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  • Concevoir la prochaine génération d'interface utilisateur multiplateformes avec Qt, un article de Jo

    Les interfaces graphiques de nos applications évoluent. Les widgets classiques sont progressivement remplacés par des images, plus explicites, plus agréables à regarder et plus conviviales. Qt 4.6 a apporté de nombreux outils permettant de faciliter le développement de telles applications. Cet article présente comment intégrer facilement des animations, des effets graphiques et des machines à états dans vos applications : http://qt-quarterly.developpez.com/q...generation-ui/ Découvrez également d'autres techniques dans nos précédents tutoriels écrits par la rédaction de Developpez (http://qt.develop...

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  • curious about the cached old domain

    - by jogesh_p
    i am a bit curious about my new Domain, actually i had a domain before let say http://example.com before expiration of that domain i bought a new one, with the name http://another-domain.com i uploaded all of my content on the second domain, but now when i search in google about some query related to my another-domain.com then i also find my old domain that is http://example.com is this provide the dulplicate content error to my http://another-domain.com ?? or any kind of penalty by Google

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  • Curious about a cached old domain

    - by jogesh_p
    I am a bit curious about my new domain. I had a domain before, let's say http://example.com/. Before expiration of that domain, I bought a new one with the name http://another-domain.com/. I uploaded all of my content on the second domain, but now when I search in Google about some query related to my http://another-domain.com/ site then I also find my old domain in the results. Will this give a duplicate content error for my new domain or any other kind of penalty from Google?

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  • C# 4: The Curious ConcurrentDictionary

