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• C++ wxWidgets Event (Focus) Handling

  - by Wallter

  Due to comments I added the following code (in BasicPanel) Connect(CTRL_ONE, wxEVT_KILL_FOCUS, (wxObjectEventFunction)&BasicPanel::OnKillFocus); Connect(CTRL_TWO,wxEVT_KILL_FOCUS, (wxObjectEventFunction)&BasicPanel::OnKillFocus); Connect(CTRL_THREE, wxEVT_KILL_FOCUS, (wxObjectEventFunction)&BasicPanel::OnKillFocus); Connect(CTRL_FOUR, wxEVT_KILL_FOCUS, (wxObjectEventFunction)&BasicPanel::OnKillFocus); Connect(CTRL_FIVE, wxEVT_KILL_FOCUS, (wxObjectEventFunction)&BasicPanel::OnKillFocus); (enums) CTRL_NAME = wxID_HIGHEST + 5, // 6004 CTRL_ADDRESS = wxID_HIGHEST + 6, // 6005 CTRL_PHONENUMBER = wxID_HIGHEST + 7, // 6006 CTRL_SS = wxID_HIGHEST + 8, // 6007 CTRL_EMPNUMBER = wxID_HIGHEST + 9 // 6008 (The OnKillFocus Function - the declaration is included as suggested) void BasicPanel::OnKillFocus(wxFocusEvent& event) { switch (event.GetId()) { case 6004: ... break; ... ... ... } All of these added to the code do nothing when the user changes focus on which text box they are using... Q1:I am using wxWidgets (C++) and have come accost a problem that i can not locate any help. I have created several wxTextCtrl boxes and would like the program to update the simple calculations in them when the user 'kills the focus.' I could not find any documentation on this subject on the wxWidgets webpage and Googling it only brought up wxPython. The two events i have found are: EVT_COMMAND_KILL_FOCUS - EVT_KILL_FOCUS for neither of which I could find any snippet for. Could anyone give me a short example or lead me to a page that would be helpful? Q2:Would i have to create an event to handle the focus being killed for each of my 8 wxTextCtrl boxes? In the case that i have to create a different event: How would i get each event to differentiate from each other? I know i will have to create new wxID's for each of the wxTextCtrl boxes but how do I get the correct one to be triggered? class BasicPanel : public wxPanel { ... wxTextCtrl* one; wxTextCtrl* two; wxTextCtrl* three; wxTextCtrl* four; ... }

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• What about race condition in multithreaded reading?

  - by themoob

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

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• MSSQL: Views that use SELECT * need to be recreated if the underlying table changes

  - by cbp

  Is there a way to make views that use SELECT * stay in sync with the underlying table. What I have discovered is that if changes are made to the underlying table, from which all columns are to be selected, the view needs to be 'recreated'. This can be achieved simly by running an ALTER VIEW statement. However this can lead to some pretty dangerous situations. If you forgot to recreate the view, it will not be returning the correct data. In fact it can be returning seriously messed up data - with the names of the columns all wrong and out of order. Nothing will pick up that the view is wrong unless you happened to have it covered by a test, or a data integrity check fails. For example, Red Gate SQL Compare doesn't pick up the fact that the view needs to be recreated. To replicate the problem, try these statements: CREATE TABLE Foobar (Bar varchar(20)) CREATE VIEW v_Foobar AS SELECT * FROM Foobar INSERT INTO Foobar (Bar) VALUES ('Hi there') SELECT * FROM v_Foobar ALTER TABLE Foobar ADD Baz varchar(20) SELECT * FROM v_Foobar DROP VIEW v_Foobar DROP TABLE Foobar I am tempted to stop using SELECT * in views, which will be a PITA. Is there a setting somewhere perhaps that could fix this behaviour?

