="1500" maxConcurrentSessions="1500"/> It does not seem to have an impact. I currently have the following settings for the WCF service. [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Single)] I ran with ConcurrencyMode.Multiple for a while, and the error still occurred. I've tried restarting IIS, restarting my underlying SQL Server, restarting the machine. All of these don't seem to have an impact. I've tried disabling the Windows firewall. It does not seem to have an impact. On the client, I have these settings: maxReceivedMessageSize="2147483647" <system.net> <connectionManagement> <add address="*" maxconnection="16"/> </connectionManagement> </system.net> My client closes its connections: var client = new MyClient(); try { return client.GetConfigurationOptions(); } finally { client.Close(); } I have changed the registry settings to allow more outgoing connections: MaxConnectionsPerServer=24, MaxConnectionsPer1_0Server=32. I have now just recently tried SvcTraceViewer.exe. I managed to catch one exception on the client end. I see that its duration is 1 minute. Looking at the server side trace, I can see that the server is not aware of this exception. The maximum duration I can see is 10 seconds. I have looked at active database connections using exec sp_who on the server. I only have a few (2-3). I have looked at TCP connections from one client using TCPview. It usually is around 2-3 and I have seen up to 5 or 6. Simply put, I am stumped. I have tried everything I could find, and must be missing something very simple that a WCF expert would be able to see. It is my gut feeling that something is blocking my clients at the low-level (TCP), before the server actually receives the message and/or that something is queuing the messages at the server level and never letting them process. If you have any performance counters I should look at, please let me know. (please indicate what values are bad, as some of these counters are hard to decypher). Also, how could I log the WCF message size? Finally, are there any tools our there that would allow me to test how many connections I can establish between my client and server (independently from my application) Thanks for your time! Extra information added June 20th: My WCF application does something similar to the following. while (true) { Step1GetConfigurationSettingsFromServerViaWCF(); // can change between calls Step2GetWorkUnitFromServerViaWCF(); DoWorkLocally(); // takes 5-15minutes. Step3SendBackResultsToServerViaWCF(); } Using WireShark, I did see that when the error occurs, I have a five TCP retransmissions followed by a TCP reset later on. My guess is the RST is coming from WCF killing the connection. The exception report I get is from Step3 timing out. I discovered this by looking at the tcp stream "tcp.stream eq 192". I then expanded my filter to "tcp.stream eq 192 and http and http.request.method eq POST" and saw 6 POSTs during this stream. This seemed odd, so I checked with another stream such as tcp.stream eq 100. I had three POSTs, which seems a bit more normal because I am doing three calls. However, I do close my connection after every WCF call, so I would have expected one call per stream (but I don't know much about TCP). Investigating a bit more, I dumped the http packet load to disk to look at what these six calls where. 1) Step3 2) Step1 3) Step2 4) Step3 - corrupted 5) Step1 6) Step2 My guess is two concurrent clients are using the same connection, that is why I saw duplicates. However, I still have a few more issues that I can't comprehend: a) Why is the packet corrupted? Random network fluke - maybe? The load is gzipped using this sample code: http://msdn.microsoft.com/en-us/library/ms751458.aspx - Could the code be buggy once in a while when used concurrently? I should test without the gzip library. b) Why would I see step 1 & step 2 running AFTER the corrupted operation timed out? It seems to me as if these operations should not have occurred. Maybe I am not looking at the right stream because my understanding of TCP is flawed. I have other streams that occur at the same time. I should investigate other streams - a quick glance at streams 190-194 show that the Step3 POST have proper payload data (not corrupted). Pushing me to look at the gzip library again.

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• Using array as map value: Cant see the error

