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  • Strategy to allow emergency access to colocation crew

    - by itsadok
    I'm setting up a server at a new colocation center half way around the world. They installed the OS for me and sent me the root password, so there's obviously a great amount of trust in them. However, I'm pretty sure I don't want them to have my root password on a regular basis. And anyway, I intend to only allow key-based login. On some cases, though, it might be useful to let their technical support log in through a physical terminal. For example, if I somehow mess up the firewall settings. Should I even bother worrying about that? Should I set up a sudoer account with a one-time password that will change if I ever use it? Is there a common strategy for handling something like this?

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  • Windows Server 2008 R2 and OSX 10.5/.6/.7, Search, Spotlight

    - by Keith Loughnane
    I'm handling a migration from a on old mac server to a Windows Server 2008 R2 machine running a 12TB(10 usable) RAID5 server. It's using an SMB share and now the OSX 10.5/.6 users can search sometimes it works but takes up to 10 minutes. The OSX 10.7 machine seems to be fine. I've looked in the root of the shared drive for a .Spotlight-V100 file (ls -a) but it doesn't seem to be there. mdutil says indexing is on for that volume and I have cleared the index using mdutil -E /Volumes/MeSharedVolume numerous times. Any ideas?

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  • How to redirect (or Alias) jump page with Apache

    - by Meltemi
    I'm not an Apache expert but need to make a small change to a web server. We are introducing a "jump page" URL that is different from a primary URL (for tracking reasons). /productA/index.html /productA/jump_index.html Basically i want to log that jump_index.html was requested and then return index.html. I don't want the client to wait 8 seconds or so for a redirect. How should we be handling this? Simply symlink (or alias) the file in the filesystem? Use mod_alias Alias Match (if so how exactly)? something better still?

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  • Distributed file systems

    - by Neeraj
    I need to implement a distributed storage system for a set of nodes(devices) connected in a mesh network. So what basically my design goals are: The storage system should be capable of handling dynamic entry and exit of nodes. Replication (for fault tolerance). For this i am thinking of using a Distributed file system. Every node could access data in the other nodes in a transparent manner. Are there some simple, easily pluggable opensource implementations? Thanks for your thoughts!

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  • how to get vendor id and product id of a plugged usb device on windows

    - by new
    Hello all, I am using Qt on windows platform. i want to get and display vendor id and product id of a plugged usb device from my local system. Below is my full source code to get the vendor id and product id from the usb device. when i run the my qt application it does not throw me any errors . so i plug the usb device into the system. but my print statement displays the result as below qDebug ()<DevicePath; i get the result as 0x4 Whether i have any implementation mistakes in my source code ? if so please guide me what i am doing wrong.. Have i missed out any other functions ? Is it possible to get the vendor id and product id from the usb device based on my source code .( my implementation of the code ) ? kindly find my source code below static GUID GUID_DEVINTERFACE_USB_DEVICE = { 0xA5DCBF10L, 0x6530, 0x11D2, { 0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED } }; HANDLE hInfo = SetupDiGetClassDevs(&GUID_DEVINTERFACE_USB_DEVICE,NULL,NULL,DIGCF_PRESENT | DIGCF_INTERFACEDEVICE); if ( hInfo == INVALID_HANDLE_VALUE ) { qDebug ()<<"invalid"; } else { qDebug ()<<"valid handle"; SP_DEVINFO_DATA DeviceInfoData; DeviceInfoData.cbSize = sizeof(SP_DEVINFO_DATA); SP_INTERFACE_DEVICE_DATA Interface_Info; Interface_Info.cbSize = sizeof(Interface_Info); BYTE Buf[1024]; DWORD i; DWORD InterfaceNumber= 0; PSP_DEVICE_INTERFACE_DETAIL_DATA pspdidd = (PSP_DEVICE_INTERFACE_DETAIL_DATA)Buf; for (i=0;SetupDiEnumDeviceInfo(hInfo,i,&DeviceInfoData);i++) { DWORD DataT; LPTSTR buffer = NULL; DWORD buffersize = 0; while (!SetupDiGetDeviceRegistryProperty( hInfo,&DeviceInfoData,SPDRP_DEVICEDESC,&DataT,(PBYTE)buffer,buffersize,&buffersize)) { if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) { // Change the buffer size. if (buffer) LocalFree(buffer); buffer = (LPTSTR)LocalAlloc(LPTR,buffersize); } else { // Insert error handling here. break; } qDebug ()<<(TEXT("Device Number %i is: %s\n"),i, buffer); if (buffer) LocalFree(buffer); if ( GetLastError()!=NO_ERROR && GetLastError()!=ERROR_NO_MORE_ITEMS ) { // Insert error handling here. qDebug ()<<"return false"; } InterfaceNumber = 0; // this just returns the first one, you can iterate on this if (SetupDiEnumDeviceInterfaces(hInfo,NULL,&GUID_DEVINTERFACE_USB_DEVICE,InterfaceNumber,&Interface_Info)) { printf("Got interface"); DWORD needed; pspdidd->cbSize = sizeof(*pspdidd); SP_DEVICE_INTERFACE_DETAIL_DATA *pDetData = NULL; DWORD dwDetDataSize = sizeof (SP_DEVICE_INTERFACE_DETAIL_DATA) + 256; SetupDiGetDeviceInterfaceDetail(hInfo, &Interface_Info, pDetData,dwDetDataSize, NULL,&DeviceInfoData); qDebug ()<<pDetData->DevicePath; //qDebug ()<<QString::fromWCharArray(pDetData->DevicePath); } else { printf("\nNo interface"); //ErrorExit((LPTSTR) "SetupDiEnumDeviceInterfaces"); if ( GetLastError() == ERROR_NO_MORE_ITEMS) printf(", since there are no more items found."); else printf(", unknown reason."); } // Cleanup SetupDiDestroyDeviceInfoList(hInfo); qDebug ()<<"return true"; } } }