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• Cassandra Batch_insert example in C#.net

  - by Sandeep

  Can any one please give me an example on how to work on Cassandra batch_insert in C# thrift client? If possible please let me know where am I going wrong in the following code. Dictionary dictionary = new Dictionary(); Dictionary subColumns = new Dictionary(); List listOfMutations = new List(); listOfMutations.Add(new Mutation() { Column_or_supercolumn = new ColumnOrSuperColumn() { Column = new Column() { Name = utf8Encoding.GetBytes("AA"), Value = utf8Encoding.GetBytes("Answer Automation"), Timestamp = timeStamp } } }); listOfMutations.Add(new Mutation() { Column_or_supercolumn = new ColumnOrSuperColumn() { Column = new Column() { Name = utf8Encoding.GetBytes("CT"), Value = utf8Encoding.GetBytes("Call Tracker"), Timestamp = timeStamp } } }); listOfMutations.Add( new Mutation() { Column_or_supercolumn = new ColumnOrSuperColumn() { Column = new Column() { Name = utf8Encoding.GetBytes("TL"), Value = utf8Encoding.GetBytes("Track That Lead"), Timestamp = timeStamp } } }); SuperColumn superColumn = new SuperColumn() { Name=utf8Encoding.GetBytes("Indatus") }; subColumns.Add("Super1", listOfMutations); dictionary.Add("Indatus", subColumns); client.batch_mutate("Keyspace1",dictionary, ConsistencyLevel.ONE); I understand that SuperColumn struct expects List but I does not have a list of Columns. Rather I have List. Thanks in Advance.

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• Does Hibernate support one-to-one associations as pkeys?

  - by Andrzej Doyle

  Hi all, Can anyone tell me whether Hibernate supports associations as the pkey of an entity? I thought that this would be supported but I am having a lot of trouble getting any kind of mapping that represents this to work. In particular, with the straight mapping below: @Entity public class EntityBar { @Id @OneToOne(optional = false, mappedBy = "bar") EntityFoo foo // other stuff } I get an org.hibernate.MappingException: "Could not determine type for: EntityFoo, at table: ENTITY_BAR, for columns: [org.hibernate.mapping.Column(foo)]" Diving into the code it seems the ID is always considered a Value type; i.e. "anything that is persisted by value, instead of by reference. It is essentially a Hibernate Type, together with zero or more columns." I could make my EntityFoo a value type by declaring it serializable, but I wouldn't expect this would lead to the right outcome either. I would have thought that Hibernate would consider the type of the column to be integer (or whatever the actual type of the parent's ID is), just like it would with a normal one-to-one link, but this doesn't appear to kick in when I also declare it an ID. Am I going beyond what is possible by trying to combine @OneToOne with @Id? And if so, how could one model this relationship sensibly?

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• What is the performance impact of CSS's universal selector?

  - by Bungle

  I'm trying to find some simple client-side performance tweaks in a page that receives millions of monthly pageviews. One concern that I have is the use of the CSS universal selector (*). As an example, consider a very simple HTML document like the following: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> <title>Example</title> <style type="text/css"> * { margin: 0; padding: 0; } </head> <body> <h1>This is a heading</h1> <p>This is a paragraph of text.</p> </body> </html> The universal selector will apply the above declaration to the body, h1 and p elements, since those are the only ones in the document. In general, would I see better performance from a rule such as: body, h1, p { margin: 0; padding: 0; } Or would this have exactly the same net effect? Essentially, what I'm asking is if these rules are effectively equivalent in this case, or if the universal selector has to perform more unnecessary work that I may not be aware of. I realize that the performance impact in this example may be very small, but I'm hoping to learn something that may lead to more significant performance improvements in real-world situations. Thanks for any help!

