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  • Lightweight spinlocks built from GCC atomic operations?

    - by Thomas
    I'd like to minimize synchronization and write lock-free code when possible in a project of mine. When absolutely necessary I'd love to substitute light-weight spinlocks built from atomic operations for pthread and win32 mutex locks. My understanding is that these are system calls underneath and could cause a context switch (which may be unnecessary for very quick critical sections where simply spinning a few times would be preferable). The atomic operations I'm referring to are well documented here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Atomic-Builtins.html Here is an example to illustrate what I'm talking about. Imagine a RB-tree with multiple readers and writers possible. RBTree::exists() is read-only and thread safe, RBTree::insert() would require exclusive access by a single writer (and no readers) to be safe. Some code: class IntSetTest { private: unsigned short lock; RBTree<int>* myset; public: // ... void add_number(int n) { // Aquire once locked==false (atomic) while (__sync_bool_compare_and_swap(&lock, 0, 0xffff) == false); // Perform a thread-unsafe operation on the set myset->insert(n); // Unlock (atomic) __sync_bool_compare_and_swap(&lock, 0xffff, 0); } bool check_number(int n) { // Increment once the lock is below 0xffff u16 savedlock = lock; while (savedlock == 0xffff || __sync_bool_compare_and_swap(&lock, savedlock, savedlock+1) == false) savedlock = lock; // Perform read-only operation bool exists = tree->exists(n); // Decrement savedlock = lock; while (__sync_bool_compare_and_swap(&lock, savedlock, savedlock-1) == false) savedlock = lock; return exists; } }; (lets assume it need not be exception-safe) Is this code indeed thread-safe? Are there any pros/cons to this idea? Any advice? Is the use of spinlocks like this a bad idea if the threads are not truly concurrent? Thanks in advance. ;)

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  • Hooking the http/https protocol in IE causes GET requests to be sequential

    - by watsonmw
    I'm using the PassthruAPP method to hook into HTTP/HTTPS requests made by IE. It's working well for the most part, however I noticed a problem. Only one download thread is active at a time. I can see two IInternetProtocol objects getting created, but IE uses only one at a time. This is happening with IE7. The odd thing is that the problem occurs when overriding the existing default HTTP/HTTPS handler, even if the handler is not the one being used to make the request. E.g. Registering a handler for the HTTPS protocol will cause HTTP requests to be made sequentially, even though HTTP requests are not hooked. I installed Google Gears and it has the same problem. This always happens for the first few items on the page, but it seems that after the document complete is issued, concurrent downloads can occur again. For example Javascript code that is executed after the page has finished loading can load images concurrently just fine. One option is to try to IAT patch the 'IInternetProtocol' registered for HTTP requests, but Google Gears does this already and it has the same problem. I know installing a HTTP Proxy is another option, but I don't want to monkey with the users' HTTP Proxy settings if there another option.

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  • A copy of ApplicationController has been removed from the module tree but is still active

    - by Matchu
    Whenever two concurrent HTTP requests go to my Rails app, the second always returns the following error: A copy of ApplicationController has been removed from the module tree but is still active! From there it gives an unhelpful stack trace to the effect of "we went through the standard server stuff, ran your first before_filter on ApplicationController (and I checked; it's just whichever filter runs first)", then offers the following: /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:414:in `load_missing_constant' /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:96:in `const_missing' which I'm assuming is a generic response and doesn't really say much. Google seems to tell me that people developing Rails Engines will encounter this, but I don't do that. All I've done is upgrade my Rails app from 2.2 (2.1?) to 2.3. What are some possible causes for this error, and how can I go about tracking down what's really going on? I know this question is vague, so would any other information be helpful? More importantly: I tried doing a test run in a "production" environment just now, and the error doesn't seem to persist. Does this only affect development, then, and need I not worry too much?

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  • dynamically created radiobuttonlist

    - by Janet
    Have a master page. The content page has a list with hyperlinks containing request variables. You click on one of the links to go to the page containing the radiobuttonlist (maybe). First problem: When I get to the new page, I use one of the variables to determine whether to add a radiobuttonlist to a placeholder on the page. I tried to do it in page)_load but then couldn't get the values selected. When I played around doing it in preInit, the first time the page is there, I can't get to the page's controls. (Object reference not set to an instance of an object.) I think it has something to do with the MasterPage and page content? The controls aren't instantiated until later? (using vb by the way) Second problem: Say I get that to work, once I hit a button, can I still access the passed request variable to determine the selected item in the radiobuttonlist? Protected Sub Page_PreInit(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreInit 'get sessions for concurrent Dim Master As New MasterPage Master = Me.Master Dim myContent As ContentPlaceHolder = CType(Page.Master.FindControl("ContentPlaceHolder1"), ContentPlaceHolder) If Request("str") = "1" Then Dim myList As dsSql = New dsSql() ''''instantiate the function to get dataset Dim ds As New Data.DataSet ds = myList.dsConSessionTimes(Request("eid")) If ds.Tables("conSessionTimes").Rows.Count > 0 Then Dim conY As Integer = 1 CType(myContent.FindControl("lblSidCount"), Label).Text = ds.Tables("conSessionTimes").Rows.Count.ToString Sorry to be so needy - but maybe someone could direct me to a page with examples? Maybe seeing it would help it make sense? Thanks....JB

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  • Blocking on DBCP connection pool (open and close connnection). Is database connection pooling in OpenEJB pluggable?