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  • How to structure a Kohana MVC application with dynamically added fields and provide validation and f

    - by Matt H
    I've got a bit of a problem. I have a Kohana application that has dynamically added fields. The fields that are added are called DISA numbers. In the model I look these up and the result is returned as an array. I encode the array into a JSON string and use JQuery to populate them The View knows the length of the array and so creates as many DISA elements as required before display. See the code below for a summary of how that works. What I'm finding is that this is starting to get difficult to manage. The code is becoming messy. Error handling of this type of dynamic content is ending up being spread all over the place. Not only that, it doesn't work how I want. What you see here is just a small snippet of code. For error handling I am using the validation library. I started by using add_rules on all the fields that come back in the post. As they are always phone numbers I set a required rule (when it's there) and a digit rule on the validation-as_array() keys. That works. The difficulty is actually giving it back to the view. i.e. dynamically added javascript field. Submits back to form. Save contents into a session. View has to load up fields from database + those from the previous post and signal the fields that have problems. It's all quite messy and I'm getting this code spread through both the view the controller and the model. So my question is. Have you done this before in Kohana and how have you handled it? There must be an easier way right? Code snippet. -- edit.php -- public function phone($id){ ... $this->template->content->disa_numbers = $phones->fetch_disa_numbers($this->account, $id); ... } -- phones.php -- public function fetch_disa_numbers($account, $id) { $query = $this->db->query("SELECT id, cid_in FROM disa WHERE owner_ext=?", array($id)); if (!$query){ return ''; } return $query; } -- edit_phones.php --- <script type="text/javascript"> var disaId = 1; function delDisaNumber(element){ /* Put 'X_' on the front of the element name to mark this for deletion */ $(element).prev().attr('name', 'X_'+$(element).prev().attr('name')); $(element).parent().hide(); } function addDisaNumber(){ /* input name is prepended with 'N_' which means new */ $("#disa_numbers").append("<li><input name='N_disa"+disaId+"' id='disa'"+ "type='text'/><a class='hide' onClick='delDisaNumber(this)'></a></li>"); disaId++; } </script> ... <php echo form::open("edit/saveDisaNumbers/".$phone, array("class"=>"section", "id"=>"disa_form")); echo form::open_fieldset(array("class"=>"balanced-grid")); ?> <ul class="fields" id="disa_numbers"> <?php $disaId = 1; foreach ( $disa_numbers as $disa_number ){ echo '<li>'; echo form::input('disa'.$disaId, $disa_number->cid_in); echo'<a class="hide" onclick="delDisaNumber(this)"></a>'; echo "</li>"; $disaId++; } ?> </ul> <button type="button"onclick="addDisaNumber()"><a class="add"></a>Add number</button> <?php echo form::submit('submit', 'Save'); echo form::close(); ?>