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• Static Vs Non-Static Method Performance C#

  - by dotnetguts

  Hello All, I have few global methods declared in public class in my asp.net web application. I have habbit of declaring all global methods in public class in following format public static string MethodName(parameters) { } I want to know how it would impact on performance point of view? 1) Which one is Better? Static Method or Non-Static Method? 2) Reason why it is better? Following link shows Non-Static methods are good because, static methods are using locks to be Thread-safe. The always do internally a Monitor.Enter() and Monitor.exit() to ensure Thread-safety. http://bytes.com/topic/c-sharp/answers/231701-static-vs-non-static-function-performance And Following link shows Static Methods are good static methods are normally faster to invoke on the call stack than instance methods. There are several reasons for this in the C# programming language. Instance methods actually use the 'this' instance pointer as the first parameter, so an instance method will always have that overhead. Instance methods are also implemented with the callvirt instruction in the intermediate language, which imposes a slight overhead. Please note that changing your methods to static methods is unlikely to help much on ambitious performance goals, but it can help a tiny bit and possibly lead to further reductions. http://dotnetperls.com/static-method I am little confuse which one to use? Thanks

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• What is the procedure for debugging a production-only error?

  - by Lord Torgamus

  Let me say upfront that I'm so ignorant on this topic that I don't even know whether this question has objective answers or not. If it ends up being "not," I'll delete or vote to close the post. Here's the scenario: I just wrote a little web service. It works on my machine. It works on my team lead's machine. It works, as far as I can tell, on every machine except for the production server. The exception that the production server spits out upon failure originates from a third-party JAR file, and is skimpy on information. I search the web for hours, but don't come up with anything useful. So what's the procedure for tracking down an issue that occurs only on production machines? Is there a standard methodology, or perhaps category/family of tools, for this? The error that inspired this question has already been fixed, but that was due more to good fortune than a solid approach to debugging. I'm asking this question for future reference. Some related questions: Test accounts and products in a production system Running test on Production Code/Server

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• Usage of VIsual Memory Leak Detector

  - by Yan Cheng CHEOK

  I found a very interesting memory leak detector by using Visual C++. http://www.codeproject.com/KB/applications/visualleakdetector.aspx I try it out, but cannot make it works to detect a memory leak code. I am using MS Visual Studio 2008. Any step I had missed out? #include "stdafx.h" #include "vld.h" #include <iostream> void fun() { new int[1000]; } int _tmain(int argc, _TCHAR* argv[]) { fun(); std::cout << "lead?" << std::endl; getchar(); return 0; } The output when I run in debug mode is : ... ... 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.4053_x-ww_e6967989\msvcr80.dll', Symbols loaded. 'Test.exe': Loaded 'C:\WINDOWS\system32\msvcrt.dll', Symbols loaded (source information stripped). 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC90.DebugCRT_1fc8b3b9a1e18e3b_9.0.30729.1_x-ww_f863c71f\msvcp90d.dll', Symbols loaded. 'Test.exe': Loaded 'C:\Program Files\Visual Leak Detector\bin\dbghelp.dll', Symbols loaded (source information stripped). Visual Leak Detector Version 1.9d installed. No memory leaks detected. Visual Leak Detector is now exiting. The program '[5468] Test.exe: Native' has exited with code 0 (0x0).

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• BlackBerry Deployment Strategies

  - by cagreen

  I'm new to large scale BB app deployment and I'm looking for some clarification on the various methods of deployment. Please bear with me as I'm sure there is more to it than my naive view would lead me to believe. My app is very targeted to corporate users and requires a subscription to some additional services before it can be used. In other words, it's not targeted towards the consumer market, so I'm not worried about people not being able to easily find it online. What do I need to be aware of when looking at deployment strategies? Any gotchas? From my understanding my choices are: - App World small upfront vendor fee users can easily search for and find my app billing handled by RIM 4 licensing models (static, single, pool, dynamic). Though I'm not sure I've seen enough info on the pool and dynamic to fully appreciate how it might help me. - Download from my website billing is handled by me can I enforce the number of licenses that are in use within an organization? is this easier/harder for a user? - What else am I missing?