    - by topchef
    We use OpenEJB on Tomcat (used to run on JBoss, Weblogic, etc.). While running load tests we experience significant performance problems with handling JMS messages (queues). Problem was localized to blocking on database connection pool getting or releasing connection to the pool. Blocking prevented concurrent MDB instances (threads) from running hence performance suffered 10-fold and worse. The same code used to run on application servers (with their respective connection pool implementations) with no blocking at all. Example of thread blocked: Name: JMS Resource Adapter-worker-23 State: BLOCKED on org.apache.commons.pool.impl.GenericObjectPool@1ea6b4a owned by: JMS Resource Adapter-worker-19 Total blocked: 18,426 Total waited: 0 Stack trace: org.apache.commons.pool.impl.GenericObjectPool.returnObject(GenericObjectPool.java:916) org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:91) - locked org.apache.commons.dbcp.PoolableConnection@1bcba8 org.apache.commons.dbcp.managed.ManagedConnection.close(ManagedConnection.java:147) com.xxxxx.persistence.DbHelper.closeConnection(DbHelper.java:290) .... Couple of questions. I am almost certain that some transactional attributes and properties contribute to this blocking, but MDBs are defined as non-transactional (we use both annotations and ejb-jar.xml). Some EJBs do use container-managed transactions though (and we can observe blocking there as well). Are there any DBCP configurations that may fix blocking? Is DBCP connection pool implementation replaceable in OpenEJB? How easy (difficult) to replace it with another library? Just in case this is how we define data source in OpenEJB (openejb.xml): <Resource id="MyDataSource" type="DataSource"> JdbcDriver oracle.jdbc.driver.OracleDriver JdbcUrl ${oracle.jdbc} UserName ${oracle.user} Password ${oracle.password} JtaManaged true InitialSize 5 MaxActive 30 ValidationQuery SELECT 1 FROM DUAL TestOnBorrow true </Resource>

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  • What's the fastest way to bulk insert a lot of data in SQL Server (C# client)

    - by Andrew
    I am hitting some performance bottlenecks with my C# client inserting bulk data into a SQL Server 2005 database and I'm looking for ways in which to speed up the process. I am already using the SqlClient.SqlBulkCopy (which is based on TDS) to speed up the data transfer across the wire which helped a lot, but I'm still looking for more. I have a simple table that looks like this: CREATE TABLE [BulkData]( [ContainerId] [int] NOT NULL, [BinId] [smallint] NOT NULL, [Sequence] [smallint] NOT NULL, [ItemId] [int] NOT NULL, [Left] [smallint] NOT NULL, [Top] [smallint] NOT NULL, [Right] [smallint] NOT NULL, [Bottom] [smallint] NOT NULL, CONSTRAINT [PKBulkData] PRIMARY KEY CLUSTERED ( [ContainerIdId] ASC, [BinId] ASC, [Sequence] ASC )) I'm inserting data in chunks that average about 300 rows where ContainerId and BinId are constant in each chunk and the Sequence value is 0-n and the values are pre-sorted based on the primary key. The %Disk time performance counter spends a lot of time at 100% so it is clear that disk IO is the main issue but the speeds I'm getting are several orders of magnitude below a raw file copy. Does it help any if I: Drop the Primary key while I am doing the inserting and recreate it later Do inserts into a temporary table with the same schema and periodically transfer them into the main table to keep the size of the table where insertions are happening small Anything else? -- Based on the responses I have gotten, let me clarify a little bit: Portman: I'm using a clustered index because when the data is all imported I will need to access data sequentially in that order. I don't particularly need the index to be there while importing the data. Is there any advantage to having a nonclustered PK index while doing the inserts as opposed to dropping the constraint entirely for import? Chopeen: The data is being generated remotely on many other machines (my SQL server can only handle about 10 currently, but I would love to be able to add more). It's not practical to run the entire process on the local machine because it would then have to process 50 times as much input data to generate the output. Jason: I am not doing any concurrent queries against the table during the import process, I will try dropping the primary key and see if that helps. ~ Andrew

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  • PostgreSQL insert on primary key failing with contention, even at serializable level

    - by Steven Schlansker
    I'm trying to insert or update data in a PostgreSQL db. The simplest case is a key-value pairing (the actual data is more complicated, but this is the smallest clear example) When you set a value, I'd like it to insert if the key is not there, otherwise update. Sadly Postgres does not have an insert or update statement, so I have to emulate it myself. I've been working with the idea of basically SELECTing whether the key exists, and then running the appropriate INSERT or UPDATE. Now clearly this needs to be be in a transaction or all manner of bad things could happen. However, this is not working exactly how I'd like it to - I understand that there are limitations to serializable transactions, but I'm not sure how to work around this one. Here's the situation - ab: => set transaction isolation level serializable; a: => select count(1) from table where id=1; --> 0 b: => select count(1) from table where id=1; --> 0 a: => insert into table values(1); --> 1 b: => insert into table values(1); --> ERROR: duplicate key value violates unique constraint "serial_test_pkey" Now I would expect it to throw the usual "couldn't commit due to concurrent update" but I'm guessing since the inserts are different "rows" this does not happen. Is there an easy way to work around this?

