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• Count of memory copies in *nix systems between packet at NIC and user application?

  - by Michael_73

  Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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• Odd optimization problem under MSVC

  - by Goz

  I've seen this blog: http://igoro.com/archive/gallery-of-processor-cache-effects/ The "weirdness" in part 7 is what caught my interest. My first thought was "Thats just C# being weird". Its not I wrote the following C++ code. volatile int* p = (volatile int*)_aligned_malloc( sizeof( int ) * 8, 64 ); memset( (void*)p, 0, sizeof( int ) * 8 ); double dStart = t.GetTime(); for (int i = 0; i < 200000000; i++) { //p[0]++;p[1]++;p[2]++;p[3]++; // Option 1 //p[0]++;p[2]++;p[4]++;p[6]++; // Option 2 p[0]++;p[2]++; // Option 3 } double dTime = t.GetTime() - dStart; The timing I get on my 2.4 Ghz Core 2 Quad go as follows: Option 1 = ~8 cycles per loop. Option 2 = ~4 cycles per loop. Option 3 = ~6 cycles per loop. Now This is confusing. My reasoning behind the difference comes down to the cache write latency (3 cycles) on my chip and an assumption that the cache has a 128-bit write port (This is pure guess work on my part). On that basis in Option 1: It will increment p[0] (1 cycle) then increment p[2] (1 cycle) then it has to wait 1 cycle (for cache) then p[1] (1 cycle) then wait 1 cycle (for cache) then p[3] (1 cycle). Finally 2 cycles for increment and jump (Though its usually implemented as decrement and jump). This gives a total of 8 cycles. In Option 2: It can increment p[0] and p[4] in one cycle then increment p[2] and p[6] in another cycle. Then 2 cycles for subtract and jump. No waits needed on cache. Total 4 cycles. In option 3: It can increment p[0] then has to wait 2 cycles then increment p[2] then subtract and jump. The problem is if you set case 3 to increment p[0] and p[4] it STILL takes 6 cycles (which kinda blows my 128-bit read/write port out of the water). So ... can anyone tell me what the hell is going on here? Why DOES case 3 take longer? Also I'd love to know what I've got wrong in my thinking above, as i obviously have something wrong! Any ideas would be much appreciated! :) It'd also be interesting to see how GCC or any other compiler copes with it as well! Edit: Jerry Coffin's idea gave me some thoughts. I've done some more tests (on a different machine so forgive the change in timings) with and without nops and with different counts of nops case 2 - 0.46 00401ABD jne (401AB0h) 0 nops - 0.68 00401AB7 jne (401AB0h) 1 nop - 0.61 00401AB8 jne (401AB0h) 2 nops - 0.636 00401AB9 jne (401AB0h) 3 nops - 0.632 00401ABA jne (401AB0h) 4 nops - 0.66 00401ABB jne (401AB0h) 5 nops - 0.52 00401ABC jne (401AB0h) 6 nops - 0.46 00401ABD jne (401AB0h) 7 nops - 0.46 00401ABE jne (401AB0h) 8 nops - 0.46 00401ABF jne (401AB0h) 9 nops - 0.55 00401AC0 jne (401AB0h) I've included the jump statetements so you can see that the source and destination are in one cache line. You can also see that we start to get a difference when we are 13 bytes or more apart. Until we hit 16 ... then it all goes wrong. So Jerry isn't right (though his suggestion DOES help a bit), however something IS going on. I'm more and more intrigued to try and figure out what it is now. It does appear to be more some sort of memory alignment oddity rather than some sort of instruction throughput oddity. Anyone want to explain this for an inquisitive mind? :D Edit 3: Interjay has a point on the unrolling that blows the previous edit out of the water. With an unrolled loop the performance does not improve. You need to add a nop in to make the gap between jump source and destination the same as for my good nop count above. Performance still sucks. Its interesting that I need 6 nops to improve performance though. I wonder how many nops the processor can issue per cycle? If its 3 then that account for the cache write latency ... But, if thats it, why is the latency occurring? Curiouser and curiouser ...

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• Database Modelling - Conceptually different entities with near identical fields

  - by Andrew Shepherd

  Suppose you have two sets of conceptual entities: MarketPriceDataSet which has multiple ForwardPriceEntries PoolPriceForecastDataSet which has multiple PoolPriceForecastEntry Both different child objects have near identical fields: ForwardPriceEntry has StartDate EndDate SimulationItemId ForwardPrice MarketPriceDataSetId (foreign key to parent table) PoolPriceForecastEntry has StartDate EndDate SimulationItemId ForecastPoolPrice PoolPriceForecastDataSetId (foreign key to parent table) If I modelled them as separate tables, the only difference would be the foreign key, and the name of the price field. There has been a debate as to whether the two near identical tables should be merged into one. Options I've thought of to model this is: Just keep them as two independent, separate tables Have both sets in the one table with an additional "type" field, and a parent_id equalling a foreign key to either parent table. This would sacrifice referential integrity checks. Have both sets in the one table with an additional "type" field, and create a complicated sequence of joining tables to maintain referential integrity. What do you think I should do, and why?

