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• Are some data structures more suitable for functional programming than others?

  - by Rob Lachlan

  In Real World Haskell, there is a section titled "Life without arrays or hash tables" where the authors suggest that list and trees are preferred in functional programming, whereas an array or a hash table might be used instead in an imperative program. This makes sense, since it's much easier to reuse part of an (immutable) list or tree when creating a new one than to do so with an array. So my questions are: Are there really significantly different usage patterns for data structures between functional and imperative programming? If so, is this a problem? What if you really do need a hash table for some application? Do you simply swallow the extra expense incurred for modifications?

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• Can zlib.crc32 or zlib.adler32 be safely used to mask primary keys in URLs?

  - by David Eyk

  In Django Design Patterns, the author recommends using zlib.crc32 to mask primary keys in URLs. After some quick testing, I noticed that crc32 produces negative integers about half the time, which seems undesirable for use in a URL. zlib.adler32 does not appear to produce negatives, but is described as "weaker" than CRC. Is this method (either CRC or Adler-32) safe for usage in a URL as an alternate to a primary key? (i.e. is it collision-safe?) Is the "weaker" Adler-32 a satisfactory alternative for this task? How the heck do you reverse this?! That is, how do you determine the original primary key from the checksum?

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• Getting the battery current values for the Android Phone

  - by themangoman

  I am trying to collect power usage statistics for the Android G1 Phone. I am interested in knowing the values of Voltage and Current, and then able to collect statistics as reported in this PDF. I am able to get the value of Battery voltage through registering for an intent receiver to receive the Broadcast for ACTION_BATTERY_CHANGED. But the problem is that Android does not expose the value of current through this SDK interface. One way I tried is via sysfs interface, where I can view the battery current value from adb shell, using the following command $cat /sys/class/power_supply/battery/batt_current 449 But that too works only if the phone is connected via USB interface. If I disconnect the phone, I see the value of batt_current as '0'. I am not sure why the value of current reported is zero. It should be more than zero, right? Any suggestion / pointers for getting battery current value? Also please correct me if I am wrong.

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• In a multithreaded app, would a multi-core or multiprocessor arrangement be better?

  - by Michael

  I've read a lot on this topic already both here (e.g., stackoverflow.com/questions/1713554/threads-processes-vs-multithreading-multi-core-multiprocessor-how-they-are or http://stackoverflow.com/questions/680684/multi-cpu-multi-core-and-hyper-thread) and elsewhere (e.g., ixbtlabs.com/articles2/cpu/rmmt-l2-cache.html or software.intel.com/en-us/articles/multi-core-introduction/), but I still am not sure about a couple things that seem very straightforward. So I thought I'd just ask. (1) Is a multi-core processor in which each core has dedicated cache effectively the same as a multiprocessor system (balanced of course for processor speed, cache size, and so on)? (2) Let's say I have some images to analyze (i.e., computer vision), and I have these images loaded into RAM. My app spawns a thread for each image that needs to be analyzed. Will this app on a shared cache multi-core processor run slower than on a dedicated cache multi-core processor, and would the latter run at the same speed as on an equivalent single-core multiprocessor machine? Thank you for the help!

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• Problem in populating a dictionary using Enumerable.Range()

  - by Newbie

  If I do for (int i = 0; i < appSettings.Count; i++) { string key = appSettings.Keys[i]; euFileDictionary.Add(key, appSettings[i]); } It is working fine. When I am trying the same thing using Enumerable.Range(0, appSettings.Count).Select(i => { string Key = appSettings.Keys[i]; string Value = appSettings[i]; euFileDictionary.Add(Key, Value); }).ToDictionary<string,string>(); I am getting a compile time error The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. Any idea? Using C#3.0 Thanks

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• Using numeric_limits::max() in constant expressions

