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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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• Pseudo code for instruction description

  - by Claus

  Hi, I am just trying to fiddle around what is the best and shortest way to describe two simple instructions with C-like pseudo code. The extract instruction is defined as follows: extract rd, rs, imm This instruction extracts the appropriate byte from the 32-bit source register rs and right justifies it in the destination register. The byte is specified by imm and thus can take the values 0 (for the least-significant byte) and 3 (for the most-significant byte). rd = 0x0; // zero-extend result, ie to make sure bits 31 to 8 are set to zero in the result rd = (rs && (0xff << imm)) >> imm; // this extracts the approriate byte and stores it in rd The insert instruction can be regarded as the inverse operation and it takes a right justified byte from the source register rs and deposits it in the appropriate byte of the destination register rd; again, this byte is determined by the value of imm tmp = 0x0 XOR (rs << imm)) // shift the byte to the appropriate byte determined by imm rd = (rd && (0x00 << imm)) // set appropriate byte to zero in rd rd = rd XOR tmp // XOR the byte into the destination register This looks all a bit horrible, so I wonder if there is a little bit a more elegant way to describe this bahaviour in C-like style ;) Many thanks, Claus

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• gdb reverse debugging error

  - by Werner

  Hi, i started to try reverse debugging with gdb 7, followin the tutorial: http://www.sourceware.org/gdb/wiki/ProcessRecord/Tutorial and I thought, great! Then I started to debug a real program which gives an error at the end. So I run it with gdb, and I put a breakpoint just before the place I think the error appears. Then I type "record" in order to start to recrd actions for future reverse-debugging. But after some steps I get Process record doesn't support instruction 0xf0d at address 0x2aaaab4c4b4e. Process record: failed to record execution log. Program received signal SIGTRAP, Trace/breakpoint trap. 0x00002aaaab4c4b4e in memcpy () from /lib64/libc.so.6 (gdb) n Single stepping until exit from function memcpy, which has no line number information. Process record doesn't support instruction 0xf0d at address 0x2aaaab4c4b4e. Process record: failed to record execution log. Program received signal SIGABRT, Aborted. 0x00002aaaab4c4b4e in memcpy () from /lib64/libc.so.6 Before I look at in in detail, I wonder if this feature is still buggy, or if I should start to record from the beginning. Where this "record" error happens, just an object is created as a copy of other: Thanks

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• Efficient algorithm to find first available name

  - by Avrahamshuk

  I have an array containing names of items. I want to give the user the option to create items without specifying their name, so my program will have to supply a unique default name, like "Item 1". The challenge is that the name has to be unique so i have to check all the array for that default name, and if there is an item with the same name i have to change the name to be "Item 2" and so on until i find an available name. The obvious solution will be something like that: String name; for (int i = 0 , name = "Item " + i ; !isAvailable(name) ; i++); My problem with that algorithm is that it runs at O(N^2). I wonder if there is a known (or new) more efficient algorithm to solve this case. In other words my question is this: Is there any algorithm that finds the first greater-than-zero number that dose NOT exist in a given array, and runs at less that N^2? Thanks!

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• what's an effective way to build a csproj file in C#?

  - by jcollum

  I'd like to avoid a command line for this. I've been using the MSBuild API ( Microsoft.Build.Framework and Microsoft.Build.BuildEngine) with code that looks like this: this.buildEngine = new Engine(); BuildPropertyGroup props = new BuildPropertyGroup(); props.SetProperty("Configuration", "Debug"); this.buildEngine.RegisterLogger(this.logger); Project proj = new Project(this.buildEngine); proj.LoadXml(this.projectFileAndPath, ProjectLoadSettings.None); this.buildEngine.BuildProject(proj, "Build"); However I've run into enough problems that I can't find answers for that I'm really wondering if I'm doing this right. First, I can't find the output (there's no bin directory in any of the places where I figured the dll's would end up). Second, I tried building a project that I had made in VS2008 and the line proj.LoadXml( fails for invalid xml encoding. But of course the xml file is valid, since VS2008 can build it (I checked). At this point I'm beginning to wonder if I've picked up some code that's way out of date or a methodology that's been superseded by something else. Opinions?