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  • Sql Server Maintenance Plan Tasks & Completion

    - by Ben
    Hi All, I have a maintenance plan that looks like this... Client 1 Import Data (Success) -> Process Data (Success) -> Post Process (Completion) -> Next Client Client 2 Import Data (Success) -> Process Data (Success) -> Post Process (Completion) -> Next Client Client N ... Import Data and Process Data are calling jobs and Post Process is an Execute Sql task. If Import Data or Process Data Fail, it goes to the next client Import Data... Both Import Data and Process Data are jobs that contain SSIS packages that are using the built-in SQL logging provider. My expectation with the configuration as it stands is: Client 1 Import Data Runs: Failure - Client 2 Import Data | Success Process Data Process Data Runs: Failure - Client 2 Import Data | Success Post Process Post Process Runs: Completion - Success or Failure - Next Client Import Data This isn't what I'm seeing in my logs though... I see several Client Import Data SSIS log entries, then several Post Process log entries, then back to Client Import Data! Arg!! What am I doing wrong? I didn't think the "success" piece of Client 1 Import Data would kick off until it... well... succeeded aka finished! The logs seem to indicate otherwise though... I really need these tasks to be consecutive not concurrent. Is this possible? Thanks!

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  • Log4Net GetLogger creates rolling files even for the unreferenced files

    - by ybastiand
    Hi, I have a C# solution that contains three executables. I have each of these three executables sharing the same log4net configuration file. At startup of each of the executable, they retrieve a logger (one logger per executable, as per configuration file further below). When one of the executable performs Log.GetLogger(), it creates all the rolling files instead of only the one rolling file that is referred to as appender-ref in the executable's logger configuration. For instance, when I startup my sending daemon executable, it performs Log.GetLogger("SendingDaemonLogger") which creates 3 files Log/RuleScheduler.txt, Log/NotificationGenerator.txt and Log/NotificationSender.txt instead of only the desired Log/NotificationSender.txt. Then when I startup another of the executables, for instance the rule scheduler daemon, this other process cannot write in Log/RuleScheduler.txt because it has been created and locked by the sending daemon process. I am guessing that there may be three different solutions to my problem: The GetLogger should only create the rolling file appenders that are referenced in the config I should have one config file per executable, this way each config file could list only one rolling file appender and starting each of the executable would not create the rolling files of the other daemons. I am however reluctant to do this because some of the configuration (SMTP appender, console appender) is shared between the daemons and I don't want to have duplicate copies to maintain. Unless there is a way to have a config file including another one? Maybe there is a way to configure the rolling file so that concurrent access across processes is allowed? This solution still isn't perfect in my opinion because any of the daemons should not be creating the rolling files of some other daemons. Thanks in advance for your help! I have difficulties for posting the config file properly here (this website interprets as HTML). Please go to the following link for seeing my log4net configuration file: log4Net configuration file

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  • Sending jQuery.ajax data simultaneous to a form submit

    - by dscher
    I have a bit of a conundrum. I have a form which has numerous fields. There is one field for links where you enter a link, click an add button, and the link(using jQuery) gets added to a link_array. I want this array to be sent via the jQuery.ajax method when the form is submitted. If I send the link_array using $.ajax like this: $.ajax({ type: "POST", url: "add_stock", dataType: "json", data: { "links": link_array } }); when the add link button is selected the data goes no problem to the correct place and gets put in the db correctly. If I bind the above function to the submit form button using $(#stock_form).submit(..... then the rest of the form data is sent but not the link_array. I can obviously pass the link array back into a hidden field in HTML but then I'd have to unpack the array into comma separate values and break the comma-separated string apart in PHP. It just seems 100X easier to unpack the Javascript array in PHP without an other fuss. So, how is it that you can send an array from javascript using $.ajax concurrent to the rest of the $_POST data in HTML? Please note that I'm using Kohana 3.0 framework but really that shouldn't make a difference, what I want to do is add this js array to the $_POST array that is already going. Thanks!

