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• Java Swingworker: Not as encapsulated class

  - by Thomas Matthews

  I'm having problems passing information, updating progress and indicating "done" with a SwingWorker class that is not an encapsulated class. I have a simple class that processes files and directories on a hard drive. The user clicks on the Start button and that launches an instance of the SwingWorker. I would like to print the names of the files that are processed on the JTextArea in the Event Driven Thread from the SwingWorker as update a progress bar. All the examples on the web are for an nested class, and the nested class accesses variables in the outer class (such as the done method). I would also like to signal the Event Driven Thread that the SwingWorker is finished so the EDT can perform actions such as enabling the Start button (and clearing fields). Here are my questions: 1. How does the SwingWorker class put text into the JTextArea of the Event Driven Thread and update a progress bar? How does the EDT determine when the {external} SwingWorker thread is finished? {I don't want the SwingWorker as a nested class because there is a lot of code (and processing) done.}

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• WPF Update Binding when Bound directly to DataContext w/ Converter

  - by Adam

  Normally when you want a databound control to 'update,' you use the "PropertyChanged" event to signal to the interface that the data has changed behind the scenes. For instance, you could have a textblock that is bound to the datacontext with a property "DisplayText" <TextBlock Text="{Binding Path=DisplayText}"/> From here, if the DataContext raises the PropertyChanged event with PropertyName "DisplayText," then this textblock's text should update (assuming you didn't change the Mode of the binding). However, I have a more complicated binding that uses many properties off of the datacontext to determine the final look and feel of the control. To accomplish this, I bind directly to the datacontext and use a converter. In this case I am working with an image source. <Image Source="{Binding Converter={StaticResource ImageConverter}}"/> As you can see, I use a {Binding} with no path to bind directly to the datacontext, and I use an ImageConverter to select the image I'm looking for. But now I have no way (that I know of) to tell that binding to update. I tried raising the propertychanged event with "." as the propertyname, which did not work. Is this possible? Do I have to wrap up the converting logic into a property that the binding can attach to, or is there a way to tell the binding to refresh (without explicitly refreshing the binding)? Any help would be greatly appreciated. Thanks! -Adam

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• Eclipse RCP: Using different JUnit version (4.3.1) than shipped with eclipse galileo (4.5.0)

  - by Skrrytch

  Hallo, I have the following situation: We are developing an Eclipse RCP Application and want to switch from Eclipse 3.4 to Eclipse 3.5. Our JUnit-Tests are using JUnit 4.3.1 and we have a launch configuration to start our test suite. I think I don't need to go into more details here. The problem is: Running the tests with Eclipse 3.5 does not work: JUnit cannot find any annotations in the test classes (neither (at)Test nor (at)RunWith). I patched the junit library with some logging output to check what is going on. I found out that this problem is a classloading issue: The test class passed to JUnit 'lies in' a ClassLoader which is different from the one JUnit uses to load the annotation classes like 'RunWith'. This is not the case in Eclipse 3.4 in org.junit.internal.requests.ClassRequest: public Runner getRunner() { log("TestClass ClassLoader: "+this.fTestClass.getClassLoader()); log("RunWith.class ClassLoader: "+RunWith.class.getClassLoader()); ... // validating test class: searching for annotations and more } The first line prints another classloader than the second line. This is bad because JUnit cannot match the annotations in the test class with the Annotation-Class (here: RunWith.class): "RunWith" in CL1 is not equal to "RunWith" in CL2. I have a solution which points to the core problem: Replace JUnit 4.5 in Eclipse Galileo with JUnit 4.3.1 so that there is only one JUnit-Version: The Test-Run and the tests classes are both using JUnit 4.3.1 (I had to patch "org.eclipse.jdt.junit4.runtime" to accept an ealier junit version). I think I can also replace JUnit 4.3.1 in my test class with Version 4.5, but that is not an option yet. Guess: The classloaders are different because the classes 'come from' different JUnit-Bundles: the testclass with its annotations from version 4.3.1 and the test runs in version 4.5 What I want to know: Is there any other solution besides patching Eclipse (replace JUnit versions)? Any commandline argument or such? Any configuration to force Eclipse to Use JUnit 4.3.1? Any hints on the above described analysis are welcome!