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• Why is distributed source control considered harder?

  - by Will Robertson

  It seems rather common (around here, at least) for people to recommend SVN to newcomers to source control because it's "easier" than one of the distributed options. As a very casual user of SVN before switching to Git for many of my projects, I found this to be not the case at all. It is conceptually easier to set up a DCVS repository with git init (or whichever), without the problem of having to set up an external repository in the case of SVN. And the base functionality between SVN, Git, Mercurial, Bazaar all use essentially identical commands to commit, view diffs, and so on. Which is all a newcomer is really going to be doing. The small difference in the way Git requires changes to be explicitly added before they're committed, as opposed to SVN's "commit everything" policy, is conceptually simple and, unless I'm mistaken, not even an issue when using Mercurial or Bazaar. So why is SVN considered easier? I would argue that this is simply not true.

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• xgettext vs gettext

  - by Kentor

  I have a few questions: I know what gettext is. I've read a few posts where they mentioned xgettext and was curious as to what is the difference between the two. How can I install xgettext on Windows? And finally, does anybody have a tutorial on how to install the library php-gettext http://savannah.nongnu.org/projects/php-gettext/ (this one usually doesn't come with PHP) I've read about it in an article but I'm not sure how to get it working in Windows. The thing is, sometimes when you make changes, you need to restart Apache to see the new data with the gettext that comes with PHP (but with the library you don't need to restart it) so I wanted to use the library for development. Thanks!

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• What is the purpose of OCaml's Lazy.lazy_from_val?

  - by Ricardo

  The doc of Lazy.lazy_from_val states that this function is for special cases: val lazy_from_val : 'a -> 'a t lazy_from_val v returns an already-forced suspension of v This is for special purposes only and should not be confused with lazy (v). Which cases are they talking about? If I create a pair of suspended computation from a value like: let l1 = lazy 123 let l2 = Lazy.lazy_from_val 123 What is the difference between these two? Because Lazy.lazy_is_val l1 and Lazy.lazy_is_val l2 both return true saying that the value is already forced!

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• number of months between two dates - using boost's date

  - by MartinP

  I've used boost::gregorian::date a bit now. I can see that there are the related months & years & weeks duration types. I can see how to use known durations to advance a given date. Qu: But how can I get the difference between two dates in months (or years or weeks) ? I was hoping to find a function like: template<typename DURATION> DURATION date_diff<DURATION>(const date& d1,const date& d2); There would need to be some handling of rounding too.

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• need help with db-query on sql-server 2005.

  - by Avinash

  We're seeing strange behavior when running two versions of a query on SQL Server 2005: version A: SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = 1234 ORDER BY name ASC version B: DECLARE @Id AS INT; SET @Id = 1234; SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @Id ORDER BY name ASC Both queries return 1000 rows; version A takes on average 15s; version B on average takes 4s. Could anyone help us understand the difference in execution times of these two versions of SQL? If we invoke this query via named parameters using NHibernate, we see the following query via SQL Server profiler: EXEC sp_executesql N'SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @id ORDER BY name ASC', N'@id INT', @id=1234; ...and this tends to perform as badly as version A. Thanks in advance,

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• C++/CLI value class constraint won't compile. Why?

  - by Simon

  Hello, a few weeks ago a co-worker of mine spent about two hours finding out why this piece of C++/CLI code won't compile with Visual Studio 2008 (I just tested it with Visual Studio 2010... same story). public ref class Test { generic<class T> where T : value class void MyMethod(Nullable<T> nullable) { } }; The compiler says: Error 1 error C3214: 'T' : invalid type argument for generic parameter 'T' of generic 'System::Nullable', does not meet constraint 'System::ValueType ^' C:\Users\Simon\Desktop\Projektdokumentation\GridLayoutPanel\Generics\Generics.cpp 11 1 Generics Adding ValueType will make the code compile. public ref class Test { generic<class T> where T : value class, ValueType void MyMethod(Nullable<T> nullable) { } }; My question is now. Why? What is the difference between value class and ValueType?

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• Actionscript 3 svg XML parsing bug?

