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• Strange profiling results: definitely non-bottleneck method pops up

  - by jkff

  I'm profiling a program using sampling profiling in YourKit and JProfiler, and also "manually" (I launch it and press Ctrl-Break several times to get thread dumps). All three methods give me extremely strange results: some tens of percents of time spent in a 3-line method that does not even do any allocation or synchronization and doesn't have loops etc. Moreover, after I made this method into a NOP and even removed its invocation completely, the observable program performance didn't change at all (although it got a negligible memory leak, since it was a method for freeing a cheap resource). I'm thinking that this might be because of the constraints that JVM puts on the moments at which a thread's stacktrace may be taken, and it somehow turns out that in my program it is exactly the moments where this method is invoked, although there is absolutely nothing special about it or the context in which it is invoked. What can be the explanation for this phenomenon? What are the aforementioned constraints? What further measurements can I take to clarify the situation?

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• How to diganose an unlogged Error 500 on Apache?

  - by samuel morhaim

  We are running a very simple Symfony script, that randomly returns an Error 500. The system administrator says he can't find any trace of an Error 500 on the error logs, however using Curl or Firebug, it is obvious that an Error 500 is being returned. The script simply parses a POST request submitted to an URL on our server. We already checked for performance, memory etc but nothing seems to be the problem. How is this possible? We already enabled all debugging, logging, on Apache, PHP, etc and nothing.

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• Are bit operations quick?

  - by flashnik

  I'm dealing with a problem which needs to work with a lot of data. Currently its' values are represented as unsigned int. I know that real values do not exceed some limit, say 1000. That means that I can use unsigned short to store it. One profit is that it'll use less space. Do I have to pay for it by loosing in performance? Another assumption. I decided to store data as short but all calling functions use int, so I need to convert between these datatypes when storing/extracting values. Wiil the performance lost be dramatic? Third assumption. Due to great wish to econom memory I decided to use not short but just 10 bits packed into array of unsigned int. What will happen in this case comparing with previous ones?

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• How to implement arrays in an interpreter?

  - by Ray

  I have managed to write several interpreters including Tokenizing Parsing, including more complicated expressions such as ((x+y)*z)/2 Building bytecode from syntax trees Actual bytecode execution What I didn't manage: Implementation of dictionaries/lists/arrays. I always got stuck with getting multiple values into one variable. My value structure (used for all values passed around, including variables) looks like this, for example: class Value { public: ValueType type; int integerValue; string stringValue; } Works fine with integers and strings, but how could I implement arrays? (From now on with array I mean arrays in my experimental language, not in C++) How can I fit the array concept into the Value class above? Is it possible? How should I make arrays able to be passed around just as you could pass around integers and strings in my language, using the class above? Accessing array elements or memory allocation wouldn't be the problem, I just don't know how to store them.

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• VS2010's "Public Property <PropertyName> As <DataType> vs. Public var

  - by Velika2

  In VS2008, I used to type Public Property <PropName> As <dataType> and hit the Enter key and the IDE editor would automatically expand it out to a full blown property block. Now, from what I understand, a new feature of 2010 is that the compiler automatically "expands" the short syntax above into the same IL code that you would get with the full property GET AND SET sub methods that were are accustomed to seeing before in the editor. But functionality, how the heck is this any different than just having a Public class level variable? If the only diff is what it compiles to and if otehrwise there is no functional difference, isn't the new way less efficient than the old since it involves more code than just having a class level memory variable? Public as I thought that if you weren't going to have code behind your properties that they were essentially the same. I guess the diffrenece is that they just added the keyword "Property" but functionality, their is no diff, eh?

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• Why should I reuse XmlHttpRequest objects?

  - by Xavi

  From what I understand, it's a best practice to reuse XmlHttpRequest objects whenever possible. Unfortunately, I'm having a hard time understanding why. It seems like trying to reuse XHR objects can increase code complexity, introduce possible browser incompatibilities, and lead to other subtle bugs. After researching this question for a while, I did come up with a list of possible explanations: Fewer objects created means less garbage collecting Reusing XHR objects reduces the chance of memory leaks The overhead of creating a new XHR object is high The browser is able to perform some sort of network optimization under hood But I'm not sure if any of these reasons are actually valid. Any light you can shed on this question would be much appreciated.

