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• Why do people say that Ruby is slow?

  - by stephen murdoch

  I like Ruby on Rails and I use it for all my web development projects. A few years ago there was a lot of talk about Rails being a memory hog and about how it didn't scale very well but these suggestions were put to bed by Gregg Pollack here. Lately though, I've been hearing people saying that Ruby itself is slow. Why is Ruby considered slow? I do not find Ruby to be slow but then again, I'm just using it to make simple CRUD apps and company blogs. What sort of projects would I need to be doing before I find Ruby becoming slow? Or is this slowness just something that affects all programming languages? What are your options as a Ruby programmer if you want to deal with this "slowness"? Which version of Ruby would best suit an application like Stack Overflow where speed is critical and traffic is intense? The questions are subjective, and I realise that architectural setup (EC2 vs standalone servers etc) makes a big difference but I'd like to hear what people think about Ruby being slow. Finally, I can't find much news on Ruby 2.0 - I take it we're a good few years away from that then?

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• UIView Controller mysteriously getting deallocated

  - by Dan Ray

  I have a UINavigation scheme with a "welcome" page, a middle page, and a detail page. In the middle page, there's a segmented controller that can swap the main body of that page between a table, a calendar, and a MKMapView, each implemented with their own view controller classes. Today I implemented the MapView and its annotations and all of that. It's nice. And a detail disclosure on each callout takes you to the detail page just the same way as if you'd gotten there via the table. Lovely. I also have a right-button-bar button that pushes in a "search" view. From there you can search the data I'm navigating. When it's done filtering the data (an array of objects I'm keeping in a data singleton), it makes the table reload its data, and calls my annotation-clearer-and-builder methods on the map view, and then pops itself out, so the "middle" page (including whatever view was in the guts of it) is back on the screen. Problem is, if I go back and forth between the map and the search a couple times, any mention of the table view causes us to crash with: *** -[CALayer retain]: message sent to deallocated instance 0x710b810. (I obviously have NSZombies turned on.) I put an NSLog in the dealloc method of my table view controller. That thing's never getting called. I don't know if we're ditching it behind the scenes for memory purposes, or if I'm leaking it and can't get my hands back on it, or what. I'm sort of at a loss about where to look. Any hints?

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• priority queue with limited space: looking for a good algorithm

  - by SigTerm

  This is not a homework. I'm using a small "priority queue" (implemented as array at the moment) for storing last N items with smallest value. This is a bit slow - O(N) item insertion time. Current implementation keeps track of largest item in array and discards any items that wouldn't fit into array, but I still would like to reduce number of operations further. looking for a priority queue algorithm that matches following requirements: queue can be implemented as array, which has fixed size and _cannot_ grow. Dynamic memory allocation during any queue operation is strictly forbidden. Anything that doesn't fit into array is discarded, but queue keeps all smallest elements ever encountered. O(log(N)) insertion time (i.e. adding element into queue should take up to O(log(N))). (optional) O(1) access for *largest* item in queue (queue stores *smallest* items, so the largest item will be discarded first and I'll need them to reduce number of operations) Easy to implement/understand. Ideally - something similar to binary search - once you understand it, you remember it forever. Elements need not to be sorted in any way. I just need to keep N smallest value ever encountered. When I'll need them, I'll access all of them at once. So technically it doesn't have to be a queue, I just need N last smallest values to be stored. I initially thought about using binary heaps (they can be easily implemented via arrays), but apparently they don't behave well when array can't grow anymore. Linked lists and arrays will require extra time for moving things around. stl priority queue grows and uses dynamic allocation (I may be wrong about it, though). So, any other ideas?

