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• How to verify if the private key matches with the certificate..?

  - by surendhar_s

  I have the private key stored as .key file.. -----BEGIN RSA PRIVATE KEY----- MIICXAIBAAKBgQD5YBS6V3APdgqaWAkijIUHRK4KQ6eChSaRWaw9L/4u8o3T1s8J rUFHQhcIo5LPaQ4BrIuzHS8yzZf0m3viCTdZAiDn1ZjC2koquJ53rfDzqYxZFrId 7a4QYUCvM0gqx5nQ+lw1KoY/CDAoZN+sO7IJ4WkMg5XbgTWlSLBeBg0gMwIDAQAB AoGASKDKCKdUlLwtRFxldLF2QPKouYaQr7u1ytlSB5QFtIih89N5Avl5rJY7/SEe rdeL48LsAON8DpDAM9Zg0ykZ+/gsYI/C8b5Ch3QVgU9m50j9q8pVT04EOCYmsFi0 DBnwNBRLDESvm1p6NqKEc7zO9zjABgBvwL+loEVa1JFcp5ECQQD9/sekGTzzvKa5 SSVQOZmbwttPBjD44KRKi6LC7rQahM1PDqmCwPFgMVpRZL6dViBzYyWeWxN08Fuv p+sIwwLrAkEA+1f3VnSgIduzF9McMfZoNIkkZongcDAzjQ8sIHXwwTklkZcCqn69 qTVPmhyEDA/dJeAK3GhalcSqOFRFEC812QJAXStgQCmh2iaRYdYbAdqfJivMFqjG vgRpP48JHUhCeJfOV/mg5H2yDP8Nil3SLhSxwqHT4sq10Gd6umx2IrimEQJAFNA1 ACjKNeOOkhN+SzjfajJNHFyghEnJiw3NlqaNmEKWNNcvdlTmecObYuSnnqQVqRRD cfsGPU661c1MpslyCQJBAPqN0VXRMwfU29a3Ve0TF4Aiu1iq88aIPHsT3GKVURpO XNatMFINBW8ywN5euu8oYaeeKdrVSMW415a5+XEzEBY= -----END RSA PRIVATE KEY----- And i extracted public key from ssl certificate file.. Below is the code i tried to verify if private key matches with ssl certificate or not.. I used the modulus[i.e. private key get modulus==public key get modulus] to check if they are matching.. And this seems to hold only for RSAKEYS.. But i want to check for other keys as well.. Is there any other alternative to do the same..?? private static boolean verifySignature(File serverCertificateFile, File serverCertificateKey) { try { byte[] certificateBytes = FileUtils.readFileToByteArray(serverCertificateFile); //byte[] keyBytes = FileUtils.readFileToByteArray(serverCertificateKey); RandomAccessFile raf = new RandomAccessFile(serverCertificateKey, "r"); byte[] buf = new byte[(int) raf.length()]; raf.readFully(buf); raf.close(); PKCS8EncodedKeySpec kspec = new PKCS8EncodedKeySpec(buf); KeyFactory kf; try { kf = KeyFactory.getInstance("RSA"); RSAPrivateKey privKey = (RSAPrivateKey) kf.generatePrivate(kspec); CertificateFactory certFactory = CertificateFactory.getInstance("X.509"); InputStream in = new ByteArrayInputStream(certificateBytes); //Generate Certificate in X509 Format X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in); RSAPublicKey publicKey = (RSAPublicKey) cert.getPublicKey(); in.close(); return privKey.getModulus() == publicKey.getModulus(); } catch (NoSuchAlgorithmException ex) { logger.log(Level.SEVERE, "Such algorithm is not found", ex); } catch (CertificateException ex) { logger.log(Level.SEVERE, "certificate exception", ex); } catch (InvalidKeySpecException ex) { Logger.getLogger(CertificateConversion.class.getName()).log(Level.SEVERE, null, ex); } } catch (IOException ex) { logger.log(Level.SEVERE, "Signature verification failed.. This could be because the file is in use", ex); } return false; } And the code isn't working either.. throws invalidkeyspec exception

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• quick java question

  - by j-unit-122

  private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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• ActionResult - Service