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• Problem with cruise control and visual svn

  - by Andrew

  Hi Wonder if anyone can help, I am experiencing a strange issue with my configuration of cruisecontrol.net and visual svn. I am setting the current ccnet.config <sourcecontrol type="svn"> <trunkUrl>https://bladerunner.azullo.local:8443/svn/application/trunk</trunkUrl> <executable>C:\Program Files (x86)\VisualSVN Server\bin\svn.exe</executable> <username>test</username> <password>test</password> <workingDirectory>D:\Development\Build\application\</workingDirectory> </sourcecontrol> <publishers> <xmllogger/> </publishers> <modificationDelaySeconds>10</modificationDelaySeconds> </project> When I run this I expect it to go to https://bladerunner.azullo.local:8443/svn/application/trunk, however i get the following ThoughtWorks.CruiseControl.Core.CruiseControlException: Source control operation failed: svn: OPTIONS of 'http://bladerunner.azullo.local:8080/svn/application/trunk': could not connect to server (http://bladerunner.azullo.local:8080) . Process command: C:\Program Files (x86)\VisualSVN Server\bin\svn.exe update D:\Development\build\application\ --username test --password ** --no-auth-cache --non-interactive at ThoughtWorks.CruiseControl.Core.Sourcecontrol.ProcessSourceControl.Execute(ProcessInfo processInfo) at ThoughtWorks.CruiseControl.Core.Sourcecontrol.Svn.UpdateSource(IIntegrationResult result) at ThoughtWorks.CruiseControl.Core.IntegrationRunner.Build(IIntegrationResult result) at ThoughtWorks.CruiseControl.Core.IntegrationRunner.Integrate(IntegrationRequest request) So for some reason it goes to 'http://bladerunner.azullo.local:8080/svn/application/trunk' If I remove the username and password elements in the ccnet.config. It goes to the correct url. I dont understand this behaviour. I have configured visual svn with a certificate using Active directory Certificate Services, if this was the problem I would expect it to show an error regarding the certificate instead of changing the url. I have cleared our state etc Any Ideas

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• Memory Bandwidth Performance for Modern Machines

  - by porgarmingduod

  I'm designing a real-time system that occasionally has to duplicate a large amount of memory. The memory consists of non-tiny regions, so I expect the copying performance will be fairly close to the maximum bandwidth the relevant components (CPU, RAM, MB) can do. This led me to wonder what kind of raw memory bandwidth modern commodity machine can muster? My aging Core2Duo gives me 1.5 GB/s if I use 1 thread to memcpy() (and understandably less if I memcpy() with both cores simultaneously.) While 1.5 GB is a fair amount of data, the real-time application I'm working on will have have something like 1/50th of a second, which means 30 MB. Basically, almost nothing. And perhaps worst of all, as I add multiple cores, I can process a lot more data without any increased performance for the needed duplication step. But a low-end Core2Due isn't exactly hot stuff these days. Are there any sites with information, such as actual benchmarks, on raw memory bandwidth on current and near-future hardware? Furthermore, for duplicating large amounts of data in memory, are there any shortcuts, or is memcpy() as good as it will get? Given a bunch of cores with nothing to do but duplicate as much memory as possible in a short amount of time, what's the best I can do?

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• What are the security implications of making a clientaccesspolicy proxy workaround?

  - by Edward Tanguay

  I wanted to use a published GoogleDocs document as the datasource of a Silverlight application but ran into clientaccesspolicy issues. I read many articles like this and this about how difficult it is to get around the clientaccesspolicy issue. So I wrote this 15-line CURL script and put it on my PHP site and now I can get the text of any GoogleDocs document and any text from any URL into my Silverlight application: <?php $url = filter_input(INPUT_GET, 'url',FILTER_SANITIZE_STRING); $user_agent = 'Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)'; $ch = curl_init(); curl_setopt($ch, CURLOPT_COOKIEJAR, "/tmp/cookie"); curl_setopt($ch, CURLOPT_COOKIEFILE, "/tmp/cookie"); curl_setopt($ch, CURLOPT_URL, $url ); // set url to post to curl_setopt($ch, CURLOPT_FAILONERROR, 1); // Fail on errors curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 0); // allow redirects curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); // return into a variable curl_setopt($ch, CURLOPT_TIMEOUT, 15); curl_setopt($ch, CURLOPT_USERAGENT, $user_agent); curl_setopt($ch, CURLOPT_VERBOSE, 0); echo curl_exec($ch); ?> So it makes me wonder: Why is there so much discussion about whether or not URLs support clientaccesspolicy or not, since you just have to write a simple proxy script and get the information through it? Why aren't there services, e.g. like the URL shortening services, which supply this functionality? What are the security implications of having a script like this?

