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  • College Courses through distance learning

    - by Matt
    I realize this isn't really a programming question, but didn't really know where to post this in the stackexchange and because I am a computer science major i thought id ask here. This is pretty unique to the programmer community since my degree is about 95% programming. I have 1 semester left, but i work full time. I would like to finish up in December, but to make things easier i like to take online classes whenever I can. So, my question is does anyone know of any colleges that offer distance learning courses for computer science? I have been searching around and found a few potential classes, but not sure yet. I would like to gather some classes and see what i can get approval for. Class I need: Only need one C SC 437 Geometric Algorithms C SC 445 Algorithms C SC 473 Automata Only need one C SC 452 Operating Systems C SC 453 Compilers/Systems Software While i only need of each of the above courses i still need to take two more electives. These also have to be upper 400 level classes. So i can take multiple in each category. Some other classes I can take are: CSC 447 - Green Computing CSC 425 - Computer Networking CSC 460 - Database Design CSC 466 - Computer Security I hoping to take one or two of these courses over the summer. If not, then online over the regular semester would be ok too. Any help in helping find these classes would be awesome. Maybe you went to a college that offered distance learning. Some of these classes may be considered to be graduate courses too. Descriptions are listed below if you need. Thanks! Descriptions Computer Security This is an introductory course covering the fundamentals of computer security. In particular, the course will cover basic concepts of computer security such as threat models and security policies, and will show how these concepts apply to specific areas such as communication security, software security, operating systems security, network security, web security, and hardware-based security. Computer Networking Theory and practice of computer networks, emphasizing the principles underlying the design of network software and the role of the communications system in distributed computing. Topics include routing, flow and congestion control, end-to-end protocols, and multicast. Database Design Functions of a database system. Data modeling and logical database design. Query languages and query optimization. Efficient data storage and access. Database access through standalone and web applications. Green Computing This course covers fundamental principles of energy management faced by designers of hardware, operating systems, and data centers. We will explore basic energy management option in individual components such as CPUs, network interfaces, hard drives, memory. We will further present the energy management policies at the operating system level that consider performance vs. energy saving tradeoffs. Finally we will consider large scale data centers where energy management is done at multiple layers from individual components in the system to shutting down entries subset of machines. We will also discuss energy generation and delivery and well as cooling issues in large data centers. Compilers/Systems Software Basic concepts of compilation and related systems software. Topics include lexical analysis, parsing, semantic analysis, code generation; assemblers, loaders, linkers; debuggers. Operating Systems Concepts of modern operating systems; concurrent processes; process synchronization and communication; resource allocation; kernels; deadlock; memory management; file systems. Algorithms Introduction to the design and analysis of algorithms: basic analysis techniques (asymptotics, sums, recurrences); basic design techniques (divide and conquer, dynamic programming, greedy, amortization); acquiring an algorithm repertoire (sorting, median finding, strong components, spanning trees, shortest paths, maximum flow, string matching); and handling intractability (approximation algorithms, branch and bound). Automata Introduction to models of computation (finite automata, pushdown automata, Turing machines), representations of languages (regular expressions, context-free grammars), and the basic hierarchy of languages (regular, context-free, decidable, and undecidable languages). Geometric Algorithms The study of algorithms for geometric objects, using a computational geometry approach, with an emphasis on applications for graphics, VLSI, GIS, robotics, and sensor networks. Topics may include the representation and overlaying of maps, finding nearest neighbors, solving linear programming problems, and searching geometric databases.