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• qt on Win CE 5.0 crash

  - by Michael

  Good day all, It's the first time I am using Qt on Windows CE and I ran into an issue. Maybe someone can help me with it. I will describe my set up. I am using XP with Visual Studio 2005 an Qt Add-in version 1.1.2. I downloaded Qt source for Windows CE and followed the instructions on these (http://doc.trolltech.com/4.4/install-wince.html) instructions to build the library for CE. I then used the Visual Studio to create a minimal Qt Windows CE Application. The program runs fine in the CE emulator, but once I try to deploy it on the device it crashes with the following message: Load module: qt_ce_3.exe Load module: QtGui4.dll Load module: msvcr80.dll Load module: QtCore4.dll Load module: CEShell.DLL Load module: OLEAUT32.dll Load module: commctrl.dll.0409.MUI Load module: commctrl.dll Load module: aygshell.dll Load module: WS2.dll Load module: WINSOCK.dll Load module: coredll.dll.0409.MUI Load module: ossvcs.dll Load module: ole32.dll Load module: coredll.dll Load module: MMTimer.dll Data Abort: Thread=8fb09a40 Proc=8c4ecea0 'qt_ce_3.exe' AKY=00040001 PC=012a80b0(qtcore4.dll+0x000680b0) RA=012a8168(qtcore4.dll+0x00068168) BVA=676e4574 FSR=000000f5 Unhandled exception at 0x012a80b0 in qt_ce_3.exe: 0xC0000005: Access violation reading location 0x676e4574. I tried it on two devices from different manufacturers, and the result is the same. Debug version worked on one of them, ran out of memory on the other. Does anyone have any idea what this could be? Thanks in advance, Michael

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• What would be the safest way to store objects of classes derived from a common interface in a common

  - by Svenstaro

  I'd like to manage a bunch of objects of classes derived from a shared interface class in a common container. To illustrate the problem, let's say I'm building a game which will contain different actors. Let's call the interface IActor and derive Enemy and Civilian from it. Now, the idea is to have my game main loop be able to do this: // somewhere during init std::vector<IActor> ActorList; Enemy EvilGuy; Civilian CoolGuy; ActorList.push_back(EvilGuy); ActorList.push_back(CoolGuy); and // main loop while(!done) { BOOST_FOREACH(IActor CurrentActor, ActorList) { CurrentActor.Update(); CurrentActor.Draw(); } } ... or something along those lines. This example obviously won't work but that is pretty much the reason I'm asking here. I'd like to know: What would be the best, safest, highest-level way to manage those objects in a common heterogeneous container? I know about a variety of approaches (Boost::Any, void*, handler class with boost::shared_ptr, Boost.Pointer Container, dynamic_cast) but I can't decide which would be the way to go here. Also I'd like to emphasize that I want to stay away as far as possible from manual memory management or nested pointers. Help much appreciated :).

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• Best practices for Java logging from multiple threads?

  - by Jason S

  I want to have a diagnostic log that is produced by several tasks managing data. These tasks may be in multiple threads. Each task needs to write an element (possibly with subelements) to the log; get in and get out quickly. If this were a single-task situation I'd use XMLStreamWriter as it seems like the best match for simplicity/functionality without having to hold a ballooning XML document in memory. But it's not a single-task situation, and I'm not sure how to best make sure this is "threadsafe", where "threadsafe" in this application means that each log element should be written to the log correctly and serially (one after the other and not interleaved in any way). Any suggestions? I have a vague intuition that the way to go is to use a queue of log elements (with each one able to be produced quickly: my application is busy doing real work that's performance-sensitive), and have a separate thread which handles the log elements and sends them to a file so the logging doesn't interrupt the producers. The logging doesn't necessarily have to be XML, but I do want it to be structured and machine-readable. edit: I put "threadsafe" in quotes. Log4j seems to be the obvious choice (new to me but old to the community), why reinvent the wheel...

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• hudson.util.ProcessTreeTest test error