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• Is it valid to use unsafe struct * as an opaque type instead of IntPtr in .NET Platform Invoke?

  - by David Jeske

  .NET Platform Invoke advocates declaring pointer types as IntPtr. For example, the following [DllImport("user32.dll")] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam); However, I find when interfacing with interesting native interfaces, that have many pointer types, flattening everything into IntPtr makes the code very hard to read and removes the typical typechecking that a compiler can do. I've been using a pattern where I declare an unsafe struct to be an opaque pointer type. I can store this pointer type in a managed object, and the compiler can typecheck it form me. For example: class Foo { unsafe struct FOO {}; // opaque type unsafe FOO *my_foo; class if { [DllImport("mydll")] extern static unsafe FOO* get_foo(); [DllImport("mydll")] extern static unsafe void do_something_foo(FOO *foo); } public unsafe Foo() { this.my_foo = if.get_foo(); } public unsafe do_something_foo() { if.do_something_foo(this.my_foo); } While this example may not seem different than using IntPtr, when there are several pointer types moving between managed and native code, using these opaque pointer types for typechecking is a godsend. I have not run into any trouble using this technique in practice. However, I also have not seen an examples of anyone using this technique, and I wonder why. Is there any reason that the above code is invalid in the eyes of the .NET runtime? My main question is about how the .NET GC system treats "unsafe FOO *my_foo". Is this pointer something the GC system is going to try to trace, or is it simply going to ignore it? My hope is that because the underlying type is a struct, and it's declared unsafe, that the GC would ignore it. However, I don't know for sure. Thoughts?

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• How to stop ejabberd from using mnesia

  - by Eldad Mor

  I'm trying to establish a procedure for restoring my database from a crashed server to a new server. My server is running Ejabberd as an XMPP server, and I configured it to use postgresql instead of mnesia - or so I thought. My procedure goes something like "dump the contents of the original DB, run the new server, restore the contents of the DBs using psql, then run the system". However, when I try running Ejabberd again I get a crash: =CRASH REPORT==== 3-Dec-2010::22:05:00 === crasher: pid: <0.36.0> registered_name: [] exception exit: {bad_return,{{ejabberd_app,start,[normal,[]]}, {'EXIT',"Error reading Mnesia database"}}} in function application_master:init/4 Here I was thinking that my system is running on PostgreSQL, while it seems I was still using Mnesia. I have several questions: How can I make sure mnesia is not being used? How can I divert all the ejabberd activities to PGSQL? This is the modules part in my ejabberd.cfg file: {modules, [ {mod_adhoc, []}, {mod_announce, [{access, announce}]}, % requires mod_adhoc {mod_caps, []}, {mod_configure,[]}, % requires mod_adhoc {mod_ctlextra, []}, {mod_disco, []}, {mod_irc, []}, {mod_last_odbc, []}, {mod_muc, [ {access, muc}, {access_create, muc}, {access_persistent, muc}, {access_admin, muc_admin}, {max_users, 500} ]}, {mod_offline_odbc, []}, {mod_privacy_odbc, []}, {mod_private_odbc, []}, {mod_pubsub, [ % requires mod_caps {access_createnode, pubsub_createnode}, {plugins, ["default", "pep"]} ]}, {mod_register, [ {welcome_message, none}, {access, register} ]}, {mod_roster_odbc, []}, {mod_stats, []}, {mod_time, []}, {mod_vcard_odbc, []}, {mod_version, []} ]}. What am I missing? I am assuming the crash is due to the mnesia DB being used by Ejabberd, and since it's out of sync with the PGSQL DB, it cannot operate correctly - but maybe I'm totally off track here, and would love some direction. EDIT: One problem solved. Since I'm using amazon cloud, I needed to hardcode the ERLANG_NODE so it won't be defined by the hostname (which changes on reboot). This got my ejabberd running, but still I wish to stop using mnesia, and I wonder what part of ejabberd is still using it and how can I found it.

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• encodeURIComponent is really useful?

