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• Mixing stored procedures and ORM

  - by Jason

  The company I work for develops a large application which is almost entirely based on stored procedures. We use classic ASP and SQL Server and the major part of the business logic is contained inside those stored procedures. For example, (I know, this is bad...) a single stored procedure can be used for different purposes (insert, update, delete, make some calculations, ...). Most of the time, a stored procedure is used for operations on related tables, but this is not always the case. We are planning to move to ASP.NET in a near future. I have read a lot of posts on StackOverflow recommending that I move the business logic outside the database. The thing is, I have tried to convince the people who takes the decisions at our company and there is nothing I can do to change their mind. Since I want to be able to use the advantages of object-oriented programming, I want to map the tables to actual classes. So far, my solution is to use an ORM (Entity Framework 4 or nHibernate) to avoid mapping the objects manually (mostly to retrieve the data) and use some kind of Data Access Layer to call the existing stored procedures (for saving). I want your advice on this. Do you think it is a good solution? Any ideas?

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• Theme-aware XAML resources in a WP7 project

  - by SandRock

  I'm making a Windows Phone 7 application and I'm a bit confused with dark/light themes. With a panorama, you very often set a background image. The issue is it's very hard to make a picture which is right for both dark and light themes. How are we supposed to proceed? Is there a way to force a dark/light theme for a panorama? This will avoid making theme-specific panorama background pictures. Then how do I do? I found xaml files in C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.0\Design. If this is a right way to proceed, how can I import them for my panorama? Or if there's no way (or if it's wrong) to force a dark/light theme: how to write conditional XAML to set correct resources? Now I have the following XAML which is fine with the dark theme: <ImageBrush x:Key="PageBackground" ImageSource="Resources/PageBackground.png" Stretch="None" /> <ImageBrush x:Key="PanoramaBackground" ImageSource="Resources/PanoramaBackground.png" Stretch="None" /> But when I use a light theme, black controls and black texts are hard to read with my dark background pictures. So I made different pictures that I can use this way: <ImageBrush x:Key="PageBackground" ImageSource="Resources/PageBackgroundLight.png" Stretch="None" /> <ImageBrush x:Key="PanoramaBackground" ImageSource="Resources/PanoramaBackgroundLight.png" Stretch="None" /> Now my issue is to make XAML conditionnal to declare the right thing depending on the current theme. I found no relevant way on the Internet. I would prefer not to use code or code-behind for that because I believe XAML is able to do this (I just don't know how).

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• Array indexOf implentation for Internet Explorer

  - by Daemon

  There are plenty of solutions on how to get the indexOf implementation into the Array prototype so that it works under Internet Explorer, however I've stumbled upon an issue that doesn't seem to be addressed anywhere I've looked so far. Using the pretty well agreed upon implementation at MDC, I have the following code that's being problematic now: // indexOf support for IE (from MDC) if (!Array.prototype.indexOf) { Array.prototype.indexOf = function(elt /*, from*/) { var len = this.length >>> 0; var from = Number(arguments[1]) || 0; from = (from < 0) ? Math.ceil(from) : Math.floor(from); if (from < 0) from += len; for (; from < len; from++) { if (from in this && this[from] === elt) return from; } return -1; }; } var i = [1,2,3,4]; for (j in i) { alert(i[j]); } I am expecting to receive 4 alerts, each one containing one of the elements of the array. In Firefox and Chrome, that's exactly what I see, however in IE8 I get an additional alert containing the indexOf function code. What can be done to avoid this?

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• Send email from webpage without postback/refresh

  - by jb

  Hi all. Long time reader, first time writer. Quick query i hope someone can help me with. I have a webpage (php, javascript) which has a small contact form for a user to fill in and email us. Not a problem in itself, i have a working form already. Nothing noteworthy, just a form posting to a php page which sends an email. <form id="myform" name="myform" method="post" action="Mailer.php"> So user fills in form, hits submit and the page changes to mailer.php and they find their way back to where they were. What I want instead is for the to stay on the same page when submit is pushed. The form div to update itself to just say 'message sent' or something. I just want to avoid a full page refresh. Much like how on say facebook, commenting on a status only updates that div. Hope that is phrased clearly enough. Cheers all,

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• Adding new elements into DOM using JavaScript (appendChild)

  - by KatieK

  I sometimes need to add elements (such as a new link and image) to an existing HTML page, but I only have access to a small portion of the page far from where I need to insert elements. I want to use DOM based JavaScript techniques, and I must avoid using document.write(). Thus far, I've been using something like this: // Create new image element var newImg = document.createElement("img"); newImg.src = "images/button.jpg"; newImg.height = "50"; newImg.width = "150"; newImg.alt = "Click Me"; // Create new link element var newLink = document.createElement("a"); newLink.href = "/dir/signup.html"; // Append new image into new link newLink.appendChild(newImg); // Append new link (with image) into its destination on the page document.getElementById("newLinkDestination").appendChild(newLink); Is there a more efficient way that I could use to accomplish the same thing? It all seems necessary, but I'd like to know if there's a better way I could be doing this. Thanks!