  - by cem

  I bored, writing same code for service and ui. Then i tried to write a converter for simple actions. This converter, converting Service Results to MVC result, seems like good solution for me but anyway i think this gonna opposite MVC pattern. So here, I need help, what you think about algorithm - is this good or not? Thanks ServiceResult - Base: public abstract class ServiceResult { public static NoPermissionResult Permission() { return new NoPermissionResult(); } public static SuccessResult Success() { return new SuccessResult(); } public static SuccessResult<T> Success<T>(T result) { return new SuccessResult<T>(result); } protected ServiceResult(ServiceResultType serviceResultType) { _resultType = serviceResultType; } private readonly ServiceResultType _resultType; public ServiceResultType ResultType { get { return _resultType; } } } public class SuccessResult<T> : ServiceResult { public SuccessResult(T result) : base(ServiceResultType.Success) { _result = result; } private readonly T _result; public T Result { get { return _result; } } } public class SuccessResult : SuccessResult<object> { public SuccessResult() : this(null) { } public SuccessResult(object o) : base(o) { } } Service - eg. ForumService: public ServiceResult Delete(IVUser user, int id) { Forum forum = Repository.GetDelete(id); if (!Permission.CanDelete(user, forum)) { return ServiceResult.Permission(); } Repository.Delete(forum); return ServiceResult.Success(); } Controller: public class BaseController { public ActionResult GetResult(ServiceResult result) { switch (result.ResultType) { case ServiceResultType.Success: var successResult = (SuccessResult)result; return View(successResult.Result); break; case ServiceResultType.NoPermission: return View("Error"); break; default: return View(); break; } } } [HandleError] public class ForumsController : BaseController { [ValidateAntiForgeryToken] [Transaction] [AcceptVerbs(HttpVerbs.Post)] public ActionResult Delete(int id) { ServiceResult result = ForumService.Delete(WebUser.Current, id); /* Custom result */ if (result.ResultType == ServiceResultType.Success) { TempData[ControllerEnums.GlobalViewDataProperty.PageMessage.ToString()] = "The forum was successfully deleted."; return this.RedirectToAction(ec => Index()); } /* Custom result */ /* Execute Permission result etc. */ TempData[ControllerEnums.GlobalViewDataProperty.PageMessage.ToString()] = "A problem was encountered preventing the forum from being deleted. " + "Another item likely depends on this forum."; return GetResult(result); } }

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• Blending pixels from Two Bitmaps

  - by MarkPowell

  I'm beating my head against a wall here, and I'm fairly certain I'm doing something stupid, so time to make my stupidity public. I'm trying to take two images, blend them together into a third image using standard blending algorithms (Hardlight, softlight, overlay, multiply, etc). Because Android does not have such blend properties build in, I've gone down the path of taking each pixel and combine them using an algorithm. However, the results are garbage. Any help would be appreciated. Below is the code, which I've tried to strip out all the "junk", but some may have made it through. I'll clean it up if something isn't clear. Bitmap src = BitmapFactory.decodeResource(getResources(), R.drawable.base, options); Bitmap mutableBitmap = src.copy(Bitmap.Config.RGB_565, true); int imageId = getResources().getIdentifier("drawable/" + filter, null, getPackageName()); Bitmap filterBitmap = BitmapFactory.decodeResource(getResources(), imageId, options); float scaleWidth = ((float) mutableBitmap.getWidth()) / filterBitmap.getWidth(); float scaleHeight = ((float) mutableBitmap.getHeight()) / filterBitmap.getHeight(); IntBuffer buffSrc = IntBuffer.allocate(src.getWidth() * src.getHeight()); mutableBitmap.copyPixelsToBuffer(buffSrc); buffSrc.rewind(); IntBuffer buffFilter = IntBuffer.allocate(resizedFilterBitmap.getWidth() * resizedFilterBitmap.getHeight()); resizedFilterBitmap.copyPixelsToBuffer(buffFilter); buffFilter.rewind(); IntBuffer buffOut = IntBuffer.allocate(src.getWidth() * src.getHeight()); buffOut.rewind(); while (buffOut.position() < buffOut.limit()) { int filterInt = buffFilter.get(); int srcInt = buffSrc.get(); int alphaValueFilter = Color.alpha(filterInt); int redValueFilter = Color.red(filterInt); int greenValueFilter = Color.green(filterInt); int blueValueFilter = Color.blue(filterInt); int alphaValueSrc = Color.alpha(srcInt); int redValueSrc = Color.red(srcInt); int greenValueSrc = Color.green(srcInt); int blueValueSrc = Color.blue(srcInt); int alphaValueFinal = convert(alphaValueFilter, alphaValueSrc); int redValueFinal = convert(redValueFilter, redValueSrc); int greenValueFinal = convert(greenValueFilter, greenValueSrc); int blueValueFinal = convert(blueValueFilter, blueValueSrc); int pixel = Color.argb(alphaValueFinal, redValueFinal, greenValueFinal, blueValueFinal); buffOut.put(pixel); } buffOut.rewind(); mutableBitmap.copyPixelsFromBuffer(buffOut); BitmapDrawable drawable = new BitmapDrawable(getResources(), mutableBitmap); imageView.setImageDrawable(drawable); } int convert (int in1, int in2) { //simple multiply for example return in1 * in2 / 255; }