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• [C++][OpenMP] Proper use of "atomic directive" to lock STL container

  - by conradlee

  I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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• Recursive Iterators

  - by soandos

  I am having some trouble making an iterator that can traverse the following type of data structure. I have a class called Expression, which has one data member, a List<object>. This list can have any number of children, and some of those children might be other Expression objects. I want to traverse this structure, and print out every non-list object (but I do want to print out the elements of the list of course), but before entering a list, I want to return "begin nest" and after I just exited a list, I want to return "end nest". I was able to do this if I ignored the class wherever possible, and just had List<object> objects with List<object> items if I wanted a subExpression, but I would rather do away with this, and instead have an Expressions as the sublists (it would make it easier to do operations on the object. I am aware that I could use extension methods on the List<object> but it would not be appropriate (who wants an Evaluate method on their list that takes no arguments?). The code that I used to generate the origonal iterator (that works) is: public IEnumerator GetEnumerator(){ return theIterator(expr).GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is List<object>)){ yield return " begin nest "; foreach (var item in (List<object>)root){ foreach (var item2 in theIterator(item)){ yield return item2; } } yield return " end nest "; } else yield return root; } A type swap of List<object> for expression did not work, and lead to a stackOverflow error. How should the iterator be implemented? Update: Here is the swapped code: public IEnumerator GetEnumerator() { return this.GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is Expression)) { yield return " begin nest "; foreach (var item in (Expression)root) { foreach (var item2 in theIterator(item)) yield return item2; } yield return " end nest "; } else yield return root; }

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• Report Viewer Configuration error - In View Source of webpage

  - by sarada

  I found the following error message when I checked View source of the web page , but the web page works just fine. Our Test lead found the error while performing Assertion tests. Report Viewer Configuration Error The Report Viewer Web Control HTTP Handler has not been registered in the application's web.config file. Add <add verb=" * " path="Reserved.ReportViewerWebControl.axd" type = "Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> to the system.web/httpHandlers section of the web.config file, or add <add name="ReportViewerWebControlHandler" preCondition="integratedMode" verb="*" path="Reserved.ReportViewerWebControl.axd" type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> to the system.webServer/handlers section for Internet Information Services 7 or later Why is this error message coming up in view source.. Note:There is a div tag around this error message which has style="display:none" I am trying to find out why but everybody has only discussed this error message as one which is thrown in the webpage. The changes suggested to web.config are already present in our config file.

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• Django Interrupted system call when sending email

  - by mhost

  Hi, Sometimes, when submitting a form (pretty much any form on my site that sends me an email), I get the following error: File "/usr/lib/python2.5/smtplib.py", line 603, in starttls (resp, reply) = self.docmd("STARTTLS") File "/usr/lib/python2.5/smtplib.py", line 378, in docmd return self.getreply() File "/usr/lib/python2.5/smtplib.py", line 352, in getreply line = self.file.readline() File "/usr/lib/python2.5/socket.py", line 381, in readline data = self._sock.recv(self._rbufsize) error: (4, 'Interrupted system call') My code is sending email via gmail. I am also using django contact-form which does the same thing. The problem doesn't always happen. It seems very random. At one point today it got so bad that it displayed the error every time I submitted a form. Restarting apache fixes the problem for one submission and then it does it again. I have checked the RAM and there is plenty available (about 350MB available). Can someone lead me in the right direction? What does this error mean? What can I do to prevent this. Thanks.

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• Most awkward/misleading method in Java Base API ?

