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  • Are +=, |=, &= etc atomic?

    - by SF.
    Are the "modify" operators like +=, |=, &= etc atomic? I know ++ is atomic (if you perform x++; in two different threads "simultaneously", you will always end up with x increased by 2, as opposed to x=x+1 with optimization switched off.) What I wonder is whether variable |= constant, and the likes are thread-safe or do I have to protect them with a mutex? (...or is it CPU-dependent? In this case, how is it on ARM?)

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  • C++ and,or,not,xor keywords [closed]

    - by uray
    Possible Duplicate: The written versions of the logical operators. I notice that C++ define keyword and, or, not, xor, and_eq, or_eq, not_eq and xor_eq as an alternative to &&, ||, !, ^, &=, |=, != and |=. and they're rarely used! What's wrong? Are they not portable?

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  • what is this operator called and what is it used for <=>

    - by Scott
    I recently came across this magical operator when digging into Groovy: <= Groovy has really made me happy with elvis operators ?. and ?: which I use constantly now and very much wish were in Java. With this new operator, I have only found this reference. It seems to make comparators much easier. My question is how does it handle null values and how does it compare non Comparable object. Does this operator have a name, I couldn't find it Googling.

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  • Accessing local variable doesn't improve performance

    - by NicMagnier
    The short version Why is this code: var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; More performant than this one? var index = Math.floor(ref_index) * 4; The long version This week, the author of Impact js published an article about some rendering issue: http://www.phoboslab.org/log/2012/09/drawing-pixels-is-hard In the article there was the source of a function to scale an image by accessing pixels in the canvas. I wanted to suggest some traditional ways to optimize this kind of code so that the scaling would be shorter at loading time. But after testing it my result was most of the time worst that the original function. Guessing this was the JavaScript engine that was doing some smart optimization I tried to understand a bit more what was going on so I did a bunch of test. But my results are quite confusing and I would need some help to understand what's going on. I have a test page here: http://www.mx981.com/stuff/resize_bench/test.html jsPerf: http://jsperf.com/local-variable-due-to-the-scope-lookup To start the test, click the picture and the results will appear in the console. There are three different versions: The original code: for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; var indexScaled = (y * widthScaled + x) * 4; scaledPixels.data[ indexScaled ] = origPixels.data[ index ]; scaledPixels.data[ indexScaled+1 ] = origPixels.data[ index+1 ]; scaledPixels.data[ indexScaled+2 ] = origPixels.data[ index+2 ]; scaledPixels.data[ indexScaled+3 ] = origPixels.data[ index+3 ]; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance One of my attempt to optimize it: var ref_index = 0; var ref_indexScaled = 0 var ref_step = 1 / scale; for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = Math.floor(ref_index) * 4; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+1 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+2 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+3 ]; ref_index+= ref_step; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance The same optimized code but with recalculating the index variable each time (Hybrid) var ref_index = 0; var ref_indexScaled = 0 var ref_step = 1 / scale; for( var y = 0; y < heightScaled; y++ ) { for( var x = 0; x < widthScaled; x++ ) { var index = (Math.floor(y / scale) * img.width + Math.floor(x / scale)) * 4; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+1 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+2 ]; scaledPixels.data[ ref_indexScaled++ ] = origPixels.data[ index+3 ]; ref_index+= ref_step; } } jsPerf: http://jsperf.com/so-accessing-local-variable-doesn-t-improve-performance The only difference in the two last one is the calculation of the 'index' variable. And to my surprise the optimized version is slower in most browsers (except opera). Results of personal testing (not the jsPerf tests): Opera Original: 8668ms Optimized: 932ms Hybrid: 8696ms Chrome Original: 139ms Optimized: 145ms Hybrid: 136ms Safari Original: 433ms Optimized: 853ms Hybrid: 451ms Firefox Original: 343ms Optimized: 422ms Hybrid: 350ms After digging around, it seems an usual good practice is to access mainly local variable due to the scope lookup. Because The optimized version only call one local variable it should be faster that the Hybrid code which call multiple variable and object in addition to the various operation involved. So why the "optimized" version is slower? I thought that it might be because some JavaScript engine don't optimize the Optimized version because it is not hot enough but after using --trace-opt in chrome, it seems all version are properly compiled by V8. At this point I am a bit clueless and wonder if somebody would know what is going on? I did also some more test cases in this page: http://www.mx981.com/stuff/resize_bench/index.html