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• Threading best practice when using SFTP in C#

  - by Christian

  Ok, this is more one of these "conceptual questions", but I hope I got some pointers in the right direction. First the desired scenario: I want to query an SFTP server for directory and file lists I want to upload or download files simulaneously Both things are pretty easy using a SFTP class provided by Tamir.SharpSsh, but if I only use one thread, it is kind of slow. Especially the recursion into subdirs gets very "UI blocking", because we are talking about 10.000 of directories. My basic approach is simple, create some kind of "pool" where I keep 10 open SFTP connections. Then query the first worker for a list of dirs. If this list was obtained, send the next free workers (e.g. 1-10, first one is also free again) to get the subdirectory details. As soon as there is a worker free, send him for the subsubdirs. And so on... I know the ThreadPool, simple Threads and did some Tests. What confuses me a little bit is the following: I basically need... A list of threads I create, say 10 Connect all threads to the server If a connection drops, create a new thread / sftp client If there is work to do, take the first free thread and handle the work I am currently not sure about the implementation details, especially the "work to do" and the "maintain list of threads" parts. Is it a good idea to: Enclose the work in an object, containing a job description (path) and a callback Send the threads into an infinite loop with 100ms wait to wait for work If SFTP is dead, either revive it, or kill the whole thread and create a new one How to encapsulate this, do I write my own "10ThreadsManager" or are there some out Ok, so far... Btw, I could also use PRISM events and commands, but I think the problem is unrelated. Perhaps the EventModel to signal a done processing of a "work package"... Thanks for any ideas, critic.. Chris

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• Developing a GPS car tracking system in C#

  - by Click Ok

  I'm in the brainstorming phase to develop a GPS car tracking system requested by a customer. I myself know the directions to build some GPS system to mobile phones and etc. But sincerely I don't know how to start in that project. That is the scenario: 1) The cars will get a device with a SIM CARD that will emit GPS signals. 2) My customer will in any place (home, work, etc) with a web connection will see in the map where the car is located. For me, I have not problems at get the GPS data, convert to usable info and show the position in some map system (like Google Maps or MS Bing Maps, by example). My problem is, how I do to retrieve that "GPS Signal" from device in the car? I will need some kind of "Receiver Device" connected to a web server machine in order to my application to consume that data? Or "automagically" my sodtware will receive the info from a third-party web-service? Or what? I thank for any help!

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• BN_hex2bn magicaly segfaults in openSSL

  - by xunil154

  Greetings, this is my first post on stackoverflow, and i'm sorry if its a bit long. I'm trying to build a handshake protocol for my own project and am having issues with the server converting the clients RSA's public key to a Bignum. It works in my clent code, but the server segfaults when attempting to convert the hex value of the clients public RSA to a bignum. I have already checked that there is no garbidge before or after the RSA data, and have looked online, but i'm stuck. header segment: typedef struct KEYS { RSA *serv; char* serv_pub; int pub_size; RSA *clnt; } KEYS; KEYS keys; Initializing function: // Generates and validates the servers key /* code for generating server RSA left out, it's working */ //Set client exponent keys.clnt = 0; keys.clnt = RSA_new(); BN_dec2bn(&keys.clnt->e, RSA_E_S); // RSA_E_S contains the public exponent Problem code (in Network::server_handshake): // *Recieved an encrypted message from the network and decrypt into 'buffer' (1024 byte long)* cout << "Assigning clients RSA" << endl; // I have verified that 'buffer' contains the proper key if (BN_hex2bn(&keys.clnt->n, buffer) < 0) { Error("ERROR reading server RSA"); } cout << "clients RSA has been assigned" << endl; The program segfaults at BN_hex2bn(&keys.clnt->n, buffer) with the error (valgrind output) Invalid read of size 8 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) by 0x40F23E: Network::server_handshake() (Network.cpp:177) by 0x40EF42: Network::startNet() (Network.cpp:126) by 0x403C38: main (server.cpp:51) Address 0x20 is not stack'd, malloc'd or (recently) free'd Process terminating with default action of signal 11 (SIGSEGV) Access not within mapped region at address 0x20 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) And I don't know why it is, Im using the exact same code in the client program, and it works just fine. Any input is greatly appriciated!