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  • Can't start the portable version of NetBeans 6.9.1 IDE

    - by Coder
    I downloaded the portable version of netbeans netbeans-6.9.1-201007282301-ml.zip from the netbeans site and changed the config file in etc/netbeans.conf as indicated on the netbeans site. The file contents are below. # ${HOME} will be replaced by JVM user.home system property #netbeans_default_userdir="${HOME}/.netbeans/6.9" netbeans_default_userdir=".netbeans/6.9" # Options used by NetBeans launcher by default, can be overridden by explicit # command line switches: netbeans_default_options="-J-client -J-Xss2m -J-Xms32m -J-XX:PermSize=32m -J-XX:MaxPermSize=200m -J-Dapple.laf.useScreenMenuBar=true -J-Dapple.awt.graphics.UseQuartz=true -J-Dsun.java2d.noddraw=true" # Note that a default -Xmx is selected for you automatically. # You can find this value in var/log/messages.log file in your userdir. # The automatically selected value can be overridden by specifying -J-Xmx here # or on the command line. # If you specify the heap size (-Xmx) explicitely, you may also want to enable # Concurrent Mark & Sweep garbage collector. In such case add the following # options to the netbeans_default_options: # -J-XX:+UseConcMarkSweepGC -J-XX:+CMSClassUnloadingEnabled -J-XX:+CMSPermGenSweepingEnabled # (see http://wiki.netbeans.org/wiki/view/FaqGCPauses) # Default location of JDK, can be overridden by using --jdkhome <dir>: #netbeans_jdkhome="/path/to/jdk" netbeans_jdkhome="C:\Program Files\Java\jdk1.6.0_24\" # Additional module clusters, using ${path.separator} (';' on Windows or ':' on Unix): #netbeans_extraclusters="/absolute/path/to/cluster1:/absolute/path/to/cluster2" # If you have some problems with detect of proxy settings, you may want to enable # detect the proxy settings provided by JDK5 or higher. # In such case add -J-Djava.net.useSystemProxies=true to the netbeans_default_options. But it refuses to start when i try to run it. If i change the JDK path to something incorrect it complains that it can't find the jdk so i think the jdk path is correct. It also creates a .netbeans directory when i try to start it. I don't see any errors and it just doesn't do anything else observable. Does anybody know how to set up this version of netbeans? Thanks.

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  • Design Decision - Scaling out web based application's architecture

    - by Vadi
    This question is about design decision. I am currently working on a web project that will have 40K users to start with and in couple of month expected to grow 50M users (not concurrent users though). I would like to have a architecture that can be scaled out easily without much effort. In order to explain, I would like to use a trivial scenario. Lets say, User entities and services such as CreateUser, AuthenticateUser etc., are a simple method calls for the Page Controllers. But once the traffic increases, for example, authenticating user (or such services related to user entities) has to be moved out to a different internal server to spread the load. But at the same time using RPC calls over the network when the user count is 40K would become overkill. My proposal was to use IPC initially and when we need to scale out we can interally switch to TCP based RPC calls so that it can easily scale out. For example, I am referring to System.IO.Pipes.NamedPipeStreamServer to start with and move on to a TcpListener later on. If we have proper design that can encapsulate above said approach, it would easy for us to scale out services into multiple network servers but at the same time avoid network calls when the user count is small. Is this is a best approach? Any suggestions would be great .. Note: The database scaling is definetly the second phase optimization so we have already made architectural design in place to easily partition data when traffic increases. The primary bottleneck would be application servers over the time period.

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  • Trying to randomise a jQuery content slider

