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• Are we asking too much of transactional memory?

  - by Carl Seleborg

  I've been reading up a lot about transactional memory lately. There is a bit of hype around TM, so a lot of people are enthusiastic about it, and it does provide solutions for painful problems with locking, but you regularly also see complaints: You can't do I/O You have to write your atomic sections so they can run several times (be careful with your local variables!) Software transactional memory offers poor performance [Insert your pet peeve here] I understand these concerns: more often than not, you find articles about STMs that only run on some particular hardware that supports some really nifty atomic operation (like LL/SC), or it has to be supported by some imaginary compiler, or it requires that all accesses to memory be transactional, it introduces type constraints monad-style, etc. And above all: these are real problems. This has lead me to ask myself: what speaks against local use of transactional memory as a replacement for locks? Would this already bring enough value, or must transactional memory be used all over the place if used at all?

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• How exactly does linking in C# work?

  - by akosch

  I want to use a GPL'd library in my C# application, but not necessarily release my own code under the GPL. If I understand correctly linking against a GPL'd library using dynamic linking and not distributing the library in question means I can license my own app in any way I want (the users of my software would then be required to install the library themselves). Please correct me if I'm wrong. My question is: how can I link against a DLL this way in C#? Do I only need to use C#'s using directive and add the DLL as a reference to the compiler? Is the distribution of the resulting bytecode legal?

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• All possible values of int from the smallest to the largest, using Java.

  - by Totophil

  Write a program to print out all possible values of int data type from the smallest to the largest, using Java. Some notable solutions as of 8th of May 2009, 10:44 GMT: 1) Daniel Lew was the first to post correctly working code. 2) Kris has provided the simplest solution for the given problem. 3) Tom Hawtin - tackline, came up arguably with the most elegant solution. 4) mmyers pointed out that printing is likely to become a bottleneck and can be improved through buffering. 5) Jay's brute force approach is notable since, besides defying the core point of programming, the resulting source code takes about 128 GB and will blow compiler limits. As a side note I believe that the answers do demonstrate that it could be a good interview question, as long as the emphasis is not on the ability to remember trivia about the data type overflow and its implications (that can be easily spotted during unit testing), or the way of obtaining MAX and MIN limits (can easily be looked up in the documentation) but rather on the analysis of various ways of dealing with the problem.

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• Java: Local Enums

  - by bruno conde

  Today, I found myself coding something like this ... public class LocalEnums { public LocalEnums() { } public void foo() { enum LocalEnum { A,B,C }; // .... // class LocalClass { } } } and I was kind of surprised when the compiler reported an error on the local enum: The member enum LocalEnum cannot be local Why can't enums be declared local like classes? I found this very useful in certain situations. In the case I was working, the rest of the code didn't need to know anything about the enum. Is there any structural/design conflict that explains why this is not possible or could this be a future feature of Java?

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• Problem with signals and slots

  - by Jen

  I am creating a class with custom slots in Qt: class CustomEdit : public QTextEdit { Q_OBJECT public: CustomEdit(QWidget* parent); public slots: void onTextChanged (); }; However, I'm getting thise linker error: undefined reference to 'vtable for CustomEdit' The documentation says: if you get compiler errors along the lines of "undefined reference to vtable for LcdNumber", you have probably forgotten to run the moc or to include the moc output in the link command. ... but it is not obvious what that means. Is there something I need to add to my class, or to the .pro file?

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• Linux core dumps are too large!

  - by themoondothshine

  Hey guys, Recently I've been noticing an increase in the size of the core dumps generated by my application. Initially, they were just around 5MB in size and contained around 5 stack frames, and now I have core dumps of 2GBs and the information contained within them are no different from the smaller dumps. Is there any way I can control the size of core dumps generated? Shouldn't they be at least smaller than the application binary itself? Binaries are compiled in this way: Compiled in release mode with debug symbols (ie, -g compiler option in GCC). Debug symbols are copied onto a separate file and stripped from the binary. A GNU debug symbols link is added to the binary. At the beginning of the application, there's a call to setrlimit which sets the core limit to infinity -- Is this the problem?

