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  • 'is instanceof' Interface bad design

    - by peterRit
    Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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  • Scalable (half-million files) version control system

    - by hashable
    We use SVN for our source-code revision control and are experimenting using it for non-source-code files. We are working with a large set (300-500k) of short (1-4kB) text files that will be updated on a regular basis and need to version control it. We tried using SVN in flat-file mode and it is struggling to handle the first commit (500k files checked in) taking about 36 hours. On a daily basis, we need the system to be able to handle 10k modified files per commit transaction in a short time (<5 min). My questions: Is SVN the right solution for my purpose. The initial speed seems too slow for practical use. If Yes, is there a particular svn server implementation that is fast? (We are currently using the gnu/linux default svn server and command line client.) If No, what are the best f/oss/commercial alternatives Thanks

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  • Check if a string substitution rule will ever generate another string.

    - by Mgccl
    Given two strings S and T of same length. Given a set of replacement rules, that find substring A in S and replace it with string B. A and B have the same length. Is there a sequence of rule application, such that it make string S into string T? I believe there is no better way to answer this than try every single rule in every single state. Which would be exponential time. But I don't know if there are better solutions to it.

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  • Build Process failed with maven package

    - by vijay.shad
    Hi I am working on a maven project to build a simple utility api. The same source code when build on my office win XP machine, was successful. Now i am at home and working with same source code on CentOS machine. Here the build process failed strangely. The error it reports is ideally in my points should we warning message. As shown below. [ERROR] com.vsd.Provider:[12,240] The import java.util.Set is never used Can you please give me some idea, where can I look into?

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  • How can I compile an autotools project with statically linked dependancies?

    - by flyx
    There's an open source library I want to use. As I want to spread my software as binary package, I do not want the library to have dependancies on other libraries, so I need to link the dependancies statically. Now as the library is open source and there are no binaries provided, I compile it myself. The library uses autotools, and I didn't find any useful documentation on how to link dependancies statically. What I did try is to call the configure script with --enable-static, but this apparently only tells configure to compile a static version of the library - but what I need is a dynamic library that includes all the libraries it depends on. So, I need a way to either tell configure to link against dependancies statically, or a way to post-process the built library to include all dependancies. Can anyone tell me how to do this? Oh, and if it matters: I'm on 64bit Snow Leopard.

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  • In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

    - by ali01
    My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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  • help me understand cuda

    - by scatman
    i am having some troubles understanding threads in NVIDIA gpu architecture with cuda. please could anybody clarify these info: an 8800 gpu has 16 SMs with 8 SPs each. so we have 128 SPs. i was viewing stanford's video presentation and it was saying that every SP is capable of running 96 threads cuncurrently. does this mean that it (SP) can run 96/32=3 warps concurrently? moreover, since every SP can run 96 threads and we have 8 SPs in every SM. does this mean that every SM can run 96*8=768 threads concurrently?? but if every SM can run a single Block at a time, and the maximum number of threads in a block is 512, so what is the purpose of running 768 threads concurrently and have a max of 512 threads? a more general question is:how are blocks,threads,and warps distributed to SMs and SPs? i read that every SM gets a single block to execute at a time and threads in a block is divided into warps (32 threads), and SPs execute warps.

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  • CRC32 calculations for png chunk doesn't match the real one

    - by user2507197
    I'm attempting to mimic the function used for creating CRC's in PNG files, I'm using the autodin II polynomial and the source code from: http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/libkern/crc32.c My tests have all been for the IHDR chunk, so my parameters have been: crc - 0xffffffff and 0 (both have been suggested) buff - the address of the IHDR Chunk's type. length - the IHDR Chunk's length + 4 (the length of the chunk's data + the length of the type) I printed the calculated CRC in binary, which I compared to the actual CRC of the chunk. I can see no similarities (little-big endian, reversed bits, XOR'd, etc). This is the data for the IHDR chunk (hexadecimal format): length(big endian): d0 00 00 00 (13) type: 49 48 44 52 data: 00 00 01 77 00 00 01 68 08 06 00 00 00 existing CRC: b0 bb 40 ac If anyone can tell me why my calculations are off, or give me a CRC32 function that will work I would greatly appreciate it. Thank-you!

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  • Is a many-to-many relationship with extra fields the right tool for my job?