  - by Tom

  Hi all, Im trying to create a map, where the key is an int, and the value is an array int red[3] = {1,0,0}; int green[3] = {0,1,0}; int blue[3] = {0,0,1}; std::map<int, int[3]> colours; colours.insert(std::pair<int,int[3]>(GLUT_LEFT_BUTTON,red)); //THIS IS LINE 24 ! colours.insert(std::pair<int,int[3]>(GLUT_MIDDLE_BUTTON,blue)); colours.insert(std::pair<int,int[3]>(GLUT_RIGHT_BUTTON,green)); However, when I try to compile this code, I get the following error. g++ (Ubuntu 4.4.1-4ubuntu8) 4.4.1 In file included from /usr/include/c++/4.4/bits/stl_algobase.h:66, from /usr/include/c++/4.4/bits/stl_tree.h:62, from /usr/include/c++/4.4/map:60, from ../src/utils.cpp:9: /usr/include/c++/4.4/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _T1 = int, _T2 = int [3]]’: ../src/utils.cpp:24: instantiated from here /usr/include/c++/4.4/bits/stl_pair.h:84: error: array used as initializer /usr/include/c++/4.4/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&) [with _U1 = int, _U2 = int [3], _T1 = const int, _T2 = int [3]]’: ../src/utils.cpp:24: instantiated from here /usr/include/c++/4.4/bits/stl_pair.h:101: error: array used as initializer In file included from /usr/include/c++/4.4/map:61, from ../src/utils.cpp:9: /usr/include/c++/4.4/bits/stl_map.h: In member function ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = int, _Tp = int [3], _Compare = std::less<int>, _Alloc = std::allocator<std::pair<const int, int [3]> >]’: ../src/utils.cpp:30: instantiated from here /usr/include/c++/4.4/bits/stl_map.h:450: error: conversion from ‘int’ to non-scalar type ‘int [3]’ requested make: *** [src/utils.o] Error 1 I really cant see where the error is. Or even if there's an error. Any help (please include an explanation to help me avoid this mistake) will be appreciated. Thanks in advance.

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• NHibernate criteria query question

  - by Chris

  I have 3 related objects (Entry, GamePlay, Prize) and I'm trying to find the best way to query them for what I need using NHibernate. When a request comes in, I need to query the Entries table for a matching entry and, if found, get a) the latest game play along with the first game play that has a prize attached. Prize is a child of GamePlay and each Entry object has a GamePlays property (IList). Currently, I'm working on a method that pulls the matching Entry and eagerly loads all game plays and associated prizes, but it seems wasteful to load all game plays just to find the latest one and any that contain a prize. Right now, my query looks like this: var entry = session.CreateCriteria<Entry>() .Add(Restrictions.Eq("Phone", phone)) .AddOrder(Order.Desc("Created")) .SetFetchMode("GamePlays", FetchMode.Join) .SetMaxResults(1).UniqueResult<Entry>(); Two problems with this: It loads all game plays up front. With 365 days of data, this could easily balloon to 300k of data per query. It doesn't eagerly load the Prize child property for each game. Therefore, my code that loops through the GamePlays list looking for a non-null Prize must make a call to load each Prize property I check. I'm not an nhibernate expert, but I know there has to be a better way to do this. Ideally, I'd like to do the following (pseudocode): entry = findEntry(phoneNumber) lastPlay = getLatestGamePlay(Entry) firstWinningPlay = getFirstWinningGamePlay(Entry) The end result of course is that I have the entry details, the latest game play, and the first winning game play. The catch is that I want to do this in as few database calls as possible, otherwise I'd just execute 3 separate queries. The object definitions look like: public class Entry { public Guid Id {get;set;} public string Phone {get;set;} public IList<GamePlay> GamePlays {get;set;} // ... other properties } public class GamePlay { public Guid Id {get;set;} public Entry Entry {get;set;} public Prize Prize {get;set;} // ... other properties } public class Prize { public Guid Id {get;set;} // ... other properties } The proper NHibernate mappings are in place, so I just need help figuring out how to set up the criteria query (not looking for HQL, don't use it).

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• Hosting a WCF Service Lib through a Windows service get a System.InvalidOperationException: attempti