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  • SVN Error 403 Forbidden

    - by Chris
    I can't figure this out. I try to import a new project into a svn repository from Netbeans and get 403 Forbidden. I just setup svn on my serverbox today. I can get to it through a browser just fine, though its empty as I haven't imported my project yet. Apache's path for html files is /var/www I setup the svn repo in /var/svn This is the structure of /var/svn [root@localhost svn]# ls -lR /var/svn /var/svn: total 4 drwxrwxrwx 7 apache apache 4096 2010-03-26 10:18 repo /var/svn/repo: total 36 drwxrwxrwx 2 apache apache 4096 2010-03-26 09:47 conf drwxrwxrwx 3 apache apache 4096 2010-03-26 10:18 dav drwxrwsrwx 6 apache apache 4096 2010-03-26 11:19 db -rwxrwxrwx 1 apache apache 2 2010-03-26 09:47 format drwxrwxrwx 2 apache apache 4096 2010-03-26 09:47 hooks drwxrwxrwx 2 apache apache 4096 2010-03-26 09:47 locks -rwxrwxrwx 1 apache apache 229 2010-03-26 09:47 README.txt -rwxrwxrwx 1 apache apache 15 2010-03-26 09:47 svnauth -rwxrwxrwx 1 apache apache 43 2010-03-26 09:48 svnpass /var/svn/repo/conf: total 12 -rwxrwxrwx 1 apache apache 1080 2010-03-26 09:47 authz -rwxrwxrwx 1 apache apache 309 2010-03-26 09:47 passwd -rwxrwxrwx 1 apache apache 2279 2010-03-26 09:47 svnserve.conf /var/svn/repo/dav: total 4 drwxrwxrwx 2 apache apache 4096 2010-03-26 11:19 activities.d /var/svn/repo/dav/activities.d: total 0 /var/svn/repo/db: total 48 -rwxrwxrwx 1 apache apache 2 2010-03-26 09:47 current -rwxrwxrwx 1 apache apache 22 2010-03-26 09:47 format -rwxrwxrwx 1 apache apache 1920 2010-03-26 09:47 fsfs.conf -rwxrwxrwx 1 apache apache 5 2010-03-26 09:47 fs-type -rwxrwxrwx 1 apache apache 2 2010-03-26 09:47 min-unpacked-rev -rwxrwxrwx 1 apache apache 4096 2010-03-26 09:47 rep-cache.db drwxrwsrwx 3 apache apache 4096 2010-03-26 09:47 revprops drwxrwsrwx 3 apache apache 4096 2010-03-26 09:47 revs drwxrwsrwx 2 apache apache 4096 2010-03-26 11:19 transactions -rwxrwxrwx 1 apache apache 2 2010-03-26 11:19 txn-current -rwxrwxrwx 1 apache apache 0 2010-03-26 09:47 txn-current-lock drwxrwsrwx 2 apache apache 4096 2010-03-26 11:19 txn-protorevs -rwxrwxrwx 1 apache apache 37 2010-03-26 09:47 uuid -rwxrwxrwx 1 apache apache 0 2010-03-26 09:47 write-lock /var/svn/repo/db/revprops: total 4 drwxrwsrwx 2 apache apache 4096 2010-03-26 09:47 0 /var/svn/repo/db/revprops/0: total 4 -rwxrwxrwx 1 apache apache 50 2010-03-26 09:47 0 /var/svn/repo/db/revs: total 4 drwxrwsrwx 2 apache apache 4096 2010-03-26 09:47 0 /var/svn/repo/db/revs/0: total 4 -rwxrwxrwx 1 apache apache 115 2010-03-26 09:47 0 /var/svn/repo/db/transactions: total 0 /var/svn/repo/db/txn-protorevs: total 0 /var/svn/repo/hooks: total 36 -rwxrwxrwx 1 apache apache 1955 2010-03-26 09:47 post-commit.tmpl -rwxrwxrwx 1 apache apache 1638 2010-03-26 09:47 post-lock.tmpl -rwxrwxrwx 1 apache apache 2267 2010-03-26 09:47 post-revprop-change.tmpl -rwxrwxrwx 1 apache apache 1567 2010-03-26 09:47 post-unlock.tmpl -rwxrwxrwx 1 apache apache 3404 2010-03-26 09:47 pre-commit.tmpl -rwxrwxrwx 1 apache apache 2410 2010-03-26 09:47 pre-lock.tmpl -rwxrwxrwx 1 apache apache 2764 2010-03-26 09:47 pre-revprop-change.tmpl -rwxrwxrwx 1 apache apache 2100 2010-03-26 09:47 pre-unlock.tmpl -rwxrwxrwx 1 apache apache 2758 2010-03-26 09:47 start-commit.tmpl /var/svn/repo/locks: total 8 -rwxrwxrwx 1 apache apache 139 2010-03-26 09:47 db.lock -rwxrwxrwx 1 apache apache 139 2010-03-26 09:47 db-logs.lock I've got httpd.conf loading svn.conf which contains: <Location /svn> DAV on DAV svn #SVNParentPath /var/svn SVNPath /var/svn/repo Authtype Basic AuthName "Subversion" AuthUserFile /var/svn/repo/svnpass Require valid-user AuthzSVNAccessFile /var/svn/repo/svnauth </Location> Full error message is: org.tigris.subversion.javahl.ClientException: RA layer request failed Server sent unexpected return value (403 Forbidden) in response to CHECKOUT request for '/svn/!svn/bln/0' Sorry for the incredibly long post, but I thought more info would be better than less. I've been fidgeting with this problem for a long time now.