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• UCA + Natural Sorting

  - by Alix Axel

  I recently learnt that PHP already supports the Unicode Collation Algorithm via the intl extension: $array = array ( 'al', 'be', 'Alpha', 'Beta', 'Álpha', 'Àlpha', 'Älpha', '????', 'img10.png', 'img12.png', 'img1.png', 'img2.png', ); if (extension_loaded('intl') === true) { collator_asort(collator_create('root'), $array); } Array ( [0] => al [2] => Alpha [4] => Álpha [5] => Àlpha [6] => Älpha [1] => be [3] => Beta [11] => img1.png [9] => img10.png [8] => img12.png [10] => img2.png [7] => ???? ) As you can see this seems to work perfectly, even with mixed case strings! The only drawback I've encountered so far is that there is no support for natural sorting and I'm wondering what would be the best way to work around that, so that I can merge the best of the two worlds. I've tried to specify the Collator::SORT_NUMERIC sort flag but the result is way messier: collator_asort(collator_create('root'), $array, Collator::SORT_NUMERIC); Array ( [8] => img12.png [7] => ???? [9] => img10.png [10] => img2.png [11] => img1.png [6] => Älpha [5] => Àlpha [1] => be [2] => Alpha [3] => Beta [4] => Álpha [0] => al ) However, if I run the same test with only the img*.png values I get the ideal output: Array ( [3] => img1.png [2] => img2.png [1] => img10.png [0] => img12.png ) Can anyone think of a way to preserve the Unicode sorting while adding natural sorting capabilities?

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• passing a class method as opposed to a function in std::sort

  - by memC

  hi, Within a class, I am trying to sort a vector, by passing a method of the same class. But it gives errors at the time of compilation. Can anyone tell what the problem is? Thank you! it gives the following error: argument of type bool (Sorter::)(D&, D&)' does not matchbool (Sorter::*)(D&, D&)' I have also tried using sortBynumber(D const& d1, D const& d2) #include<vector> #include<stdio.h> #include<iostream> #include<algorithm> class D { public: int getNumber(); D(int val); ~D(){}; private: int num; }; D::D(int val){ num = val; }; int D::getNumber(){ return num; }; class Sorter { public: void doSorting(); bool sortByNumber(D& d1, D& d2); std::vector<D> vec_D; Sorter(); ~Sorter(){}; private: int num; }; Sorter::Sorter(){ int i; for ( i = 0; i < 10; i++){ vec_D.push_back(D(i)); } }; bool Sorter::sortByNumber(D& d1, D& d2){ return d1.getNumber() < d2.getNumber(); }; void Sorter::doSorting(){ std::sort(vec_D.begin(), vec_D.end(), this->sortByNumber); }; int main(){ Sorter s; s.doSorting(); std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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• Security review of an authenticated Diffie Hellman variant