  - by JohnL

  I have a WCF Service Library containing five service contracts. The library is hosted through a Windows Service. Most if not all my configuration for the WCF Library is declaritive. The only thing I am doing in code for configuration is to pass the type of the class implementing the service contracts into ServiceHost. I then call Open on each of the services during the Windows Service OnStart event. Here is the error message I get: Service cannot be started. System.InvalidOperationException: Service '[Fubu.Conversion.Service1' has zero application (non-infrastructure) endpoints. This might be because no configuration file was found for your application, or because no service element matching the service name could be found in the configuration file, or because no endpoints were defined in the service element. at System.ServiceModel.Description.DispatcherBuilder.EnsureThereAreNonMexEndpoints(ServiceDescription description) at System.ServiceModel.Description.DispatcherBuilder.InitializeServiceHost(ServiceDescription description, ServiceHostBase serviceHost) at System.ServiceModel.ServiceHostBase.InitializeRuntime() at System.ServiceModel.ServiceHostBase.OnBeginOpen() at System.ServiceModel.ServiceHostBase.OnOpen(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open(TimeSpan timeout) at System.ServiceModel.Channels.CommunicationObject.Open() at Fubu.RemotingHost.RemotingHost.StartServ... protected override void OnStart(string[] args) { // Uncomment to debug this properly //System.Diagnostics.Debugger.Break(); StartService1(); StartService2(); StartService3(); StartService4(); StartService5(); } Each of the above simply do the following: private void StartSecurityService() { host = new ServiceHost(typeof(Service1)); host.Open(); } Service Lib app.congfig summary <services> <service behaviorConfiguration="DefaultServiceBehavior" name="Fubu.Conversion.Service1"> <endpoint address="" binding="netTcpBinding" bindingConfiguration="TCPBindingConfig" name="Service1" bindingName="TCPEndPoint" contract="Fubu.Conversion.IService1"> <identity> <dns value="localhost" /> </identity> </endpoint> <endpoint address="mex" binding="mexTcpBinding" bindingConfiguration="" name="mexSecurity" bindingName="TcpMetaData" contract="IMetadataExchange" /> <host> <baseAddresses> <add baseAddress="net.tcp://localhost:8025/Fubu/Conversion/Service1/" /> </baseAddresses> </host> </service> ... Contract is set up as follows: namespace Fubu.Conversion.Service1 { [ServiceContract(Namespace = "net.tcp://localhost:8025/Fubu")] public interface IService1 { I have looked "high and low" for a solution without any luck. Is the answer obvious? The solution to this does not appear to be. Thanks

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• Tracking upstream svn changes with git-svn and github?

  - by Joseph Turian

  How do I track upstream SVN changes using git-svn and github? I used git-svn to convert an SVN repo to git on github: $ git svn clone -s http://svn.osqa.net/svnroot/osqa/ osqa $ cd osqa $ git remote add origin [email protected]:turian/osqa.git $ git push origin master I then made a few changes in my git repo, committed, and pushed to github. Now, I am on a new machine. I want to take upstream SVN changes, merge them with my github repo, and push them to my github repo. This documentation says: "If you ever lose your local copy, just run the import again with the same settings, and you’ll get another working directory with all the necessary SVN metainfo." So I did the following. But none of the commands work as desired. How do I track upstream SVN changes using git-svn and github? What am I doing wrong? $ git svn clone -s http://svn.osqa.net/svnroot/osqa/ osqa $ cd osqa $ git remote add origin [email protected]:turian/osqa.git $ git push origin master To [email protected]:turian/osqa.git ! [rejected] master -> master (non-fast forward) error: failed to push some refs to '[email protected]:turian/osqa.git' $ git pull remote: Counting objects: 21, done. remote: Compressing objects: 100% (17/17), done. remote: Total 17 (delta 7), reused 9 (delta 0) Unpacking objects: 100% (17/17), done. From [email protected]:turian/osqa * [new branch] master -> origin/master From [email protected]:turian/osqa * [new tag] master -> master You asked me to pull without telling me which branch you want to merge with, and 'branch.master.merge' in your configuration file does not tell me either. Please name which branch you want to merge on the command line and try again (e.g. 'git pull <repository> <refspec>'). See git-pull(1) for details on the refspec. ... $ /usr//lib/git-core/git-svn rebase warning: refname 'master' is ambiguous. First, rewinding head to replay your work on top of it... Applying: Added forum/management/commands/dumpsettings.py error: Ref refs/heads/master is at 6acd747f95aef6d9bce37f86798a32c14e04b82e but expected a7109d94d813b20c230a029ecd67801e6067a452 fatal: Cannot lock the ref 'refs/heads/master'. Could not move back to refs/heads/master rebase refs/remotes/trunk: command returned error: 1

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• What does N years of experience with a language really mean?