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  • Cannot connect with Cisco VPN but can connect with ShrewSoft VPN

    - by rodey
    EDIT: We connected an air card to the computer to use a different Internet connection and using the Cisco software, we were able to successfully connect to our VPN server. I just don't understand why the ShrewSoft VPN client would connect but the Cisco connection won't. I'm not our network admin so sorry if I butcher some of the terminology. I have a computer at remote site that connects to our network through Cisco VPN. It uses the Cisco VPN software to do so. The problem is that the computer at this site cannot connect to our VPN because it is getting error "Reason 412: The remote peer is no longer responding." To see if perhaps something on their network was blocking the connection, I installed the ShrewSoft VPN client on the computer, imported our .pcf file and connected with no problem. I have tried two different versions of the Cisco VPN software (4.8.0.* and 5.0.03.*) and have the same problem. I installed Wireshark on the computer and have confirmed (while trying to connect through Cisco) that the computer is trying to contact the VPN server but is not receiving a response. We are not having any other problems regarding users not being able to connect. I'm at a loss at what else to check. I'll be monitoring this and have access to the computer at any time.

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  • HTML5 web storage: can different websites overwrite each other’s data on a user’s computer?

    - by Deepak Mahalingam
    I have a few questions regarding the concept of HTML5 storage. I went through the w3c specification, books and tutorials on the same, but still I am a bit unclear about certain concepts: Assume that I access Website A. Some JavaScript runs in my browser that sets a key value pair, say ('username','deepak'). Then I access Website B which also adds a key,value pair in the localstorage as ('username','mahalingam'). How will they both be differentiated? Will Website B override the value set by website A in my localstorage? How can we ensure that a website would not erase all of my localstorage?

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  • Sql server version error...655 version needed but you computer has 612 or earlier version ? error

    - by xpugur
    Hi i have a error like " dbFileName cannot be opened because it is version 655. This server supports version 612 and earlier. " what should i do ? some friend of mine done a project but i guess he done it with sql 2008 and i have sql 2005 is that the reason why i got this error? can i fix it ? if i setup a newer version of sql does it will solve the problem? www.microsoft.com/express/Database/default.aspx#Installation_Options here sql server 2008 R2 express is available can it be the solution? thank you... by the way i found a link of an update http://www.microsoft.com/downloads/details.aspx?FamilyID=E1109AEF-1AA2-408D-AA0F-9DF094F993BF&displaylang=en is this a solution to my problem ?

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  • What is the correct way to synchronize a shared, static object in Java?

