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• How to determine a text block of a file in one version come from which file in the previous version?

  - by Muhammad Asaduzzaman

  The problem is described below: Suppose I have a list of files in one version(say A,B,C,D). In the next version I have the following files(A,E,F,G). There are some similarities in their contents. The files in the later version comes from the previous version by file name renaming, content addition, deletion or partial modification or without any change( for example A is not changed). I take a block of text from a file(E, 2nd version) and check which files(in the 1st version) contain this text block. I found that B,C and D contain the text fragment. I want to determine from which file(B or c or d) this text block actually comes from.(I assume that E is a file whose name change in the second version). Since the contents may be changed, added or deleted in the later version, so in order to determine similarity I use LCS algorithm. But I cannot map the file with its previous version. I think one possible approach might be to use the location information of the match text blocks. But this heuristics not always work. Is there any research or algorithm exist to find so. Any direction will be helpful. Thanks in advance.

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• issue with vhdl structural coding

  - by user3699982

  The code below is a simple vhdl structural architecture, however, the concurrent assignment to the signal, comb1, is upsetting the simulation with the outputs (tb_lfsr_out) and comb1 becoming undefined. Please, please help, thank you, Louise. library IEEE; use IEEE.STD_LOGIC_1164.all; entity testbench is end testbench; architecture behavioural of testbench is CONSTANT clock_frequency : REAL := 1.0e9; CONSTANT clock_period : REAL := (1.0/clock_frequency)/2.0; signal tb_master_clk, comb1: STD_LOGIC := '0'; signal tb_lfsr_out : std_logic_vector(2 DOWNTO 0) := "111"; component dff port ( q: out STD_LOGIC; d, clk: in STD_LOGIC ); end component; begin -- Clock/Start Conversion Generator tb_master_clk <= (NOT tb_master_clk) AFTER (1 SEC * clock_period); comb1 <= tb_lfsr_out(0) xor tb_lfsr_out(2); dff6: dff port map (tb_lfsr_out(2), tb_lfsr_out(1), tb_master_clk); dff7: dff port map (tb_lfsr_out(1), tb_lfsr_out(0), tb_master_clk); dff8: dff port map (tb_lfsr_out(0), comb1, tb_master_clk); end behavioural;

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• Java: design for using many executors services and only few threads

  - by Guillaume

  I need to run in parallel multiple threads to perform some tests. My 'test engine' will have n tests to perform, each one doing k sub-tests. Each test result is stored for a later usage. So I have n*k processes that can be ran concurrently. I'm trying to figure how to use the java concurrent tools efficiently. Right now I have an executor service at test level and n executor service at sub test level. I create my list of Callables for the test level. Each test callable will then create another list of callables for the subtest level. When invoked a test callable will subsequently invoke all subtest callables test 1 subtest a1 subtest ...1 subtest k1 test n subtest a2 subtest ...2 subtest k2 call sequence: test manager create test 1 callable test1 callable create subtest a1 to k1 testn callable create subtest an to kn test manager invoke all test callables test1 callable invoke all subtest a1 to k1 testn callable invoke all subtest an to kn This is working fine, but I have a lot of new treads that are created. I can not share executor service since I need to call 'shutdown' on the executors. My idea to fix this problem is to provide the same fixed size thread pool to each executor service. Do you think it is a good design ? Do I miss something more appropriate/simple for doing this ?

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• PHP/MySQL time zone migration