  - by marcgg

  I've been looking at jobs descriptions since I'm graduating soon and looking for a job and what's always coming back - I'm not teaching you anything - is the "N years of experience in this language". It has been discussed in this question that if you work professionally with let's say Ruby for 2 years, but during these two years you also did some C# and PHP and were actually coding in Ruby 50% of the time. Do you say you have 1 year of experience in Ruby? 2 years? Another issue that hasn't been reviewed in the other post is for "non-professional experience". I'll give you a personal example: I've been working with Ruby on Rails since 2004 while at school. I did a lot of personal projects and school projects using this technology. I also used Rails in 2 6-month internships. Do I have 5 years of Rails experience (2004-now)? Do I have 1 year(2 internships)? Do I have nothing? I feel like I don't deserve the credit for 5 years, because the first years I wasn't working a lot with rails, but since last year I launched some websites and invested myself a lot in this technology and just saying 1 year doesn't really reflect how much I know the technology... Another example: I Learned C++ at school and did 1 big project with it (2-3 month of work and a semester of classes). I never used it in a company but I'd be able to be productive fairly quickly if I had to work on a C++ project and I have a good grasp of the concepts. Do I have no experience? 3 months? 6 months? ... something else? What I'm really trying to do is to find a way to present my skill set in a way that is compliant to what recruiters expect. I also don't want to end up at an interview that would go something like this... Recruiter (finding out the horrible truth): Oh but you said that you had 2 years of experience with this when you have none! / slaps me in the face / Me (in pain): Oh! The irony! Recruiter (yelling): Get out of my office / calls security, punches me in the throat /

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• Why won't this hit test fire a second time? wpf

  - by csciguy

  All, I have a main window that contains two custom objects (AnimatedCharacter). These objects are nothing but images. These images might contain transparent portions. One of these objects slightly overlaps the other object. There is a listener attached to the main window and is as follows. private void Window_MouseLeftButtonUp_1(object sender, MouseButtonEventArgs e) { Point pt = e.GetPosition((UIElement)sender); //store off the mouse pt hitPointMouse = pt; //clear the result list hitResultsSubList.Clear(); EllipseGeometry m_egHitArea = new EllipseGeometry(pt, 1, 1); VisualTreeHelper.HitTest(sender as Visual, HitTestFilterFuncNew, new HitTestResultCallback(HitTestCallback), new GeometryHitTestParameters(m_egHitArea)); //Check all sub items you have now hit if (hitResultsSubList.Count > 0) { CheckSubHitItems(hitResultsSubList); } } The idea is to filter out only a select group of items (called AnimatedCharacters). The hittest and filters are as follows public HitTestResultBehavior HitTestCallback(HitTestResult htrResult) { IntersectionDetail idDetail = ((GeometryHitTestResult)htrResult).IntersectionDetail; switch (idDetail) { case IntersectionDetail.FullyContains: return HitTestResultBehavior.Continue; case IntersectionDetail.Intersects: return HitTestResultBehavior.Continue; case IntersectionDetail.FullyInside: return HitTestResultBehavior.Continue; default: return HitTestResultBehavior.Stop; } } public HitTestFilterBehavior HitTestFilterFuncNew(DependencyObject potentialHitTestTarget) { if (potentialHitTestTarget.GetType() == typeof(AnimatedCharacter)) { hitResultsSubList.Add(potentialHitTestTarget as AnimatedCharacter); } return HitTestFilterBehavior.Continue; } This returns me back a list (called hitResultsSubList) that I attempt to then process further. I want to take everything in the hitResultsSubList and run a hit test on it again. This time, the hit test will be checking alpha levels on the particular animatedCharacter object. private void CheckSubHitItems(List<DependencyObject> hitResultsSub) { for(int i = 0; i<hitResultsSub.Count; i++) { hitResultsList.Clear(); AnimatedCharacter ac = hitResultsSub[i] as AnimatedCharacter; try { //DEBUGGER SKIPS THIS NEXT LINE EVERY SINGLE TIME. VisualTreeHelper.HitTest(ac, null, new HitTestResultCallback(hitCallBack), new PointHitTestParameters(hitPointMouse)); } catch (Exception e) { System.Diagnostics.Debug.WriteLine(e.StackTrace); } if (hitResultsList.Count > 0) { //do something here } } } Here is my problem now. The hit test in the second function (CheckSubHitItems) never gets called. There are definitely items (DependencyObjects of the type AnimatedCharacter) in the hitResultSub, but no matter what, the second hit test will not fire. I can walk the for loop fine, but when that line is hit, I get the following console statement. Step into: Stepping over non-user code 'System.MulticastDelegate.CtorClosed' No exceptions are thrown. Any help is appreciated.

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• One entityManger finds entity , the other does not.