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• Hidden features of Perl?

  - by Adam Bellaire

  What are some really useful but esoteric language features in Perl that you've actually been able to employ to do useful work? Guidelines: Try to limit answers to the Perl core and not CPAN Please give an example and a short description Hidden Features also found in other languages' Hidden Features: (These are all from Corion's answer) C# Duff's Device Portability and Standardness Quotes for whitespace delimited lists and strings Aliasable namespaces Java Static Initalizers JavaScript Functions are First Class citizens Block scope and closure Calling methods and accessors indirectly through a variable Ruby Defining methods through code PHP Pervasive online documentation Magic methods Symbolic references Python One line value swapping Ability to replace even core functions with your own functionality Other Hidden Features: Operators: The bool quasi-operator The flip-flop operator Also used for list construction The ++ and unary - operators work on strings The repetition operator The spaceship operator The || operator (and // operator) to select from a set of choices The diamond operator Special cases of the m// operator The tilde-tilde "operator" Quoting constructs: The qw operator Letters can be used as quote delimiters in q{}-like constructs Quoting mechanisms Syntax and Names: There can be a space after a sigil You can give subs numeric names with symbolic references Legal trailing commas Grouped Integer Literals hash slices Populating keys of a hash from an array Modules, Pragmas, and command-line options: use strict and use warnings Taint checking Esoteric use of -n and -p CPAN overload::constant IO::Handle module Safe compartments Attributes Variables: Autovivification The $[ variable tie Dynamic Scoping Variable swapping with a single statement Loops and flow control: Magic goto for on a single variable continue clause Desperation mode Regular expressions: The \G anchor (?{}) and '(??{})` in regexes Other features: The debugger Special code blocks such as BEGIN, CHECK, and END The DATA block New Block Operations Source Filters Signal Hooks map (twice) Wrapping built-in functions The eof function The dbmopen function Turning warnings into errors Other tricks, and meta-answers: cat files, decompressing gzips if needed Perl Tips See Also: Hidden features of C Hidden features of C# Hidden features of C++ Hidden features of Java Hidden features of JavaScript Hidden features of Ruby Hidden features of PHP Hidden features of Python

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• How to avoid XCode framework weak-linking problems?

  - by Frank R.

  Hi, I'm building an application that takes advantage of Mac OS X 10.6-only technologies, but without giving up backwards compatibility to 10.5 Leopard. The way I do this is by setting the 10.6 SDK as the base SDK, weak-linking all frameworks and setting the deployment target to 10.5 as described in: http://developer.apple.com/mac/library/DOCUMENTATION/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html This works fine; before making a call that is Snow Leopard-only I need to check that the selector or indeed the class actually exist. Or I can just check the OS version before making the call. The problem is that this is incredibly fragile. If I make a single call that is 10.6 only I blow Leopard-compatibility. So using even the normal code code completion feature can be dangerous. My question: is there any way of checking which calls are not defined on 10.5 before doing a release build? Some kind of static analysis, or even just a trick (a target set the other SDK?) would do. I obviously should test on a Leopard machine before releasing anything, but even so I can't possibly go through all paths of the program before every release. Any advice would be appreciated. Best regards, Frank

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• using ghostscript in server mode to convert pdfs to pngs

  - by emh

  while i am able to convert a specific page of a PDF to a PNG like so: gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=png16m -dGraphicsAlphaBits=4 -sOutputFile=gymnastics-20.png -dFirstPage=20 -dLastPage=20 gymnastics.pdf i am wondering if i can somehow use ghostscript's JOBSERVER mode to process several conversions without having to incur the cost of starting up ghostscript each time. from: http://pages.cs.wisc.edu/~ghost/doc/svn/Use.htm -dJOBSERVER Define \004 (^D) to start a new encapsulated job used for compatibility with Adobe PS Interpreters that ordinarily run under a job server. The -dNOOUTERSAVE switch is ignored if -dJOBSERVER is specified since job servers always execute the input PostScript under a save level, although the exitserver operator can be used to escape from the encapsulated job and execute as if the -dNOOUTERSAVE was specified. This also requires that the input be from stdin, otherwise an error will result (Error: /invalidrestore in --restore--). Example usage is: gs ... -dJOBSERVER - < inputfile.ps -or- cat inputfile.ps | gs ... -dJOBSERVER - Note: The ^D does not result in an end-of-file action on stdin as it may on some PostScript printers that rely on TBCP (Tagged Binary Communication Protocol) to cause an out-of-band ^D to signal EOF in a stream input data. This means that direct file actions on stdin such as flushfile and closefile will affect processing of data beyond the ^D in the stream. the idea is to run ghostscript in-process. the script would receive a request for a particular page of a pdf and would use ghostscript to generate the specified image. i'd rather not start up a new ghostscript process every time.