    - by johnrock
    This is a question concerning what is the proper way to synchronize a shared object in java. One caveat is that the object that I want to share must be accessed from static methods. My question is, If I synchronize on a static field, does that lock the class the field belongs to similar to the way a synchronized static method would? Or, will this only lock the field itself? In my specific example I am asking: Will calling PayloadService.getPayload() or PayloadService.setPayload() lock PayloadService.payload? Or will it lock the entire PayloadService class? public class PayloadService extends Service { private static PayloadDTO payload = new PayloadDTO(); public static void setPayload(PayloadDTO payload){ synchronized(PayloadService.payload){ PayloadService.payload = payload; } } public static PayloadDTO getPayload() { synchronized(PayloadService.payload){ return PayloadService.payload ; } } ... Is this a correct/acceptable approach ? In my example the PayloadService is a separate thread, updating the payload object at regular intervals - other threads need to call PayloadService.getPayload() at random intervals to get the latest data and I need to make sure that they don't lock the PayloadService from carrying out its timer task

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  • NSIS takes ownership of IIS system files

    - by Lucas
    I recently encountered an issue with NSIS that I believe is related to an interaction with UAC, but I am at a loss to explain it and I do not know how to prevent it in the future. I have an installer that creates and removes IIS virtual directories using the NsisIIS plugin. The installer appeared worked correctly on my Windows 7 workstation. When the installer was run on a Windows 2008 R2 server it installed properly, but the uninstaller removed all of the virtual directories and put IIS is an unusable state; to the point that I had to remove the Default Web Site and re-add it. What I eventually found was that all of the IIS configuration files under C:\Windows\System32\inetsrv\config had a lock icon on them. Some investigation seem to indicate that this means a user account has taken ownership of the file, however all the files listed SYSTEM as the file owner. I did check a different server that I have not run the installer on, and it does not have the lock icon applied to the IIS files. I have also seen the same lock icon appear on other files that the NSIS installer creates. For instance, I have a Web.Config.tpl file that is processed using the NSIS ReplaceInFile which also appears with the lock icon after the installer finished. After I explicitly grant another user account access to the file, the lock icon goes away. I run the installer under the local Administrator account on the 2008 R2 server, so I do not get the UAC prompt. Here is the relevant code from the install.nsi file RequestExecutionLevel admin Section "Application" APP_SECTION SectionIn RO Call InstallApp SectionEnd Section "un.Uninstaller Section" Delete "$PROGRAMFILES\${PROGRAMFILESDIR}\Uninstall.exe" Call un.InstallApp SectionEnd Function InstallApp File /oname=Web.Config Web.Config.tpl !insertmacro ReplaceInFile Web.Config %CONNECTION_STRING% $CONNECTION_STRING FunctionEnd Function un.InstallApp ReadRegStr $0 HKLM "Software\${REGKEY}" "VirtualDir" NsisIIS::DeleteVDir "$0" Pop $0 FunctionEnd I have three questions stemming from this incident: How did this happen? How can I fix my installer to prevent it from happening again? How can I repair the permissions on the IIS config files.

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  • Is there an Outlook or Gmail plugin to manage multiple tasks in an email?

    - by Matthew Lock
    I often get client emails containing 10 or more tasks written as text in the email. I know Outlook and Gmail let you turn an email into a single task, but this doesn't help too much when there are 10 tasks in that email. Are there any plugins for Outlook or Gmail that let put checkboxes into the email or something so I can check off each item as they are done? Ideally I'd like the checkboxes/to do items to be inside the email itself so I can see my progress by looking at the email, rather than just letting me copy text from the email into some other task list.

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  • Can't Get Mac Mini to turn on - no screen, no beep, only the fan, power light, and optical drive noi

    - by pibyers
    I have an Intel-based Mac mini mid-2007 (Model A1176). This is the computer my kids use so I don't use it regularly. The computer had been working fine until one day my kids told me that it no longer works. The computer will not boot up. When I turn it on the fan turns, the white power light in the front turns on, and there is a sound that appears to be from the optical drive (rather than hard drive). I don't get anything to the monitor, nor do I get any dings or other start up sounds from the computer. Here is what I've tried thus far to no avail: 1) Swapped out the monitors early on since I figured that was my weak link - no change 2) Reset the PMU - no change 3) Tried to boot up from the System Disk - The mini loaded the dvd into the drive, but nothing else (I can't eject the disk so I can put it back) 3) Start up the computer in target mode connected to another mac - I tried this too, but I never received a chime or the disk show up on the other mac. I'm about out of ideas apart from scraping the computer. Does anyone have any ideas that I can try? Again, nothing has been done to the computer in at least 6 months when I upgraded the RAM. I'm also still on Leopard. Thanks.

