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• How do I handle the messages for a simple web-based live chat, on the server side?

  - by Carson Myers

  I'm building a simple live chat into a web application running on Django, but one thing I'm confused about is how I should store the messages between users. The chat will support multiple users, and a chat "session" is composed of users connected to one user that is the "host." The application is a sort of online document collaboration thing, so user X has a document, and users Y and Z would connect to user X to talk about the document, and that would be one chat session. If user Y disconnected for five minutes, and then signed back in and reconnected to user X, he should not get any of the messages shared between users X and Z while he was away. if users X, Y, and Z can have a chat session about user X's document, then users X and Y can connect to a simultaneous, but separate discussion about user Z's document. How should I handle this? Should I keep each message in the database? Each message would have an owner user and a target user (the host), and a separate table would be used to connect users with messages (which messages are visible to what users). Or should I store each session as an HTML file on the server, which messages get appended to? The problem is, I can't just send messages directly between clients. They have to be sent to the server in a POST request, and then each client has to periodically check for the messages in a GET request. Except I can't just have each message cleared after a client fetches it, because there could be multiple clients. How should I set this up? Any suggestions?

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• Am I understanding premature optimization correctly?

  - by Ed Mazur

  I've been struggling with an application I'm writing and I think I'm beginning to see that my problem is premature optimization. The perfectionist side of me wants to make everything optimal and perfect the first time through, but I'm finding this is complicating the design quite a bit. Instead of writing small, testable functions that do one simple thing well, I'm leaning towards cramming in as much functionality as possible in order to be more efficient. For example, I'm avoiding multiple trips to the database for the same piece of information at the cost of my code becoming more complex. One part of me wants to just not worry about redundant database calls. It would make it easier to write correct code and the amount of data being fetched is small anyway. The other part of me feels very dirty and unclean doing this. :-) I'm leaning towards just going to the database multiple times, which I think is the right move here. It's more important that I finish the project and I feel like I'm getting hung up because of optimizations like this. My question is: is this the right strategy to be using when avoiding premature optimization?

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• Sharing a COM port over TCP

  - by guinness

  What would be a simple design pattern for sharing a COM port over TCP to multiple clients? For example, a local GPS device that could transmit co-ordinates to remote hosts in realtime. So I need a program that would open the serial port and accept multiple TCP connections like: class Program { public static void Main(string[] args) { SerialPort sp = new SerialPort("COM4", 19200, Parity.None, 8, StopBits.One); Socket srv = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); srv.Bind(new IPEndPoint(IPAddress.Any, 8000)); srv.Listen(20); while (true) { Socket soc = srv.Accept(); new Connection(soc); } } } I would then need a class to handle the communication between connected clients, allowing them all to see the data and keeping it synchronized so client commands are received in sequence: class Connection { static object lck = new object(); static List<Connection> cons = new List<Connection>(); public Socket socket; public StreamReader reader; public StreamWriter writer; public Connection(Socket soc) { this.socket = soc; this.reader = new StreamReader(new NetworkStream(soc, false)); this.writer = new StreamWriter(new NetworkStream(soc, true)); new Thread(ClientLoop).Start(); } void ClientLoop() { lock (lck) { connections.Add(this); } while (true) { lock (lck) { string line = reader.ReadLine(); if (String.IsNullOrEmpty(line)) break; foreach (Connection con in cons) con.writer.WriteLine(line); } } lock (lck) { cons.Remove(this); socket.Close(); } } } The problem I'm struggling to resolve is how to facilitate communication between the SerialPort instance and the threads. I'm not certain that the above code is the best way forward, so does anybody have another solution (the simpler the better)?