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• HTTP POST prarameters order / REST urls

  - by pq

  Let's say that I'm uploading a large file via a POST HTTP request. Let's also say that I have another parameter (other than the file) that names the resource which the file is updating. The resource cannot be not part of the URL the way you can do it with REST (e.g. foo.com/bar/123). Let's say this is due to a combination of technical and political reasons. The server needs to ignore the file if the resource name is invalid or, say, the IP address and/or the logged in user are not authorized to update the resource. Looks like, if this POST came from an HTML form that contains the resource name first and file field second, for most (all?) browsers, this order is preserved in the POST request. But it would be naive to fully rely on that, no? In other words the order of HTTP parameters is insignificant and a client is free to construct the POST in any order. Isn't that true? Which means that, at least in theory, the server may end up storing the whole large file before it can deny the request. It seems to me that this is a clear case where RESTful urls have an advantage, since you don't have to look at the POST content to perform certain authorization/error checking on the request. Do you agree? What are your thoughts, experiences?

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• Can obfuscation (proguard) lead to MIDlet malfunction?

  - by eMgz

  Hi, Im trying to obfuscate a Java MIDlet with proguard. It runs ok on the PC, however, when I run it on the phone, the program opens, connects to the server, and then freezes. If I disable obfuscation, it runs ok again on the phone. Ive tryed all the obfuscation levels for apps (7, 8 and 9 at NetBeans), and none of them seems to work properly, and I cant release this app for comercial use without obfuscation. Also, the compiler throws some warnings: Note: duplicate definition of library class [java.io.ByteArrayOutputStream] Note: there were 14 duplicate class definitions. But I dont know if this is realy the problem. Does anyone knows what is wrong? The obfuscator arguments are listed below: Obfuscator Arguments (7): -dontusemixedcaseclassnames -default package '' -keep public class ** { public *; } Obfuscator Arguments (8): same as (7) plus -overloadaggressively. Obfuscator Arguments (9): same as (8) but -keep public class ** extends javax.microedition.midlet.MIDlet { public *; } instead. Thanks.

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• Returning structs in registers - ARM ABI in GCC

  - by jbcreix

  Hi, In the ARM ABI documentation I come across functions defined like: __value_in_regs struct bar foo(int a, int b) { ... } but GCC(4.3.3) doesn't allow it and all I could find are references to some RealView compiler. Is there any way of doing this from GCC? I have tried -freg-struct-return but it doesn't make a difference. As it is an ABI I can't change the original programs, and returning a regular struct mangles the stack. I would rather not using assembly for this if avoidable as it isn't otherwise necessary. Thanks!

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• Will more CPUs/cores help with VS.NET build times?

  - by LoveMeSomeCode

  I was wondering if anyone knew whether Visual Studio .NET had a parallel build process or not? I have a solution with lots of projects, every project has lots of markup/code, lots of types, etc. Just sitting there with intellisense on runs it up to about 700MB. But the build times are really slow and only seem to max out one of my two cpu cores. Does this mean the build process is single threaded? My solution's build dependency chain isn't linear, so I don't see why it couldn't be building some of the projects in parallel. I remember Joel Spolsky blogging about his new SSD, and how it didn't help with compile times, but he didn't mention which compiler he was using. We're using VS 2005. Anyone know how it's compilation works? And is it any different/better in 2008/2010?