  - by El Yobo

  I have an application that currently stores timestamps in MySQL DATETIME and TIMESTAMP values. However, the application needs to be able to accept data from users in multiple time zones and show the timestamps in the time zone of other users. As such, this is how I plan to amend the application; I would appreciate any suggestions to improve the approach. Database modifications All TIMESTAMPs will be converted to DATETIME values; this is to ensure consistency in approach and to avoid having MySQL try to do clever things and convert time zones (I want to keep the conversion in PHP, as it involves less modification to the application, and will be more portable when I eventually manage to escape from MySQL). All DATETIME values will be adjusted to convert them to UTC time (currently all in Australian EST) Query modifications All usage of NOW() to be replaced with UTC_TIMESTAMP() in queries, triggers, functions, etc. Application modifications The application must store the time zone and preferred date format (e.g. US vs the rest of the world) All timestamps will be converted according to the user settings before being displayed All input timestamps will be converted to UTC according to the user settings before being input Additional notes Converting formats will be done at the application level for several main reasons The approach to converting time zones varies from DB to DB, so handing it there will be non-portable (and I really hope to be migrating away from MySQL some time in the not-to-distant future). MySQL TIMESTAMPs have limited ranges to the permitted dates (~1970 to ~2038) MySQL TIMESTAMPs have other undesirable attributes, including bizarre auto-update behaviour (if not carefully disabled) and sensitivity to the server zone settings (and I suspect I might screw these up when I migrate to Amazon later in the year). Is there anything that I'm missing here, or does anyone have better suggestions for the approach?

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• How can I merge two Linq IEnumerable<T> queries without running them?

  - by makerofthings7

  How do I merge a List<T> of TPL-based tasks for later execution? public async IEnumerable<Task<string>> CreateTasks(){ /* stuff*/ } My assumption is .Concat() but that doesn't seem to work: void MainTestApp() // Full sample available upon request. { List<string> nothingList = new List<string>(); nothingList.Add("whatever"); cts = new CancellationTokenSource(); delayedExecution = from str in nothingList select AccessTheWebAsync("", cts.Token); delayedExecution2 = from str in nothingList select AccessTheWebAsync("1", cts.Token); delayedExecution = delayedExecution.Concat(delayedExecution2); } /// SNIP async Task AccessTheWebAsync(string nothing, CancellationToken ct) { // return a Task } I want to make sure that this won't spawn any task or evaluate anything. In fact, I suppose I'm asking "what logically executes an IQueryable to something that returns data"? Background Since I'm doing recursion and I don't want to execute this until the correct time, what is the correct way to merge the results if called multiple times? If it matters I'm thinking of running this command to launch all the tasks var AllRunningDataTasks = results.ToList(); followed by this code: while (AllRunningDataTasks.Count > 0) { // Identify the first task that completes. Task<TableResult> firstFinishedTask = await Task.WhenAny(AllRunningDataTasks); // ***Remove the selected task from the list so that you don't // process it more than once. AllRunningDataTasks.Remove(firstFinishedTask); // TODO: Await the completed task. var taskOfTableResult = await firstFinishedTask; // Todo: (doen't work) TrustState thisState = (TrustState)firstFinishedTask.AsyncState; // TODO: Update the concurrent dictionary with data // thisState.QueryStartPoint + thisState.ThingToSearchFor Interlocked.Decrement(ref thisState.RunningDirectQueries); Interlocked.Increment(ref thisState.CompletedDirectQueries); if (thisState.RunningDirectQueries == 0) { thisState.TimeCompleted = DateTime.UtcNow; } }

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• Is there any performance issue using Row_Number to implement table paging in Sql Server 2008?

  - by majkinetor

  I want to implement table paging using this method: SET @PageNum = 2; SET @PageSize = 10; WITH OrdersRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY OrderDate, OrderID) AS RowNum ,* FROM dbo.Orders ) SELECT * FROM OrdersRN WHERE RowNum BETWEEN (@PageNum - 1) * @PageSize + 1 AND @PageNum * @PageSize ORDER BY OrderDate ,OrderID; Is there anything I should be aware of ? Table has millions of records. Thx. EDIT: After using suggested MAXROWS method for some time (which works really really fast) I had to switch back to ROW_NUMBER method because of its greater flexibility. I am also very happy about its speed so far (I am working with View having more then 1M records with 10 columns). To use any kind of query I use following modification: PROCEDURE [dbo].[PageSelect] ( @Sql nvarchar(512), @OrderBy nvarchar(128) = 'Id', @PageNum int = 1, @PageSize int = 0 ) AS BEGIN SET NOCOUNT ON Declare @tsql as nvarchar(1024) Declare @i int, @j int if (@PageSize <= 0) OR (@PageSize > 10000) SET @PageSize = 10000 -- never return more then 10K records SET @i = (@PageNum - 1) * @PageSize + 1 SET @j = @PageNum * @PageSize SET @tsql = 'WITH MyTableOrViewRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY ' + @OrderBy + ') AS RowNum ,* FROM MyTableOrView WHERE ' + @Sql + ' ) SELECT * FROM MyTableOrViewRN WHERE RowNum BETWEEN ' + CAST(@i as varchar) + ' AND ' + cast(@j as varchar) exec(@tsql) END If you use this procedure make sure u prevented sql injection.

