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• Did they remove the automatic user authentication from liftweb 2.0 snapshot?

  - by Uruhara747

  I just started a liftweb project and decided to go version 2.0 and it didn't seem to generate. Though I could be missing something.

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• Hyper-V snapshot backup strategy appropriate for production SQL server?

  - by Chuck

  So SQL Server 2008 in Hyper-V is a supported configuration, and should perform well as long as you use fixed or pass-through disks and increase your processor/memory settings appropriately. My question is can I use snapshots as a reliable backup mechanism, or should I use the tried and trusted maintenance plan to do my backups?

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• How to current snapshot of MySQL Table and store it into CSV file(after creating it) ?

  - by Rachel

  I have large database table, approximately 5GB, now I wan to getCurrentSnapshot of Database using "Select * from MyTableName", am using PDO in PHP to interact with Database. So preparing a query and then executing it // Execute the prepared query $result->execute(); $resultCollection = $result->fetchAll(PDO::FETCH_ASSOC); is not an efficient way as lots of memory is being user for storing into the associative array data which is approximately, 5GB. My final goal is to collect data returned by Select query into an CSV file and put CSV file at an FTP Location from where Client can get it. Other Option I thought was to do: SELECT * INTO OUTFILE "c:/mydata.csv" FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY "\n" FROM my_table; But I am not sure if this would work as I have cron that initiates the complete process and we do not have an csv file, so basically for this approach, PHP Scripts will have to create an CSV file. Do a Select query on the database. Store the select query result into the CSV file. What would be the best or efficient way to do this kind of task ? Any Suggestions !!!

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• ANTS CLR and Memory Profiler In Depth Review (Part 2 of 2 &ndash; Memory Profiler)

  - by ToStringTheory

  One of the things that people might not know about me, is my obsession to make my code as efficient as possible. Many people might not realize how much of a task or undertaking that this might be, but it is surely a task as monumental as climbing Mount Everest, except this time it is a challenge for the mind… In trying to make code efficient, there are many different factors that play a part – size of project or solution, tiers, language used, experience and training of the programmer, technologies used, maintainability of the code – the list can go on for quite some time. I spend quite a bit of time when developing trying to determine what is the best way to implement a feature to accomplish the efficiency that I look to achieve. One program that I have recently come to learn about – Red Gate ANTS Performance (CLR) and Memory profiler gives me tools to accomplish that job more efficiently as well. In this review, I am going to cover some of the features of the ANTS memory profiler set by compiling some hideous example code to test against. Notice As a member of the Geeks With Blogs Influencers program, one of the perks is the ability to review products, in exchange for a free license to the program. I have not let this affect my opinions of the product in any way, and Red Gate nor Geeks With Blogs has tried to influence my opinion regarding this product in any way. Introduction – Part 2 In my last post, I reviewed the feature packed Red Gate ANTS Performance Profiler.  Separate from the Red Gate Performance Profiler is the Red Gate ANTS Memory Profiler – a simple, easy to use utility for checking how your application is handling memory management…  A tool that I wish I had had many times in the past.  This post will be focusing on the ANTS Memory Profiler and its tool set. The memory profiler has a large assortment of features just like the Performance Profiler, with the new session looking nearly exactly alike: ANTS Memory Profiler Memory profiling is not something that I have to do very often…  In the past, the few cases I’ve had to find a memory leak in an application I have usually just had to trace the code of the operations being performed to look for oddities…  Sadly, I have come across more undisposed/non-using’ed IDisposable objects, usually from ADO.Net than I would like to ever see.  Support is not fun, however using ANTS Memory Profiler makes this task easier.  For this round of testing, I am going to use the same code from my previous example, using the WPF application. This time, I will choose the ‘Profile Memory’ option from the ANTS menu in Visual Studio, which launches the solution in its currently configured state/start-up project, and then launches the ANTS Memory Profiler to help.  It prepopulates all of the fields with the current project information, and all I have to do is select the ‘Start Profiling’ option. When the window comes up, it is actually quite barren, just giving ideas on how to work the profiler.  You start by getting to the point in your application that you want to profile, and then taking a ‘Memory Snapshot’.  This performs a full garbage collection, and snapshots the managed heap.  Using the same WPF app as before, I will go ahead and take a snapshot now. As you can see, ANTS is already giving me lots of information regarding the snapshot, however this is just a snapshot.  The whole point of the profiler is to perform an action, usually one where a memory problem is being noticed, and then take another snapshot and perform a diff between them to see what has changed.  I am going to go ahead and generate 5000 primes, and then take another snapshot: As you can see, ANTS is already giving me a lot of new information about this snapshot compared to the last.  Information such as difference in memory usage, fragmentation, class usage, etc…  If you take more snapshots, you can use the dropdown at the top to set your actual comparison snapshots. If you beneath the timeline, you will see a breadcrumb trail showing how best to approach profiling memory using ANTS.  When you first do the comparison, you start on the Summary screen.  You can either use the charts at the bottom, or switch to the class list screen to get to the next step.  Here is the class list screen: As you can see, it lists information about all of the instances between the snapshots, as well as at the bottom giving you a way to filter by telling ANTS what your problem is.  I am going to go ahead and select the Int16[] to look at the Instance Categorizer Using the instance categorizer, you can travel backwards to see where all of the instances are coming from.  It may be hard to see in this image, but hopefully the lightbox (click on it) will help: I can see that all of these instances are rooted to the application through the UI TextBlock control.  This image will probably be even harder to see, however using the ‘Instance Retention Graph’, you can trace an objects memory inheritance up the chain to see its roots as well.  This is a simple example, as this is simply a known element.  Usually you would be profiling an actual problem, and comparing those differences.  I know in the past, I have spotted a problem where a new context was created per page load, and it was rooted into the application through an event.  As the application began to grow, performance and reliability problems started to emerge.  A tool like this would have been a great way to identify the problem quickly. Overview Overall, I think that the Red Gate ANTS Memory Profiler is a great utility for debugging those pesky leaks.  3 Biggest Pros: Easy to use interface with lots of options for configuring profiling session Intuitive and helpful interface for drilling down from summary, to instance, to root graphs ANTS provides an API for controlling the profiler. Not many options, but still helpful. 2 Biggest Cons: Inability to automatically snapshot the memory by interval Lack of complete integration with Visual Studio via an extension panel Ratings Ease of Use (9/10) – I really do believe that they have brought simplicity to the once difficult task of memory profiling.  I especially liked how it stepped you further into the drilldown by directing you towards the best options. Effectiveness (10/10) – I believe that the profiler does EXACTLY what it purports to do.  Features (7/10) – A really great set of features all around in the application, however, I would like to see some ability for automatically triggering snapshots based on intervals or framework level items such as events. Customer Service (10/10) – My entire experience with Red Gate personnel has been nothing but good.  their people are friendly, helpful, and happy! UI / UX (9/10) – The interface is very easy to get around, and all of the options are easy to find.  With a little bit of poking around, you’ll be optimizing Hello World in no time flat! Overall (9/10) – Overall, I am happy with the Memory Profiler and its features, as well as with the service I received when working with the Red Gate personnel.  Thank you for reading up to here, or skipping ahead – I told you it would be shorter!  Please, if you do try the product, drop me a message and let me know what you think!  I would love to hear any opinions you may have on the product. Code Feel free to download the code I used above – download via DropBox

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• Return an opaque object to the caller without violating type-safety

  - by JS Bangs

  I have a method which should return a snapshot of the current state, and another method which restores that state. public class MachineModel { public Snapshot CurrentSnapshot { get; } public void RestoreSnapshot (Snapshot saved) { /* etc */ }; } The state Snapshot class should be completely opaque to the caller--no visible methods or properties--but its properties have to be visible within the MachineModel class. I could obviously do this by downcasting, i.e. have CurrentSnapshot return an object, and have RestoreSnapshot accept an object argument which it casts back to a Snapshot. But forced casting like that makes me feel dirty. What's the best alternate design that allows me to be both type-safe and opaque?

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• VirtualBox snapshots

  - by CodeMedic

  Heres what happened. I had a snapshot on which I was working from within a linux VM. A friend requested a clean VM as a clone of mine. So I closed / shutdown my running VM, made a copy of the Disk1.vdi along with the snapshots ({uuid}.vdi). Then I restarted the VM and did merged snapshots, deleted my home directory and made a tar+bz2 for my friend. Then after I restored my backups, I am not able to mount my snapshot. The VM seems to boot from my version before snapshot. I cant seem to find a way to mount back my snapshot. Any idea how to make VirtualBox see the snapshot and mount it?

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• How should I define Pom.xml in each Module so that web module can communicate with the other two ejb modules?

  - by Kayser

  Maven, maven, maven. It must be very nice and it is nice by a small application. Now I want to build an ear project: with two EJB Modules, a web Module and ear module to build an ear file. Web Module is dependent on the other ejb modules.. How should I define Pom.xml in each Module so that web module can communicate with the other two ejb modules in ear and the ear module builds the right ear file? What I have done before: Module 1 -- Basic Module. All other modules are dependent to this Module. Basic functionality like login etc. <packaging>ejb</packaging> Module 1 -- Data Module. All Entites are here Type EJB <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_Basic</artifactId> <version>0.0.1-SNAPSHOT</version> <type>ejb</type> </dependency Module 2 -- Business Module. Businnes Facades are here. Type EJB <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_Basic</artifactId> <version>0.0.1-SNAPSHOT</version> <type>ejb</type> </dependency Web Module - Type is WAR <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_Basic</artifactId> <version>0.0.1-SNAPSHOT</version> <type>ejb</type> </dependency EAR Module -- In this project I try to build the project. <packaging>ear</packaging> <dependencies> <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_Basic</artifactId> <version>0.0.1-SNAPSHOT</version> <type>ejb</type> </dependency <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_Business</artifactId> <version>0.0.1-SNAPSHOT</version> <type>ejb</type> </dependency <dependency> <groupId>com.myCompnay</groupId> <artifactId>Modul_WEB</artifactId> <version>0.0.1-SNAPSHOT</version> <type>war</type> </dependency </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-ear-plugin</artifactId> </plugin> </plugins> </build>

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• Maven error: Unable to get resource / Server redirected too many times

