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  • QR code - where can I find (free) code to embed my own generator on a web page?

    - by Robbert Huisman
    Hi, couldn't find it exactly from earlier questions, but I am probably repeating an earlier question, so apologies upfront ;-) I am looking for a simple code to embed a QR 2D code generator on a website I am building. I assume their should be some free open source code for that but I could only find paid software. Can anyone point me in the right direction? would be mostly appreciated! best regards, Robbert

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  • (Free) Text editor on Windows with a folder view?

    - by Horace Ho
    I have to stay away from my MacBook and will use Windows for a while. I missed Textmate's folder view when editing my rails projects. Is there an editor on Windows with the folder view? I know there is the E text editor. But I'll save a few bucks if there is a free (cheaper) alternative, as I won't stay in Windows for long ...

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  • which xml validator will work perfectly for multithreading project

    - by Sunil Kumar Sahoo
    Hi All, I have used jdom for xml validation against schema. The main problem there is that it gives an error FWK005 parse may not be called while parsing The main reason was that multiple of threads working for xerces validation at the same time. SO I got the solution that i have to lock that validation. which is not good So I want to know which xml validator works perfectly for multithreading project public static HashMap validate(String xmlString, Validator validator) { HashMap<String, String> map = new HashMap<String, String>(); long t1 = System.currentTimeMillis(); DocumentBuilder builder = null; try { //obtain lock to proceed // lock.lock(); try { builder = DocumentBuilderFactory.newInstance().newDocumentBuilder(); // Source source = new DOMSource(builder.parse(new ByteArrayInputStream(xmlString.getBytes()))); validator.validate(new StreamSource(new StringReader(xmlString))); map.put("ISVALID", "TRUE"); logger.info("We have successfuly validated the schema"); } catch (Exception ioe) { ioe.printStackTrace(); logger.error("NOT2 VALID STRING IS :" + xmlString); map.put("MSG", ioe.getMessage()); // logger.error("IOException while validating the input XML", ioe); } logger.info(map); long t2 = System.currentTimeMillis(); logger.info("XML VALIDATION TOOK:::" + (t2 - t1)); } catch (Exception e) { logger.error(e); } finally { //release lock // lock.unlock(); builder = null; } return map; } Thanks Sunil Kumar Sahoo

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  • ADO.NET DataTable/DataRow Thread Safety

    - by Allen E. Scharfenberg
    Introduction A user reported to me this morning that he was having an issue with inconsistent results (namely, column values sometimes coming out null when they should not be) of some parallel execution code that we provide as part of an internal framework. This code has worked fine in the past and has not been tampered with lately, but it got me to thinking about the following snippet: Code Sample lock (ResultTable) { newRow = ResultTable.NewRow(); } newRow["Key"] = currentKey; foreach (KeyValuePair<string, object> output in outputs) { object resultValue = output.Value; newRow[output.Name] = resultValue != null ? resultValue : DBNull.Value; } lock (ResultTable) { ResultTable.Rows.Add(newRow); } (No guarantees that that compiles, hand-edited to mask proprietery information.) Explanation We have this cascading type of locking code other places in our system, and it works fine, but this is the first instance of cascading locking code that I have come across that interacts with ADO .NET. As we all know, members of framework objects are usually not thread safe (which is the case in this situation), but the cascading locking should ensure that we are not reading and writing to ResultTable.Rows concurrently. We are safe, right? Hypothesis Well, the cascading lock code does not ensure that we are not reading from or writing to ResultTable.Rows at the same time that we are assigning values to columns in the new row. What if ADO .NET uses some kind of buffer for assigning column values that is not thread safe--even when different object types are involved (DataTable vs. DataRow)? Has anyone run into anything like this before? I thought I would ask here at StackOverflow before beating my head against this for hours on end :) Conclusion Well, the consensus appears to be that changing the cascading lock to a full lock has resolved the issue. That is not the result that I expected, but the full lock version has not produced the issue after many, many, many tests. The lesson: be wary of cascading locks used on APIs that you do not control. Who knows what may be going on under the covers!