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• Check for valid IMEI

  - by Tim

  Hi, does somebody knows how to check for a valid IMEI? I have found a function to check on this page: http://www.dotnetfunda.com/articles/article597-imeivalidator-in-vbnet-.aspx But it returns false for valid IMEI's (f.e. 352972024585360). I can validate them online on this page: http://www.numberingplans.com/?page=analysis&sub=imeinr What is the correct way(in VB.Net) to check if a given IMEI is valid? Regards, Tim PS: This function from above page must be incorrect in some way: Public Shared Function isImeiValid(ByVal IMEI As String) As Boolean Dim cnt As Integer = 0 Dim nw As String = String.Empty Try For Each c As Char In IMEI cnt += 1 If cnt Mod 2 <> 0 Then nw += c Else Dim d As Integer = Integer.Parse(c) * 2 ' Every Second Digit has to be Doubled nw += d.ToString() ' Genegrated a new number with doubled digits End If Next Dim tot As Integer = 0 For Each ch As Char In nw.Remove(nw.Length - 1, 1) tot += Integer.Parse(ch) ' Adding all digits together Next Dim chDigit As Integer = 10 - (tot Mod 10) ' Finding the Check Digit my Finding the Remainder of the sum and subtracting it from 10 If chDigit = Integer.Parse(IMEI(IMEI.Length - 1)) Then ' Checking the Check Digit with the last digit of the Given IMEI code Return True Else Return False End If Catch ex As Exception Return False End Try End Function

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• Dashboard for collaborative science / data processing projects

  - by rescdsk

  Hi, Continuous Integration servers like Hudson are a pretty amazing addition to software development. I work in an academic research lab, and I'd love to apply similar principles to scientific data analysis. I want a dashboard-like view of which collections of data are fine, which ones are failing their tests (simple shell scripts, mostly), and so on. A lot like the Chromium dashboard (WARNING: page takes a long time to load). It takes work from at least 4 people, and maybe 10 or 12 hours of computer time, to bring our data (from behavioral studies) from its raw form to its final, easily-analyzed form. I've tried Hudson and buildbot, but neither is really appropriate to our workflow. We just want to run a bunch of tests on maybe fifty independent collections of subject data, and display the results nicely. SO! Does anyone have a recommendation of a way to generate this kind of report easily? Or, can you think of a good way to shoehorn this kind of workflow into a continuous integration server? Or, can you recommend a unit testing dashboard that could deal with tests that are little shell scripts rather than little functions? Thank you!

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• sharing build artifacts between jobs in hudson

  - by programming panda

  Hi I'm trying to set up our build process in hudson. Job 1 will be a super fast (hopefully) continuous integration build job that will be built frequently. Job 2, will be responsible for running a comprehensive test suite, at a regular interval or triggered manually. Job 3 will be responsible for running analysis tools across the codebase (much like Job 2). I tried using the "Advanced Projects Options use custom workspace" feature so that code compiled in Job 1 can be used in Job 2 and 3. However, it seems that all build artifacts remain inside that Job 1 workspace. I'm I doing this right? Is there a better way of doing this? I guess I'm looking for something similar to a build pipeline setup...so that things can be shared and the appropriate jobs can be executed in stages. (I also considered using 'batch tasks'...but it seems like those can't be scheduled? only triggered manually?) Any suggestions are welcomed. Thanks!