  - by senzacionale

  error: Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.011 sec Running hudson.util.ProcessTreeTest Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.181 sec <<< FAILURE! Running hudson.model.LoadStatisticsTest Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.089 sec Running hudson.util.ArgumentListBuilderTest Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.053 sec Running hudson.util.RobustReflectionConverterTest Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.029 sec Running hudson.util.VersionNumberTest Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.074 sec Running hudson.util.CyclicGraphDetectorTest Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.038 sec Results : Tests in error: testRemoting(hudson.util.ProcessTreeTest) Tests run: 102, Failures: 0, Errors: 1, Skipped: 0 [INFO] ------------------------------------------------------------------------ [ERROR] BUILD FAILURE [INFO] ------------------------------------------------------------------------ [INFO] There are test failures. Please refer to D:\PROJEKTI\Maven\hudson\main\core\target\surefire-reports for the individual test results. [INFO] ------------------------------------------------------------------------ [INFO] For more information, run Maven with the -e switch [INFO] ------------------------------------------------------------------------ [INFO] Total time: 17 minutes 58 seconds [INFO] Finished at: Fri Jun 11 21:04:46 CEST 2010 [INFO] Final Memory: 85M/152M [INFO] ------------------------------------------------------------------------ error log: ------------------------------------------------------------------------------- Test set: hudson.util.ProcessTreeTest ------------------------------------------------------------------------------- Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.181 sec <<< FAILURE! testRemoting(hudson.util.ProcessTreeTest) Time elapsed: 0.169 sec <<< ERROR! org.jvnet.winp.WinpException: Failed to read environment variable table error=299 at .\envvar-cmdline.cpp:114 at org.jvnet.winp.Native.getCmdLineAndEnvVars(Native Method) at org.jvnet.winp.WinProcess.parseCmdLineAndEnvVars(WinProcess.java:114) at org.jvnet.winp.WinProcess.getEnvironmentVariables(WinProcess.java:109) at hudson.util.ProcessTree$Windows$1.getEnvironmentVariables(ProcessTree.java:419) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at hudson.remoting.RemoteInvocationHandler$RPCRequest.perform(RemoteInvocationHandler.java:274) at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:255) at hudson.remoting.RemoteInvocationHandler$RPCRequest.call(RemoteInvocationHandler.java:215) at hudson.remoting.UserRequest.perform(UserRequest.java:114) at hudson.remoting.UserRequest.perform(UserRequest.java:48) at hudson.remoting.Request$2.run(Request.java:270) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619) does anyone have any idea what can be wrong in test? Regards

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• Behavior of retained propertie while holder is retained

  - by Aurélien Vallée

  Hello everyone, I am a beginner ObjectiveC programmer, coming from the C++ world. I find it very difficult to understand the memory management offered by NSObject :/ Say I have the following class: @interface User : NSObject { NSString* name; } @property (nonatomic,retain) NSString* name; - (id) initWithName: (NSString*) theName; - (void) release; @end @implementation User @synthetise name - (id) initWithName: (NSString*) theName { if ( self = [super init] ) { [self setName:theName]; } return self; } - (void) release { [name release]; [super release]; } @end No considering the following code, I can't understand the retain count results: NSString* name = [[NSString alloc] initWithCString:/*C string from sqlite3*/]; // (1) name retainCount = 1 User* user = [[User alloc] initWithName:name]; // (2) name retainCount = 2 [whateverMutableArray addObject:user]; // (3) name retainCount = 2 [user release]; // (4) name retainCount = 1 [name release]; // (5) name retainCount = 0 At (4), the retain count of name decreased from 2 to 1. But that's not correct, there is still the instance of user inside the array that points to name ! The retain count of a variable should only decrease when the retain count of a referring variable is 0, that is, when it is dealloced, not released.

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• Source of UIView Implicit Animation delay?

  - by iPhoneToucher

  I have a block of UIView animation code that looks like this: [UIView beginAnimations:@"pushView" context:nil]; [UIView setAnimationDelay:0]; [UIView setAnimationDuration:.5]; [UIView setAnimationDelegate:self]; [UIView setAnimationWillStartSelector:@selector(animationWillStart)]; view.frame = CGRectMake(0, 0, 320, 416); [UIView commitAnimations]; The code basically mimics the animation of a ModalView presentation and is tied to a button on my interface. When the button is pressed, I get a long (.5 sec) delay (on iPod Touch...twice as fast on iPhone 3GS) before the animationWillStart: actually gets called. My app has lots going on besides this, but I've timed various points of my code and the delay definitely occurs at this block. In other words, a timestamp immediately before this code block and a timestamp when animationWillStart: gets called shows a .5 sec difference. I'm not too experienced with Core Animation and I'm just trying to figure out what the cause of the delay is...Memory use is stable when the animation starts and CoreAnimation FPS seems to be fine in Instruments. The view that gets animated does have upwards of 20 total subviews, but if that were the issue wouldn't it cause choppiness after the animation starts, rather than before? Any ideas?

