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• What hash algorithms are paralellizable? Optimizing the hashing of large files utilizing on mult-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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• Determining if an unordered vector<T> has all unique elements

  - by Hooked

  Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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• How to copy files without slowing down my app?

  - by Kevin Gebhardt

  I have a bunch of little files in my assets which need to be copied to the SD-card on the first start of my App. The copy code i got from here placed in an IntentService works like a charm. However, when I start to copy many litte files, the whole app gets increddible slow (I'm not really sure why by the way), which is a really bad experience for the user on first start. As I realised other apps running normal in that time, I tried to start a child process for the service, which didn't work, as I can't acess my assets from another process as far as I understood. Has anybody out there an idea how a) to copy the files without blocking my app b) to get through to my assets from a private process (process=":myOtherProcess" in Manifest) or c) solve the problem in a complete different way Edit: To make this clearer: The copying allready takes place in a seperate thread (started automaticaly by IntentService). The problem is not to separate the task of copying but that the copying in a dedicated thread somehow affects the rest of the app (e.g. blocking to many app-specific resources?) but not other apps (so it's not blocking the whole CPU or someting) Edit2: Problem solved, it turns out, there wasn't really a problem. See my answer below.

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• Progressively stream the output of an ASP.NET page - or render a page outside of an HTTP request

  - by Evgeny

  I have an ASP.NET 2.0 page with many repeating blocks, including a third-party server-side control (so it's not just plain HTML). Each is quite expensive to generate, in terms of both CPU and RAM. I'm currently using a standard Repeater control for this. There are two problems with this simple approach: The entire page must be rendered before any of it is returned to the client, so the user must wait a long time before they see any data. (I write progress messages using Response.Write, so there is feedback, but no actual results.) The ASP.NET worker process must hold everything in memory at the same time. There is no inherent needs for this: once one block is processed it won't be changed, so it could be returned to the client and the memory could be freed. I would like to somehow return these blocks to the client one at a time, as each is generated. I'm thinking of extracting the stuff inside the Repeater into a separate page and getting it repeatedly using AJAX, but there are some complications involved in that and I wonder if there is some simper approach. Ideally I'd like to keep it as one page (from the client's point of view), but return it incrementally. Another way would be to do something similar, but on the server: still create a separate page, but have the server access it and then Response.Write() the HTML it gets to the response stream for the real client request. Is there a way to avoid an HTTP request here, though? Is there some ASP.NET method that would render a UserControl or a Page outside of an HTTP request and simply return the HTML to me as a string? I'm open to other ideas on how to do this as well.

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• Multithreaded linked list traversal

  - by Rob Bryce

  Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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• A simple way to put a UIImage in a UIButton

  - by Alice

  I have a UIButton in my iPhone app. I set its size to 100x100. I have an image that is 400x200 that I wish to display in the button. The button STILL needs to stay at 100x100... and I want the image to downsize to fit... but keep the correct aspect ratio. I thought that's what "Aspect Fit" was used for. Do I include my image with setImage, or setBackgroundImage? Do I set AspectFit for the button? or the image? or the background image? (I need the smaller images to INCREASE in size. While larger images should DESCREASE in size. Always keeping the button at 100x100.) I've tried countless combinations of all of the above... and I just can't seem to get everything to work at the same time: Don't change the button's size of 100x100. Don't destroy the image's aspect ratio. Always increase small images to fit the button. Always decrease large images to fit the button. Never clip any of the image edges. Never require the "put UIButtons over all your UIimages" hack. Don't require everyone to upgrade to v4.2.1 just to use new framework methods. I see so many apps, with so many fully-working image-buttons... that I can't believe I can't figure out this very simple, very common thing. Ugh.