  - by Pitelk

  Hi all, I have a very strange behavior in my program. I have 2 classes (class LogIn and CreateGame) where i have injected an EntityManager in each using the annotation @PersistenceContext(unitName="myUnitPU") EntityManager entitymanger; In some point i remove an object called "user" from the database using entitymanger.remove(user) from a method in LogIn class. The business logic is that a user can host and join games ( in the same time) so removing the user all the entries in database about the games the user has created are removed and all the entries showing in which games the user has joined are removed also. After that, i call another function which checks if the user exists using a method in the LogIn class entitymanager.find(user) which surprisingly enough, finds the user. After that I call a method in CreateGame class which tries to find the user by using again entitymanger.find(user) the entitymanger in that class fails to find the user (which is the expected result as the user is removed and it's not in the database) So the question is : Why the entitymanager in one class finds the user (which is wrong) where the other doesn't find it? Does anyone has ever the same problem? PS : This "bug" occurs when the user has hosted a game which is joined by another user (lets call him Buser) and the Buser has made a game which is joined by the current user. GAME | HOST | CLIENTS game1 | user | userB game2 | userB | user where in this case by removing the user, the game1 is deleted and the user is removed from game2 so the result is GAME | HOST | CLIENTS game2 | userB | PS2 : The Beans are EJB3.0. The methods are called from a delegate class. The beans in the delegate class are instantiated using the InitialContext.lookup() method. Note that for logging in ,creating , joining games the appropriate delegate class calls the correspondent EJB which does the transactions. In the case of logOut, the delegate calls an EJB to logout the user but becuase other stuff must be done (as said above) this EJB calls other EJB (again using lookup() ) which has methods like removegame(), removeUserFromGame() etc. After those methods are executed the user is then logged out. Maybe it has something to do with the fact the the first entity manager is called by a delegate but the second from inside an EJb and thats why the one entitymanger can see the non-existent user while the other cannot? Also all the methods have TRANSACTIONTYPE.REQUIRED Thank you in advance

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• ActiveMQ 5.2.0 + REST + HTTP POST = java.lang.OutOfMemoryError

  - by Bruce Loth

  First off, I am a newbie when it comes to JMS & ActiveMQ. I have been looking into a messaging solution to serve as middleware for a message producer that will insert XML messages into a queue via HTTP POST. The producer is an existing system written in C++ that cannot be modified (so Java and the C++ API are out). Using the "demo" examples and some trial and error, I have cobbled together a working example of what I want to do (on a windows box). The web.xml I configured in a test directory under "webapps" specifies that the HTTP POST messages received from the producer are to be handled by the MessageServlet. I added a line for the text app in "activemq.xml" ('ow' is the test app dir): I created a test script to "insert" messages into the queue which works well. The problem I am running into is that it as I continue to insert messages via REST/HTTP POST, the memory consumption and thread count used by ActiveMQ continues to rise (It happens when I have timely consumers as well as slow or non-existent consumers). When memory consumption gets around 250MB's and the thread count exceeds 5000 (as shown in windows task manager), ActiveMQ crashes and I see this in the log: Exception in thread "ActiveMQ Transport Initiator: vm://localhost#3564" java.lang.OutOfMemoryError: unable to create new native thread It is as if Jetty is spawning a new thread to handle each HTTP POST and the thread never dies. I did look at this page: http://activemq.apache.org/javalangoutofmemory.html and tried but that didn't fix the problem (although I didn't fully understand the implications of the change either). Does anyone have any ideas? Thanks! Bruce Loth PS - I included the "test message producer" python script below for what it is worth. I created batches of 100 messages and continued to run the script manually from the command line while watching the memory consumption and thread count of ActiveMQ in task manager. def foo(): import httplib, urllib body = "<?xml version='1.0' encoding='UTF-8'?>\n \ <ROOT>\n \ [snip: xml deleted to save space] </ROOT>" headers = {"content-type": "text/xml", "content-length": str(len(body))} conn = httplib.HTTPConnection("127.0.0.1:8161") conn.request("POST", "/ow/message/RDRCP_Inbox?type=queue", body, headers) response = conn.getresponse() print response.status, response.reason data = response.read() conn.close() ## end method definition ## Begin test code count = 0; while(count < 100): # Test with batches of 100 msgs count += 1 foo()

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• MySQL table organization and optimization (Rails)

