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• How can I get all content within <table></table> tags using a regex?

  - by Bob Dylan

  So I'm writing an application that will do a little screen scrapping. All the pages (about 1000 or so) contain this line: <table border="0" cellspacing="3"> <tr><td>First rows stuff</td></tr> <tr> <td> The data I want is in here <br /> and it's seperated by these annoying <br /> 's. No id's, classes, or even a single <p> tag. Just a bunch of <br /> tags. </td> </tr> </table> So I just need to get the data within the 2nd row out. How can I do this? Should I use a regex or something else?

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• Why is JavaMail Transport.send() a static method?

  - by skiphoppy

  I'm revising code I did not write that uses JavaMail, and having a little trouble understanding why the JavaMail API is designed the way it is. I have the feeling that if I understood, I could be doing a better job. We call: transport = session.getTransport("smtp"); transport.connect(hostName, port, user, password); So why is Eclipse warning me that this: transport.send(message, message.getAllRecipients()); is a call to a static method? Why am I getting a Transport object and providing settings that are specific to it if I can't use that object to send the message? How does the Transport class even know what server and other settings to use to send the message? It's working fine, which is hard to believe. What if I had instantiated Transport objects for two different servers; how would it know which one to use? In the course of writing this question, I've discovered that I should really be calling: transport.sendMessage(message, message.getAllRecipients()); So what is the purpose of the static Transport.send() method? Is this just poor design, or is there a reason it is this way?

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• Given a typical Rails 3 environment, why am I unable to execute any tests?

  - by Tom

  I'm working on writing simple unit tests for a Rails 3 project, but I'm unable to actually execute any tests. Case in point, attempting to run the test auto-generated by Rails fails: require 'test_helper' class UserTest < ActiveSupport::TestCase # Replace this with your real tests. test "the truth" do assert true end end Results in the following error: <internal:lib/rubygems/custom_require>:29:in `require': no such file to load -- test_helper (LoadError) from <internal:lib/rubygems/custom_require>:29:in `require' from user_test.rb:1:in `<main>' Commenting out the require 'test_helper' line and attempting to run the test results in this error: user_test.rb:3:in `<main>': uninitialized constant Object::ActiveSupport (NameError) The action pack gems appear to be properly installed and up to date: actionmailer (3.0.3, 2.3.5) actionpack (3.0.3, 2.3.5) activemodel (3.0.3) activerecord (3.0.3, 2.3.5) activeresource (3.0.3, 2.3.5) activesupport (3.0.3, 2.3.5) Ruby is at 1.9.2p0 and Rails is at 3.0.3. The sample dump of my test directory is as follows: /fixtures /functional /integration /performance /unit -- /helpers -- user_helper_test.rb -- user_test.rb test_helper.rb I've never seen this problem before - I've run the typical rake tasks for preparing the test environment. I have nothing out of the ordinary in my application or environment configuration files, nor have I installed any unusual gems that would interfere with the test environment. Edit Xavier Holt's suggestion, explicitly specifying the path to the test_helper worked; however, this revealed an issue with ActiveSupport. Now when I attempt to run the test, I receive the following error message (as also listed above): user_test.rb:3:in `<main>': uninitialized constant Object::ActiveSupport (NameError) But as you can see above, Action Pack is all installed and update to date.

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• Fake serial communication under Linux

  - by kigurai

  I have an application where I want to simulate the connection between a device and a "modem". The device will be connected to a serial port and will talk to the software modem through that. For testing purposes I want to be able to use a mock software device to test send and receive data. Example Python code device = Device() modem = Modem() device.connect(modem) device.write("Hello") modem_reply = device.read() Now, in my final app I will just pass /dev/ttyS1 or COM1 or whatever for the application to use. But how can I do this in software? I am running Linux and application is written in Python. I have tried making a FIFO (mkfifo ~/my_fifo) and that does work, but then I'll need one FIFO for writing and one for reading. What I want is to open ~/my_fake_serial_port and read and write to that. I have also lpayed with the ptymodule, but can't get that to work either. I can get a master and slave file descriptor from pty.openpty() but trying to read or write to them only causes IOError Bad File Descriptor error message.