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  • Routing to a Terminal Services Cluster

    - by Dave
    I am trying to connect to a Load Balanced Windows 2008 R2 cluster using Remote Desktop Services. I have no trouble connecting to the the Servers' IP addresses (.253.16 and .253.17) or the Cluster address (.253.20) from inside the subnet (.253). The trouble is when I try to connect from the other subnet(.251). I can remote to the other non-clustered servers (.253.12 and .253.15) inside the .253 subnet from the .251 without an issue. I receive a ping reply from the cluster and other servers when I am on the .251 subnet. But when I try to connect via remote desktop it times out but only to any of the IPs on the cluster (.20,.17,.16). My ASA 5510 handling the routing reports message in the log: Deny TCP (no connection) from 192.168.251.2/4283 to 192.168.253.16/3389 flag FIN PSH ACK Here is a picture if it helps http://dl.dropbox.com/u/4217864/terminal%20server.jpg Thanks for any help

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  • How do I set permissions structure for multiple users editing multiple sites in /var/www on Ubuntu 9

    - by Michael T. Smith
    I'm setting up an Ubuntu server that will have 3 or 4 VirtualHosts that I want users to be able to work in (add new files, edit old files, etc.). I currently plan on storing the sites in /var/www but wouldn't be opposed to moving it. I know how to add new users, I know how to add new groups. I'm unsure of the best way to handle users being only able to edit some sites. I read over the answers here in this question, so I was thinking I could setup a group and add users to that group, but then they'd all have essentially the same permissions. Am I just going to have to assign each user specific permissions? Or is there a better way of handling this? Added: I should also note, that I'll have each user login in via SSH/sFTP. The users would never need to do anything else on the server.

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  • How to design this class hierarchy?

    - by devoured elysium
    I have defined an Event class: Event and all the following classes inherit from Event: AEvent BEvent CEvent DEvent Now, with the info I gather from all these Event classes, I will make a chart. With AEvent and BEvent, I will generate points for that chart, while with CEvent and DEvent I will paint certain regions of the chart. Now, how should I signal this in my class hierarchy? Should I make AEvent and BEvent inherit from PointEvent while CEvent and DEvent inherit from RegionEvent, being that both RegionEvent and PointEvent inherit from Event? Should I add a field with an Enum to Event with 2 values, Point and Region, and each of the child classes set their value to it? Should I use some kind of pattern here? Which one? Thanks.

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  • How to do IIS SSL server redirects correctly? Is meta refresh needed?

    - by Jesse
    Hi all! I think our backend programmer/server admin is handling our SSL redirects pretty wonky - see it in action here: www.mchenry.edu/parentorientation First off, see how it redirects to index2.asp? Is this necessary? Can't she easily redirect to the original index.asp but have it be https:// instead? Also, she is using a meta refresh on the original index.asp page to redirect to index2.asp as well, and she says this is for backup, in case the server configs change and the server can't handle the redirect so then the webpage would take over. Finally, she said she tried using the server redirect solely but that it kept looping on itself- what did she do wrong? Is this even possible? Is she giving us a snow job or what? I want a better understanding of what is happening here so I can talk to my boss about it, because this is driving me up the wall. Thanks for any info you can provide.