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  • In C/C++ mode in Emacs, change face of code in #if 0...#endif block to comment face

    - by pogopop77
    I'm trying to add functionality found in some other code editors to my Emacs configuration, whereby C/C++ code within #if 0...#endif blocks is automatically set to the comment face/font. Based on my testing, cpp-highlight-mode does something like what I want, but requires user action. It seems like tying into the font-lock functionality is the correct option to make the behavior automatic. I have successfully followed examples in the GNU documentation to change the face of single-line regular expressions. For example: (add-hook 'c-mode-common-hook (lambda () (font-lock-add-keywords nil '(("\\<\\(FIXME\\|TODO\\|HACK\\|fixme\\|todo\\|hack\\)" 1 font-lock-warning-face t))))) works fine to highlight debug related keywords anywhere in a file. However, I am having problems matching #if 0...#endif as a multiline regular expression. I found some useful information in this post (How to compose region like ""), that suggested that Emacs must be told specifically to allow for multiline matches. But this code: (add-hook 'c-mode-common-hook (lambda () '(progn (setq font-lock-multiline t) (font-lock-add-keywords nil '(("#if 0\\(.\\|\n\\)*?#endif" 1 font-lock-comment-face t)))))) still does not work for me. Perhaps my regular expression is wrong (though it appears to work using M-x re-builder), I've messed up my syntax, or I'm following the wrong approach entirely. I'm using Aquamacs 2.1 (which is based on GNU Emacs 23.2.50.1) on OS X 10.6.5, if that makes a difference. Any assistance would be appreciated!

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  • implementing the generic interface

    - by user845405
    Could any one help me on implementing the generic interface for this class. I want to be able to use the below Cache class methods through an interface. Thank you for the help!. public class CacheStore { private Dictionary<string, object> _cache; private object _sync; public CacheStore() { _cache = new Dictionary<string, object>(); _sync = new object(); } public bool Exists<T>(string key) where T : class { Type type = typeof(T); lock (_sync) { return _cache.ContainsKey(type.Name + key); } } public bool Exists<T>() where T : class { Type type = typeof(T); lock (_sync) { return _cache.ContainsKey(type.Name); } } public T Get<T>(string key) where T : class { Type type = typeof(T); lock (_sync) { if (_cache.ContainsKey(key + type.Name) == false) throw new ApplicationException(String.Format("An object with key '{0}' does not exists", key)); lock (_sync) { return (T)_cache[key + type.Name]; } } } public void Add<T>(string key, T value) { Type type = typeof(T); if (value.GetType() != type) throw new ApplicationException(String.Format("The type of value passed to cache {0} does not match the cache type {1} for key {2}", value.GetType().FullName, type.FullName, key)); lock (_sync) { if (_cache.ContainsKey(key + type.Name)) throw new ApplicationException(String.Format("An object with key '{0}' already exists", key)); lock (_sync) { _cache.Add(key + type.Name, value); } } } } Could any one help me on implementing the generic interface for this class. I want to be able to use the below Cache class methods through an interface.

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  • How to synchronize access to many objects

    - by vividos
    I have a thread pool with some threads (e.g. as many as number of cores) that work on many objects, say thousands of objects. Normally I would give each object a mutex to protect access to its internals, lock it when I'm doing work, then release it. When two threads would try to access the same object, one of the threads has to wait. Now I want to save some resources and be scalable, as there may be thousands of objects, and still only a hand full of threads. I'm thinking about a class design where the thread has some sort of mutex or lock object, and assigns the lock to the object when the object should be accessed. This would save resources, as I only have as much lock objects as I have threads. Now comes the programming part, where I want to transfer this design into code, but don't know quite where to start. I'm programming in C++ and want to use Boost classes where possible, but self written classes that handle these special requirements are ok. How would I implement this? My first idea was to have a boost::mutex object per thread, and each object has a boost::shared_ptr that initially is unset (or NULL). Now when I want to access the object, I lock it by creating a scoped_lock object and assign it to the shared_ptr. When the shared_ptr is already set, I wait on the present lock. This idea sounds like a heap full of race conditions, so I sort of abandoned it. Is there another way to accomplish this design? A completely different way?

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  • Why does java.util.concurrent.ArrayBlockingQueue use 'while' loops instead of 'if' around calls to

    - by theFunkyEngineer
    I have been playing with my own version of this, using 'if', and all seems to be working fine. Of course this will break down horribly if signalAll() is used instead of signal(), but if only one thread at a time is notified, how can this go wrong? Their code here - check out the put() and take() methods; a simpler and more-to-the-point implementation can be seen at the top of the JavaDoc for Condition. Relevant portion of my implementation below. public Object get() { lock.lock(); try { if( items.size() < 1 ) hasItems.await(); Object poppedValue = items.getLast(); items.removeLast(); hasSpace.signal(); return poppedValue; } catch (InterruptedException e) { e.printStackTrace(); return null; } finally { lock.unlock(); } } public void put(Object item) { lock.lock(); try { if( items.size() >= capacity ) hasSpace.await(); items.addFirst(item); hasItems.signal(); return; } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } P.S. I know that generally, particularly in lib classes like this, one should let the exceptions percolate up.