  - by tewe

  Our proxy went down and I tried to update dependencies with maven while it was off. Since then I can't download anything with maven. I get this error for everything. I tried -U option, deleting my local repository and tried different maven version (2.0.9, 2.2.1) but it doesn't work. Any idea how to solve this? Earlier it also said 'repository will be blacklisted' to all of them. Downloading: http://repo1.maven.org/maven2/org/apache/maven/plugins/maven-compiler-plugin/2.1/maven-compiler-plugin-2.1.pom [WARNING] Unable to get resource 'org.apache.maven.plugins:maven-compiler-plugin:pom:2.1' from repository central (http://repo1.maven.org/maven2): Error transferring file: Server redirected too many times (20) org.apache.maven.plugins:maven-compiler-plugin:pom:2.1 from the specified remote repositories: jboss-snapshot (http://snapshots.jboss.org/maven2), central (http://repo1.maven.org/maven2), JBoss Repo (http://repository.jboss.com/maven2), spring-maven-snapshot (http://maven.springframework.org/snapshot), com.springsource.repository.bundles.external (http://repository.springsource.com/maven/bundles/external), com.springsource.repository.bundles.snapshot (http://repository.springsource.com/maven/bundles/snapshot), jboss (http://repository.jboss.com/maven2), com.springsource.repository.bundles.release (http://repository.springsource.com/maven/bundles/release), jboss-snapshot-plugins (http://snapshots.jboss.org/maven2), com.springsource.repository.bundles.milestone (http://repository.springsource.com/maven/bundles/milestone), jboss-plugins (http://repository.jboss.com/maven2) at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:228) at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:90) at org.apache.maven.project.DefaultMavenProjectBuilder.findModelFromRepository(DefaultMavenProjectBuilder.java:558) ... 25 more Caused by: org.apache.maven.wagon.ResourceDoesNotExistException: Unable to download the artifact from any repository at org.apache.maven.artifact.manager.DefaultWagonManager.getArtifact(DefaultWagonManager.java:404) at org.apache.maven.artifact.resolver.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:216) ... 27 more

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• Maven String Replace of Text Web Resources

  - by Jaco van Niekerk

  I have a Maven web application with text files in src/main/webapp/textfilesdir As I understand it, during the package phase this textfilesdir directory will be copied into the target/project-1.0-SNAPSHOT directory, which is then zipped up into a target/project-1.0-SNAPSHOT.war Problem Now, I need to do a string replacement on the contents of the text files in target/project-1.0-SNAPSHOT/textfilesdir. This must then be done after the textfilesdir is copied into target/project-1.0-SNAPSHOT, but prior to the target/project-1.0-SNAPSHOT.war file being created. I believe this is all done during the package phase. How can a plugin (potentially maven-antrun-plugin), plug into the package phase to do this. The text files don't contain properties, like ${property-name} to filter on. String replacement is likely the only option. Options Modify the text files after the copy into target/project-1.0-SNAPSHOT directory, yet prior to the WAR creation. After packaging, extract the text files from WAR, modify them, and add them back into the WAR. I'm thinking there is another option here I'm missing. Thoughts anyone?

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• ANTS Memory Profiler 7.0

  - by Sam Abraham

  In the next few lines, I would like to briefly review ANTS Memory Profiler 7.0.  I was honored to be extended the opportunity to review this valuable tool as part of the GeeksWithBlogs influencers Program, a quarterly award providing its recipients access to valuable tools and enabling them with an opportunity to provide a brief write-up reviewing the complimentary tools they receive.   Typical Usage   ANTS Memory Profiler 7.0 is very intuitive and easy to use for any user be it novice or expert. A simple yet comprehensive menu screen enables the selection of the appropriate program type to profile as well as the executable or site for this program.   A typical use case starts with establishing a baseline memory snapshot, which tells us the initial memory cost used by the program under normal or low activity conditions. We would then take a second snapshot after the program has performed an activity which we want to investigate for memory leaks. We can then compare the initial baseline snapshot against the snapshot when the program has completed processing the activity in question to study anomalies in memory that did not get freed-up after the program has completed its performed function. The following are some screenshots outlining the selection of the program to profile (an executable for this demonstration’s purposes).   Figure 1 - Getting Started   Figure 2 - Selecting an Application to Profile     Features and Options   Right after the second snapshot is generated, Memory Profiler gives us immediate access to information on memory fragmentation, size differences between snapshots, unmanaged memory allocation and statistics on the largest classes taking up un-freed memory space.   We would also have the option to itemize objects held in memory grouped by object types within which we can study the instances allocated of each type. Filtering options enable us to quickly narrow object instances we are interested in.   Figure 3 - Easily accessible Execution Memory Information   Figure 4 - Class List   Figure 5 - Instance List   Figure 6-  Retention Graph for a Particular Instance   Conclusion I greatly enjoyed the opportunity to evaluate ANTS Memory Profiler 7.0. The tool's intuitive User Interface design and easily accessible menu options enabled me to quickly identify problem areas where memory was left unfreed in my code.     Tutorials and References  FInd out more About ANTS Memory Profiler 7.0 http://www.red-gate.com/supportcenter/Product?p=ANTS Memory Profiler   Checkout what other reviewers of this valuable tool have already shared: http://geekswithblogs.net/BlackRabbitCoder/archive/2011/03/10/ants-memory-profiler-7.0.aspx http://geekswithblogs.net/mikebmcl/archive/2011/02/28/ants-memory-profiler-7.0-review.aspx

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• Maven mercurial extension constantly fails

  - by TheLQ

  After 2+ hours I was able to get the maven-scm-provider-hg extension (for pushing to mercurial repos from Maven) semi working, meaning that it was executing commands instead of just giving errors. However I think I've run into a wall with this error [INFO] [deploy:deploy {execution: default-deploy}] [INFO] Retrieving previous build number from pircbotx.googlecode.com [INFO] Removing C:\DOCUME~1\Owner\LOCALS~1\Temp\wagon-scm1210107000.checkout\pir cbotx\pircbotx\1.3-SNAPSHOT [INFO] EXECUTING: cmd.exe /X /C "hg clone -r tip https://*SNIP*@site.pircbotx.googlecode.com/hg/maven2/snapshots/pircbotx/pircbotx/1.3-SNAPSHOT C:\DOCUME~1\Owner\LOCALS~1\Temp\wagon-scm1210107000.checkout\pircbotx\pircbotx\1.3-SNAPSHOT" [INFO] EXECUTING: cmd.exe /X /C "hg locate" [INFO] repository metadata for: 'snapshot pircbotx:pircbotx:1.3-SNAPSHOT' could not be found on repository: pircbotx.googlecode.com, so will be created Uploading: scm:hg:https://site.pircbotx.googlecode.com/hg/maven2/snapshots/pircbotx/pircbotx/1.3-SNAPSHOT/pircbotx-1.3-SNAPSHOT.jar [INFO] ------------------------------------------------------------------------ [ERROR] BUILD ERROR [INFO] ------------------------------------------------------------------------ [INFO] Error deploying artifact: Error listing repository: No such command 'list'. What on earth would cause that error? I'm on a Windows box, so any commands that aren't commands give "'list' is not recognized as an internal or external command...", not "No such command 'list'." POM <build> <extensions> <extension> <groupId>org.apache.maven.scm</groupId> <artifactId>maven-scm-provider-hg</artifactId> <version>1.4</version> </extension> <extension> <groupId>org.apache.maven.wagon</groupId> <artifactId>wagon-scm</artifactId> <version>1.0-beta-7</version> </extension> </extensions> ... <distributionManagement> <snapshotRepository> <id>pircbotx.googlecode.com</id> <name>PircBotX Site</name> <url>scm:hg:https://site.pircbotx.googlecode.com/hg/maven2/snapshots</url> <uniqueVersion>false</uniqueVersion> </snapshotRepository> </distributionManagement> Mercurial version W:\programming\pircbot-hg>hg version Mercurial Distributed SCM (version 1.7.2) Any suggestions?

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• Backup VM : Copy virtual disk xxx.vmdk The virtual disk is either corrupted or not a supported forma

  - by boiteavinc

  Hi I'm french. I'm student and I use ESXI4 for my studies. When I try backup my VMs, with ghettoVCBg2.pl and vSphere Management Assistant, I get the following error message on Vsphere Client : "Copy virtual disk xxx.vmdk The virtual disk is either corrupted or not a supported format". I have no error in the log VCB ; 03-23-2010 08:31:56 -- debug: Main: Login by vi-fastpass to: esxi 03-23-2010 08:31:56 -- debug: copyTask: Task START 03-23-2010 08:31:56 -- debug: copyTask: waiting for next job and sleep ... 03-23-2010 08:32:00 -- info: Initiate backup for AD_DNS_DHCP found on esxi 03-23-2010 08:32:09 -- debug: AD_DNS_DHCP original powerState: poweredOn 03-23-2010 08:32:09 -- debug: Creating Snapshot "ghettoVCBg2-snapshot-2010-03-23" for AD_DNS_DHCP 03-23-2010 08:33:19 -- info: AD_DNS_DHCP has 1 VMDK(s) 03-23-2010 08:33:19 -- debug: backupVMDK: Backing up "Raptor1 AD_DNS_DHCP/AD_DNS_DHCP.vmdk" to "Backup_VM VM/AD_DNS_DHCP/AD_DNS_DHCP-2010-03-23/$ 03-23-2010 08:33:19 -- debug: backupVMDK: Signal copyThread to start 03-23-2010 08:33:19 -- debug: backupVMDK: Backup progress: Elapsed time 0 min 03-23-2010 08:33:19 -- debug: copyTask: Wake up and follow the white rabbit, with status: doCopy 03-23-2010 08:33:19 -- debug: CopyThread: Start backing up VMDK(s) ... 03-23-2010 08:33:25 -- debug: copyTask: send copySuccess message ... 03-23-2010 08:33:25 -- debug: copyTask: waiting for next job and sleep ... 03-23-2010 08:34:20 -- debug: backupVMDK: Successfully completed backup for Raptor1 AD_DNS_DHCP/AD_DNS_DHCP.vmdk Elapsed time: 1 min 03-23-2010 08:34:22 -- debug: Removing Snapshot "ghettoVCBg2-snapshot-2010-03-23" for AD_DNS_DHCP 03-23-2010 08:34:24 -- debug: checkVMBackupRotation: Starting ... 03-23-2010 08:34:26 -- debug: Purging Backup_VM VM/AD_DNS_DHCP/AD_DNS_DHCP-2010-03-23--1 due to rotation max 03-23-2010 08:34:28 -- info: Backup completed for AD_DNS_DHCP! 03-23-2010 08:34:28 -- debug: Main: Disconnect from: esxi 03-23-2010 08:34:28 -- debug: Main: Calling final clean up 03-23-2010 08:34:28 -- debug: cleanUP: Thread clean up starting ... 03-23-2010 08:34:28 -- debug: cleanUp: Send exit to copyThread 03-23-2010 08:34:28 -- debug: copyTask: Wake up and follow the white rabbit, with status: exit 03-23-2010 08:34:28 -- debug: copyTask: die ... 03-23-2010 08:34:28 -- debug: cleanUp: Join passed 03-23-2010 08:34:28 -- info: ============================== ghettoVCBg2 LOG END ============================== My ghetto conf file is : VM_BACKUP_DATASTORE = "Backup_VM" VM_BACKUP_DIRECTORY = "VM" VM_BACKUP_ROTATION_COUNT = "3" DISK_BACKUP_FORMAT = "thin" ADAPTER_FORMAT = "lsilogic" POWER_VM_DOWN_BEFORE_BACKUP = "0" VM_SNAPSHOT_MEMORY = "1" VM_SNAPSHOT_QUIESCE = "1" LOG_LEVEL = "info" VM_VMDK_FILES = "all" I tried several I tried several DISK_BACKUP_FORMAT, I have same error. Despite the error, even when I get files on the NFS share. But when I try to open the vmx file with vmware workstation. I get this error: Can not open the disk 'G: \ Backup ESX \ VM \ AD_DNS_DHCP \ AD_DNS_DHCP-2010-03-23 - 1 \ AD_DNS_DHCP.vmdk' or one of the snapshot disks it depends on. Reason: The called function can not be performed on partial chains. Please open the parent virtual disk. I have no snapshot on my VM on ESXi. Can you help me ?