  - by FireAphis

  Hello, I would like to define inside a class a constant which value is the maximum possible int. Something like this: class A { ... static const int ERROR_VALUE = std::numeric_limits<int>::max(); ... } This declaration fails to compile with the following message: numeric.cpp:8: error: 'std::numeric_limits::max()' cannot appear in a constant-expression numeric.cpp:8: error: a function call cannot appear in a constant-expression I understand why this doesn't work, but two things look weird to me: It seems to me a natural decision to use the value in constant expressions. Why did the language designers decide to make max() a function thus not allowing this usage? The spec claims in 18.2.1 that For all members declared static const in the numeric_limits template, specializations shall define these values in such a way that they are usable as integral constant expressions. Doesn't it mean that I should be able to use it in my scenario and doesn't it contradict the error message? Thank you.

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• What alternatives are there to Google App Engine?

  - by Chris Marasti-Georg

  What alternatives are there to GAE, given that I already have a good bit of code working that I would like to keep. In other words, I'm digging python. However, my use case is more of a low number of requests, higher CPU usage type use case, and I'm worried that I may not be able to stay with App Engine forever. I have heard a lot of people talking about Amazon Web Services and other sorts of cloud providers, but I am having a hard time seeing where most of these other offerings provide the range of services (data querying, user authentication, automatic scaling) that App Engine provides. What are my options here?

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• Detect block size for quota in Linux

  - by Chen Levy

  The limit placed on disk quota in Linux is counted in blocks. However, I found no reliable way to determine the block size. Tutorials I found refer to block size as 512 bytes, and sometimes as 1024 bytes. I got confused reading a post on LinuxForum.org for what a block size really means. So I tried to find that meaning in the context of quota. I found a "Determine the block size on hard disk filesystem for disk quota" tip on NixCraft, that suggested the command: dumpe2fs /dev/sdXN | grep -i 'Block size' or blockdev --getbsz /dev/sdXN But on my system those commands returned 4096, and when I checked the real quota block size on the same system, I got a block size of 1024 bytes. Is there a scriptable way to determine the quota block size on a device, short of creating a known sized file, and checking it's quota usage?

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• JVM memory initializazion error after windows update

  - by Pier Luigi

  Hi all, I have three Windows Server 2003 with 2 GB RAM. Server1 tomcat 5.5.25 jvm version SUN 1.6.0_11-b03 Server2 tomcat 5.5.25 jvm version SUN 1.6.0_14-b08 Server3 tomcat 6.0.18 jvm version SUN 1.6.0_14-b08 For the three servers JVM parameters are: -XX:MaxPermSize=256m -Dcatalina.base=C:\Apache Group\apache-tomcat-5.5.25 -Dcatalina.home=C:\Apache Group\apache-tomcat-5.5.25 -Djava.endorsed.dirs=C:\Apache Group\apache-tomcat-5.5.25\common\endorsed -Djava.io.tmpdir=C:\Apache Group\apache-tomcat-5.5.25\temp vfprintf -Xms512m -Xmx1024m For some months everithing worked fine. Last friday we installed some windows updates. After the reboot tomcat doesn't start anymore, with error: Error occurred during initialization of VM Could not reserve enough space for object heap We reduced the parameter -Xmx1024m to -Xmx768m and now tomcat starts. But we need greater max heap size What happened to our servers ? Thanks in advance.

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• learning the Lower levels of computing

  - by Ben

  I am a software developer with four years experience in .Net development, I always like to keep up to date with the latest technologies (.net related normally) being released and love learning them. I didn't however go to university and learnt all I know through helpful colleagues, .Net courses, the internet and good old books. I feel that I am a good developer, but without learning the lower levels of a computer as you would in the first year of a computer related Uni course, I get lost when talking to people about a lot of more technical lower level computing. Is there a book(s) that anyone could recommend, that would cover the lower levels of what is going on when I click "Run" in Visual Studio? I feel out of my depth when my boss says to me "Thats running in the CPU cache" or "you're limited by disk reads there", and would like to feel more confident when talking about how the hardware talks to each other (CPU to RAM etc). Apologise if thats a vague question, or has been asked before (i did check and couldn't find anything on here that answers my question).