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  • Debian keyring error: "No keyring installed"

    - by donatello
    I have a Debian Squeeze EC2 AMI. On booting up an instance with it and trying to install packages with apt-get I get errors saying there is no keyring installed. Here is the error with apt-get update: root@ip:~# apt-get update Get:1 http://ftp.us.debian.org squeeze Release.gpg [1672 B] Ign http://ftp.us.debian.org/debian/ squeeze/contrib Translation-en Ign http://ftp.us.debian.org/debian/ squeeze/main Translation-en Ign http://ftp.us.debian.org/debian/ squeeze/non-free Translation-en Get:2 http://security.debian.org squeeze/updates Release.gpg [836 B] Ign http://security.debian.org/ squeeze/updates/contrib Translation-en Ign http://security.debian.org/ squeeze/updates/main Translation-en Hit http://ftp.us.debian.org squeeze Release Ign http://ftp.us.debian.org squeeze Release Ign http://security.debian.org/ squeeze/updates/non-free Translation-en Ign http://ftp.us.debian.org squeeze/main Sources/DiffIndex Get:3 http://security.debian.org squeeze/updates Release [86.9 kB] Ign http://security.debian.org squeeze/updates Release Ign http://ftp.us.debian.org squeeze/contrib Sources/DiffIndex Ign http://ftp.us.debian.org squeeze/non-free Sources/DiffIndex Ign http://ftp.us.debian.org squeeze/main amd64 Packages/DiffIndex Ign http://ftp.us.debian.org squeeze/contrib amd64 Packages/DiffIndex Ign http://ftp.us.debian.org squeeze/non-free amd64 Packages/DiffIndex Ign http://security.debian.org squeeze/updates/main Sources/DiffIndex Hit http://ftp.us.debian.org squeeze/main Sources Hit http://ftp.us.debian.org squeeze/contrib Sources Hit http://ftp.us.debian.org squeeze/non-free Sources Hit http://ftp.us.debian.org squeeze/main amd64 Packages Hit http://ftp.us.debian.org squeeze/contrib amd64 Packages Ign http://security.debian.org squeeze/updates/contrib Sources/DiffIndex Ign http://security.debian.org squeeze/updates/non-free Sources/DiffIndex Ign http://security.debian.org squeeze/updates/main amd64 Packages/DiffIndex Ign http://security.debian.org squeeze/updates/contrib amd64 Packages/DiffIndex Ign http://security.debian.org squeeze/updates/non-free amd64 Packages/DiffIndex Hit http://ftp.us.debian.org squeeze/non-free amd64 Packages Get:4 http://backports.debian.org squeeze-backports Release.gpg [836 B] Ign http://backports.debian.org/debian-backports/ squeeze-backports/main Translation-en Hit http://security.debian.org squeeze/updates/main Sources Hit http://security.debian.org squeeze/updates/contrib Sources Hit http://security.debian.org squeeze/updates/non-free Sources Hit http://security.debian.org squeeze/updates/main amd64 Packages Hit http://security.debian.org squeeze/updates/contrib amd64 Packages Hit http://security.debian.org squeeze/updates/non-free amd64 Packages Get:5 http://backports.debian.org squeeze-backports Release [77.6 kB] Ign http://backports.debian.org squeeze-backports Release Hit http://backports.debian.org squeeze-backports/main amd64 Packages/DiffIndex Hit http://backports.debian.org squeeze-backports/main amd64 Packages Fetched 3346 B in 0s (5298 B/s) Reading package lists... Done W: GPG error: http://ftp.us.debian.org squeeze Release: No keyring installed in /etc/apt/trusted.gpg.d/. W: GPG error: http://security.debian.org squeeze/updates Release: No keyring installed in /etc/apt/trusted.gpg.d/. W: GPG error: http://backports.debian.org squeeze-backports Release: No keyring installed in /etc/apt/trusted.gpg.d/. Googling around didn't really help me fix this problem. I tried installing the packages "debian-keyring" and "debian-archive-keyring" but the error does not go away. I'd like to avoid installing unstrusted packages. Any help is appreciated! Why does this error happen and where can I learn more?

