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• How do I lock the workstation from a windows service?

  - by Brad Mathews

  Hello, I need to lock the workstation from a windows service written in VB.Net. I am writing the app on Windows 7 but it needs to work under Vista and XP as well. User32 API LockWorkStation does not work as it requires an interactive desktop and I get return value of 0. I tried calling %windir%\System32\rundll32.exe user32.dll,LockWorkStation from both a Process and from Shell, but still nothing happens. Setting the service to interact with the desktop is a no-go as I am running the service under the admin account so it can do some other stuff that requires admin rights - like disabling the network, and you can only select the interact with desktop option if running under Local System Account. That would be secondary question - how to run another app with admin rights from a service running under Local System Account without bugging the user. I am writing an app to control my kids computer/internet access (which I plan to open source when done) so I need everything to happen as stealthily as possible. I have a UI that handles settings and status notifications in the taskbar, but that is easy to kill and thus defeat the locking. I could make another hidden Windows Forms app to handle the locking, but that just seems a rather inelegant solution. Better ideas anyone? Thanks! Brad

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• Map element position in data file to class property

  - by Augusto

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

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• Rails model relations depending on count of nested relations

  - by Lowgain

  I am putting together a messaging system for a rails app I am working on. I am building it in a similar fashion to facebook's system, so messages are grouped into threads, etc. My related models are: MsgThread - main container of a thread Message - each message/reply in thread Recipience - ties to user to define which users should subscribe to this thread Read - determines whether or not a user has read a specific message My relationships look like class User < ActiveRecord::Base #stuff... has_many :msg_threads, :foreign_key => 'originator_id' #threads the user has started has_many :recipiences has_many :subscribed_threads, :through => :recipiences, :source => :msg_thread #threads the user is subscribed to end class MsgThread < ActiveRecord::Base has_many :messages has_many :recipiences belongs_to :originator, :class_name => "User", :foreign_key => "originator_id" end class Recipience < ActiveRecord::Base belongs_to :user belongs_to :msg_thread end class Message < ActiveRecord::Base belongs_to :msg_thread belongs_to :author, :class_name => "User", :foreign_key => "author_id" end class Read < ActiveRecord::Base belongs_to :user belongs_to :message end I'd like to create a new selector in the user sort of like: has_many :updated_threads, :through => :recipiencies, :source => :msg_thread, :conditions => {THREAD CONTAINS MESSAGES WHICH ARE UNREAD (have no 'read' models tying a user to a message)} I was thinking of either writing a long condition with multiple joins, or possibly writing giving the model an updated_threads method to return this, but I'd like to see if there is an easier way first. Any ideas? Also, if there is something fundamentally wrong with my structure for this functionality let me know! Thanks!!

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• C# - File Encoding Problem.

  - by user301330

  Hello, I'm have a StringBuilder that is writing content to a file. Towards the end of each file, I'm writing the copyright symbol. Oddly, I have noticed that whenever the copyright symbol is written, it is preceeded by a "Â". My code that generates the content of the file looks like this: using (StringWriter stringWriter = new StringWriter()) { stringWriter = GetFileContent(); string targetPath = ConfigurationManager.AppSettings["TargetPath"]; using (StreamWriter streamWriter = new StreamWriter(targetPath, false)) { StringBuilder sb = new StringBuilder(stringWriter.ToString()); // Attempted fix string content = sb.ToString(); content = content.Replace("Â", ""); streamWriter.Write(content); } } As you can tell, I tried to do a find-and-replace. In the process, I noticed that a "Â" was not in the content itself. This makes me believe there is something occurring in the streamWriter. However, I'm not sure what it could be. Can someone please tell me why a "Â" would be popping up before the "©" symbol and how to fix it? I believe it has something to do with encoding, but I'm not sure Thank you!