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• Standard term for a thread I/O reorder buffer?

  - by Crashworks

  I have a case where many threads all concurrently generate data that is ultimately written to one long, serial file. I need to somehow serialize these writes so that the file gets written in the right order. ie, I have an input queue of 2048 jobs j0..jn, each of which produces a chunk of data oi. The jobs run in parallel on, say, eight threads, but the output blocks have to appear in the file in the same order as the corresponding input blocks — the output file has to be in the order o0o1o2... The solution to this is pretty self evident: I need some kind of buffer that accumulates and writes the output blocks in the correct order, similar to a CPU reorder buffer in Tomasulo's algorithm, or to the way that TCP reassembles out-of-order packets before passing them to the application layer. Before I go code it, I'd like to do a quick literature search to see if there are any papers that have solved this problem in a particularly clever or efficient way, since I have severe realtime and memory constraints. I can't seem to find any papers describing this though; a Scholar search on every permutation of [threads, concurrent, reorder buffer, reassembly, io, serialize] hasn't yielded anything useful. I feel like I must just not be searching the right terms. Is there a common academic name or keyword for this kind of pattern that I can search on?

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• Concurrency problem with arrays (Java)

  - by Johannes

  For an algorithm I'm working on I tried to develop a blacklisting mechanism that can blacklist arrays in a specific way: If "1, 2, 3" is blacklisted "1, 2, 3, 4, 5" is also considered blacklisted. I'm quite happy with the solution I've come up with so far. But there seem to be some serious problems when I access a blacklist from multiple threads. The method "contains" (see code below) sometimes returns true, even if an array is not blacklisted. This problem does not occur if I only use one thread, so it most likely is a concurrency problem. I've tried adding some synchronization, but it didn't change anything. I also tried some slightly different implementations using java.util.concurrent classes. Any ideas on how to fix this? public class Blacklist { private static final int ARRAY_GROWTH = 10; private final Node root = new Node(); private static class Node{ private volatile Node[] childNodes = new Node[ARRAY_GROWTH]; private volatile boolean blacklisted = false; public void blacklist(){ this.blacklisted = true; this.childNodes = null; } } public void add(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return; else if(currentNode.childNodes.length <= edge) { currentNode.childNodes = Arrays.copyOf(currentNode.childNodes, edge + ARRAY_GROWTH); } if(currentNode.childNodes[edge] == null) { currentNode.childNodes[edge] = new Node(); } currentNode = currentNode.childNodes[edge]; } currentNode.blacklist(); } } public boolean contains(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return true; else if(currentNode.childNodes.length <= edge || currentNode.childNodes[edge] == null) return false; currentNode = currentNode.childNodes[edge]; } return currentNode.blacklisted; } } }

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• Preventing ActiveRecord save() on an instance

  - by Craig Walker

  I have an ActiveRecord model object Foo; it represents a standard database row. I want to be able to display modified versions of instances of this object. I'd like to reuse the class itself, as it already has all the hooks & aspects I'll need. (For example: I already have a view that displays the appropriate attributes). Basically I want to clone the model instance, modify some of its properties, and feed it back to the caller (view, test, etc). I do not want these attribute modifications getting back into the database. However, I do want to include the id attribute in the cloned version, as it makes dealing with the route-helpers much easier. Thus, I plan on calling ActiveRecord::Base.clone(), manually setting the ID of the cloned instance, and then making the appropriate attribute changes to the new instance. This has me worried though; one save() on the modified instance and my original data will get clobbered. So, I'm looking to lock down the new instance so that it won't hurt anything else. I'm already planning on calling freeze() (on the understanding that this prevents further modification to the object, though the documentation isn't terribly clear). However, I don't see any obvious way to prevent a save(). What would be the best approach to achieving this?