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• Django upload failing on request data read error

  - by Jake

  Hi All, I've got a Django app that accepts uploads from jQuery uploadify, a jQ plugin that uses flash to upload files and give a progress bar. Files under about 150k work, but bigger files always fail and almost always at around 192k (that's 3 chunks) completed, sometimes at around 160k. The Exception I get is below. exceptions.IOError request data read error File "/usr/lib/python2.4/site-packages/django/core/handlers/wsgi.py", line 171, in _get_post self._load_post_and_files() File "/usr/lib/python2.4/site-packages/django/core/handlers/wsgi.py", line 137, in _load_post_and_files self._post, self._files = self.parse_file_upload(self.META, self.environ[\'wsgi.input\']) File "/usr/lib/python2.4/site-packages/django/http/__init__.py", line 124, in parse_file_upload return parser.parse() File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 192, in parse for chunk in field_stream: File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 314, in next output = self._producer.next() File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 468, in next for bytes in stream: File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 314, in next output = self._producer.next() File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 375, in next data = self.flo.read(self.chunk_size) File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 405, in read return self._file.read(num_bytes) When running locally on the Django development server, big files work. I've tried setting my FILE_UPLOAD_HANDLERS = ("django.core.files.uploadhandler.TemporaryFileUploadHandler",) in case it was the memory upload handler, but it made no difference. Does anyone know how to fix this?

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• How to get the "real" colors when exporting a GDI drawing to bmp

  - by Rodrigo

  Hi guys I'm developing a ASP.Net web handler that returns images making a in-memory System.Windows.Forms.Control and then exports the rendered control as a bitmap compressed to PNG, using the method DrawToBitmap(). The classes are fully working by now, except for a problem with the color assignment. By example, this is a Gauge generated by the web handler. The colors assigned to the inner parts of the gauge are red (#FF0000), yellow (#FFFF00) and green (#00FF00) but I only get a dully version of each color (#CB100F for red, #CCB70D for yellow and #04D50D for green). The background is a bmp file containing the color gradient. The color loss happens whether the background is a gradient as the sample, a black canvas, a white canvas, a transparent canvas, even when there is not a background set. With black background With transparent background With a white background Without a background set With pixel format in Format32bppArgb I've tried multiple bitmap color deeps, output formats, compression level, etc. but none of them seems to work. Any ideas? This is a excerpt of the source code: Bitmap bmp = new Bitmap(w, h, System.Drawing.Imaging.PixelFormat.Format32bppPArgb); Image bgimage = (Image) HttpContext.GetGlobalResourceObject("GraphicResources", "GaugeBackgroundImage"); Canvas control_canvas = new Canvas(); .... //the routine that makes the gauge .... control_canvas.DrawToBitmap(bmp, new Rectangle(0, 0, w, h));

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• Map element position in data file to class property

  - by Augusto

  I need to read/write files, following a format provided by a third party specification. The specification itself is pretty simple: it says the position and the size of the data that will be saved in the file. For example: Position Size Description -------------------------------------------------- 0001 10 Device serial number 0011 02 Hour 0013 02 Minute 0015 02 Second 0017 02 Day 0019 02 Month 0021 02 Year The list is very long, it has about 400 elements. But lots of them can be combined. For example, hour, minute, second, day, month and year can be combined in a single DateTime object. I've splitted the elements into about 4 categories, and created separeted classes for holding the data. So, instead of a big structure representing the data, I have some smaller classes. I've also created different classes for reading and writing the data. The problem is: how to map the positions in the file to the objects properties, so that I don't need to repeat the values in the reading/writing class? I could use some custom attributes and retrieve them via reflection. But since the code will be running on devices with small memory and processor, it would be nice to find another way. My current read code looks like this: public void Read() { DataFile dataFile = new DataFile(); // the arguments are: position, size dataFile.SerialNumber = ReadLong(1, 10); //... } Any ideas on this one? Thanks!