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• C1083 : Permission denied on .sbr files

  - by speps

  Hello, I am using Visual Studio 2005 (with SP1) and I am getting weird errors concerning .sbr files. These files, as I read on MSDN, are intermediate files for BSCMAKE to generate a .bsc file. The errors I get are, for example (on different builds) : 11string.cpp : fatal error C1083: Impossible d'ouvrir le fichier généré(e) par le compilateur : '.\debug\String.sbr' : Permission denied 58type.cpp : fatal error C1083: Impossible d'ouvrir le fichier généré(e) par le compilateur : '.\Debug/Type.sbr' : Permission denied Translation : cannot open compiler intermediate file It seems to be consistent (I have at least 5 or 6 examples like this) with a .cpp file being compiled twice in the same project, respectively : 11String.cpp *some warnings, 2 lines* 11String.cpp 58Type.cpp *some warnings and other files compiled, a lot of lines* 58Type.cpp I already checked the .vcproj files for duplicate entries and it does not seem to be the problem. I would appreciate any help regarding this issue. Deactivating the build of .bsc files seems to be a workaround but maybe someone has better information than this. Thanks.

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• Operator precedence and struct definition in C

  - by Yktula

  struct struct0 { int a; }; struct struct1 { struct struct0 structure0; int b; } rho; &rho->structure0; /* Reference 1 */ (struct struct0 *)rho; /* Reference 2 */ (struct struct0)rho; /* Reference 3 */ From reference 1, does the compiler take the address of rho, and then access structure0, or vice-versa? What does the line at reference 2 do? Since structure0 is the first member of struct1, would reference 3 be equivalent to reference 1?

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• C# Language Design: explicit interface implementation of an event

  - by ControlFlow

  Small question about C# language design :)) If I had an interface like this: interface IFoo { int Value { get; set; } } It's possible to explicitly implement such interface using C# 3.0 auto-implemented properties: sealed class Foo : IFoo { int IFoo.Value { get; set; } } But if I had an event in the interface: interface IFoo { event EventHandler Event; } And trying to explicitly implement it using field-like event: sealed class Foo : IFoo { event EventHandler IFoo.Event; } I will get the following compiler error: error CS0071: An explicit interface implementation of an event must use event accessor syntax I think that field-like events is the some kind of dualism for auto-implemented properties. So my question is: what is the design reason for such restriction done?

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• how useful is Turing completeness? are neural nets turing complete?

  - by Albert

  While reading some papers about the Turing completeness of recurrent neural nets (for example: Turing computability with neural nets, Hava T. Siegelmann and Eduardo D. Sontag, 1991), I got the feeling that the proof which was given there was not really that practical. For example the referenced paper needs a neural network which neuron activity must be of infinity exactness (to reliable represent any rational number). Other proofs need a neural network of infinite size. Clearly, that is not really that practical. But I started to wonder now if it does make sense at all to ask for Turing completeness. By the strict definition, no computer system nowadays is Turing complete because none of them will be able to simulate the infinite tape. Interestingly, programming language specification leaves it most often open if they are turing complete or not. It all boils down to the question if they will always be able to allocate more memory and if the function call stack size is infinite. Most specification don't really specify this. Of course all available implementations are limited here, so all practical implementations of programming languages are not Turing complete. So, what you can say is that all computer systems are just equally powerful as finite state machines and not more. And that brings me to the question: How useful is the term Turing complete at all? And back to neural nets: For any practical implementation of a neural net (including our own brain), they will not be able to represent an infinite number of states, i.e. by the strict definition of Turing completeness, they are not Turing complete. So does the question if neural nets are Turing complete make sense at all? The question if they are as powerful as finite state machines was answered already much earlier (1954 by Minsky, the answer of course: yes) and also seems easier to answer. I.e., at least in theory, that was already the proof that they are as powerful as any computer.

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• Intel Assembler optimization

  - by Søren Haagerup

  I'm currently trying to optimize the code emitted from a home-made compiler, for a home-made language. I've tried out Intel VTune to see where the bottlenecks are: http://www.imada.sdu.dk/~sorenh07/misc/vtune-assembly-optimization.png I find it very impressive that a "subl"-instruction is responsible for over 38% of the clockticks in a program running for 30-90 seconds! Can anybody give an explanation why? The "optimization report" feature in VTune apparently doesn't exist for programs not compiled with icc. Does there exist a program which suggests optimization for assembler code? (that is, not code coming from a high-level language).