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• Major performance difference between two Oracle database instances

  - by jrdioko

  I am working with two instances of an Oracle database, call them one and two. two is running on better hardware (hard disk, memory, CPU) than one, and two is one minor version behind one in terms of Oracle version (both are 11g). Both have the exact same table table_name with exactly the same indexes defined. I load 500,000 identical rows into table_name on both instances. I then run, on both instances: delete from table_name; This command takes 30 seconds to complete on one and 40 minutes to complete on two. Doing INSERTs and UPDATEs on the two tables has similar performance differences. Does anyone have any suggestions on what could have such a drastic impact on performance between the two databases?

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• What is your favourite Windbg tip/trick?

  - by user15071

  I have come to realize that Windbg is a very powerful debugger for the Windows platform & I learn something new about it once in a while. Can fellow Windbg users share some of their mad skills? ps: I am not looking for a nifty command, those can be found in the documentation. How about sharing tips on doing something that one couldn't otherwise imagine could be done with windbg? e.g. Some way to generate statistics about memory allocations when a process is run under windbg.

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• About enumerations in Delphi and c++ in 64-bit environments

  - by sum1stolemyname

  I recently had to work around the different default sizes used for enumerations in Delphi and c++ since i have to use a c++ dll from a delphi application. On function call returns an array of structs (or records in delphi), the first element of which is an enum. To make this work, I use packed records (or aligned(1)-structs). However, since delphi selects the size of an enum-variable dynamically by default and uses the smallest datatype possible (it was a byte in my case), but C++ uses an int for enums, my data was not interpreted correctly. Delphi offers a compiler switch to work around this, so the declaration of the enum becomes {$Z4} TTypeofLight = ( V3d_AMBIENT, V3d_DIRECTIONAL, V3d_POSITIONAL, V3d_SPOT ); {$Z1} My Questions are: What will become of my structs when they are compiled on/for a 64-bit environment? Does the default c++ integer grow to 8 Bytes? Are there other memory alignment / data type size modifications (other than pointers)?

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• vector<vector<largeObject>> vs. vector<vector<largeObject>*> in c++

  - by Leif Andersen

  Obviously it will vary depending on the compiler you use, but I'm curious as to the performance issues when doing vector<vector<largeObject>> vs. vector<vector<largeObject>*>, especially in c++. In specific: let's say that you have the outer vector full, and you want to start inserting elements into first inner vector. How will that be stored in memory if the outer vector is just storing pointers, as apposed to storing the whole inner vector. Will the whole outer vector have to be moved to gain more space, or will the inner vector be moved (assuming that space wasn't pre-allocated), causing problems with the outer vector? Thank you

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• Java threadpool functionality

  - by cpf

  Hi stackoverflow, I need to make a program with a limited amount of threads (currently using newFixedThreadPool) but I have the problem that all threads get created from start, filling up memory at alarming rate. I wish to prevent this. Threads should only be created shortly before they are executed. e.g.: I call the program and instruct it to use 2 threads in the pool. The program should create & launch the first 2 Threads immediately (obviously), create the next 2 to wait for the previous 2, and at that point wait until one or both of the first 2 ended executing. I thought about extending executor or FixedThreadPool or such. However I have no clue on how to start there and doubt it is the best solution. Easiest would have my main Thread sleeping on intervals, which is not really good either... Thanks in advance!

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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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• Compression Array of Bytes

  - by Pedro Magalhaes

  Hi, My problem is: I want to store a array of bytes in compressed file, and then I want to read it with a good performance. So I create a array of bytes then pass to a ZLIB algorithm then store it in the file. For my surprise the algorithm doesn't work well., probably because the array is a random sample. Using this approach, it will will be ber easy to read. Just copy the stream to memory, decompress them and copy it to a array of bytes. But i need to compress the file. Do I have to use a algorithm, like RLE, for compresse the byte array? I think that I can store the byte array like a string and then compress it. But i think I am going to have a poor performance on reading data. Sorry for my poor english. Thanks

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• How can I integrate graphs and JPEG images with RAVE Reports?