    - by James Michael Hare
    In my previous post (here) I did a comparison of the new ConcurrentQueue versus the old standard of a System.Collections.Generic Queue with simple locking.  The results were exactly what I would have hoped, that the ConcurrentQueue was faster with multi-threading for most all situations.  In addition, concurrent collections have the added benefit that you can enumerate them even if they're being modified. So I set out to see what the improvements would be for the ConcurrentDictionary, would it have the same performance benefits as the ConcurrentQueue did?  Well, after running some tests and multiple tweaks and tunes, I have good and bad news. But first, let's look at the tests.  Obviously there's many things we can do with a dictionary.  One of the most notable uses, of course, in a multi-threaded environment is for a small, local in-memory cache.  So I set about to do a very simple simulation of a cache where I would create a test class that I'll just call an Accessor.  This accessor will attempt to look up a key in the dictionary, and if the key exists, it stops (i.e. a cache "hit").  However, if the lookup fails, it will then try to add the key and value to the dictionary (i.e. a cache "miss").  So here's the Accessor that will run the tests: 1: internal class Accessor 2: { 3: public int Hits { get; set; } 4: public int Misses { get; set; } 5: public Func<int, string> GetDelegate { get; set; } 6: public Action<int, string> AddDelegate { get; set; } 7: public int Iterations { get; set; } 8: public int MaxRange { get; set; } 9: public int Seed { get; set; } 10:  11: public void Access() 12: { 13: var randomGenerator = new Random(Seed); 14:  15: for (int i=0; i<Iterations; i++) 16: { 17: // give a wide spread so will have some duplicates and some unique 18: var target = randomGenerator.Next(1, MaxRange); 19:  20: // attempt to grab the item from the cache 21: var result = GetDelegate(target); 22:  23: // if the item doesn't exist, add it 24: if(result == null) 25: { 26: AddDelegate(target, target.ToString()); 27: Misses++; 28: } 29: else 30: { 31: Hits++; 32: } 33: } 34: } 35: } Note that so I could test different implementations, I defined a GetDelegate and AddDelegate that will call the appropriate dictionary methods to add or retrieve items in the cache using various techniques. So let's examine the three techniques I decided to test: Dictionary with mutex - Just your standard generic Dictionary with a simple lock construct on an internal object. Dictionary with ReaderWriterLockSlim - Same Dictionary, but now using a lock designed to let multiple readers access simultaneously and then locked when a writer needs access. ConcurrentDictionary - The new ConcurrentDictionary from System.Collections.Concurrent that is supposed to be optimized to allow multiple threads to access safely. So the approach to each of these is also fairly straight-forward.  Let's look at the GetDelegate and AddDelegate implementations for the Dictionary with mutex lock: 1: var addDelegate = (key,val) => 2: { 3: lock (_mutex) 4: { 5: _dictionary[key] = val; 6: } 7: }; 8: var getDelegate = (key) => 9: { 10: lock (_mutex) 11: { 12: string val; 13: return _dictionary.TryGetValue(key, out val) ? val : null; 14: } 15: }; Nothing new or fancy here, just your basic lock on a private object and then query/insert into the Dictionary. Now, for the Dictionary with ReadWriteLockSlim it's a little more complex: 1: var addDelegate = (key,val) => 2: { 3: _readerWriterLock.EnterWriteLock(); 4: _dictionary[key] = val; 5: _readerWriterLock.ExitWriteLock(); 6: }; 7: var getDelegate = (key) => 8: { 9: string val; 10: _readerWriterLock.EnterReadLock(); 11: if(!_dictionary.TryGetValue(key, out val)) 12: { 13: val = null; 14: } 15: _readerWriterLock.ExitReadLock(); 16: return val; 17: }; And finally, the ConcurrentDictionary, which since it does all it's own concurrency control, is remarkably elegant and simple: 1: var addDelegate = (key,val) => 2: { 3: _concurrentDictionary[key] = val; 4: }; 5: var getDelegate = (key) => 6: { 7: string s; 8: return _concurrentDictionary.TryGetValue(key, out s) ? s : null; 9: };                    Then, I set up a test harness that would simply ask the user for the number of concurrent Accessors to attempt to Access the cache (as specified in Accessor.Access() above) and then let them fly and see how long it took them all to complete.  Each of these tests was run with 10,000,000 cache accesses divided among the available Accessor instances.  All times are in milliseconds. 1: Dictionary with Mutex Locking 2: --------------------------------------------------- 3: Accessors Mostly Misses Mostly Hits 4: 1 7916 3285 5: 10 8293 3481 6: 100 8799 3532 7: 1000 8815 3584 8:  9:  10: Dictionary with ReaderWriterLockSlim Locking 11: --------------------------------------------------- 12: Accessors Mostly Misses Mostly Hits 13: 1 8445 3624 14: 10 11002 4119 15: 100 11076 3992 16: 1000 14794 4861 17:  18:  19: Concurrent Dictionary 20: --------------------------------------------------- 21: Accessors Mostly Misses Mostly Hits 22: 1 17443 3726 23: 10 14181 1897 24: 100 15141 1994 25: 1000 17209 2128 The first test I did across the board is the Mostly Misses category.  The mostly misses (more adds because data requested was not in the dictionary) shows an interesting trend.  In both cases the Dictionary with the simple mutex lock is much faster, and the ConcurrentDictionary is the slowest solution.  But this got me thinking, and a little research seemed to confirm it, maybe the ConcurrentDictionary is more optimized to concurrent "gets" than "adds".  So since the ratio of misses to hits were 2 to 1, I decided to reverse that and see the results. So I tweaked the data so that the number of keys were much smaller than the number of iterations to give me about a 2 to 1 ration of hits to misses (twice as likely to already find the item in the cache than to need to add it).  And yes, indeed here we see that the ConcurrentDictionary is indeed faster than the standard Dictionary here.  I have a strong feeling that as the ration of hits-to-misses gets higher and higher these number gets even better as well.  This makes sense since the ConcurrentDictionary is read-optimized. Also note that I tried the tests with capacity and concurrency hints on the ConcurrentDictionary but saw very little improvement, I think this is largely because on the 10,000,000 hit test it quickly ramped up to the correct capacity and concurrency and thus the impact was limited to the first few milliseconds of the run. So what does this tell us?  Well, as in all things, ConcurrentDictionary is not a panacea.  It won't solve all your woes and it shouldn't be the only Dictionary you ever use.  So when should we use each? Use System.Collections.Generic.Dictionary when: You need a single-threaded Dictionary (no locking needed). You need a multi-threaded Dictionary that is loaded only once at creation and never modified (no locking needed). You need a multi-threaded Dictionary to store items where writes are far more prevalent than reads (locking needed). And use System.Collections.Concurrent.ConcurrentDictionary when: You need a multi-threaded Dictionary where the writes are far more prevalent than reads. You need to be able to iterate over the collection without locking it even if its being modified. Both Dictionaries have their strong suits, I have a feeling this is just one where you need to know from design what you hope to use it for and make your decision based on that criteria.

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  • The curious case(s) of the Microsoft product naming department

    - by AaronBertrand
    A long time ago, in a galaxy far, far away... Okay, it was here on earth, a little over 5 years ago. With SQL Server 2005, Microsoft introduced a very useful feature called the DAC. DAC stands for "dedicated administrator connection"... you can read about it here , but essentially, it allows you a single connection into the server with priority resource allocation - so you can actually get in and kill a rogue process that is otherwise taking over the server. On its own this was a fine acronym choice,...(read more)

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  • The curious case of SOA Human tasks' automatic completion