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  • postfix- are these connects in the log anything to worry about?

    - by Lock
    I am noticing the following in my maillog. Lots of these: Sep 10 10:29:56 westc01-01-01 postfix/smtpd[26788]: connect from unknown[85.111.7.182] And these: Sep 10 10:34:58 westc01-01-01 postfix/smtpd[26768]: disconnect from unknown[85.111.7.182] Sep 10 10:34:58 westc01-01-01 postfix/smtpd[26758]: timeout after AUTH from unknown[85.111.7.182] And these: Sep 10 10:29:56 westc01-01-01 postfix/smtpd[26737]: warning: unknown[85.111.7.182]: SASL LOGIN authentication failed: UGFzc3dvcmQ6 Are these anything to worry about?

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  • Overclock Failed

    - by John
    This morning when I tried to turn on my computer, the monitor would not display anything. The computer is on, but no UI on the monitor and no beep. I turned off the computer and turn it back on again. This time, the computer was on for about 2 seconds and automatically turned itself off for about 2 second and automatically turned itself back on. This happened two times without the monitor displaying any UI. On the third try, the computer did the same thing but when it turned itself back on, the monitor displayed this: American Megatrends Asus P8P67 Le ACPI bios Revision 1011 CPU Intel Core i5 2500K CPU @ 3.30GHz Speed: 3300MHz Total Memory 4096 MB (DDR3-1333) USB Devices Total: 0 Drive, 1 Keyboard, 1 Mouse, 2 Hubs Detected ATA/ATAPI Deivces SATA6G_2 Hitachi HDs821010CLA 332 SATA3G_1 Corsair force 3 SSD SATA3G_2 HL-DT-ST DB-RE UH12CS28 Overclocking Failed! Please enter setup to reconfigure your system. Press F1 to Run Setup. After I pressed F1, it went into the Asus EF1 Bios Utility. I couldn't do anything in there so I just exited. After which, the computer auto turned off and on again and I was able to use the PC like regular. This has never happened to this computer before and the day before, nothing seemed wrong, just regular use and some gaming.

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  • How to let MSN or Yahoo Messenger set you to be Invisible or Offline when you are idle for an hour?

    - by Jian Lin
    The short question is: How do we let MSN or Yahoo Messenger set us to be Invisible or Offline when we are idle for half an hour or an hour? The reason is: if I am on 24 hours a day, some people see me as weird. Some people see my value as low, because I am always there. There are ways to set me to "Away" or "Busy" after 10 minutes, but there seems to be no way to set myself to invisible or offline after 1 hour. As I am a software developer, I am very used to turning the computer on 24 hours a day. (for example, for checking email for urgent fixes, and fix issue and push to web server). We don't turn off computer usually even when we sleep, because we may sometimes can't sleep yet and come check on the computer, or wake up in the morning and immediately need to check if everything is ok. But, my MSN and Yahoo Messenger is always on for 24 hours a day, and I found that some girls start to ask me why I am always there 24 hours a day (even though they see me as away or busy, their feeling is that I am always there). What's more, I found that since I am always there, my value actually drop in their eyes, because hard to get = high value, and always there = low value. Some people feel me as having nothing much to do, always in front of computer, or what is he doing in front of computer so much? Now since it is my job, and I need to read emails once in a while, I am in fact in front of the computer more than some other people. I am in front of the computer maybe 10 hours a day, far from 24 hours a day. Is there an easy and automatic solution to this?

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  • what does "Net user administrator /active:yes" do to a computer?