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• Base class deleted before subclass during python __del__ processing

  - by Oddthinking

  Context I am aware that if I ask a question about Python destructors, the standard argument will be to use contexts instead. Let me start by explaining why I am not doing that. I am writing a subclass to logging.Handler. When an instance is closed, it posts a sentinel value to a Queue.Queue. If it doesn't, a second thread will be left running forever, waiting for Queue.Queue.get() to complete. I am writing this with other developers in mind, so I don't want a failure to call close() on a handler object to cause the program to hang. Therefore, I am adding a check in __del__() to ensure the object was closed properly. I understand circular references may cause it to fail in some circumstances. There's not a lot I can do about that. Problem Here is some simple example code: explicit_delete = True class Base: def __del__(self): print "Base class cleaning up." class Sub(Base): def __del__(self): print "Sub-class cleaning up." Base.__del__(self) x = Sub() if explicit_delete: del x print "End of thread" When I run this I get, as expected: Sub-class cleaning up. Base class cleaning up. End of thread If I set explicit_delete to False in the first line, I get: End of thread Sub-class cleaning up. Exception AttributeError: "'NoneType' object has no attribute '__del__'" in <bound method Sub.__del__ of <__main__.Sub instance at 0x00F0B698>> ignored It seems the definition of Base is removed before the x._del_() is called. The Python Documentation on _del_() warns that the subclass needs to call the base-class to get a clean deletion, but here that appears to be impossible. Can you see where I made a bad step?

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• Zend: Fetching row from session db table after generating session id

  - by Nux

  Hi, I'm trying to update the session table used by Zend_Session_SaveHandler_DbTable directly after authenticating the user and writing the session to the DB. But I can neither update nor fetch the newly inserted row, even though the session id I use to check (Zend_Session::getId()) is valid and the row is indeed inserted into the table. Upon fetching all session ids (on the same request) the one I newly inserted is missing from the results. It does appear in the results if I fetch it with something else. I've checked whether it is a problem with transactions and that does not seem to be the problem - there is no active transaction when I'm fetching the results. I've also tried fetching a few seconds after writing using sleep(), which doesn't help. $auth->getStorage()->write($ident); //sleep(1) $update = $this->db->update('session', array('uid' => $ident->user_id), 'id='.$this->db->quote(Zend_Session::getId())); $qload = 'SELECT id FROM session'; $load = $this->db->fetchAll($qload); echo $qload; print_r($load); $update fails. $load doesn't contain the row that was written with $auth-getStorage()-write($identity). $qload does contain the correct query - copying it to somewhere else leads to the expected result, that is the inserted row is included in the results. Database used is MySQL - InnoDB. If someone knows how to directly fix this (i.e. on the same request, not doing something like updating after redirecting to another page) without modifying Zend_Session_SaveHandler_DbTable: Thank you very much!

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• How do I supply extra info to IApplicationSettingsProvider class?

  - by joebeazelman

  Perhaps this question has been asked before in a different way, but I haven’t been able to find it. I have one or more plugin adapter assemblies in my application all having the type IPlugin, for instance. Each adapter has its own settings structures stored in a common directory. Whether they are stored in one contiguous file or in separate ones doesn’t matter. Each adapter can have one or more settings associated with it. The settings will have both a name and the Plugin it will be used for. How would I create such a configuration system using the following requirements: I want to use .NETs built in settings system and avoid writing one from scratch The host application will be responsible for locating the plugin settings and passing it to the plugin Each plugin will be responsible for reading and writing its own settings to separate concerns. The host application should call Plugin.Save(thePath) and it does its thing. All settings are user scoped So far, I realize that I would need to write my own SettingsProvider, but the provider seems to work in isolation in that there’s no way to pass it parameters such as the path of the plugin directory and the name of the settings. All of the example code I've seen has the provider getting the data from the runtime environment.

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• Qt Socket blocking functions required to run in QThread where created. Any way past this?