    - by Kavitha Srinivasan
    A large south-Asian insurance industry customer using Oracle BPM and SOA ran into this. I have survived this ordeal previously myself but didnt think to blog it then. However, it seems like a good idea to share this knowledge with this reader community and so here goes.. Symptom: A human task (in a SOA/BPEL/BPM process) completes automatically while it should have been assigned to a proper user.There are no stack traces, no related exceptions in the logs. Why: The product is designed to treat human tasks that don't have assignees as one that is eligible for completion. And hence no warning/error messages are recorded in the logs. Usecase variant: A variant of this usecase, where an assignee doesnt exist in the repository is treated as a recoverable error. One can find this in the 'pending recovery' instances in EM and reactivate the task by changing the assignees in the bpm workspace as a process owner /administrator. But back to the usecase when tasks get completed automatically... When: This happens when the users/groups assigned to a task are 'empty' or null. This has been seen only on tasks whose assignees are derived from an assignment expression - ie at runtime an XPath is used to determine who to assign the task to. (This should not happen if task assignees are populated via swim-lane roles.) How to detect this in EM For instances that are auto-completed thus, one will notice in the Audit Trail of such instances, that the 'outcome' of the task is empty. The 'acquired by' element will also show as empty/null. Enabling the oracle.soa.services.workflow.* logger in em should print more verbose messages about this. How to fix this The application code needs two fixes: input to HT: The XSLT/XPath used  to set the task 'assignee' and the process itself should be enhanced to handle nulls better. For eg: if no-data-found, set assignees to alternate value, force default assignees etc. output from HT: Additionally, in the application code, check that the 'outcome' of the HT is not-null. If null, route the task to be performed again after setting the assignee correctly. Beginning PS4FP, one should be able to use 'grab' to route back to the task to fire again. Hope this helps. 

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  • Code Monster Helps Introduce Kids (and Curious Adults) to the Basics of Programming

    - by Jason Fitzpatrick
    If you’re looking for a fun way to introduce a kid to programming (or sate your own curiosity), Crunchzilla’s Code Monster is a real-time introduction to basic programming concepts. How does Code Monster work? Users are guided through the programming experience (using JavaScript) by a talkative blue monster that asks questions about the code and suggests courses of action. Play long enough and you travel from simple variables to more complex ideas like conditionals, expressions, and more. It’s not a comprehensive programming curriculum (nor does it claim to be) but it’s a great way to introduce people of all ages to programming. Hit up the link below to take it for a spin. Code Monster [via O'Reilly Radar] 8 Deadly Commands You Should Never Run on Linux 14 Special Google Searches That Show Instant Answers How To Create a Customized Windows 7 Installation Disc With Integrated Updates

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  • Curious About Oracle's BI and Analytics Strategy?

    - by Bob Zurek
    Normally we use this blog space for discussing our business intelligence and analytic efforts along with our views and perspective on this very fast growing marketplace. However, I can't resist mentioning that we are having a great webcast coming up next week, so please do join Oracle's Mark Hurd and Balaji Yelamanchili as they unveil the latest advances in Oracle's strategy for placing analytics into the hands of every one of your decision makers-so that they can see more, think smarter, and act faster. Register now at http://bit.ly/HpAOJk for the Webcast and Live Chat: Wednesday, April 4, 2012 at 9 a.m. PT, 12 p.m. ET, 10 a.m. GMT.  You don't want to miss this event and thank you very much. 

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  • just curious if anybody every tried this- hyper-v r2

    - by tony roth
    I have a server that san boots that I want to p2v. I have many options disk2vhd, scvmm etc but I was thinking about cloning the lun (flexclone, netapp) presenting it to my hyper-v r2 server. Within the hv manager do a create new disk then have it copy the cloned lun to a vhd file. Then do the bcdedit\bootsect stuff to it. Should work right? I'm also curious if anybodys booting vhd's that are on bootable luns? I've booted native vhd's just fine was just curious about the running them off a bootable lun. I think that this has quite a few advantages like instant p2v etc.. any thoughts on this? hmm dang as I was typing this I realized that I should not use the hv manager new disk copy routine, I should just disk2vhd the mounted lun. This has advantages in that it should be a lot faster!! thanks

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  • Curious problem using VirtualDub

    - by RCIX
    I have a simple video which i've cropped and trimmed down in VirtualDub. I've then re-saved it as AVI; however the video now plays very slowly/cchoppily in Windows Media Player. Is there any particular reason for this?