    - by Rees
    i just purchased a new laptop and had some issues with it... I called tech support and they had me run this command in cmd prompt by right clicking the cmd icon and selecting "run as administrator" with root C:\windows\system32: "Net user administrator /active:no" after it was determined that it didn't fix the issue we ran this code "Net user administrator /active:yes" i then rebooted..and was asked for my windows login for my user account "Rees" as usual.. however ALL my settings where gone (including my desktop files) as though it was the first time I booted up. WHAT in the world happened with this command?? I desperately NEED my user accounts and files back to how they were!! (running windows 7) Please help!

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  • Printing to a remote printer through the internet

    - by Lock
    I have a remote network (A) that is connected to a head office (B) through a private network. Network A only has 1 PC that requires the connection, and this is into a terminal server at network B. We want to save money by getting rid of the private network as only 1 PC now access it and it seems silly to pay ~$400 per month for something that is accessed by 1 PC. A VPN tunnel is out of the question as the provider wants to charge $600 a month for a VPN tunnel (more than a private network? I might get them to check these numbers). I was thinking of 2 options: 1) VPN client on the PC. This wouldn't cost a thing as we already have VPN users available. 2) Open up a port on the firewall of network B, forwarding to the terminal server. Now the problem is this: On the terminal server, the program that is accessed is for printing labels to the printer that is at network A. The program is setup to send all print jobs to a printer that is setup locally on the terminal server, which has its port mapped to the IP address of the printer that is at network A. If we got rid of the VPN tunnel and used clients/open up firewall port, the printer would no longer be able to find network A, and hence printing would not work. Any ideas to combat this issue? Can the printers at the remote network be setup as internet printers? I've never had any experience with internet printers. Can you open up ports and map to a public static IP address?

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  • Acer recovering windows vista

    - by Charlie Pigarelli
    My computer history is very long even of my computer has 4 years of life. An year ago I installed Windows 7 on this acer m1610 that had Vista before. My technic left me 2 recovery disc for "acer vista" before updating it to Windows 7. Then the computer had some trouble. The graphic card broke and we decided to use another computer. Yesterday I had the great idea to fuse the two computer to have a better one... So I moved the graphic card of the latter computer to the acer and everything gone well. Then the trouble of speed, it had before, come back. So I decided to reinstall the very first Windows: Vista back again. I booted the computer with those 2 DVD-R my technic left me and at the end of the process it asked me to insert "the backup cd number one or the system disk". I found 2 original Acer "Blank Recovery Disc" DVD-R and tried with those: rejected. Tried with empty DVD-+R: rejected. I tried with CDs: rejected. I don't have any system disc with me. Except for those 2 DVD-R my technic left me. What am I supposed to do now? I even tried with these fantomatic alt+f9/f10 that should start the recovery without any disc... But nothing happened. PS: the installation cannot complete if I do not insert the right disk. (The recovery disc uses Acer eRecovery Management as recovery software.

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  • Is there a way to watch all COM activity on a computer?

    - by Fake Name
    I'm trying to deal with a piece of specialized hardware, that presents it's interface as a COM object, using win32com in Python. However, the documentation for how to actually set up the hardware through the COM object is sparse (it requires a significant amount of initialization), and entirely oriented at using a bunch of pre-built libraries for Visual Studio, which are not accessible through python. That said, is there any way to watch all local COM activity, so I can sort through the activity logs to try and figure out how the existing demo programs properly initialize the hardware, and replicate the behavior in my python script? Ideally, there would be something in the vein of wireshark for doing this. Note: I have very little (read: basically no) experience using COM, as my focus is mostly embedded hardware (and a little python dev on the side). However, I'm stuck with this particular device.

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  • How to implement Session timeout in Web Server Side?