  - by Marco Demaio

  Something I still don't understand when perfoming an http-get request to the server is what the advantage is in using JS fucntion encodeURIcomponent to encode each component of the http-get. Doing some tests I saw the server (using PHP) gets the values of the http-get request properly also if I don't use encodeURIcomponent!!! Obviuosly I still need to encode at client level the special character & ? = / : otherwise an http-get value like this "peace&love=virtue" would be considered as new key value pair of the http-get request instead of a one single value. But why does encodeURIcompenent encodes also many other charcaters like 'è' for example wich is translated into %C3%A8 that must be decoded on a PHP server using the utf8_decode function. By using encodeURIcomponent all values of the http-get request are utf8 encoded, therefor when getting them in PHP I have to call each time the utf8_decode function on each $_GET value which is quite annoying. Why can't we just encode only the & ? = / : charcaters??? see also: http://stackoverflow.com/questions/2607946/js-encodeuricomponent-result-different-from-the-one-created-by-form It shows that encodeURIComponent does not even encode properly because a simple browser FORM GET encodes charactrs like '€', in different way. So I still wonder what does this encodeURIComponent is for?

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• what's an effective way to build a csproj file in code?

  - by jcollum

  I'd like to avoid a command line for this. I've been using the MSBuild API ( Microsoft.Build.Framework and Microsoft.Build.BuildEngine) with code that looks like this: this.buildEngine = new Engine(); BuildPropertyGroup props = new BuildPropertyGroup(); props.SetProperty("Configuration", "Debug"); this.buildEngine.RegisterLogger(this.logger); Project proj = new Project(this.buildEngine); proj.LoadXml(this.projectFileAndPath, ProjectLoadSettings.None); this.buildEngine.BuildProject(proj, "Build"); However I've run into enough problems that I can't find answers for that I'm really wondering if I'm doing this right. First, I can't find the output (there's no bin directory in any of the places where I figured the dll's would end up). Second, I tried building a project that I had made in VS2008 and the line proj.LoadXml( fails for invalid xml encoding. But of course the xml file is valid, since VS2008 can build it (I checked). At this point I'm beginning to wonder if I've picked up some code that's way out of date or a methodology that's been superseded by something else. Opinions?

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• MyMessage<T> throws an exception when calling XmlSerializer

  - by Arthis

  I am very new to nservicebus. I am using version 3.0.1, the last one up to date. And I wonder if my case is a normal limitation of NSB, I am not aware of. I have an asp.net MVC application, I am trying to setup and in my global.asax, I have the following : var configure = Configure.WithWeb() .DefaultBuilder() .ForMvc() .XmlSerializer(); But I have an error with the XmlSerializer when dealing with one of my object: [Serializable] public class MyMessage<T> : IMessage { public T myobject { get; set; } } I pass trough : XmlSerializer() instance.Initialize(types); this.InitType(type, moduleBuilder); this.InitType(info2.PropertyType, moduleBuilder); and then when dealing With T, string typeName = GetTypeName(t); typename is null and the following instruction : if (!nameToType.ContainsKey(typeName)) ends in error. null value not allowed. Is this some limitations to Nservicebus, or am I messing something up?

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• Can per-user randomized salts be replaced with iterative hashing?

  - by Chas Emerick

  In the process of building what I'd like to hope is a properly-architected authentication mechanism, I've come across a lot of materials that specify that: user passwords must be salted the salt used should be sufficiently random and generated per-user ...therefore, the salt must be stored with the user record in order to support verification of the user password I wholeheartedly agree with the first and second points, but it seems like there's an easy workaround for the latter. Instead of doing the equivalent of (pseudocode here): salt = random(); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword, salt); Why not use the hash of the username as the salt? This yields a domain of salts that is well-distributed, (roughly) random, and each individual salt is as complex as your salt function provides for. Even better, you don't have to store the salt in the database -- just regenerate it at authentication-time. More pseudocode: salt = hash(username); hashedPassword = hash(salt . password); storeUserRecord(username, hashedPassword); (Of course, hash in the examples above should be something reasonable, like SHA-512, or some other strong hash.) This seems reasonable to me given what (little) I know of crypto, but the fact that it's a simplification over widely-recommended practice makes me wonder whether there's some obvious reason I've gone astray that I'm not aware of.

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• Iphone CATextLayer doesn't show it's text.

