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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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• Running Firefox in the Windows service mode

  - by Leonid

  I'm writing a server running as a Windows service that by request invokes Firefox to generate a pdf snapshot of a webpage. I know it is a bad idea to run a GUI program in service mode, but the server nature of my program restricts from running it in the user mode. Running a user-level 'proxy' also is not an option, since there might be no interactive user logged-in on the machine with the server running. In my experiments Firefox successfully produced pdf when the service was running under a user account that was already logged-in. Obviously it didn't work in other cases: for Local System and user accounts that weren't logged-in. Under LocalSystem with 'Allow service to interact with desktop' option enabled I could see the Firefox started that reports that it's unable to find a printer. Since it wouldn't be practical to require an opened user session for the pdf server to run, is there any workaround for this except running the whole thing from a virtual machine?

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• Why is super.super.method(); not allowed in Java?

  - by Tim Büthe

  I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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• sql data source re binding question

  - by Keith

  In my gridview after an insert operation has been done I am filtering the sqldatasource by ID. I am getting an error that the item drop down box selected value is not in the list. To test my theory I created a new sql data source with only the select statement and after the insert operation I am binding it to my grid view and filtering by Id and I get my result. The question Having a second data source is not the solution so is it possible that there is some way to use sqldatasource1? what I tried is sqldatasource.databind() and gridview.databind() on the inserted and inserting metheds in many test cases but still that doesnt work. I dont have any filters applied on the original data source?

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• Sorting a 2D numpy array by multiple axes

  - by perimosocordiae

  I have a 2D numpy array of shape (N,2) which is holding N points (x and y coordinates). For example: array([[3, 2], [6, 2], [3, 6], [3, 4], [5, 3]]) I'd like to sort it such that my points are ordered by x-coordinate, and then by y in cases where the x coordinate is the same. So the array above should look like this: array([[3, 2], [3, 4], [3, 6], [5, 3], [6, 2]]) If this was a normal Python list, I would simply define a comparator to do what I want, but as far as I can tell, numpy's sort function doesn't accept user-defined comparators. Any ideas?

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• How to check if my string is equal to null?

  - by Roman

  I want to perform some action ONLY IF my string has a meaningful value. So, I tried this. if (!myString.eqauls("")) { doSomething } and this if (!myString.eqauls(null)) { doSomething } and this if ( (!myString.eqauls("")) && (!myString.eqauls(null))) { doSomething } and this if ( (!myString.eqauls("")) && (myString!=null)) { doSomething } and this if ( myString.length()>0) { doSomething } And in all cases my program doSomething in spite on the fact that my string IS EMPTY. It equals to null. So, what is wrong with that?

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• Any valid use of goto in PHP?

  - by nikic

  I know, there are other questions about the goto statement introduced in PHP 5.3. But I couldn't find any decent answer in there, all were of the type "last resort", "xkcd", "evil", "bad", "EVIL!!!". But no valid example. Only statements that there aren't any uses. Or statements that there are some rare use cases (again, without examples). So, the question is: "Which are the valid uses of goto in PHP". Answers for "Is goto evil" are not welcome and will get downvoted. Thanks :) Or does somebody have a link to an RFC where the decision is explained - I couldn't find one.

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• my output parameters are always null when i use BeginExecuteNonQuery

  - by CharlesO

  I have a stored procedure that returns a varchar(160) as an output parameter of a stored procedure. Everything works fine when i use ExecuteNonQuery, i always get back the expected value. However, once i switch to use BeginExecuteNonQuery, i get a null value for the output. I am using connString + "Asynchronous Processing=true;" in both cases. Sadly the BeginExecuteNonQuery is about 1.5 times faster in my case...but i really need the output parameter. Thanks!

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• Faking a Single Address Space

  - by dsimcha

  I have a large scientific computing task that parallelizes very well with SMP, but at too fine grained a level to be easily parallelized via explicit message passing. I'd like to parallelize it across address spaces and physical machines. Is it feasible to create a scheduler that would parallelize already multithreaded code across multiple physical computers under the following conditions: The code is already multithreaded and can scale pretty well on SMP configurations. The fact that not all of the threads are running in the same address space or on the same physical machine must be transparent to the program, even if this comes at a significant performance penalty in some use cases. You may assume that all of the physical machines involved are running operating systems and CPU architectures that are binary compatible. Things like locks and atomic operations may be slow (having network latency to deal with and all) but must "just work".

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• Optimize MySQL database query

  - by rajeeesh

  I had a commenting application in my web site. The comments will store in a MySQL table . table structure as follows id | Comment | user | created_date ------------------------------------------------------ 12 | comment he | 1245 | 2012-03-30 12:15:00 ------------------------------------------------------ I need to run a query for listing all the comments after a specific time. ie .. a query like this SELECT * FROM comments WHERE created_date > "2012-03-29 12:15:00" ORDER BY created_date DESC Its working fine.. My question is if I got a 1-2 lakh entry in this table is this query is sufficient for the purpose ? or this query will take time to execute ? In most cases I have to show last 2 days data + periodically ( interval of 10 mins ) checking for updates with ajax from this table ... Please help Thanks

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• Style question about existing piece of code (C/C++)

  - by Leif Ericson

  I just hope the following doesn't seem to you like redundant jabber :) Anyway, there is that: for (p = fmt; *p; p++) { if (*p != '%') { putchar(*p); continue; } switch (*++p) { /* Some cases here */ ... } } And I wondered why the writer (Kernighan / Ritchie) used the continue in the if statement. I thought it was for the mere reason that he deemed it would be more elegant than indenting the whole switch under an else statement, what do you think?