  - by Alexander Kondratskiy

  The title is very cryptic, so here goes! I am writing a client that behaves in a very synchronous manner. Due to the design of the protocol and the server, everything has to happen sequentially (send request, wait for reply, service reply etc.), so I am using blocking sockets. Here is where Qt comes in. In my application I have a GUI thread, a command processing thread and a scripting engine thread. I create the QTcpSocket in the command processing thread, as part of my Client class. The Client class has various methods that boil down to writing to the socket, reading back a specific number of bytes, and returning a result. The problem comes when I try to directly call Client methods from the scripting engine thread. The Qt sockets randomly time out and when using a debug build of Qt, I get these warnings: QSocketNotifier: socket notifiers cannot be enabled from another thread QSocketNotifier: socket notifiers cannot be disabled from another thread Anytime I call these methods from the command processing thread (where Client was created), I do not get these problems. To simply phrase the situation: Calling blocking functions of QAbstractSocket, like waitForReadyRead(), from a thread other than the one where the socket was created (dynamically allocated), causes random behaviour and debug asserts/warnings. Anyone else experienced this? Ways around it? Thanks in advance.

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• Linear feedback shift register?

  - by Mattia Gobbi

  Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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• calling template function without <>; type inference

  - by Oops

  Hi, if I have a function template with typename T, where the compiler can set the type by itself, I do not have to write the type explicitely when I call the function like: template < typename T > T min( T v1, T v2 ) { return ( v1 < v2 ) ? v1: v2; } int i1 = 1, i2 = 2; int i3 = min( i1, i2 ); //no explicit <type> but if I have a function template with two different typenames like... template < typename TOut, typename TIn > TOut round( TIn v ) { return (TOut)( v + 0.5 ); } double d = 1.54; int i = round<int>(d); //explicit <int> Is it true that I have to specify at least 1 typename, always? I assume the reason is because C++ can not distinguish functions between different return types, true? but if I use a void function and handover a reference, again I must not explicitely specify the return typename: template < typename TOut, typename TIn > void round( TOut & vret, TIn vin ) { vret = (TOut)(vin + 0.5); } double d = 1.54; int i; round(i, d); //no explicit <int> should the conclusion be to avoid functions with return and more prefer void functions that return via a reference when writing templates? Or is there a possibility to avoid explicitely writing the return type? something like "type inference" for templates... is "type inference" possible in C++0x? I hope I was not too unclear. many thanks in advance Oops

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• Bioperl, equivalent of IO::ScalarArray for array of Seq objects?

  - by Ryan Thompson

  In perl, we have IO::ScalarArray for treating the elements of an array like the lines of a file. In BioPerl, we have Bio::SeqIO, which can produce a filehandle that reads and writes Bio::Seq objects instead of strings representing lines of text. I would like to do a combination of the two: I would like to obtain a handle that reads successive Bio::Seq objects from an array of such objects. Is there any way to do this? Would it be trivial for me to implement a module that does this? My reason for wanting this is that I would like to be able to write a subroutine that accepts either a Bio::SeqIO handle or an array of Bio::Seq objects, and I'd like to avoid writing separate loops based on what kind of input I get. Perhaps the following would be better than writing my own IO module? sub process_sequences { my $input = $_[0]; # read either from array of Bio::Seq or from Bio::SeqIO my $nextseq; if (ref $input eq 'ARRAY') { my $pos = 0 $nextseq = sub { return $input->[$pos++] if $pos < @$input}; } } else { $nextseq = sub { $input->getline(); } } while (my $seq = $nextseq->()) { do_cool_stuff_with($seq) } }

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• Misalignement in the output Bitmap created from a byte array