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  • Anyone willing to help out a javascript n00b? :-)

    - by Splynx
    Since I am asking for a lot, and know it, the following is a wall of text for those who might show some interest and want to know a little before offering their help to me. First a little about my level of programming skills, and a little about what I ask for. Where I'm at: I am not totally new to Javascript, and have dabbled a little with PHP earlier - well have dabbled a lot with PHP in fact, but never got good at it because I program alone. And I have until now never used forums to get help etc. other that searching to see if anyone else had my problem before and what the solution was. So I am not a intuitive or talented programmer, I'm more of a very maticulate programmer and you would be surprised how far you can get with if else... (ok that's a joke hehe). My solutions are usually (I am guessing here) not the best ones - and slow I take it, and the code is usually too long and I have to look up most of the stuff I use (really a lot of it is not done in "freehand"). I have a LOT of experience with HTML and CSS, and have always done well formed markup, as well as I am really into x-browsing and always require that my work validates when it's done. I also worry about optimizing a lot, and work with sprites for images, minimize the number of http requests etc, using H1,H2 etc. where it is logically correct, as well as use the correct elements and not just div span or p it... So because I am a workhorse and very maticulate I can actually pull off some quite "advanced" features, but it's always the basics that bite me in the end. Not fully understanding the syntax and so on usually gives me problems. Have recently discovered jQuery - wich is a lot of fun.... But I want to use it for the DOM node manipulation/handling only. As I mentioned I worry about optimizing, and jQuery used for everything seems... well not optimal, it strikes me as doing it yourself when possible is faster than accesing another script that may take a whole lot of other considerations into perspective when handling your variables and objects (and I am just guessing here since I as explained know nothing). So thats where I'm at... As mentioned I just started with javascript for "real" so I do not have much to show, but at the end of my WOT you can see two unfinisheded scripts I have made so you can see where I'm at roughly - just check out the URL without the /feedback.html for the second example (I am only allowed to post 1 link since I am also a SO n00b) (and for those rushing over to a validation service, remember I wrote "when it's done"...) What I ask for: I am figuring this... I have a piece of code I am working on at the moment, and this little project has taught me a whole lot already, and I have "grown" a lot as a javascript programmer. If I add a whole lot of comments to the script, and explain what it is intended to do, will you then show me where: I am writing incorrect code - making mistakes Where/how my code could be more optimal Where I am just simply being a muppet The code I want to use as the background for the tuition is the one here http://projects.1000monkeys.dk/feedback.html Use firebug and have a quick look see...

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  • error: ‘struct mcontext_t’ has no member named ‘eip’

    - by user353573
    original is struct sigcontext *sc; after changing to struct mcontext_t, error occur. How to fix it? error: ‘struct mcontext_t’ has no member named ‘eip’ #include <stdio.h> #include <signal.h> #include <asm/ucontext.h> static unsigned long target; void handler(int signum, siginfo_t *siginfo, void *uc0){ struct ucontext *uc; mcontext_t *sc; uc = (struct ucontext *)uc0; sc = &uc->uc_mcontext; sc->eip = target; }

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  • Torrent, ISA Server 2006 and packet dropped due to TCP_NOT_SYNC

    - by Pascal
    Hi, I'm trying to get uTorrent 2.0.4 to work in a DMZ machine, protected by a ISA Server 2006. I've opened 1 inbound port (via publishing) and opened all the higher ports for that specific machine that runs uTorrent on my DMZ, and it's working almost fine. The problem is that I keep getting packets dropped with 0xc0040017 FWX_E_TCP_NOT_SYN_PACKET_DROPPED. Is there any way to disable this via registry? Is there any way around this? The download speed fluctuates a lot, and when I starts hitting the upper limit that I've defined in uTorrent, the errors start poping up a lot, and the download speed goes way down, and the process repeats on and on Tks Edit My outbound rules are: Port Range: TCP 10000-65535 Outbound Port Range: UDP 10000-65535 Send Edit It's probably a bug handling requests from Windows 7. When I installed the uTorrent on a XP machine, the problem went away

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  • Are Plesk server backups useful?

    - by Michael T. Smith
    I'm working for a startup now, and I'm the programmer. Because of our small team size, I'm also handling the server management for now (until we get a dedicated server administrator.) I've never used Plesk before, and the server we're using (a Media Temple Dedicated Virtual server) had it installed when I got here. One of my first jobs was to set up backups: Plesk was already running it's nightly server-wide backups. I created a small script to dump the web app, it's DBs and any assets, tar them, store them, and then copy them to another small server we have (to backup the backups.) But, we're constantly running into hard drive space issues because of the Plesk backups. And I'm wondering, are they useful? If I have the web app and all of it's assets, I could easily enough get another server up and running. Do we need to keep running Plesk's backups? Thoughts?