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• How to make safe cast using generics in C#?

  - by TN

  I want to implement a generic method on a generic class which would allow to cast safely, see example: public class Foo<T> : IEnumerable<T> { ... public IEnumerable<R> SafeCast<R>() where T : R { return this.Select(item => (R)item); } } However, the compiler tells me that Foo<T>.SafeCast<R>() does not define parameter 'T'. I understand this message that I cannot specify a constraint on T in the method since it is not defined in the method. But how can I specify an inverse constraint?

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• Help needed in grokking password hashes and salts

  - by javafueled

  I've read a number of SO questions on this topic, but grokking the applied practice of storing a salted hash of a password eludes me. Let's start with some ground rules: a password, "foobar12" (we are not discussing the strength of the password). a language, Java 1.6 for this discussion a database, postgreSQL, MySQL, SQL Server, Oracle Several options are available to storing the password, but I want to think about one (1): Store the password hashed with random salt in the DB, one column Found on SO and elsewhere is the automatic fail of plaintext, MD5/SHA1, and dual-columns. The latter have pros and cons MD5/SHA1 is simple. MessageDigest in Java provides MD5, SHA1 (through SHA512 in modern implementations, certainly 1.6). Additionally, most RDBMSs listed provide methods for MD5 encryption functions on inserts, updates, etc. The problems become evident once one groks "rainbow tables" and MD5 collisions (and I've grokked these concepts). Dual-column solutions rest on the idea that the salt does not need to be secret (grok it). However, a second column introduces a complexity that might not be a luxury if you have a legacy system with one (1) column for the password and the cost of updating the table and the code could be too high. But it is storing the password hashed with a random salt in single DB column that I need to understand better, with practical application. I like this solution for a couple of reasons: a salt is expected and considers legacy boundaries. Here's where I get lost: if the salt is random and hashed with the password, how can the system ever match the password? I have theory on this, and as I type I might be grokking the concept: Given a random salt of 128 bytes and a password of 8 bytes ('foobar12'), it could be programmatically possible to remove the part of the hash that was the salt, by hashing a random 128 byte salt and getting the substring of the original hash that is the hashed password. Then re hashing to match using the hash algorithm...??? So... any takers on helping. :) Am I close?

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• Yield In VB.NET

  - by MagicKat

  C# has the keyword called yield. VB.NET lacks this keyword. I am curious how some of the VB programmers have gotten around the lack of this keyword. Do you implement your own iterator class? Or do you try and code to avoid the need of an iterator? The yield keyword does force the compiler to do some coding behind the scenes. http://blogs.msdn.com/oldnewthing/archive/2008/08/12/8849519.aspx is a good example of that.

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• sOperator as and generic classes

  - by abatishchev

  I'm writing .NET On-the-Fly compiler for CLR scripting and want execution method make generic acceptable: object Execute() { return type.InvokeMember(..); } T Execute<T>() { return Execute() as T; /* doesn't work: The type parameter 'T' cannot be used with the 'as' operator because it does not have a class type constraint nor a 'class' constraint */ // also neither typeof(T) not T.GetType(), so on are possible return (T) Execute(); // ok } But I think operator as will be very useful: if result type isn't T method will return null, instead of an exception! Is it possible to do?