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• Which languages support class replacement?

  - by Alix

  Hi, I'm writing my master thesis, which deals with AOP in .NET, among other things, and I mention the lack of support for replacing classes at load time as an important factor in the fact that there are currently no .NET AOP frameworks that perform true dynamic weaving -- not without imposing the requirement that woven classes must extend ContextBoundObject or MarshalByRefObject or expose all their semantics on an interface. You can however do this in Java thanks to ClassFileTransformer: You extend ClassFileTransformer. You subscribe to the class load event. On class load, you rewrite the class and replace it. All this is very well, but my project director has asked me, quite in the last minute, to give him a list of languages that do / do not support class replacement. I really have no time to look for this now: I wouldn't feel comfortable just doing a superficial research and potentially putting erroneous information in my thesis. So I ask you, oh almighty programming community, can you help out? Of course, I'm not asking you to research this yourselves. Simply, if you know for sure that a particular language supports / doesn't support this, leave it as an answer. If you're not sure please don't forget to point it out. Thanks so much!

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• PHP form processing - how to capture text from field that has variable Name/ID

  - by user80151

  I have a form that has a field pulled from the database as a dropdown. I need to get the text selected in the dropdown but I don't know in advance what the field ID will be. This is basically just a form that has already been generated. I don't need to pull anything from the database, it's already on this page. All I need to do is get the form information and email it, no writing to the database. I know how to do the _Request for the other fields based on the ID but I'm not sure how to do this one. The ID changes. It can be ID=1, ID-2, etc. I need to do something like: _REQUEST form element where ID is LIKE "ID[*]" or something similar. Any suggestions or links to tutorials? Here are a couple samples of what the dropdown renders on the page: <div class="wrapperAttribsOptions"> <h4 class="optionName back"><label class="attribsSelect" for="attrib- 1">Model</label></h4> <div class="back"> <select name="id[1]" id="attrib-1"> <option value="45">VC3-4C</option> <option value="1">VC3-4PG</option> <option value="3">VC3-4SG</option> <div class="wrapperAttribsOptions"> <h4 class="optionName back"><label class="attribsSelect" for="attrib-14">SPK Model</label></h4> <div class="back"> <select name="id[14]" id="attrib-14"> <option value="43">SPK-4</option> <option value="44">SPK-8</option> </select> TIA

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• how to clear XFixes regions

  - by ~buratinas

  Hi, I'm writing some low level code for X11 platform. To achieve best data copying performance I use XFixes/XDamage extensions. How can I clear the contents of XFixes region after one refresh cycle? Or do they clean themselves after I use XFixesSetPictureClipRegion? My code is something like that: Display xdpy; XShamPixmap pixmap_; XFixesRegion region_; damage_event_callback(damage_geometry_t geometry, XDamage damage,...) { unsigned curr_region = XFixesCreateRegion(xdpy, 0, 0); XDamageSubtract(xdpy, damage, None, curr_region); XFixesTranslateRegion( xdpy, curr_region, geometry.left(), geometry.top() ); XFixesUnionRegion (xdpy, region_, region_, curr_region); } process_damage_events(...) { XFixesSetPictureClipRegion( xdpy, pixmap_, 0, 0, region_); XCopyArea (xdpy, window_->id(), pixmap_, XDefaultGC(xdpy, XDefaultScreen(xdpy)), 0,0,width(),height(),0,0); /*Should clear region_ here */ ... } Currently I clear the region by deleting and recreating, but I guess it's not the best way to do that.