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• Automating an SSRS 2008 R2 Report Snapshots and run report with most recent data

  - by Mr Shoubs

  I would like to automate a report snapshot, but there is only an option to take a snapshot in the Report History Tab. All the resources I've found suggest I need to go to processing options and select "Render this report from a snapshot". But I don't want to do that - when I go to a report, I want to get the most recent data. However daily at midnight I'd like to take a snapshot and store it in the history in case I want to compare the reports as of midnight for the last few weeks. Or am I doing this wrong and have to create a subscription instead? Note: this is for an auditing database and has way to much data in to query a range with more than 1 day in it - reports are restricted as such. (1 day has over 1 million rows on it's own).

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• Unable to mount Amazon Public Dataset using ec2-create-volume

  - by the0ther

  I am trying to use a Public Dataset with the snapshot id of snap-­e1608d88. I am looking at these instructions, but they do not seem to help. The first suggestion there says I should click on Volumes and create a new volume, set it's size and availability zone, as well as specifying the snapshot id. The problem is, snapshot id is a dropdown, not a text field, and there are over 100 options in the dropdown. Next I installed the ec2 command line tools and tried to run the ec2-create-volume command. For my first attempt I tried ec2-create-volume --snapshot snap-­e1608d88 --availability-zone us-east-1 but that gave output indicating I need to provide a certificate with the --cert switch. Which certficate exactly? I tried my SSH cert at ~/.ssh/id_rsa. No dice. I got the following Java error: "org.codehaus.xfire.fault.XFireFault: General security error;"

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• What happens when I delete the first of several AWS EBS snapshots?

  - by Jepper

  On http://aws.amazon.com/ebs/pricing/ it says: "EBS Snapshots [...] For the first snapshot of a volume, Amazon EBS saves a full copy of your data to Amazon S3. For each incremental snapshot, only the changed part of your Amazon EBS volume is saved." I intend to snapshot some of my instances daily and keep snapshots for 7 days after which the snapshots are destroyed. What happens when, eventually, I destroy the first snapshot? Will the subsequent snapshots be worthless given the first is no longer available?

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• Can a hard poweroff / outage / crash corrupt VMware snapshots?

  - by basic6

  Assuming a host system is running virtual machines (in VMware Workstation) and all their data is on a reliable storage (so no data corruption due to hdd failure). If that host crashes (kernel panic) while a vm is running, files on the virtual filesystem could be corrupted. But there's a snapshot (of the vm), taken before the crash. Is it safe to assume that reverting to the snapshot, the vm will be back in a clean state - or is there any way that this snapshot could have been corrupted by the crash?

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• Debugging the NetBeans Platform

  - by Geertjan

  Once you've set up the NetBeans Platform sources as your NetBeans Platform, you're able to debug the NetBeans Platform itself. That's an occasional question (certainly not a frequent question) on the mailing list and in NetBeans Platform courses: "Is it possible to debug the NetBeans Platform?" Well, here's how: Firstly, set up the NetBeans Platform sources as your NetBeans Platform. Now, open into NetBeans IDE the NetBeans module where you'd like to place a breakpoint. That in itself is the hardest part of this task. I.e., you know you want to debug the NetBeans Platform, but have no idea where to place your breakpoint. One way to figure that out, from 7.1 onwards, is to take a visual snapshot of the NetBeans Platform and then analyze that snapshot in NetBeans IDE. To do this, right-click a module that you've set as using the NetBeans Platform sources as your NetBeans Platform and then choose Debug. The application, i.e., the NetBeans Platform, including your custom module, starts up and you'll see this, i.e., NetBeans IDE in debug mode together with your NetBeans Platform application:Notice there's a new toolbar button (new in NetBeans IDE 7.1) that resembles an orange camera. Click that button and the IDE creates a visual snapshot of the running application, which in this case is the NetBeans Platform. When you click components in the visual snapshot, the Navigator and Properties window display information about the related GUI component: By clicking the above components, you can end up identifying the component you'd like to debug and even the module where it is found. Open that module. Set a breakpoint on the line of interest. Right-click the module again and choose Debug. A debug session starts and when the breakpoint is hit, the Debugger in the IDE will open and there you can step through the NetBeans Platform sources.

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• SQL Server Database Settings

  - by rbishop

  For those using Data Relationship Management on Oracle DB this does not apply, but for those using Microsoft SQL Server it is highly recommended that you run with Snapshot Isolation Mode. The Data Governance module will not function correctly without this mode enabled. All new Data Relationship Management repositories are created with this mode enabled by default. This mode makes SQL Server (2005+) behave more like Oracle DB where readers simply see older versions of rows while a write is in progress, instead of readers being blocked by locks while a write takes place. Many common sources of deadlocks are eliminated. For example, if one user starts a 5 minute transaction updating half the rows in a table, without snapshot isolation everyone else reading the table will be blocked waiting. With snapshot isolation, they will see the rows as they were before the write transaction started. Conversely, if the readers had started first, the writer won't be stuck waiting for them to finish reading... the writes can begin immediately without affecting the current transactions. To make this change, make sure no one is using the target database (eg: put it into single-user mode), then run these commands: ALTER DATABASE [DB] SET ALLOW_SNAPSHOT_ISOLATION ONALTER DATABASE [DB] SET READ_COMMITTED_SNAPSHOT ON Please make sure you coordinate with your DBA team to ensure tempdb is appropriately setup to support snapshot isolation mode, as the extra row versions are stored in tempdb until the transactions are committed. Let me take this opportunity to extremely strongly highly recommend that you use solid state storage for your databases with appropriate iSCSI, FiberChannel, or SAN bandwidth. The performance gains are significant and there is no excuse for not using 100% solid state storage in 2013. Actually unless you need to store petabytes of archival data, there is no excuse for using hard drives in any systems, whether laptops, desktops, application servers, or database servers. The productivity benefits alone are tremendous, not to mention power consumption, heat, etc.

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• How to use Nexus groups with Hudson to deploy artifacts post-build?