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  • Django template call function

    - by cleg
    I'm passing to Django's template a function, which returns me some records. I want to call this function and iterate over it's result. {% for item in my_func(10) %} That doesn't work. I've tried to set fuction's return value to a variable and iterate over variable, but there seems to be no way to set variable in Django template. Is there any normal way to do it?

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  • MySQL - How To Avoid Repair With Keycache?

    - by dvancouver
    I have had some experience with optimizing the my.cnf file but my database has around 4 million records (MyISAM). I am trying to restore from a mysqldump but every time I do I eventually get the dreaded "Repair With Keycache", that may take days. Is there anyway to get past this and let it roll as "Repair By Sorting"? I have 2GB RAM, Dual Cores, lots of extra hard-drive space. Snip out of my.cnf: set-variable = max_connections=650 set-variable = key_buffer=256M set-variable = myisam_sort_buffer_size=64M set-variable = join_buffer=1M set-variable = record_buffer=1M set-variable = sort_buffer_size=2M set-variable = read_buffer_size=2M set-variable = query_cache_size=32M set-variable = table_cache=1024 set-variable = thread_cache_size=256 set-variable = wait_timeout=7200 set-variable = connect_timeout=10 set-variable = max_allowed_packet=16M set-variable = max_connect_errors=10 set-variable = thread_concurrency=8

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  • Delphi Unit local variables - how to make each instance unique?

    - by Justin
    Ok, this, I'm sure is something simple that is easy to do. The problem : I've inherited scary spaghetti code and am slowly trying to better it when new features need adding - generally when a refactor makes adding the new feature neater. I've got a bunch of code I'm packing into a single unit which, in different places in the application, controls the same physical thing in the outside world. The control appears in several places in the application and operates slightly differently in each instance. What I've done is to create a unit with all of the features I need which I can simply drop, as a frame, into each form that requires it. Each form then uses the unit's interface methods to customise the behaviour for each instance. The problem within the problem : In the unit in question (the frame) I have a variable declared in the IMPLEMENTATION section - local to the unit. I also have a procedure, declared in the TYPE section which takes an argument and assigns that argument to the local variable in question - each form passes a unique variable to each instance of the frame/unit. What I want it to do is for each instance of the frame to keep its own version of that variable, different from the others, and use that to define how it operates. What seems to be happening, however, is that all instances are using the same value, even if I explicitly pass each instance a different variable. ie: Unit FlexibleUnit; interface uses //the uses stuff type TFlexibleUnit=class(TFrame) //declarations including procedure makeThisInstanceX(passMeTheVar:integer); private // public // end; implementation uses //the uses var myLocalVar; procedure makeThisInstanceX(passMeTheVar:integer); begin myLocalVar:=passMeTheVar; end; //other procedures using myLocalVar //etc to the end; Now somewhere in another Form I've dropped this Frame onto the Design pane, sometimes two of these frames on one Form, and have it declared in the proper places, etc. Each is unique in that : ThisFlexibleUnit : TFlexibleUnit; ThatFlexibleUnit : TFlexibleUnit; and when I do a: ThisFlexibleUnit.makeThisInstanceX(var1); //want to behave in way "var1" ThatFlexibleUnit.makeThisInstanceX(var2); //want to behave in way "var2" it seems that they both share the same variable "myLocalVar". Am I doing this wrong, in principle? If this is the correct method then it's a matter of debugging what I have (which is too huge to post) but if this is not correct in principle then is there a way to do what I am suggesting? Thanks in advance, Stack Overflow - you guys (and gals!) are legendary.