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• PHP's openssl_sign generates different signature than SSCrypto's sign

  - by pascalj

  I'm writing an OS X client for a software that is written in PHP. This software uses a simple RPC interface to receive and execute commands. The RPC client has to sign the commands he sends to ensure that no MITM can modify any of them. However, as the server was not accepting the signatures I sent from my OS X client, I started investigating and found out that PHP's openssl_sign function generates a different signature for a given private key/data combination than the Objective-C SSCrypto framework (which is only a wrapper for the openssl lib): SSCrypto *crypto = [[SSCrypto alloc] initWithPrivateKey:self.localPrivKey]; NSData *shaed = [self sha1:@"hello"]; [crypto setClearTextWithData:shaed]; NSData *data = [crypto sign]; generates a signature like CtbkSxvqNZ+mAN... The PHP code openssl_sign("hello", $signature, $privateKey); generates a signature like 6u0d2qjFiMbZ+... (For my certain key, of course. base64 encoded) I'm not quite shure why this is happening and I unsuccessfully experimented with different hash-algorithms. As the PHP documentation states SHA1 is used by default. So why do these two functions generate different signatures and how can I get my Objective-C part to generate a signature that PHPs openssl_verify will accept? Note: I double checked that the keys and the data is correct!

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• Shortcut to create automatic properties using Visual Studio 2008/2010 or Resharper 5

  - by Piers Myers

  I have a class that contains a load of properties that contain results of some calculations e.g: public class Results { public double Result1 { get; set; } public double Result2 { get; set; } } In a different class I am doing calculations to populate the above properties, e.g: public class Calc { private Results Calc() { Results res = new Results(); res.Result1 = ... some calculation res.Result2 = ... some other calculation res.Result3 = ... // not yet defined in 'Results' class return res; } } When I am writing the Calc class, 'Result3' will be highlighted in red as it is not yet defined in the 'Results' class. Currently I am using the Resharper ALT-Enter shortcut, selecting "Create Property 'Result3'" which will create the following code int the 'Results' class: public double Result3 { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } } Which I need to manually change to: public double Result3 { get; set; } Then I use the CTRL-Shift-Backspace shortcut to take me back to the 'Calc' class. How can I easily create automatic properties in the 'Results' class if they are not yet defined directly from the 'Calc' class?

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• looping problem while appending data to existing text file

  - by Manu

  try { stmt = conn.createStatement(); stmt1 = conn.createStatement(); stmt2 = conn.createStatement(); rs = stmt.executeQuery("select cust from trip1"); rs1 = stmt1.executeQuery("select cust from trip2"); rs2 = stmt2.executeQuery("select cust from trip3"); File f = new File(strFileGenLoc); OutputStream os = (OutputStream)new FileOutputStream(f,true); String encoding = "UTF8"; OutputStreamWriter osw = new OutputStreamWriter(os, encoding); BufferedWriter bw = new BufferedWriter(osw); } while ( rs.next() ) { while(rs1.next()){ while(rs2.next()){ bw.write(rs.getString(1)==null? "":rs.getString(1)); bw.write("\t"); bw.write(rs1.getString(1)==null? "":rs1.getString(1)); bw.write("\t"); bw.write(rs2.getString(1)==null? "":rs2.getString(1)); bw.write("\t"); bw.newLine(); } } } Above code working fine. My problem is 1. "rs" resultset contains one record in the table 2. "rs1" resultset contains 5 record in the table 3. "rs2" resultset contains 5 record in the table "rs" data is getting recursive. while writing to the same text file , the output i am getting like 1 2 3 1 12 21 1 23 25 1 10 5 1 8 54 but i need output like below 1 2 3 12 21 23 25 10 5 8 54 What things i need to change in my code.. Please advice

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• Keeping sync in multiplayer RTS game that uses floating point arithmetic

  - by Calmarius

  I'm writing a 2D space RTS game in C#. Single player works. Now I want to add some multiplayer functionality. I googled for it and it seems there is only one way to have thousands of units continuously moving without a powerful net connection: send only the commands through the network while running the same simulation at every player. And now there is a problem the entire engine uses doubles everywhere. And floating point calculations are depends heavily on compiler optimalizations and cpu architecture so it is very hard to keep things syncronized. And it is not grid based at all, and have a simple phisics engine to move the space-ships (space ships have impulse and angular-momentum...). So recoding the entire stuff to use fixed point would be quite cumbersome (but probably the only solution). So I have 2 options so far: Say bye to the current code and restart from scratch using integers Make the game LAN only where there is enough bandwidth to have 8 players with thousands of units and sending the positions and orientation etc in (almost) every frame... So I looking for better opinions, (or even tips on migrating the code to fixed-point without messing everything up...)