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• Why are my bound parameters all identical (using Linq)?

  - by Scott Stafford

  When I run this snippet of code: string[] words = new string[] { "foo", "bar" }; var results = from row in Assets select row; foreach (string word in words) { results = results.Where(row => row.Name.Contains(word)); } I get this SQL: -- Region Parameters DECLARE @p0 VarChar(5) = '%bar%' DECLARE @p1 VarChar(5) = '%bar%' -- EndRegion SELECT ... FROM [Assets] AS [t0] WHERE ([t0].[Name] LIKE @p0) AND ([t0].[Name] LIKE @p1) Note that @p0 and @p1 are both bar, when I wanted them to be foo and bar. I guess Linq is somehow binding a reference to the variable word rather than a reference to the string currently referenced by word? What is the best way to avoid this problem? (Also, if you have any suggestions for a better title for this question, please put it in the comments.) Note that I tried this with regular Linq also, with the same results (you can paste this right into Linqpad): string[] words = new string[] { "f", "a" }; string[] dictionary = new string[] { "foo", "bar", "jack", "splat" }; var results = from row in dictionary select row; foreach (string word in words) { results = results.Where(row => row.Contains(word)); } results.Dump(); Dumps: bar jack splat

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• Temporarily disable vim plugin without relaunching

  - by simont

  I'm using c-support in Vim. One of it's features is the automatic comment expansion. When I'm pasting code into Vim from an external editor, the comments are expanded (which gives me double-comments and messes up the paste - see below for example). I'd like to be able to disable the plugin, paste, then re-enable it, without relaunching Vim. I'm not sure if this is possible. The SO questions here, here and here all describe methods to disable plugins, but they all require me to close Vim, mess with my .vimrc or similar, and relaunch; if I have to close Vim, I might as well cat file1 >> myfile; vim myfile, then shift the lines internally, which will be just as quick. Is it possible to disable a plugin while running vim without relaunching, preferably in a way which allows me to map a hot-key toggle-plugin (so re-sourcing ~/.vimrc is alright; that's mappable to a hotkey [I imagine, haven't tried it yet])? Messed up comments: /* * * Authors: * * A Name * * * * Copyright: * * A Name, 2012 * */ EDIT: It turns out you can :set paste, :set nopaste (which, to quote :help paste, will "avoid unexpected effects [while pasting]". (See the comments). However, I'm still curious whether you can disable/enable a plugin as per the original question, so I shall leave the question open.

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• How to terminate a request in JSP (not the "return;")

  - by Genom

  I am programming a website with JSP. There are pages where user must be logged in to see it. If they are not logged in, they should see a login form. I have seen in a php code that you can make a .jsp page (single file), which checkes, whether the user is logged in or not. If not it will show the login form. If the user is logged in, nothing will be done. So in order to do that I use this structure in my JSPs: Headers, menus, etc. etc... normal stuff which would be shown such as body, footer to a logged in user. This structure is very easy to apply to all webpages. So I don't have to apply checking algorithm to each webpage! I can simply add this "" and the page is secure! So my problem is that if the user is not logged in, then only the log in form should be shown and the footer. So code should bypass the body. Therefore structured my checklogin.jsp so: If user is not logged in show the login form and footer and terminate request. The problem is that I don't know how to terminate the request... If I use "return;" then only the checklogin.jsp stops but server continues to process parent page! Therefore page has 2 footers! (1 from parent page and 1 from checklogin.jsp). How can I avoid this? (There is exit(); in php for this by the way!) Thanks for any suggestions!

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• Is it possible to anti alias using Copy swap effect?