  - by Mahir

  Hey I get two different results when using the for each loop below. As far as I can tell there's no difference aside from attributes in the two XML literals. for each (var pathXML:XML in svg.path) { // do stuff... trace(pathXML.@stroke) } // This one works, the loop iterates once over the single path element... var svg:XML = <svg> <path stroke="#00FF00" /> </svg> // This one doesn't, the loop just exits. var svg:XML = <svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="612px" height="792px" viewBox="0 0 612 792" enable-background="new 0 0 612 792" xml:space="preserve"> <path fill="#FFFFFF" stroke="#000000" d="M160.333,372.444c0,0,17.778-115.555,60-63.333s27.778-106.666,78.889,40" /> </svg>

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• CLI design and implementation?

  - by Majid

  I am developing a time management tool for my personal use. I prefer using keyboard over mouse, and on the interface have a general purpose text box which will act like a command line. I have just started thinking about what commands I need, what to use for the command names, how to pass in switches and parameters, and so forth. I wonder if some of you have come across a good read along these lines; something that describes the choices you have for designing a cli, and how those affect the complexity of the interpreter, and extendability of the commands. It makes no difference if the descriptions are language-specific or in general terms. However, my implementation will be with javascript. Thank you.

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• Real thing about "->" and "."

  - by fsdfa

  I always wanted to know what is the real thing difference of how the compiler see a pointer to a struct (in C suppose) and a struct itself. struct person p; struct person *pp; pp->age, I always imagine that the compiler does: "value of pp + offset of atribute "age" in the struct". But what it does with person.p? It would be almost the same. For me "the programmer", p is not a memory address, its like "the structure itself", but of course this is not how the compiler deal with it. My guess is it's more of a syntactic thing, and the compiler always does (&p)->age. I'm correct?

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• PHP/MySQL: Storing and retrieving UUIDS

  - by Greg

  I'm trying to add UUIDs to a couple of tables, but I'm not sure what the best way to store/retrieve these would be. I understand it's far more efficient to use BINARY(16) instead of VARCHAR(36). After doing a bit of research, I also found that you can convert a UUID string to binary with: UNHEX(REPLACE(UUID(),'-','')) Pardon my ignorance, but is there an easy way to this with PHP and then turn it back to a string, when needed, for readability? Also, would it make much difference if I used this as a primary key instead of auto_increment? EDIT: Found part of the answer: $bin = pack("h*", str_replace('-', '', $guid)); How would you unpack it?

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• RSA encrypted data block size

  - by calccrypto

  how do you store an rsa encrypted data block? the output might be significantly greater than the original input data block size, and i dont think people waste memory by padding bucket loads of 0s in front of each data block. besides, how would they be removed? or is each block stored on new lines within the file? if that is the case, how would you tell the difference between legitimate new line and a '\n' char written into the file? what am i missing? im writing the "write to file" part in python, so maybe its one of the differences between: open(file,'w') open(file,'w+b') open(file,'wb') that i dont know. or is it something else?

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• Move Global.asax to iHttpModule when using ASP.NET MVC

  - by rockinthesixstring

  I have successfully created an iHttpModule to replace my Global.asax file in many Web Forms applications. But in looking at the Global.asax file in my MVC application, the methods are totally different. I'm wondering if it is still possible to create this same thing in an MVC app. I know it's not necessary and the Global.asax works just fine. I suppose I just want to have nothing but the web.config in the root directory of my application. Also, I am putting all of my classes in a separate class library project instead of a folder in my MVC application. Not sure if this makes a difference or not.

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• ssrs 2008 programmatically add tables rows

  - by davethecoder

  Above is how my report looks, the part in yellow in hidden, and is only shown when the user clicks the + icon on the [name]. the result is basically the percentage difference from the Past [X] - [TERM] i.e there is a dropdown with, [weeks, months, days, hours] and a textbox of qty. so choosing qty = 4 and term = weeks will delivery a result set spread over 4 weeks based on the parent result sets date range and name ID I wish to populate here the number of rows, dependant on the value set by the user and the data will be from a dataset. Is it possible to dynamically add more sub rows ( like on row data bound ) if my first row is ID 123 [name], is it possible to send this value [123] to a dataset in order that all subrows are only relevant to the name with ID of 123? this is my first bash at SSRS so please no half cut answers, that just lead to more questions about the answer given :-) if this makes sense. Thanks

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• ssrs: one static row matrix, multiple columns will not filter out nulls

  - by pbarton99

  Using a ssrs 2005 matrix client side. I want to list the multiple addresses of one person, hence one row, multiple columns. The Column field is =Fields!StreetName.Value. The data details field is =First(Fields!StreetPrefix.Value) & " " & First(Fields!StreetName.Value). The datasource has a row for each address; however, some rows will have nulls since the datasource is composed of outer joins. The column grouping works, but the first column is always empty, (first 2 rows of datasource are null) addresses appear only after the empty column. I want to filter out nulls on the matrix, but its like the filter is ignored. I have also tried having the dataset return an empty string for a null streetname and setting the filter to =Fields!StreetName.Value != ="" but no difference. What am I missing?