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• Nagios dropping ICMP packets

  - by Ankh2054

  I am running a Nagios server on vmware 4.0 and every now and again during the day it alerts that some of servers cannot be reached via ICMP, clearly staging that a certain percentage of packets send are lost. This does not happen to all servers. I know the servers are actually up, because I have done a parallel test from another windows box, just using simple ping and no packets were lost. I also now from the way we monitor out switch that no packets were lost on those particular ports. Could anyone suggest a way to troubelshoot this further ? AT present this points to the nagios server itself loosing packets. thanks

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• Dependency injection in constructors

  - by andre

  Hello everyone. I'm starting a new project and setting up the base to work on. A few questions have risen and I'll probably be asking quite a few in here, hopefully I'll find some answers. First step is to handle dependencies for objects. I've decided to go with the dependency injection design pattern, to which I'm somewhat new, to handle all of this for the application. When actually coding it I came across a problem. If a class has multiple dependencies and you want to pass on multiple dependencies via the constructor (so that they cannot be changed after you instantiate the object). How do you do it without passing an array of dependencies, using call_user_func_array(), eval() or Reflection? This is what i'm looking for: <?php class DI { public function getClass($classname) { if(!$this->pool[$classname]) { # Load dependencies $deps = $this->loadDependencies($classname); # Here is where the magic should happen $instance = new $classname($dep1, $dep2, $dep3); # Add to pool $this->pool[$classname] = $instance; return $instance; } else { return $this->pool[$classname]; } } } Again, I would like to avoid the most costly methods to call the class. Any other suggestions?

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• windows 2008r2 SNMP hrStorageSize reporting wrong values

  - by Giannis Nohj

  I'm trying to monitor disks on windows 2008 R2 system, but I'm getting wrong values returned from hrStorageSize and hrStorageUsed for one of the 2 disks the system has. Local disk C: is returning correct values, whereas D: disk, which is an SAN disk, is reporting 32G instead of 500G. Output of snmpwalk -v 2c -c public hostname-01 .1.3.6.1.2.1.25.2 : HOST-RESOURCES-MIB::hrStorageDescr.1 = STRING: C:\ Label: Serial Number 7ff87ca6 HOST-RESOURCES-MIB::hrStorageDescr.2 = STRING: D:\ Label:Data Serial Number dab5b0b9 ... HOST-RESOURCES-MIB::hrStorageAllocationUnits.1 = INTEGER: 4096 Bytes HOST-RESOURCES-MIB::hrStorageAllocationUnits.2 = INTEGER: 4096 Bytes ... HOST-RESOURCES-MIB::hrStorageSize.1 = INTEGER: 35834383 HOST-RESOURCES-MIB::hrStorageSize.2 = INTEGER: 7864320 ... HOST-RESOURCES-MIB::hrStorageUsed.1 = INTEGER: 32460169 HOST-RESOURCES-MIB::hrStorageUsed.2 = INTEGER: 3192302 I have calculated the first disk (C:) size as 136G, which is correct. On the other hand, D: is calculated as 30G, where it should be 500G. I also tried fsutil on the system and the output was correct. Anyone have any ideas?

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• Jetty 7 will not allow me to customize a session cookie path

  - by Bob Obringer

  Using Jetty 7.0.2, I am unable to set a custom session cookie path. I am hosting multiple sites on the same server using apache to proxy requests to the proper context. (replaced http as htp as stackoverflow thinks my multiple links might be spam) <VirtualHost *:80> ServerName context.domain.com ProxyRequests On ProxyPreserveHost Off <Proxy *:80> Order deny,allow Allow from 127.0.0.1 </Proxy> ProxyPass / htp://localhost:8080/context/ ProxyPassReverse / htp://localhost:8080/context/ <Location /> Order allow,deny Allow from all </Location> </VirtualHost> Jetty is running on the same server on port 8080 and my context is available @ /context The user accesses the application @ htp://context.domain.com but jetty is setting the path for the session cookie @ /context. This prevents the browser from accessing the cookie since the the actual path to the context is not being used. I need to override Jetty's default setting to set the cookie for the context, and set the path at the root ( / ). In my Jetty's webdefault.xml I have the following, which is partially working: <context-param> <param-name>org.eclipse.jetty.servlet.SessionCookie</param-name> <param-value>CustomCookieName</param-value> </context-param> <context-param> <param-name>org.eclipse.jetty.servlet.SessionPath</param-name> <param-value>/</param-value> </context-param> The cookie is properly set with a custom name, but it is NOT setting the SessionPath. No matter what I set the value to... it refuses to set a cookie at any path but /context. This has been driving me crazy so any help would be greatly appreciated.