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• Useful training courses that aren't specific to a single technology

  - by Dave Turvey

  I have possibly the best problem in the world. I have about £1600 left in a training budget and I need to find something to spend it on. I can spend it on anything that could be considered training. Books, courses, conferences, etc. I would like to find a course that would benifit a software developer but is not about learning a specific programming technology. I don't really want to spend it on a technical training course. These topics are usually best learned with a good book and some trial and error. I have also already been on a general business/management training course and a PRINCE2 project management course. I am currently working on a project on my own so am responsible for communicating with the client, requirements gathering, project management, etc., as well as the coding. What training have you found useful outside the usual technical stuff? Has anyone done any business analysis courses? What were they like? Are there any courses on some of the practicalities of working with software, e.g. automated test and deployment strategies, handling technical support? I would prefer a course in the UK but I can travel if necessary.

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• EXC_BAD_ACCESS NSUrlConnection

  - by Lars

  Hi all, i got an EXC_BAD_ACCESS when i perform the last line of the function (webData). -(void)requestSoap{ NSString *requestUrl = @"http://www.website.com/webservice.php"; NSString *soapMessage = @"the soap message"; //website and soapmessage are valid in original code. NSError **error; NSURLResponse *response; //Convert parameter string to url NSURL *url = [NSURL URLWithString:requestUrl]; NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10]; NSString *msgLength = [NSString stringWithFormat:@"%d", [soapMessage length]]; //Create an XML message for webservice [theRequest addValue: @"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"]; [theRequest addValue: msgLength forHTTPHeaderField:@"Content-Length"]; [theRequest setHTTPMethod:@"POST"]; [theRequest setHTTPBody: [soapMessage dataUsingEncoding:NSUTF8StringEncoding]]; NSData *webData = [NSURLConnection sendSynchronousRequest:theRequest returningResponse:&response error:error]; } I tried not to release a thing, because what i read on the net is it's almost always a memory thing. When i debug the code (NSZombieEnabled = YES) this is what i get: [Session started at 2010-05-31 15:56:13 +0200.] GNU gdb 6.3.50-20050815 (Apple version gdb-1461.2) (Fri Mar 5 04:43:10 UTC 2010) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "x86_64-apple-darwin".sharedlibrary apply-load-rules all Attaching to process 19856. test(19856) malloc: recording malloc stacks to disk using standard recorder test(19856) malloc: enabling scribbling to detect mods to free blocks test(19856) malloc: process 19832 no longer exists, stack logs deleted from /tmp/stack-logs.19832.test.w9Ek4L.index test(19856) malloc: stack logs being written into /tmp/stack-logs.19856.test.URRpQF.index Program received signal: “EXC_BAD_ACCESS”. Does anybody have a clue?? Thanks a lot! Lars

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• How do I debug a crash when I run my garbage-collected app in Rosetta?

  - by Rob Keniger

  I have a Universal app which is targeting 10.5 and which uses garbage collection. I am building for ppc, i386 and x86_64. I don't have access to a physical PowerPC machine so I am trying to use Rosetta to confirm that the PowerPC portion of the app works correctly. However, as soon as the app is launched in Rosetta it immediately crashes with the following crash log: Process: FooApp [91567] Path: /Users/rob/Development/src/FooApp/build/Release 64-bit/FooApp.app/Contents/MacOS/FooApp Identifier: com.companyX.FooApp Version: 0.9 (build d540e05) (2) Code Type: PPC (Translated) Parent Process: launchd [708] Date/Time: 2010-04-09 18:32:23.962 +1000 OS Version: Mac OS X 10.6.3 (10D573) Report Version: 6 Exception Type: EXC_CRASH (SIGTRAP) Exception Codes: 0x0000000000000000, 0x0000000000000000 Crashed Thread: 5 ...snip non-relevant threads... Thread 5 Crashed: 0 libSystem.B.dylib 0x8023656a __pthread_kill + 10 1 libSystem.B.dylib 0x80235e17 pthread_kill + 95 2 com.companyX.FooApp 0xb80bfb30 0xb8000000 + 785200 3 com.companyX.FooApp 0xb80c0037 0xb8000000 + 786487 4 com.companyX.FooApp 0xb80dd8e8 0xb8000000 + 907496 5 com.companyX.FooApp 0xb8145397 spin_lock_wrapper + 1791 6 com.companyX.FooApp 0xb801ceb7 0xb8000000 + 118455 I have used the Apple docs on debugging translated apps and the information on this page to attach gdb to the app when it's running in Rosetta. The app immediately breaks into the debugger upon launch: Program received signal SIGTRAP, Trace/breakpoint trap. [Switching to thread 15107] 0x9151fdd4 in auto_fatal () (gdb) bt #0 0x9151fdd4 in auto_fatal () #1 0x91536d84 in Auto::Thread::get_register_state () #2 0x915372f8 in Auto::Thread::scan_other_thread () #3 0x91529be4 in Auto::Zone::scan_registered_threads () #4 0x91539114 in Auto::MemoryScanner::scan_thread_ranges () #5 0x9153b000 in Auto::MemoryScanner::scan () #6 0x9153049c in Auto::Zone::collect () #7 0x915198f4 in auto_collect_internal () #8 0x9151a094 in auto_collection_work () #9 0x96687434 in _dispatch_call_block_and_release () #10 0x9668912c in _dispatch_queue_drain () #11 0x96689350 in _dispatch_queue_invoke () #12 0x966895c0 in _dispatch_worker_thread2 () #13 0x966896fc in _dispatch_worker_thread () #14 0x965a97e8 in _pthread_body () (gdb) I have no idea where to start with this. It looks like the Garbage Collector is failing very badly. Are garbage-collected PowerPC apps not supported in Rosetta? I can't see any mention of this limitation in the docs if so. Does anyone have any ideas?