  - by JG

  I was recently trying to convert a string literal into a boolean, when the method "boolean Boolean.getBoolean(String name)" popped out of the auto-complete window. There was also another method ("boolean Boolean.parseBoolean(String s)") appearing right after, which lead me to search to find out what were the differences between these two, as they both seemed to do the same. It turns out that what Boolean.getBoolean(String name) really does is to check if there exists a System property (!) of the given name and if its value is true. I think this is very misleading, as I'm definitely not expecting that a method of Boolean is actually making a call to System.getProperty, and just by looking at the method signature, it sure looks (at least to me) like it should be used to parse a String as a boolean. Sure, the javadoc states it clearly, but I still think the method has a misleading name and is not in the right place. Other primitive type wrappers, such as Integer also have a similar method. Also, it doesn't seem to be a very useful method to belong in the base API, as I think it's not very common to have something like -Darg=true. Maybe it's a good question for a Java position interview: "What is the output of Boolean.getBoolean("true")?". I believe a more appropriate place for those methods would be in the System class, e.g., getPropertyAsBoolean; but again, I still think it's unnecessary to have these methods in the base API. It'd make sense to have these in something like the Properties class, where it's very common to do this kind of type conversions. What do you think of all this ? Also, if there's another "awkward" method that you're aware of, please post it. N.B. I know I can use Boolean.valueOf or Boolean.parseBoolean to convert a string literal into a boolean, but I'm just looking to discuss the API design.

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• Android Java writing text file to sd card

  - by Paul

  I have a strange problem I've come across. My app can write a simple textfile to SD card and sometimes it works for some people but not for others and I have no idea why. Some people it force closes if they put some characters like "..." in it and such. I cannot seem to reproduce it as I've had no troubles but this is the code that handles it. Can anyone think of something that may lead to problems or a better to way to do it? public void generateNoteOnSD(String sFileName, String sBody){ try { File root = new File(Environment.getExternalStorageDirectory(), "Notes"); if (!root.exists()) { root.mkdirs(); } File gpxfile = new File(root, sFileName); FileWriter writer = new FileWriter(gpxfile); writer.append(sBody); writer.flush(); writer.close(); Toast.makeText(this, "Saved", Toast.LENGTH_SHORT).show(); } catch(IOException e) { e.printStackTrace(); importError = e.getMessage(); iError(); } }

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• Why would paperclip not assign an ID to my uploaded photos?