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• Implement a threading to prevent UI block on a bug in an async function

  - by Marcx

  I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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• Fastest XML parser for small, simple documents in Java

  - by Varkhan

  I have to objectify very simple and small XML documents (less than 1k, and it's almost SGML: no namespaces, plain UTF-8, you name it...), read from a stream, in Java. I am using JAXP to process the data from my stream into a Document object. I have tried Xerces, it's way too big and slow... I am using Dom4j, but I am still spending way too much time in org.dom4j.io.SAXReader. Does anybody out there have any suggestion on a faster, more efficient implementation, keeping in mind I have very tough CPU and memory constraints? [Edit 1] Keep in mind that my documents are very small, so the overhead of staring the parser can be important. For instance I am spending as much time in org.xml.sax.helpers.XMLReaderFactory.createXMLReader as in org.dom4j.io.SAXReader.read [Edit 2] The result has to be in Dom format, as I pass the document to decision tools that do arbitrary processing on it, like switching code based on the value of arbitrary XPaths, but also extracting lists of values packed as children of a predefined node. [Edit 3] In any case I eventually need to load/parse the complete document, since all the information it contains is going to be used at some point. (This question is related to, but different from, http://stackoverflow.com/questions/373833/best-xml-parser-for-java )

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• What's the best Linux backup solution?

  - by Jon Bright

  We have a four Linux boxes (all running Debian or Ubuntu) on our office network. None of these boxes are especially critical and they're all using RAID. To date, I've therefore been doing backups of the boxes by having a cron job upload tarballs containing the contents of /etc, MySQL dumps and other such changing, non-packaged data to a box at our geographically separate hosting centre. I've realised, however that the tarballs are sufficient to rebuild from, but it's certainly not a painless process to do so (I recently tried this out as part of a hardware upgrade of one of the boxes) long-term, the process isn't sustainable. Each of the boxes is currently producing a tarball of a couple of hundred MB each day, 99% of which is the same as the previous day partly due to the size issue, the backup process requires more manual intervention than I want (to find whatever 5GB file is inflating the size of the tarball and kill it) again due to the size issue, I'm leaving stuff out which it would be nice to include - the contents of users' home directories, for example. There's almost nothing of value there that isn't in source control (and these aren't our main dev boxes), but it would be nice to keep them anyway. there must be a better way So, my question is, how should I be doing this properly? The requirements are: needs to be an offsite backup (one of the main things I'm doing here is protecting against fire/whatever) should require as little manual intervention as possible (I'm lazy, and box-herding isn't my main job) should continue to scale with a couple more boxes, slightly more data, etc. preferably free/open source (cost isn't the issue, but especially for backups, openness seems like a good thing) an option to produce some kind of DVD/Blu-Ray/whatever backup from time to time wouldn't be bad My first thought was that this kind of incremental backup was what tar was created for - create a tar file once each month, add incrementally to it. rsync results to remote box. But others probably have better suggestions.

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• NHibernate + Fluent long startup time

  - by PaRa

  Hi all, am new to NHibernate. When performing below test took 11.2 seconds (debug mode) i am seeing this large startup time in all my tests (basically creating the first session takes a tone of time) setup = Windows 2003 SP2 / Oracle10gR2 latest CPU / ODP.net 2.111.7.20 / FNH 1.0.0.636 / NHibernate 2.1.2.4000 / NUnit 2.5.2.9222 / VS2008 SP1 using System; using System.Collections; using System.Data; using System.Globalization; using System.IO; using System.Text; using System.Data; using NUnit.Framework; using System.Collections.Generic; using System.Data.Common; using NHibernate; using log4net.Config; using System.Configuration; using FluentNHibernate; [Test()] public void GetEmailById() { Email result; using (EmailRepository repository = new EmailRepository()) { results = repository.GetById(1111); } Assert.IsTrue(results != null); } public class EmailRepository : RepositoryBase { public EmailRepository():base() { } } In my RepositoryBase public T GetById(object id) { using (var session = sessionFactory.OpenSession()) using (var transaction = session.BeginTransaction()) { try { T returnVal = session.Get(id); transaction.Commit(); return returnVal; } catch (HibernateException ex) { // Logging here transaction.Rollback(); return null; } } } The query time is very small. The resulting entity is really small. Subsequent queries are fine. Its seems to be getting the first session started. Has anyone else seen something similar?