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  • How to implement Comet in database side?

    - by Morgan Cheng
    I have been searched for this question for a long time. How to implement Comet in database side? To support Comet, we'd better have a web server stack that supports asynchronous operation. So, Apache is not a option. There are some open source web server such as tornado can do asynchronous http handling. This is in web server level. In database level, how to make web server know that some event happens in database? There should be a asynchronous way to let web server know that something updated in database. Polling is not a option. Is there any example available?

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  • svn commit is hung at start of commit

    - by jwhitlock
    I'm commiting a large changeset, including a large binary file (180 MB) over a slow VPN connection. It looks for all the world like it is stalled. How can I diagnose where it is stuck? The output is: $ svn commit -m "My commit message" Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)` Local subversion is 1.6.9 on Linux, KDE 4.3, and svn status shows ML . L ws M ws/manage.py L ws/locales L ws/locales/ja_JP L ws/locales/ja_JP/LC_MESSAGES The process isn't using much of any resources. The server is Linux, served by Apache and mod_dav_svn, same subversion 1.6.9. I can't see any process that is handling the commit.

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  • Django: How to create a model dynamically just for testing

    - by muhuk
    I have a Django app that requires a settings attribute in the form of: RELATED_MODELS = ('appname1.modelname1.attribute1', 'appname1.modelname2.attribute2', 'appname2.modelname3.attribute3', ...) Then hooks their post_save signal to update some other fixed model depending on the attributeN defined. I would like to test this behaviour and tests should work even if this app is the only one in the project (except for its own dependencies, no other wrapper app need to be installed). How can I create and attach/register/activate mock models just for the test database? (or is it possible at all?) Solutions that allow me to use test fixtures would be great.

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  • Apache2 memory usage when uploading large files

    - by abhaga
    Hi, I am running apache2.2.12 along with PHP 5.2.10. PHP is configured to run as a separate process through fcgid. The problem is that when users upload a file, size of the apache process swells by almost the same amount. So if somebody tries to upload a 200 MB file, one of the child process swells to current size+200 MB. If 2 users simultaneously start uploading, my server crashes. Now it is the virtual memory size which is increasing but since I am on a OpenVZ based VPS, that is what counts. My questions are: Is it the normal Apache behavior or can I do something to fix this? If not, is there a more memory efficient way of handling big file uploads. Going by the current behavior, I will need 1 GB of free RAM for every apache child accepting a upload. Thanks! Abhaya -

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  • Music tagging software more consistent than Tag&Rename?

    - by Billy ONeal
    A few years ago I spent an insane amount of time using the excellent Tag&Rename program. However, I find that for random, inexplicable reasons, some music tools simply disregard my tags, drop or destroy the album art, or have strange handling around some characters. For example, "AC/DC" is poorly handled by most music players when I use Tag&Rename to write the tags. And if I write the tag in iTunes, Winamp seems to not like it, vice versa, and neither of those work with Amarok. Is there a piece of software that works like Tag&Rename but is more compatible, or is there a way to ensure Tag&Rename writes more compatible tags?

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  • Forcing a transaction to rollback on validation errors in Seam

