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• Update n number of records using JPA with Optimistic locking

  - by Jacques René Mesrine

  I have a table with a column called "count" and I want to run a cron job that will trigger a statement that performs a SQL like this: update summaryTable set count=4; Note that there might be concurrent threads reading & changing the value for "count" when this cron job is triggered. The table has a version column to support Optimistic Locking. What's an efficient way to update the count in JPA ?

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• jpa @version optimistic locking

  - by cometta

  I loaded same entity record on 2 separate browser window then press submit (hibernate template.merge), version number incremented for both browser window, but never caught any problem with optimistic lock.. so how to test this? my save() look like this hibernatetemplate().merge(..); setJPAObject(null); //reset after save

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• Formula for PERT - Pessimistic time and optimistic time

  - by karthi

  I found PERT examples include a formula (a + 4m + b)/6 where a= optimistic time , b= pessimistic time and m= actual time to complete the task but how to calculate a and b? please help me as soon as possible

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• NHibernate Optimistic Concurrency

  - by initforthemoney

  I'm investigating optimistic concurrency in NHibernate. I have a scenario that is very similar to what is being described here: http://weblogs.asp.net/stefansedich/archive/2008/10/01/set-the-value-of-a-version-column-in-nhibernate-manually.aspx Would you recommend going with the proposed solution in this blog post? Thanks

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• Method for SharePoint list/item locking across processes/machines?

  - by Steve

  In general, is there a decent way in SharePoint to control race conditions due to two processes or even two machines in the farm operating on the same list or list item at the same time? That is, is there any mechanism either built in or that can be fabricated via the Object Model for doing cross-process or cross-machine locking of individual list items? I want to write a timer job that performs a bunch of manipulations on a list. This list is written to by the SharePoint UI and then read by the UI. I want to be able to make sure that the UI doesn't either write to or read from the list when it is in an inconsistent state due to the timer job being in the middle of a manipulation. Is there any way to do this? Also, I want to allow for multiple instances of the timer job to run simultaneously. This, again, will require a lock to be sure that the two jobs don't attempt to operate on the same list/item at the same time. TIA for any help!

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• .NET 3.5 C# does not offer what I need for locking: Count async saves until 0 again.

  - by Frank Michael Kraft

  I have some records, that I want to save to database asynchronously. I organize them into batches, then send them. As time passes, the batches are processed. In the meanwhile the user can work on. There are some critical operations, that I want to lock him out from, while any save batch is still running asynchronously. The save is done using a TableServiceContext and method .BeginSave() - but I think this should be irrelevant. What I want to do is whenever an async save is started, increase a lock count, and when it completes, decrease the lock count so that it will be zero as soon as all have finished. I want to lock out the critical operation as long as the count is not zero. Furthermore I want to qualify the lock - by business object - for example. I did not find a .NET 3.5 c# locking method, that does fulfil this requirement. A semaphore does not contain a method to check, if the count is 0. Otherwise a semaphore with unlimited max count would do.

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• Entity Framework - Optimistic Concurrency Issue

  - by Cranialsurge

  I have a windows service that runs every 10 seconds ... each time it runs, it takes some test data, modifies it and persists it to the database using the EntityFramework. However, on every second run, when I try to persist the change I get the following Optimistic Concurrency Exception:- Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries I know for a fact that there is nothing else writing to that DB but my service which updates records every 10 seconds. What could be causing the concurrency exception here ?

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• JPA optimistic lock - setting @Version to entity class cause query to include VERSION as column

  - by masato-san

  I'm using JPA Toplink Essential, Netbean6.8, GlassFish v3 In my Entity class I added @Version annotation to enable optimistic locking at transaction commit however after I added the annotation, my query started including VERSION as column thus throwing SQL exception. None of this is mentioned in any tutorial I've seen so far. What could be wrong? Snippet public class MasatosanTest2 implements Serializable { private static final long serialVersionUID = 1L; @Id @Basic(optional = false) @Column(name = "id") private Integer id; @Column(name = "username") private String username; @Column(name = "note") private String note; //here adding Version @Version int version; query used: SELECT m FROM MasatosanTest2 m Internal Exception: com.microsoft.sqlserver.jdbc.SQLServerException Call: SELECT id, username, note, VERSION FROM MasatosanTest2

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• How to share a dictionary between multiple processes in python without locking

  - by RandomVector

  I need to share a huge dictionary (around 1 gb in size) between multiple processs, however since all processes will always read from it. I dont need locking. Is there any way to share a dictionary without locking? The multiprocessing module in python provides an Array class which allows sharing without locking by setting lock=false however There is no such option for Dictionary provided by manager in multiprocessing module.