  - by John

  Hi there. I'm currently setting up Hudson to push artifacts to my Nexus repository upon succesful builds. Unfortunately I am having some trouble with getting Hudson to deploy using Nexus groups. I have two groups, upbeat.nexus (private) and public.nexus (public). I've set up the associated repositories in Nexus already. Here's my settings.xml: <settings> <mirrors> <mirror> <id>upbeat.nexus</id> <mirrorOf>*</mirrorOf> <url>http://localhost:8099/nexus/content/groups/upbeat</url> </mirror> <mirror> <id>public.nexus</id> <mirrorOf>*</mirrorOf> <url>http://localhost:8099/nexus/content/groups/public</url> </mirror> </mirrors> <profiles> <profile> <id>upbeat.nexus</id> <repositories> <repository> <id>upbeat.central</id> <url>http://central</url> <releases><enabled>true</enabled></releases> <snapshots><enabled>true</enabled></snapshots> </repository> </repositories> </profile> <profile> <id>public.nexus</id> <repositories> <repository> <id>public.central</id> <url>http://central</url> <releases><enabled>true</enabled></releases> <snapshots><enabled>true</enabled></snapshots> </repository> </repositories> </profile> </profiles> <servers> <server> <id>upbeat.nexus</id> <username>build</username> <password></password> </server> <server> <id>public.nexus</id> <username>build</username> <password></password> </server> </servers> <activeProfiles> <activeProfile>upbeat.nexus</activeProfile> <activeProfile>public.nexus</activeProfile> </activeProfiles> In Hudson, when setting the "Deploy artifacts to Maven repository", I need to specify the repository URL and the repository ID. I've set the repository ID to "public.nexus" but if I set the URL to http://forge.upbeat.no/nexus/content/repositories/public and the ID to public.nexus I get the following error: Deploying artifacts to http://forge.upbeat.no/nexus/content/repositories/public Deploying the main artifact pom.xml [INFO ] Retrieving previous build number from public.nexus [INFO ] repository metadata for: 'snapshot com.upbeat.appl:skuldweb:1.0-SNAPSHOT' could not be found on repository: public.nexus, so will be created ERROR: Error deploying artifact: Failed to transfer file: http://forge.upbeat.no/nexus/content/repositories/public/com/upbeat/appl/skuldweb/1.0-SNAPSHOT/skuldweb-1.0-SNAPSHOT.pom. Return code is: 400 org.apache.maven.artifact.deployer.ArtifactDeploymentException: Error deploying artifact: Failed to transfer file: http://forge.upbeat.no/nexus/content/repositories/public/com/upbeat/appl/skuldweb/1.0-SNAPSHOT/skuldweb-1.0-SNAPSHOT.pom. Return code is: 400 at org.apache.maven.artifact.deployer.DefaultArtifactDeployer.deploy(DefaultArtifactDeployer.java:94) at hudson.maven.reporters.MavenArtifactRecord.deploy(MavenArtifactRecord.java:119) at hudson.maven.reporters.MavenAggregatedArtifactRecord.deploy(MavenAggregatedArtifactRecord.java:79) at hudson.maven.RedeployPublisher.perform(RedeployPublisher.java:109) at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19) at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:601) at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:580) at hudson.maven.MavenModuleSetBuild$RunnerImpl.post2(MavenModuleSetBuild.java:598) at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:528) at hudson.model.Run.run(Run.java:1264) at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:306) at hudson.model.ResourceController.execute(ResourceController.java:88) at hudson.model.Executor.run(Executor.java:124) Caused by: org.apache.maven.wagon.TransferFailedException: Failed to transfer file: http://forge.upbeat.no/nexus/content/repositories/public/com/upbeat/appl/skuldweb/1.0-SNAPSHOT/skuldweb-1.0-SNAPSHOT.pom. Return code is: 400 at org.apache.maven.wagon.providers.http.LightweightHttpWagon.put(LightweightHttpWagon.java:172) at org.apache.maven.artifact.manager.DefaultWagonManager.putRemoteFile(DefaultWagonManager.java:244) at org.apache.maven.artifact.manager.DefaultWagonManager.putArtifact(DefaultWagonManager.java:160) at org.apache.maven.artifact.deployer.DefaultArtifactDeployer.deploy(DefaultArtifactDeployer.java:80) ... 12 more Finished: FAILURE Any tips on how to deploy to a group so I don't have to specify (in Hudson) whether or not I am building a snapshot or a release version, and instead have it look at the version-tag in the pom to automatically place the artifact in the correct repository?

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• C#/.NET Little Wonders: The Concurrent Collections (1 of 3)

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In the next few weeks, we will discuss the concurrent collections and how they have changed the face of concurrent programming. This week’s post will begin with a general introduction and discuss the ConcurrentStack<T> and ConcurrentQueue<T>.  Then in the following post we’ll discuss the ConcurrentDictionary<T> and ConcurrentBag<T>.  Finally, we shall close on the third post with a discussion of the BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. A brief history of collections In the beginning was the .NET 1.0 Framework.  And out of this framework emerged the System.Collections namespace, and it was good.  It contained all the basic things a growing programming language needs like the ArrayList and Hashtable collections.  The main problem, of course, with these original collections is that they held items of type object which means you had to be disciplined enough to use them correctly or you could end up with runtime errors if you got an object of a type you weren't expecting. Then came .NET 2.0 and generics and our world changed forever!  With generics the C# language finally got an equivalent of the very powerful C++ templates.  As such, the System.Collections.Generic was born and we got type-safe versions of all are favorite collections.  The List<T> succeeded the ArrayList and the Dictionary<TKey,TValue> succeeded the Hashtable and so on.  The new versions of the library were not only safer because they checked types at compile-time, in many cases they were more performant as well.  So much so that it's Microsoft's recommendation that the System.Collections original collections only be used for backwards compatibility. So we as developers came to know and love the generic collections and took them into our hearts and embraced them.  The problem is, thread safety in both the original collections and the generic collections can be problematic, for very different reasons. Now, if you are only doing single-threaded development you may not care – after all, no locking is required.  Even if you do have multiple threads, if a collection is “load-once, read-many” you don’t need to do anything to protect that container from multi-threaded access, as illustrated below: 1: public static class OrderTypeTranslator 2: { 3: // because this dictionary is loaded once before it is ever accessed, we don't need to synchronize 4: // multi-threaded read access 5: private static readonly Dictionary<string, char> _translator = new Dictionary<string, char> 6: { 7: {"New", 'N'}, 8: {"Update", 'U'}, 9: {"Cancel", 'X'} 10: }; 11:  12: // the only public interface into the dictionary is for reading, so inherently thread-safe 13: public static char? Translate(string orderType) 14: { 15: char charValue; 16: if (_translator.TryGetValue(orderType, out charValue)) 17: { 18: return charValue; 19: } 20:  21: return null; 22: } 23: } Unfortunately, most of our computer science problems cannot get by with just single-threaded applications or with multi-threading in a load-once manner.  Looking at  today's trends, it's clear to see that computers are not so much getting faster because of faster processor speeds -- we've nearly reached the limits we can push through with today's technologies -- but more because we're adding more cores to the boxes.  With this new hardware paradigm, it is even more important to use multi-threaded applications to take full advantage of parallel processing to achieve higher application speeds. So let's look at how to use collections in a thread-safe manner. Using historical collections in a concurrent fashion The early .NET collections (System.Collections) had a Synchronized() static method that could be used to wrap the early collections to make them completely thread-safe.  This paradigm was dropped in the generic collections (System.Collections.Generic) because having a synchronized wrapper resulted in atomic locks for all operations, which could prove overkill in many multithreading situations.  Thus the paradigm shifted to having the user of the collection specify their own locking, usually with an external object: 1: public class OrderAggregator 2: { 3: private static readonly Dictionary<string, List<Order>> _orders = new Dictionary<string, List<Order>>(); 4: private static readonly _orderLock = new object(); 5:  6: public void Add(string accountNumber, Order newOrder) 7: { 8: List<Order> ordersForAccount; 9:  10: // a complex operation like this should all be protected 11: lock (_orderLock) 12: { 13: if (!_orders.TryGetValue(accountNumber, out ordersForAccount)) 14: { 15: _orders.Add(accountNumber, ordersForAccount = new List<Order>()); 16: } 17:  18: ordersForAccount.Add(newOrder); 19: } 20: } 21: } Notice how we’re performing several operations on the dictionary under one lock.  With the Synchronized() static methods of the early collections, you wouldn’t be able to specify this level of locking (a more macro-level).  So in the generic collections, it was decided that if a user needed synchronization, they could implement their own locking scheme instead so that they could provide synchronization as needed. The need for better concurrent access to collections Here’s the problem: it’s relatively easy to write a collection that locks itself down completely for access, but anything more complex than that can be difficult and error-prone to write, and much less to make it perform efficiently!  For example, what if you have a Dictionary that has frequent reads but in-frequent updates?  Do you want to lock down the entire Dictionary for every access?  This would be overkill and would prevent concurrent reads.  In such cases you could use something like a ReaderWriterLockSlim which allows for multiple readers in a lock, and then once a writer grabs the lock it blocks all further readers until the writer is done (in a nutshell).  This is all very complex stuff to consider. Fortunately, this is where the Concurrent Collections come in.  