  - by aguynamedloren

  I've been learning Ruby on Rails over the past few months with no prior programming experience. Lately, I've been thinking about database optimization and table organization. I know there are great books on the subject, but I typically learn by example / as I go. Here's a hypothetical situation: Let's say I am building a social network for a niche community with 250,000 members (users). The users have the ability to attend events. Let's say there are 50,000 past/present/future events. Much like Facebook events, a user can attend any number of events and an event can have any number of attendees. In the database, there would be a table for users and a table for events. Somehow I would have to create an association between the users and events. I could create an "events" column in the users table such that each user row would contain a hash of event IDs, or I could create an "attendees" column in the events table such that each event row would contain a hash of user IDs. Neither of these solutions seem ideal, however. On a users profile page, I want to display the list of events they are associated with, which would require scanning the 50,000 event rows for the user ID of said user if I include an "attendees" column in the events table. Likewise, on an event page, I want to display a list of attendees for the event, which would require scanning the 250,000 user rows for the event ID of said event if I include an "events" column in the users table. Option 3 would be to create a third table that contains the attendee information for each and every event - but I don't see how this would solve any problems. Are these non-issues? Rails makes accessing all of this information easy, but I guess I'm worried about scale. It is entirely possible that I am under-estimating the speed and processing power of modern databases / servers / etc. How long would it take to scan 250,000 user rows for specific event IDs - 10ms? 100ms? 1,000ms? I guess that's not that bad. Am I just over-thinking this?

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• Problem getting correct parameters for C# P/Invoke call to C++ dll

  - by Jim Jones

  Trying to Interop a functionality from the Outside In API from Oracle. Have the following function: SCCERR EXOpenExport {VTHDOC hDoc, VTDWORD dwOutputId, VTDWORD dwSpecType, VTLPVOID pSpec, VTDWORD dwFlags, VTSYSPARAM dwReserved, VTLPVOID pCallbackFunc, VTSYSPARAM dwCallbackData, VTLPHEXPORT phExport); From the header files I reduced the parameters to: typedef VTSYSPARAM VTHDOC, VTLPHDOC * typedef DWORD_PTR VTSYSPARAM typedef unsigned long DWORD_PTR typedef unsigned long VTDWORD typedef VTVOID* VTLPVOID #define VTVOID void typedef VTHDOC VTHEXPORT, *VTLPEXPORT These are for 32 bit windows Going through the header files, the example programs, and the documentation I found: 1. That pSpec could be a pointer to a buffer or NULL, so I set it to a IntPtr.Zero (documentation). 2. That dwFlags and dwReserved according to the documentation "Must be set by the developer to 0". 3. That pCallbackFunc can be set to NULL if I don't want to handle callbacks. 4. That the last two are based on structs that I wrote C# wrappers for using the [StructLayout(LayoutKind.Sequential)]. Then instatiated an instance and generated the parameters by first creating a IntPtr with Marshal.AllocHGlobal(Marshal.SizeOf(instance)), then getting the address value which is passed as a uint for dwCallbackData and a IntPtr for phExport. The final parameter list is as follows: 1. phDoc as a IntPtr which was loaded with an address by the DAOpenDocument function called before. 2. dwOutputId as uint set to 1535 which represents FI_JPEGFIF 3. dwSpecType as int set to 2 which represents IOTYPE_ANSIPATH 4. pSpec as an IntPtr.Zero where the output will be written 5. dwFlags as uint set to 0 as directed 6. dwReserved as uint set to 0 as directed 7. pCallbackFunc as IntPtr set to NULL as I will handle results 8. dwCallBackDate as uint the address of a buffer for a struct 9. phExport as IntPtr to another struct buffer still get an undefined error from the API. Meaning that the call returns a 961 which is not defined in any of the header files. In the past I have gotten this when my choice of parameter types are incorrect. I started out using Interop Assistant which was helpful in learning how many of the parameter types get translated. It is however limited by how well I am able to glean the correct native type from the header files. For example the hDoc parameter used in the preceding function was defined as a non-filesytem handle, so attempted to use Marshal to create a handle, then used an IntPtr, and finally it turned out to be an int (actually it was &phDoc used here). So is there a more scientific way of doing this, other than trial and error? Jim

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• Purpose of Explicit Default Constructors