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• RequestBuilder timeouts and browser connection limits per domain.

  - by WesleyJohnson

  This is specifically about GWT's RequestBuilder, but should apply to general XHR as well. My company is having me build a near realtime chat application over HTTP. Yes, I do realize there are better ways to do chat aplications, but this is what they want. Eventually we want it working on the iPad/iPhone as well so flash is out, which rules out websockets and comet as well, I think? Anyway, I'm running into issues were I've set GWT's RequestBuilder timeout to 10 seconds and we get very random and sporadic timeouts. We've got error handling and emailing on the server side and never get any errors, which suggests the underlying XHR request that RequestBuilder is built on, never gets to the server and times out after 10 seconds. We're using these request to poll the server for new messages rather often and also for sending new messages to the server and also polling (less frequently) for other parts of application. What I'm afraid of is that we're running into the browsers limit on concurrent connections to the same domain (2 for IE by default?). Now my question is - If I construct a RequestBuilder and call it's send() method and the browser blocks it from sending until one of the 2 connections per domain is free, does the timeout still start while the request is being blocked or will it not start until the browser actually releases the underlying XHR? I hope that's clear, if not please let me know and I'll try to explain more.

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• hosting a high traffic facebook app (game)

  - by z3cko

  we are currently developing a high traffic facebook application. all the traffic will be within one month, where there are 500.000 to 1.000.000 expected users. after that month, the game is over and we have a winner - so the app will be archived. we are currently planning to develop the application with ruby on rails and searching for hosting options that can deal with the traffic. the problem is not so much the users, but the peak values: we will have around 500.000 requests coming daily within a short timeframe (lets say within 3 minutes in the worst case) we are expecting 500.000 to 1.000.000 users of the application, with peaks at 1:00pm (timezone GMT+1), where most (up to 80% of the users) will send most of the requests. the requests are from 11th of june to 11.july - after that, the app/game is closed/over. we are currently developing an aggressive caching mechanism - currently we are thinking about 2 or 3 small apps/webservices, that will handle the load. the load is distributed as follows: a) main application, cached data (11 screens, 200k each) b) voting: every day until 1:00pm (timezone GMT+1) - every user votes with about 10k data sent, high concurrent peak values! questions: is there any specific application setup that is recommendable? are there any hosting partners that can be recommended? thanks!

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• Problems with i18n using django translation on App-Engine with Korean and Hindi

  - by Greg

  I've got a setup based on the post here, and it works perfectly. Adding more languages to the mix, it recognises them fine, except for Korean (ko) and Hindi (hi). Chinese/Japanese/Hebrew are all fine, so nothing to do with encodings/charsets I don't think. Taking a look into the django code inside the app-engine SDK, I notice that all the languages that I'm using except for ko and hi are ones that ship with django - in the default settings.py and inside the locale folder they are missing. If I copy one of the locale folders inside the /usr/local/google_appengine/lib/django[...]/conf/locale and rename it to be 'ko', then it starts working in my app, but I won't be able to replicate this modification when I deploy to app-engine, so need a bit of help understanding what I might be doing wrong. my settings.py is definitely being taken into account, as if I remove languages from there then they stop working (as they should). If I copied the django modules into my app, under 'lib' there say, could I use those instead of the ones app-engine tries to use, maybe? I'm brand new to python/django/app-engine, and developing on a Mac with Leopard, if that makes any difference. I have the latest app-engine SDK as of tuesday.

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• What are salesforce.com and Apex like as an application development platform?