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• GRUB2 Boot Configuration

  - by MA1

  Recently i installed GRUB2, everything is working fine. When my system is started my monitor is showing something like the following "Minimal BASH-Like line editing is supported. For the first word, TAB lists possible command completions. Anywhere else TAB lists the possible completions of a device/filename." Press "Esc" key to enter the menu. Boot windows... and when i press the Esc key it then shows the GRUB2 menu showing list of operating systems installed on my system How the remove "Minimal BASH-Like line editing ...." text. I only need this line Press "Esc" key to enter the menu. Boot windows... Note: Both my WindowsXP and Fedora12 are working fine and loading with no problem.

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• MS-DOS application sending screen output to LPT printer

  - by gadget00

  We have a MS-DOS application(coded in FoxPro), and recently had this glitch: the screen menu of the application without reason starts printing in an LPT Panasonic KX-1150 printer. It's a never ending print of all the screens of the application, as if the main output instead of sending it to the monitor, sends it to the printer! It creates a unnamed document with N/D pages and keeps printing forever. We have to turn the printer off and then kill the document in the spool to stop it... The printer is installed with a Generic/Text driver, and has happened to us both in WindowsXP and Win7. What can this be? Thanks in advance

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• How to design data storage for partitioned tagging system?

  - by Morgan Cheng

  How to design data storage for huge tagging system (like digg or delicious)? There is already discussion about it, but it is about centralized database. Since the data is supposed to grow, we'll need to partition the data into multiple shards soon or later. So, the question turns to be: How to design data storage for partitioned tagging system? The tagging system basically has 3 tables: Item (item_id, item_content) Tag (tag_id, tag_title) TagMapping(map_id, tag_id, item_id) That works fine for finding all items for given tag and finding all tags for given item, if the table is stored in one database instance. If we need to partition the data into multiple database instances, it is not that easy. For table Item, we can partition its content with its key item_id. For table Tag, we can partition its content with its key tag_id. For example, we want to partition table Tag into K databases. We can simply choose number (tag_id % K) database to store given tag. But, how to partition table TagMapping? The TagMapping table represents the many-to-many relationship. I can only image to have duplication. That is, same content of TagMappping has two copies. One is partitioned with tag_id and the other is partitioned with item_id. In scenario to find tags for given item, we use partition with tag_id. If scenario to find items for given tag, we use partition with item_id. As a result, there is data redundancy. And, the application level should keep the consistency of all tables. It looks hard. Is there any better solution to solve this many-to-many partition problem?

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• How to track my kid's Multi-Browser website history

  - by Rachel

  My kid is 14, homeschooled and capable computer user. All of her school work is done online; the computer literacy course even uses 3 different browsers, Chrome, IE, and Firefox. I have 2 laptops, running Win7 (one is Pro, the other Home). Is there a way to get all of her browser history in one place? I have to account for 60 minutes of class time per subject per day, but trying to do this across all 3 is getting too complicated. Thanks! PS. My kid and I talk about internet safety and usage regularly and she knows that I monitor where she goes and how long she is there. Secrecy is not an issue.

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• Internet printing : print to iOS gateway -> AirPrint / something -> Laser printers

  - by user75129

  I've done a bit of research on the Internet, and it looks like I'm on a dead end. My goal is to minimize cost, and be able to send and print documents AUTOMATICALLY (may be 10 or 20 pages per day) to a laser printer in a remote office. The preliminary method is to use: iOS 5.1.1 (JB'ed) with 3G connection, HP (or other brands) printer with AirPrint, iCloud's Documents and may be write some launchd scripts to monitor any new documents in iCloud. May be with other software. I am not sure yet. By using the cloud, I can upload new docs to the cloud anywhere in my city, and the iOS will be able to see them within a reasonable amount of time, then print it. But it seems this combo is not workable. Anyone got any advice on how to make this set up work, or propose other alternatives that requires NO PC or Mac? Currently I have a 3GS with 3G connectivity spare. Need to buy a new printer though.