  - by Daniel

  I am trying to understand why I have troubles creating a Bitmap from a byte array. I post this after a careful scrutiny of the existing posts about Bitmap creation from byte arrays, like the followings: Creating a bitmap from a byte[], Working with Image and Bitmap in c#?, C#: Bitmap Creation using bytes array My code is aimed to execute a filter on a digital image 8bppIndexed writing the pixel value on a byte [] buffer to be converted again (after some processing to manage gray levels) in a 8BppIndexed Bitmap My input image is a trivial image created by means of specific perl code: https://www.box.com/shared/zqt46c4pcvmxhc92i7ct Of course, after executing the filter the output image has lost the first and last rows and the first and last columns, due to the way the filter manage borders, so from the original 256 x 256 image i get a 254 x 254 image. Just to stay focused on the issue I have commented the code responsible for executing the filter so that the operation really performed is an obvious: ComputedPixel = InputImage.GetPixel(myColumn, myRow).R; I know, i should use lock and unlock but I prefer one headache one by one. Anyway this code should be a sort of identity transform, and at last i use: private unsafe void FillOutputImage() { OutputImage = new Bitmap (OutputImageCols, OutputImageRows , PixelFormat .Format8bppIndexed); ColorPalette ncp = OutputImage.Palette; for (int i = 0; i < 256; i++) ncp.Entries[i] = Color .FromArgb(255, i, i, i); OutputImage.Palette = ncp; Rectangle area = new Rectangle(0, 0, OutputImageCols, OutputImageRows); var data = OutputImage.LockBits(area, ImageLockMode.WriteOnly, OutputImage.PixelFormat); Marshal .Copy (byteBuffer, 0, data.Scan0, byteBuffer.Length); OutputImage.UnlockBits(data); } The output image I get is the following: https://www.box.com/shared/p6tubyi6dsf7cyregg9e It is quite clear that I am losing a pixel per row, but i cannot understand why: I have carefully controlled all the parameters: OutputImageCols, OutputImageRows and the byte [] byteBuffer length and content even writing known values as way to test. The code is nearly identical to other code posted in stackOverflow and elsewhere. Someone maybe could help to identify where the problem is? Thanks a lot

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• Solver Foundation Optimization - 1D Bin Packing

  - by Val Nolav

  I want to optimize loading marbles into trucks. I do not know, if I can use Solver Foundation class for that purpose. Before, I start writing code, I wanted to ask it here. 1- Marbles can be in any weight between 1 to 24 Tons. 2 - A truck can hold maximum of 24 Tons. 3- It can be loaded as many marble cubes, as it can take for upto 24 tones, which means there is no Volume limitation. 4- There can be between 200 up to 500 different marbles depending on time. GOAL - The goal is to load marbles in minimum truck shipment. How can I do that without writing a lot of if conditions and for loops? Can I use Microsoft Solver Foundation for that purpose? I read the documentation provided by Microsoft however, I could not find a scenario similar to mine. M1+ M2 + M3 + .... Mn <=24 this is for one truck shipment. Let say there are 200 different Marbles and Marble weights are Float. Thanks

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• Is there a website to look up common, already written functions?

  - by pinnacler

  I'm sitting here writing a function that I'm positive has been written before, somewhere on earth. It's just too common to have not been attempted, and I'm wondering why I can't just go to a website and search for a function that I can then copy and paste into my project in 2 seconds, instead of wasting my day reinventing the wheel. Sure there are certain libraries you can use, but where do you find these libraries and when they are absent, is there a site like I'm describing? Possibly a wiki of some type that contains free code that anybody can edit and improve? Edit: I can code things fine, I just don't know HOW to do them. So for example, right now, I'm trying to localize a robot/car/point in space. I KNOW there is a way to do it, just based off of range and distance. Triangulation and Trilateration. How to code that is a different story. A site that could have psuedo code, step by step how to do that would be ridiculously helpful. It would also ensure the optimal solution since everybody can edit it. I'm also writing in Matlab, which I hate because it's quirky, adding to my desire for creating a website like I describe.

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• Is F# a good language for card game AI?