  - by Nor

  I'm developing an application in VB.Net using Managed DirectX that runs in windowed mode and renders onto a picture box that is smaller than the form. Whenever I resize the form, the back buffer is streched to fit the picture box. This is not what I would like. The backbuffer size is the same as screen size, however, I only want to render a part of the back buffer, whose size is controlled by the size of the picture box into which I'm rendering. Resetting the device with new presentation parameters is something I would like to avoid. I'm aware that I can use an overload of Device.Present if I set the swap effect to copy, but this doesn't allow me to use Multi Sample Anti Alias (which requires the Discard swap effect). It seems to me that the overload Device.Present is not usable with any other swap effect than copy, and throws an exception. An other alternative I considered is the PresentFlags.DeviceClip, however it seems that it works only for Windows XP. I'm using Windows 7 and it doesn't seem to be doing anything. So, is it even possible that I use anti-aliasing in this situation?

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• Linear Interpolation. How to implement this algorithm in C ? (Python version is given)

  - by psihodelia

  There exists one very good linear interpolation method. It performs linear interpolation requiring at most one multiply per output sample. I found its description in a third edition of Understanding DSP by Lyons. This method involves a special hold buffer. Given a number of samples to be inserted between any two input samples, it produces output points using linear interpolation. Here, I have rewritten this algorithm using Python: temp1, temp2 = 0, 0 iL = 1.0 / L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 *iL) where x contains input samples, L is a number of points to be inserted, y will contain output samples. My question is how to implement such algorithm in ANSI C in a most effective way, e.g. is it possible to avoid the second loop? NOTE: presented Python code is just to understand how this algorithm works. UPDATE: here is an example how it works in Python: x=[] y=[] hold=[] num_points=20 points_inbetween = 2 temp1,temp2=0,0 for i in range(num_points): x.append( sin(i*2.0*pi * 0.1) ) L = points_inbetween iL = 1.0/L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 * iL) Let's say x=[.... 10, 20, 30 ....]. Then, if L=1, it will produce [... 10, 15, 20, 25, 30 ...]

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• howto catch jQuery for multiple links but not all

  - by user247245

  I'm trying to dig into jQuery but would like some feedback on how to do things the best way, I have a list with items, which each contains a hidden div that should show upon click on it's parent, list div:ed item1 with link hidden div div:ed item2 with link hidden div .. My current solution is to trace the calling link by it's id and then reusing that ID for showing the correct hidden one: $(document).ready(function() { //jQ should only trigger on links with id="cmLinkINT" $("a").click(function() { //see if it's a comment request. var s = $(this).attr("id"); if (s.indexOf('cmLink') != -1) { //ok, it was a 'show'-link, get the id.. var j = s.substring(6); //ok, now I have the id i want to show (detailsINT) return false; } }); }); What's not clear to me is the best approach, Should I use id for requesting a or trace the id of the parent div. How to avoid that the code triggers on any link? Class? Thankful for any feedback, regards //t

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• How to enforce that HTTP client uses conditional requests for updates?

  - by Day

  In a (proper RMM level 3) RESTful HTTP API, I want to enforce the fact that clients should make conditional requests when updating resources, in order to avoid the lost update problem. What would be an appropriate response to return to clients that incorrectly attempt unconditional PUT requests? I note that the (abandoned?) mod_atom returns a 405 Method Not Allowed with an Allow header set to GET, HEAD (view source) when an unconditional update is attempted. This seems slightly misleading - to me this implies that PUT is never a valid method to attempt on the resource. Perhaps the response just needs to have an entity body explaining that If-Match or If-Unmodified-Since must be used to make the PUT request conditional in which case it would be allowed? Or perhaps a 400 Bad Request with a suitable explanation in the entity body would be a better solution? But again, this doesn't feel quite right because it's using a 400 response for a violation of application specific semantics when RFC 2616 says (my emphasis): The request could not be understood by the server due to malformed syntax. But than again, I think that using 400 Bad Request for application specific semantics is becoming a widely accepted pragmatic solution (citation needed!), and I'm just being overly pedantic.

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• close other infowindows nicely.

  - by raklos

  Im currently doing this to create markers for my google map. function createMarker(posn, title, html) { var marker = new google.maps.Marker({ position: posn, title: title, draggable: false }); marker['infowindow'] = new google.maps.InfoWindow({ content: html }); infoWindows.push(marker['infowindow']); google.maps.event.addListener(marker, "click", function () { for (i = 0; i < infoWindows.length; i++) { infoWindows[i].close(); } this['infowindow'].open(map, this); }); return marker; } im not happy with the for loop, for closing the markers, i know something similar to this can be done by using one refernce: if (infowindow) infowindow.close(); the reason I am using code like above is because i am doing something like markers[myPoint]['infowindow'].open(map, markers[myPoint]); else where, (myPoint is a number). how can i avoid this for loop to close open infowindows and do it the nice way?