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  • HTML form -> Flash submit button -> Set a PHP variable in flash button -> Submit form

    - by RobHardgood
    Okay, I'm sorry that this is pretty complicated, but it shouldn't be that hard to solve... Here's what I want to do. I have an HTML form that I want to upload to MySQL with PHP. That part's easy, but the thing is I want the submit button to be a Flash object. Somehow I need the Flash button to submit the form, but I think I can figure that out. The tricky part is that I need it to set another PHP variable before submitting the form. The variable will be determined by a bunch of stuff, but I can code that in actionscript later. I just need to figure out how to pass the variable back to the webpage. A $_POST variable would probably be fine. Thanks!! Let me know if I need to clarify more...

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  • Environment variable retrieve from NAnt script is not recognize in Jenkins nant build step

    - by user1670340
    In my nant script I retrieve my environment variable in this way: but when I run it through jenkins using nant as build step I got an error like this. Expression: ${environment::get-variable('MAIN_PROJECT_PATH')} ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Environment variable "MAIN_PROJECT_PATH" does not exist. Is there configuration for this? so that Jenkins will recognize environment variables access by my nant script? Help is greatly appreciated. Thanks.

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  • python global variable trouble

    - by Guanidene
    I am having troubles using global variables in python... In my program, i have declared 2 global variables, global SYNC_DATA and global SYNC_TOTAL_SIZE Now in one of my functions, I am able to use the global variable SYNC_DATA without declaring it as global again in the function; however , I am not able to use the other global variable SYNC_TOTAL_SIZE in the same way. I have to declare the latter as global in the function again to use it. I get this error if i use it without declaring as global in the function - "UnboundLocalError: local variable 'SYNC_TOTAL_SIZE' referenced before assignment" Why is it so that sometimes I can access global variables without declaring them as global in functions and sometimes not? And why Is it that we have to again declare it as global in the function when it is already declared once in the beginning... Why doesn`t the function just check the variable in the global namespace if it does not find it in its namespace directly?

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  • Unable to set enviornment variable in platform builder win CE 6.0

    - by mukesh
    Actually while building the win ce project getting the two errors -: Error 1 BUILD: [00:0000000015:ERRORE] C:\WINCE600\PLATFORM\ICOP_Vortex86_60CS\SRC\OAL\OALLIB\obj\x86\debug_objects.mac: create file failed. 2 Error 3 BLDDEMO: There were errors building mytest I think it's comes, due to unset of environmnet variable. facing problem to set environment variable IMGRAM128 in the project proerties, giving the error :- "The variable IMGRAM128 is associated with the 128 RAM catalog item.Would you like to set this variable by adding catalog item in OS design? The varible will not be added to the environmmet tab.............."

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  • asp.net mvc post variable to controller

    - by Erwin
    Hello fellow programmer I came from PHP language(codeigniter), but now I learning ASP.Net MVC :) In PHP codeigniter we can catch the post variable easily with $this->input->post("theinput"); I know that in ASP.Net MVC we can create an action method that will accepts variable from post request like this public ActionResult Edit(string theinput) Or by public ActionResult Edit(FormCollection formCol) Is there a way to catch post variable in ASP.Net like PHP's codeigniter, so that we don't have to write FormCollection object nor have to write parameter in the action method (because it can get very crowded there if we pass many variable into it) Is there a simple getter method from ASP.Net to catch these post variables?

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  • Problem retrieving multiple instances of the same asp.net session variable