  - by JonDave of the Philippines

  I really love RAVE Reports in creating multiple reports especially with formulas and accounting systems... but recently I am having problems with integrating JPEG Pictures and Graphs with my newly Delphi Language developed Little ERP System. I bought some JPEG Components but it seems problematic. I also experienced some irregularities with my RAVE Reports now. When I run my program then try to preview some reports, it seems to be running fine, but when I close the program, the EXE file is still in the taskbar. I need to ctrl-alt-delete first for me to use Report Previews normally. If I don't, RAVE REPORT ERROR message will appear everytime I click the PRINT button; it says "STREAM READ ERROR" even though I used to "FreeAndNil" to free the memory stream when Report Preview Form closes. When I tried to run the My Applications without previewing RAVE reports, the program closes perfectly. Any suggestions and recommendations will be an enormous help. Thank you.

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• SQLserver multithreaded locking with TABLOCKX

  - by WilfriedVS

  I have a table "tbluser" with 2 fields: userid = integer (autoincrement) user = nvarchar(100) I have a multithreaded/multi server application that uses this table. I want to accomplish the following: Guarantee that field user is unique in my table Guarantee that combination userid/user is unique in each server's memory I have the following stored procedure: CREATE PROCEDURE uniqueuser @user nvarchar(100) AS BEGIN BEGIN TRAN DECLARE @userID int SET nocount ON SET @userID = (SELECT @userID FROM tbluser WITH (TABLOCKX) WHERE [user] = @user) IF @userID <> '' BEGIN SELECT userID = @userID END ELSE BEGIN INSERT INTO tbluser([user]) VALUES (@user) SELECT userID = SCOPE_IDENTITY() END COMMIT TRAN END Basically the application calls the stored procedure and provides a username as parameter. The stored procedure either gets the userid or insert the user if it is a new user. Am I correct to assume that the table is locked (only one server can insert/query)?

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• Converting MS Word Documents to PDF in ASP.NET

  - by glaxaco

  Similar questions have been asked, but nothing exactly like mine, so here goes. We have a collection of Microsoft Word documents on an ASP.NET web server with merge fields whose values are filled in as a result of user form submissions. After the field merge, the server must convert the document to PDF and stream it down to the browser. Our first inclination was to use the Visual Studio Tools for Office API; however, we ran into this warning from Microsoft: Microsoft does not currently recommend, and does not support, Automation of Microsoft Office applications from any unattended, non-interactive client application or component (including ASP, ASP.NET, DCOM, and NT Services), because Office may exhibit unstable behavior and/or deadlock when Office is run in this environment. It looks like the field manipulation can be done using the Open XML SDK, but what's the best way to convert Word 2007 documents to PDF without opening Word? The optimal solution would be low-cost, scalable, have a low memory footprint, be easy to deploy, and have a .NET API.

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• What interprocess locking calls should I monitor?

  - by Matt Joiner

  I'm monitoring a process with strace/ltrace in the hope to find and intercept a call that checks, and potentially activates some kind of globally shared lock. While I've dealt with and read about several forms of interprocess locking on Linux before, I'm drawing a blank on what to calls to look for. Currently my only suspect is futex() which comes up very early on in the process' execution. Update0 There is some confusion about what I'm after. I'm monitoring an existing process for calls to persistent interprocess memory or equivalent. I'd like to know what system and library calls to look for. I have no intention call these myself, so naturally futex() will come up, I'm sure many libraries will implement their locking calls in terms of this, etc. Update1 I'd like a list of function names or a link to documentation, that I should monitor at the ltrace and strace levels (and specifying which). Any other good advice about how to track and locate the global lock in mind would be great.

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• #define vs enum in an embedded environment (How do they compile?)

  - by Alexander Kondratskiy

  This question has been done to death, and I would agree that enums are the way to go. However, I am curious as to how enums compile in the final code- #defines are just string replacements, but do enums add anything to the compiled binary? Or are they both equivalent at that stage. When writing firmware and memory is very limited, is there any advantage, no matter how small, to using #defines? Thanks! EDIT: As requested by the comment below, by embedded, I mean a digital camera. Thanks for the answers! I am all for enums!