  - by lovecactus

  Here is my new bee issue: I was simply trying to add a CATextlayer in an UIView layer. However, according to the following code, I only get the CATextlayer's background color be displayed in the UIView, without any text. Just wonder what did I missed to display the text. Could anyone ofter a hint/sample how to use CATextlayer? Thanks. (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])) { // Custom initialization CATextLayer *TextLayer = [CATextLayer layer]; TextLayer.bounds = CGRectMake(0.0f, 0.0f, 100.0f, 100.0f); TextLayer.string = @"Test"; TextLayer.font = [UIFont boldSystemFontOfSize:18].fontName; TextLayer.backgroundColor = [UIColor whiteColor].CGColor; TextLayer.wrapped = NO; //TextLayer.backgroundColor = [UIColor blueColor]; self.view = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 100.0f, 100.0f)]; self.view.backgroundColor = [UIColor blueColor]; [self.view.layer addSublayer:TextLayer]; [self.view.layer layoutSublayers]; } return self; }

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• How to bind data from a view of type List<List<MyViewModelClass>>?

  - by Robert Koritnik

  I have a strong type view of type List<List<MyViewModelClass>> The outer list will always have two lists of List<MyViewModelClass>. For each of the two outer lists I want to display a group of checkboxes. Each set can have an arbitrary number of choices. My view model class looks similar to this: public class MyViewModelClass { public Area Area { get; set; } public bool IsGeneric { get; set; } public string Code { get; set; } public bool IsChecked { get; set; } } So the final view will look something like: Please select those that apply: First set of choices: x Option 1 x Option 2 x Option 3 etc. Second set of choices: x Second Option 1 x Second Option 2 x Second Option 3 x Second Option 4 etc. Checkboxes should display MyViewModelClass.Area.Name, and their value should be related to MyViewModelClass.Area.Id. Checked state is of course related to MyViewModel.IsChecked. Question I wonder how should I use Html.CheckBox() or Html.CheckBoxFor() helper to display my checkboxes? I have to get these values back to the server on a postback of course. If it makes things simpler, I could make a separate view model type like: public class Options { public List<MyViewModelClass> General { get; set; } public List<MyViewModelClass> Others { get; set; } }

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• What issues to consider when rolling your own data-backend for Silverlight / AJAX on non-ASP.NET ser

  - by Edward Tanguay

  I have read-only Silverlight and AJAX apps which read static text and XML files from a PHP/Apache server, which works very nicely with features such as asynchronous loading, lazy-loading only what I need for each page, loading in the background, developed a little query language to get a PHP script to create custom XML files etc. it's pragmatic read-only REST, and all works fast and fine for read-only sites. Now I want to also add the ability to write data from these apps to a database on the same PHP/Apache server. For those of you who have built similar data-access layers, what do I need to consider while building this, especially regarding security so that not just any client can write and alter my database, e.g.: check HTTP_USER_AGENT for security check REMOTE_ADDR for security require a special code for security, perhaps a list of TAN codes (such as banks use for online transactions) each which can only be used once, both the client and server have these I wonder if there is some kind of standard REST query I should lean on for e.g. building SQL-like statements in the URL parameters, e.g. http://www.thedatalayersite.com/query?insertinto=customers&... Any thoughts, notes from experience, ideas, gotchas, especially ideas on tightening down security in this endeavor would be helpful.

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• Can a class inherit from LambdaExpression in .NET? Or is this not recommended?

  - by d.

  Consider the following code (C# 4.0): public class Foo : LambdaExpression { } This throws the following design-time error: Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) There's absolutely no problem with public class Foo : Expression { } but, out of curiosity and for the sake of learning, I've searched in Google System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) and guess what: zero results returned (when was the last time you saw that?). Needless to say, I haven't found any documentation on this method anywhere else. As I said, one can easily inherit from Expression; on the other hand LambdaExpression, while not marked as sealed (Expression<TDelegate> inherits from it), seems to be designed to prevent inheriting from it. Is this actually the case? Does anyone out there know what this method is about? EDIT (1): More info based on the first answers - If you try to implement Accept, the editor (C# 2010 Express) automatically gives you the following stub: protected override Expression Accept(System.Linq.Expressions.ExpressionVisitor visitor) { return base.Accept(visitor); } But you still get the same error. If you try to use a parameter of type StackSpiller directly, the compiler throws a different error: System.Linq.Expressions.Compiler.StackSpiller is inaccessible due to its protection level. EDIT (2): Based on other answers, inheriting from LambdaExpression is not possible so the question as to whether or not it is recommended becomes irrelevant. I wonder if, in cases like this, the error message should be Foo cannot implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) because [reasons go here]; the current error message (as some answers prove) seems to tell me that all I need to do is implement Accept (which I can't do).