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  • Curious enigma of a network cable / connection / quality

    - by Foo Bar
    So, the situation is like this: I'm renting an apartment in a large house and I'm sharing internet with the landlord who lives downstairs. The internet is (in my best guess) optical 20/20Mbit. I don't know how it's all wired in his flat (haven't been there / seen it). Anyway, in my flat comes a cable which seems to be connected directly to the optic to ethernet router (and the password is the default one, so I have access, he he). There was a switch connected to that and to wires that go around the flat, and the wiring is terrible. It's even mixing phone and ethernet, and from what I see some cables are even interconnected!? Anyways, this cable that comes to my flat is very short. I can barely connect my computer on it, but if I do, I seem to get decent speed / performance. Not great, but decent. If, however, I connect switch to it (tried 2 different switches and a wifi switch) it's all blinking but I can't even connect to 192.168.1.1 (the router). DHCP fails, ping is losing 80-100% of replies. So I connected this cable directly to the other cable which goes to my work room, with a connector that has two female jacks and no electronics. Now when I connect my computer in my room, again, the performance is decent. When I connect WRT54GL (with tomato, DHCP disabled) to it and I plug a cable in this WRT and to my computer... the performance is gone. Download seems okay on Speedtest, but upload is .2Mbps and it's connecting forever. So what kind cable troll am I having here? Any ideas?

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  • curious ill conditioned numerical problem

    - by aaa
    hello. somebody today showed me this curious ill conditioned problem (apparently pretty famous), which looks relatively simple ƒ = (333.75 - a^2)b^6 + a^2 (11a^2 b^2 - 121b^4 - 2) + 5.5b^8 + a/(2^b) where a = 77617 and b = 33096 can you determine correct answer?

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  • [Haskell]Curious about the Hash Table problem

    - by astamatto
    I read that hash tables in haskell are crippled ( citation: http://flyingfrogblog.blogspot.com/2009/04/more-on-haskells-hash-table-problems.html ) and since i like haskell it worried me. Since the blog-post one year has passed and im curious, The hash table problem in haskell was "fixed" in the traditional compilers? (like ghc) ps: I love stack overflow, im a long time visitor but only today i decided to try to post a question.

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  • Curious redirection problem using location.href

    - by Jose M Balaguer
    I face a curious problem with redirection... Look at this small example: it works only if I add the alert() call after the redirection sentence! If I remove the alert() it does not work anymore!!! Any idea why (I'm using Firefox 3)? Thanks. <html> <script type="text/javascript"> function GotoPage() { location.href = "http://www.yahoo.com"; // Without this alert redirection does not work!!! alert("Hello!"); } </script> <body> <form> <button onclick="javascript:GotoPage()">Go</button> </form> </body> </html>

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  • Java curious Loop Performance

    - by user1680583
    I have a big problem while evaluate my java code. To simplify the problem I wrote the following code which produce the same curious behavior. Important is the method run() and given double value rate. For my runtime test (in the main method) I set the rate to 0.5 one times and 1.0 the other time. With the value 1.0 the if-statement will be executed in each loop iteration and with the value 0.5 the if-statement will be executed half as much. For this reason I expected longer runtime by the first case but opposite is true. Can anybody explain me this phenomenon?? The result of main: Test mit rate = 0.5 Length: 50000000, IF executions: 25000856 Execution time was 4329 ms. Length: 50000000, IF executions: 24999141 Execution time was 4307 ms. Length: 50000000, IF executions: 25001582 Execution time was 4223 ms. Length: 50000000, IF executions: 25000694 Execution time was 4328 ms. Length: 50000000, IF executions: 25004766 Execution time was 4346 ms. ================================= Test mit rate = 1.0 Length: 50000000, IF executions: 50000000 Execution time was 3482 ms. Length: 50000000, IF executions: 50000000 Execution time was 3572 ms. Length: 50000000, IF executions: 50000000 Execution time was 3529 ms. Length: 50000000, IF executions: 50000000 Execution time was 3479 ms. Length: 50000000, IF executions: 50000000 Execution time was 3473 ms. The Code public ArrayList<Byte> list = new ArrayList<Byte>(); public final int LENGTH = 50000000; public PerformanceTest(){ byte[]arr = new byte[LENGTH]; Random random = new Random(); random.nextBytes(arr); for(byte b : arr) list.add(b); } public void run(double rate){ byte b = 0; int count = 0; for (int i = 0; i < LENGTH; i++) { if(getRate(rate)){ list.set(i, b); count++; } } System.out.println("Length: " + LENGTH + ", IF executions: " + count); } public boolean getRate(double rate){ return Math.random() < rate; } public static void main(String[] args) throws InterruptedException { PerformanceTest test = new PerformanceTest(); long start, end; System.out.println("Test mit rate = 0.5"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(0.5); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } System.out.println("================================="); System.out.println("Test mit rate = 1.0"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(1.0); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } }

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  • WPF Textbox & Borders - curious resizing behavior