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• Is this an F# quotations bug?

  - by ControlFlow

  [<ReflectedDefinition>] let rec x = (fun() -> x + "abc") () The sample code with the recursive value above produces the following F# compiler error: error FS0432: [<ReflectedDefinition>] terms cannot contain uses of the prefix splice operator '%' I can't see any slicing operator usage in the code above, looks like a bug... :) Looks like this is the problem with the quotation via ReflectedDefinitionAttribute only, normal quotation works well: let quotation = <@ let rec x = (fun() -> x + "abc") () in x @> produces expected result with the hidden Lazy.create and Lazy.force usages: val quotation : Quotations.Expr<string> = LetRecursive ([(x, Lambda (unitVar, Application (Lambda (unitVar0, Call (None, String op_Addition[String,String,String](String, String), [Call (None, String Force[String](Lazy`1[System.String]), [x]), Value ("abc")])), Value (<null>)))), (x, Call (None, Lazy`1[String] Create[String](FSharpFunc`2[Unit,String]), [x])), (x, Call (None, String Force[String](Lazy`1[String]), [x]))], x) So the question is: is this an F# compiler bug or not?

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• UIImages on UITableView?

  - by babu Kong

  what is the best method to display about 300 png images into a UITableView.. i dont wanna display them at the same time... i have 3 tableViewControllers that will each display about 100 imgaes.. (its for a catalog so the images are important to display) i used [uiimage imageNamed:] but that method caches the images and they dont get released so the memory usage is big.... is there any way to release the cache when the nav controller pushes a different view controller? i also tried [uiimage alloc] initWithContentsOfFile] but the images wont display.... any help?

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• LISP: Keyword parameters, supplied-p

  - by echox

  At the moment I'm working through "Practical Common Lisp" from Peter Seibel. In the chapter "Practical: A Simple Database" (http://www.gigamonkeys.com/book/practical-a-simple-database.html) Seibel explains keyword parameters and the usage of a supplied-parameter with the following example: (defun foo (&key a (b 20) (c 30 c-p)) (list a b c c-p)) Results: (foo :a 1 :b 2 :c 3) ==> (1 2 3 T) (foo :c 3 :b 2 :a 1) ==> (1 2 3 T) (foo :a 1 :c 3) ==> (1 20 3 T) (foo) ==> (NIL 20 30 NIL) So if I use &key at the beginning of my parameter list, I have the possibility to use a list of 3 parameters name, default value and the third if the parameter as been supplied or not. Ok. But looking at the code in the above example: (list a b c c-p) How does the lisp interpreter know that c-p is my "supplied parameter"?

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• McAfee Virus Scan and Oracle RAC

  - by Lee Gathercole

  Hi, We're experiencing a strange problem with Oracle RAC and McAfee anti-virus. As part of the installation of the Oracle RAC we disable anti virus as directed. We have had our RAC running fine, but when we came to re-enable the AV and reboot we got the BSOD. Abnormal Program Termination (BugCheck, STOP: 0x00000035 (0x8E984678, 0x00000000, 0x00000000, 0x00000000 NO_MORE_IRP_STACK_LOCATIONS Following the standard process of raising this problem with Microsoft they identify the problem and also a fix. Microsoft talk about too many file filter drivers being present and pushing the DFS upper limit beyond the default size. Upping this value, as per msdn, has no impact. We're able to recover from this BSOD by disabling AV. We don't have the problem if we run the AV service manually whilst the system is up. However, if we make the service automatic we fail to boot. Tech Details 2 Node Oracle 10g Cluster 2 * Windows 2003 SP2, 16GB RAM, Quad Core 3ghz Processor SAN attached storage McAfee VirusScan Enterprise 8.5.0i, Scan Engine (5300.2777), DAT Version (5536.0000) Thanks Lee