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• Problem with .Contains

  - by Rene

  Hello there, I have a little problem which i can't solve. I want to use an SQL-In-Statement in Linq. I've read in this Forum and in other Forums that I have to use the .Contains (with reverse-thinking-notation :-)). As input i have a List of Guids. I first copied them into an array and then did something like that : datatoget = (from p in objectContext.MyDataSet where ArrayToSearch.Contains(p.Subtable.Id.ToString()) select p).ToList(); datatoget is the result in which all records matching the Subtable.Id (which is a Guid) should be stored. Subtable is a Detail-Table from MyData, and the Id is a Guid-Type. I've tried several things (Convert Guid to String, and then using .Contains, etc), but I always get an Exception which says : 'Linq to Entities' doesn't recognize the Method 'Boolean Contains(System.Guid) and is not able to Translate this method into a memory expression. (Something like that, because I'm using the German Version of VS2008) I am using L2E with .NET 3.5 and am programming in C# with VS 2008. I've read several Examples, but it doesn't work. Is it perhaps because of using Guid's instead of strings ? I've also tried to write my own compare-function, but I don't know how to integrate it so that .NET calls my function for comparing.

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• NonStop ODBC: how the connections (ODBC servers) are assigned to CPUs?

  - by Vladimir Dyuzhev

  We have an ODBC pool running on a NonStop server. The pool is connected to SQL/MX. This pool is used by a few external Java applications, each of which has an JDBC pool connected to ODBC pool (e.g. 14 connections per application). With time (after a few application recycles) we see an imbalance between CPUs -- some have 8 ODBC processes running, some only 5. That leads to CPU time imbalance too. Up to this point we assumed that a CPU is assigned to ODBC process in round-robin fashion. That would maintain the number of ODBC processes more or less equally distributed. It's not the case though. Is there any information on how ODBC pool decided which CPU to choose for every new allocated process? Does it look at CPU load? Available memory? Something else? Sadly, even HP's own people (available to us, that is) couldn't answer those questions with certainty. :-(

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• Tips on managing dependencies for a release?

  - by Andrew Murray

  Our system comprises many .NET websites, class libraries, and a MSSQL database. We use SVN for source control and TeamCity to automatically build to a Test server. Our team is normally working on 4 or 5 projects at a time. We try to lump many changes into a largish rollout every 2-4 weeks. My problem is with keeping track of all the dependencies for a rollout. Example: Website A cannot go live until we've rolled out Branch X of Class library B, built in turn against the Trunk of Class library C, which needs Config Updates Y and Z and Database Update D, which needs Migration Script E... It gets even more complex - like making sure each developer's project is actually compatible with the others and are building against the same versions. Yes, this is a management issue as much as a technical issue. Currently our non-optimal solution is: a whiteboard listing features that haven't gone live yet relying on our memory and intuition when planning the rollout, until we're pretty sure we've thought of everything... a dry-run on our Staging environment. It's a good indication but we're often not sure if Staging is 100% in sync with Live - part of the problem I'm hoping to solve. some amount of winging it on rollout day. So far so good, minus a few close calls. But as our system grows, I'd like a more scientific release management system allowing for more flexibility, like being able to roll out a single change or bugfix on it's own, safe in the knowledge that it won't break anything else. I'm guessing the best solution involves some sort of version numbering system, and perhaps using a project management tool. We're a start-up, so we're not too hot on religiously sticking to rigid processes, but we're happy to start, providing it doesn't add more overhead than it's worth. I'd love to hear advice from other teams who have solved this problem.

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• Files not waiting for each other