  - by mtraut

  EDIT I'm still hoping for some advice on this, i tried to clarify my intentions... When i came upon device pairing in my mobile communication framework i studied a lot of papers on this topic and and also got some input from previous questions here. But, i didn't find a ready to implement protocol solution - so i invented a derivate and as i'm no crypto geek i'm not sure about the security caveats of the final solution: The main questions are Is SHA256 sufficient as a commit function? Is the addition of the shared secret as an authentication info in the commit string safe? What is the overall security of the 1024 bit group DH I assume at most 2^-24 bit probability of succesful MITM attack (because of 24 bit challenge). Is this plausible? What may be the most promising attack (besides ripping the device out off my numb, cold hands) This is the algorithm sketch For first time pairing, a solution proposed in "Key agreement in peer-to-peer wireless networks" (DH-SC) is implemented. I based it on a commitment derived from: A fix "UUID" for the communicating entity/role (128 bit, sent at protocol start, before commitment) The public DH key (192 bit private key, based on the 1024 bit Oakley group) A 24 bit random challenge Commit is computed using SHA256 c = sha256( UUID || DH pub || Chall) Both parties exchange this commitment, open and transfer the plain content of the above values. The 24 bit random is displayed to the user for manual authentication DH session key (128 bytes, see above) is computed When the user opts for persistent pairing, the session key is stored with the remote UUID as a shared secret Next time devices connect, commit is computed by additionally hashing the previous DH session key before the random challenge. For sure it is not transfered when opening. c = sha256( UUID || DH pub || DH sess || Chall) Now the user is not bothered authenticating when the local party can derive the same commitment using his own, stored previous DH session key. After succesful connection the new DH session key becomes the new shared secret. As this does not exactly fit the protocols i found so far (and as such their security proofs), i'd be very interested to get an opinion from some more crypto enabled guys here. BTW. i did read about the "EKE" protocol, but i'm not sure what the extra security level is.

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• How to manually (bitwise) perform (float)x? (homework)

  - by Silver

  Now, here is the function header of the function I'm supposed to implement: /* * float_from_int - Return bit-level equivalent of expression (float) x * Result is returned as unsigned int, but * it is to be interpreted as the bit-level representation of a * single-precision floating point values. * Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while * Max ops: 30 * Rating: 4 */ unsigned float_from_int(int x) { ... } We aren't allowed to do float operations, or any kind of casting. Now I tried to implement the first algorithm given at this site: http://locklessinc.com/articles/i2f/ Here's my code: unsigned float_from_int(int x) { // grab sign bit int xIsNegative = 0; int absValOfX = x; if(x < 0){ xIsNegative = 1; absValOfX = -x; } // zero case if(x == 0){ return 0; } //int shiftsNeeded = 0; /*while(){ shiftsNeeded++; }*/ unsigned I2F_MAX_BITS = 15; unsigned I2F_MAX_INPUT = ((1 << I2F_MAX_BITS) - 1); unsigned I2F_SHIFT = (24 - I2F_MAX_BITS); unsigned result, i, exponent, fraction; if ((absValOfX & I2F_MAX_INPUT) == 0) result = 0; else { exponent = 126 + I2F_MAX_BITS; fraction = (absValOfX & I2F_MAX_INPUT) << I2F_SHIFT; i = 0; while(i < I2F_MAX_BITS) { if (fraction & 0x800000) break; else { fraction = fraction << 1; exponent = exponent - 1; } i++; } result = (xIsNegative << 31) | exponent << 23 | (fraction & 0x7fffff); } return result; } But it didn't work (see test error below): Test float_from_int(-2147483648[0x80000000]) failed... ...Gives 0[0x0]. Should be -822083584[0xcf000000] 4 4 0 float_times_four I don't know where to go from here. How should I go about parsing the float from this int?

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• hashing password giving different results

