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• Reading and writing to SysV shared memory without synchronization (use of semaphores, C/C++, Linux)

  - by user363778

  Hi, I use SysV shared memory to let two processes communicate with each other. I do not want the code to become to complex so I wondered if I really had to use semaphores to synchronize the access to the shared memory. In my C/C++ program the parent process reads from the shared memory and the child process writes to the shared memory. I wrote two test applications to see if I could produce some kind of error like a segmentation fault, but I couldn't (Ubuntu 10.04 64bit). Even two processes writing non stop in a while loop to the same shared memory did not produce any error. I hope someone has experience concerning this matter and can tell me if I really must use semaphores to synchronize the access or if I am OK without synchronization. Thanks

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• Set Pivot Items from Cell Range? Excel 2007

  - by Ben

  I have developed code which identifies the multiple item selections from a Pivot field and writes the list of items to a table. I then wish to take this contents of the list and use it to populate a number of other Pivot Tables on other tabs. I currently have the ability to do this for single Pivot items selections, but I need to do this for multiple selections. If I select multiple items in the Pivot Table and attempt to pass these selections to the other Pivot Tables it creates an error because it sees only hte text "Multiple Items" instead of a list of each item that was checked in the upstream Pivot field. I need some VBA code that allows me to use the list to set another Pivot Field's selections. All the Pivot fields in question here are page fields. I am using Excel 2007. Any help is appreciated. Thanks!

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• Cuda program results are always zero in HW, correct in EMU??

  - by Orion Nebula

  Hi all! I am having a weird problem .. I have written a CUDA code which executes correctly in emulation and all results show up.. however, when executed on hardware "G210" .. the results in the result memory are always 0 I am passing two vectors to the kernel, one with random variables the other is initialized to zero, the code copies the first vector to shared memory, does some swapping and other operations and then writes back the results on the second vector (the one with the initial 0's) I am using double precision, the -arch sm13 flag is used, all memory allocation also use sizeof(double) .. I have checked if the kernel is invoked, it does .. so no problems here .. the cudaMemCpy has no problems .. what could be the problem .. :( why would it work in emulation but not on HW I am quite confused .. any ideas?

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• Unresponsive UI when using BeginInvoke

  - by Kazoom

  Bckground I have a networked application written in C#. my server program has a UI and several communication threads, that read from tcp sockets and display messages on controller UI. Communication with each client is done through a seprate thread. When i recieve some stream of messages from one client , the thread for that client writes on UI, which is a richtextbox on a Form. I call SetTextHelper(string text) method of the form. which looks like this private delegate void MyTextUpdateHandler(string text); public void SetTextHelper(string text) { BeginInvoke(new MyTextUpdateHandler(SetText), new object[] { text }); } public setText(string text) { richtext.Text= text; } Question - If i use BeginInvoke my UI is entirely unresponsive when i m writing large stream of data to UI - Invoke solves that problem, but i read that for multi threaded environment where many thereads are sharing same resource Invoke can lead to deadlocks I share the common ichtextbox between around 16 threads - What would be a good desing for my situation?

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• How to implement a mailing system with Rails that sends emails in the background

  - by Tam

  I want to implement a reliable mailing system with Ruby on Rails that sends emails in the background as sending email sometimes takes like 10 seconds or more so I don't want the user to wait. Some ideas I thought of: 1- Write to a table in DB a have a background process that go over and send email (concern: potential many reads/writes to DB slows down my application) 2- Messaging Queue background process / Rake task (concern: if server crashes queued mails will be lost also might eat up a lot of memory if many emails) I was wondering if you a know of a good solution that provides a balance between reliability and performance.

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• How to integrate an open source C program instead of calling its executable through a system call?

  - by ihamer

  I have an executable (fossil scm) that is being invoked by my program externally through ::CreateProcess windows call. The stdout and stderr are then captured. Since the source code for fossil is available, I would prefer to create a static library out of it and issue calls directly. Currently, communication to fossil is done through the command line parameters, and the communication back is through the process return code, stdout and stderr. Fossil writes to stdout/err through printf and fprintf calls. What is the best way to solve this with minimum alteration of fossil source? Is there a reliable and cross-platform way to intercept stdout/err and send it into a memory buffer?