    - by alecrust
    Hi everyone, I'm using a very nice jQuery content slider called Easy Slider on my site that I downloaded from Css Globe. The script is excellent and does just what I want - except I can't make it randomise the list, it always scrolls from left to right or right to left! I'm far from good with JavaScript, so my attempts at solving this have been feeble. Although I'm sure it must be an easy fix! If anyone wouldn't mind taking a glance over the script to see if they can spot what I need to change to make it random it would be greatly appreciated! I've tried contacting the original plugin developer but have had no response yet. The comments on the Easy Slider page didn't bear much fruit either unfortunately. I've pasted the script I'm using on my site below: /* * Easy Slider 1.7 - jQuery plugin * written by Alen Grakalic * http://cssglobe.com/post/4004/easy-slider-15-the-easiest-jquery-plugin-for-sliding * * Copyright (c) 2009 Alen Grakalic (http://cssglobe.com) * Dual licensed under the MIT (MIT-LICENSE.txt) * and GPL (GPL-LICENSE.txt) licenses. * * Built for jQuery library * http://jquery.com * */ (function($) { $.fn.easySlider = function(options){ // default configuration properties var defaults = { prevId: 'prevBtn', prevText: 'Previous', nextId: 'nextBtn', nextText: 'Next', controlsShow: true, controlsBefore: '', controlsAfter: '', controlsFade: true, firstId: 'firstBtn', firstText: 'First', firstShow: false, lastId: 'lastBtn', lastText: 'Last', lastShow: false, vertical: false, speed: 800, auto: false, pause: 7000, continuous: false, numeric: false, numericId: 'controls' }; var options = $.extend(defaults, options); this.each(function() { var obj = $(this); var s = $("li", obj).length; var w = $("li", obj).width(); var h = $("li", obj).height(); var clickable = true; obj.width(w); obj.height(h); obj.css("overflow","hidden"); var ts = s-1; var t = 0; $("ul", obj).css('width',s*w); if(options.continuous){ $("ul", obj).prepend($("ul li:last-child", obj).clone().css("margin-left","-"+ w +"px")); $("ul", obj).append($("ul li:nth-child(2)", obj).clone()); $("ul", obj).css('width',(s+1)*w); }; if(!options.vertical) $("li", obj).css('float','left'); if(options.controlsShow){ var html = options.controlsBefore; if(options.numeric){ html += '<ol id="'+ options.numericId +'"></ol>'; } else { if(options.firstShow) html += '<span id="'+ options.firstId +'"><a href=\"javascript:void(0);\">'+ options.firstText +'</a></span>'; html += ' <span id="'+ options.prevId +'"><a href=\"javascript:void(0);\">'+ options.prevText +'</a></span>'; html += ' <span id="'+ options.nextId +'"><a href=\"javascript:void(0);\">'+ options.nextText +'</a></span>'; if(options.lastShow) html += ' <span id="'+ options.lastId +'"><a href=\"javascript:void(0);\">'+ options.lastText +'</a></span>'; }; html += options.controlsAfter; $(obj).after(html); }; if(options.numeric){ for(var i=0;i<s;i++){ $(document.createElement("li")) .attr('id',options.numericId + (i+1)) .html('<a rel='+ i +' href=\"javascript:void(0);\">'+ (i+1) +'</a>') .appendTo($("#"+ options.numericId)) .click(function(){ animate($("a",$(this)).attr('rel'),true); }); }; } else { $("a","#"+options.nextId).click(function(){ animate("next",true); }); $("a","#"+options.prevId).click(function(){ animate("prev",true); }); $("a","#"+options.firstId).click(function(){ animate("first",true); }); $("a","#"+options.lastId).click(function(){ animate("last",true); }); }; function setCurrent(i){ i = parseInt(i)+1; $("li", "#" + options.numericId).removeClass("current"); $("li#" + options.numericId + i).addClass("current"); }; function adjust(){ if(t>ts) t=0; if(t<0) t=ts; if(!options.vertical) { $("ul",obj).css("margin-left",(t*w*-1)); } else { $("ul",obj).css("margin-left",(t*h*-1)); } clickable = true; if(options.numeric) setCurrent(t); }; function animate(dir,clicked){ if (clickable){ clickable = false; var ot = t; switch(dir){ case "next": t = (ot>=ts) ? (options.continuous ? t+1 : ts) : t+1; break; case "prev": t = (t<=0) ? (options.continuous ? t-1 : 0) : t-1; break; case "first": t = 0; break; case "last": t = ts; break; default: t = dir; break; }; var diff = Math.abs(ot-t); var speed = diff*options.speed; if(!options.vertical) { p = (t*w*-1); $("ul",obj).animate( { marginLeft: p }, { queue:false, duration:speed, complete:adjust } ); } else { p = (t*h*-1); $("ul",obj).animate( { marginTop: p }, { queue:false, duration:speed, complete:adjust } ); }; if(!options.continuous && options.controlsFade){ if(t==ts){ $("a","#"+options.nextId).hide(); $("a","#"+options.lastId).hide(); } else { $("a","#"+options.nextId).show(); $("a","#"+options.lastId).show(); }; if(t==0){ $("a","#"+options.prevId).hide(); $("a","#"+options.firstId).hide(); } else { $("a","#"+options.prevId).show(); $("a","#"+options.firstId).show(); }; }; if(clicked) clearTimeout(timeout); if(options.auto && dir=="next" && !clicked){; timeout = setTimeout(function(){ animate("next",false); },diff*options.speed+options.pause); }; }; }; // init var timeout; if(options.auto){; timeout = setTimeout(function(){ animate("next",false); },options.pause); }; if(options.numeric) setCurrent(0); if(!options.continuous && options.controlsFade){ $("a","#"+options.prevId).hide(); $("a","#"+options.firstId).hide(); }; }); }; })(jQuery); Many thanks again! Alec

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  • Cache consistency & spawning a thread

    - by Dave Keck
    Background I've been reading through various books and articles to learn about processor caches, cache consistency, and memory barriers in the context of concurrent execution. So far though, I have been unable to determine whether a common coding practice of mine is safe in the strictest sense. Assumptions The following pseudo-code is executed on a two-processor machine: int sharedVar = 0; myThread() { print(sharedVar); } main() { sharedVar = 1; spawnThread(myThread); sleep(-1); } main() executes on processor 1 (P1), while myThread() executes on P2. Initially, sharedVar exists in the caches of both P1 and P2 with the initial value of 0 (due to some "warm-up code" that isn't shown above.) Question Strictly speaking – preferably without assuming any particular CPU – is myThread() guaranteed to print 1? With my newfound knowledge of processor caches, it seems entirely possible that at the time of the print() statement, P2 may not have received the invalidation request for sharedVar caused by P1's assignment in main(). Therefore, it seems possible that myThread() could print 0. References These are the related articles and books I've been reading. (It wouldn't allow me to format these as links because I'm a new user - sorry.) Shared Memory Consistency Models: A Tutorial hpl.hp.com/techreports/Compaq-DEC/WRL-95-7.pdf Memory Barriers: a Hardware View for Software Hackers rdrop.com/users/paulmck/scalability/paper/whymb.2009.04.05a.pdf Linux Kernel Memory Barriers kernel.org/doc/Documentation/memory-barriers.txt Computer Architecture: A Quantitative Approach amazon.com/Computer-Architecture-Quantitative-Approach-4th/dp/0123704901/ref=dp_ob_title_bk