  - by Anthony Brien

  I'm writing a Mahjong Game in C# (the Chinese traditional game, not the solitaire kind). While writing the code for the bot player's AI, I'm wondering if a functional language like F# would be a more suitable language than what I currently use which is C# with a lot of Linq. I don't know much about F# which is why I ask here. To illustrate what I try to solve, here's a quick summary of Mahjong: Mahjong plays a bit like Gin Rummy. You have 13 tiles in your hand, and each turn, you draw a tile and discard another one, trying to improve your hand towards a winning Mahjong hand, which consists or 4 sets and a pair. Sets can be a 3 of a kind (pungs), 4 of a kind (kongs) or a sequence of 3 consecutive tiles (chows). You can also steal another player's discard, if it can complete one of your sets. The code I had to write to detect if the bot can declare 3 consecutive tiles set (chow) is pretty tedious. I have to find all the unique tiles in the hand, and then start checking if there's a sequence of 3 tiles that contain that one in the hand. Detecting if the bot can go Mahjong is even more complicated since it's a combination of detecting if there's 4 sets and a pair in his hand. And that's just a standard Mahjong hand. There's also numerous "special" hands that break those rules but are still a Mahjong hand. For example, "13 unique wonders" consists of 13 specific tiles, "Jade Empire" consists of only tiles colored green, etc. In a perfect world, I'd love to be able to just state the 'rules' of Mahjong, and have the language be able to match a set of 13 tiles against those rules to retrieve which rules it fulfills, for example, checking if it's a Mahjong hand or if it includes a 4 of a kind. Is this something F#'s pattern matching feature can help solve?

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• Do you like Twisted?

  - by Luca

  I use Python Twisted for web development, and I don't like it? I know async programming is a great idea, I know there are may async web servers now, I know it's the only way to solve some problems you'd have with threads but I don't like. The problem is that, you're forced to program in a twisted way. So, the architecture you have in mind, very often have to be modified to fit the way twisted works. The architecture have to follow the technology, I don't think this is good. When we use callback in javascript, we don't have too many difficulties: things are usually simpler, we use a callback in response to an Ajax call. But in a server web app things are, very often, a bit more complex. Writing chain of callbacks don't seem to me a wonderful way of programming. The code is not simple, and so it is difficult to understand and to maintain. Writing twisted code we very often lost the linear intuitive idea of the algorithm we wanted to implement, especially when things grow in complexity. What's your point of view?

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• Regular expression to match empty HTML tags that may contain embedded JSTL?

  - by Keith Bentrup

  I'm trying to construct a regular expression to look for empty html tags that may have embedded JSTL. I'm using Perl for my matching. So far I can match any empty html tag that does not contain JSTL with the following? /<\w+\b(?!:)[^<]*?>\s*<\/\w+/si The \b(?!:) will avoid matching an opening JTSL tag but that doesn't address the whether JSTL may be within the HTML tag itself (which is allowable). I only want to know if this HTML tag has no children (only whitespace or empty). So I'm looking for a pattern that would match both the following: <div id="my-id"> </div> <div class="<c:out var="${my.property}" />"></div> Currently the first div matches. The second does not. Is it doable? I tried several variations using lookahead assertions, and I'm starting to think it's not. However, I can't say for certain or articulate why it's not. Edit: I'm not writing something to interpret the code, and I'm not interested in using a parser. I'm writing a script to point out potential issues/oversights. And at this point, I'm curious, too, to see if there is something clever with lookaheads or lookbehinds that I may be missing. If it bothers you that I'm trying to "solve" a problem this way, don't think of it as looking for a solution. To me it's more of a challenge now, and an opportunity to learn more about regular expressions. Also, if it helps, you can assume that the html is xhtml strict.