    - by whichhand
    Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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  • Is there simple way to play an rtp video/audio stream in WPF?

    - by Robin
    I need to create a WPF control that will play an rtp stream with the requirement that the latency needs to be as low as possible. I've looked at the following two projects: http://vlcdotnet.codeplex.com/ http://wpfmediakit.codeplex.com/ As far as I know, I can't use VLC because we're shipping a commercial application with a more restrictive license than GPL (i.e. we can't ship our source). Wpf media kit is nice, but I can't seem to find a good/free rtp directshow source filter and I wanted to ask if there is a simpler solution out there that I'm missing before I jump into writing my own. Any ideas?

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  • ReaderWriterLockSlim question.

    - by Kamarey
    There are lots written about the ReaderWriterLockSlim class which allows multiple read and a single write. All of these (at least that I had found) tell how to use it without much explanation why and how it works. The standard code sample is: lock.EnterUpgradeableReadLock(); try { if (test if write is required) { lock.EnterWriteLock(); try { change the resourse here. } finally { lock.ExitWriteLock(); } } } finally { lock.ExitUpgradeableReadLock(); } The question is: if upgradeable lock permits only a single thread to enter its section, why I should call EnterWriteLock method within? What will happen if I don't? Or what will happen if instead of EnterUpgradeableReadLock I will call EnterWriteLock and will write to a resource without using upgradeable lock at all?

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  • Maven : Is it possible to override the configuration of a plugin already defined for a profile in a parent POM

    - by Guillaume Cernier
    In a POM parent file of my project, I have such a profile defining some configurations useful for this project (so that I can't get rid of this parent POM) : <profile> <id>wls7</id> ... <build> <plugins> <!-- use java 1.4 --> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <fork>true</fork> <source>1.4</source> <target>1.4</target> <meminitial>128m</meminitial> <maxmem>1024m</maxmem> <executable>%${jdk14.executable}</executable> </configuration> </plugin> </plugins> </build> ... </profile> But in my project I just would like to override the configuration of the maven-compiler-plugin in order to use jdk5 instead of jdk4 for compiling test-classes. That's why I did this section in the POM of my project : <profiles> <profile> <id>wls7</id> <activation> <property> <name>jdk</name> <value>4</value> </property> </activation> <build> <directory>target-1.4</directory> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <executions> <execution> <id>my-testCompile</id> <phase>test-compile</phase> <goals> <goal>testCompile</goal> </goals> <configuration> <fork>true</fork> <executable>${jdk15.executable}</executable> <compilerVersion>1.5</compilerVersion> <source>1.5</source> <target>1.5</target> <verbose>true</verbose> </configuration> </execution> </executions> </plugin> </plugins> </build> </profile> ... </profiles> and it's not working ... I even tried to override the configuration in regular plugin sections of my POM (I mean, not for a specific profile but for my whole POM). What could be the problem ? To clarify some of my requirements : I don't want to get rid of the parent POM and the profile (wls7) defined inside it (since I need many and many properties, configurations, ...) and that is not the process in my company. A solution based on duplicating the parent POM and/or the profile defined inside it is not a good one. Since if the responsible of the parent POM change something, I would have to report it in mine. It's just an inheritance matter (extend or override a profile, a configuration from an upper-level POM) so I think it should be possible with maven2.

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  • how is a macro expanded in clojure?

    - by john wang
    In the book Programming Clojure(Stuart), when read how macros are expanded I got confused. user=> (defmacro chain ([x form] (list '. x form)) ([x form & more] (concat (list 'chain (list '. x form)) more))) #'user/chain The above macro can be expanded as: user=> (macroexpand '(chain a b c)) (. (. a b) c) But the following is only expanded to the first level: user=> (macroexpand '(and a b c)) (let* [and__3822__auto__ a] (if and__3822__auto__ (clojure.core/and b c) and__3822__auto__)) The and macro source: user=> (source and) (defmacro and([] true) ([x] x) ([x & next] `(let [and# ~x] (if and# (and ~@next) and#)))) Why is the chain macro expanded all the way but the and not ? Why is it not expanded to something like the following: user=> (macroexpand '(chain a b c d)) (. (chain a b c) d)

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  • JPQL: What kind of objects contains a result list when querying multiple columns?