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• How can I use Qt to get html code of the redirected page??

  - by Claire Huang

  I'm trying to use Qt to download the html code from the following url: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=nucleotide&cmd=search&term=AB100362 this url will re-direct to www.ncbi.nlm.nih.gov/nuccore/27884304 I try to do it by following way, but I cannot get anything. it works for some webpage such as www.google.com, but not for this NCBI page. is there any way to get this page?? QNetworkReply::NetworkError downloadURL(const QUrl &url, QByteArray &data) { QNetworkAccessManager manager; QNetworkRequest request(url); QNetworkReply *reply = manager.get(request); QEventLoop loop; QObject::connect(reply, SIGNAL(finished()), &loop, SLOT(quit())); loop.exec(); if (reply->error() != QNetworkReply::NoError) { return reply->error(); } data = reply->readAll(); delete reply; return QNetworkReply::NoError; } void GetGi() { int pos; QString sGetFromURL = "http://www.ncbi.nlm.nih.gov/entrez/query.fcgi"; QUrl url(sGetFromURL); url.addQueryItem("db", "nucleotide"); url.addQueryItem("cmd", "search"); url.addQueryItem("term", "AB100362"); QByteArray InfoNCBI; int errorCode = downloadURL(url, InfoNCBI); if (errorCode != 0 ) { QMessageBox::about(0,tr("Internet Error "), tr("Internet Error %1: Failed to connect to NCBI.\t\nPlease check your internect connection.").arg(errorCode)); return "ERROR"; } }

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• POSIX AIO Library and Callback Handlers

  - by Charles Salvia

  According to the documentation on aio_read/write, there are basically 2 ways that the AIO library can inform your application that an async file I/O operation has completed. Either 1) you can use a signal, 2) you can use a callback function I think that callback functions are vastly preferable to signals, and would probably be much easier to integrate into higher-level multi-threaded libraries. Unfortunately, the documentation for this functionality is a mess to say the least. Some sources, such as the man page for the sigevent struct, indicate that you need to set the sigev_notify data member in the sigevent struct to SIGEV_CALLBACK and then provide a function handler. Presumably, the handler is invoked in the same thread. Other documentation indicates you need to set sigev_notify to SIGEV_THREAD, which will invoke the callback handler in a newly created thread. In any case, on my Linux system (Ubuntu with a 2.6.28 kernel) SIGEV_CALLBACK doesn't seem to be defined anywhere, but SIGEV_THREAD works as advertised. Unfortunately, creating a new thread to invoke the callback handler seems really inefficient, especially if you need to invoke many handlers. It would be better to use an existing pool of threads, similar to the way most network I/O event demultiplexers work. Some versions of UNIX, such as QNX, include a SIGEV_SIGNAL_THREAD flag, which allows you to invoke handlers using a specified existing thread, but this doesn't seem to be available on Linux, nor does it seem to even be a part of the POSIX standard. So, is it possible to use the POSIX AIO library in a way that invokes user handlers in a pre-allocated background thread/threadpool, rather than creating/destroying a new thread everytime a handler is invoked?