  - by geoff

  I am taking over a system that a previous developer wrote. The system has an administrator approve a user account and when they do that the system uses the following method to hash a password and save it to the database. It sends the unhashed password to the user. When the user logs in the system uses the exact same method to hash what the user enters and compares it to the database value. We've run into a couple of times when the database entry doesn't match the user's entry whey they should. So it appears that the method isn't always hashing the value the same. Does anyone know if this method of hashing isn't reliable and how to make it reliable? Thanks. private string HashPassword(string password) { string hashedPassword = string.Empty; // Convert plain text into a byte array. byte[] plainTextBytes = Encoding.UTF8.GetBytes(password); // Allocate array, which will hold plain text and salt. byte[] plainTextWithSaltBytes = new byte[plainTextBytes.Length + SALT.Length]; // Copy plain text bytes into resulting array. for(int i = 0; i < plainTextBytes.Length; i++) plainTextWithSaltBytes[i] = plainTextBytes[i]; // Append salt bytes to the resulting array. for(int i = 0; i < SALT.Length; i++) plainTextWithSaltBytes[plainTextBytes.Length + i] = SALT[i]; // Because we support multiple hashing algorithms, we must define // hash object as a common (abstract) base class. We will specify the // actual hashing algorithm class later during object creation. HashAlgorithm hash = new SHA256Managed(); // Compute hash value of our plain text with appended salt. byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes); // Create array which will hold hash and original salt bytes. byte[] hashWithSaltBytes = new byte[hashBytes.Length + SALT.Length]; // Copy hash bytes into resulting array. for(int i = 0; i < hashBytes.Length; i++) hashWithSaltBytes[i] = hashBytes[i]; // Append salt bytes to the result. for(int i = 0; i < SALT.Length; i++) hashWithSaltBytes[hashBytes.Length + i] = SALT[i]; // Convert result into a base64-encoded string. hashedPassword = Convert.ToBase64String(hashWithSaltBytes); return hashedPassword; }

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• getting Cannot identify image file when trying to create thumbnail in django

  - by Mo J. Mughrabi

  Am trying to create a thumbnail in django, am trying to build a custom class specifically to be used for generating thumbnails. As following from StringIO import StringIO from PIL import Image class Thumbnail(object): source = '' size = (50, 50) output = '' def __init__(self): pass @staticmethod def load(src): self = Thumbnail() self.source = src return self def generate(self, size=(50, 50)): if not isinstance(size, tuple): raise Exception('Thumbnail class: The size parameter must be an instance of a tuple.') self.size = size # resize properties box = self.size factor = 1 fit = True image = Image.open(self.source) # Convert to RGB if necessary if image.mode not in ('L', 'RGB'): image = image.convert('RGB') while image.size[0]/factor > 2*box[0] and image.size[1]*2/factor > 2*box[1]: factor *=2 if factor > 1: image.thumbnail((image.size[0]/factor, image.size[1]/factor), Image.NEAREST) #calculate the cropping box and get the cropped part if fit: x1 = y1 = 0 x2, y2 = image.size wRatio = 1.0 * x2/box[0] hRatio = 1.0 * y2/box[1] if hRatio > wRatio: y1 = int(y2/2-box[1]*wRatio/2) y2 = int(y2/2+box[1]*wRatio/2) else: x1 = int(x2/2-box[0]*hRatio/2) x2 = int(x2/2+box[0]*hRatio/2) image = image.crop((x1,y1,x2,y2)) #Resize the image with best quality algorithm ANTI-ALIAS image.thumbnail(box, Image.ANTIALIAS) # save image to memory temp_handle = StringIO() image.save(temp_handle, 'png') temp_handle.seek(0) self.output = temp_handle return self def get_output(self): return self.output.read() the purpose of the class is so i can use it inside different locations to generate thumbnails on the fly. The class works perfectly, I've tested it directly under a view.. I've implemented the thumbnail class inside the save method of the forms to resize the original images on saving. in my design, I have two fields for thumbnails. I was able to generate one thumbnail, if I try to generate two it crashes and I've been stuck for hours not sure whats the problem. Here is my model class Image(models.Model): article = models.ForeignKey(Article) title = models.CharField(max_length=100, null=True, blank=True) src = models.ImageField(upload_to='publication/image/') r128 = models.ImageField(upload_to='publication/image/128/', blank=True, null=True) r200 = models.ImageField(upload_to='publication/image/200/', blank=True, null=True) uploaded_at = models.DateTimeField(auto_now=True) Here is my forms class ImageForm(models.ModelForm): """ """ class Meta: model = Image fields = ('src',) def save(self, commit=True): instance = super(ImageForm, self).save(commit=True) file = Thumbnail.load(instance.src) instance.r128 = SimpleUploadedFile( instance.src.name, file.generate((128, 128)).get_output(), content_type='image/png' ) instance.r200 = SimpleUploadedFile( instance.src.name, file.generate((200, 200)).get_output(), content_type='image/png' ) if commit: instance.save() return instance the strange part is, when i remove the line which contains instance.r200 in the form save. It works fine, and it does the thumbnail and stores it successfully. Once I add the second thumbnail it fails.. Any ideas what am doing wrong here? Thanks Update: I tried earlier doing the following but I still got the same error class ImageForm(models.ModelForm): """ """ class Meta: model = Image fields = ('src',) def save(self, commit=True): instance = super(ImageForm, self).save(commit=True) instance.r128 = SimpleUploadedFile( instance.src.name, Thumbnail.load(instance.src).generate((128, 128)).get_output(), content_type='image/png' ) instance.r200 = SimpleUploadedFile( instance.src.name, Thumbnail.load(instance.src).generate((200, 200)).get_output(), content_type='image/png' ) if commit: instance.save() return instance