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• How to retrieve content via .load() or $.get() with this line

  - by Sin

  hello :) I posted a question a day or two ago about how to retrieve php via ajax method in this modal I was using. I kinda found out the right way to go about it, but there's still something I'm not doing right (obviously lol) Here's the section thats giving me the issues: jQuery('div that holds content').fadeIn(200).css({ 'width': Number( popWidth ) }); $('').load('/something/somewhere/this #content'); So, im using safari, and a local server (mamp), when I check activity in my browser, it shows that it is loading the content with every click, AND the pop up pops up, but no content. When I simply retrieve content via hidden div, ofcourse, i get it. This is what I'm trying to avoid. right now I have that div in my footer stashed as hidden. I'd rather just make a call when its needed, instead of loading it every single time a page is accessed. you can go here to see the whole script i posted in my last question: How to use ajax to show php in a modal pop up Anyone have any idea? I read that .load() has the ability to grab specific content from a request, but im not sure the major difference between that and $.get() I've tried both, and I get the same results. Im using wordpress, and wordpress's ajax requests run smooth as ever, so I know its not a local problem, i'ts my coding lol Ok....Im done typing :)

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• Web page for IPhone - Large fonts instead of scrolling?

  - by chris_l

  I'm planning the layout of my web page, which should also be usable on the IPhone. I don't really have much experience with the IPhone yet - I just installed the IPhone Simulator on my Mac. The page's contents are flexible, so I think it would be better to use this flexibility to avoid that the user has to scroll around the entire page. Especially I have A header and a sidebar that will be used all the time to perform several actions. A main content area with a number of elements (e.g. images). The UI would stay usable pretty well, if the number of elements shown at one time is reduced for a small screen (e.g. by JavaScript). It would also be okay to make the main content area scrollable (as opposed to the entire page). The problem: If I simply display the page on the IPhone, it uses an extremely small font size, so that users must zoom in first, and then scroll around - so that they can't see the header and sidebar all the time. What's the best way to deal with this situation? Just leave it this way (very small fonts), because users expect that behaviour on the IPhone? Increase the font size (by specifying it in em or px or with xx-large, or what would be the best way?), if I detect - somehow - that it's being displayed on the IPhone. Or is there some way to restrict the viewport size to the screen size, and make it zoom in automatically? I think that would be the easiest solution in my case. Or ...?

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• Caching vector addition over changing collections

  - by DRMacIver

  I have the following setup: I have a largish number of uuids (currently about 10k but expected to grow unboundedly - they're user IDs) and a function f : id - sparse vector with 32-bit integer values (no need to worry about precision). The function is reasonably expensive (not outrageously so, but probably on the order of a few 100ms for a given id). The dimension of the sparse vectors should be assumed to be infinite, as new dimensions can appear over time, but in practice is unlikely to ever exceed about 20k (and individual results of f are unlikely to have more than a few hundred non-zero values). I want to support the following operations efficiently: add a new ID to the collection invalidate an existing ID retrieve sum f(id) in O(changes since last retrieval) i.e. I want to cache the sum of the vectors in a way that's reasonable to do incrementally. One option would be to support a remove ID operation and treat invalidation as a remove followed by an add. The problem with this is that it requires us to keep track of all the old values of f, which is expensive in space. I potentially need to use many instances of this sort of cached structure, so I would like to avoid that. The likely usage pattern is that new IDs are added at a fairly continuous rate and are frequently invalidated at first. Ids which have been invalidated recently are much more likely to be invalidated again than ones which have remained valid for a long time, but in principle an old Id can still be invalidated. Ideally I don't want to do this in memory (or at least I want a way that lets me save the result to disk efficiently), so an idea which lets me piggyback off an existing DB implementation of some sort would be especially appreciated.

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• finding long repeated substrings in a massive string

  - by Will

  I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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• How can I "reset" styles for a given HTML element?