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• Unboxing object containing a value which is known to be assignable to an integer variable

  - by Wim Coenen

  If I have an object instance and I know it is actually a boxed integer, then I can simply cast it back to int like this: object o = GetSomethingByName("foo"); int i = (int)o; However, I don't actually know that the value is an integer. I only know that it can be assigned to an integer. For example, it could be a byte, and the above code would throw InvalidCastException in that case. Instead I would have to do this: object o = GetSomethingByName("foo"); int i = (int)(byte)o; The value could also be a short, or something else which can be assigned to an int. How do I generalize my code to handle all those cases (without handling each possibility separately)?

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• How to limit the number of post values on UpdatePanel ?

  - by Aristos

  I have notice that the UpdatePanel post every field included on the form on every trigger. But in most of my cases I use 2-3 UpdatePanels at the same page, and each one is independent. When I click for update the one panel, then my page receive all the input data of the page (ok this is logical) but I won to read only this UpdatePanels data and act according, and not the other panels data. So I see that a lot of traffic is happened this way. So is there a way to say to one UpdatePanel - send only my input data, and not everything found on the page. ? Thank you in advanced.

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• Calling a method on a Object says "disallows late binding"

  - by Maury Markowitz

  I have a calls called DtaDate that stores an integer "key", a string name, a string for the date, and a Date object that is created from that string. I have some code that needs to accept a date-like object. I'd like the user to be able to pass in anything date like - a Date object which I'll extract the information from, another DtaDate, a string with the date in it, or even the key, which I'll use to look up the DtaDate from a collection. So I have this: Friend Sub New(NameIn As String, DateFormulaIn As String, Optional FromDateIn As Object = Nothing) [stuff that works] [check that we got a FromDateIn...] If TypeOf FromDateIn Is DtaDate Then fdk = FromDateIn.Key Ans.FromDate = fdk VB tells me that "Option Strict On disallows late binding". The other cases, where a string or integer is the TypeOf, I use CInt or CStr. But this is the first time I've actually run into a case where the casting is a non-base type. What's the trick?

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• How good is the Rails sanitize() method?

  - by Horace Loeb

  Can I use ActionView::Helpers::SanitizeHelper#sanitize on user-entered text that I plan on showing to other users? E.g., will it properly handle all cases described on this site? Also, the documentation mentions: Please note that sanitizing user-provided text does not guarantee that the resulting markup is valid (conforming to a document type) or even well-formed. The output may still contain e.g. unescaped ’<’, ’’, ’&’ characters and confuse browsers. What's the best way to handle this? Pass the sanitized text through Hpricot before displaying?

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• Combining XSLT transforms

  - by Flynn1179

  Is there a way to combine two XSLT documents into a single XSLT document that does the same as transforming using the original two in sequence? i.e. Combining XSLTA and XSLTB into XSLTC such that XSLTB( XSLTA( xml )) == XSLTC( xml )? There's three reasons I'd like to be able to do this: Simplifies development; some operations need sequential transforms, and although I can generate a combined one by hand, it's a lot more difficult to maintain that two much simpler, separate transforms. Speed; one transform is in most cases hopefully faster than two. I'm currently working on a program that literally just transforms a data file in XML into an XHTML page capable of editing it using one XSLT, and a second XSLT that transforms the XHTML page back into the data file when it's saved. One test I hope to be able to do is to combine the two, and easily confirm that the 'combined' XSLT should leave the data unchanged.

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• Fastest method for SQL Server inserts, updates, selects

  - by Ian

  I use SPs and this isn't an SP vs code-behind "Build your SQL command" question. I'm looking for a high-throughput method for a backend app that handles many small transactions. I use SQLDataReader for most of the returns since forward only works in most cases for me. I've seen it done many ways, and used most of them myself. Methods that define and accept the stored procedure parameters as parameters themselves and build using cmd.Parameters.Add (with or without specifying the DB value type and/or length) Assembling your SP params and their values into an array or hashtable, then passing to a more abstract method that parses the collection and then runs cmd.Parameters.Add Classes that represent tables, initializing the class upon need, setting the public properties that represent the table fields, and calling methods like Save, Load, etc I'm sure there are others I've seen but can't think of at the moment as well. I'm open to all suggestions.

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• Undocumented overload of string.Split() ?