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• iOS Efficiency File Saving Efficiency

  - by Guvvy Aba

  I was working on my iOS app and my goal is to save a file that I am receiving from the internet bit by bit. My current setup is that I have a NSMutableData object and I add a bit of data to it as I receive my file. After the last "packet" is received, I write the NSData to a file and the process is complete. I'm kind of worried that this isn't the ideal way to do it because of the limitations of RAM in a mobile device and it would be problematic to receive large files. My next thought was to implement a NSFileHandle so that as the file arrives, it would be saved to the disk, rather than the virtual memory. In terms of speed and efficiency, which method do you think will work decently on an iOS device. I am currently using the first, NSMutableData approach. Is it worth changing my app to use the NSFileHandle? Thanks in advance, Guvvy

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• Is it possible to tell IIS 7 to process the request queue in parallel?

  - by Uwe Keim

  Currently we are developing an ASMX, ASP 2.0, IIS 7 web service that does some calculations (and return a dynamically generated document) and will take approx. 60 seconds to run. Since whe have a big machine with multiple cores and lots of RAM, I expected that IIS tries its best to route the requests that arrive in its requests queue to all available threads of the app pool's thread pool. But we experience quiet the opposite: When we issue requests to the ASMX web service URL from multiple different clients, the IIS seems to serially process these requests. I.e. request 1 arrives, is being processed, then request 2 is being processed, then request 3, etc. Question: Is it possible (without changing the C# code of the web service) to configure IIS to process requests in parallel, if enough threads are available? If yes: how should I do it? It no: any workarounds/tips? Thanks Uwe

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• Sharepoint Foundation 2010 development single machine installation problems

  - by Robert Koritnik

  I'm having problems installing development machine for Sharepoint (Foundation) 2010. This is what I did so far on the same machine: Installed a clean Windows 7 x64 with 4GB of RAM without being part of any domain. Just a simple standalone machine. Enabled IIS related features as described here except IIS6 related ones (two of them) Installed SQL Server 2008 R2 Development Edition (DB Engine and Writer being enabled but not SQL Agent) Installed Visual Studio 2010 Premium Started installing Sharepoint Foundation 2010 with first extracting files, changing config to enable Windows 7 installation and then installed it as Server Farm (then Complete) to avoid installing SQL Express. Created a separate SPF_CONFIG local user with Logon on as a service right. Opened SPF Management Shell and run New-SPConfigurationDatabase so I am able to use a non-domain username (SPF_CONFIG that I created in the previous step) But all I get is this: The outcome after this error is: Database Sharepoint2010Config is created User SPF_CONFIG is added to SQL Server and attached to this newly created database as dbowner and checking SQL server security logins this user has following rights: dbcreator securityadmin public

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• Small web-framework like Sinatra, Ramaze etc in .NET

  - by Christian W

  Are there any similar frameworks like Sinatra, Ramaze etc in .NET? I'm in theory after a framework that let's me create an entire webapp with just one classfile (conceptually) like Sinatra. I'm going to use it for something work-internal, where ASP.NET MVC is too "big" (and I get confused by it's usage) and I have WebForms up to my ears right now (doing a big webforms based project, currently hating it ;) ) Any suggestions? Oh, and I need to be able to host it in IIS. I would go for IronRuby with Sinatra, but I can't find a step-by-step tut for setting it up in IIS ;)

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• shell script output in html + email that html

  - by Kimi

  Using Solaris I have a monitoring script that uses other scripts as plugins. Theses pugins are also scripts which work in difffernt ways like: 1. Sending an alert while high memory uilization 2. High Cpu usage 3. Full disk Space 4. chekcking the core file dump Now all this is dispalyed on my terminal and I want to put them in a HTML file/format and send it as a body of the mail not as attachment. Thanks .