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• Sharing some info with all DLLs pulled into a process

  - by JBRWilkinson

  Hi all, We've got an Enterprise system which has many processes (EXEs, services, DCOM servers, COM+ apps, ISAPI, MMC snapins) all of which make use of many COM components. We've recently seen failures in some of the customer deployments, but are finding it hard to troubleshoot the cause. In order to track down the problem, we've augmented the entire source with logging statements where errors occur. In order to identify which logs came from what processes, the C++ logging code (compiled into all components) uses the EXE name to name the log. This is good for some cases, but not all - COM+ apps, ISAPI and MMC snapins all have system EXE names and the logs end up interleaved. I saw this post about shared data sections which might help, but what I don't understand is who decides what goes in the shared section. Is there any way I can guarantee that a particular piece of code writes into the shared section before anyone else reads it? Or is there a better solution to this problem?

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• Use stringWithFormat: as a file path in cocoa

  - by Cam

  Hello, I'm having a problem with a cocoa application that takes the value of a text field, and writes it to a file. The file path is made using stringWithFormat: to combine 2 strings. For some reason it will not create the file and the console says nothing. Here is my code: //Get the values of the text field NSString *fileName = [fileNameTextField stringValue]; NSString *username = [usernameTextField stringValue]; //Use stringWithFormat: to create the file path NSString *filePath = [NSString stringWithFormat:@"~/Library/Application Support/Test/%@.txt", fileName]; //Write the username to filePath [username writeToFile:filePath atomically:YES]; Thanks for any help

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• How can two threads access a common array of buffers with minimal blocking ? (c#)

  - by Jelly Amma

  Hello, I'm working on an image processing application where I have two threads on top of my main thread: 1 - CameraThread that captures images from the webcam and writes them into a buffer 2 - ImageProcessingThread that takes the latest image from that buffer for filtering. The reason why this is multithreaded is because speed is critical and I need to have CameraThread to keep grabbing pictures and making the latest capture ready to pick up by ImageProcessingThread while it's still processing the previous image. My problem is about finding a fast and thread-safe way to access that common buffer and I've figured that, ideally, it should be a triple buffer (image[3]) so that if ImageProcessingThread is slow, then CameraThread can keep on writing on the two other images and vice versa. What sort of locking mechanism would be the most appropriate for this to be thread-safe ? I looked at the lock statement but it seems like it would make a thread block-waiting for another one to be finished and that would be against the point of triple buffering. Thanks in advance for any idea or advice. J.

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• Capturing stdout within the same process in Python

  - by danben

  I've got a python script that calls a bunch of functions, each of which writes output to stdout. Sometimes when I run it, I'd like to send the output in an e-mail (along with a generated file). I'd like to know how I can capture the output in memory so I can use the email module to build the e-mail. My ideas so far were: use a memory-mapped file (but it seems like I have to reserve space on disk for this, and I don't know how long the output will be) bypass all this and pipe the output to sendmail (but this may be difficult if I also want to attach the file)

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• MCV/MVP Patterns and Applications that interface with Hardware (DAQ/PLC/etc)

  - by Ryan

  I've been reading a lot about the MCV and MVP patterns for use with UI and it seems like a really nice powerful way to handle user interfaces. I am - however - having a difficult time deciding how this could integrate into a system where data in the model is created from a Data Acquisition System or Serial/Ethernet devices. There is also the added step that 70% of application interaction is performed by a PLC instead of a live user. It seems that for apps that just read/write & manipulate information from a database this works great, but how does does hardware and automation fit into these patterns? Is it as simple as another controller (for lack of a better term) that interacts with hardware that manipulates data and writes to a model? Maybe I am over thinking this or thinking too simply, so any advice would be great. I'm not quite sure where I'm going with this, so if something doesn't make sense or I was too vague leave me a comment. Thanks!

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• Connecting to MSSQL Express in silverlight 4 appl, the db doesn't shows up in Management Studio Expr

  - by Gabriel

  I'm using MSSQLExpress named instance in my Silverlight 4 application. The database located in the web application data folder. I attached the db via VS2010. The program works, but the db doesn't show up in Management Studio Express. If I delete the connection from within VS2010, and Try to attach to db via Management Studio Express, on writes, that the database with same the name already exists. Why the database connected via VS2010 doesn't show up in Management Studio Express? Thanks in advance Gabor

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• How to store the result of a JSP in a string?