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• Debugging SIGABRT within NSManagedObjectContext -save:

  - by westsider

  From inside NSManagedObjectContext -save: I am getting this message: Assertion failed: (_Unwind_SjLj_Resume() can't return), function _Unwind_SjLj_Resume, file /SourceCache/libunwind/libunwind-24.1/src/Unwind-sjlj.c, line 326. Program received signal: “SIGABRT”. warning: Unable to read symbols for /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1 (8C148)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib (file not found). This happens when I delete an Experiment object with to-many with Run which has to-many with Sample which has to-one with Data. Experiment also has to-many with Page which has to-many with Display which has to-many to Run. I mention this to point out the cyclical nature of the graph. Here is a simplified graph of model: I had been using Delete Rules but have now switched to "No Action" delete rules in combination with -prepareForDeletion methods for all of these classes. This change made no difference. In both cases, the error message is the same. Interestingly, when I relaunch the app, all the objects that were marked for deletion have been deleted. Also, if an Experiment has no Run objects, then deletion works without incidence. For that matter, deleting a single Run from an Experiment also works. I am hoping that someone has seen something like this and can offer advice on what would cause this. Or, if someone has advice on how to get libXcodeDebuggerSupport.dylib for iOS 4.2.1, that might also be helpful. Update: I followed advice found here and was able to get Xcode to find libXcodeDebuggerSupport.dylib for iOS 4.2.1. But this did not help at all in diagnosing problem - which persists.

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• Can I make a "TCP packet modifier" using tun/tap and raw sockets?

  - by benhoyt

  I have a Linux application that talks TCP, and to help with analysis and statistics, I'd like to modify the data in some of the TCP packets that it sends out. I'd prefer to do this without hacking the Linux TCP stack. The idea I have so far is to make a bridge which acts as a "TCP packet modifier". My idea is to connect to the application via a tun/tap device on one side of the bridge, and to the network card via raw sockets on the other side of the bridge. My concern is that when you open a raw socket it still sends packets up to Linux's TCP stack, and so I couldn't modify them and send them on even if I wanted to. Is this correct? A pseudo-C-code sketch of the bridge looks like: tap_fd = open_tap_device("/dev/net/tun"); raw_fd = open_raw_socket(); for (;;) { select(fds = [tap_fd, raw_fd]); if (FD_ISSET(tap_fd, &fds)) { read_packet(tap_fd); modify_packet_if_needed(); write_packet(raw_fd); } if (FD_ISSET(raw_fd, &fds)) { read_packet(raw_fd); modify_packet_if_needed(); write_packet(tap_fd); } } Does this look possible, or are there other better ways of achieving the same thing? (TCP packet bridging and modification.)

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• Database warehouse design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to seek some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• Problems with QDialog in Qt

  - by Martin

  I'm using Qt for Symbian. I have some problems with a QDialog that I open from a QMenu. The QDialog shows up fine and in the QDialog I have a QDialogButtonBox with a button to Close the QDialog. BUT if I close the QDialog and then open it from the QMenu again, it will show up but the button from the QDialogButtonBox will not show up. Instead the buttons from the QMainWindow will show but they are grayed out. How can I get the QDialog buttons to show every time? Maybe I have some problems with setting focus on the QDialog? I really can't see what I'm doing wrong here. It's not much code that I use, you can try it yourself. This is my code: In QMainWindow I use the following to create the menu: QAction *menuButton = new QAction("Menu", this); menuButton->setSoftKeyRole(QAction::PositiveSoftKey); QMenu *menu = new QMenu(this); menuButton->setMenu(menu); QAction *popup = new QAction("Show popup",this); connect(popup, SIGNAL(triggered()), this, SLOT(showPopup())); menu->addAction(popup); addAction(menuButton); This shows the QDialog: void MyMainWindow::showPopup(){ TestDialog *test = new TestDialog(this); test->setAttribute(Qt::WA_DeleteOnClose); test->show(); } This is the TestDialog: TestDialog::TestDialog(QWidget *parent) : QDialog(parent) { ui.setupUi(this); QDesktopWidget* desktopWidget = QApplication::desktop(); QRect rect = desktopWidget->availableGeometry(); this->setFixedWidth(rect.width()); }