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• Safari Web Inspector is not updating when I update an element with ajax

  - by Ashley

  I have a checkout page http://www.oipolloi.com/oipolloi/shop/viewbasket.php with multiple ajax calls after certain items update (EG look up postage cost when country is changed, then update discount boxes etc). I've asked for help in the past about the best method of making sure ALL calls have returned before allowing the form to be submitted for payment processing: http://stackoverflow.com/questions/2290372/how-do-i-prevent-form-submission-until-multiple-ajax-calls-have-finished-jquery I was fairly happy that the logic in the finished solution was correct, but I have still been receiving reports that people using Safari are able to submit the form without the ajax calls returning properly. I have tried using the Safari Web Inspector to debug but it seems that when you Inspect Element, then update an element with an ajax call, the Inspector doesn't seem to update. I am updating hidden fields, so it's hard to be able to know whether the problem lies with the DOM not being updated properly, or the Inspector itself. I'm using Safari 4.0.5 on PC and you can reproduce the problem above by looking for a div id="countryFieldsBilling" with Web Inspector. It should contain three hidden fields that are initially empty. You can try to make it update (or not) by choosing a country from the select menu at the bottom of 'Shipping Address' box, and then clicking the 'click to use Shipping Address' link at the top of the 'Billing Address' just below. The behaviour I am seeing is that the country chosen in the shipping select gets copied correctly to the country in the billing select, but the hidden inputs in the Web Inspector do not get updated. When these hidden inputs do not get updated, this causes the problem that Mac Safari users report. If you can let me know either how to get Web Inspector to work properly, or something else I may have missed in the behaviour of Mac Safari that may cause these problems, that would be great. Thanks in advance

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• Entity Framework and WCf

  - by Nihilist

  Hi I am little confused on designing WCf services with EF. When using WCf and EF, where do we draw this line on what properties to return and what not to with the entity. Here is my scenario I have User. Here are the relations. User [1 to many] Address, User [ 1 to many] Email, User [ 1 to many] Phone So now on the webform, on page1 I can edit user information. say I can edit few properties on the user entity and can also edit address, phone, email entities[ like add / delete and update any] On page2, i can only update user properties and nothing related to navigation properties [ address, email, phone]. So when I return the User Entity [ OR DTO] should i be returning the navigation properties too? Or should the client make multiple calls to get navigation properites. Also, how does it go with Save? Like should the client make multiple calls to save user and related entites or just one call to save the graph? Lets say, if I just have a Save(User user) [ where user has all the related entities too] both page1 and page2 will call save and pass me the user. but one page1 i will need a lot more information. but on page2 i just need the user primitive properties. So my question is, where do we draw this line, how do we design theses services ? Is the WCF operation designed on the page and the fields it has ? I am hoping i explained my problem well enough.

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• NSNotification vs. Delegate Protocols?

  - by jr

  I have an iPhone application which basically is getting information from an API (in XML, but maybe JSON eventually). The result objects are typically displayed in view controllers (tables mainly). Here is the architecture right now. I have NSOperation classes which fetch the different objects from the remote server. Each of these NSOperation classes, will take a custom delegate method which will fire back the resulting objects as they are parsed, and then finally a method when no more results are available. So, the protocol for the delegates will be something like: (void) ObjectTypeResult:(ObjectType *)result; (void) ObjectTypeNoMoreResults; I think the solution works well, but I do end up with a bunch of delegate protocols around and then my view controllers have to implement all these delegate methods. I don't think its that bad, but I'm always on the lookout for a better design. So, I'm thinking about using NSNotifications to remove the use of the delegates. I could include the object in the userInfo part of the notification and just post objects as received, and then a final event when no more are available. Then I could just have one method in each view controller to receive all the data, even when using multiple objects in one controller.† So, can someone share with me some pros/cons of each approach. Should I consider refactoring my code to use Events rather then the delegates? Is one better then the other in certain situations? In my scenario I'm really not looking to receive notifications in multiple places, so maybe the protocol based delegates are the way to go. Thanks!

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• PC powers up but there is no display

  - by Matthew

  I built a computer with standard components I bought from Newegg about three years ago. It ran great for 2 years and has sat powered down for the last year. I tried to power it up today and the display was blank. It powers up, lights come on, drives start spinning but there is nothing on the display. I verified that the monitor and video adapter work. I also tried the video adapter in a different slot on the mother board with no luck. What's the next thing I should try? Is the mother board shot? Thanks.