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• forcing stack w/i 32bit when -m64 -mcmodel=small

  - by chaosless

  have C sources that must compile in 32bit and 64bit for multiple platforms. structure that takes the address of a buffer - need to fit address in a 32bit value. obviously where possible these structures will use natural sized void * or char * pointers. however for some parts an api specifies the size of these pointers as 32bit. on x86_64 linux with -m64 -mcmodel=small tboth static data and malloc()'d data fit within the 2Gb range. data on the stack, however, still starts in high memory. so given a small utility _to_32() such as: int _to_32( long l ) { int i = l & 0xffffffff; assert( i == l ); return i; } then: char *cp = malloc( 100 ); int a = _to_32( cp ); will work reliably, as would: static char buff[ 100 ]; int a = _to_32( buff ); but: char buff[ 100 ]; int a = _to_32( buff ); will fail the assert(). anyone have a solution for this without writing custom linker scripts? or any ideas how to arrange the linker section for stack data, would appear it is being put in this section in the linker script: .lbss : { *(.dynlbss) *(.lbss .lbss.* .gnu.linkonce.lb.*) *(LARGE_COMMON) } thanks!

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• Controlling shell command line wildcard expansion in C or C++

  - by Adrian McCarthy

  I'm writing a program, foo, in C++. It's typically invoked on the command line like this: foo *.txt My main() receives the arguments in the normal way. On many systems, argv[1] is literally *.txt, and I have to call system routines to do the wildcard expansion. On Unix systems, however, the shell expands the wildcard before invoking my program, and all of the matching filenames will be in argv. Suppose I wanted to add a switch to foo that causes it to recurse into subdirectories. foo -a *.txt would process all text files in the current directory and all of its subdirectories. I don't see how this is done, since, by the time my program gets a chance to see the -a, then shell has already done the expansion and the user's *.txt input is lost. Yet there are common Unix programs that work this way. How do they do it? In Unix land, how can I control the wildcard expansion? (Recursing through subdirectories is just one example. Ideally, I'm trying to understand the general solution to controlling the wildcard expansion.)

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• Common Lisp condition system for transfer of control

  - by Ken

  I'll admit right up front that the following is a pretty terrible description of what I want to do. Apologies in advance. Please ask questions to help me explain. :-) I've written ETLs in other languages that consist of individual operations that look something like: // in class CountOperation IEnumerable<Row> Execute(IEnumerable<Row> rows) { var count = 0; foreach (var row in rows) { row["record number"] = count++; yield return row; } } Then you string a number of these operations together, and call The Dispatcher, which is responsible for calling Operations and pushing data between them. I'm trying to do something similar in Common Lisp, and I want to use the same basic structure, i.e., each operation is defined like a normal function that inputs a list and outputs a list, but lazily. I can define-condition a condition (have-value) to use for yield-like behavior, and I can run it in a single loop, and it works great. I'm defining the operations the same way, looping through the inputs: (defun count-records (rows) (loop for count from 0 for row in rows do (signal 'have-value :value `(:count ,count @,row)))) The trouble is if I want to string together several operations, and run them. My first attempt at writing a dispatcher for these looks something like: (let ((next-op ...)) ;; pick an op from the set of all ops (loop (handler-bind ((have-value (...))) ;; records output from operation (setq next-op ...) ;; pick a new next-op (call next-op))) But restarts have only dynamic extent: each operation will have the same restart names. The restart isn't a Lisp object I can store, to store the state of a function: it's something you call by name (symbol) inside the handler block, not a continuation you can store for later use. Is it possible to do something like I want here? Or am I better off just making each operation function explicitly look at its input queue, and explicitly place values on the output queue?