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• Over Optimistic Daily Productivity

  - by Dan Revell

  I'm a junior developer and have been working since I graduated last summer so coming up to a year now. I have this issue that is starting to get to me. Every night I think back to what I did that day, feel bad that I didn't get as much done as I would have liked and then tick off in my head all the things I'll get done the following day. Come the end of the following day I end haven't gotten through half of what I wanted to. This over optimism that I'm suffering from. Might it be just because I'm relatively new to the profession and aren't aware of how long things will actually take me. The work might be quick to think through in my head but all sorts of time sync's involved can bleed away the hours. If not that then perhaps it's the technology stack that I'm working on. SharePoint isn't the easiest thing to develop for and it's certainly something I came into not knowing a whole lot about. If it's because I'm not yet skilled enough to predict how long things will take me, is this trait of over optimistic predictions universal to the profession? I'd appreciate any input from those experienced with working with younger developers and those that might have suffered from this themselves. [EDIT] Perhaps I worded the question badly. I'm interested in just general day to day work rather than overall project completion estimation.

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• How to prevent nginx from locking files on mounted samba partition in Centos 6

  - by Bruce Kirkpatrick

  I'm using nginx 1.3.8 inside a centos 6.3 virtualbox 4.2.4 virtual machine. The system is running the latest software available via yum update. The host OS is windows 7. The site files nginx is serving are on mounted samba partition, which is a folder on the host Windows system. I.e., inside linux, nginx paths are referring to /home/vhosts and this is mounted from D:\vhosts\ on windows. The samba partition is mounted as root with 777 privileges. /etc/fstab looks like this, but with real ip, username, password: //hostip/vhosts /home/vhosts cifs username=username,password=SECRETPASSWORD,uid=root,gid=root,file_mode=0777,dir_mode=0777,rw,_netdev 0 0 I.e. linux/nginx reads from the windows share, and not the opposite. in /etc/samba/smb.conf, I have tried to disable all samba locking features, but it seems to have no effect even after rebooting the virtual machine. locking=no share modes=no oplocks = no level2 oplocks = no kernel oplocks =no I'm receiving "Access is denied" errors in Windows or linux when attempting to overwrite the javascript file in windows that has been accessed at least once with nginx. If I run "service nginx reload", the lock is removed and I'm able to save the file. That's why I think it is nginx causing the lock. The same problem occurs with directories. However, that may be a different issue not related to the use of samba. I'm using samba so that I can manage the source code outside of the virtual machine. Also note that after I run "service nginx reload", the file I'm editing is actually automatically deleted from the windows host. SOLVED: I just reviewed my nginx.conf file. It appears the "open_file_cache" feature is what is causing the lock and deleted files. When I set this option to open_file_cache off;, My problem is resolved. I will repost as the answer when it allows me to do so.

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• bash and flock (file lock) - Doesn't seem to be locking....

  - by Rory

  I am playing with using flock, a bash command for file locks to prevent 2 different instances of the code from running more than once. I am using this testing code: ( ( flock -x 200 ; sleep 10 ; echo "original finished" ; ) 200>./test.lock ) & ( sleep 2 ; ( flock -x -w 2 200 ; echo "a finished" ) 200>./test.lock ) & I am running 2 subshells (backgrounded). The (flock NUM; ...) NUM>FILE syntax is from flock's man page. I expect that the first subshell will get an exclusive lock on test.lock, then wait 10 seconds, then print "original finished", all the time holding the lock. The second subshell will start at more or less the same time, wait 2 seconds, then try to get a lock on test.lock, but timeout after 2 seconds. If it gets a lock, then it'll print "a finished". If it doesn't get the lock, that subshell should stop, and nothing should be printed. Since the first subshell is waiting longer, it will keep the lock for 10 seconds, so the second subshell should not get the lock, and shouldn't finish. i.e. one should see "original finished" printed and not both. What actually happens is that "a finished" is printed, then "original finished" is printed. This implies that that the second subshell is either (a) not using the same lock as the first subhsell or (b) that it fails to get the lock, but continues to execute or (c) something else. Why don't those locks work?

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• Xen domain migration locking problem