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• puzzled with java if else performance

  - by user1906966

  I am doing an investigation on a method's performance and finally identified the overhead was caused by the "else" portion of the if else statement. I have written a small program to illustrate the performance difference even when the else portion of the code never gets executed: public class TestIfPerf { public static void main( String[] args ) { boolean condition = true; long time = 0L; int value = 0; // warm up test for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } // benchmark if condition only time = System.nanoTime(); for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } } time = System.nanoTime() - time; System.out.println( "1) performance " + time ); time = System.nanoTime(); // benchmark if else condition for( int count=0; count<10000000; count++ ) { if ( condition ) { value = 1 + 2; } else { value = 1 + 3; } } time = System.nanoTime() - time; System.out.println( "2) performance " + time ); } } and run the test program with java -classpath . -Dmx=800m -Dms=800m TestIfPerf. I performed this on both Mac and Linux Java with 1.6 latest build. Consistently the first benchmark, without the else is much faster than the second benchmark with the else section even though the code is structured such that the else portion is never executed because of the condition. I understand that to some, the difference might not be significant but the relative performance difference is large. I wonder if anyone has any insight to this (or maybe there is something I did incorrectly). Linux benchmark (in nano) performance 1215488 performance 2629531 Mac benchmark (in nano) performance 1667000 performance 4208000

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• Flex 3: should I provide prepared data to my component or make it to process data before display?

  - by grapkulec

  I'm starting to learn a little Flex just for fun and maybe to prove that I still can learn something new :) I have some idea for a project and one of its parts is a tree component which could display data in different ways depending on configuration. The idea There is list of objects having properties like id, date, time, name, description. And sometimes list should be displayed like this: first level: date second level: time third level: name and sometimes like this: first level: year second level: month third level: day fourth level: time and name By level I mean level of nesting of course. So, we can have years, that have months, that have days, that have hours and so forth. The problem What could be the best way to do it? I mean, should I prepare data for different ways of nesting outside of component or even outside of flex? I can do it at web service level in C# where I plan to have database access layer and send to flex nice and ready to display XML or array of objects. But I wonder if that won't cause additional and maybe unneccessary network traffic. I tried to hack some code in my component to convert my data objects into XML or ArrayCollection but I don't know enough of Flex and got stuck on elimination of duplicates or getting specific data by some key value. Usually to do such things I have STL with maps, sets and vectors and I find Flex arrays and even Dictionary a little bit confusing (I've read language reference and googled without any significant luck). The question So, to sum things up: should I give my tree component data prepared just for chosen type of display or should I try to do it internally inside component (or some helper class written in ActionScript)?

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• send message to a web service according to its schema

  - by hguser

  Hi: When I request a web servcie,it give me a response which show me the required parameters and its schema,for example: the response of the web service for the descriptin of the parameter Then I start to organize the next requset according to the parameter,for the parameter "bandWith" I set it as the following: <InputParameter parameterID="bandWidth"> <value> <commonData> <swe:Category> <swe:quality> <swe:Text> <swe:value>low</swe:value> </swe:Text> </swe:quality> </swe:Category> </commonData> </value> </InputParameter> However I got a exception : error information Also I tried the following format,things does not chage: <InputParameter parameterID="bandWidth"> <value> <commonData> <swe:Category> <swe:value>low</swe:value> </swe:Category> </commonData> </value> </InputParameter> So, I wonder how do define the parameter to match the format it defined? The schema can be found there: The schema