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  • Inverted schedctl usage in the JVM

    - by Dave
    The schedctl facility in Solaris allows a thread to request that the kernel defer involuntary preemption for a brief period. The mechanism is strictly advisory - the kernel can opt to ignore the request. Schedctl is typically used to bracket lock critical sections. That, in turn, can avoid convoying -- threads piling up on a critical section behind a preempted lock-holder -- and other lock-related performance pathologies. If you're interested see the man pages for schedctl_start() and schedctl_stop() and the schedctl.h include file. The implementation is very efficient. schedctl_start(), which asks that preemption be deferred, simply stores into a thread-specific structure -- the schedctl block -- that the kernel maps into user-space. Similarly, schedctl_stop() clears the flag set by schedctl_stop() and then checks a "preemption pending" flag in the block. Normally, this will be false, but if set schedctl_stop() will yield to politely grant the CPU to other threads. Note that you can't abuse this facility for long-term preemption avoidance as the deferral is brief. If your thread exceeds the grace period the kernel will preempt it and transiently degrade its effective scheduling priority. Further reading : US05937187 and various papers by Andy Tucker. We'll now switch topics to the implementation of the "synchronized" locking construct in the HotSpot JVM. If a lock is contended then on multiprocessor systems we'll spin briefly to try to avoid context switching. Context switching is wasted work and inflicts various cache and TLB penalties on the threads involved. If context switching were "free" then we'd never spin to avoid switching, but that's not the case. We use an adaptive spin-then-park strategy. One potentially undesirable outcome is that we can be preempted while spinning. When our spinning thread is finally rescheduled the lock may or may not be available. If not, we'll spin and then potentially park (block) again, thus suffering a 2nd context switch. Recall that the reason we spin is to avoid context switching. To avoid this scenario I've found it useful to enable schedctl to request deferral while spinning. But while spinning I've arranged for the code to periodically check or poll the "preemption pending" flag. If that's found set we simply abandon our spinning attempt and park immediately. This avoids the double context-switch scenario above. One annoyance is that the schedctl blocks for the threads in a given process are tightly packed on special pages mapped from kernel space into user-land. As such, writes to the schedctl blocks can cause false sharing on other adjacent blocks. Hopefully the kernel folks will make changes to avoid this by padding and aligning the blocks to ensure that one cache line underlies at most one schedctl block at any one time.

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  • Pet Peeves with the Windows Phone 7 Marketplace

    - by Bil Simser
    Have you ever noticed how something things just gnaw at your very being. This is the case with the WP7 marketplace, the Zune software, and the things that drive me batshit crazy with a side of fries. To go. I wanted to share. XBox Live is Not the Centre of the Universe Okay, it’s fine that the Zune software has an XBox live tag for games so can see them clearly but do we really need to have it shoved down our throats. On every click? Click on Games in the marketplace: The first thing that it defaults to on the filters on the right is XBox Live: Okay. Fine. However if you change it (say to Paid) then click onto a title when you come back from that title is the filter still set to Paid? No. It’s back to XBox Live again. Really? Give us a break. If you change to any filter on any other genre then click on the selected title, it doesn’t revert back to anything. It stays on the selection you picked. Let’s be fair here. The Games genre should behave just like every other one. If I pick Paid then when I come back to the list please remember that. Double Dipping On the subject of XBox Live titles, Microsoft (and developers who have an agreement with Microsoft to produce Live titles, which generally rules out indie game developers) is double dipping with regards to exposure of their titles. Here’s the Puzzle and Trivia Game section on the Marketplace for XBox Live titles: And here’s the same category filtered on Paid titles: See the problem? Two indie titles while the rest are XBox Live ones. So while XBL has it’s filter, they also get to showcase their wares in the Paid and Free filters as well. If you’re going to have an XBox Live filter then use it and stop pushing down indie titles until they’re off the screen (on some genres this is already the case). Free and Paid titles should be just that and not include XBox Live ones. If you’re really stoked that people can’t find the Free XBox Live titles vs. the paid ones, then create a Free XBox Live filter and a Paid XBox Live filter. I don’t think we would mind much. Whose Trial is it Anyways? You might notice apps in the marketplace with titles like “My Fart App Professional Lite” or “Silicon Lamb Spleen Builder Free”. When you submit and app to the marketplace it can either be free or paid. If it’s a paid app you also have the option to submit it with Trial capabilities. It’s up to you to decide what you offer in the trial version but trial versions can be purchased from within the app so after someone trys out your app (for free) and wants to unlock the Super Secret Obama Spy Ring Level, they can just go to the marketplace from your app (if you built that functionality in) and upgrade to the paid version. However it creates a rift of sorts when it comes to visibility. Some developers go the route of the paid app with a trial version, others decide to submit *two* apps instead of one. One app is the “Free” or “Lite” verions and the other is the paid version. Why go to the hassle of submitting two apps when you can just create a trial version in the same app? Again, visibility. There’s no way to tell Paid apps with Trial versions and ones without (it’s an option, you don’t have to provide trial versions, although I think it’s a good idea). However there is a way to see the Free apps from the Paid ones so some submit the two apps and have the Free version have links to buy the paid one (again through the Marketplace tasks in the API). What we as developers need for visibility is a new filter. Trial. That’s it. It would simply filter on Paid apps that have trial capabilities and surface up those apps just like the free ones. If Microsoft added this filter to the marketplace, it would eliminate the need for people to submit their “Free” and “Lite” versions and make it easier for the developer not to have to maintain two systems. I mean, is it really that hard? Can’t be any more difficult than the XBox Live Filter that’s already there. Location is Everything The last thing on my bucket list is about location. When I launch Zune I’m running in my native location setting, Canada. What’s great is that I navigate to the Travel Tools section where I have one of my apps and behold the splendour that I see: There are my apps in the number 1 and number 4 slot for top selling in that category. I show it to my wife to make up for the sleepless nights writing this stuff and we dance around and celebrate. Then I change my location on my operation system to United States and re-launch Zune. WTF? My flight app has slipped to the 10th spot (I’m only showing 4 across here out of the 7 in Zune) and my border check app that was #1 is now in the 32nd spot! End of celebration. Not only is relevance being looked at here, I value the comments people make on may apps as do most developers. I want to respond to them and show them that I’m listening. The next version of my border app will provide multiple camera angles. However when I’m running in my native Canada location, I only see two reviews. Changing over to United States I see fourteen! While there are tools out there to provide with you a unified view, I shouldn’t have to rely on them. My own Zune desktop software should allow me to see everything. I realize that some developers will submit an app and only target it for some locations and that’s their choice. However I shouldn’t have to jump through hoops to see what apps are ahead of mine, or see people comments and ratings. Another proposal. Either unify the marketplace (i.e. when I’m looking at it show me everything combined) or let me choose a filter. I think the first option might be difficult as you’re trying to average out top selling apps across all markets and have to deal with some apps that have been omitted from some markets. Although I think you could come up with a set of use cases that would handle that, maybe that’s too much work. At the very least, let us developers view the markets in a drop down or something from within the Zune desktop. Having to shut down Zune, change our location, and re-launch Zune to see other perspectives is just too onerous. A Call to Action These are just one mans opinion. Do you agree? Disagree? Feel hungry for a bacon sandwich? Let everyone know via the comments below. Perhaps someone from Microsoft will be reading and take some of these ideas under advisement. Maybe not, but at least let’s get the word out that we really want to see some change. Egypt can do it, why not WP7 developers!