    - by Chris Williams
    Quick version: We're looking for a way to force a transaction to rollback when specific situations occur during the execution of a method on a backing bean but we'd like the rollback to happen without having to show the user a generic 500 error page. Instead, we'd like the user to see the form she just submitted and a FacesMessage that indicates what the problem was. Long version: We've got a few backing beans that use components to perform a few related operations in the database (using JPA/Hibernate). During the process, an error can occur after some of the database operations have happened. This could be for a few different reasons but for this question, let's assume there's been a validation error that is detected after some DB writes have happened that weren't detectible before the writes occurred. When this happens, we'd like to make sure all of the db changes up to this point will be rolled back. Seam can deal with this because if you throw a RuntimeException out of the current FacesRequest, Seam will rollback the current transaction. The problem with this is that the user is shown a generic error page. In our case, we'd actually like the user to be shown the page she was on with a descriptive message about what went wrong, and have the opportunity to correct the bad input that caused the problem. The solution we've come up with is to throw an Exception from the component that discovers the validation problem with the annotation: @ApplicationException( rollback = true ) Then our backing bean can catch this exception, assume the component that threw it has published the appropriate FacesMessage, and simply return null to take the user back to the input page with the error displayed. The ApplicationException annotation tells Seam to rollback the transaction and we're not showing the user a generic error page. This worked well for the first place we used it that happened to only be doing inserts. The second place we tried to use it, we have to delete something during the process. In this second case, everything works if there's no validation error. If a validation error does happen, the rollback Exception is thrown and the transaction is marked for rollback. Even if no database modifications have happened to be rolled back, when the user fixes the bad data and re-submits the page, we're getting: java.lang.IllegalArgumentException: Removing a detached instance The detached instance is lazily loaded from another object (there's a many to one relationship). That parent object is loaded when the backing bean is instantiated. Because the transaction was rolled back after the validation error, the object is now detached. Our next step was to change this page from conversation scope to page scope. When we did this, Seam can't even render the page after the validation error because our page has to hit the DB to render and the transaction has been marked for rollback. So my question is: how are other people dealing with handling errors cleanly and properly managing transactions at the same time? Better yet, I'd love to be able to use everything we have now if someone can spot something I'm doing wrong that would be relatively easy to fix. I've read the Seam Framework article on Unified error page and exception handling but this is geared more towards more generic errors your application might encounter.

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  • using performSelector

    - by zebra
    Hi all, i've my method that implement a reverseGeocoder - (void)reversing { geoCoder=[[MKReverseGeocoder alloc] initWithCoordinate:locManager.location.coordinate]; geoCoder.delegate=self; [geoCoder start]; } i recall reversing in another method with this: [self performSelector:@selector(reversing) withObject:nil afterDelay:10]; and i receive 2010-04-30 17:44:17.616 high[1167:207] Retrive City Milano 2010-04-30 17:44:17.628 high[1167:207] geocoder released 2010-04-30 17:44:18.723 high[1167:207] Error Domain=MKErrorDomain Code=4 "Operation could not be completed. (MKErrorDomain error 4.)" Program received signal: “EXC_BAD_ACCESS”. Can someone help me? :D

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  • Does kern.hz still have any relevance in FreeBSD if "dynamic tick mode" is enabled?

    - by Frerich Raabe
    I'm running a FreeBSD 9.0 setup as a virtual machine in a KVM setup. In previous versions of FreeBSD it was common to force the kern.hz setting to a lower value so that the virtual machine does not keep the host busy because it's handling timer interrupts without having any work to do - the FreeBSD Handbook explains: The most important step is to reduce the kern.hz tunable to reduce the CPU utilization of FreeBSD under the Parallels environment. This is accomplished by adding the following line to /boot/loader.conf: kern.hz=100 Without this setting, an idle FreeBSD Parallels guest OS will use roughly 15% of the CPU of a single processor iMac®. After this change the usage will be closer to a mere 5%. However, in FreeBSD 9, the "dynamic tick mode" (aka "tickless mode") is the default, controlled by the kern.eventtimer.periodic setting which defaults to 0 (read: tickless mode). This makes me wonder - does the tip of lowering kern.hz still have any relevance for making FreeBSD 9 play nicely in a virtual machine setup?

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  • C# Is it possible to interrupt a specific thread inside a ThreadPool?

    - by Lirik
    Suppose that I've queued a work item in a ThreadPool, but the work item blocks if there is no data to process (reading from a BlockingQueue). If the queue is empty and there will be no more work going into the queue, then I must call the Thread.Interrupt method if I want to interrupt the blocking task, but how does one do the same thing with a ThreadPool? The code might look like this: void Run() { try { while(true) { blockingQueue.Dequeue(); doSomething(); } } finally { countDownLatch.Signal(); } } I'm aware that the best thing to do in this situation is use a regular Thread, but I'm wondering if there is a ThreadPool equivalent way to interrupt a work item.

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  • How to associate Wi-Fi beacon info with a virtual "location"?