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• C++ Builder 2010 Exception Dead Lock ???

  - by James

  Hello Is this some kind of exception dead lock i am facing? How to avoid it ? Have a look at below line where i have TIdContext objects of connected clients stored in an objlist and at times i need to process it. But if one user is disconnected while another thread is processing the list, then for that freed TIdContext-Data object I am getting Access voilation, Ok its fine i am using try/catch but problem is that at below line there is some kind of dead lock and process hangs , if i attach a debuger it show Access voilation Again and Again and Again, and cpu coonsumption goes up because of that exception dead lock. AnsiString UserID = ((Tmyobject*) ((TIdContext*) ObjList->Objects[i])->Data)->UserID; i know i can check before accessing the object, if object is not Null, It works.. But my question is what if once in a blue moon the Data object is freed at the point when NULL check is performed and on next line when again i am accessing the object i get same dead lock ??? So how to avoid/handle this dead lock exception ? Here is the call stack... :005F07C0 System::AnsiStringBase::AnsiStringBase(this=:0285FCE0, src=????) :0040223F System::AnsiStringT<0>::AnsiStringT<0>(this=:0285FCE0, src=:00000008) :00457996 TSomeClass::SomeFunction(this=:009D8230, UserID={ }, DataSize={ }, ) :0047BFF1 __linkproc__ ThreadProc(Thread=:009561C0) :004AD00E __linkproc__ ThreadWrapper(Parameter=:009EAA30) :7c80b729 ; C:\WINDOWS\system32\kernel32.dll Please helppppppppppppppppppppp Thanks

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• With Maven2, how would I zip a directory in my resources?

  - by Benny

  I'm trying to upgrade my project from using Maven 1 to Maven 2, but I'm having a problem with one of the goals. I have the following Maven 1 goal in my maven.xml file: <goal name="jar:init"> <ant:delete file="${basedir}/src/installpack.zip"/> <ant:zip destfile="${basedir}/src/installpack.zip" basedir="${basedir}/src/installpack" /> <copy todir="${destination.location}"> <fileset dir="${source.location}"> <exclude name="installpack/**"/> </fileset> </copy> </goal> I'm unable to find a way to do this in Maven2, however. Right now, the installpack directory is in the resources directory of my standard Maven2 directory structure, which works well since it just gets copied over. I need it to be zipped though. I found this page on creating ant plugins: http://maven.apache.org/guides/plugin/guide-ant-plugin-development.html. It looks like I could create my own ant plugin to do what I need. I was just wondering if there was a way to do it using only Maven2. Any suggestions would be much appreciated. Thanks, B.J.

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• MySQL 5.5.8 Gets Periodic Lag

  - by CYREX

  Am using MySQL 5.5.8 on an Ubuntu system and every X amount of time it creates a huge lag that lasts a couple of seconds. Then all goes back to normal until the next lag. The time period varies but it looks like it happen periodically. Am using InnoDB. It is like hiccups in the MySQL. What could be creating this sort of periodic problem. Do not have any cron jobs or process running every time the X period happens. The X period could be between 30 minutes to 2 hours. So for example it could happen every 30 minutes for the next 12 hours or it could happen every 2 hours for the next 8 hours. key_buffer_size = 256M max_allowed_packet = 1M table_cache = 1024 table_open_cache = 1024 sort_buffer_size = 2M read_buffer_size = 2M read_rnd_buffer_size = 4M myisam_sort_buffer_size = 32M thread_cache_size = 128 query_cache_size= 128M log-slow-queries = slow.log long_query_time = 5 log-queries-not-using-indexes # Try number of CPU's*2 for thread_concurrency thread_concurrency = 4 max_connections=512 #innodb_data_file_path = ibdata1:10M:autoextend #innodb_log_group_home_dir = /usr/local/mysql/data # You can set .._buffer_pool_size up to 50 - 80 % # of RAM but beware of setting memory usage too high innodb_buffer_pool_size = 1G #innodb_additional_mem_pool_size = 20M # Set .._log_file_size to 25 % of buffer pool size #innodb_log_file_size = 64M #innodb_log_buffer_size = 8M #innodb_flush_log_at_trx_commit = 0 #innodb_lock_wait_timeout = 50 [mysqldump] quick max_allowed_packet = 16M [myisamchk] key_buffer_size = 64M sort_buffer_size = 64M read_buffer = 2M write_buffer = 2M There are about 200+ tables divided in 3 databases. The most written too is in InnoDB. The other ones are more read. Several of the tables in the InnoDB have more than 2 million records. The other databases top at about 400 thousand records and do not change so often. The PC is a Core 2 Duo 8400 with 4GB RAM, 32Bit Ubuntu.