  - by mhollers

  I have recently discovered that salesforce.com is much more than an online CRM after coming across a Morrison's Case Study in which they develop a works management application. I've been trying it out with a view to recreating our own Works Management system on the platform. My background is in Microsoft and .Net, and the obvious 1st choice would be asp.net. However, there's only really myself with .net experience and my manager with a more legacy Synergy programming background, and I am self taught and am looking at evaluating other RAD options (eg Ironspeed). the nature of the business is in the main 2-5 concurrent construction type contracts that run for 3-5 yrs each, each requiring 15-50 system users. Traditionally we have used our character based Works Mangement system for everything and tweaked it for each contract. The Salesforce licensing model on the face of it suits this sort of flexibilty, but I'm worried about the development flexibilty/learning curve and all the issues that surround lock-in. There doesn't seem to be much neutral sober analysis of the platform on the web that isn't salesforce's own material/blogs Has anyone any experience of developing an application on salesforce as compared to the more 'traditional' .Net route?

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• Implementing Tagging System with PHP and mySQL. Caching help!!!

  - by Hamid Sarfraz

  With reference to this post: http://stackoverflow.com/questions/2122546/how-to-implement-tag-counting I have implemented the suggested 3 table tagging system completely. To count the number of Articles per tag, i am using another column named tagArticleCount in the tag definition table. (other columns are tagId, tagText, tagUrl, tagArticleCount). If i implement realtime editing of this table, so that whenever user adds another tag to article or deletes an existing tag, the tag_definition_table is updated to update the counter of the added/removed tag. This will cost an extra query each time any modification is made. (at the same time, related link entry for tag and article is deleted from tagLinkTable). An alternative to this is not allowing any real time editing to the counter, instead use CRONs to update counter of each tag after a specified time period. Here comes the problem that i want to discuss. This can be seen as caching the article count in database. Can you please help me find a way to present the articles in a list when a tag is explored and when the article counter for that tag is not up to date. For example: 1. Counter shows 50 articles, but there are infact 55 entries in the tag link table (that links tags and articles). 2. Counter shows 50 articles, but there are infact 45 extries in the tag link table. How to handle these 2 scenerios given in example. I am going to use APC to keep cache of these counters. Consider it too in your solution. Also discuss performance in the realtime / CRONNED counter updates.

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• Rollback doesn't work in MySQLdb

  - by Anton Barycheuski

  I have next code ... db = MySQLdb.connect(host=host, user=user, passwd=passwd, db=db, charset='utf8', use_unicode=True) db.autocommit(False) cursor = db.cursor() ... for col in ws.columns[1:]: data = (col[NUM_ROW_GENERATION].value, 1, type_topliv_dict[col[NUM_ROW_FUEL].value]) fullgeneration_id = data[0] type_topliv = data[2] if data in completions_set: compl_id = completions_dict[data] else: ... sql = u"INSERT INTO completions (type, mark, model, car_id, type_topliv, fullgeneration_id, mark_id, model_id, production_period, year_from, year_to, production_period_url) VALUES (1, '%s', '%s', 0, %s, %s, %s, %s, '%s', '%s', '%s', '%s')" % (marks_dict[mark_id], models_dict[model_id], type_topliv, fullgeneration_id, mark_id, model_id, production_period, year_from, year_to, production_period.replace(' ', '_').replace(u'?.?.', 'nv') ) inserted_completion += cursor.execute(sql) cursor.execute("SELECT fullgeneration_id, type, type_topliv, id FROM completions where fullgeneration_id = %s AND type_topliv = %s" % (fullgeneration_id, type_topliv)) row = cursor.fetchone() compl_id = row[3] if is_first_car: deleted_compl_rus = cursor.execute("delete from compl_rus where compl_id = %s" % compl_id) for param, row_id in params: sql = u"INSERT INTO compl_rus (compl_id, modification, groupparam, param, paramvalue) VALUES (%s, '%s', '%s', '%s', %s)" % (compl_id, col[NUM_ROW_MODIFICATION].value, param[0], param[1], col[row_id].value) inserted_compl_rus += cursor.execute(sql) is_first_car = False db.rollback() print '\nSTATISTICS:' print 'Inserted completion:', inserted_completion print 'Inserted compl_rus:', inserted_compl_rus print 'Deleted compl_rus:', deleted_compl_rus ans = raw_input('Commit changes? (y/n)') db.close() I has manually deleted records from table and than run script two times. See https://dpaste.de/MwMa . I think, that rollback in my code doesn't work. Why?