  - by Spines

  I want to store the result of a JSP in a string. For example, I want to be able to call a function like: String result = ProcessJsp("/jspfile.jsp"); Also, this must be rather efficient. Making a url request to the jsp and then storing it would definitely be too slow. How could I do this? Here are my thoughts on how to do this, though I'm not sure if it would work, and I'm hoping there is something simpler: Do RequestDispatcher("/jspfile.jsp").include(hreq, hresp), but instead of putting the real HttpResponse object in there, you put your own where the getWriter() method returns something that writes to your String or a memory buffer, etc.

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• Question regarding Ajax Hacking

  - by Vincent

  All, I have a PHP website written in Zend Framework and MVC. Most of the controller actions check if the request is an Ajax request or not, else they redirect the user to home page. I am thinking about various ways to break that site. I am considering the following scenario: A user creates his own PHP project on his Local machine. User writes a JQuery ajax post request to one of the controllers on my site and tries to post malicious info. Ex: $.ajax({ type: 'POST', url: "https://marketsite/getinfo/getstuff", cache: false, dataType: "html", success: function(html_response){ alert(html_response); }, error: function(xhr,ajaxOptions,errorThrown){ alert(errorThrown); } }); My Question is does "url" attribute in the ajax request above take absolute path? I know it takes relative path. Also, is it possible to break any site by sending such requests? Thanks

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• ASP.NET MCV 2 controller-url problems

  - by cc0

  I am still very new to the MVC framework, but I managed to create a controller that reads from a database and writes JSON to an url; host.com/Controllername?minValue=something&maxValue=something However when I move the site to a subfolder; host.com/mvc/ it doesn't seem to be able to call the controller from there when I do it like this; host.com/mvc/Procedure?minValue=something&maxValue=something Did I forget to do something somewhere to make this url call valid from that subfolder? Any help here would be greatly appreciated.

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• entity framework and dirty reads

  - by bryanjonker

  I have Entity Framework (.NET 4.0) going against SQL Server 2008. The database is (theoretically) getting updated during business hours -- delete, then insert, all through a transaction. Practically, it's not going to happen that often. But, I need to make sure I can always read data in the database. The application I'm writing will never do any types of writes to the data -- read-only. If I do a dirty read, I can always access the data; the worst that happens is I get old data (which is acceptable). However, can I tell Entity Framework to always use dirty reads? Are there performance or data integrity issues I need to worry about if I set up EF this way? Or should I take a step back and see about rewriting the process that's doing the delete/insert process?

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• Best way to collect and store data daily?

  - by mktb

  I have a bunch of statistics: # of users, # of families, ratio user/family, etc. I'd like to store these daily so I can view this data historically. However, I'm looking for the most effective way to store this data. Should I run a cron job that writes to the database DATE: today USERS: 123 FAMILIES: 456 RATIO: 7.89 or whatever? (or should I write multiple rows like DATE: today DATATYPE: users VALUE: 123?) Or is there another option I can use that is more efficient or more effective? Thanks!

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• What is the optimal number of threads for performing IO operations in java?

  - by marc

  In Goetz's "Java Concurrency in Practice", in a footnote on page 101, he writes "For computational problems like this that do not I/O and access no shared data, Ncpu or Ncpu+1 threads yield optimal throughput; more threads do not help, and may in fact degrade performance..." My question is, when performing I/O operations such as file writing, file reading, file deleting, etc, are there guidelines for the number of threads to use to achieve maximum performance? I understand this will be just a guide number, since disk speeds and a host of other factors play into this. Still, I'm wondering: can 20 threads write 1000 separate files to disk faster than 4 threads can on a 4-cpu machine?

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• mysqli and php requesting rows returned in object oriented scripting...