  - by Sunny

  I have two batch files as follows in which file2.bat is dependent on file1.bat's output: file1.bat @ECHO OFF setlocal enabledelayedexpansion SET "keystring1=" ( FOR /f "delims=" %%a IN ( Source.txt ) DO ( ECHO %%a|FIND "Appprocess.exe" >NUL IF NOT ERRORLEVEL 1 SET keystring1=%%a FOR %%b IN (App1 App2 App3 App4 App5 App6 ) DO ( ECHO %%a|FIND "%%b" >NUL IF NOT ERRORLEVEL 1 IF DEFINED keystring1 CALL ECHO(%%keystring1%% %%b&SET "keystring1=" )))>result.txt GOTO :EOF file2.bat @echo off setlocal enabledelayedexpansion (for /f "tokens=1,2" %%a in (memory.txt) do ( for /f "tokens=5" %%c in ('find " %%a " ^< result.txt ') do echo %%c %%b ))> new.txt file1.bat usually takes 60 sec to complete its execution. In master.bat file i am calling above two files as: call file1.bat call file2.bat but file2.bat is not waiting for file1.bat to complete its execution. Even , i tried to call file2.bat within file1.bat as below but still its not waiting for file1.bat to get completed: @ECHO OFF setlocal enabledelayedexpansion SET "keystring1=" ( FOR /f "delims=" %%a IN ( Source.txt ) DO ( ECHO %%a|FIND "HsvDataSource.exe" >NUL IF NOT ERRORLEVEL 1 SET keystring1=%%a FOR %%b IN (EUHFMPROD USHFMPROD TL2TEST GSHFMPROD TL2PROD GSARCH1213 TL2FY13) DO ( ECHO %%a|FIND "%%b" >NUL IF NOT ERRORLEVEL 1 IF DEFINED keystring1 CALL ECHO(%%keystring1%% %%b&SET "keystring1=" )))>file2.txt GOTO :EOF call file1.bat I also tried below start option, but no effect.: start file1.bat /wait call file2.bat Not getting ..why its happening..?

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• should std::auto_ptr<>::operator = reset / deallocate its existing pointee ?

  - by afriza

  I read here about std::auto_ptr<::operator= Notice however that the left-hand side object is not automatically deallocated when it already points to some object. You can explicitly do this by calling member function reset before assigning it a new value. However, when I read the source code for header file C:\Program Files\Microsoft Visual Studio 8\VC\ce\include\memory template<class _Other> auto_ptr<_Ty>& operator=(auto_ptr<_Other>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr<_Ty>& _Right) _THROW0() { // assign compatible _Right (assume pointer) reset(_Right.release()); return (*this); } auto_ptr<_Ty>& operator=(auto_ptr_ref<_Ty> _Right) _THROW0() { // assign compatible _Right._Ref (assume pointer) _Ty **_Pptr = (_Ty **)_Right._Ref; _Ty *_Ptr = *_Pptr; *_Pptr = 0; // release old reset(_Ptr); // set new return (*this); } What is the correct/standard behavior? How do other STL implementations behave?

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• JConsole does not connect when a program is waiting for a console input

  - by Calm Storm

  Hi, I have a problem similar to the one mentioned here. I have a program which launches a selenium browser and refreshes it every 2 seconds. My idea here was to monitor the memory usage of my application as the page is being hit. This console program does a "System.in.read" and when a user presses enter key, this stops the browser refresh thread. I run the program and it runs as I would expect it to. But when I fire jconsole and attach it to the process, it looks like jconsole waits forever to attach. This is because of the "System.in.read", apparently as shown in the JConsole source. In my code it makes perfect sense for me to terminte the browser when user presses something so is there any alternative available at all ? (Posted code sample below) package com.ekanathk; import java.util.ArrayList; import java.util.List; import org.junit.Test; public class MultiThread { @Test public void testSimple() throws Exception { List<Integer> x = new ArrayList<Integer>(); for(int i = 0; i < 1000; i++) { x.add(i); } System.out.print("Press Enter to stop (try attach a jconsole now...."); System.in.read(); } } The problem here seems to be that any System.in.read (either in Main thread or any threads) seems to completely block jconsole. I guess the problem essentially boils down to multiple threads requesting system inputs at the same time? Is there a solution ?

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• Creating a DataTable by filtering another DataTable

  - by Jeff Dege

  I'm working on a system that currently has a fairly complicated function that returns a DataTable, which it then binds to a GUI control on a ASP.NET WebForm. My problem is that I need to filter the data returned - some of the data that is being returned should not be displayed to the user. I'm aware of DataTable.select(), but that's not really what I need. First, it returns an array of DataRows, and I need a DataTable, so I can databind it to the GUI control. But more importantly, the filtering I need to do isn't something that can be easily put into a simple expression. I have an array of the elements which I do not want displayed, and I need to compare each element from the DataTable against that array. What I could do, of course, is to create a new DataTable, reading everything out of the original, adding to the new what is appropriate, then databinding the new to the GUI control. But that just seems wrong, somehow. In this case, the number of elements in the original DataTable aren't likely to be enough that copying them all in memory is going to cause too much trouble, but I'm wondering if there is another way. Does the .NET DataTable have functionality that would allow me to filter via a callback function?