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  • Ideas for multiplatform encrypted java mobile storage system

    - by Fernando Miguélez
    Objective I am currently designing the API for a multiplatform storage system that would offer same interface and capabilities accross following supported mobile Java Platforms: J2ME. Minimum configuration/profile CLDC 1.1/MIDP 2.0 with support for some necessary JSRs (JSR-75 for file storage). Android. No minimum platform version decided yet, but rather likely could be API level 7. Blackberry. It would use the same base source of J2ME but taking advantage of some advaced capabilities of the platform. No minimum configuration decided yet (maybe 4.6 because of 64 KB limitation for RMS on 4.5). Basically the API would sport three kind of stores: Files. These would allow standard directory/file manipulation (read/write through streams, create, mkdir, etc.). Preferences. It is a special store that handles properties accessed through keys (Similar to plain old java properties file but supporting some improvements such as different value data types such as SharedPreferences on Android platform) Local Message Queues. This store would offer basic message queue functionality. Considerations Inspired on JSR-75, all types of stores would be accessed in an uniform way by means of an URL following RFC 1738 conventions, but with custom defined prefixes (i.e. "file://" for files, "prefs://" for preferences or "queue://" for message queues). The address would refer to a virtual location that would be mapped to a physical storage object by each mobile platform implementation. Only files would allow hierarchical storage (folders) and access to external extorage memory cards (by means of a unit name, the same way as in JSR-75, but that would not change regardless of underlying platform). The other types would only support flat storage. The system should also support a secure version of all basic types. The user would indicate it by prefixing "s" to the URL (i.e. "sfile://" instead of "file://"). The API would only require one PIN (introduced only once) to access any kind of secure object types. Implementation issues For the implementation of both plaintext and encrypted stores, I would use the functionality available on the underlying platforms: Files. These are available on all platforms (J2ME only with JSR-75, but it is mandatory for our needs). The abstract File to actual File mapping is straight except for addressing issues. RMS. This type of store available on J2ME (and Blackberry) platforms is convenient for Preferences and maybe Message Queues (though depending on performance or size requirements these could be implemented by means of normal files). SharedPreferences. This type of storage, only available on Android, would match Preferences needs. SQLite databases. This could be used for message queues on Android (and maybe Blackberry). When it comes to encryption some requirements should be met: To ease the implementation it will be carried out on read/write operations basis on streams (for files), RMS Records, SharedPreferences key-value pairs, SQLite database columns. Every underlying storage object should use the same encryption key. Handling of encrypted stores should be the same as the unencrypted counterpart. The only difference (from the user point of view) accessing an encrypted store would be the addressing. The user PIN provides access to any secure storage object, but the change of it would not require to decrypt/re-encrypt all the encrypted data. Cryptographic capabilities of underlying platform should be used whenever it is possible, so we would use: J2ME: SATSA-CRYPTO if it is available (not mandatory) or lightweight BoncyCastle cryptographic framework for J2ME. Blackberry: RIM Cryptographic API or BouncyCastle Android: JCE with integraced cryptographic provider (BouncyCastle?) Doubts Having reached this point I was struck by some doubts about what solution would be more convenient, taking into account the limitation of the plataforms. These are some of my doubts: Encryption Algorithm for data. Would AES-128 be strong and fast enough? What alternatives for such scenario would you suggest? Encryption Mode. I have read about the weakness of ECB encryption versus CBC, but in this case the first would have the advantage of random access to blocks, which is interesting for seek functionality on files. What type of encryption mode would you choose instead? Is stream encryption suitable for this case? Key generation. There could be one key generated for each storage object (file, RMS RecordStore, etc.) or just use one for all the objects of the same type. The first seems "safer", though it would require some extra space on device. In your opinion what would the trade-offs of each? Key storage. For this case using a standard JKS (or PKCS#12) KeyStore file could be suited to store encryption keys, but I could also define a smaller structure (encryption-transformation / key data / checksum) that could be attached to each storage store (i.e. using addition files with the same name and special extension for plain files or embedded inside other types of objects such as RMS Record Stores). What approach would you prefer? And when it comes to using a standard KeyStore with multiple-key generation (given this is your preference), would it be better to use a record-store per storage object or just a global KeyStore keeping all keys (i.e. using the URL identifier of abstract storage object as alias)? Master key. The use of a master key seems obvious. This key should be protected by user PIN (introduced only once) and would allow access to the rest of encryption keys (they would be encrypted by means of this master key). Changing the PIN would only require to reencrypt this key and not all the encrypted data. Where would you keep it taking into account that if this got lost all data would be no further accesible? What further considerations should I take into account? Platform cryptography support. Do SATSA-CRYPTO-enabled J2ME phones really take advantage of some dedicated hardware acceleration (or other advantage I have not foreseen) and would this approach be prefered (whenever possible) over just BouncyCastle implementation? For the same reason is RIM Cryptographic API worth the license cost over BouncyCastle? Any comments, critics, further considerations or different approaches are welcome.