    - by leander
    We have a piece of embedded hardware that will sense 802.11 beacons, and we're using this to make a map of currently visible bssid -> signalStrength. Given this map, we would like to make a determination: Is this likely to be a location I have been to before? If so, what is its ID? If not, I should remember this location: generate a new ID. Now what should I store (and how should I store it) to make future determinations easier? This is for an augmented-reality app/game. We will be using it to associate particular characters and events with "locations". The device does not have internet or cellular access, so using a geolocation service is out of consideration for the time being. (We don't really need to know where we are in reality, just be able to determine if we return there.) It isn't crucial that it be extremely accurate, but it would be nice if it was tolerant to signal strength changes or the occasional missing beacon. It should be usable in relatively low numbers of access points (e.g. rural house with one wireless router) or many (wandering around a dense metropolis). In the case of a city, it should change location every few minutes of walking (continuously-overlapping signals make this a bit more tricky in naive code). A reasonable number of false positives (match a location when we aren't actually there) is acceptable. The wrong character/event showing up just adds a bit of variety. False negatives (no location match) are a bit more troublesome: this will tend to add a better-matching new location to the saved locations, masking the old one. While we will have additional logic to ensure locations that the device hasn't seen in a while will "orphan" any associated characters or events (if e.g. you move to a different country), we'd prefer not to mask and eventually orphan locations you do visit regularly. Some technical complications: signalStrength is returned as 1-4; presumably it's related to dB, but we are not sure exactly how; in my experiments it tends to stick to either 1 or 4, but occasionally we see numbers in between. (Tech docs on the hardware are sparse.) The device completes a scan of one-quarter of the channel space every second; so it takes about 4-5 seconds to get a complete picture of what's around. The list isn't always complete. (We are making strides to fix this using some slight sampling period randomization, as recommended by the library docs. We're also investigating ways to increase the number of scans without killing our performance; the hardware/libs are poorly behaved when it comes to saturating the bus.) We have only kilobytes to store our history. We have a "working" impl now, but it is relatively naive, and flaky in the face of real-world Wi-Fi behavior. Rough pseudocode: // recordLocation() -- only store strength 4 locations m_savedLocations[g_nextId++] = filterForStrengthGE( m_currentAPs, 4 ); // determineLocation() bestPoints = -inf; foreach ( oldLoc in m_savedLocations ) { points = 0.0; foreach ( ap in m_currentAPs ) { if ( oldLoc.has( ap ) ) { switch ( ap.signalStrength ) { case 3: points += 1.0; break; case 4: points += 2.0; break; } } } points /= oldLoc.numAPs; if ( points > bestPoints ) { bestLoc = oldLoc; bestPoints = points; } } if ( bestLoc && bestPoints > 1.0 ) { if ( bestPoints >= (2.0 - epsilon) ) { // near-perfect match. // update location with any new high-strength APs that have appeared bestLoc.addAPs( filterForStrengthGE( m_currentAPs, 4 ) ); } return bestLoc; } else { return NO_MATCH; } We record a location currently only when we have NO_MATCH and the app determines it's time for a new event. (The "near-perfect match" code above would appear to make it harder to match in the future... It's mostly to keep new powerful APs from being associated with other locations, but you'd think we'd need something to counter this if e.g. an AP doesn't show up in the next 10 times I match a location.) I have a feeling that we're missing some things from set theory or graph theory that would assist in grouping/classification of this data, and perhaps providing a better "confidence level" on matches, and better robustness against missed beacons, signal strength changes, and the like. Also it would be useful to have a good method for mutating locations over time. Any useful resources out there for this sort of thing? Simple and/or robust approaches we're missing?

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  • What are the prerequisites for learning embedded systems programming ?

    - by WarDoGG
    I have completed my graduation in Computer engineering. We had some basic electronics courses in Digital signal processing, Information theory etc but my primary field is Programming. However, i was looking to get into Embedded sytems programming with NO knowledge of how it is done. However, i am very keen on going into this field. My questions : what are the languages used to program embedded system programs ? Will i be able to learn without having any basics in electronics ? any other prerequisites that i should know ?

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