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• I Cannot retrieve ARPINSTALLLOCATION so we know where to install a new version [WIX]

  - by Birkoff

  I am trying to retrieve the ARPINSTALLLOCATION during the installation of a Major Upgrade version of the software. Following this info I managed to set the ARPINSTALLLOCATION to the custom path. However, retrieving it again isn't working. I've tried many things over the past days but it keeps defaulting back to the default installation path instead of the custom one. <InstallUISequence> <AppSearch After="FindRelatedProducts"/> ... </InstallUISequence> <Property Id="WIXUI_INSTALLDIR" Value="APPROOTDIRECTORY"> <RegistrySearch Id="FindInstallLocation" Root="HKLM" Key="Software\Microsoft\Windows\CurrentVersion\Uninstall\[OLDERVERSIONBEINGUPGRADED]" Name="InstallLocation" Type="raw" /> </Property> In the custom WixUI_InstallDir UI I have this in the CustomInstallDirDlg <Control Id="Folder" Type="PathEdit" X="20" Y="90" Width="260" Height="18" Property="WIXUI_INSTALLDIR" Indirect="yes" /> The alternative install path is in the registry, but it isn't retrieved and shown in the control. What am I doing wrong here? -Birkoff

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• An Erroneous SQL Query makes browser hang until script timeout exceeded

  - by Jimbo

  I have an admin page in a Classic ASP web application that allows the admin user to run queries against the database (SQL Server 2000) Whats really strange is that if the query you send has an error in it (an invalid table join, a column you've forgotten to group by etc) the BROWSER hangs (CPU usage goes to maximum) until the SERVER script timeout is exceeded and then spits out a timeout exceeded error (server and browser are on different machines, so not sure how this happens!) I have tried this in IE 8 and FF 3 with the same result. If you run that same query (with errors) directly from SQL Enterprise Manager, it returns the real error immediately. Is this a security feature? Does anyone know how to turn it off? It even happens when the connection to the database is using 'sa' credentials so I dont think its a security setting :( Dim oRS Set oRS = Server.CreateObject("ADODB.Recordset") oRS.ActiveConnection = sConnectionString // run the query - this is for the admin only so doesnt check for sql safe commands etc. oRS.Open Request.Form("txtSQL") If Not oRS.EOF Then // list the field names from the recordset For i = 0 to oRS.Fields.Count - 1 Response.Write oRS.Fields(i).name & "&nbsp;" Next // show the data for each record in the recordset While Not oRS.EOF For i = 0 to oRS.Fields.Count - 1 Response.Write oRS.Fields(i).value & "&nbsp;" Next Response.Write "<br />" oRS.Movenext() Wend End If

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• Big-O for GPS data

  - by HH

  A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is an arbitrary constants Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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• Programming Environment for a Motorola 68000 in Linux

  - by Nick Presta

  Greetings all, I am taking a Structure and Application of Microcomputers course this semester and we're programming with the Motorola 68000 series CPU/board. The course syllabus suggests running something like Easy68K or Teesside Motorola 68000 Assembler/Emulator at home to test our programs. I told my prof I run x64 Linux and asked what sort of environment I would need to complete my coursework. He said that the easiest environment to use is a Windows XP 32bit VM with one of the two suggested applications installed, however, he doesn't really care what I use as long as I can test what I write at home. So I'm asking if there exists some sort of emulator or environment for Linux so I can test my code, and what sort of caveats I will run into by writing and testing my code in Linux. Also, I plan to do my editing in Vim, which probably isn't a problem, but I would like any insight into editors for 68000 assembly, if you have any. Thanks! EDIT: Just to clarify - I don't want to install Linux on the board at all - I want to program on my home machine, test the code locally, and then bring it onto the board for grading/running.