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  • Starting with versioning mysql schemata without overkill. Good solutions?

    - by tharkun
    I've arrived at the point where I realise that I must start versioning my database schemata and changes. I consequently read the existing posts on SO about that topic but I'm not sure how to proceed. I'm basically a one man company and not long ago I didn't even use version control for my code. I'm on a windows environment, using Aptana (IDE) and SVN (with Tortoise). I work on PHP/mysql projects. What's a efficient and sufficient (no overkill) way to version my database schemata? I do have a freelancer or two in some projects but I don't expect a lot of branching and merging going on. So basically I would like to keep track of concurrent schemata to my code revisions. [edit] Momentary solution: for the moment I decided I will just make a schema dump plus one with the necessary initial data whenever I'm going to commit a tag (stable version). That seems to be just enough for me at the current stage.[/edit] [edit2]plus I'm now also using a third file called increments.sql where I put all the changes with dates, etc. to make it easy to trace the change history in one file. from time to time I integrate the changes into the two other files and empty the increments.sql[/edit]

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  • Advice on a DB that can be uploaded to a website by a smart client for collecting survey feedback

    - by absfabs
    Hello, I'm hoping you can help. I'm looking for a zero config multi-user datbase that my winforms application can easily upload to a webserver folder (together with 1 or 2 classic asp pages) and am looking for some suggestions/recommendations. The idea is that the database will be used to collect feedback entered by people filling in the asp pages. The pages will write to the database using javascript. The database will subsequently be downloaded again for processing once the responses are in. In Summary: It will mostly run in MS Windows environments. I have a modest budget for this and do not mind paying for such a database. No runtime licensing costs. Should be xcopy - Once uploaded to a website folder it should be operational. It should not have a dotnet CLR dependency. It should support a resonable level of concurrent access. Average respondent count would be around 20-30 but one never knows. Should be a reasonable size so that uploads/downloads to and from the site will be reasonably fast. Would appreciate your suggestions/comments Many thanks Abz To clarify - this is a desktop commercial application for feedback management in a vertical market. It uses SQL Server as the backing store. The application currently provides feedback management from email and paper feedback. I now want to add web feedback capability. Getting users to to make their SQL servers accessible to a website is not at option at this time as I am want to make getting up and running as painless as possible. I intend to release a web based implementation of the software in the near future but for now am looking at the above as a pragmatic way to provide web based feedback collection.

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  • what libraries or platforms should I use to build web apps that provide real-time, asynchronous data

    - by Daniel Sterling
    This is a less a question with a simple, practical answer and more a question to foster discussion on the real-time data exchange topic. I'll begin with an example: Google Wave is, at its core, a real-time asynchronous data synchronization engine. Wave supports (or plans to support) concurrent (real-time) document collaboration, disconnected (offline) document editing, conflict resolution, document history and playback with attribution, and server federation. A core part of Wave is the Operational Transformation engine: http://www.waveprotocol.org/whitepapers/operational-transform The OT engine manages document state. Changes between clients are merged and each client has a sane and consistent view of the document at all times; the final document is eventually consistent between all connected clients. My question is: is this system abstract or general enough to be used as a library or generic framework upon which to build web apps that synchronize real-time, asynchronous state in each client? Is the Wave protocol directly used by any current web applications (besides Google's client)? Would it make sense to directly use it for generic state synchronization in a web app? What other existing libraries or frameworks would you consider using when building such a web app? How much code in such an app might be domain-specific logic vs generic state synchronization logic? Or, put another way, how leaky might the state synchronization abstractions be? Comments and discussion welcomed!

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  • SQL Server 2000 intermittent connection exceptions on production server - specific environment probl

    - by StickyMcGinty
    We've been having intermittent problems causing users to be forcibly logged out of out application. Our set-up is ASP.Net/C# web application on Windows Server 2003 Standard Edition with SQL Server 2000 on the back end. We've recently performed a major product upgrade on our client's VMWare server (we have a guest instance dedicated to us) and whereas we had none of these issues with the previous release the added complexity that the new upgrade brings to the product has caused a lot of issues. We are also running SQL Server 2000 (build 8.00.2039, or SP4) and the IIS/ASP.NET (.Net v2.0.50727) application on the same box and connecting to each other via a TCP/IP connection. Primarily, the exceptions being thrown are: System.IndexOutOfRangeException: Cannot find table 0. System.ArgumentException: Column 'password' does not belong to table Table. [This exception occurs in the log in script, even though there is clearly a password column available] System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first. [This one is occurring very regularly] System.InvalidOperationException: This SqlTransaction has completed; it is no longer usable. System.ApplicationException: ExecuteReader requires an open and available Connection. The connection's current state is connecting. System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. And just today, for the first time: System.Web.UI.ViewStateException: Invalid viewstate. We have load tested the app using the same number of concurrent users as the production server and cannot reproduce these errors. They are very intermittent and occur even when there are only 8/9/10 user connections. My gut is telling me its ASP.NET - SQL Server 2000 connection issues.. We've pretty much ruled out code-level Data Access Layer errors at this stage (we've a development team of 15 experienced developers working on this) so we think its a specific production server environment issue.