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• What libraries are available for manipulating super large images in .Net

  - by tpower

  I have some really large files for example 320 MB tif file with 14000 X 9000 pixels. The operations I need to perform are basically scaling the images to get smaller versions of it and breaking the image into tiles. My code works fine with small files and I use the .Net Bitmap objects but I will occasionally get Out of Memory exceptions for larger files. I've tried using the FreeImage libraries FreeImageBitmap but have the same problems. I'm using something like the following to scale the image: using (Graphics g = Graphics.FromImage((Image)result)) { g.DrawImage( source, xOffset, yOffset, source.Width * scale, source.Height * scale ); } Ideally I'd like a third party library to do all the hardwork, but if you have any tips or resources with more information I would appreciate it.

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• C++ smart pointer for non-object type?

  - by Brian

  Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just malloc'ed memory, not object. Is there a way to use the smart pointers for the storage variable? Thank you.

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• Keeping a large volume of data in Session - Suggestions / alternatives?

  - by Fishcake

  I'm developing a web app for which the client wants us to query their data as little as possible. The data will be coming from a Microsoft CRM instance. So we've agreed that data will only be queried as and when it is needed, therefore if a web user wants to see a list of contacts (for example) that list is fetched into a local DataTable. Then if a new contact is created on the website the new contact is sent to CRM and added to the local DataTable at the same time. Likewise for edits. If the user then looks at their contacts again the data will just come from the local DataTable. At the moment local data is being kept in Session but my concern is that too much memory will start being used up. However traffic is expected to be pretty small, perhaps no more than 20 concurrent users so am I worrying about nothing or is there a better way you can suggest to handle this?

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• Conseqences of assigning self

  - by Vegar

  Hi, Found a piece of code today, that I find a little smelly... TMyObject.LoadFromFile(const filename: String); begin if fileExists(filename) then self := TSomeObjectStreamer.ReadObjectFromFile(filename); end; If this code works, it will atleast leak some memory, but does it work? Is OK to assign to self in this manner? What if the streamed object is of a different subclass then the original self? What if the streamed object is of a different class with no common ancestore to the original self?

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• Plugin architecture in .net: unloading

  - by henchman

  Hello everybody, I need to implement a plugin architecture within c#/.net in order to load custom user defined actions data type handling code for a custom data grid / conversion / ... from non-static linked assembly files. Because the application has to handle many custom user defined actions, Iam in need for unloading them once executed in order to reduce memory usage. I found several good articles about plugin architectures, eg: ExtensionManager PluginArchitecture ... but none of them gave me enough sausage for properly unloading an assembly. As the program is to be distributed and the user defined actions are (as the name states) user defined: how to i prevent the assembly from executing malicious code (eg. closing my progra, deleting files)? Are there any other pitfalls one of you has encountered?

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• Clone LINQ To SQL object Extension Method throws object dispose exception....

  - by gtas

  Hello all, I have this extension method for cloning my LINQ To SQL objects: public static T CloneObjectGraph<T>(this T obj) where T : class { var serializer = new DataContractSerializer(typeof(T), null, int.MaxValue, false, true, null); using (var ms = new System.IO.MemoryStream()) { serializer.WriteObject(ms, obj); ms.Position = 0; return (T)serializer.ReadObject(ms); } } But while i carry objects with not all references loaded, while qyuerying with DataLoadOptions, sometimes it throws the object disposed exception, but thing is I don't ask for references that is not loaded (null). e.g. I have Customer with many references and i just need to carry on memory the Address reference EntityRef< and i don't Load anything else. But while i clone the object this exception forces me to load all the EntitySet< references with the Customer object, which might be too much and slow down the application speed. Any suggestions?

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• Object sent -autorelease too many times

  - by mongeta

  I have this code that simple returns Today's date as a string formatted: +(NSString*) getTodayString_YYYY_MM_DD { NSDate * today = [NSDate date]; NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setDateFormat:@"yyyy-MM-dd"]; return [[formatter stringFromDate:today] autorelease]; } With instruments I'm not getting a memory leak, but when I Analyze, XCode says: Object sent -autorelease too many times If I understand correctly, I have to release manually the formatter as I'm creating it using 'alloc', but I can't release here because I have to return the value, so I add the autorelease. How I can do it better to improve it ? thanks, r.

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