  - by Trip

  I just deployed to a cluster server, and my delayed_jobs recipe was overwritten in the process. I solved that, delayed_jobs is up and running but can't find the ID of images that are uploaded. The images are saved correctly : Processing PhotosController#create (for 173.161.167.41 at 2010-06-01 05:09:14) [POST] Parameters: {"Filename"="1.jpg", "gallery_id"="1298", "action"="create", "amp"=nil, "authenticity_token"="qmbnpwFY8a5E3YtS/4fMWF/Z8evCE4hMxqKVJw0I7Ek=", "Upload"="Submit Query", "controller"="photos", "organization_id"="470", "_hq_channel_session"="BAh7CSIYdXNlcl9jcmVkZW50aWFsc19pZGkHIhV1c2VyX2NyZWRlbnRpYWxzIgGAOGRlZDc0NGJlOWU3NTNlNDFlYmVlMDdjMzIzYjA1ZjQxNGE5ZDY4YjNmYjFmNjNkMDQ2OWY2ZDQyOTljZDhiMDFlNmRkMDljNThmMzBmOWJhMTIwNDhkMDI5MTMxYmU5MDczYjIxZmI4YmQxMDVlMTBmNjZmOWFhODE1ZTBjMGM6EF9jc3JmX3Rva2VuIjFxbWJucHdGWThhNUUzWXRTLzRmTVdGL1o4ZXZDRTRoTXhxS1ZKdzBJN0VrPToPc2Vzc2lvbl9pZCIlMjAwMDQ3ZDQ3ZWUyZTgzODIxYzdjOGI3OTdmZGJiMDM=--ac6aa580262938bf5a4d6b9a740722b680eb5d48", "Filedata"=#} [paperclip] Saving attachments. [paperclip] saving /data/HQ_Channel/releases/20100530153454/public/system/photos/9253/original/1.jpg [paperclip] Saving attachments. [paperclip] Saving attachments. Completed in 127ms (View: 2, DB: 91) | 200 OK [http://invent.hqchannel.com/organizations/470/media/galleries/1298/photos?_hq_channel_session=BAh7CSIYdXNlcl9jcmVkZW50aWFsc19pZGkHIhV1c2VyX2NyZWRlbnRpYWxzIgGAOGRlZDc0NGJlOWU3NTNlNDFlYmVlMDdjMzIzYjA1ZjQxNGE5ZDY4YjNmYjFmNjNkMDQ2OWY2ZDQyOTljZDhiMDFlNmRkMDljNThmMzBmOWJhMTIwNDhkMDI5MTMxYmU5MDczYjIxZmI4YmQxMDVlMTBmNjZmOWFhODE1ZTBjMGM6EF9jc3JmX3Rva2VuIjFxbWJucHdGWThhNUUzWXRTLzRmTVdGL1o4ZXZDRTRoTXhxS1ZKdzBJN0VrPToPc2Vzc2lvbl9pZCIlMjAwMDQ3ZDQ3ZWUyZTgzODIxYzdjOGI3OTdmZGJiMDM%3D--ac6aa580262938bf5a4d6b9a740722b680eb5d48&authenticity_token=qmbnpwFY8a5E3YtS%2F4fMWF%2FZ8evCE4hMxqKVJw0I7Ek%3D] And then delayed_jobs keeps spinning around in circles on this one : 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob 2010-06-01T05:09:02-0700: * [JOB] delayed_job host:ip-10-251-197-159 pid:19994 failed with ActiveRecord::RecordNotFound: Couldn't find Photo with ID=9247 - 0 failed attempts 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob 2010-06-01T05:09:02-0700: * [JOB] delayed_job host:ip-10-251-197-159 pid:19994 failed with ActiveRecord::RecordNotFound: Couldn't find Photo with ID=9245 - 0 failed attempts 2010-06-01T05:09:02-0700: * [Worker(delayed_job host:ip-10-251-197-159 pid:19994)] acquired lock on PhotoJob So what I get is that the photos are not being assigned ID's by paperclip. Anyone know where I could poke and pry from here? UPDATE: I created a clone application on a single server. And there are no problems. The images on the cluster do show up (occassionally). If I keep clicking on the folders that lead to photos, it will 50% of the time return a 404 with it not being able to find the photo, and the other half it will present the photo. So the problem has got to be with the server interaction between the ActiveRecord through multiple servers.

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• How to catch unintentional function interpositioning?

  - by SiegeX

  Reading through my book Expert C Programming, I came across the chapter on function interpositioning and how it can lead to some serious hard to find bugs if done unintentionally. The example given in the book is the following: my_source.c mktemp() { ... } main() { mktemp(); getwd(); } libc mktemp(){ ... } getwd(){ ...; mktemp(); ... } According to the book, what happens in main() is that mktemp() (a standard C library function) is interposed by the implementation in my_source.c. Although having main() call my implementation of mktemp() is intended behavior, having getwd() (another C library function) also call my implementation of mktemp() is not. Apparently, this example was a real life bug that existed in SunOS 4.0.3's version of lpr. The book goes on to explain the fix was to add the keyword static to the definition of mktemp() in my_source.c; although changing the name altogether should have fixed this problem as well. This chapter leaves me with some unresolved questions that I hope you guys could answer: Does GCC have a way to warn about function interposition? We certainly don't ever intend on this happening and I'd like to know about it if it does. Should our software group adopt the practice of putting the keyword static in front of all functions that we don't want to be exposed? Can interposition happen with functions introduced by static libraries? Thanks for the help. EDIT I should note that my question is not just aimed at interposing over standard C library functions, but also functions contained in other libraries, perhaps 3rd party, perhaps ones created in-house. Essentially, I want to catch any instance of interpositioning regardless of where the interposed function resides.