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• Java hangs when trying to close a ProcessBuilder OutputStream

  - by Jeff Bullard

  I have the following Java code to start a ProcessBuilder, open an OutputStream, have the process write a string to an OutputStream, and then close the OutputStream. The whole thing hangs indefinitely when I try to close the OutputStream. This only happens on Windows, never on Mac or Linux. Some of the related questions seem to be close to the same problem I'm having, but I haven't been able to figure out how to apply the answers to my problem, as I am a relative newbie with Java. Here is the code. You can see I have put in a lot of println statements to try to isolate the problem. System.out.println("GenMic trying to get the input file now"); System.out.flush(); OutputStream out = child.getOutputStream(); try { System.out.println("GenMic getting ready to write the input file to out"); System.out.flush(); out.write(intext.getBytes()); System.out.println("GenMic finished writing to out"); System.out.flush(); out.close(); System.out.println("GenMic closed OutputStream"); System.out.flush(); } catch (IOException iox) { System.out.println("GenMic caught IOException 2"); System.out.flush(); String detailedMessage = iox.getMessage(); System.out.println("Exception: " + detailedMessage); System.out.flush(); throw new RuntimeException(iox); } And here is the output when this chunk is executed: GenMic trying to get the input file now GenMic getting ready to write the input file to out GenMic finished writing to out

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• How can I SETF an element in a tree by an accessor?

  - by Willi Ballenthin

  We've been using Lisp in my AI course. The assignments I've received have involved searching and generating tree-like structures. For each assignment, I've ended up writing something like: (defun initial-state () (list 0 ; score nil ; children 0 ; value 0)) ; something else and building my functions around these "states", which are really just nested lists with some loosely defined structure. To make the structure more rigid, I've tried to write accessors, such as: (defun state-score ( state ) (nth 2 state)) This works for reading the value (which should be all I need to do in a nicely functional world. However, as time crunches, and I start to madly hack, sometimes I want a mutable structure). I don't seem to be able to SETF the returned ...thing (place? value? pointer?). I get an error with something like: (setf (state-score *state*) 10) Sometimes I seem to have a little more luck writing the accessor/mutator as a macro: (defmacro state-score ( state ) `(nth 2 ,state)) However I don't know why this should be a macro, so I certainly shouldn't write it as a macro (except that sometimes it works. Programming by coincidence is bad). What is an appropriate strategy to build up such structures? More importantly, where can I learn about whats going on here (what operations affect the memory in what way)?

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• Why do my CouchDB databases grow so fast?

  - by konrad

  I was wondering why my CouchDB database was growing to fast so I wrote a little test script. This script changes an attributed of a CouchDB document 1200 times and takes the size of the database after each change. After performing these 1200 writing steps the database is doing a compaction step and the db size is measured again. In the end the script plots the databases size against the revision numbers. The benchmarking is run twice: The first time the default number of document revision (=1000) is used (_revs_limit). The second time the number of document revisions is set to 1. The first run produces the following plot The second run produces this plot For me this is quite an unexpected behavior. In the first run I would have expected a linear growth as every change produces a new revision. When the 1000 revisions are reached the size value should be constant as the older revisions are discarded. After the compaction the size should fall significantly. In the second run the first revision should result in certain database size that is then keeps during the following writing steps as every new revision leads to the deletion of the previous one. I could understand if there is a little bit of overhead needed to manage the changes but this growth behavior seems weird to me. Can anybody explain this phenomenon or correct my assumptions that lead to the wrong expectations?

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• Concurrent WCF calls via shared channel

  - by Kent Boogaart

  I have a web tier that forwards calls onto an application tier. The web tier uses a shared, cached channel to do so. The application tier services in question are stateless and have concurrency enabled. But they are not being called concurrently. If I alter the web tier to create a new channel on every call, then I do get concurrent calls onto the application tier. But I wanted to avoid that cost since it is functionally unnecessary for my scenario. I have no session state, and nor do I need to re-authenticate the caller each time. I understand that the creation of the channel factory is far more expensive than than the creation of the channels, but it is still a cost I'd like to avoid if possible. I found this article on MSDN that states: While channels and clients created by the channels are thread-safe, they might not support writing more than one message to the wire concurrently. If you are sending large messages, particularly if streaming, the send operation might block waiting for another send to complete. Firstly, I'm not sending large messages (just a lot of small ones since I'm doing load testing) but am still seeing the blocking behavior. Secondly, this is rather open-ended and unhelpful documentation. It says they "might not" support writing more than one message but doesn't explain the scenarios under which they would support concurrent messages. Can anyone shed some light on this?