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• True / false evaluation doesn't work as expected in Scheme

  - by ron

  I'm trying to compare two booleans : (if (equal? #f (string->number "123b")) "not a number" "indeed a number") When I run this in the command line of DrRacket I get "not a number" , however , when I put that piece of code in my larger code , the function doesn't return that string ("not a number") , here's the code : (define (testing x y z) (define badInput "ERROR") (if (equal? #f (string->number "123b")) "not a number" "indeed a number") (display x)) And from command line : (testing "123" 1 2) displays : 123 Why ? Furthermore , how can I return a value , whenever I choose ? Here is my "real" problem : I want to do some input check to the input of the user , but the thing is , that I want to return the error message if I need , before the code is executed , because if won't - then I would run the algorithm of my code for some incorrect input : (define (convert originalNumber s_oldBase s_newBase) (define badInput "ERROR") ; Input check - if one of the inputs is not a number then return ERROR (if (equal? #f (string->number originalNumber)) badInput) (if (equal? #f (string->number s_oldBase)) badInput) (if (equal? #f (string->number s_newBase)) badInput) (define oldBase (string->number s_oldBase)) (define newBase (string->number s_newBase)) (define outDecimal (convertIntoDecimal originalNumber oldBase)) (define result "") ; holds the new number (define remainder 0) ; remainder for each iteration (define whole 0) ; the whole number after dividing (define temp 0) (do() ((= outDecimal 0)) ; stop when the decimal value reaches 0 (set! whole (quotient outDecimal newBase)) ; calc the whole number (set! temp (* whole newBase)) (set! remainder (- outDecimal temp)) ; calc the remainder (set! result (appending result remainder)) ; append the result (set! outDecimal (+ whole 0)) ; set outDecimal = whole ) ; end of do (if (> 1 0) (string->number (list->string(reverse (string->list result))))) ) ;end of method This code won't work since it uses another method that I didn't attach to the post (but it's irrelevant to the problem . Please take a look at those three IF-s ... I want to return "ERROR" if the user put some incorrect value , for example (convert "23asb4" "b5" "9") Thanks

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• get return value from 2 threads in C

  - by polslinux

  #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <stdint.h> #include <inttypes.h> typedef struct tmp_num{ int tmp_1; int tmp_2; }t_num; t_num t_nums; void *num_mezzo_1(void *num_orig); void *num_mezzo_2(void *num_orig); int main(int argc, char *argv[]){ pthread_t thread1, thread2; int tmp=0,rc1,rc2,num; num=atoi(argv[1]); if(num <= 3){ printf("Questo è un numero primo: %d\n", num); exit(0); } if( (rc1=pthread_create( &thread1, NULL, &num_mezzo_1, (void *)&num)) ){ printf("Creazione del thread fallita: %d\n", rc1); exit(1); } if( (rc2=pthread_create( &thread2, NULL, &num_mezzo_2, (void *)&num)) ){ printf("Creazione del thread fallita: %d\n", rc2); exit(1); } t_nums.tmp_1 = 0; t_nums.tmp_2 = 0; pthread_join(thread1, (void **)(&t_nums.tmp_1)); pthread_join(thread2, (void **)(&t_nums.tmp_2)); tmp=t_nums.tmp_1+t_nums.tmp_2; printf("%d %d %d\n", tmp, t_nums.tmp_1, t_nums.tmp_2); if(tmp>2){ printf("Questo NON è un numero primo: %d\n", num); } else{ printf("Questo è un numero primo: %d\n", num); } exit(0); } void *num_mezzo_1(void *num_orig){ int cont_1; int *n_orig=(int *)num_orig; t_nums.tmp_1 = 0; for(cont_1=1; cont_1<=(*n_orig/2); cont_1++){ if((*n_orig % cont_1) == 0){ (t_nums.tmp_1)++; } } pthread_exit((void *)(&t_nums.tmp_1)); return NULL; } void *num_mezzo_2(void *num_orig){ int cont_2; int *n_orig=(int *)num_orig; t_nums.tmp_2 = 0; for(cont_2=((*n_orig/2)+1); cont_2<=*n_orig; cont_2++){ if((*n_orig % cont_2) == 0){ (t_nums.tmp_2)++; } } pthread_exit((void *)(&t_nums.tmp_2)); return NULL; } How this program works: i have to input a number and this program will calculate if it is a prime number or not (i know that it is a bad algorithm but i only need to learn pthread). The problem is that the returned values are too much big.For example if i write "12" the value of tmp tmp_1 tmp_2 into the main are 12590412 6295204 6295208.Why i got those numbers??