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• Which is the best license for my Open Source project?

  - by coderex

  I am a web developer, and I don't have enough knowledge about software licenses. I wish to publish some of my works, and I need to select licenses for them. My software product is free of cost. But I have some restrictions on the distribution/modification of the code. It's free of cost (but donations are acceptable ;-)). The source code is freely available. You can use, customize or edit/remove code (as long as the basic nature of the software is not changed). You don't have any permission to change the product name. There are some libraries and classes which are in a folder caller "myname". You don't have the permission to rename "myname". You can contribute any additions or modifications to my project, to the original source repository (the contributors name/email/site link will be listed on the credit file). You can't remove the original author's name from the license. You can put the license file or license code anywhere in the project file or folder. You can redistribute this code as free or commercial software. :) Do you think all these restrictions are valid? Given these restrictions, which license should I use? Edit 1:- My main intention is to make the product more popular with free source code while ensuring the original author is not ignored. The product is open. Edit 2:- Thank you all, the above points are because of my lack of knowledge of license terms. You can help me to correct or remove some of the above points. What I'm basically looking for is in my Edit 1.

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• My website keeps crashing IE, can't debug

  - by Ninja rhino

  I have a website that suddenly started to crash internet explorer. The website loads and starts executing javascript but somewhere in there the machinery explodes. I don't even get a script error, it just crashes. I've tried to manually step through every single line of js with the built in debugger but then of course the problem doesn't occur. If i choose to debug the application when it crashes i see the following message. Unhandled exception at 0x6c5dedf5 in iexplore.exe: 0xC0000005: Access violation reading location 0x00000090. The top 5 items in the call stack looks like this VGX.dll!6c5dedf5() [Frames below may be incorrect and/or missing, no symbols loaded for VGX.dll] VGX.dll!6c594d70() VGX.dll!6c594f63() VGX.dll!6c595350() VGX.dll!6c58f5e3() mshtml.dll!6f88dd17() VGX.dll seems to be part of the vml renderer and i am in fact using VML. I'm not suprised because i've had so many problems with vml, attributes has to be set in specific order, sometimes you cant set attributes when you have elements attached to the dom or vice versa (everything undocumented btw) but then the problems can usually be reproduced when debugging but not now :( The problem also occurs in no plugin-mode. Is there a better approach than trial and error to solve this? Edit: Adding a console outputting every suspect modification to the DOM made the problem only occur sometimes. (the console is also implemented in javascript on the same page, i'm able to see the output even after a crash as the window is still visible) Apparently it seems to be some kind of race condition. I managed to track it down even further, and it seems to occur when you remove an object from the DOM too quickly after it's just been added. (most likely only for vml-elements with some special attribute, didn't try further) And it can't be fixed by adding a dead loop in front of removeChild(pretty bad solution anyway), the page has to be rendered by the browser once after the addChild before you can call removeChild. sigh

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• Callers block until getFoo() has a value ready?

  - by Sean Owen

  I have a Java Thread which exposes a property which other threads want to access: class MyThread extends Thread { private Foo foo; ... Foo getFoo() { return foo; } ... public void run() { ... foo = makeTheFoo(); ... } } The problem is that it takes some short time from the time this runs until foo is available. Callers may call getFoo() before this and get a null. I'd rather they simply block, wait, and get the value once initialization has occurred. (foo is never changed afterwards.) It will be a matter of milliseconds until it's ready, so I'm comfortable with this approach. Now, I can make this happen with wait() and notifyAll() and there's a 95% chance I'll do it right. But I'm wondering how you all would do it; is there a primitive in java.util.concurrent that would do this, that I've missed? Or, how would you structure it? Yes, make foo volatile. Yes, synchronize on an internal lock Object and put the check in a while loop until it's not null. Am I missing anything?