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• Proper QUuid usage in Qt ? (7-Zip DLL usage problems (QLibrary, QUuid GUID conversion, interfaces))

  - by whipsnap

  Hi, I'm trying to write a program that would use 7-Zip DLL for reading files from inside archive files (7z, zip etc). Here's where I'm so far: #include QtCore/QCoreApplication #include QLibrary #include QUuid #include iostream using namespace std; #include "7z910/CPP/7zip/Archive/IArchive.h" #include "7z910/CPP/7zip/IStream.h" #include "MyCom.h" // {23170F69-40C1-278A-1000-000110070000} QUuid CLSID_CFormat7z(0x23170F69, 0x40C1, 0x278A, 0x10, 0x00, 0x00, 0x01, 0x10, 0x07, 0x00, 0x00); typedef int (*CreateObjectFunc)( const GUID *clsID, const GUID *interfaceID, void **outObject); void readFileInArchive() { QLibrary myLib("7z.dll"); CreateObjectFunc myFunction = (CreateObjectFunc)myLib.resolve("CreateObject"); if (myFunction == 0) { cout outArchive; myFunction(&CLSID_CFormat7z, &IID_IOutArchive, (void **)&outArchive); } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); readFileInArchive(); return a.exec(); } Trying to build that in Qt Creator will lead to following error: cannot convert 'QUuid*' to 'const GUID*' in argument passing How should QUuid be correctly used in this context? Also, being a C++ and Qt newbie I haven't yet quite grasped templates or interfaces, so overall I'm having trouble getting through these first steps. If someone could give tips or even example code on how for example an image file could be extracted from ZIP file (to be shown in Qt GUI later on*), I would highly appreciate that. My main goal at the moment is to write a program with GUI for selecting archive files containing image files (PNG, JPG etc) and displaying those files one at a time in the GUI. A Qt based CDisplayEx in short.

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• Should a C++ constructor do real work?

  - by Wade Williams

  I'm strugging with some advice I have in the back of my mind but for which I can't remember the reasoning. I seem to remember at some point reading some advice (can't remember the source) that C++ constructors should not do real work. Rather, they should initialize variables only. The advice when on to explain that real work should be done in some sort of init() method, to be called separately after the instance was created. The situation is I have a class that represents a hardware device. It makes logical sense to me for the constructor to call the routines that query the device in order to build up the instance variables that describe the device. In other words, once new instantiates the object, the developer receives an object which is ready to be used, no separate call to object-init() required. Is there a good reason why constructors shouldn't do real work? Obviously it could slow allocation time, but that wouldn't be any different if calling a separate method immediately after allocation. Just trying to figure out what gotchas I not currently considering that might have lead to such advice.

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• Hibernate: fetching multiple bags efficiently

  - by Jens Jansson

  Hi! I'm developing a multilingual application. For this reason many objects have in their name and description fields collections of something I call LocalizedStrings instead of plain strings. Every LocalizedString is basically a pair of a locale and a string localized to that locale. Let's take an example an entity, let's say a book -object. public class Book{ @OneToMany private List<LocalizedString> names; @OneToMany private List<LocalizedString> description; //and so on... } When a user asks for a list of books, it does a query to get all the books, fetches the name and description of every book in the locale the user has selected to run the app in, and displays it back to the user. This works but it is a major performance issue. For the moment hibernate makes one query to fetch all the books, and after that it goes through every single object and asks hibernate for the localized strings for that specific object, resulting in a "n+1 select problem". Fetching a list of 50 entities produces about 6000 rows of sql commands in my server log. I tried making the collections eager but that lead me to the "cannot simultaneously fetch multiple bags"-issue. Then I tried setting the fetch strategy on the collections to subselect, hoping that it would do one query for all books, and after that do one query that fetches all LocalizedStrings for all the books. Subselects didn't work in this case how i would have hoped and it basically just did exactly the same as my first case. I'm starting to run out of ideas on how to optimize this. So in short, what fetching strategy alternatives are there when you are fetching a collection and every element in that collection has one or multiple collections in itself, which has to be fetch simultaneously.