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• Program structure in long running data processing python script

  - by fmark

  For my current job I am writing some long-running (think hours to days) scripts that do CPU intensive data-processing. The program flow is very simple - it proceeds into the main loop, completes the main loop, saves output and terminates: The basic structure of my programs tends to be like so: <import statements> <constant declarations> <misc function declarations> def main(): for blah in blahs(): <lots of local variables> <lots of tightly coupled computation> for something in somethings(): <lots more local variables> <lots more computation> <etc., etc.> <save results> if __name__ == "__main__": main() This gets unmanageable quickly, so I want to refactor it into something more manageable. I want to make this more maintainable, without sacrificing execution speed. Each chuck of code relies on a large number of variables however, so refactoring parts of the computation out to functions would make parameters list grow out of hand very quickly. Should I put this sort of code into a python class, and change the local variables into class variables? It doesn't make a great deal of sense tp me conceptually to turn the program into a class, as the class would never be reused, and only one instance would ever be created per instance. What is the best practice structure for this kind of program? I am using python but the question is relatively language-agnostic, assuming a modern object-oriented language features.

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• How do I use InputType=numberDecimal with the "phone" soft keypad?

  - by Adam Dunn

  For an EditText box, the user should only be entering valid numbers, so I am using android:inputType="numberDecimal". Unfortunately, the soft keyboard that Android brings up has numbers only along the top row, while the next three rows have various other symbols (dollar sign, percent sign, exclamation mark, space, etc). Since the numberDecimal only accepts numbers 0-9, negative sign, and decimal point, it would make more sense to use the "phone" soft keyboard (0-9 in a 3x3 grid, plus some other symbols). This would make the buttons larger and easier to hit (since it's a 4x4 grid rather than a 10x4 grid in the same screen area). Unfortunately, using android:inputType="phone" allows non-numeric characters such as parentheses I have attempted to use android:inputType="numberDecimal|phone", but the numberDecimal aspect of the bit flag seems to be ignored. I have also tried using android:inputType="phone" in combination with android:digits="0123456789-.", but that still allows multiple negative signs or decimal points (inputType="number" has really good error checking for things like that, and won't let the user even type it in). I have also tried using android:inputType="phone" in the xml layout file, while using a DigitsKeyListener in the java code, but then that just uses the default number soft keyboard (the one that has numbers only along top row) (it appears to set InputType.TYPE_CLASS_NUMBER, which voids the InputType.TYPE_CLASS_PHONE set by the xml layout). Writing a custom IME wouldn't work, since the user would have to select the IME as a global option outside the app. Is there any way to use the "phone" style soft keyboard while also using the "number" restrictions on what is entered?

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• std::string.resize() and std::string.length()

  - by dreamlax

  I'm relatively new to C++ and I'm still getting to grips with the C++ Standard Library. To help transition from C, I want to format a std::string using printf-style formatters. I realise stringstream is a more type-safe approach, but I find myself finding printf-style much easier to read and deal with (at least, for the time being). This is my function: using namespace std; string formatStdString(const string &format, ...) { va_list va; string output; size_t needed; size_t used; va_start(va, format); needed = vsnprintf(&output[0], 0, format.c_str(), va); output.resize(needed + 1); // for null terminator?? used = vsnprintf(&output[0], output.capacity(), format.c_str(), va); // assert(used == needed); va_end(va); return output; } This works, kinda. A few things that I am not sure about are: Do I need to make room for a null terminator, or is this unnecessary? Is capacity() the right function to call here? I keep thinking length() would return 0 since the first character in the string is a '\0'. Occasionally while writing this string's contents to a socket (using its c_str() and length()), I have null bytes popping up on the receiving end, which is causing a bit of grief, but they seem to appear inconsistently. If I don't use this function at all, no null bytes appear.

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• How do I use Core Data with the Cocoa Text Input system?

  - by the Joel

  Hobbyist Cocoa programmer here. Have been looking around all the usual places, but this seems relatively under-explained: I am writing something a little out of the ordinary. It is much simpler than, but similar to, a desktop publishing app. I want editable text boxes on a canvas, arbitrarily placed. This is document-based and I’d really like to use Core Data. Now, The cocoa text-handling system seems to deal with a four-class structure: NSTextStorage, NSLayoutManager, NSTextContainer and finally NSTextView. I have looked into these and know how to use them, sort of. Have been making some prototypes and it works for simple apps. The problem arrives when I get into persistency. I don't know how to, by way of Cocoa Bindings or something else, store the contents of NSTextStorage (= the actual text) in my managed object context. I have considered overriding methods pairs like -words, -setWords: in these objects. This would let me link the words to a String, which I know how to store in Core Data. However, I’d have to override any method that affects the text - and that seems a little much. Thankful for any insights.