    - by CitizenParker
    The following XAML produces a window with strange behavior around the textbox: <Window x:Class="WpfSandbox.CuriousExample" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="CuriousExample" Height="300" Width="300"> <DockPanel Margin="15"> <TextBox BorderThickness="1" BorderBrush="#FF000000"></TextBox> </DockPanel> </Window> What happens, at least during my limited testing, is that the textbox renders with an inset border pattern (top/left is black, right/bottom is grey). However, when you resize to any position except the original, the entire textbox border goes to black. Whenever you return the window to the exact number of on-screen pixels the form had when it first loaded, it's inset again. I'm guessing it isn't pixel snapping as I can easily correct the problem with this code: <Window x:Class="WpfSandbox.CuriousExample" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="CuriousExample" Height="300" Width="300"> <DockPanel Margin="15"> <Border BorderThickness="1" BorderBrush="#FF000000"> <TextBox BorderThickness="0" ></TextBox> </Border> </DockPanel> </Window> Anyone care to venture an explanation as to what I'm seeing? Or is it all in my head? Like I said, the above workaround can resolve this problem - just trying to understand what is happening here. Thanks, -Scott

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  • Login Website, curious Cookie Problem

    - by Collin Peters
    Hello, Language: C# Development Environment: Visual Studio 2008 Sorry if the english is not perfect. I want to login to a Website and get some Data from there. My Problem is that the Cookies does not work. Everytime the Website says that I should activate Cookies but i activated the Cookies trough a Cookiecontainer. I sniffed the traffic serveral times for the login progress and I see no problem there. I tried different methods to login and I have searched if someone else have this Problem but no results... Login Page is: "www.uploaded.to", Here is my Code to Login in Short Form: private void login() { //Global CookieContainer for all the Cookies CookieContainer _cookieContainer = new CookieContainer(); //First Login to the Website HttpWebRequest _request1 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/login"); _request1.Method = "POST"; _request1.CookieContainer = _cookieContainer; string _postData = "email=XXXXX&password=XXXXX"; byte[] _byteArray = Encoding.UTF8.GetBytes(_postData); Stream _reqStream = _request1.GetRequestStream(); _reqStream.Write(_byteArray, 0, _byteArray.Length); _reqStream.Close(); HttpWebResponse _response1 = (HttpWebResponse)_request1.GetResponse(); _response1.Close(); //######################## //Follow the Link from Request1 HttpWebRequest _request2 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/login?coo=1"); _request2.Method = "GET"; _request2.CookieContainer = _cookieContainer; HttpWebResponse _response2 = (HttpWebResponse)_request2.GetResponse(); _response2.Close(); //####################### //Get the Data from the Page after Login HttpWebRequest _request3 = (HttpWebRequest)WebRequest.Create("http://uploaded.to/home"); _request3.Method = "GET"; _request3.CookieContainer = _cookieContainer; HttpWebResponse _response3 = (HttpWebResponse)_request3.GetResponse(); _response3.Close(); } I'm stuck at this problem since many weeks and i found no solution that works, please help...

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  • Curious to Know what Eclipse 'Show Heap Status' does

    - by GustlyWind
    Hi All In Eclipse (I am using 3.4 Ganymede) there is an option under Preferences>General>Show Heap Status which when checked shows near bottom of IDE like 46M of 98M and if we move the mouse over 'Recycle Bin' it says 'Run Garbage Collector'. I am curoius to know how this works.What will happen when 'Run Garbage Collector' is clicked. My enivroment set up is something like jdk6 is insatlled and IDE used for development and run in Tomcat server. So my understanding is all the objects which are run through Tomcat should be garbage collected. Is this correct. Is there a way to see what objects Eclipse identified as Garbage Cheers

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  • Curious about python installation paths, especially on OSX.

    - by chiggsy
    First: I'm running Macports. No problems with that, except: /opt/local/Library/Frameworks/Python.framework/Versions/2.6/bin which is the value of sys.exec_prefix, for my macports python even though: /opt/local/lib/python2.6/site-packages/ seems to be quite a logical place to put things, /opt/local being the macports --prefix, as it were. Why does easy_install put things in this odd Frameworks/Python.framework thing? More importantly, can i use the methods here, to ensure that all my systemwide python, particularly the scripts which I really want in /opt/local/bin, things I use all over the place like (i|b)python for example are accessible?