The Parallel Computing Platform team at Microsoft went through great pains to determine how to make a set of concurrent collections that would have the best performance characteristics for general case multi-threaded use. Now, as in all things involving threading, you should always make sure you evaluate all your container options based on the particular usage scenario and the degree of parallelism you wish to acheive. This article should not be taken to understand that these collections are always supperior to the generic collections. Each fills a particular need for a particular situation. Understanding what each container is optimized for is key to the success of your application whether it be single-threaded or multi-threaded. General points to consider with the concurrent collections The MSDN points out that the concurrent collections all support the ICollection interface. However, since the collections are already synchronized, the IsSynchronized property always returns false, and SyncRoot always returns null.  Thus you should not attempt to use these properties for synchronization purposes. Note that since the concurrent collections also may have different operations than the traditional data structures you may be used to.  Now you may ask why they did this, but it was done out of necessity to keep operations safe and atomic.  For example, in order to do a Pop() on a stack you have to know the stack is non-empty, but between the time you check the stack’s IsEmpty property and then do the Pop() another thread may have come in and made the stack empty!  This is why some of the traditional operations have been changed to make them safe for concurrent use. In addition, some properties and methods in the concurrent collections achieve concurrency by creating a snapshot of the collection, which means that some operations that were traditionally O(1) may now be O(n) in the concurrent models.  I’ll try to point these out as we talk about each collection so you can be aware of any potential performance impacts.  Finally, all the concurrent containers are safe for enumeration even while being modified, but some of the containers support this in different ways (snapshot vs. dirty iteration).  Once again I’ll highlight how thread-safe enumeration works for each collection. ConcurrentStack<T>: The thread-safe LIFO container The ConcurrentStack<T> is the thread-safe counterpart to the System.Collections.Generic.Stack<T>, which as you may remember is your standard last-in-first-out container.  If you think of algorithms that favor stack usage (for example, depth-first searches of graphs and trees) then you can see how using a thread-safe stack would be of benefit. The ConcurrentStack<T> achieves thread-safe access by using System.Threading.Interlocked operations.  This means that the multi-threaded access to the stack requires no traditional locking and is very, very fast! For the most part, the ConcurrentStack<T> behaves like it’s Stack<T> counterpart with a few differences: Pop() was removed in favor of TryPop() Returns true if an item existed and was popped and false if empty. PushRange() and TryPopRange() were added Allows you to push multiple items and pop multiple items atomically. Count takes a snapshot of the stack and then counts the items. This means it is a O(n) operation, if you just want to check for an empty stack, call IsEmpty instead which is O(1). ToArray() and GetEnumerator() both also take snapshots. This means that iteration over a stack will give you a static view at the time of the call and will not reflect updates. Pushing on a ConcurrentStack<T> works just like you’d expect except for the aforementioned PushRange() method that was added to allow you to push a range of items concurrently. 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: // but you can also push multiple items in one atomic operation (no interleaves) 7: stack.PushRange(new [] { "Second", "Third", "Fourth" }); For looking at the top item of the stack (without removing it) the Peek() method has been removed in favor of a TryPeek().  This is because in order to do a peek the stack must be non-empty, but between the time you check for empty and the time you execute the peek the stack contents may have changed.  Thus the TryPeek() was created to be an atomic check for empty, and then peek if not empty: 1: // to look at top item of stack without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (stack.TryPeek(out item)) 5: { 6: Console.WriteLine("Top item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Stack was empty."); 11: } Finally, to remove items from the stack, we have the TryPop() for single, and TryPopRange() for multiple items.  Just like the TryPeek(), these operations replace Pop() since we need to ensure atomically that the stack is non-empty before we pop from it: 1: // to remove items, use TryPop or TryPopRange to get multiple items atomically (no interleaves) 2: if (stack.TryPop(out item)) 3: { 4: Console.WriteLine("Popped " + item); 5: } 6:  7: // TryPopRange will only pop up to the number of spaces in the array, the actual number popped is returned. 8: var poppedItems = new string[2]; 9: int numPopped = stack.TryPopRange(poppedItems); 10:  11: foreach (var theItem in poppedItems.Take(numPopped)) 12: { 13: Console.WriteLine("Popped " + theItem); 14: } Finally, note that as stated before, GetEnumerator() and ToArray() gets a snapshot of the data at the time of the call.  That means if you are enumerating the stack you will get a snapshot of the stack at the time of the call.  This is illustrated below: 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: var results = stack.GetEnumerator(); 7:  8: // but you can also push multiple items in one atomic operation (no interleaves) 9: stack.PushRange(new [] { "Second", "Third", "Fourth" }); 10:  11: while(results.MoveNext()) 12: { 13: Console.WriteLine("Stack only has: " + results.Current); 14: } The only item that will be printed out in the above code is "First" because the snapshot was taken before the other items were added. This may sound like an issue, but it’s really for safety and is more correct.  You don’t want to enumerate a stack and have half a view of the stack before an update and half a view of the stack after an update, after all.  In addition, note that this is still thread-safe, whereas iterating through a non-concurrent collection while updating it in the old collections would cause an exception. ConcurrentQueue<T>: The thread-safe FIFO container The ConcurrentQueue<T> is the thread-safe counterpart of the System.Collections.Generic.Queue<T> class.  The concurrent queue uses an underlying list of small arrays and lock-free System.Threading.Interlocked operations on the head and tail arrays.  Once again, this allows us to do thread-safe operations without the need for heavy locks! The ConcurrentQueue<T> (like the ConcurrentStack<T>) has some departures from the non-concurrent counterpart.  Most notably: Dequeue() was removed in favor of TryDequeue(). Returns true if an item existed and was dequeued and false if empty. Count does not take a snapshot It subtracts the head and tail index to get the count.  This results overall in a O(1) complexity which is quite good.  It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. ToArray() and GetEnumerator() both take snapshots. This means that iteration over a queue will give you a static view at the time of the call and will not reflect updates. The Enqueue() method on the ConcurrentQueue<T> works much the same as the generic Queue<T>: 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5: queue.Enqueue("Second"); 6: queue.Enqueue("Third"); For front item access, the TryPeek() method must be used to attempt to see the first item if the queue.  There is no Peek() method since, as you’ll remember, we can only peek on a non-empty queue, so we must have an atomic TryPeek() that checks for empty and then returns the first item if the queue is non-empty. 1: // to look at first item in queue without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (queue.TryPeek(out item)) 5: { 6: Console.WriteLine("First item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Queue was empty."); 11: } Then, to remove items you use TryDequeue().  Once again this is for the same reason we have TryPeek() and not Peek(): 1: // to remove items, use TryDequeue. If queue is empty returns false. 2: if (queue.TryDequeue(out item)) 3: { 4: Console.WriteLine("Dequeued first item " + item); 5: } Just like the concurrent stack, the ConcurrentQueue<T> takes a snapshot when you call ToArray() or GetEnumerator() which means that subsequent updates to the queue will not be seen when you iterate over the results.  Thus once again the code below will only show the first item, since the other items were added after the snapshot. 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5:  6: var iterator = queue.GetEnumerator(); 7:  8: queue.Enqueue("Second"); 9: queue.Enqueue("Third"); 10:  11: // only shows First 12: while (iterator.MoveNext()) 13: { 14: Console.WriteLine("Dequeued item " + iterator.Current); 15: } Using collections concurrently You’ll notice in the examples above I stuck to using single-threaded examples so as to make them deterministic and the results obvious.  Of course, if we used these collections in a truly multi-threaded way the results would be less deterministic, but would still be thread-safe and with no locking on your part required! For example, say you have an order processor that takes an IEnumerable<Order> and handles each other in a multi-threaded fashion, then groups the responses together in a concurrent collection for aggregation.  This can be done easily with the TPL’s Parallel.ForEach(): 1: public static IEnumerable<OrderResult> ProcessOrders(IEnumerable<Order> orderList) 2: { 3: var proxy = new OrderProxy(); 4: var results = new ConcurrentQueue<OrderResult>(); 5:  6: // notice that we can process all these in parallel and put the results 7: // into our concurrent collection without needing any external locking! 8: Parallel.ForEach(orderList, 9: order => 10: { 11: var result = proxy.PlaceOrder(order); 12:  13: results.Enqueue(result); 14: }); 15:  16: return results; 17: } Summary Obviously, if you do not need multi-threaded safety, you don’t need to use these collections, but when you do need multi-threaded collections these are just the ticket! The plethora of features (I always think of the movie The Three Amigos when I say plethora) built into these containers and the amazing way they acheive thread-safe access in an efficient manner is wonderful to behold. Stay tuned next week where we’ll continue our discussion with the ConcurrentBag<T> and the ConcurrentDictionary<TKey,TValue>. For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here.   Tweet Technorati Tags: C#,.NET,Concurrent Collections,Collections,Multi-Threading,Little Wonders,BlackRabbitCoder,James Michael Hare