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• IE7 Problem with sIFR when <br> is inside an H3

  - by David Fox

  I have a problem I just discovered when viewing certain pages in IE7. If I have a very long header that wraps to a second line, or worse, if I put a BR in the middle, that throws off the spacing. One page to look at: broken example1 You'll notice that the margin at the top of the page gets offset as the headings are rendered, throwing everything off. I'm using code like this: <h3 style="margin:0"><a href="../books/msc1.html">Middle School Confidential™<br> Book 1: Be Confident in Who You Are</a></h3> but repeated many times to exaggerate the problem. I tried another test where I removed the BR and let the lines wrap naturally. This is an improvement in terms of the spacing, but it doesn't fix the problem. (Same URL but make it m1.html) In the third example, each heading takes up only one line (m2.html) One option would be to just split up the heading onto two lines, each with its on H tags. But since these are links, then it will appear that the first line might go to one place, and the second to another, since they wouldn't change color simultaneously as you roll over them. So, any solutions to this? I believe I have the current version of sIFR 3. I don't want to upgrade to IE8 until I know this is resolved. Thanks!

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• trouble calculating offset index into 3D array

  - by Derek

  Hello, I am writing a CUDA kernel to create a 3x3 covariance matrix for each location in the rows*cols main matrix. So that 3D matrix is rows*cols*9 in size, which i allocated in a single malloc accordingly. I need to access this in a single index value the 9 values of the 3x3 covariance matrix get their values set according to the appropriate row r and column c from some other 2D arrays. In other words - I need to calculate the appropriate index to access the 9 elements of the 3x3 covariance matrix, as well as the row and column offset of the 2D matrices that are inputs to the value, as well as the appropriate index for the storage array. i have tried to simplify it down to the following: //I am calling this kernel with 1D blocks who are 512 cols x 1row. TILE_WIDTH=512 int bx = blockIdx.x; int by = blockIdx.y; int tx = threadIdx.x; int ty = threadIdx.y; int r = by + ty; int c = bx*TILE_WIDTH + tx; int offset = r*cols+c; int ndx = r*cols*rows + c*cols; if((r < rows) && (c < cols)){ //this IF statement is trying to avoid the case where a threadblock went bigger than my original array..not sure if correct d_cov[ndx + 0] = otherArray[offset]; d_cov[ndx + 1] = otherArray[offset] d_cov[ndx + 2] = otherArray[offset] d_cov[ndx + 3] = otherArray[offset] d_cov[ndx + 4] = otherArray[offset] d_cov[ndx + 5] = otherArray[offset] d_cov[ndx + 6] = otherArray[offset] d_cov[ndx + 7] = otherArray[offset] d_cov[ndx + 8] = otherArray[offset] } When I check this array with the values calculated on the CPU, which loops over i=rows, j=cols, k = 1..9 The results do not match up. in other words d_cov[i*rows*cols + j*cols + k] != correctAnswer[i][j][k] Can anyone give me any tips on how to sovle this problem? Is it an indexing problem, or some other logic error?

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• Using JMX classes to notify on events over time

  - by Cincinnati Joe

  I've been looking at JMX for monitoring application and system metrics (partially because MBeans can accessed by various tools such as JConsole). It would seem like the classes included with JMX would be useful for things like notification when metrics have exceeded thresholds. But I'm not sure they fit with the way I want to measure these over a specified time period. For example, let's say I want to notify an admin when the average CPU load is over 95% for more than 5 minutes. Is that something can be done with a GaugeMonitor? From the docs, it doesn't seem quite suited for this, and I'm wondering if instead I should write my own MBean with the necessary logic. A more relevant example is when the login times for users exceed 10s over a period of 5 mins. Slightly different would be the last 20 logins took more than 10s on average. Another case would be when a process crashes 4+ times in an hour. Or the request queue exceeds 15 for 5 mins. Are the JMX Monitor classes useful for this kind of thing?