  - by brodie

  I am trying to live migrate a VM (domain) between two Xen servers. I have xen locking (xend-domain-lock = yes) configured with a ocfs2 shared storage between them. This locking is working fine. If I try to start up the VM on the secondary server it refuses to start (which is correct). The problem I am having is when trying to do live migration, it seems like it is trying to remove the lock twice. The first lock it removes is for "domain test", the second is for "migrating-test" which does not exist. Should their be a lock for this "migrating-test" VM? These are the relevant options in the xen config file: (xend-relocation-server yes) (xend-relocation-port 8002) (xend-relocation-address '') (xend-relocation-hosts-allow '') (xend-domain-lock yes) (xend-domain-lock-path /var/lib/xen/lock) This is the section of the log: [2010-06-10 10:45:57 14488] DEBUG (XendDomainInfo:4054) Releasing lock for domain test [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) SUSPEND shinfo 000c6ceb [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) delta 21ms, dom0 95%, target 0%, sent 57Mb/s, dirtied 173Mb/s 111 pages 4: sent 111, skipped 0, delta 6ms, dom0 100%, target 0%, sent 606Mb/s, dirtied 606Mb/s 111 pages [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) Total pages sent= 131295 (0.99x) [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) (of which 0 were fixups) [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) All memory is saved [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:474) Save exit rc=0 [2010-06-10 10:45:57 14488] INFO (XendCheckpoint:123) Domain 22 suspended. [2010-06-10 10:45:57 14488] DEBUG (XendDomainInfo:2757) XendDomainInfo.destroy: domid=22 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2227) Destroying device model [2010-06-10 10:45:58 14488] INFO (image:567) migrating-test device model terminated [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2234) Releasing devices [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vif/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vif, device = vif/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vkbd/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vkbd, device = vkbd/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing console/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = console, device = console/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vbd/51712 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vbd, device = vbd/51712 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:2247) Removing vfb/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:1137) XendDomainInfo.destroyDevice: deviceClass = vfb, device = vfb/0 [2010-06-10 10:45:58 14488] DEBUG (XendDomainInfo:4054) Releasing lock for domain migrating-test [2010-06-10 10:45:59 14488] ERROR (XendDomainInfo:4070) Failed to remove unmanaged directory /var/lib/xen/lock/b01515ae-9173-03cb-0cb7-06f3dfbede8b.

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• Any way to select without causing locking in MySQL?

  - by Shore

  Query: SELECT COUNT(online.account_id) cnt from online; But online table is also modified by an event, so frequently I can see lock by running show processlist. Is there any grammar in MySQL that can make select statement not causing locks? And I've forgotten to mention above that it's on a MySQL slave database. After I added into my.cnf:transaction-isolation = READ-UNCOMMITTED the slave will meet with error: Error 'Binary logging not possible. Message: Transaction level 'READ-UNCOMMITTED' in InnoDB is not safe for binlog mode 'STATEMENT'' on query So, is there a compatible way to do this?

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• Locking a file to verify a single execution of a service. How reliable?

  - by Camilo Díaz

  Hello, I am deploying a little service to an UNIX(AIX) system. I want to check if there is no active instance of that service running when starting it. How reliable is to implement that check like this? Try to acquire a lock on a file (w/ FileChannel) If succeeds, keep lock and continue execution If fails, exit and refuse to run the main body I am aware of software like the Tanuki wrapper, however, I'm longing for a simpler(maybe not portable) solution. Regarding PIDFILE(s): I want to avoid using them if possible, as I don't have administrative rights on the machine, neither knowledge in AIX's shell programming.

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• What is wrong with locking non-static fields? What is the correct way to lock a particular instance?

  - by smartcaveman

  Why is it considered bad practice to lock non-static fields? And, if I am not locking non-static fields, then how do I lock an instance method without locking the method on all other instances of the same or derived class? I wrote an example to make my question more clear. public abstract class BaseClass { private readonly object NonStaticLockObject = new object(); private static readonly object StaticLockObject = new object(); protected void DoThreadSafeAction<T>(Action<T> action) where T: BaseClass { var derived = this as T; if(derived == null) { throw new Exception(); } lock(NonStaticLockObject) { action(derived); } } } public class DerivedClass :BaseClass { private readonly Queue<object> _queue; public void Enqueue(object obj) { DoThreadSafeAction<DerivedClass>(x=>x._queue.Enqueue(obj)); } } If I make the lock on the StaticLockObject, then the DoThreadSafeAction method will be locked for all instances of all classes that derive from BaseClass and that is not what I want. I want to make sure that no other threads can call a method on a particular instance of an object while it is locked.

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• Apache / PHP Begins to Deny SQL Requests after about 2000

  - by Daniel Stern

  We have a web page on our server that we use to run administrative scripts. For example, we might run the script "unenrolStudents()" which runs 5,000 SQL SET commands one after another and sets 5000 student entries in an SQL database to unenrolled. However, we are finding that after running a few thousand queries (it is not totally consistent) we will be "locked out" by our server. SYMPTOMS OF LOCKING OUT: - unable to connect to server with winSCP - opening putty with that connection shows a blank screen (no login / pass) - clearing cookies / cache in chrome does NOT fix locking out - other computers in the office ALSO become locked out - locking out can be triggered with a high frequency of requests (10000 in 1 second) or by less over time (10000 in 500 seconds - this will still cause a lockout even though the frequency is much less) We believe this is a security feature of our own Apache. I know we are using Suhosin but I didn't configure it so I don't know. How can I disable this locking effect so that I can confidently run all my SQL requests and they will go through? Has anyone else dealt with this and found workarounds? Thanks DS

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• GAC locking problem when running deployment