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• string manipulations in C

  - by Vivek27

  Following are some basic questions that I have with respect to strings in C. If string literals are stored in read-only data segment and cannot be changed after initialisation, then what is the difference between the following two initialisations. char *string = "Hello world"; const char *string = "Hello world"; When we dynamically allocate memory for strings, I see the following allocation is capable enough to hold a string of arbitary length.Though this allocation work, I undersand/beleive that it is always good practice to allocate the actual size of actual string rather than the size of data type.Please guide on proper usage of dynamic allocation for strings. char *string = (char *)malloc(sizeof(char));

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• How do I fix JavaHL (JNI) Not available after I have changed the logon password on my Mac?

  - by INeedHelp

  I have installed Eclipse 3.5.2 and the plugin Subversion JavaHL Native Library Adapter 1.6.9.2 and this worked without any problems. However, this morning I was forced to change the password to logon to my Mac and since then I get the message that "Subversion native library not available" when I try to save any changes. Can anyone help? I have tried to add this line (-Djava.library.path=/usr/lib/jni) to the eclipse.ini file but this didn´t seem to make any difference. Can anyone help?

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• Calling member method on unmanaged C++ pointer from C# (I think)

  - by Jacob G

  I apologize in advance if this is a trivial question... I'm pretty C++ / unmanaged dumb. Here's a simplified analog to my setup: --In myUnmanagedObject.h in DLL: class myUnmanagedObject { public: virtual void myMethod(){} } --In MyControl.h in Assembly #1: #pragma make_public(myUnmanagedObject) [event_source(managed)] public ref class MyControl : public System::Windows::Forms::UserControl { public: myUnmanagedObject* GetMyUnmanagedObject(); } --in C# in Assembly #2: unsafe { MyControl temp = new MyControl(); myUnmanagedObject* obj = temp.GetMyUnmanagedObject(); obj-myMethod(); } I get a compile error saying that myUnmanagedObject does not contain a definition for myMethod. Assembly #2 references Assembly #1. Assembly #1 references DLL. If I compile the DLL with /clr and reference it directly from Assembly #2, it makes no difference. How, from C#, do I execute myMethod ?

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• Do I need to invoke MessageBox calls?

  - by mafutrct

  To pop-up a message box, I'm using MessageBox.Show(...). I usually wrap this call in an Invoke: BeginInvoke (new Action (() => { MessageBox.Show ()); })); I've got 2 questions: Do I always need to wrap the MessageBox call in an Invoke if I'm calling from a non-GUI thread? If so, should I use BeginInvoke or Invoke? I found not much difference in my tests, BeginInvoke is, as expected (and unlike Invoke), displayed with a slight delay.

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• Where do Java Applets live?

  - by Wendy Peters

  I'm trying to figure out where java Applets that I run from the browser get downloaded to. I'm using Firefox 3.0 on Windows XP with Java 1.6 if that makes any difference. From the Java Control Panel on the toolbar, I can access "Temporary Internet Files - Settings" to find the Java cache. From there I can show the resources and see a file called "dws2010066.dat". Does this resource correspond to a file on disk? I did a search in the Java cache (and my whole computer) but came up empty handed.

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• How can I tell Visual Studio to not catch a particular exception?

  - by Noel Kennedy

  I have a particular type of exception that I would like Visual Studio to not catch with the Exception Assistant. Essentially I would like it just to let my normal exception handling infrastructure deal with it. The exception is an inheritor of System.Exception which I wrote and have the source code for. Any where this is thrown I want VS to not catch it, ie it is not useful to just supress a single throw new BlahException(); in code. This is because the exception is thrown a lot, and I don't want to have to supress every single instance individually. In case it makes a difference I am on Visual Studio 2010 Ultimate, Framework 3.5 SP1.

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• JavaScript based diff utility

  - by poke

  I'm looking for a diff equivalent written in JavaScript that only returns/prints relevant lines. I don't want both full text displayed next to each other with the differences highlighted, but just want the actual differences (plus some buffer lines to know where the difference is), similar to the output from the linux diff utility. Does anybody know a javascript function that does this? All differences should be recognized (even changed whitespace). Thanks. edit I have seen jsdifflib but in the example it always shows the full source, so unless there is a way to change the output somehow, it doesn't fully meet my requirements.

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