    - by Morgan Cheng
    I beheld a web framework implementing in-memory session in this way. The session object is added to Cache with timeout. When the time is out, the session is removed from Cache automatically. To protect race condition, each request should acquire lock on given session object to proceed. Each request will "touch" the session in Cache to refresh the timeout. Everything looks fine, until this scenario is discovered. Say, one operation takes a long time, longer than timeout. Another request comes and wait on session lock which is currently hold by the long-time request. Finally, the long-time request is over, it releases the lock. But, since it already takes longer time than timeout, the session object is already removed from Cache. This is obvious because the only request holding the lock doesn't have a chance to "touch" the session object in cache. The second request gets the lock but cannot retrieve the expired Session object. Oops... To fix this issue, the second request has to re-create the Session object. But, this is just like digging a buried dead body from tomb and try to bring it back to life. It causes buggy code. I'm wondering what's the best way to implement timeout in session to handle such scenario. I know that current platform must have good session mechanism. I just want to know the under-the-hood how.

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  • Modelling boost::Lockable with semaphore rather than mutex (previously titled: Unlocking a mutex fr

    - by dan
    I'm using the C++ boost::thread library, which in my case means I'm using pthreads. Officially, a mutex must be unlocked from the same thread which locks it, and I want the effect of being able to lock in one thread and then unlock in another. There are many ways to accomplish this. One possibility would be to write a new mutex class which allows this behavior. For example: class inter_thread_mutex{ bool locked; boost::mutex mx; boost::condition_variable cv; public: void lock(){ boost::unique_lock<boost::mutex> lck(mx); while(locked) cv.wait(lck); locked=true; } void unlock(){ { boost::lock_guard<boost::mutex> lck(mx); if(!locked) error(); locked=false; } cv.notify_one(); } // bool try_lock(); void error(); etc. } I should point out that the above code doesn't guarantee FIFO access, since if one thread calls lock() while another calls unlock(), this first thread may acquire the lock ahead of other threads which are waiting. (Come to think of it, the boost::thread documentation doesn't appear to make any explicit scheduling guarantees for either mutexes or condition variables). But let's just ignore that (and any other bugs) for now. My question is, if I decide to go this route, would I be able to use such a mutex as a model for the boost Lockable concept. For example, would anything go wrong if I use a boost::unique_lock< inter_thread_mutex for RAII-style access, and then pass this lock to boost::condition_variable_any.wait(), etc. On one hand I don't see why not. On the other hand, "I don't see why not" is usually a very bad way of determining whether something will work. The reason I ask is that if it turns out that I have to write wrapper classes for RAII locks and condition variables and whatever else, then I'd rather just find some other way to achieve the same effect. EDIT: The kind of behavior I want is basically as follows. I have an object, and it needs to be locked whenever it is modified. I want to lock the object from one thread, and do some work on it. Then I want to keep the object locked while I tell another worker thread to complete the work. So the first thread can go on and do something else while the worker thread finishes up. When the worker thread gets done, it unlocks the mutex. And I want the transition to be seemless so nobody else can get the mutex lock in between when thread 1 starts the work and thread 2 completes it. Something like inter_thread_mutex seems like it would work, and it would also allow the program to interact with it as if it were an ordinary mutex. So it seems like a clean solution. If there's a better solution, I'd be happy to hear that also. EDIT AGAIN: The reason I need locks to begin with is that there are multiple master threads, and the locks are there to prevent them from accessing shared objects concurrently in invalid ways. So the code already uses loop-level lock-free sequencing of operations at the master thread level. Also, in the original implementation, there were no worker threads, and the mutexes were ordinary kosher mutexes. The inter_thread_thingy came up as an optimization, primarily to improve response time. In many cases, it was sufficient to guarantee that the "first part" of operation A, occurs before the "first part" of operation B. As a dumb example, say I punch object 1 and give it a black eye. Then I tell object 1 to change it's internal structure to reflect all the tissue damage. I don't want to wait around for the tissue damage before I move on to punch object 2. However, I do want the tissue damage to occur as part of the same operation; for example, in the interim, I don't want any other thread to reconfigure the object in such a way that would make tissue damage an invalid operation. (yes, this example is imperfect in many ways, and no I'm not working on a game) So we made the change to a model where ownership of an object can be passed to a worker thread to complete an operation, and it actually works quite nicely; each master thread is able to get a lot more operations done because it doesn't need to wait for them all to complete. And, since the event sequencing at the master thread level is still loop-based, it is easy to write high-level master-thread operations, as they can be based on the assumption that an operation is complete when the corresponding function call returns. Finally, I thought it would be nice to use inter_thread mutex/semaphore thingies using RAII with boost locks to encapsulate the necessary synchronization that is required to make the whole thing work.