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• Help! I'm a Haskell Newbie

  - by Darknight

  I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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• Limiting object allocation over multiple threads

  - by John

  I have an application which retrieves and caches the results of a clients query. The client then requests different chunks of data and the application sends the relevant results and removes them from the cache. A new requirement for this application is that there needs to be a run-time configurable maximum number of results which may be cached. I've taken the naive approach and implemented this by using a counter under a lock which is incremented every time a result is cached and decremented whenever a result is removed from the cache. Unfortunately, this has drastically reduced the applications performance when processing a large number of concurrent requests. I have tried both a critical section lock and spin-lock; the performance improves a bit with a spin-lock, but is still unacceptably slow. Is there a better way to solve this problem which may improve performance? Right now I have a thread pool that services requests and each request is tied to a Request object which stores that cached results for that particular request. Here is a simplified pseudo code version of my current implementation: void ResultCallback( Result result, Request *request ) { lock totalResultsCached lock cachedLimit if( totalResultsCached + 1 > cachedLimit ) { unlock cachedLimit unlock totalResultsCached //cancel the request return; } ++totalResultsCached; unlock cachedLimit unlock totalResultsCached request.add(result) } void SendResults( int resultsToSend, Request *request ) { while ( resultsToSend > 0 ) { send(request.remove()) lock totalResultsCached --totalResultsCached unlock totalResultsCached --resultsToSend; } }

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• How to provide warnings during validation in ASP.NET MVC?

  - by Alex

  Sometimes user input is not strictly invalid but can be considered problematic. For example: A user enters a long sentence in a single-line Name field. He probably should have used the Description field instead. A user enters a Name that is very similar to that of an existing entity. Perhaps he's inputting the same entity but didn't realize it already exists, or some concurrent user has just entered it. Some of these can easily be checked client-side, some require server-side checks. What's the best way, perhaps something similar to DataAnnotations validation, to provide warnings to the user in such cases? The key here is that the user has to be able to override the warning and still submit the form (or re-submit the form, depending on the implementation). The most viable solution that comes to mind is to create some attribute, similar to a CustomValidationAttribute, that may make an AJAX call and would display some warning text but doesn't affect the ModelState. The intended usage is this: [WarningOnFieldLength(MaxLength = 150)] [WarningOnPossibleDuplicate()] public string Name { get; set; } In the view: @Html.EditorFor(model => model.Name) @Html.WarningMessageFor(model => model.Name) @Html.ValidationMessageFor(model => model.Name) So, any ideas?

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• Is NFS capable of preserving order of operations?

  - by JustJeff

  I have a diskless host 'A', that has a directory NFS mounted on server 'B'. A process on A writes to two files F1 and F2 in that directory, and a process on B monitors these files for changes. Assume that B polls for changes faster than A is expected to make them. Process A seeks the head of the files, writes data, and flushes. Process B seeks the head of the files and does reads. Are there any guarantees about how the order of the changes performed by A will be detected at B? Specifically, if A alternately writes to one file, and then the other, is it reasonable to expect that B will notice alternating changes to F1 and F2? Or could B conceivably detect a series of changes on F1 and then a series on F2? I know there are a lot of assumptions embedded in the question. For instance, I am virtually certain that, even operating on just one file, if A performs 100 operations on the file, B may see a smaller number of changes that give the same result, due to NFS caching some of the actions on A before they are communicated to B. And of course there would be issues with concurrent file access even if NFS weren't involved and both the reading and the writing process were running on the same real file system. The reason I'm even putting the question up here is that it seems like most of the time, the setup described above does detect the changes at B in the same order they are made at A, but that occasionally some events come through in transposed order. So, is it worth trying to make this work? Is there some way to tune NFS to make it work, perhaps cache settings or something? Or is fine-grained behavior like this just too much expect from NFS?

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• List with non-null elements ends up containing null. A synchronization issue?