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• How to use named_scope to incrementally construct a complex query?

  - by wbharding

  I want to use Rails named_scope to incrementally build complex queries that are returned from external methods. I believe I can get the behavior I want with anonymous scopes like so: def filter_turkeys Farm.scoped(:conditions => {:animal => 'turkey'}) end def filter_tasty Farm.scoped(:conditions => {:tasty => true}) end turkeys = filter_turkeys is_tasty = filter_tasty tasty_turkeys = filter_turkeys.filter_tasty But say that I already have a named_scope that does what these anonymous scopes do, can I just use that, rather than having to declare anonymous scopes? Obviously one solution would be to pass my growing query to each of the filter methods, a la def filter_turkey(existing_query) existing_query.turkey # turkey is a named_scoped that filters for turkey end But that feels like an un-DRY way to solve the problem. Oh, and if you're wondering why I would want to return named_scope pieces from methods, rather than just build all the named scopes I need and concatenate them together, it's because my queries are too complex to be nicely handled with named_scopes themselves, and the queries get used in multiple places, so I don't want to manually build the same big hairy concatenation multiple times.

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• check_ssh executed from Nagios server returns "Server answer: ", nothing else

  - by phs

  Commmand works on the host I need to monitor (its IP is denoted as $HOSTADDRESS$ here): [root@host ~]# /usr/local/nagios/libexec/check_ssh localhost SSH OK - OpenSSH_4.3 (protocol 2.0) However, on the Nagios server, it does not: root@server:~# /usr/lib/nagios/plugins/check_ssh -H $HOSTADDRESS$ Server answer: I can see that the port is open: root@server:~# /usr/lib/nagios/plugins/check_tcp -H $HOSTADDRESS$ -p 22 TCP OK - 0.123 second response time on port 22|time=0.123277s;;;0.000000;10.000000 And I can verify with telnet: root@server:/etc/nagios3/conf.d# telnet $HOSTADDRESS$ 22 Trying $HOSTADDRESS$... Connected to $HOSTADDRESS$. Escape character is '^]'. After searching the web for two hours and trying different suggestions I am out of ideas. I have several other hosts with similar setup, and they don't have this problem. I have compared the configs and they look the same (I think). I am clearly missing something here.

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• Should i write my own forum? If my site has banning/PM/etc?

  - by acidzombie24

  I built a site from scratch (already done). It has banning, PM, comments, etc. The PMs and comments are done using markdown (like SO system). Should i write my own forum code or should i find one already made? What are reasons for or against writing my own? There are pros and cons for writing my own or using another software. But some cons keeping me from using another forum software is Multiple Logins: One for the site, one for separate forums. Need to Customization code: I'll need to change the toolbar in the forum software so i can access pages on the regular site. Look consistency: It may look drastically different from my site even after applying lots of css changes. Banning and User consistency. Users may be ban on site or on forums but not the other. users may select a different or multiple usernames on the forum instead of being forced to use the same username on both site and forum. What are reasons for or against writing my own and using forum software?

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• Is Zabbix the right tool for me?

  - by hortitude

  I just want to monitor a small handful of servers (less than 10). From reading various places it sounds like the top leading contenders (for open source at least) are: nagios munin zabbix From what I have read a lot of people tend to use munin and nagios together -- munin for history and graphs, and nagios for alerting. On the other hand it sounds like Zabbix is a more complete solution and easier to configure than either of the other two. So I was thinking of going that route. My thoughts right now are: What are the general disadvantages of Zabbix? Does Zabbix have a small footprint on boxes it is monitoring? Do I really need to setup an entire other server for it? I currently have a server that is under very light load -- can I dual purpose it?