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• Simple POSIX threads question

  - by Andy

  Hi, I have this POSIX thread: void subthread(void) { while(!quit_thread) { // do something ... // don't waste cpu cycles if(!quit_thread) usleep(500); } // free resources ... // tell main thread we're done quit_thread = FALSE; } Now I want to terminate subthread() from my main thread. I've tried the following: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread); But it does not work! The while() clause does never exit although my subthread clearly sets quit_thread to FALSE after having freed its resources! If I modify my shutdown code like this: quit_thread = TRUE; // wait until subthread() has cleaned its resources while(quit_thread) usleep(10); Then everything is working fine! Could someone explain to me why the first solution does not work and why the version with usleep(10) suddenly works? I know that this is not a pretty solution. I could use semaphores/signals for this but I'd like to learn something about multithreading, so I'd like to know why my first solution doesn't work. Thanks!

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• Queuing using table or MSMQ?

  - by Lieven Cardoen

  A part of the application I'm working on is an swf that shows a test with some 80 questions. Each question is saved to a sql server through WebORB and asp.net. If a candidate finisheds the test, the session needs to be validated. Problem now is that sometimes 350 candidates finish their test at the same moment, and cpu on webserver and sql server explodes (350 validations concurrently). Now, how would I implement queuing here? In the database, there's a table that has a record for each session. One column holds the status. 1 is finished, 2 is validated. I could implement queuing in two ways (as I see it, maybe you have other propositions): A process that checks the table for records with status 1. If it finds one, it validates the session. So, sessions are validated one after one. If a candidate finishes its session, a message is sent to a MSMQ queue. Another process listens to the queue and validates sessions one after one. Now, What would be the best approach? Where do you start the process that will validate sessions? In your global.asax (application_start)? As a windows service? As an exe on the root of the website that is started in application_start? To me, using the table and looking for records with status 1 seems the easiest way.

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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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• Different programming languages possibilities

  - by b-gen-jack-o-neill

  Hello. This should be very simple question. There are many programming languages out there, compiled into machine code or managed code. I first started with ASM back in high school. Assembler is very nice, since you know what exactly CPU does. Next, (as you can see from my other questions here) I decided to learn C and C++. I choosed C becouse from what I read it is the language with output most close to assembler-written programs. But, what I want to know is, can any other Windows programming language out there call win32 API? To be exact, like C has its special header and functions for win32 api interactions, is this assumed to be some important part of programming language? Or are there any languages that have no support for calling win32 API, or just use console to IO and some functions for basic file IO? Becouse, for Windows programming with graphic output, it is essential to have acess to win32 API. I know this question might seem silly, but still please, help me, I ask for study porposes. Thanks.

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• Deploy to web container, bundle web container or embed web container...

  - by Jason

  I am developing an application that needs to be as simple as possible to install for the end user. While the end users will likely be experience Linux users (or sales engineers), they don't really know anything about Tomcat, Jetty, etc, nor do I think they should. So I see 3 ways to deploy our applications. I should also state that this is the first app that I have had to deploy that had a web interface, so I haven't really faced this question before. First is to deploy the application into an existing web container. Since we only deploy to Suse or RedHat this seems easy enough to do. However, we're not big on the idea of multiple apps running in one web container. It makes it harder to take down just one app. The next option is to just bundle Tomcat or Jetty and have the startup/shutdown scripts launch our bundled web container. Or 3rd, embed.. This will probably provide the same user experience as the second option. I'm curious what others do when faced with this problem to make it as fool proof as possible on the end user. I've almost ruled out deploying into an existing web container as we often like to set per application resource limits and CPU affinity, which I believe would affect all apps deployed into a web container/app server and not just a specific application. Thank you.

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