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  • Biztalk vs API for databroker layer

    - by jdt199
    My company is about to undergo a large project in which our client wants a large customer portal with a cms, crm implementing. This will require interaction with data from multiple sources across our customers business, these sources include XML office backend systems, sql datbases, webservices etc. Our proposed solution would be to write an API in c# to provide a common interface with all these systems. This would be scalable for future and concurrent projects within the company. Our client expressed an interest in using Biztalk rather than a custom API for this integration, as they feel it is an enterprise solution that any of their suppliers could pick up and use, and it will be better supported. We feel that the configuration work using Biztalk would be rather heavy for all their custom business rules which are required and an interface for the new application to get data to and from Biztalk would still need to be written. Are we right to prefer a custom API solution above Biztalk? Would Biztalk be suitable as a databroker layer to provide an interface for the new Customer portal we are writing. We have not experience with using Biztalk before so any input would be appreciated.

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  • Load Spikes on a Apache MySQL Server with Wordpress MU

    - by Vikram Goyal
    Hi there, I am trying to investigate the reasons for some mysterious load spikes on a Linux Apache server (2.2.14) running PHP 5.2.9 on a dedicated server with enough processing power and memory. My primary web application is a Wordpress MU (2.9.2) installation. I have investigated and ruled out DOS attack, MySQL or Apache configuration issues. The log files don't give me anything of interest, except to tell me that there is severe load. The load (which can go up to 100) just seems to come and go. It helps that I have a script that checks every 3 minutes for the load, and restarts Apache. Restarting it helps, and the server comes back, till it happens again. There seems to be no set time frame, or visitor numbers on the site that can trigger this. Even a low number of concurrent visitors (20) can trigger it. I am almost convinced that there is a rewrite loop somewhere that is causing Apache to go mad. Apache is trying to serve something that is causing it to spawn more and more processes till it keels over. My question is: Given that I am convinced that this is a rewrite issue or something similar, how can I try and figure out what the issue is? What should I monitor? Apache logs are voluminous, and not very helpful. Of course, if this is not the issue, then at least knowing what to look for will help me eliminate this as an issue and look for something else. Thanks! Vikram

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  • A linked list with multiple heads in Java

    - by Emile
    Hi, I have a list in which I'd like to keep several head pointers. I've tried to create multiple ListIterators on the same list but this forbid me to add new elements in my list... (see Concurrent Modification exception). I could create my own class but I'd rather use a built-in implementation ;) To be more specific, here is an inefficient implementation of two basic operations and the one wich doesn't work : class MyList <E { private int[] _heads; private List<E _l; public MyList ( int nbHeads ) { _heads = new int[nbHeads]; _l = new LinkedList<E(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { return _l.get(_heads[head++]); // ugly } } class MyList <E { private Vector<ListIterator<E _iters; private List<E _l; public MyList ( int nbHeads ) { _iters = new Vector<ListIterator<E(nbHeads); _l = new LinkedList<E(); for( ListIterator<E iter : _iters ) iter = _l.listIterator(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { // ConcurrentModificationException because of the add() return _iters.get(head).next(); } } Emile

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  • Optimizing processing and management of large Java data arrays

    - by mikera
    I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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  • I am confused -- Will this code always work?

    - by Shekhar
    Hello, I have written this piece of code public class Test{ public static void main(String[] args) { List<Integer> list = new ArrayList<Integer>(); for(int i = 1;i<= 4;i++){ new Thread(new TestTask(i, list)).start(); } while(list.size() != 4){ // this while loop required so that all threads complete their work } System.out.println("List "+list); } } class TestTask implements Runnable{ private int sequence; private List<Integer> list; public TestTask(int sequence, List<Integer> list) { this.sequence = sequence; this.list = list; } @Override public void run() { list.add(sequence); } } This code works and prints all the four elements of list on my machine. My question is that will this code always work. I think there might be a issue in this code when two/or more threads add element to this list at the same point. In that case it while loop will never end and code will fail. Can anybody suggest a better way to do this? I am not very good at multithreading and don't know which concurrent collection i can use? Thanks Shekhar

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  • Atomic int writes on file

    - by Waneck
    Hello! I'm writing an application that will have to be able to handle many concurrent accesses to it, either by threads as by processes. So no mutex'es or locks should be applied to this. To make the use of locks go down to a minimum, I'm designing for the file to be "append-only", so all data is first appended to disk, and then the address pointing to the info it has updated, is changed to refer to the new one. So I will need to implement a small lock system only to change this one int so it refers to the new address. How is the best way to do it? I was thinking about maybe putting a flag before the address, that when it's set, the readers will use a spin lock until it's released. But I'm afraid that it isn't at all atomic, is it? e.g. a reader reads the flag, and it is unset on the same time, a writer writes the flag and changes the value of the int the reader may read an inconsistent value! I'm looking for locking techniques but all I find is either for thread locking techniques, or to lock an entire file, not fields. Is it not possible to do this? How do append-only databases handle this? Thanks! Cauê

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