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  • Using boost locks for RAII access to a semaphore

    - by dan
    Suppose I write a C++ semaphore class with an interface that models the boost Lockable concept (i.e. lock(); unlock(); try_lock(); etc.). Is it safe/recommended to use boost locks for RAII access to such an object? In other words, do boost locks (and/or other related parts of the boost thread library) assume that the Lockable concept will only be modeled by mutex-like objects which are locked and unlocked from the same thread? My guess is that it should be OK to use a semaphore as a model for Lockable. I've browsed through some of the boost source and it "seems" OK. The locks don't appear to store explicit references to this_thread or anything like that. Moreover, the Lockable concept doesn't have any function like whichThreadOwnsMe(). It also looks like I should even be able to pass a boost::unique_lock<MySemaphore> reference to boost::condition_variable_any::wait. However, the documentation is not explicitly clear about the requirements. To illustrate what I mean, consider a bare-bones binary semaphore class along these lines: class MySemaphore{ bool locked; boost::mutex mx; boost::condition_variable cv; public: void lock(){ boost::unique_lock<boost::mutex> lck(mx); while(locked) cv.wait(lck); locked=true; } void unlock(){ { boost::lock_guard<boost::mutex> lck(mx); if(!locked) error(); locked=false; } cv.notify_one(); } // bool try_lock(); void error(); etc. } Now suppose that somewhere, either on an object or globally, I have MySemaphore sem; I want to lock and unlock it using RAII. Also I want to be able to "pass" ownership of the lock from one thread to another. For example, in one thread I execute void doTask() { boost::unique_lock<MySemaphore> lock(sem); doSomeWorkWithSharedObject(); signalToSecondThread(); waitForSignalAck(); lock.release(); } While another thread is executing something like { waitForSignalFromFirstThread(); ackSignal(); boost::unique_lock<MySemaphore>(sem,boost::adopt_lock_t()); doMoreWorkWithSameSharedObject(); } The reason I am doing this is that I don't want anyone else to be able to get the lock on sem in between the time that the first thread executes doSomeWorkWithSharedObject() and the time the second executes doMoreWorkWithSameSharedObject(). Basically, I'm splitting one task into two parts. And the reason I'm splitting the task up is because (1) I want the first part of the task to get started as soon as possible, (2) I want to guarantee that the first part is complete before doTask() returns, and (3) I want the second, more time-consuming part of the task to be completed by another thread, possibly chosen from a pool of slave threads that are waiting around to finish tasks that have been started by master threads. NOTE: I recently posted this same question (sort of) here http://stackoverflow.com/questions/2754884/unlocking-a-mutex-from-a-different-thread-c but I confused mutexes with semaphores, and so the question about using boost locks didn't really get addressed.

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  • Shrew VPN Client gives default route- changing the policy stops me from accessing VPN network

    - by Lock
    I am using the shrew client to connect to what I believe is a Netscreen VPN. Now, when connected, the client adds the VPN as the default route. I do not want this- there is only 1 network behind the VPN that I need to access. I found that with the shrew client, you can change the "Policy" settings on the connection, and can add your own networks in that should tunnel over the VPN. I do this, and add my network in, but when I connect the VPN, I get nothing. Can't access the network. Any idea why this would be? I can see my network in the routing table, and its correctly pointing to the correct gateway. A traceroute shows all time-outs, so I can't be 100% sure that it is trying to tunnel over the VPN. Any idea how I can troubleshoot this?

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