  - by Dennis Zickefoose

  I recently noticed a class in C++0x that calls for an explicit default constructor. However, I'm failing to come up with a scenario in which a default constructor can be called implicitly. It seems like a rather pointless specifier. I thought maybe it would disallow Class c; in favor of Class c = Class(); but that does not appear to be the case. Some relevant quotes from the C++0x FCD, since it is easier for me to navigate [similar text exists in C++03, if not in the same places] 12.3.1.3 [class.conv.ctor] A default constructor may be an explicit constructor; such a constructor will be used to perform default-initialization or value initialization (8.5). It goes on to provide an example of an explicit default constructor, but it simply mimics the example I provided above. 8.5.6 [decl.init] To default-initialize an object of type T means: — if T is a (possibly cv-qualified) class type (Clause 9), the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor); 8.5.7 [decl.init] To value-initialize an object of type T means: — if T is a (possibly cv-qualified) class type (Clause 9) with a user-provided constructor (12.1), then the default constructor for T is called (and the initialization is ill-formed if T has no accessible default constructor); In both cases, the standard calls for the default constructor to be called. But that is what would happen if the default constructor were non-explicit. For completeness sake: 8.5.11 [decl.init] If no initializer is specified for an object, the object is default-initialized; From what I can tell, this just leaves conversion from no data. Which doesn't make sense. The best I can come up with would be the following: void function(Class c); int main() { function(); //implicitly convert from no parameter to a single parameter } But obviously that isn't the way C++ handles default arguments. What else is there that would make explicit Class(); behave differently from Class();? The specific example that generated this question was std::function [20.8.14.2 func.wrap.func]. It requires several converting constructors, none of which are marked explicit, but the default constructor is.

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• How does MySQL's ORDER BY RAND() work?

  - by Eugene

  Hi, I've been doing some research and testing on how to do fast random selection in MySQL. In the process I've faced some unexpected results and now I am not fully sure I know how ORDER BY RAND() really works. I always thought that when you do ORDER BY RAND() on the table, MySQL adds a new column to the table which is filled with random values, then it sorts data by that column and then e.g. you take the above value which got there randomly. I've done lots of googling and testing and finally found that the query Jay offers in his blog is indeed the fastest solution: SELECT * FROM Table T JOIN (SELECT CEIL(MAX(ID)*RAND()) AS ID FROM Table) AS x ON T.ID >= x.ID LIMIT 1; While common ORDER BY RAND() takes 30-40 seconds on my test table, his query does the work in 0.1 seconds. He explains how this functions in the blog so I'll just skip this and finally move to the odd thing. My table is a common table with a PRIMARY KEY id and other non-indexed stuff like username, age, etc. Here's the thing I am struggling to explain SELECT * FROM table ORDER BY RAND() LIMIT 1; /*30-40 seconds*/ SELECT id FROM table ORDER BY RAND() LIMIT 1; /*0.25 seconds*/ SELECT id, username FROM table ORDER BY RAND() LIMIT 1; /*90 seconds*/ I was sort of expecting to see approximately the same time for all three queries since I am always sorting on a single column. But for some reason this didn't happen. Please let me know if you any ideas about this. I have a project where I need to do fast ORDER BY RAND() and personally I would prefer to use SELECT id FROM table ORDER BY RAND() LIMIT 1; SELECT * FROM table WHERE id=ID_FROM_PREVIOUS_QUERY LIMIT 1; which, yes, is slower than Jay's method, however it is smaller and easier to understand. My queries are rather big ones with several JOINs and with WHERE clause and while Jay's method still works, the query grows really big and complex because I need to use all the JOINs and WHERE in the JOINed (called x in his query) sub request. Thanks for your time!

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• Fairness: Where can it be better handled?

  - by Srinivas Nayak

  Hi, I would like to share one of my practical experience with multiprogramming here. Yesterday I had written a multiprogram. Modifications to sharable resources were put under critical sections protected by P(mutex) and V(mutex) and those critical section code were put in a common library. The library will be used by concurrent applications (of my own). I had three applications that will use the common code from library and do their stuff independently. my library --------- work_on_shared_resource { P(mutex) get_shared_resource work_with_it V(mutex) } --------- my application ----------- application1 { *[ work_on_shared_resource do_something_else_non_ctitical ] } application2 { *[ work_on_shared_resource do_something_else_non_ctitical ] } application3 { *[ work_on_shared_resource ] } *[...] denote a loop. ------------ I had to run the applications on Linux OS. I had a thought in my mind, hanging over years, that, OS shall schedule all the processes running under him with all fairness. In other words, it will give all the processes, their pie of resource-usage equally well. When first two applications were put to work, they run perfectly well without deadlock. But when the third application started running, always the third one got the resources, but since it is not doing anything in its non-critical region, it gets the shared resource more often when other tasks are doing something else. So the other two applications were found almost totally halted. When the third application got terminated forcefully, the previous two applications resumed their work as before. I think, this is a case of starvation, first two applications had to starve. Now how can we ensure fairness? Now I started believing that OS scheduler is innocent and blind. It depends upon who won the race; he got the largest pie of CPU and resource. Shall we attempt to ensure fairness of resource users in the critical-section code in library? Or shall we leave it up to the applications to ensure fairness by being liberal, not greedy? To my knowledge, adding code to ensure fairness to the common library shall be an overwhelming task. On the other hand, believing on the applications will also never ensure 100% fairness. The application which does a very little task after working with shared resources shall win the race where as the application which does heavy processing after their work with shared resources shall always starve. What is the best practice in this case? Where we ensure fairness and how? Sincerely, Srinivas Nayak

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• List of Django model instance foreign keys losing consistency during state changes.