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• E-Business Suite Technology Stack Roadmap (April 2010) Now Available

  - by Steven Chan

  Keeping up with our E-Business Suite technology stack roadmap can be challenging.  Regular readers of this blog know that we certify new combinations and versions of Oracle products with the E-Business Suite every few weeks.  We also update our certification plans and roadmap as new third-party products like Microsoft Office 2010 and Firefox are announced or released.  Complicating matters further, various Oracle products leave Premier Support or are superceded by more-recent versions.This constant state of change means that any static representation of our roadmap is really a snapshot in time, and a snapshot that might begin to yellow and fade fairly quickly.  With that caveat in mind, here's this month's snapshot that I presented at the OAUG/Collaborate 2010 conference in Las Vegas last week:EBS Technology Stack Roadmap (April 2010)

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• ANTS Memory Profiler 7.0 Review

  - by Michael B. McLaughlin

  (This is my first review as a part of the GeeksWithBlogs.net Influencers program. It’s a program in which I (and the others who have been selected for it) get the opportunity to check out new products and services and write reviews about them. We don’t get paid for this, but we do generally get to keep a copy of the software or retain an account for some period of time on the service that we review. In this case I received a copy of Red Gate Software’s ANTS Memory Profiler 7.0, which was released in January. I don’t have any upgrade rights nor is my review guided, restrained, influenced, or otherwise controlled by Red Gate or anyone else. But I do get to keep the software license. I will always be clear about what I received whenever I do a review – I leave it up to you to decide whether you believe I can be objective. I believe I can be. If I used something and really didn’t like it, keeping a copy of it wouldn’t be worth anything to me. In that case though, I would simply uninstall/deactivate/whatever the software or service and tell the company what I didn’t like about it so they could (hopefully) make it better in the future. I don’t think it’d be polite to write up a terrible review, nor do I think it would be a particularly good use of my time. There are people who get paid for a living to review things, so I leave it to them to tell you what they think is bad and why. I’ll only spend my time telling you about things I think are good.) Overview of Common .NET Memory Problems When coming to land of managed memory from the wilds of unmanaged code, it’s easy to say to one’s self, “Wow! Now I never have to worry about memory problems again!” But this simply isn’t true. Managed code environments, such as .NET, make many, many things easier. You will never have to worry about memory corruption due to a bad pointer, for example (unless you’re working with unsafe code, of course). But managed code has its own set of memory concerns. For example, failing to unsubscribe from events when you are done with them leaves the publisher of an event with a reference to the subscriber. If you eliminate all your own references to the subscriber, then that memory is effectively lost since the GC won’t delete it because of the publishing object’s reference. When the publishing object itself becomes subject to garbage collection then you’ll get that memory back finally, but that could take a very long time depending of the life of the publisher. Another common source of resource leaks is failing to properly release unmanaged resources. When writing a class that contains members that hold unmanaged resources (e.g. any of the Stream-derived classes, IsolatedStorageFile, most classes ending in “Reader” or “Writer”), you should always implement IDisposable, making sure to use a properly written Dispose method. And when you are using an instance of a class that implements IDisposable, you should always make sure to use a 'using' statement in order to ensure that the object’s unmanaged resources are disposed of properly. (A ‘using’ statement is a nicer, cleaner looking, and easier to use version of a try-finally block. The compiler actually translates it as though it were a try-finally block. Note that Code Analysis warning 2202 (CA2202) will often be triggered by nested using blocks. A properly written dispose method ensures that it only runs once such that calling dispose multiple times should not be a problem. Nonetheless, CA2202 exists and if you want to avoid triggering it then you should write your code such that only the innermost IDisposable object uses a ‘using’ statement, with any outer code making use of appropriate try-finally blocks instead). Then, of course, there are situations where you are operating in a memory-constrained environment or else you want to limit or even eliminate allocations within a certain part of your program (e.g. within the main game loop of an XNA game) in order to avoid having the GC run. On the Xbox 360 and Windows Phone 7, for example, for every 1 MB of heap allocations you make, the GC runs; the added time of a GC collection can cause a game to drop frames or run slowly thereby making it look bad. Eliminating allocations (or else minimizing them and calling an explicit Collect at an appropriate time) is a common way of avoiding this (the other way is to simplify your heap so that the GC’s latency is low enough not to cause performance issues). ANTS Memory Profiler 7.0 When the opportunity to review Red Gate’s recently released ANTS Memory Profiler 7.0 arose, I jumped at it. In order to review it, I was given a free copy (which does not include upgrade rights for future versions) which I am allowed to keep. For those of you who are familiar with ANTS Memory Profiler, you can find a list of new features and enhancements here. If you are an experienced .NET developer who is familiar with .NET memory management issues, ANTS Memory Profiler is great. More importantly still, if you are new to .NET development or you have no experience or limited experience with memory profiling, ANTS Memory Profiler is awesome. From the very beginning, it guides you through the process of memory profiling. If you’re experienced and just want dive in however, it doesn’t get in your way. The help items GAHSFLASHDAJLDJA are well designed and located right next to the UI controls so that they are easy to find without being intrusive. When you first launch it, it presents you with a “Getting Started” screen that contains links to “Memory profiling video tutorials”, “Strategies for memory profiling”, and the “ANTS Memory Profiler forum”. I’m normally the kind of person who looks at a screen like that only to find the “Don’t show this again” checkbox. Since I was doing a review, though, I decided I should examine them. I was pleasantly surprised. The overview video clocks in at three minutes and fifty seconds. It begins by showing you how to get started profiling an application. It explains that profiling is done by taking memory snapshots periodically while your program is running and then comparing them. ANTS Memory Profiler (I’m just going to call it “ANTS MP” from here) analyzes these snapshots in the background while your application is running. It briefly mentions a new feature in Version 7, a new API that give you the ability to trigger snapshots from within your application’s source code (more about this below). You can also, and this is the more common way you would do it, take a memory snapshot at any time from within the ANTS MP window by clicking the “Take Memory Snapshot” button in the upper right corner. The overview video goes on to demonstrate a basic profiling session on an application that pulls information from a database and displays it. It shows how to switch which snapshots you are comparing, explains the different sections of the Summary view and what they are showing, and proceeds to show you how to investigate memory problems using the “Instance Categorizer” to track the path from an object (or set of objects) to the GC’s root in order to find what things along the path are holding a reference to it/them. For a set of objects, you can then click on it and get the “Instance List” view. This displays all of the individual objects (including their individual sizes, values, etc.) of that type which share the same path to the GC root. You can then click on one of the objects to generate an “Instance Retention Graph” view. This lets you track directly up to see the reference chain for that individual object. In the overview video, it turned out that there was an event handler which was holding on to a reference, thereby keeping a large number of strings that should have been freed in memory. Lastly the video shows the “Class List” view, which lets you dig in deeply to find problems that might not have been clear when following the previous workflow. Once you have at least one memory snapshot you can begin analyzing. The main interface is in the “Analysis” tab. You can also switch to the “Session Overview” tab, which gives you several bar charts highlighting basic memory data about the snapshots you’ve taken. If you hover over the individual bars (and the individual colors in bars that have more than one), you will see a detailed text description of what the bar is representing visually. The Session Overview is good for a quick summary of memory usage and information about the different heaps. You are going to spend most of your time in the Analysis tab, but it’s good to remember that the Session Overview is there to give you some quick feedback on basic memory usage stats. As described above in the summary of the overview video, there is a certain natural workflow to the Analysis tab. You’ll spin up your application and take some snapshots at various times such as before and after clicking a button to open a window or before and after closing a window. Taking these snapshots lets you examine what is happening with memory. You would normally expect that a lot of memory would be freed up when closing a window or exiting a document. By taking snapshots before and after performing an action like that you can see whether or not the memory is really being freed. If you already know an area that’s giving you trouble, you can run your application just like normal until just before getting to that part and then you can take a few strategic snapshots that should help you pin down the problem. Something the overview didn’t go into is how to use the “Filters” section at the bottom of ANTS MP together with the Class List view in order to narrow things down. The video tutorials page has a nice 3 minute intro video called “How to use the filters”. It’s a nice introduction and covers some of the basics. I’m going to cover a bit more because I think they’re a really neat, really helpful feature. Large programs can bring up thousands of classes. Even simple programs can instantiate far more classes than you might realize. In a basic .NET 4 WPF application for example (and when I say basic, I mean just MainWindow.xaml with a button added to it), the unfiltered Class List view will have in excess of 1000 classes (my simple test app had anywhere from 1066 to 1148 classes depending on which snapshot I was using as the “Current” snapshot). This is amazing in some ways as it shows you how in stark detail just how immensely powerful the WPF framework is. But hunting through 1100 classes isn’t productive, no matter how cool it is that there are that many classes instantiated and doing all sorts of awesome things. Let’s say you wanted to examine just the classes your application contains source code for (in my simple example, that would be the MainWindow and App). Under “Basic Filters”, click on “Classes with source” under “Show only…”. Voilà. Down from 1070 classes in the snapshot I was using as “Current” to 2 classes. If you then click on a class’s name, it will show you (to the right of the class name) two little icon buttons. Hover over them and you will see that you can click one to view the Instance Categorizer for the class and another to view the Instance List for the class. You can also show classes based on which heap they live on. If you chose both a Baseline snapshot and a Current snapshot then you can use the “Comparing snapshots” filters to show only: “New objects”; “Surviving objects”; “Survivors in growing classes”; or “Zombie objects” (if you aren’t sure what one of these means, you can click the helpful “?” in a green circle icon to bring up a popup that explains them and provides context). Remember that your selection(s) under the “Show only…” heading will still apply, so you should update those selections to make sure you are seeing the view you want. There are also links under the “What is my memory problem?” heading that can help you diagnose the problems you are seeing including one for “I don’t know which kind I have” for situations where you know generally that your application has some problems but aren’t sure what the behavior you have been seeing (OutOfMemoryExceptions, continually growing memory usage, larger memory use than expected at certain points in the program). The Basic Filters are not the only filters there are. “Filter by Object Type” gives you the ability to filter by: “Objects that are disposable”; “Objects that are/are not disposed”; “Objects that are/are not GC roots” (GC roots are things like static variables); and “Objects that implement _______”. “Objects that implement” is particularly neat. Once you check the box, you can then add one or more classes and interfaces that an object must implement in order to survive the filtering. Lastly there is “Filter by Reference”, which gives you the option to pare down the list based on whether an object is “Kept in memory exclusively by” a particular item, a class/interface, or a namespace; whether an object is “Referenced by” one or more of those choices; and whether an object is “Never referenced by” one or more of those choices. Remember that filtering is cumulative, so anything you had set in one of the filter sections still remains in effect unless and until you go back and change it. There’s quite a bit more to ANTS MP – it’s a very full featured product – but I think I touched on all of the most significant pieces. You can use it to debug: a .NET executable; an ASP.NET web application (running on IIS); an ASP.NET web application (running on Visual Studio’s built-in web development server); a Silverlight 4 browser application; a Windows service; a COM+ server; and even something called an XBAP (local XAML browser application). You can also attach to a .NET 4 process to profile an application that’s already running. The startup screen also has a large number of “Charting Options” that let you adjust which statistics ANTS MP should collect. The default selection is a good, minimal set. It’s worth your time to browse through the charting options to examine other statistics that may also help you diagnose a particular problem. The more statistics ANTS MP collects, the longer it will take to collect statistics. So just turning everything on is probably a bad idea. But the option to selectively add in additional performance counters from the extensive list could be a very helpful thing for your memory profiling as it lets you see additional data that might provide clues about a particular problem that has been bothering you. ANTS MP integrates very nicely with all versions of Visual Studio that support plugins (i.e. all of the non-Express versions). Just note that if you choose “Profile Memory” from the “ANTS” menu that it will launch profiling for whichever project you have set as the Startup project. One quick tip from my experience so far using ANTS MP: if you want to properly understand your memory usage in an application you’ve written, first create an “empty” version of the type of project you are going to profile (a WPF application, an XNA game, etc.) and do a quick profiling session on that so that you know the baseline memory usage of the framework itself. By “empty” I mean just create a new project of that type in Visual Studio then compile it and run it with profiling – don’t do anything special or add in anything (except perhaps for any external libraries you’re planning to use). The first thing I tried ANTS MP out on was a demo XNA project of an editor that I’ve been working on for quite some time that involves a custom extension to XNA’s content pipeline. The first time I ran it and saw the unmanaged memory usage I was convinced I had some horrible bug that was creating extra copies of texture data (the demo project didn’t have a lot of texture data so when I saw a lot of unmanaged memory I instantly figured I was doing something wrong). Then I thought to run an empty project through and when I saw that the amount of unmanaged memory was virtually identical, it dawned on me that the CLR itself sits in unmanaged memory and that (thankfully) there was nothing wrong with my code! Quite a relief. Earlier, when discussing the overview video, I mentioned the API that lets you take snapshots from within your application. I gave it a quick trial and it’s very easy to integrate and make use of and is a really nice addition (especially for projects where you want to know what, if any, allocations there are in a specific, complicated section of code). The only concern I had was that if I hadn’t watched the overview video I might never have known it existed. Even then it took me five minutes of hunting around Red Gate’s website before I found the “Taking snapshots from your code" article that explains what DLL you need to add as a reference and what method of what class you should call in order to take an automatic snapshot (including the helpful warning to wrap it in a try-catch block since, under certain circumstances, it can raise an exception, such as trying to call it more than 5 times in 30 seconds. The difficulty in discovering and then finding information about the automatic snapshots API was one thing I thought could use improvement. Another thing I think would make it even better would be local copies of the webpages it links to. Although I’m generally always connected to the internet, I imagine there are more than a few developers who aren’t or who are behind very restrictive firewalls. For them (and for me, too, if my internet connection happens to be down), it would be nice to have those documents installed locally or to have the option to download an additional “documentation” package that would add local copies. Another thing that I wish could be easier to manage is the Filters area. Finding and setting individual filters is very easy as is understanding what those filter do. And breaking it up into three sections (basic, by object, and by reference) makes sense. But I could easily see myself running a long profiling session and forgetting that I had set some filter a long while earlier in a different filter section and then spending quite a bit of time trying to figure out why some problem that was clearly visible in the data wasn’t showing up in, e.g. the instance list before remembering to check all the filters for that one setting that was only culling a few things from view. Some sort of indicator icon next to the filter section names that appears you have at least one filter set in that area would be a nice visual clue to remind me that “oh yeah, I told it to only show objects on the Gen 2 heap! That’s why I’m not seeing those instances of the SuperMagic class!” Something that would be nice (but that Red Gate cannot really do anything about) would be if this could be used in Windows Phone 7 development. If Microsoft and Red Gate could work together to make this happen (even if just on the WP7 emulator), that would be amazing. Especially given the memory constraints that apps and games running on mobile devices need to work within, a good memory profiler would be a phenomenally helpful tool. If anyone at Microsoft reads this, it’d be really great if you could make something like that happen. Perhaps even a (subsidized) custom version just for WP7 development. (For XNA games, of course, you can create a Windows version of the game and use ANTS MP on the Windows version in order to get a better picture of your memory situation. For Silverlight on WP7, though, there’s quite a bit of educated guess work and WeakReference creation followed by forced collections in order to find the source of a memory problem.) The only other thing I found myself wanting was a “Back” button. Between my Windows Phone 7, Zune, and other things, I’ve grown very used to having a “back stack” that lets me just navigate back to where I came from. The ANTS MP interface is surprisingly easy to use given how much it lets you do, and once you start using it for any amount of time, you learn all of the different areas such that you know where to go. And it does remember the state of the areas you were previously in, of course. So if you go to, e.g., the Instance Retention Graph from the Class List and then return back to the Class List, it will remember which class you had selected and all that other state information. Still, a “Back” button would be a welcome addition to a future release. Bottom Line ANTS Memory Profiler is not an inexpensive tool. But my time is valuable. I can easily see ANTS MP saving me enough time tracking down memory problems to justify it on a cost basis. More importantly to me, knowing what is happening memory-wise in my programs and having the confidence that my code doesn’t have any hidden time bombs in it that will cause it to OOM if I leave it running for longer than I do when I spin it up real quickly for debugging or just to see how a new feature looks and feels is a good feeling. It’s a feeling that I like having and want to continue to have. I got the current version for free in order to review it. Having done so, I’ve now added it to my must-have tools and will gladly lay out the money for the next version when it comes out. It has a 14 day free trial, so if you aren’t sure if it’s right for you or if you think it seems interesting but aren’t really sure if it’s worth shelling out the money for it, give it a try.