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• Carriage Return\Line feed in Java

  - by Manu

  Guys, i have created text file in unix enviroment using java code. For writing the text file i am using java.io.FileWriter and BufferedWriter. and for newline after each row i am using bw.newLine() method. (where bw is object of BufferedWriter ) and sending that text file by attaching in mail from unix environment itself (automated that using unix commands). My issue is, after i download the text file from mail in windows system, if i opened that text file the data's are not properly aligned. newline() character is not working i think so. I want same text file alignment as it is in unix environment, if i opened the text file in windows environment also. How to resolve the problem.Please help ASAP. Thanks for your help in advance. pasting my java code here for your reference..(running java code in unix environment) File f = new File(strFileGenLoc); BufferedWriter bw = new BufferedWriter(new FileWriter(f, false)); rs = stmt.executeQuery("select * from jpdata"); while ( rs.next() ) { bw.write(rs.getString(1)==null? "":rs.getString(1)); bw.newLine(); }

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• Fast, easy, and secure method to perform DB actions with GET

  - by rob - not a robber

  Hey All, Sort of a methods/best practices question here that I am sure has been addressed, yet I can't find a solution based on the vague search terms I enter. I know starting off the question with "Fast and easy" will probably draw out a few sighs, so my apologies. Here is the deal. I have a logged in area where an ADMIN can do a whole host of POST operations to input data relating to their profile. The way I have data structured is pretty distinct and well segmented in most tables as it relates to the ID of the admin. Now, I have a table where I dump one type of data into and differentiate this data by assigning the ADMIN's unique ID to each record. In other words, all ADMINs have this one type of data writing to this table. I just differentiate by the ADMIN ID with each record. I was planning on letting the ADMIN remove these records by clicking on a link with a query string - obviously using GET. Obviously, the query structure is in the link so any logged in admin could then exploit the URL and delete a competitor's records. Is the only way to safely do this through POST or should I pass through the session info that includes password and validate it against the ADMIN ID that is requesting the delete? This is obviously much more work for me. As they said in the auto repair biz I used to work in... there are 3 ways to do a job: Fast, Good, and Cheap. You can only have two at a time. Fast and cheap will not be good. Good and cheap will not have fast turnaround. Fast and good will NOT be cheap. haha I guess that applies here... can never have Fast, Easy and Secure all at once ;) Thanks in advance...

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• Achieving Thread-Safety

  - by Smasher

  Question How can I make sure my application is thread-safe? Are their any common practices, testing methods, things to avoid, things to look for? Background I'm currently developing a server application that performs a number of background tasks in different threads and communicates with clients using Indy (using another bunch of automatically generated threads for the communication). Since the application should be highly availabe, a program crash is a very bad thing and I want to make sure that the application is thread-safe. No matter what, from time to time I discover a piece of code that throws an exception that never occured before and in most cases I realize that it is some kind of synchronization bug, where I forgot to synchronize my objects properly. Hence my question concerning best practices, testing of thread-safety and things like that. mghie: Thanks for the answer! I should perhaps be a little bit more precise. Just to be clear, I know about the principles of multithreading, I use synchronization (monitors) throughout my program and I know how to differentiate threading problems from other implementation problems. But nevertheless, I keep forgetting to add proper synchronization from time to time. Just to give an example, I used the RTL sort function in my code. Looked something like FKeyList.Sort (CompareKeysFunc); Turns out, that I had to synchronize FKeyList while sorting. It just don't came to my mind when initially writing that simple line of code. It's these thins I wanna talk about. What are the places where one easily forgets to add synchronization code? How do YOU make sure that you added sync code in all important places?