  - by Joshua

  I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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• Android: dynamically setting links to text in strings.xml

  - by Martyn

  I'm trying to make an app with localisation built in, but I want a way that I can create a web link within the text, the URL being defined elsewhere (for ease of maintenance). So, I have my links in res/values/strings.xml: <?xml version="1.0" encoding="utf-8"?> <resources> ... <string name="link1">http://some.link.com</string> <string name="link2">http://some.link2.com</string> </resources> and my localised text in res/values-en-rGB/strings.xml <?xml version="1.0" encoding="utf-8"?> <resources> ... <string name="sampleText">Sample text\nMore text and link1\nMore text and link2.</string> </resources> I've not tested this bit, but from the localization section of developer.android.com it says that this approach to reducing content duplication should work, although I'm not sure what folder I should put Italian, for example. Would it be in 'res/values-it-rIT/strings.xml'? Lets assume that I have various other languages too. I'm looking for a way of taking the base localised 'sampleText' and inserting my html links in, and getting them to work when clicked on. I've tried two approaches so far: 1, Putting some formatting in the 'sampleText' (%s): <string name="sampleText">Sample text\nMore text and <a href="%s">link1</a>\nMore text and <a href="%s">link2</a>.</string> and then processing the text like this: TextView tv = (TextView) findViewById(R.id.textHolder); tv.setText(getResources().getString(R.string.sampleText, getResources().getString(R.string.link1), getResources().getString(R.string.link2))); But this didn't work when I click on the link, even though the link text is being put in to the correct places. 2, I tried to use Linkify but the regular expression route may be difficult as I'm looking at supporting non-Latin based languages. I tried to put a custom xml tag around the link text and then do something like this: Pattern wordMatcher = Pattern.compile("<span1>.*</span1>"); String viewURL = "content://" + getResources().getString(R.string.someLink); Linkify.addLinks(tv, wordMatcher , viewURL ); But this didn't work either. So, I'd like to know if there's a way of dynamically adding multiple URLs to different sections of the same text which will link to web content? Thank you, Martyn

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• What is the best way to archive data in a relational database?

  - by GenericTypeTea

  I have a bit of an issue with a particular aspect of a program I'm working on. I need the ability to archive (fix) a table so that a change anywhere in the system will not affect the results it returns. This is the basic structure of what I need to fix: Recipe --> Recipe (as sub recipe) Recipe --> Ingredients So, if I fix a Recipe, I need to ensure all the sub recipes (including all the sub recipes sub recipes and so forth) are fixed and all its ingredients are fixed. The problem is that the sub recipe and ingredients still need to be modifiable as they are used by other recipes that are not fixed. I came up with a solution whereby I serialize (with protobuf-net) a master object that deals with the recipe and all the sub recipes and ingredients and save the archive data to a table like follows: Archive{ ReferenceId, (i.e. RecipeId) ReferenceTypeId, (i.e. Recipe) ArchiveData varbinary(max) } Now, this works great and is almost perfect... however I totally forgot (I'd love to blame the agile development mentally, however this was just short sighted) that this information needs to be reported on. As far as I'm aware I can't think how I could inflate the serialized data back into my Recipe Object and use it in a Report. I'm using the standard SQL 2005 report services at the moment. Alternatively, I guess I could do the following: Duplicate every table and tag the word "Archive" on the end of the table name. This would then give me an area of specific archive data... but ignoring my simplified example, there'd actually be about 15 tables duplicated. Add a nullable, non-foreign key property called "CopiedFromId" to every table that contains fixed data and duplicate every record that the recipe (and all it's sub recipes and all their sub recipes) touches. Create some sort of denormalised structure that could be restored from at a later date to the original, unfixed recipe. Although I think this would be like option 1 and involve a lot of extra tables. Anyway, I'm at a total loss and do not like any of the ideas particularly. Can anyone please advise the best course of action? EDIT: Or 4) Create tables specific to what the report requires and populate them with the data when the user clicks the report button? This would cause about 4 extra tables for the report in question.

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