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• Starting out NLP - Python + large data set

  - by pencilNero

  Hi, I've been wanting to learn python and do some NLP, so have finally gotten round to starting. Downloaded the english wikipedia mirror for a nice chunky dataset to start on, and have been playing around a bit, at this stage just getting some of it into a sqlite db (havent worked with dbs in the past unfort). But I'm guessing sqlite is not the way to go for a full blown nlp project(/experiment :) - what would be the sort of things I should look at ? HBase (.. and hadoop) seem interesting, i guess i could run then im java, prototype in python and maybe migrate the really slow bits to java... alternatively just run Mysql.. but the dataset is 12gb, i wonder if that will be a problem? Also looked at lucene, but not sure how (other than breaking the wiki articles into chunks) i'd get that to work.. What comes to mind for a really flexible NLP platform (i dont really know at this stage WHAT i want to do.. just want to learn large scale lang analysis tbh) ? Many thanks.

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• Is there any special tool for interactive GUI development

  - by niko

  Hi, Currently I am preparing exercises about networks and mobile communications for students. I was thinking about creating an interactive user-interface which enables the user to drag&drop predefined elements and then implement a logic based upon element distances etc. An example would be to place two base stations (a predefined element with several properties), set the scale in the interface and then check the signal interferrence in the environment (user-interface). The first part might be too abstract whereas the example might be too specific, but I was wondering whether there already exists any friendly framework or language which enables developers to create interactive interfaces (for teaching/learning purpouses) in short ammount of time. Usually I write applications for PC environment in .NET but in this case it would take too much time to create a specific interface for every exercise. I would appreciate if anyone could suggest any way to create interactive user-interface in short ammount of time. Are there any special programming languages or development tools for this kind of applications or are there any useful frameworks for .NET, Java or any other language to speed up the development of user-interfaces? Thank you!

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• Reference for proper handling of PID file on Unix

  - by bignose

  Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when it starts up whether the PID file exists and, if the file does exist, exit with an error. So it's a kind of advisory, collaborative locking mechanism. The file contains a single line of text, being the numeric process ID (hence the name “PID file”) of the process that currently holds the lock; this allows an easy way to automate sending a signal to the process that holds the lock. What I can't find is a good reference on expected or “best practice” behaviour for handling PID files. There are various nuances: how to actually lock the file (don't bother? use the kernel? what about platform incompatibilities?), handling stale locks (silently delete them? when to check?), when exactly to acquire and release the lock, and so forth. Where can I find a respected, most-authoritative reference (ideally on the level of W. Richard Stevens) for this small topic?

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• iPhone - Failed to save the videos metadata to the filesystem.

  - by cameron

  My application uses the UIImagePicker to allow the user to use the camera and capture a photo to edit/etc. I am getting the error message below: 2010-02-03 10:41:24.018 LivingRoom[5333:5303] Failed to save the videos metadata to the filesystem. Maybe the information did not conform to a plist. Program received signal: “EXC_BAD_ACCESS”. A search in Google brings up a number of threads in various forums, with no ultimate response/root cause/suggestions on how to fix/debug. An example is the thread below with code which is very similar to my app: http://groups.google.com/group/iphonesdkdevelopment/browse_thread/thread/6b7b396c62bef398 The error disappears for a while (10 tests in a row, no errors) if I reboot the iPhone. I have not been able to determine what makes it reoccur after a reboot, but it does. I am not using the video source and the fact that a reboot solves the problem for a while points to some sort of mem leak (perhaps?). The problem always shows up on both the iPhone (even after the reboot) and the simulator when choosing a photo from the album, but the app does not crash on the iPhone or the simulator. The same app with exact code did not have the error message when compiled using SDK 3.0 (last August/September). But 3.1.x has always produced the error message, which means that once a week or so the iPhone needs to be rebooted for the error to disappear. The users are not happy with that solution any longer!! Any suggestion/clues would be greatly appreciated.

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