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• question about MySQL database migration

  - by WilliamLou

  Hi there: If I have a MySQL database with several tables on a live server, now I would like to migrate this database to another server. Of course, the migration I mean here involves some database tables, for example: add some new columns to several tables, add some new tables etc.. Now, the only method I can think of is to use some php/python(two scripts I know) script, connect two databases, dump the data from the old database, and then write into the new database. However, this method is not efficient at all. For example: in old database, table A has 28 columns; in new database, table A has 29 columns, but the extra column will have default value 0 for all the old rows. My script still needs to dump the data row by row and insert each row into the new database. Is there any tools or a better method than writing a script yourself? Here, I dont need to worry about multithread writing problems etc.., I mean the old database will be down (not open to public usage etc.., only for upgrade ) for a while. Thanks!!

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• Should I write more SQL to be more efficient, or less SQL to be less buggy?

  - by RenderIn

  I've been writing a lot of one-off SQL queries to return exactly what a certain page needs and no more. I could reuse existing queries and issue a number of SQL requests linear to the number of records on the page. As an example, I have a query to return People and a query to return Job Details for a person. To return a list of people with their job details I could query once for people and then once for each person to retrieve their job details. I've found that in most cases that solution returns things in a reasonable amount of time, but I don't know how well it will scale in my environment. Instead I've been writing queries to join people + job details, or people + salary history, etc. I'm looking at my models and I see how I could shave off maybe 30% of my code if I were to re-use existing queries. This is a big temptation. Is it a bad thing to go for reuse over efficiency in general or does it all come down to the specific situation? Should I first do it the easy way and then optimize later, or is it best to get the code knocked out while everything is fresh in my mind? Thoughts, experiences?

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• Returning true or error message in Ruby

  - by seaneshbaugh

  I'm wondering if writing functions like this is considered good or bad form. def test(x) if x == 1 return true else return "Error: x is not equal to one." end end And then to use it we do something like this: result = test(1) if result != true puts result end result = test(2) if result != true puts result end Which just displays the error message for the second call to test. I'm considering doing this because in a rails project I'm working on inside my controller code I make calls to a model's instance methods and if something goes wrong I want the model to return the error message to the controller and the controller takes that error message and puts it in the flash and redirects. Kinda like this def create @item = Item.new(params[:item]) if [email protected]? result = @item.save_image(params[:attachment][:file]) if result != true flash[:notice] = result redirect_to(new_item_url) and return end #and so on... That way I'm not constructing the error messages in the controller, merely passing them along, because I really don't want the controller to be concerned with what the save_image method itself does just whether or not it worked. It makes sense to me, but I'm curious as to whether or not this is considered a good or bad way of writing methods. Keep in mind I'm asking this in the most general sense pertaining mostly to ruby, it just happens that I'm doing this in a rails project, the actual logic of the controller really isn't my concern.

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• How 'terse' is too terse? -- Practical guidelines for expressing as much intent in as few characters

  - by Christopher Altman

  First, I love writing as little code as possible. I think, and please correct me, one of the golden rules of programming is to express your code in as few of character as possible while maintaining human readability. But I can get a little carried away. I can pack three or four lines into one statement, something like $startDate = $dateTime > time() ? mktime(0,0,0,date('m',time()-86400),date('d',time()*2),2011) : time(); (Note: this is a notional example) I can comprehend the above code when reading it. I prefer 'mushing' it all together because having less lines per page is a good thing to me. So my question: When writing code and thinking about how compact or terse you can express yourself, what are some guidelines you use? Do you write multiple lines because you think it helps other people? Do you write as little as possible, but use comments? Or do you always look for the way to write as little code as possible and enjoy the rewards of compact statements? (Just one slightly off topic comment: I love the Perl one-liners, but that is not what I am talking about here)

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