    - by Bunkerbewohner
    Hello! I'm trying to do something which is easy as pie in PHP & Co: SELECT COUNT(x) as numItems, AVG(y) as average, ... FROM Z In PHP I would get a simple array like [{ numItems: 0, average: 0 }] which I could use like this: echo "Number of Items: " . $result[0]['numItems']; Usually in JPQL you only query single objects or single columns and get Lists types, for example List or List. But what do you get, when querying multiple columns?

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  • How do i create a nice looking image fadein onload with mootools?

    - by woobione
    Hi everyone! I´m creating a website for a photographer who would like a fine fadein on his images. I have excluded flash as a solution and would like to use those fine-looking effects of mootools fx. But the problem is that I'm really lousy when it comes to javascript. So if anyone could give me an easy solution for fading in one single image onload and when the image is loaded I would be really happy. I know there is a lot of different people out there who have this. But the problem is that i don't know how the code works even if it is a complete solution. So most important. If anyone has got the time to explain what every single line of code does i would be more than grateful. Thanks!

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  • Firefox HTML5 video playback inconsistancy

    - by Daniel Redwood
    Hey all, I've got an HTML5 video on a page. When tested locally, Chrome, Safari, and Opera work beautifully. Firefox plays it, but doesn't loop as efficiently as the others. The real problem is when it's tested off a server. Firefox doesn't play the video, but recognizes there is one there. I was wondering if all that open ended three-different-ways syntax can be swung in Firefox's favor. Thanks! HTML: <video id="vid_home" width="780" height="520" autoplay="autoplay" loop="loop"> <source src="Video/fernando.ogv" type="video/ogg" /> <source src="Video/fernando.m4v" type="video/mp4" /> Your browser does not support this videos playback. </video>

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  • SVG via dynamic XML+XSL

    - by Daniel
    This is a bit of a vague notion which I have been running over in my head, and which I am very curious if there is an elegant method of solving. Perhaps it should be taken as a thought experiment. Imagine you have an XML schema with a corresponding XSL transform, which renders the XML as SVG in the browser. The XSL generates SVG with appropriate Javascript handlers that, ultimately, implement editing-like functionality such that properties of the objects or their locations on the SVG canvas can be edited by the user. For instance, an element can be dragged from one location to another. Now, this isn't particularly difficult - the drag/drop example is simply a matter of changing the (x,y) coordinates of the SVG object, or a resize operation would be a simple matter of changing its width or height. But is there an elegant way to have Javascript work on the DOM of the source XML document instead of the rendered SVG? Why, you ask? Well, imagine you have very complex XSL transforms, where the modification of one property results in complex changes to the SVG. You want to maintain simplicity in your Javascript code, but also a simple way to persist the modified XML back to the server. Some possibilities of how this may function: After modification of the source DOM, simply re-run the XSL transform and replace the original. Downside: brute force, potentially expensive operation. Create id/class naming conventions in the source and target XML/SVG so elements can be related back to each other, and do an XSL transform on only a subset of the new DOM. In other words, modify temporary DOM, apply XSL to it, remove changed elements from SVG, and insert the new one. Downside: May not be possible to apply XSL to temporary in-browser DOMs(?). Also, perhaps a bit convoluted or ugly to maintain. I think that it may be possible to come up with a framework that handles the second scenario, but the challenge would be making it lightweight and not heavily tied to the actual XML schema. Any ideas or other possibilities? Or is there maybe an existing method of doing this which I'm not aware of? UPDATE: To clarify, as I mentioned in a comment below, this aids in separating the draw code from the edit code. For a more concrete example of how this is useful, imagine an element which determines how it is drawn dependent on the value of a property of an adjacent element. It's better to condense that logic directly in the draw code instead of also duplicating it in the edit code.

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  • Modular HTML in Adobe AIR? Is It Possible?

    - by Greg Bulmash
    When I write HTML with a PHP backend, I usually have a single header file and a single footer file with some PHP variables in them. The base skeleton for every page calls the header, contains the body content, and then calls the footer. That way, if I want to make changes to the header sitewide, I change one file. I'm working on developing the UI in my first Adobe AIR app and I'm wondering if there's some way to include such files in an HTML based page template there. Obviously, with the file read/write abilities in AIR, I can write a Javascript routine to pull data from a header file, parse it, and inject it into a placeholder. It just seems like such a kludge. I'm thinking there's gotta be some simple way to import a block of HTML into a page without an iFrame or complex post-processor. Something like a PHP include statement or perhaps the old Server Side Includes. Any methods you guys can recommend?