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• How would you answer this job-interview question?

  - by ahmed

  One of the five people who interviewed me asked a question that resulted in an hour-long discussion: "Explain how you would develop a frequency-sorted list of the ten thousand most-used words in the English language." My initial response was to assail the assumptions underlying the problem. Language is a fluid thing, I argued. It changes in real time. Vocabulary and usage patterns shift day-to-day. To develop a list of words and their frequencies means taking a snapshot of a moving target. Whatever snapshot you take today isn't going to look like the snapshot you take tomorrow or even five minutes from now. Thanking you advance for your answers and consideration.

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• C#/.NET Little Wonders: Interlocked CompareExchange()

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Two posts ago, I discussed the Interlocked Add(), Increment(), and Decrement() methods (here) for adding and subtracting values in a thread-safe, lightweight manner.  Then, last post I talked about the Interlocked Read() and Exchange() methods (here) for safely and efficiently reading and setting 32 or 64 bit values (or references).  This week, we’ll round out the discussion by talking about the Interlocked CompareExchange() method and how it can be put to use to exchange a value if the current value is what you expected it to be. Dirty reads can lead to bad results Many of the uses of Interlocked that we’ve explored so far have centered around either reading, setting, or adding values.  But what happens if you want to do something more complex such as setting a value based on the previous value in some manner? Perhaps you were creating an application that reads a current balance, applies a deposit, and then saves the new modified balance, where of course you’d want that to happen atomically.  If you read the balance, then go to save the new balance and between that time the previous balance has already changed, you’ll have an issue!  Think about it, if we read the current balance as $400, and we are applying a new deposit of $50.75, but meanwhile someone else deposits $200 and sets the total to $600, but then we write a total of $450.75 we’ve lost $200! Now, certainly for int and long values we can use Interlocked.Add() to handles these cases, and it works well for that.  But what if we want to work with doubles, for example?  Let’s say we wanted to add the numbers from 0 to 99,999 in parallel.  We could do this by spawning several parallel tasks to continuously add to a total: 1: double total = 0; 2:  3: Parallel.For(0, 10000, next => 4: { 5: total += next; 6: }); Were this run on one thread using a standard for loop, we’d expect an answer of 4,999,950,000 (the sum of all numbers from 0 to 99,999).  But when we run this in parallel as written above, we’ll likely get something far off.  The result of one of my runs, for example, was 1,281,880,740.  That is way off!  If this were banking software we’d be in big trouble with our clients.  So what happened?  The += operator is not atomic, it will read in the current value, add the result, then store it back into the total.  At any point in all of this another thread could read a “dirty” current total and accidentally “skip” our add.   So, to clean this up, we could use a lock to guarantee concurrency: 1: double total = 0.0; 2: object locker = new object(); 3:  4: Parallel.For(0, count, next => 5: { 6: lock (locker) 7: { 8: total += next; 9: } 10: }); Which will give us the correct result of 4,999,950,000.  One thing to note is that locking can be heavy, especially if the operation being locked over is trivial, or the life of the lock is a high percentage of the work being performed concurrently.  In the case above, the lock consumes pretty much all of the time of each parallel task – and the task being locked on is relatively trivial. Now, let me put in a disclaimer here before we go further: For most uses, lock is more than sufficient for your needs, and is often the simplest solution!    So, if lock is sufficient for most needs, why would we ever consider another solution?  The problem with locking is that it can suspend execution of your thread while it waits for the signal that the lock is free.  Moreover, if the operation being locked over is trivial, the lock can add a very high level of overhead.  This is why things like Interlocked.Increment() perform so well, instead of locking just to perform an increment, we perform the increment with an atomic, lockless method. As with all things performance related, it’s important to profile before jumping to the conclusion that you should optimize everything in your path.  If your profiling shows that locking is causing a high level of waiting in your application, then it’s time to consider lighter alternatives such as Interlocked. CompareExchange() – Exchange existing value if equal some value So let’s look at how we could use CompareExchange() to solve our problem above.  The general syntax of CompareExchange() is: T CompareExchange<T>(ref T location, T newValue, T expectedValue) If the value in location == expectedValue, then newValue is exchanged.  Either way, the value in location (before exchange) is returned. Actually, CompareExchange() is not one method, but a family of overloaded methods that can take int, long, float, double, pointers, or references.  It cannot take other value types (that is, can’t CompareExchange() two DateTime instances directly).  Also keep in mind that the version that takes any reference type (the generic overload) only checks for reference equality, it does not call any overridden Equals(). So how does this help us?  Well, we can grab the current total, and exchange the new value if total hasn’t changed.  This would look like this: 1: // grab the snapshot 2: double current = total; 3:  4: // if the total hasn’t changed since I grabbed the snapshot, then 5: // set it to the new total 6: Interlocked.CompareExchange(ref total, current + next, current); So what the code above says is: if the amount in total (1st arg) is the same as the amount in current (3rd arg), then set total to current + next (2nd arg).  This check and exchange pair is atomic (and thus thread-safe). This works if total is the same as our snapshot in current, but the problem, is what happens if they aren’t the same?  Well, we know that in either case we will get the previous value of total (before the exchange), back as a result.  Thus, we can test this against our snapshot to see if it was the value we expected: 1: // if the value returned is != current, then our snapshot must be out of date 2: // which means we didn't (and shouldn't) apply current + next 3: if (Interlocked.CompareExchange(ref total, current + next, current) != current) 4: { 5: // ooops, total was not equal to our snapshot in current, what should we do??? 6: } So what do we do if we fail?  That’s up to you and the problem you are trying to solve.  It’s possible you would decide to abort the whole transaction, or perhaps do a lightweight spin and try again.  Let’s try that: 1: double current = total; 2:  3: // make first attempt... 4: if (Interlocked.CompareExchange(ref total, current + i, current) != current) 5: { 6: // if we fail, go into a spin wait, spin, and try again until succeed 7: var spinner = new SpinWait(); 8:  9: do 10: { 11: spinner.SpinOnce(); 12: current = total; 13: } 14: while (Interlocked.CompareExchange(ref total, current + i, current) != current); 15: } 16:  This is not trivial code, but it illustrates a possible use of CompareExchange().  What we are doing is first checking to see if we succeed on the first try, and if so great!  If not, we create a SpinWait and then repeat the process of SpinOnce(), grab a fresh snapshot, and repeat until CompareExchnage() succeeds.  You may wonder why not a simple do-while here, and the reason it’s more efficient to only create the SpinWait until we absolutely know we need one, for optimal efficiency. Though not as simple (or maintainable) as a simple lock, this will perform better in many situations.  Comparing an unlocked (and wrong) version, a version using lock, and the Interlocked of the code, we get the following average times for multiple iterations of adding the sum of 100,000 numbers: 1: Unlocked money average time: 2.1 ms 2: Locked money average time: 5.1 ms 3: Interlocked money average time: 3 ms So the Interlocked.CompareExchange(), while heavier to code, came in lighter than the lock, offering a good compromise of safety and performance when we need to reduce contention. CompareExchange() - it’s not just for adding stuff… So that was one simple use of CompareExchange() in the context of adding double values -- which meant we couldn’t have used the simpler Interlocked.Add() -- but it has other uses as well. If you think about it, this really works anytime you want to create something new based on a current value without using a full lock.  For example, you could use it to create a simple lazy instantiation implementation.  In this case, we want to set the lazy instance only if the previous value was null: 1: public static class Lazy<T> where T : class, new() 2: { 3: private static T _instance; 4:  5: public static T Instance 6: { 7: get 8: { 9: // if current is null, we need to create new instance 10: if (_instance == null) 11: { 12: // attempt create, it will only set if previous was null 13: Interlocked.CompareExchange(ref _instance, new T(), (T)null); 14: } 15:  16: return _instance; 17: } 18: } 19: } So, if _instance == null, this will create a new T() and attempt to exchange it with _instance.  If _instance is not null, then it does nothing and we discard the new T() we created. This is a way to create lazy instances of a type where we are more concerned about locking overhead than creating an accidental duplicate which is not used.  In fact, the BCL implementation of Lazy<T> offers a similar thread-safety choice for Publication thread safety, where it will not guarantee only one instance was created, but it will guarantee that all readers get the same instance.  Another possible use would be in concurrent collections.  Let’s say, for example, that you are creating your own brand new super stack that uses a linked list paradigm and is “lock free”.  We could use Interlocked.CompareExchange() to be able to do a lockless Push() which could be more efficient in multi-threaded applications where several threads are pushing and popping on the stack concurrently. Yes, there are already concurrent collections in the BCL (in .NET 4.0 as part of the TPL), but it’s a fun exercise!  So let’s assume we have a node like this: 1: public sealed class Node<T> 2: { 3: // the data for this node 4: public T Data { get; set; } 5:  6: // the link to the next instance 7: internal Node<T> Next { get; set; } 8: } Then, perhaps, our stack’s Push() operation might look something like: 1: public sealed class SuperStack<T> 2: { 3: private volatile T _head; 4:  5: public void Push(T value) 6: { 7: var newNode = new Node<int> { Data = value, Next = _head }; 8:  9: if (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next) 10: { 11: var spinner = new SpinWait(); 12:  13: do 14: { 15: spinner.SpinOnce(); 16: newNode.Next = _head; 17: } 18: while (Interlocked.CompareExchange(ref _head, newNode, newNode.Next) != newNode.Next); 19: } 20: } 21:  22: // ... 23: } Notice a similar paradigm here as with adding our doubles before.  What we are doing is creating the new Node with the data to push, and with a Next value being the original node referenced by _head.  This will create our stack behavior (LIFO – Last In, First Out).  Now, we have to set _head to now refer to the newNode, but we must first make sure it hasn’t changed! So we check to see if _head has the same value we saved in our snapshot as newNode.Next, and if so, we set _head to newNode.  This is all done atomically, and the result is _head’s original value, as long as the original value was what we assumed it was with newNode.Next, then we are good and we set it without a lock!  If not, we SpinWait and try again. Once again, this is much lighter than locking in highly parallelized code with lots of contention.  If I compare the method above with a similar class using lock, I get the following results for pushing 100,000 items: 1: Locked SuperStack average time: 6 ms 2: Interlocked SuperStack average time: 4.5 ms So, once again, we can get more efficient than a lock, though there is the cost of added code complexity.  Fortunately for you, most of the concurrent collection you’d ever need are already created for you in the System.Collections.Concurrent (here) namespace – for more information, see my Little Wonders – The Concurent Collections Part 1 (here), Part 2 (here), and Part 3 (here). Summary We’ve seen before how the Interlocked class can be used to safely and efficiently add, increment, decrement, read, and exchange values in a multi-threaded environment.  In addition to these, Interlocked CompareExchange() can be used to perform more complex logic without the need of a lock when lock contention is a concern. The added efficiency, though, comes at the cost of more complex code.  As such, the standard lock is often sufficient for most thread-safety needs.  But if profiling indicates you spend a lot of time waiting for locks, or if you just need a lock for something simple such as an increment, decrement, read, exchange, etc., then consider using the Interlocked class’s methods to reduce wait. Technorati Tags: C#,CSharp,.NET,Little Wonders,Interlocked,CompareExchange,threading,concurrency