  - by Kieran

  We have a NANT script that uses msbuild to compile our visual studio solutions and deploys the .dlls into the GAC. This works well on our integration/test servers as part of continuous integration, cruise control uses the NANT scripts and every time the dlls are put into the GAC without problem. On our local development machines, where we use subversion/vs.net etc. for development, frequently certain dlls do not make it to the GAC when we run the build. We think we have narrowed this down to visual studio and/or a plug in locking the GAC or the dlls for some reason. Strangely if we run the build a second time all the dlls make it to the GAC. We have added various iisreset's to the NANT script in the hope of releasing the lock but to no avail. Can anyone suggest a good approach to attack this problem? All the best

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• SLES 11 - ocfs2 - Locking does not appear to work

  - by Autobyte

  Hi I have two SLES 11 servers that are SAN attached to a Clarion CX-340. The SAN partition has been formatted with ocfs2 and I have both machines setup in a cluster and the cluster is running (all appears to be normal). I have a small java application as a locking test and when I run the application on both machines at the same time, I should get the lock on one server and the other should refuse the lock since the first already holds a lock on that file but in this case both servers get a lock on the same file. Basically my cluster.conf looks like this: node: ip_port = 7777 ip_address = 192.168.10.121 number = 1 name = osrsles10node1 cluster = osrsles10 node: ip_port = 7777 ip_address = 192.168.10.122 number = 2 name = osrsles10node2 cluster = osrsles10 cluster: node_count = 2 name = osrsles10 Please ask for any other info - I really need these locks to be exclusive to each server. Thanks.

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• How safe is locking the screen?

  - by D Connors

  So, both windows and linux have a pretty useful feature that allows you to leave everything running on the PC while also keeping invaders away by locking the screen. My question is: Say I leave my laptop with the screen locked while I go get a donnut, and then it gets stolen. Assuming the thief has access to whatever software he needs, how easy/hard would it be for him to access my (currently logged-in) account? Now let me be clear. I'm not asking if he can access the data on the harddrive. I know he can, and that issue would go under data encryption, which is not my question here. I'm focusing on how hard would it be to get around the "Insert Password" screen, and have full access to my account. I'm looking for answers regarding both OS's; but, if needed, assume Ubuntu. Thank you.

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• Windows 7 Locking up Randomly

  - by Michael Moore

  I've got a Windows 7 machine that is locking up randomly. It can be in the first thirty seconds, or it can be hours later. There is nothing specific I can find that is running when it happens. When it locks, the screen doesn't change, but nothing moves. The waiting icon stops, the mouse stops, keyboard doesn't work, etc. I've even tried the crash on ctrl-scrl registry hack, and it won't even dump the kernel. I've run hardware diagnostics on the RAM and it doesn't find any problems. I would think it is a hardware issue, but on this exact same machine, I can run 64 Bit Ubuntu and it has zero problems. I've even tried reinstalling Windows7 from scratch, and it still happens. Anyone have any ideas? Any good diagnostic tools to recommend? Thanks! Michael

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• Locking down remote desktop using AD GPO

  - by Brettski

  I am currently locking down a companies remote desktop access via a VPN. What I need to do is disable remote printing, file transfer and clipboard via active directory for the workstations that will be accessed. I am having trouble figuring out which GPO's are used to restrict this. My basic approach is to restrict VPN users to port 3389 so the will be able to access their work computers remotely but nothing else (I will look into layer 7 scanning later). With this I want to ensure they are unable to transfer and data via files, printing or the clipboard. The environment is Windows Server 2003

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• optimistic lock-free FIFO queues impl?

  - by uray

  is there any C++ implementation (source codes) of "optmistic approach to lock-free FIFO queues" algorithm?

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• MySQLDump without locking the tables

  - by Raul Singahn

  It seems that if you have many tables, you can only perform a MySQLDump without locking them all, otherwise you can an error. What are the side effects of performing a MySQLDump without locking all the tables; Is the DB snapshot I get this way, consistent? Do I have any other alternative for getting a backup of a MySQL DB with many tables?

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• Compaq R4000 laptop randomly locking up

  - by Josh

  I have a Compaq R4000 laptop with 2GB of RAM, running Ubuntu Linux 9.10. It is randomly locking up on me, approximately once every two days. I have a second partition with Windows XP Home installed, and I have had the system lock up in XP as well, meaning I believe this is a hardware issue. I have run two passes of Memtest86+ with no errors. The system has a fan that has died, so I initially suspected overheating. However the system just locked up on me while I was in the middle of typing a script to warn me / shut down if the temperature was too high. When the lockup happened the temperature was 88°F, so I am now starting to believe that may not be the issue. When the system locks up, I cannot SSH in nor ping it. Nothing shows in syslog when I reboot. I have configured it to send syslog messages to a local server as well and no messages appear on that server when the lockup happens. I am open to any and all advice!

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