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• Moving from a non-clustered PK to a clustered PK in SQL 2005

  - by adaptr

  HI all, I recently asked this question in another thread, and thought I would reproduce it here with my solution: What if I have an auto-increment INT as my non-clustered primary key, and there are about 15 foreign keys defined to it ? (snide comment about original designer being braindead in the original :) ) This is a 15M row table, on a live database, SQL Standard, so dropping indexes is out of the question. Even temporarily dropping the foreign key constraints will be difficult. I'm curious if anybody has a solution that causes minimal downtime. I tested this in our testing environment and finally found that the downtime wasn't as severe as I had originally feared. I ended up writing a script that drops all FK constraints, then drops the non-clustered key, re-creates the PK as a clustered index, and finally re-created all FKs WITH NOCHECK to avoid trawling through all FKs to check constraint compliance. Then I just enable the CHECK constraints to enable constraint checking from that point onwards, and all is dandy :) The most important thing to realize is that during the time the FKs are absent, there MUST NOT be any INSERTs or DELETEs on the parent table, as this may break the constraints and cause issues in the future. The total time taken for clustering a 15M row, 800MB index was ~4 minutes :)

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• LINQ-SQL Updating Multiple Rows in a single transaction

  - by RPM1984

  Hi guys, I need help re-factoring this legacy LINQ-SQL code which is generating around 100 update statements. I'll keep playing around with the best solution, but would appreciate some ideas/past experience with this issue. Here's my code: List<Foo> foos; int userId = 123; using (DataClassesDataContext db = new FooDatabase()) { foos = (from f in db.FooBars where f.UserId = userId select f).ToList(); foreach (FooBar fooBar in foos) { fooBar.IsFoo = false; } db.SubmitChanges() } Essentially i want to update the IsFoo field to false for all records that have a particular UserId value. Whats happening is the .ToList() is firing off a query to get all the FooBars for a particular user, then for each Foo object, its executing an UPDATE statement updating the IsFoo property. Can the above code be re-factored to one single UPDATE statement? Ideally, the only SQL i want fired is the below: UPDATE FooBars SET IsFoo = FALSE WHERE UserId = 123 EDIT Ok so looks like it cant be done without using db.ExecuteCommand. Grr...! What i'll probably end up doing is creating another extension method for the DLINQ namespace. Still require some hardcoding (ie writing "WHERE" and "UPDATE"), but at least it hides most of the implementation details away from the actual LINQ query syntax.

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• R plotting multiple histograms on single plot to .pdf as a part of R batch script

  - by Bryce Thomas

  I am writing R scripts which play just a small role in a chain of commands I am executing from a terminal. Basically, I do much of my data manipulation in a Python script and then pipe the output to my R script for plotting. So, from the terminal I execute commands which look something like $python whatever.py | R CMD BATCH do_some_plotting.R. This workflow has been working well for me so far, though I have now reached a point where I want to overlay multiple histograms on the same plot, inspired by this answer to another user's question on Stackoverflow. Inside my R script, my plotting code looks like this: pdf("my_output.pdf") plot(hist(d$original,breaks="FD",prob=TRUE), col=rgb(0,0,1,1/4),xlim=c(0,4000),main="original - This plot is in beta") plot(hist(d$minus_thirty_minutes,breaks="FD",prob=TRUE), col=rgb(1,0,0,1/4),add=T,xlim=c(0,4000),main="minus_thirty_minutes - This plot is in beta") Notably, I am using add=T, which is presumably meant to specify that the second plot should be overlaid on top of the first. When my script has finished, the result I am getting is not two histograms overlaid on top of each other, but rather a 3-page PDF whose 3 individual plots contain the titles: i) Histogram of d$original ii) original - This plot is in beta iii) Histogram of d$minus_thirty_minutes So there's two points here I'm looking to clarify. Firstly, even if the plots weren't overlaid, I would expect just a 2-page PDF, not a 3-page PDF. Can someone explain why I am getting a 3-page PDF? Secondly, is there a correction I can make here somewhere to get just the two histograms plotted, and both of them on the same plot (i.e. 1-page PDF)? The other Stackoverflow question/answer I linked to in the first paragraph did mention that alpha-blending isn't supported on all devices, and so I'm curious whether this has anything to do with it. Either way, it would be good to know if there is a R-based solution to my problem or whether I'm going to have to pipe my data into a different language/plotting engine.

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• Thread Safety of C# List<T> for readers

  - by ILIA BROUDNO

  I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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