    - by sw1sh
    I'm having problems with retrieving multiple instances of a session variable from an InProc session state. In the following code I persist a simple BusinessObject into a session variable on the Page_Load event. On the click of a button I try to retrieve the object back into 2 new declared instances of the same BusinessObject. All works great until I change one of the properties in the first instance, it changes the second instance as well. Is this normal behaviour? I would have thought as these were new instances they wouldn’t demonstrate static behaviour? Any ideas where I'm going wrong? Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not Page.IsPostBack Then ' create a new instance of a business object and set a containg variable Dim BO As New BusinessObject BO.SomeVariable = "test" ' persist to inproc session Session("BO") = BO End If End Sub Protected Sub btnRetrieveSessionVariable_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnRetrieveSessionVariable.Click ' retrieve the session variable to a new instance of BusinessObject Dim BO1 As New BusinessObject If Not Session("BO") Is Nothing Then BO1 = Session("BO") ' retrieve the session variable to a new instance of BusinessObject Dim BO2 As New BusinessObject If Not Session("BO") Is Nothing Then BO2 = Session("BO") ' change the property value on the first instance BO1.SomeVariable = "test2" ' why has this changed on both instances? Dim strBO1Property As String = BO1.SomeVariable Dim strBO2Property As String = BO2.SomeVariable End Sub ' simple BusinessObject class Public Class BusinessObject Private _SomeVariable As String Public Property SomeVariable() As String Get Return _SomeVariable End Get Set(ByVal value As String) _SomeVariable = value End Set End Property End Class

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  • global variable and Python

    - by rejinacm
    A global variable created in one function cannot be used in another function directly. Instead I need to store the global variable in a local variable of the function which needs its access. Am I correct? Why is it so?

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  • ASP.NET variable scope

    - by c11ada
    hey all, im really new to ASP.Net and still havnt got my head round most of the concepts, im really having problems with variable, when creating a desktop application, any variable created in code for example int n = 10; this variable will be there until the program is running right. but in asp iv created variables which are supposed to last until the user gets of that page, so for example say i have a page which takes the users value ( call this variable n say the user type in 10) and every time the user presses the next button the code add 10 to this value. so the first time the user presses the next button n= n + 10; what i have found is no matter how many times i press the next button n will always equal 20, because the previous value is not saved !! these values are populated the first time the user enters that page, once the user clicks the next button the content of these values disappear! how can stop this from happening ?? hope this makes sense !! thanks

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  • Biztalk - local variable in expression shape

    - by Jeremy Stein
    Sometimes when I'm writing XLANG/s code in an expression shape, it would be more readable if I could just use a temporary variable within the scope of that one code block. I hate to clutter up the entire orchestration with a variable declaration. Is there a way to declare a variable within an expression shape?

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  • how i got the name of the string variable in the strange attempt to debug unknown variable ?

    - by justjoe
    i got several variable. One is variable string, object, and array. $mystring = "hello im input"; $myobject = new userclass; $myarray = array ( 0 = 'zero', 1 = "one"); i want to create a new array with its variable name as key before send it to as function parameter with it's first line use extract function. the multi_array will be like this multi_array = array ( 'mystring' = "hello im input", 'myobject' = new userclass, 'myarray' = array ( 0 = 'zero', 1 = "one") ) i use key to get the name of array and getclass to get the name of object. But how i got the name of the string variable ? function i_do_extract($multi_array) { extract($multi_array); // Do Rest }

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  • Variable declared with variable keyword in sql plus(oracle 9i)?

    - by Vineet
    I am trying to declare g_num ,number data type with size it gives an error but in case of varchar2,char it does not. variable g_name varchar2(5);//correct accept size for varchar 2 variable g_num number(23);//Gives an error " VAR[IABLE] [ <variable> [ NUMBER | CHAR | CHAR (n [CHAR|BYTE]) | VARCHAR2 (n [CHAR|BYTE]) | NCHAR | NCHAR (n) | NVARCHAR2 (n) | CLOB | NCLOB | REFCURSOR ] ]" Please suggest!

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  • dos batch assign returned values from a command into a variable (from powershell)

    - by nokheat
    i am refering to this question ASSIGN win XP dos commandline output to variable http://stackoverflow.com/questions/537404/assign-win-xp-dos-commandline-output-to-variable i am trying to use it on a powershell code segment so i typed powershell date (get-date).AddDays(-1) -format yyyyMMdd and confirm it returns like 20100601 but then if i tried to for /f "tokens=*" %a in ('powershell date get-date -format yyyyMMdd ') do set var=%a then it failed to work as expected. how can i transfer the date to a variable?

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