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  • GPL vs plugin interfaces not designed with a specific application in mind

    - by Kristóf Marussy
    I am not seeking or in need of legal advice, but an interesting though experiment came to my mind. Imagine the following situtation (I cannot really think about a concrete example and I am unsure if a real manifestation even exists): there is a free (libre) api A licensed under some permissive license or even LGPL. Non-free application B implements this api in order host plugins, but there are other free software doing the same thing. Moreover, there is plugin C acting as a plugin under api A. It links to library D, that is under GPL, so C is also under GPL. Plugins using A are loaded into hosts via a dlopen-like mechanism and use complex data structure for host-plugin communication. Neither B nor C distribute any files that may be required for A to function properly (like headers containing the structure definitions of A or dynamic libraries containing helper functions for A written by the authors of A), but such things may exist. Now some user installs application B and plugin C on his machine, along with anything that may be required for api A to function properly. Then he proceeds and loads C into B and creates some intellectual property with B which is not a piece of software. Did a GPL violation happend at some point, and if so, who violated GPL and why? The authors of C violate D's license by making C possible to be used in non-free host B? This is a possibility because they can't give and exception of GPL (like one described in http://www.gnu.org/licenses/gpl-faq.html#GPLPluginsInNF or http://www.gnu.org/licenses/gpl-faq.html#LinkingOverControlledInterface) due to D's license terms. The authors of B violate C's and D's license by making C possible to be loaded in B? This is a possibility because http://www.gnu.org/licenses/gpl-faq.html#NFUseGPLPlugins disallows the mechanisms A uses for communitation between the free and non-free modules. The authors of A, because the api may be used (and in this case, was used) for communication between GPL'd and non-free software. This would be extremely absurd. The user, because at the moment of loading B into C, he made a derived work of C. I think this is impossible, because he does not distribute it. But would the situation change is he decided to release a configuration file of B which makes B load C as a plugin? Nobody, because A counts as a 'system library', and both B and C directly interact only with A, not eachother. In a sane world, this would happen... A concrete example of A could be some kind of audio (think LADSPA) or image processing api. However, I could find no such interface (that is free software, generic and is also implemented by commercial tools). A real-world example could also be quite enlightening.

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