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• Using Library files in Linux

  - by paultop6

  Hi Guys, Im trying to use some of the functions that are in the /lib/libproc-3.2.6.so library in my Ubuntu Distribution. I have downloaded and installed the header files and they are defined in my source files. Currently this is all im trying to do, just for starters... proc_t **read_proc = readproctab(0); But i get the following compiler error: /tmp/cclqMImG.o: In function `Sysmon::initialise_sysmon()': sysmon.cpp:(.text+0x494): undefined reference to `readproctab' collect2: ld returned 1 exit status Im aware im probably doing some wrong with the command im using to compile it, but due to lack of experience im not sure what im doign wrong. This is the g++ command im using to compile my cpp file: g++ -o sysmon.o sysmon.cpp `pkg-config --libs --cflags gtk+-2.0` Can someone please give me some pointers as to where im going wrong Regards Paul

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• Reliable portability for C code without relying on the preprocessor

  - by Yktula

  Relying on the preprocessor and predefined compiler macros for achieving portability seems hard to manage. What's a better way to achieve portability for a C project? I want to put environment-specific code in headers that behave the same way. Is there a way to have the build environment choose which headers to include? I was thinking that I'd put the environment-specific headers into directories for specific environments. The build environment would then just copy the headers from the platform's directory into the root directory, build the project, and then remove the copies.

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• Should boost library be dependent on structure member alignments?

  - by Sorin Sbarnea

  I found, the hard way, that at least boost::program_options is dependent of the compiler configured structure member alignment. If you build boost using default settings and link it with a project using 4 bytes alignment (/Zp4) it will fail at runtime (made a minimal test with program_options). Boost will generate an assert indicating a possible bad calling convention but the real reason is the structure member alignment. Is there any way to prevent this? If the alignment makes the code incompatible shouldn't this be included in library naming?

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• msvcrt: memory usage goes wild, but not under debugger

  - by al_miro

  I have a C++ code compiled with Intel compiler, 32bit, in MS VC6 mode, so using either msvcrt.dll or msvcrtd.dll. The process makes heavy memory allocation and deallocation. I monitor the memory usage with WMI and look at VirtualSize and WorkingSetSize. with debug runtime (msvcrtd.dll): virtual constant 1.7GB, working constant 1.2GB with non-debug runtime (msvcrt.dll): virtual raising 1.7-- 2.1GB, working raising 1.2-1.4GB with non-debug runtime but under debugger (windbg): virtual constant 1.7GB, working constant At 2.1 GB virtual the process is crashing (as expected). But why would the virtual usage increase only with (non-debug) msvcrt.dll and only if not under debugger? In all cases compilation flags are identical, only runtime libs are different.

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• Getting started with massive data

  - by Max

  I'm a math guy and occasionally do some statistics/machine learning analysis consulting projects on the side. The data I have access to are usually on the smaller side, at most a couple hundred of megabytes (and almost always far less), but I want to learn more about handling and analyzing data on the gigabyte/terabyte scale. What do I need to know and what are some good resources to learn from? Hadoop/MapReduce is one obvious start. Is there a particular programming language I should pick up? (I primarily work now in Python, Ruby, R, and occasionally Java, but it seems like C and Clojure are often used for large-scale data analysis?) I'm not really familiar with the whole NoSQL movement, except that it's associated with big data. What's a good place to learn about it, and is there a particular implementation (Cassandra, CouchDB, etc.) I should get familiar with? Where can I learn about applying machine learning algorithms to huge amounts of data? My math background is mostly on the theory side, definitely not on the numerical or approximation side, and I'm guessing most of the standard ML algorithms don't really scale. Any other suggestions on things to learn would be great!

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• C2244 when trying to call the pow function from inline assembly

  - by schrödingers cat

  I would like to call the pow function from inline assembly. The problem is i'm getting error C2244: 'pow' : unable to match function definition to an existing declaration. I'm new to assembly so this may be a trivial question but how do i resolve this? I guess it has something to do with the compiler not beeing able to properly resolve the overload of pow. The following code fragment is causing the error: do_POW: // push first argument to the stack sub esp, size value_type fld qword ptr [ecx] fstp qword ptr [esp] // push second argument to the stack sub esp, size value_type fld qword ptr [ecx - size value_type] fstp qword ptr [esp]and pop fpu stack // call the pow function call pow sub ecx, size value_type fstp qword ptr [ecx] add esp, 2 * size value_type jmp loop_start

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