  - by Sambo

  I am working on an embeddable javascript which inserts HTML elements onto unknown pages. I have no control of the stylesheets of the pages I'll be inserting HTML into. The problem is that the HTML I insert will mistakenly stylized by the page, and I want to prevent that. What's the least verbose and/or resource intensive to go about ensuring the elements I insert are exactly as I'd like them to be? Is there an easy way to clear all styling for a given HTML element and children? In firebug, for instance, you can remove all styling. I feel like there must, and the very least should, be a native way to exempt certain HTML elements from stylesheet rules? Example: var myHTML = $("<div>my html in here</div>"); myHTML.resetAllStyles(); //<--- what would this function do? myHTML.appendTo("body"); I really want to avoid explicitly stating the attributes I want for each element I insert... PS: I have a lot of experience with JS and CSS, so you can assume that I'll understand pretty much anything you're going to tell me.

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• Performance when querying a View

  - by Nate Bross

  I'm wondering if this is a bad practice or if in general this is the correct approach. Lets say that I've created a view that combines a few attributes from a few tables. My question, what do I need to do so I can query against this view as if it were a table without worrying about performance? All attributes in the original tables are indexed, my concern is that the result view will have hundreds of thousands of records, which I will want to narrow down quite a bit based on user input. What I'd like to avoid, is having multiple versions of the code that generates this view floating around with a few extra "where" conditions to facilitate the user input filtering. For example, assume my view has this header VIEW(Name, Type, DateEntered) this may have 100,000+ rows (possibly millions). I'd like to be able to make this view in SQL Server, and then in my application write querlies like this: SELECT Name, Type, DateEntered FROM MyView WHERE DateEntered BETWEEN @date1 and @date2; Basically, I am denormalizing my data for a series of reports that need to be run, and I'd like to centralize where I pull the data from, maybe I'm not looking at this problem from the right angle though, so I'm open to alternative ways to attack this.

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• Modeling Buyers & Sellers in a Rails Ecommerce App

  - by MikeH

  I'm building a Rails app that has Etsy.com style functionality. In other words, it's like a mall. There are many buyers and many sellers. I'm torn about how to model the sellers. Key facts: There won't be many sellers. Perhaps less than 20 sellers in total. There will be many buyers. Hopefully many thousands :) I already have a standard user model in place with account creation and roles. I've created a 'role' of 'seller', which the admin will manually apply to the proper users. Since we'll have very few sellers, this is not an issue. I'm considering two approaches: (1) Create a 'store' model, which will contain all the relevant store information. Products would :belong_to :store, rather than belonging to the seller. The relationship between the user and store models would be: user :has_one store. My main problem with this is that I've always found has_one associations to be a little funky, and I usually try to avoid them. The app is fairly complex, and I'm worried about running into a cascade of problems connected to the has_one association as I get further along into development. (2) Simply include the relevant 'store' information as part of the user model. But in this case, the store-related db columns would only apply to a very small percentage of users since very few users will also be sellers. I'm not sure if this is a valid concern or not. It's very possible that I'm thinking about this incorrectly. I appreciate any thoughts. Thanks.

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• Consecutive absences in MySQL

  - by pepersview

  Hi, I have 2 tables in my db: students and absences. In students: id_student, s_name; and in absences: id_student, date, day(the day of the week as number-it's not so important); I would like to get the students that were absent for more than 2 days consecutive and the dates. At the moment I have the next query: /*To control when the days are in the same week*/ SELECT id_student, date, dayname(date),date_add(date, INTERVAL 1 DAY) AS a, dayname(date_add(date, INTERVAL 1 DAY)) AS an, date_add(date, INTERVAL 2 DAY) AS b, dayname(date_add(date, INTERVAL 2 DAY)) AS bn FROM absences AS a WHERE id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date, INTERVAL 1 DAY) ) AND id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date,INTERVAL 2 DAY) ) UNION /*To control when the days jump to the next week*/ SELECT id_student, date, dayname(date),date_add(date, INTERVAL 3 DAY) AS a, dayname(date_add(date, INTERVAL 3 DAY)) AS an, date_add(date, INTERVAL 4 DAY) AS b, dayname(date_add(date, INTERVAL 4 DAY)) AS bn FROM absences AS a WHERE id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date, INTERVAL 3 DAY) ) AND id_student IN (SELECT id_student FROM absences WHERE id_student = a.id_student AND date = date_add(a.date,INTERVAL 4 DAY) ) /* To avoid the case (Monday-Thursday-Friday) to be consider as consecutive days*/ AND WEEKDAY(date) !=0 Thanks

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• a basic issue in implementing validations through properties ? Please guide me.