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• How to implement Session timeout in Web Server Side?

  - by Morgan Cheng

  I beheld a web framework implementing in-memory session in this way. The session object is added to Cache with timeout. When the time is out, the session is removed from Cache automatically. To protect race condition, each request should acquire lock on given session object to proceed. Each request will "touch" the session in Cache to refresh the timeout. Everything looks fine, until this scenario is discovered. Say, one operation takes a long time, longer than timeout. Another request comes and wait on session lock which is currently hold by the long-time request. Finally, the long-time request is over, it releases the lock. But, since it already takes longer time than timeout, the session object is already removed from Cache. This is obvious because the only request holding the lock doesn't have a chance to "touch" the session object in cache. The second request gets the lock but cannot retrieve the expired Session object. Oops... To fix this issue, the second request has to re-create the Session object. But, this is just like digging a buried dead body from tomb and try to bring it back to life. It causes buggy code. I'm wondering what's the best way to implement timeout in session to handle such scenario. I know that current platform must have good session mechanism. I just want to know the under-the-hood how.

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• ASP.NET 2.0 and COM Port Communication

  - by theaviator

  ASP.NET 2.0 and COM Port Communication Hello Guys, I have a managed DLL which communicates with the devices attached on COM/Serial ports. The desktop Winforms application sends requests on ports and receives/stores data in memory. In Winforms app I have added a reference to DLL and I am using the methods. This works well. Now, there is a situation where I need to show this data from serial/com port on a web-page. And also users should be able to send requests to the ports using this DLL. I have made a web app in ASP.NET (2.0). Added a reference to the DLL. I am able to use this DLL, the DLL communicates on the COM upon button click on web-page and also the response is shown on web page. However I am not happy with the approach and strongly feel that this is a bad approach. Also the development server crashes after 3 -4 requests. What is the best approach in this scenario. If I use a windows service then how would my ASP.net app will communicate with the Weindows service. Or can this be easily done using WCF. I have not used WCF any time nor any of .net remoting technique. Please suggest me the best architecture in this scenario. Thank you

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• C++ -- Is there an implicit cast here from Fred* to auto_ptr<Fred>?

  - by q0987

  Hello all, I saw the following code, #include <new> #include <memory> using namespace std; class Fred; // Forward declaration typedef auto_ptr<Fred> FredPtr; class Fred { public: static FredPtr create(int i) { return new Fred(i); // Is there an implicit casting here? If not, how can we return // a Fred* with return value as FredPtr? } private: Fred(int i=10) : i_(i) { } Fred(const Fred& x) : i_(x.i_) { } int i_; }; Please see the question listed in function create. Thank you // Updated based on comments Yes, the code cannot pass the VC8.0 error C2664: 'std::auto_ptr<_Ty::auto_ptr(std::auto_ptr<_Ty &) throw()' : cannot convert parameter 1 from 'Fred *' to 'std::auto_ptr<_Ty &' The code was copied from the C++ FAQ 12.15. However, after making the following changes, replace return new Fred(i); with return auto_ptr<Fred>(new Fred(i)); This code can pass the VC8.0 compiler. But I am not sure whether or not this is a correct fix.

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• NHibernate.MappingException - Troubles Shooting Checklist (no persister for)