  - by Matt

  in object oriented php mysqli I am trying to request a username, and return if it matches a row, without actually returning any user data. How would I write this?...so far I have... $sql = "SELECT NULL FROM database WHERE usernick=?"; $stmt = $link->prepare($sql) $stmt->bind_param('s', $snr); $stmt->execute(); After this step I need to see if a row matched the query...but I have no idea how to write it, everyone here pretty much writes in mysql if I dont mention I want object oriented mysqli :S

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• PDF Viewer Showing Last Page...

  - by steve

  I have a asp.net app that writes a pdf to file. Then, later that file is opened into a window (standard acrobat reader) for viewing. No problems there. The weird part... The entire document loads as it should, but the Reader initially shows the last page in the document on the screen. The user must then scroll up to the first page. It doesn't happen all the time (about 50%) and occurs across several test computers. Is there a switch in the code I'm suppose to use in creating the file or displaying the file to tell the reader to "start displaying the document on the first page?" Environment particulars: asp.net 3.5 vb, websupergoo's abcpdf.net pro 7 (assembly that creates the pdf file), Windows 2008 Server, IIS7 Thanks

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• Python - network buffer handling question...

  - by Patrick Moriarty

  Hi, I want to design a game server in python. The game will mostly just be passing small packets filled with ints, strings, and bytes stuffed into one message. As I'm using a different language to write the game, a normal packet would be sent like so: Writebyte(buffer, 5); // Delimit type of message Writestring(buffer, "Hello"); Sendmessage(buffer, socket); As you can see, it writes the bytes to the buffer, and sends the buffer. Is there any way to read something like this in python? I am aware of the struct module, and I've used it to pack things, but I've never used it to actually read something with mixed types stuck into one message. Thanks for the help.

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• Use google analytics custom events for feedback form.

  - by chacko

  I was thinking of having a simple feedback form in my website. It would be something like: Your Feedback will help us improve. [ ] and then a textfield/textarea where the user can type (let's say) up to 100 characters of feedback. Rather than handling it all myself on the serverside I was thinking to use google analytics (since my site is already wireup) and everytime a user writes a comment send a custom event to google analytics. I think it might work. Can people suggest a better approach or point out any problem with this idea thanks

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• C++ program runs slow in VS2008

  - by Nima

  I have a program written in C++, that opens a binary file(test.bin), reads it object by object, and puts each object into a new file (it opens the new file, writes into it(append), and closes it). I use fopen/fclose, fread and fwrite. test.bin contains 20,000 objects. This program runs under linux with g++ in 1 sec but in VS2008 in debug/release mode in 1min! There are reasons why I don't do them in batches or don't keep them in memory or any other kind of optimizations. I just wonder why it is that much slow under windows. Thanks,

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• C# StringBuilder question

  - by andrew

  in a C# file i have a class Archiver { [DllImport("Archiver.dll")] public static extern void archive(string data, StringBuilder response); } string data is an input, and StringBuilder response is where the function writes something the archive function prototype (written in C) looks like this: void archive(char * dataChr, char * outChr); and it receives a string in dataChr, and then does a strcpy(outChr,"some big text"); from C# i call it something like this: string message = "some text here"; StringBuilder response = new StringBuilder(10000); Archiver.archive(message,response); this works, but the problem, as you might see is that i give a value to the StringBuilder size, but the archive function might give back a (way) larger text than the size i've given to my StringBuilder. any way to fix this?

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• How to put PrintWriter object content in to table cell

  - by user3599482

  I have a small problem about a content returning from servlet to put in table cell. In javascript I am calling servlet method using post, it returns some content and I have to put it in two different <td> cells. here is my code, In javascript, $.post('<%=request.getContextPath()%>/controller/UserLockController',{'userName':userName,'status':status}, function(data) { document.getElementById("status_"+userName).innerHTML=data; document.getElementById("td_"+userName).innerHTML=data; }); in servlet it writes as, out.println("<td id=\"status_"+inputParam+"\">Locked</td>"); out.println("<td id=\"td_"+inputParam+"\"><a href=\"#\" class=\"btn btn-sm btn-primary unlockBtn\" id=\"togBtn_"+inputParam+"\" onClick=\"LockAccount('"+inputParam+"','"+status+"')\">UnLock</td>"); Here content is returning but problem is the both <td> return from servlet will fit in single cell of html table. how to solve this please help me.

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