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  • VSC++, virtual method at bad adress, curious bug

    - by antoon.groenewoud
    Hello, This guy: virtual phTreeClass* GetTreeClass() const { return (phTreeClass*)m_entity_class; } When called, crashed the program with an access violation, even after a full recompile. All member functions and virtual member functions had correct memory adresses (I hovered mouse over the methods in debug mode), but this function had a bad memory adress: 0xfffffffc. Everything looked okay: the 'this' pointer, and everything works fine up until this function call. This function is also pretty old and I didn't change it for a long time. The problem just suddenly popped up after some work, which I commented all out to see what was doing it, without any success. So I removed the virtual, compiled, and it works fine. I add virtual, compiled, and it still works fine! I basically changed nothing, and remember that I did do a full recompile earlier, and still had the error back then. I wasn't able to reproduce the problem. But now it is back. I didn't change anything. Removing virtual fixes the problem. Sincerely, Antoon

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  • Why doesn't this list comprehension do what I expect it to do?

    - by Az
    The original list project_keys = sorted(projects.keys()) is [101, 102, 103, 104, 105, 106, 107, 108, 109, 110] where the following projects were deemed invalid this year: 108, 109, 110. Thus: for project in projects.itervalues(): # The projects dictionary is mapped to the Project class if project.invalid: # Where invalid is a Bool parameter in the Project class project_keys.remove(project.proj_id) print project_keys This will return a list of integers (which are project id's) as such: [101, 102, 103, 104, 105, 106, 107] Sweet. Now, I wanted it try the same thing using a list comprehension. project_keys = [project_keys.remove(project.proj_id) for project in projects.itervalues() if project.invalid print project_keys This returns: [None, None, None] So I'm populating a list with the same number as the removed elements but they're Nones? Can someone point out what I'm doing wrong? Additionally, why would I use a list comprehension over the for-if block at the top? Conciseness? Looks nicer?

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  • SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – T-SQL Example – Part 2 of 2

    - by pinaldave
    Yesterday I wrote a real world story of how a friend who thought they have an issue with intrusion or virus whereas the issue was really in the code. I strongly suggest you read my earlier blog post Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2 before continuing this blog post as this is second part of the first blog post. Let me reproduce the simple scenario in T-SQL. Building Sample Data USE [TestDB] GO -- Creating Table Products CREATE TABLE [dbo].[Products]( [ProductID] [int] NOT NULL, [ProductDesc] [varchar](50) NOT NULL, CONSTRAINT [PK_Products] PRIMARY KEY CLUSTERED ( [ProductID] ASC )) ON [PRIMARY] GO -- Creating Table ProductDetails CREATE TABLE [dbo].[ProductDetails]( [ProductDetailID] [int] NOT NULL, [ProductID] [int] NOT NULL, [Total] [int] NOT NULL, CONSTRAINT [PK_ProductDetails] PRIMARY KEY CLUSTERED ( [ProductDetailID] ASC )) ON [PRIMARY] GO ALTER TABLE [dbo].[ProductDetails] WITH CHECK ADD CONSTRAINT [FK_ProductDetails_Products] FOREIGN KEY([ProductID]) REFERENCES [dbo].[Products] ([ProductID]) ON UPDATE CASCADE ON DELETE CASCADE GO -- Insert Data into Table USE TestDB GO INSERT INTO Products (ProductID, ProductDesc) SELECT 1, 'Bike' UNION ALL SELECT 2, 'Car' UNION ALL SELECT 3, 'Books' GO INSERT INTO ProductDetails ([ProductDetailID],[ProductID],[Total]) SELECT 1, 1, 200 UNION ALL SELECT 2, 1, 100 UNION ALL SELECT 3, 1, 111 UNION ALL SELECT 4, 2, 200 UNION ALL SELECT 5, 3, 100 UNION ALL SELECT 6, 3, 100 UNION ALL SELECT 7, 3, 200 GO Select Data from Tables -- Selecting Data SELECT * FROM Products SELECT * FROM ProductDetails GO Delete Data from Products Table -- Deleting Data DELETE FROM Products WHERE ProductID = 1 GO Select Data from Tables Again -- Selecting Data SELECT * FROM Products SELECT * FROM ProductDetails GO Clean up Data -- Clean up DROP TABLE ProductDetails DROP TABLE Products GO My friend was confused as there was no delete was firing over ProductsDetails Table still there was a delete happening. The reason was because there is a foreign key created between Products and ProductsDetails Table with the keywords ON DELETE CASCADE. Due to ON DELETE CASCADE whenever is specified when the data from Table A is deleted and if it is referenced in another table using foreign key it will be deleted as well. Workaround 1: Design Changes – 3 Tables Change the design to have more than two tables. Create One Product Mater Table with all the products. It should historically store all the products list in it. No products should be ever removed from it. Add another table called Current Product and it should contain only the table which should be visible in the product catalogue. Another table should be called as ProductHistory table. There should be no use of CASCADE keyword among them. Workaround 2: Design Changes - Column IsVisible You can keep the same two tables. 1) Products and 2) ProductsDetails. Add a column with BIT datatype to it and name it as a IsVisible. Now change your application code to display the catalogue based on this column. There should be no need to delete anything. Workaround 3: Bad Advices (Bad advises begins here) The reason I have said bad advices because these are going to be bad advices for sure. You should make necessary design changes and not use poor workarounds which can damage the system and database integrity further. Here are the examples 1) Do not delete the data – well, this is not a real solution but can give time to implement design changes. 2) Do not have ON CASCADE DELETE – in this case, you will have entry in productsdetails which will have no corresponding product id and later on there will be lots of confusion. 3) Duplicate Data – you can have all the data of the product table move to the product details table and repeat them at each row. Now remove CASCADE code. This will let you delete the product table rows without any issue. There are so many things wrong this suggestion, that I will not even start here. (Bad advises ends here)  Well, did I miss anything? Please help me with your suggestions. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Curious about IObservable? Here’s a quick example to get you started!