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• PHP Object Access Syntax Question with the $

  - by ImperialLion

  I've been having trouble searching for this answer because I am not quite sure how to phrase it. I am new to PHP and still getting my feet on the ground. I was writing a page with a class in it that had the property name. When I originally wrote the page there was no class so I just had a variable called $name. When I went to encapsulate it in a class I accidental changed it to be $myClass->$name. It tool me a while to realize that the syntax I needed was $myClass->name. The reason it took so long was the error I kept getting was "Attempt to access a null property" or something along those lines. The error lead me to believe it was a data population error. My question is does $myClass->$name have a valid meaning? In other words is there a time you would use this and a reason why it doesn't create a syntax error? If so what is the semantic meaning of that code? When would I use it if it is valid? If its not valid, is there a reason that it doesn't create a syntax error?

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• Why represent shopping carts and order invoices differently in a domain model?

  - by Todd

  I've built some shopping cart systems in the past, but I always designed them such that the final order invoice is just a shopping cart that has been marked as "purchased". All the logic for adding/removing/changing items in a cart is also the logic for the order. All data is stored in the same tables in the database. But it seems this is not the proper way to design an e-commerce site.. Can someone explain the benefit of separating the shopping cart from invoices in the domain model? It seems to me this would lead to a lot of duplicated code, an extra set of tables in the database, and make it harder to maintain in the event the system need to start accommodating more complicated orders (like specifying selected options for an item which may or may not change the price/availability/shipping time of the order). I'm assuming I just haven't seen the light, as every book and other example I see seems to separate these two seemingly similar concerns -- but I can't find any explanation as to the benefit of doing such! It's also the case in the systems that I design that changes are often made after the initial order is confirmed. It's not uncommon for items to be removed, replaced, or added afterwards (but prior to fulfillment).

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• How to catch unintentional function interpositioning with GCC?

  - by SiegeX

  Reading through my book Expert C Programming, I came across the chapter on function interpositioning and how it can lead to some serious hard to find bugs if done unintentionally. The example given in the book is the following: my_source.c mktemp() { ... } main() { mktemp(); getwd(); } libc mktemp(){ ... } getwd(){ ...; mktemp(); ... } According to the book, what happens in main() is that mktemp() (a standard C library function) is interposed by the implementation in my_source.c. Although having main() call my implementation of mktemp() is intended behavior, having getwd() (another C library function) also call my implementation of mktemp() is not. Apparently, this example was a real life bug that existed in SunOS 4.0.3's version of lpr. The book goes on to explain the fix was to add the keyword static to the definition of mktemp() in my_source.c; although changing the name altogether should have fixed this problem as well. This chapter leaves me with some unresolved questions that I hope you guys could answer: Should our software group adopt the practice of putting the keyword static in front of all functions that we don't want to be exposed? Does GCC have a way to warn about function interposition? We certainly don't ever intend on this happening and I'd like to know about it if it does. Can interposition happen with functions introduced by static libraries? Thanks for the help.

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• Problem when compressing SWF in Linux with java.util.zip

  - by CaioToOn

  Hi! I've created a servlet that changes the binaries of a SWF file and output it to the user. The SWF is compressed by ZLIB by default. Then I inflate, change the binaries, deflate and output the result. Everything was running right on a Windows Server 2008 (also in 2003). Currently, we need change the server to Linux, and then, this servlet is somehow outputing a corrupted SWF File... what could be the problem? What intrigues me more is that there is no difference between the Windows and Linux servlet versions. Is there any undocumented linux specific behaviour for the java.util.zip package? My Windows Server is (where the servlet is working): Windows Server 2008 (6.0 - x86) Apache 2.2.11 Tomcat 6.0.16.0 Java JDK 1.6.0_12-b04 My CentOS Server is (where te servlet doesn't work) CentOS 5.4 (2.6.18-164.15.1.el5 - i386) Apache 2.2.3 Tomcat 6.0.16.0 Java JDK 1.6.0_12-b04 Any lead would be appreciated! Cheers, CaioToOn!

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