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• Ejb 2.0 deployment issues on Jboss 5.1

  - by Ravi

  I am deploying an ear application on Jboss 5.1.0. and i facing some issues. I had two ears one i had copied to deploy folder and the other in deploy-hasingleton. The ear which is in deploy-hasingleton is throwing some errors.when i serached in google i came to know that there is some issue with EJB 2.x on jboss 5.1.i was not able to find the solution. Below is the log. profileservice-secured.jar 11:16:17,162 INFO [JBossASKernel] installing bean: jboss.j2ee:jar=profileservice-secured.jar,name=SecureManagementView,service=EJB3 11:16:17,162 INFO [JBossASKernel] with dependencies: 11:16:17,162 INFO [JBossASKernel] and demands: 11:16:17,162 INFO [JBossASKernel] jboss.ejb:service=EJBTimerService 11:16:17,162 INFO [JBossASKernel] and supplies: 11:16:17,162 INFO [JBossASKernel] jndi:SecureManagementView/remote-org.jboss.deployers.spi.management.ManagementView 11:16:17,162 INFO [JBossASKernel] Class:org.jboss.deployers.spi.management.ManagementView 11:16:17,162 INFO [JBossASKernel] jndi:SecureManagementView/remote 11:16:17,162 INFO [JBossASKernel] Added bean(jboss.j2ee:jar=profileservice-secured.jar,name=SecureManagementView,service=EJB3) to KernelDeployment of: profileservice-secured.jar 11:16:17,162 INFO [EJB3EndpointDeployer] Deploy AbstractBeanMetaData@17cabbb{name=jboss.j2ee:jar=profileservice-secured.jar,name=SecureProfileService,service=EJB3_endpoint bean=org.jboss.ejb3.endpoint.deployers.impl.EndpointImpl properties=[container] constructor=null autowireCandidate=true} 11:16:17,162 INFO [EJB3EndpointDeployer] Deploy AbstractBeanMetaData@1fedd5c{name=jboss.j2ee:jar=profileservice-secured.jar,name=SecureDeploymentManager,service=EJB3_endpoint bean=org.jboss.ejb3.endpoint.deployers.impl.EndpointImpl properties=[container] constructor=null autowireCandidate=true} 11:16:17,162 INFO [EJB3EndpointDeployer] Deploy AbstractBeanMetaData@1ef4b31{name=jboss.j2ee:jar=profileservice-secured.jar,name=SecureManagementView,service=EJB3_endpoint bean=org.jboss.ejb3.endpoint.deployers.impl.EndpointImpl properties=[container] constructor=null autowireCandidate=true} 11:16:17,833 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=profileservice-secured.jar,name=SecureDeploymentManager,service=EJB3 11:16:17,833 INFO [EJBContainer] STARTED EJB: org.jboss.profileservice.ejb.SecureDeploymentManager ejbName: SecureDeploymentManager 11:16:18,066 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: SecureDeploymentManager/remote - EJB3.x Default Remote Business Interface SecureDeploymentManager/remote-org.jboss.deployers.spi.management.deploy.DeploymentManager - EJB3.x Remote Business Interface 11:16:18,129 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=profileservice-secured.jar,name=SecureManagementView,service=EJB3 11:16:18,129 INFO [EJBContainer] STARTED EJB: org.jboss.profileservice.ejb.SecureManagementView ejbName: SecureManagementView 11:16:18,160 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: SecureManagementView/remote - EJB3.x Default Remote Business Interface SecureManagementView/remote-org.jboss.deployers.spi.management.ManagementView - EJB3.x Remote Business Interface 11:16:18,206 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=profileservice-secured.jar,name=SecureProfileService,service=EJB3 11:16:18,206 INFO [EJBContainer] STARTED EJB: org.jboss.profileservice.ejb.SecureProfileServiceBean ejbName: SecureProfileService 11:16:18,238 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI: SecureProfileService/remote - EJB3.x Default Remote Business Interface SecureProfileService/remote-org.jboss.profileservice.spi.ProfileService - EJB3.x Remote Business Interface 11:16:18,534 INFO [TomcatDeployment] deploy, ctxPath=/admin-console 11:16:18,612 INFO [config] Initializing Mojarra (1.2_12-b01-FCS) for context '/admin-console' 11:16:21,759 INFO [TomcatDeployment] deploy, ctxPath=/ 11:16:21,853 INFO [TomcatDeployment] deploy, ctxPath=/jmx-console 11:16:21,993 INFO [JBossASKernel] Created KernelDeployment for: hapi-0.5.jar 11:16:21,993 INFO [JBossASKernel] installing bean: jboss.j2ee:ear=jca-ear-1.3-SNAPSHOT.ear,jar=hapi-0.5.jar,name=hapi-0.5,service=EJB3 11:16:21,993 INFO [JBossASKernel] with dependencies: 11:16:21,993 INFO [JBossASKernel] and demands: 11:16:21,993 INFO [JBossASKernel] and supplies: 11:16:21,993 INFO [JBossASKernel] Added bean(jboss.j2ee:ear=jca-ear-1.3-SNAPSHOT.ear,jar=hapi-0.5.jar,name=hapi-0.5,service=EJB3) to KernelDeployment of: hapi-0.5.jar 11:16:23,302 INFO [ClientENCInjectionContainer] STARTED CLIENT ENC CONTAINER: hapi-0.5 11:16:23,473 INFO [SystemEventService] NODE_STARTED on node [HCA-5C1P1BS] 11:16:23,489 INFO [AbstractConnector] [aware] connector started 11:16:23,536 INFO [AbstractConnector] [datacaptor] connector started 11:16:23,536 INFO [AbstractConnector] [intellivue] connector started 11:16:23,972 ERROR [ProfileServiceBootstrap] Failed to load profile: Summary of incomplete deployments (SEE PREVIOUS ERRORS FOR DETAILS): DEPLOYMENTS MISSING DEPENDENCIES: Deployment "gehc.com:service=KernelServiceMBean" is missing the following dependencies: Dependency "jboss.j2ee:module=kernel-ejb-1.3-SNAPSHOT.jar,service=EjbModule" (should be in state "Create", but is actually in state " NOT FOUND Depends on 'jboss.j2ee:module=kernel-ejb-1.3-SNAPSHOT.jar,service=EjbModule' ") Deployment "jboss.j2ee:module="kernel-ejb-1.3-SNAPSHOT.jar",service=EjbModule" is missing the following dependencies: Dependency "gehc.com:service=KernelServiceMBean" (should be in state "Create", but is actually in state "Configured") DEPLOYMENTS IN ERROR: Deployment "jboss.j2ee:module=kernel-ejb-1.3-SNAPSHOT.jar,service=EjbModule" is in error due to the following reason(s): ** NOT FOUND Depends on 'jboss.j2ee:module=kernel-ejb-1.3-SNAPSHOT.jar,service=EjbModule' ** 11:16:24,003 INFO [Http11Protocol] Starting Coyote HTTP/1.1 on http-127.0.0.1-8080 11:16:24,034 INFO [AjpProtocol] Starting Coyote AJP/1.3 on ajp-127.0.0.1-8009 11:16:24,050 INFO [ServerImpl] JBoss (Microcontainer) [5.1.0.GA (build: SVNTag=JBoss_5_1_0_GA date=200905221053)] Started in 1m:49s:575ms I had marked the error with bold, there is some circular dependency also. Thanks Ravi S

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