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• From ASPX to WCF

  - by Barguast

  I'm hoping someone can advise me on how to solve my networking scenario. Both the client and server are to be C# / .NET based. I basically want to invoke some kind of web service from my client in order to retrieve both binary data (e.g. files) and serialised objects and lists of objects (e.g. database query results). At the moment, I'm using ASPX pages, using the query string to provide parameters and I get back either the binary data, or the binary data of the serialised messages. This affords me a lot of flexbility, and I can choose how to transmit the data, perform simulatanous requests, cancel ongoing requests, etc. Since I can control the serialised format, I can also deserialise lists of objects as they are received which is crucial. My problem isn't a problem as such, but this feels a little hack-ish and I can't help but wonder if there are better ways to go about it. I'm considering moving on to WCF or perhaps another technology to see if it helps. However, I need to know if it helps with my scenarios above that is; Can a WCF method return a list of objects, and can the client receive the items of this list as they arrive as opposed to getting the entire list on completion (i.e. streaming). Does anyone know of any examples of this? Am I likely to get any performance benefits from this? I don't know how well ASPX pages are tuned for this, as it surely isn't their primary purpose. Are there any other approaches I should consider? Thanks for your time spent reading this. I hope you can help.

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• IntegrityError: foreign key violation upon delete

  - by Lukasz Korzybski

  I have Order and Shipment model. Shipment has a foreign key to Order. class Order(...): ... class Shipment() order = m.ForeignKey('Order') ... Now in one of my views I want do delete order object along with all related objects. So I invoke order.delete(). I have Django 1.0.4, PostgreSQL 8.4 and I use transaction middleware, so whole request is enclosed in single transaction. The problem is that upon order.delete() I get: ... File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 28, in _commit return self.connection.commit() IntegrityError: update or delete on table "main_order" violates foreign key constraint "main_shipment_order_id_fkey" on table "main_shipment" DETAIL: Key (id)=(45) is still referenced from table "main_shipment". I checked in connection.queries that proper queries are executed in proper order. First shipment is deleted, after that django executes delete on order row: {'time': '0.000', 'sql': 'DELETE FROM "main_shipment" WHERE "id" IN (17)'}, {'time': '0.000', 'sql': 'DELETE FROM "main_order" WHERE "id" IN (45)'} Foreign key have ON DELETE NO ACTION (default) and is initially deferred. I don't know why I get foreign key constraint violation. I also tried to register pre_delete signal and manually delete shipment objects before delete on order is called, but it resulted in the same error. I can change ON DELETE behaviour for this key in Postgres but it would be just a hack, I wonder if anyone has a better idea what's going on here. There is also a small detail, my Order model inherits from Cart model, so it actually doesn't have id field but cart_ptr_id and after DELETE on order is executed there is also DELETE on cart, but it seems unrelated? to the shipment-order problem so I simplified it in the example.

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• Are Parameters really enough to prevent Sql injections?

  - by Rune Grimstad

  I've been preaching both to my colleagues and here on SO about the goodness of using parameters in SQL queries, especially in .NET applications. I've even gone so far as to promise them as giving immunity against SQL injection attacks. But I'm starting to wonder if this really is true. Are there any known SQL injection attacks that will be successfull against a parameterized query? Can you for example send a string that causes a buffer overflow on the server? There are of course other considerations to make to ensure that a web application is safe (like sanitizing user input and all that stuff) but now I am thinking of SQL injections. I'm especially interested in attacks against MsSQL 2005 and 2008 since they are my primary databases, but all databases are interesting. Edit: To clarify what I mean by parameters and parameterized queries. By using parameters I mean using "variables" instead of building the sql query in a string. So instead of doing this: SELECT * FROM Table WHERE Name = 'a name' We do this: SELECT * FROM Table WHERE Name = @Name and then set the value of the @Name parameter on the query / command object.

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• Using git-svn with slightly strange svn layout

  - by Ibrahim

  Hi guys, I'm doing an internship and they are using SVN (although there has been some discussion of moving to hg or git but that's not in the immediate future). I like git so I would like to use git-svn to interact with the svn repository and be able to do local commits and branches and stuff like that (rebasing before committing to svn of course). However, there is one slight wrinkle, the svn repository layout is a little weird. It basically looks like this /FOO +-branches +-tags +-trunk +-FOO +-myproject Basically, my project has been stuck into a subdirectory of trunk, and there is another project that is also a subdirectory of the trunk. If I use git-svn and only clone the directory for my project instead of the root, will it get confused or cause any problems? I just wonder because the commit numbers are incremented for the entire repository and not just my project, so would commits be off or anything like that? I probably wouldn't push any branches or tags to SVN because I'd prefer to just do those locally in git and I don't know how git-svn deals with branches and tags anyway, and no one else uses them so I find little point in doing so. Thanks for the help!

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