    - by Roman Schindlauer
    Have you heard about IObservable/IObserver support in Microsoft StreamInsight 1.1? Then you probably want to try it out. If this is your first incursion into the IObservable/IObserver pattern, this blog post is for you! StreamInsight 1.1 introduced the ability to use IEnumerable and IObservable objects as event sources and sinks. The IEnumerable case is pretty straightforward, since many data collections are already surfacing as this type. This was already covered by Colin in his blog. Creating your own IObservable event source is a little more involved but no less exciting – here is a primer: First, let’s look at a very simple Observable data source. All it does is publish an integer in regular time periods to its registered observers. (For more information on IObservable, see http://msdn.microsoft.com/en-us/library/dd990377.aspx ). sealed class RandomSubject : IObservable<int>, IDisposable {     private bool _done;     private readonly List<IObserver<int>> _observers;     private readonly Random _random;     private readonly object _sync;     private readonly Timer _timer;     private readonly int _timerPeriod;       /// <summary>     /// Random observable subject. It produces an integer in regular time periods.     /// </summary>     /// <param name="timerPeriod">Timer period (in milliseconds)</param>     public RandomSubject(int timerPeriod)     {         _done = false;         _observers = new List<IObserver<int>>();         _random = new Random();         _sync = new object();         _timer = new Timer(EmitRandomValue);         _timerPeriod = timerPeriod;         Schedule();     }       public IDisposable Subscribe(IObserver<int> observer)     {         lock (_sync)         {             _observers.Add(observer);         }         return new Subscription(this, observer);     }       public void OnNext(int value)     {         lock (_sync)         {             if (!_done)             {                 foreach (var observer in _observers)                 {                     observer.OnNext(value);                 }             }         }     }       public void OnError(Exception e)     {         lock (_sync)         {             foreach (var observer in _observers)             {                 observer.OnError(e);             }             _done = true;         }     }       public void OnCompleted()     {         lock (_sync)         {             foreach (var observer in _observers)             {                 observer.OnCompleted();             }             _done = true;         }     }       void IDisposable.Dispose()     {         _timer.Dispose();     }       private void Schedule()     {         lock (_sync)         {             if (!_done)             {                 _timer.Change(_timerPeriod, Timeout.Infinite);             }         }     }       private void EmitRandomValue(object _)     {         var value = (int)(_random.NextDouble() * 100);         Console.WriteLine("[Observable]\t" + value);         OnNext(value);         Schedule();     }       private sealed class Subscription : IDisposable     {         private readonly RandomSubject _subject;         private IObserver<int> _observer;           public Subscription(RandomSubject subject, IObserver<int> observer)         {             _subject = subject;             _observer = observer;         }           public void Dispose()         {             IObserver<int> observer = _observer;             if (null != observer)             {                 lock (_subject._sync)                 {                     _subject._observers.Remove(observer);                 }                 _observer = null;             }         }     } }   So far, so good. Now let’s write a program that consumes data emitted by the observable as a stream of point events in a Streaminsight query. First, let’s define our payload type: class Payload {     public int Value { get; set; }       public override string ToString()     {         return "[StreamInsight]\tValue: " + Value.ToString();     } }   Now, let’s write the program. First, we will instantiate the observable subject. Then we’ll use the ToPointStream() method to consume it as a stream. We can now write any query over the source - here, a simple pass-through query. class Program {     static void Main(string[] args)     {         Console.WriteLine("Starting observable source...");         using (var source = new RandomSubject(500))         {             Console.WriteLine("Started observable source.");             using (var server = Server.Create("Default"))             {                 var application = server.CreateApplication("My Application");                   var stream = source.ToPointStream(application,                     e => PointEvent.CreateInsert(DateTime.Now, new Payload { Value = e }),                     AdvanceTimeSettings.StrictlyIncreasingStartTime,                     "Observable Stream");                   var query = from e in stream                             select e;                   [...]   We’re done with consuming input and querying it! But you probably want to see the output of the query. Did you know you can turn a query into an observable subject as well? Let’s do precisely that, and exploit the Reactive Extensions for .NET (http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx) to quickly visualize the output. Notice we’re subscribing “Console.WriteLine()” to the query, a pattern you may find useful for quick debugging of your queries. Reminder: you’ll need to install the Reactive Extensions for .NET (Rx for .NET Framework 4.0), and reference System.CoreEx and System.Reactive in your project.                 [...]                   Console.ReadLine();                 Console.WriteLine("Starting query...");                 using (query.ToObservable().Subscribe(Console.WriteLine))                 {                     Console.WriteLine("Started query.");                     Console.ReadLine();                     Console.WriteLine("Stopping query...");                 }                 Console.WriteLine("Stopped query.");             }             Console.ReadLine();             Console.WriteLine("Stopping observable source...");             source.OnCompleted();         }         Console.WriteLine("Stopped observable source.");     } }   We hope this blog post gets you started. And for bonus points, you can go ahead and rewrite the observable source (the RandomSubject class) using the Reactive Extensions for .NET! The entire sample project is attached to this article. Happy querying! Regards, The StreamInsight Team