  - by Neil N

  According to both Intellisense and MSDN doc on string.Split, there are no parameterless overloads of string.Split. Yet if I type in string[] foo = bar.Split(); It compiles. And it works. I have verified this in both Visual Studio 2008 and 2010. In both cases intellisense does not show the parameterless overload. Is there a reason for this? Are there any other missing overloads from the MSDN/Intellisense docs? Usually browsing through overloads in intellisense is how I best determine which overload to use. I'd hate to think I am missing other available options throughout the .Net framework.

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• Intersection of line and rectangle with maximum segment length

  - by Aarkan

  I have a vector represented by the slope m. Then there is rectangle (assume axis aligned), which is represented by top-left and bottom-right corner. Of course, there may be many lines with slope m and intersecting the given rectangle. The problem is to find out the line whose length of line intercept inside the rectangle is maximum among all such lines. i.e., if the line intersects rectangle at P1 and P2, then the problem is to find the equation of line for which length of P1P2 is maximum. I proceeded like this. Let the line is: y = m*x + c. Then find out the intersection with each side of rectangle and finding out the maxima for distance function between each pair of points. But it will only give me the length of line segment and there seem to be many corner cases to handle. Could anyone please suggest a better way to do this. Thanks in advance.

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• How to print size_t variable portably?

  - by ArunSaha

  I have a variable of type size_t, and I want to print it using printf(). What format specifier do I use to print it portably? In 32-bit machine, %u seems right. I compiled with g++ -g -W -Wall -Werror -ansi -pedantic, and there was no warning. But when I compile that code in 64-bit machine, it produces warning. size_t x = <something>; printf( "size = %u\n", x ); warning: format '%u' expects type 'unsigned int', but argument 2 has type 'long unsigned int' The warning goes away, as expected, if I change that to %lu. The question is, how can I write the code, so that it compiles warning free on both 32- and 64- bit machines? Edit: I guess one answer might be to "cast" the variable into an unsigned long, and print using %lu. That would work in both cases. I am looking if there is any other idea. (C, C++)

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• is it safe to refactor my django models?

  - by Johnd

  My model is similar to this. Is this ok or should I make the common base class abstract? What are the differcenes between this or makeing it abstract and not having an extra table? It seems odd that there is only one primary key now that I have factored stuff out. class Input(models.Model): details = models.CharField(max_length=1000) user = models.ForeignKey(User) pub_date = models.DateTimeField('date published') rating = models.IntegerField() def __unicode__(self): return self.details class Case(Input): title = models.CharField(max_length=200) views = models.IntegerField() class Argument(Input): case = models.ForeignKey(Case) side = models.BooleanField() is this ok to factor stuff out intpu Input? I noticed Cases and Arguments share a primary Key. like this: CREATE TABLE "cases_input" ( "id" integer NOT NULL PRIMARY KEY, "details" varchar(1000) NOT NULL, "user_id" integer NOT NULL REFERENCES "auth_user" ("id"), "pub_date" datetime NOT NULL, "rating" integer NOT NULL ) ; CREATE TABLE "cases_case" ( "input_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "cases_input" ("id"), "title" varchar(200) NOT NULL, "views" integer NOT NULL ) ; CREATE TABLE "cases_argument" ( "input_ptr_id" integer NOT NULL PRIMARY KEY REFERENCES "cases_input" ("id"), "case_id" integer NOT NULL REFERENCES "cases_case" ("input_ptr_id"), "side" bool NOT NULL )

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• Optimizing Code

  - by Claudiu

  You are given a heap of code in your favorite language which combines to form a rather complicated application. It runs rather slowly, and your boss has asked you to optimize it. What are the steps you follow to most efficiently optimize the code? What strategies have you found to be unsuccessful when optimizing code? Re-writes: At what point do you decide to stop optimizing and say "This is as fast as it'll get without a complete re-write." In what cases would you advocate a simple complete re-write anyway? How would you go about designing it?

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• maching strings

  - by kiran

  Write two functions, called countSubStringMatch and countSubStringMatchRecursive that take two arguments, a key string and a target string. These functions iteratively and recursively count the number of instances of the key in the target string. You should complete definitions for def countSubStringMatch(target,key): and def countSubStringMatchRecursive (target, key): For the remaining problems, we are going to explore other substring matching ideas. These problems can be solved with either an iterative function or a recursive one. You are welcome to use either approach, though you may find iterative approaches more intuitive in these cases of matching linear structures.

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• The return value should be a list but doesn't return as expected?! - Python newbie

  - by user1432941

  Hi this must be a very simple solution that has eluded me this last hour. I've tried to build this test function where the return value of the test_cases list should match the values in the test_case_answers list but for some reason, test case 1 and test case 2 fail. When i print the return values for the test cases they return the correct answers, but for some reason test case 1 and test case 2 return False. Thanks for your help! import math test_cases = [1, 9, -3] test_case_answers = [1, 3, 0] def custom_sqrt(num): for i in range(len(test_cases)): if test_cases[i] >= 0: return math.sqrt(test_cases[i]) else: return 0 for i in range(len(test_cases)): if custom_sqrt(test_cases[i]) != test_case_answers[i]: print "Test Case #", i, "failed!" custom_sqrt(test_cases)

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