  - by Alix

  Hi. First of all, sorry about the title -- I couldn't figure out one that was short and clear enough. Here's the issue: I have a list List<MyClass> list to which I always add newly-created instances of MyClass, like this: list.Add(new MyClass()). I don't add elements any other way. However, then I iterate over the list with foreach and find that there are some null entries. That is, the following code: foreach (MyClass entry in list) if (entry == null) throw new Exception("null entry!"); will sometimes throw an exception. I should point out that the list.Add(new MyClass()) are performed from different threads running concurrently. The only thing I can think of to account for the null entries is the concurrent accesses. List<> isn't thread-safe, after all. Though I still find it strange that it ends up containing null entries, instead of just not offering any guarantees on ordering. Can you think of any other reason? Also, I don't care in which order the items are added, and I don't want the calling threads to block waiting to add their items. If synchronization is truly the issue, can you recommend a simple way to call the Add method asynchronously, i.e., create a delegate that takes care of that while my thread keeps running its code? I know I can create a delegate for Add and call BeginInvoke on it. Does that seem appropriate? Thanks.

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• Emacs: Often switching between Emacs and my IDE's editor, how can I 'synch' the file?

  - by WizardOfOdds

  I very often need to do some Emacs magic on some files and I need to go back and forth my IDE (IntelliJ IDEA) and Emacs. When a change is made under Emacs (and after I've saved the file) and I go back to IntelliJ the change appears immediately (if I recall correctly I configured IntelliJ to "always reload file when a modification is detected on disk" or something like that). I don't even need to reload: as soon as IntelliJ IDEA gains focus, it instantly reloads the file (and I hence have immediately access to the modifications I made from Emacs). So far, so very good. However "the other way round", it doesn't work yet. Can I configure Emacs so that everytime a file is changed on disk it reloads it? Or make Emacs, everytime it "gains focus", verify if any file currently opened has been modified on disk? I know I can start modifying the buffer under Emacs and it shall instantly warn that it has been modified, but I'd rather have it do it immediately (for example if I used my IDE to do some big change, when I come back to Emacs what I see may not be at all anymore what the file contains and it's a bit weird).

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• Can a Java HashMap's size() be out of sync with its actual entries' size ?

  - by trix

  I have a Java HashMap called statusCountMap. Calling size() results in 30. But if I count the entries manually, it's 31 This is in one of my TestNG unit tests. These results below are from Eclipse's Display window (type code - highlight - hit Display Result of Evaluating Selected Text). statusCountMap.size() (int) 30 statusCountMap.keySet().size() (int) 30 statusCountMap.values().size() (int) 30 statusCountMap (java.util.HashMap) {40534-INACTIVE=2, 40526-INACTIVE=1, 40528-INACTIVE=1, 40492-INACTIVE=3, 40492-TOTAL=4, 40513-TOTAL=6, 40532-DRAFT=4, 40524-TOTAL=7, 40526-DRAFT=2, 40528-ACTIVE=1, 40524-DRAFT=2, 40515-ACTIVE=1, 40513-DRAFT=4, 40534-DRAFT=1, 40514-TOTAL=3, 40529-DRAFT=4, 40515-TOTAL=3, 40492-ACTIVE=1, 40528-TOTAL=4, 40514-DRAFT=2, 40526-TOTAL=3, 40524-INACTIVE=2, 40515-DRAFT=2, 40514-ACTIVE=1, 40534-TOTAL=3, 40513-ACTIVE=2, 40528-DRAFT=2, 40532-TOTAL=4, 40524-ACTIVE=3, 40529-ACTIVE=1, 40529-TOTAL=5} statusCountMap.entrySet().size() (int) 30 What gives ? Anyone has experienced this ? I'm pretty sure statusCountMap is not being modified at this point. There are 2 methods (lets call them methodA and methodB) that modify statusCountMap concurrently, by repeatedly calling incrementCountInMap. private void incrementCountInMap(Map map, Long id, String qualifier) { String key = id + "-" + qualifier; if (map.get(key) == null) { map.put(key, 0); } synchronized (map) { map.put(key, map.get(key).intValue() + 1); } } methodD is where I'm getting the issue. methodD has a TestNG @dependsOnMethods = { "methodA", "methodB" } so when methodD is executing, statusCountMap is pretty much static already. I'm mentioning this because it might be a bug in TestNG. I'm using Sun JDK 1.6.0_24. TestNG is testng-5.9-jdk15.jar Hmmm ... after rereading my post, could it be because of concurrent execution of outside-of-synchronized-block map.get(key) == null & map.put(key,0) that's causing this issue ?

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