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  • SQL SERVER – Curious Case of Disappearing Rows – ON UPDATE CASCADE and ON DELETE CASCADE – Part 1 of 2

    - by pinaldave
    Social media has created an Always Connected World for us. Recently I enrolled myself to learn new technologies as a student. I had decided to focus on learning and decided not to stay connected on the internet while I am in the learning session. On the second day of the event after the learning was over, I noticed lots of notification from my friend on my various social media handle. He had connected with me on Twitter, Facebook, Google+, LinkedIn, YouTube as well SMS, WhatsApp on the phone, Skype messages and not to forget with a few emails. I right away called him up. The problem was very unique – let us hear the problem in his own words. “Pinal – we are in big trouble we are not able to figure out what is going on. Our product details table is continuously loosing rows. Lots of rows have disappeared since morning and we are unable to find why the rows are getting deleted. We have made sure that there is no DELETE command executed on the table as well. The matter of the fact, we have removed every single place the code which is referencing the table. We have done so many crazy things out of desperation but no luck. The rows are continuously deleted in a random pattern. Do you think we have problems with intrusion or virus?” After describing the problems he had pasted few rants about why I was not available during the day. I think it will be not smart to post those exact words here (due to many reasons). Well, my immediate reaction was to get online with him. His problem was unique to him and his team was all out to fix the issue since morning. As he said he has done quite a lot out in desperation. I started asking questions from audit, policy management and profiling the data. Very soon I realize that I think this problem was not as advanced as it looked. There was no intrusion, SQL Injection or virus issue. Well, long story short first - It was a very simple issue of foreign key created with ON UPDATE CASCADE and ON DELETE CASCADE.  CASCADE allows deletions or updates of key values to cascade through the tables defined to have foreign key relationships that can be traced back to the table on which the modification is performed. ON DELETE CASCADE specifies that if an attempt is made to delete a row with a key referenced by foreign keys in existing rows in other tables, all rows containing those foreign keys are also deleted. ON UPDATE CASCADE specifies that if an attempt is made to update a key value in a row, where the key value is referenced by foreign keys in existing rows in other tables, all of the foreign key values are also updated to the new value specified for the key. (Reference: BOL) In simple words – due to ON DELETE CASCASE whenever is specified when the data from Table A is deleted and if it is referenced in another table using foreign key it will be deleted as well. In my friend’s case, they had two tables, Products and ProductDetails. They had created foreign key referential integrity of the product id between the table. Now the as fall was up they were updating their catalogue. When they were updating the catalogue they were deleting products which are no more available. As the changes were cascading the corresponding rows were also deleted from another table. This is CORRECT. The matter of the fact, there is no error or anything and SQL Server is behaving how it should be behaving. The problem was in the understanding and inappropriate implementations of business logic.  What they needed was Product Master Table, Current Product Catalogue, and Product Order Details History tables. However, they were using only two tables and without proper understanding the relation between them was build using foreign keys. If there were only two table, they should have used soft delete which will not actually delete the record but just hide it from the original product table. This workaround could have got them saved from cascading delete issues. I will be writing a detailed post on the design implications etc in my future post as in above three lines I cannot cover every issue related to designing and it is also not the scope of the blog post. More about designing in future blog posts. Once they learn their mistake, they were happy as there was no intrusion but trust me sometime we are our own enemy and this is a great example of it. In tomorrow’s blog post we will go over their code and workarounds. Feel free to share your opinions, experiences and comments. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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