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• Database schema for a library

  - by ABach

  Hi all - I'm designing a library management system for a department at my university and I wanted to enlist your eyes on my proposed schema. This post is primarily concerned with how we store multiple copies of each book; something about what I've designed rubs me the wrong way, and I'm hoping you all can point out better ways to tackle things. For dealing with users checking out books, I've devised three tables: book, customer, and book_copy. The relationships between these tables are as follows: Every book has many book_copies (to avoid duplicating the book's information while storing the fact that we have multiple copies of that book). Every user has many book_copies (the other end of the relationship) The tables themselves are designed like this: ------------------------------------------------ book ------------------------------------------------ + id + title + author + isbn + etc. ------------------------------------------------ ------------------------------------------------ customer ------------------------------------------------ + id + first_name + first_name + email + address + city + state + zip + etc. ------------------------------------------------ ------------------------------------------------ book_copy ------------------------------------------------ + id + book_id (FK to book) + customer_id (FK to customer) + checked_out + due_date + etc. ------------------------------------------------ Something about this seems incorrect (or at least inefficient to me) - the perfectionist in me feels like I'm not normalizing this data correctly. What say ye? Is there a better, more effective way to design this schema? Thanks!

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• VGA resolution with Sony Bravia TV

  - by prestomation

  I just bought Sony Bravia KDL40S5100 tv. The VGA input is acting weird. I have a Gateway desktop with Windows 7 and Intel 945 graphics. I also have a laptop running Ubuntu 9.04. The TV will not display the gateway when the resolution is over 1360x768, I have to wait for it to time out and bring me back. The Intel driver even urges me to switch to the "recommended" 1920x1080. I just installed Win7 using this tv as the monitor. When the orginial welcome screen started after setup, it started me at 1080. I had to start in safemode to set a res that would work! When I plug my laptop into the TV, 1920x1080 works just fine. Any ideas? This laptop also has Win7, which I am going to try, but I haven't gotten a chance yet.

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• Why does my iTunes use so much CPU time?

  - by bikesandcode

  I have a roughly 2 year old Macbook (10.5). I have iTunes 10. When iTunes is playing MP3s, I see CPU usage of the iTunes process in the system monitor ranging from 65%-75%. When I pause the music, I see CPU usage of about 65%-75%. I do not have any visualisations going, to my knowledge I have not turned on any CPU destroying features, my music library isn't tiny, but it's hardly huge (3GB). This is mildly annoying when I'm plugged into the wall as I only have slightly longer compile times, but if I am out and about, this is a major drain on the battery. Using VLC I see CPU loads of ~= 10% at the most when listening to music and generally lower. What the heck is iTunes doing?

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• Using JQuery in an AJAX control and avoiding conflicts

  - by Rich Andrews

  Hi, I am using JQuery within a custom AJAX user control (part of a home grown toolkit) and I need to ensure that JQuery is present on the hosting page. There can be multiple instances of the control on a page and some controls may need to use different versions of JQuery. At the moment I am using the following code to load in JQuery when the control initializes... Page.ClientScript.RegisterClientScriptInclude(Page.GetType(), "jquery-1.4.4.min.js", this.ResolveUrl("TextControlPlugin/lib/jquery-1.4.4.min.js")); This works because the scriptmanager handles not putting multiple copies of the same script into he page. Problems... I cannot use JQuery statically in the calling page (I may not have a control on the page but need to use JQuery) The scriptmanager appears to handle only duplicate URL's and I will need to deploy it from potentially 2 different URL's (the calling page's copy and the controls copy) So, is there a way to isolate a version of JQuery to the context of my control that doesnt interfear with any use of JQuery from the calling page? The developer writing the page may not have access to the internals of the control. I have looked at JQuery.noConflict() but cannot seem to get it to work correctly - I believe I'm having problems with the order in which the scripts are injected into the page - I keep getting JQuery is undefined errors. Any help would be much appreciated

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• Can't open Control Panel or IE

  - by Josh

  I have a XP computer where when ever I try to open Control Panel nothing happens, nothing flashes on the screen. Same thing with Internet Explorer. I've scanned the computer with Malwarebytes and Avast, Malwaresbytes found some Adware which it removed without problems. Avast found nothing. I looked at the running processes with Process Explorer, nothing malicious running. And looked at a Process Monitor output when I tried to run IE, nothing obviously wrong. The process just decides to exit. What can I try next? I would suspect corrupt IE install but Control Panel doesn't work either. UPDATE: Nether work in Safe Mode under the user account. (only 1 user on the computer) But in Safe Mode, under the built in Administrator account, they work. So what ever is broken, is only broken in the one account. Anything under the HKCU registry key that could break this?

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