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  • Android quotes within an sql query string

    - by miannelle
    I want to perform a query like the following: uvalue = EditText( some user value ); p_query = "select * from mytable where name_field = '" + uvalue + "'" ; mDb.rawQuery( p_query, null ); if the user enters a single quote in their input it crashes. If you change it to: p_query = "select * from mytable where name_field = \"" + uvalue + "\"" ; it crashes if the user enters a double quote in their input. and of course they could always enter both single and double quotes.

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  • How would you structure your entity model for storing arbitrary key/value data with different data t

    - by Nathan Ridley
    I keep coming across scenarios where it will be useful to store a set of arbitrary data in a table using a per-row key/value model, rather than a rigid column/field model. The problem is, I want to store the values with their correct data type rather than converting everything to a string. This means I have to choose either a single table with multiple nullable columns, one for each data type, or a set of value tables, one for each data type. I'm also unsure as to whether I should use full third normal form and separate the keys into a separate table, referencing them via a foreign key from the value table(s), or if it would be better to keep things simple and store the string keys in the value table(s) and accept the duplication of strings. Old/bad: This solution makes adding additional values a pain in a fluid environment because the table needs to be modified regularly. MyTable ============================ ID Key1 Key2 Key3 int int string date ---------------------------- 1 Value1 Value2 Value3 2 Value4 Value5 Value6 Single Table Solution This solution allows simplicity via a single table. The querying code still needs to check for nulls to determine which data type the field is storing. A check constraint is probably also required to ensure only one of the value fields contains non-nulll data. DataValues ============================================================= ID RecordID Key IntValue StringValue DateValue int int string int string date ------------------------------------------------------------- 1 1 Key1 Value1 NULL NULL 2 1 Key2 NULL Value2 NULL 3 1 Key3 NULL NULL Value3 4 2 Key1 Value4 NULL NULL 5 2 Key2 NULL Value5 NULL 6 2 Key3 NULL NULL Value6 Multiple-Table Solution This solution allows for more concise purposing of each table, though the code needs to know the data type in advance as it needs to query a different table for each data type. Indexing is probably simpler and more efficient because there are less columns that need indexing. IntegerValues =============================== ID RecordID Key Value int int string int ------------------------------- 1 1 Key1 Value1 2 2 Key1 Value4 StringValues =============================== ID RecordID Key Value int int string string ------------------------------- 1 1 Key2 Value2 2 2 Key2 Value5 DateValues =============================== ID RecordID Key Value int int string date ------------------------------- 1 1 Key3 Value3 2 2 Key3 Value6 How do you approach this problem? Which solution is better? Also, should the key column be separated into a separate table and referenced via a foreign key or be should it be kept in the value table and bulk updated if for some reason the key name changes?

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  • How do I create a multiple-table check constraint?

    - by Zack Peterson
    Please imagine this small database... Diagram Tables Volunteer Event Shift EventVolunteer ========= ===== ===== ============== Id Id Id EventId Name Name EventId VolunteerId Email Location VolunteerId Phone Day Description Comment Description Start End Associations Volunteers may sign up for multiple events. Events may be staffed by multiple volunteers. An event may have multiple shifts. A shift belongs to only a single event. A shift may be staffed by only a single volunteer. A volunteer may staff multiple shifts. Check Constraints Can I create a check constraint to enforce that no shift is staffed by a volunteer that's not signed up for that shift's event? Can I create a check constraint to enforce that two overlapping shifts are never staffed by the same volunteer?

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  • Microsoft Team System Equivalent stack.

    - by Nix
    I am looking for a free alternative to TS. What would be the best alternative stack(source control, bug tracking, project management/planning, wiki, automated builds (ci))? Keeping in mind that it would be nice if they all integrated well. For example, it would be nice to be able to link bugs to source control, and then be able to link to a project plan and then be able to automate building. I do not have issues with using Microsoft project to manage project planing. I know i would like to use these....: SVN TeamCity NUnit But i am struggling to find a good Wiki/Project Planning/Bug tracking, that would integrate well. Any questions let me know.

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