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• High PageIOLatch_SH Waits with High Drive Idle times

  - by Marty Trenouth

  We are experiencing high volume of PageIOLatch_SH waits on our database (row counts in the Billions). However it seems that our drive Idle time Percentage hovers around 50-60 percent. CPU usage is nill. The Database Tuning Advisor gives no suggestions for optimization. The query plan (actual) from the single stored procedure used on the database puts the majority of the expense on index seek (yeah I know these should be optimial) operations. Anyone have suggestions of how to increase throughput?

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• What are the real-world benefits of declarative-UI languages such as XAML and QML?

  - by Stu Mackellar

  I'm currently evaluating QtQuick (Qt User Interface Creation Kit) which will be released as part of Qt 4.7. QML is the JavaScript-based declarative language behind QtQuick. It seems to be a very powerful concept, but I'm wondering if anybody that's made extensive use of other, more mature declarative-UI languages like XAML in WPF or Silverlight can give any insight into the real-world benefits that can be gained from this style of programming. Various advantages are often cited: Speed of development Forces separation between presentation and logic Better integration between coders and designers UI changes don't require re-compilation Also, are there any downsides? A few potential areas of concern spring to mind: Execution speed Memory usage Added complexity Are there any other considerations that should be taken into account?

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• pb with callback in the python optparse module

  - by PierrOz

  Hi Guys, I'm playing with Python 2.6 and its optparse module. I would like to convert one of my arguments to a datetime through a callback but it fails. Here is the code: def parsedate(option, opt_str, value, parser): option.date = datetime.strptime(value, "%Y/%m/%d") def parse_options(args): parser = OptionParser(usage="%prog -l LOGFOLDER [-e]", version="%prog 1.0") parser.add_option("-d", "--date", action="callback", callback="parsedate", dest="date") global options (options, args) = parser.parse_args(args) print option.date.strftime() if __name__ == "__main__": parse_options(sys.argv[1:]) I get an error File: optparse.py in _check_callback "callback not callable". I guess I'm doing something wrong in the way I define my callback but what ? and why ? Can anyone help ?

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• using addListener with WordPress audio player

  - by Jacob

  Hi, I'm trying to add a listener for the stop event in the word press audio player but usage seems to be undocumented. I'm hoping someone who knows a little flash can look at the code and tell me how it works: In the code at http://tools.assembla.com/1pixelout/browser/audio-player/trunk/source/classes/Application.as I see a snippet with this: ExternalInterface.call("AudioPlayer.onStop", _options.playerID); I was hoping that would let me capture the event in javascript with ("player" is the ID of my player) AudioPlayer.addListener("player", "AudioPlayer.onStop", function() { alert('stopped'); }); But my javascript function never seems to get called

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• UIWebView memory management

  - by wolfrevo

  Hello, I have a problem with memory management. I am developing an application that makes heavy use of UIWebView. This app generates dynamically lots of UIWebViews while loading content from my server. Some of these UIWebViews are quite large and have a lot of pictures. If I use instruments to detect leaks, I do not detect any. However, lots of objects are allocated and I suspect that has to do with the UIWebViews. When the webviews release because no longer needed, it appears that not all memory is released. I mean, after a request to my server the app creates an UITableView and many webviews (instruments say about 8Mb). When user tap back, all of them are released but memory usage only decrements about 2-3 Mb, and after 5-10 minutes using the app it crashes. Am I missing something? Anyone know what could be happening? Thank you!

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• Minix3 on Vmware

  - by mohit

  Hi, I install minix3 on vmware using installation CD i make using .iso image which is available @minix3 I make 2GB Harddisk, 512MB RAM on VMware, and installed step-by-step. It got installed and working fine. But i wana install 'packman' which is X window system. I'm not able to install it. It asks for installation CD, its still there and its detected also, but i couldn't proceed. Have any1 tried installing 'packman' i.e X window system on minix3. Please guide me. :)

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