  - by Berryl

  Here's a starter list: 1) if hbm is hand generated, is it an embedded resource? 2) if using FNH, does it pass a PerssistenceSpecification test? 3) if not using FNH, can you save and then load the persisted class? 4) more? I'm sure many of you have gotten this one at one point or another. But have you ever gotten it when you knew your mapping was set up correctly? I started getting this exception after I started using a new repository design, but only in one scenario! PersistenceSpecification tests pass, as do all repository methods (using SQLite). The scenario that leads to the exception is when legacy projects from a different db are converted to green field system. The legacy system is from a different database and has it's own session factory, which should be irrelevant because the error comes after previously unconverted Projects are retrieved and in memory. As the routine tries to save these unconverted Projects into the new database, the exception is thrown, full stack trace below. Any ideas on how to build up the trouble shooting check list and solves this problem? Cheers, Berryl === the Exception trace ===== failed: NHibernate.MappingException : No persister for: Smack.ConstructionAdmin.Domain.Model.Projects.Project at NHibernate.Impl.SessionFactoryImpl.GetEntityPersister(String entityName) at NHibernate.Impl.SessionImpl.GetEntityPersister(String entityName, Object obj) at NHibernate.Engine.ForeignKeys.IsTransient(String entityName, Object entity, Nullable`1 assumed, ISessionImplementor session) at NHibernate.Event.Default.AbstractSaveEventListener.GetEntityState(Object entity, String entityName, EntityEntry entry, ISessionImplementor source) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.PerformSaveOrUpdate(SaveOrUpdateEvent event) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.OnSaveOrUpdate(SaveOrUpdateEvent event) at NHibernate.Impl.SessionImpl.FireSaveOrUpdate(SaveOrUpdateEvent event) at NHibernate.Impl.SessionImpl.SaveOrUpdate(Object obj) NHibernate\Repository\FabioNHibRepository.cs(46,0): at Smack.Core.Data.NHibernate.Repository.FabioNHibRepository`1.Add(T item) LegacyConversion\LegacyBatchUpdater.cs(20,0): at Smack.ConstructionAdmin.Data.LegacyConversion.LegacyBatchUpdater.ConvertOpenLegacyProjects(ILegacyProjectDao legacyProjectDao, IProjectRepository greenProjectRepository) Data\Brownfield\ProjectBatchUpdate_SQLiteTests.cs(19,0): at Smack.ConstructionAdmin.Tests.Data.Brownfield.ProjectBatchUpdate_SQLiteTests.Test()

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• Extending EF4 SQL Generation

  - by Basiclife

  Hi, We're using EF4 in a fairly large system and occasionally run into problems due to EF4 being unable to convert certain expressions into SQL. At present, we either need to do some fancy footwork (DB/Code) or just accept the performance hit and allow the query to be executed in-memory. Needless to say neither of these is ideal and the hacks we've sometimes had to use reduce readability / maintainability. What we would ideally like is a way to extend the SQL generation capabilities of the EF4 SQL provider. Obviously there are some things like .Net method calls which will always have to be client-side but some functionality like date comparisons (eg Group by weeks in Linq to Entities ) should be do-able. I've Googled but perhaps I'm using the wrong terminology as all I get is information about the new features of EF4 SQL Generation. For such a flexible and extensible framework, I'd be surprised if this isn't possible. In my head, I'm imagining inheriting from the [SQL 2008] provider and extending it to handle additional expressions / similar in the expression tree it's given to convert to SQL. Any help/pointers appreciated. We're using VS2010 Ultimate, .Net 4 (non-client profile) and EF4. The app is in ASP.Net and is running in a 64-Bit environment in case it makes a difference.

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• Compiling C lib and OCaml exe using it, all using ocamlfind

  - by Magnus

  I'm trying to work out how to use ocamlfind to compile a C library and an OCaml executable using that C library. I put together a set of rather silly example files. % cat sillystubs.c #include <stdio.h> #include <caml/mlvalues.h> #include <caml/memory.h> #include <caml/alloc.h> #include <caml/custom.h> value caml_silly_silly( value unit ) { CAMLparam1( unit ); printf( "%s\n", __FILE__ ); CAMLreturn( Val_unit ); } % cat silly.mli external silly : unit -> unit = "silly_silly" % cat foo.ml open Silly open String let _ = print_string "About to call into silly"; silly (); print_string "Called into silly" I believe the following is the way to compile up the library: % ocamlfind ocamlc -c sillystubs.c % ar rc libsillystubs.a sillystubs.o % ocamlfind ocamlc -c silly.mli % ocamlfind ocmalc -a -o silly.cma -ccopt -L${PWD} -cclib -lsillystubs Now I don't seem to be able to use the created library though: % ocamlfind ocamlc -custom -o foo foo.cmo silly.cma /usr/bin/ld: cannot find -lsillystubs collect2: ld returned 1 exit status File "_none_", line 1, characters 0-1: Error: Error while building custom runtime system The OCaml tools are somewhat mysterious to me, so any pointers would be most welcome.

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