  - by haansi

  hello, thanks for your attention and time. I want to implement validations in settter of properties. Here is an issue where your expert help is required please. I have idea of how I will do validations before setting value. but not getting what to do if passed value is not correct. Just not setting is not a acceptable solution as I want to return an appropriate message to user (in a label in web form). My example code is: private int id; public int Id { get { return id; } set { bool result = IsNumber(value); if (result==false) { // What to do if passed data is not valid ? how to give a appropriate message to user that what is wrong ? } id = value; } } A thought was to use return but it is not allowed. Throwing error looks not good as generally we avoid thorwing custom errors. Please guide and help me. thanks in anticipation haansi

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• Is there a way to receive data as unsigned char over UDP on Qt?

  - by user269037

  I need to send floating point numbers using a UDP connection to a Qt application. Now in Qt the only function available is qint64 readDatagram ( char * data, qint64 maxSize, QHostAddress * address = 0, quint16 * port = 0 ) which accepts data in the form of signed character buffer. I can convert my float into a string and send it but it will obviously not be very efficient converting a 4 byte float into a much longer sized character buffer. I got hold of these 2 functions to convert a 4 byte float into an unsinged 32 bit integer to transfer over network which works fine for a simple C++ UDP program but for Qt I need to receive the data as unsigned char. Is it possible to avoid converting the floatinf point data into a string and then sending it? uint32_t htonf(float f) { uint32_t p; uint32_t sign; if (f < 0) { sign = 1; f = -f; } else { sign = 0; } p = ((((uint32_t)f)&0x7fff)<<16) | (sign<<31); // Whole part and sign. p |= (uint32_t)(((f - (int)f) * 65536.0f))&0xffff; // Fraction. return p; } float ntohf(uint32_t p) { float f = ((p>>16)&0x7fff); // Whole part. f += (p&0xffff) / 65536.0f; // Fraction. if (((p>>31)&0x1) == 0x1) { f = -f; } // Sign bit set. return f; }

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• Does the Java Memory Model (JSR-133) imply that entering a monitor flushes the CPU data cache(s)?

  - by Durandal

  There is something that bugs me with the Java memory model (if i even understand everything correctly). If there are two threads A and B, there are no guarantees that B will ever see a value written by A, unless both A and B synchronize on the same monitor. For any system architecture that guarantees cache coherency between threads, there is no problem. But if the architecture does not support cache coherency in hardware, this essentially means that whenever a thread enters a monitor, all memory changes made before must be commited to main memory, and the cache must be invalidated. And it needs to be the entire data cache, not just a few lines, since the monitor has no information which variables in memory it guards. But that would surely impact performance of any application that needs to synchronize frequently (especially things like job queues with short running jobs). So can Java work reasonably well on architectures without hardware cache-coherency? If not, why doesn't the memory model make stronger guarantees about visibility? Wouldn't it be more efficient if the language would require information what is guarded by a monitor? As i see it the memory model gives us the worst of both worlds, the absolute need to synchronize, even if cache coherency is guaranteed in hardware, and on the other hand bad performance on incoherent architectures (full cache flushes). So shouldn't it be more strict (require information what is guarded by a monitor) or more lose and restrict potential platforms to cache-coherent architectures? As it is now, it doesn't make too much sense to me. Can somebody clear up why this specific memory model was choosen? EDIT: My use of strict and lose was a bad choice in retrospect. I used "strict" for the case where less guarantees are made and "lose" for the opposite. To avoid confusion, its probably better to speak in terms of stronger or weaker guarantees.

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• Does using functional languages help against computing values repeatedly?

  - by sharptooth

  Consider a function f(x,y): f(x,0) = x*x; f(0,y) = y*(y + 1); f(x,y) = f(x,y-1) + f(x-1,y); If one tries to implement that recursively in some language like C++ he will encounter a problem. Suppose the function is first called with x = x0 and y = y0. Then for any pair (x,y) where 0 <= x < x0 and 0 <= y < y0 the intermediate values will be computed multiple times - recursive calls will form a huge tree in which multiple leaves will in fact contain the same pairs (x,y). For pairs (x,y) where x and y are both close to 0 values will be computed numerous times. For instance, I tested a similar function implemented in C++ - for x=20 and y=20 its computation takes about 4 hours (yes, four Earth hours!). Obviously the implementation can be rewritten in such way that repeated computation doesn't occur - either iteratively or with a cache table. The question is: will functional languages perform any better and avoid repeated computations when implementing a function like above recursively?

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