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• Swing: How do I run a job from AWT thread, but after a window was layed out?

  - by java.is.for.desktop

  My complete GUI runs inside the AWT thread, because I start the main window using SwingUtilities.invokeAndWait(...). Now I have a JDialog which has just to display a JLabel, which indicates that a certain job is in progress, and close that dialog after the job was finished. The problem is: the label is not displayed. That job seems to be started before JDialog was fully layed-out. When I just let the dialog open without waiting for a job and closing, the label is displayed. The last thing the dialog does in its ctor is setVisible(true). Things such as revalidate(), repaint(), ... don't help either. Even when I start a thread for the monitored job, and wait for it using someThread.join() it doesn't help, because the current thread (which is the AWT thread) is blocked by join, I guess. Replacing JDialog with JFrame doesn't help either. So, is the concept wrong in general? Or can I manage it to do certain job after it is ensured that a JDialog (or JFrame) is fully layed-out? Simplified algorithm of what I'm trying to achieve: Create a subclass of JDialog Ensure that it and its contents are fully layed-out Start a process and wait for it to finish (threaded or not, doesn't matter) Close the dialog I managed to write a reproducible test case: EDIT Problem from an answer is now addressed: This use case does display the label, but it fails to close after the "simulated process", because of dialog's modality. import java.awt.*; import javax.swing.*; public class _DialogTest2 { public static void main(String[] args) throws Exception { SwingUtilities.invokeAndWait(new Runnable() { final JLabel jLabel = new JLabel("Please wait..."); @Override public void run() { JFrame myFrame = new JFrame("Main frame"); myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); myFrame.setSize(750, 500); myFrame.setLocationRelativeTo(null); myFrame.setVisible(true); JDialog d = new JDialog(myFrame, "I'm waiting"); d.setModalityType(Dialog.ModalityType.APPLICATION_MODAL); d.add(jLabel); d.setSize(300, 200); d.setLocationRelativeTo(null); d.setVisible(true); SwingUtilities.invokeLater(new Runnable() { @Override public void run() { try { Thread.sleep(3000); // simulate process jLabel.setText("Done"); } catch (InterruptedException ex) { } } }); d.setVisible(false); d.dispose(); myFrame.setVisible(false); myFrame.dispose(); } }); } }

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• C++ Filling an 1D array to represent a n-dimensional object based on a straight line segment

  - by Ben

  I'm struggling to find a good way to put this question but here goes. I'm making a system that uses a 1D array implemented as double * parts_ = new double[some_variable];. I want to use this to hold co-ordinates for a particle system that can run in various dimensions. What I want to be able to do is write a generic fill algorithm for filling this in n-dimensions with a common increment in all direction to a variable size. Examples will serve best I think. Consider the case where the number of particles stored by the array is 4 In 1D this produces 4 elements in the array because each particle only has one co-ordinate. 1D: {0, 25, 50, 75}; In 2D this produces 8 elements in the array because each particle has two co-ordinates.. 2D: {0, 0, 0, 25, 25, 0, 25, 25} In 3D this produces 12 elements in the array because each particle now has three co-ordinates {0, 0, 0, 0, 0, 25, 0, 0, 50, ... } These examples are still not quite accurate, but they hopefully will suffice. The way I would do this normally for two dimensions: int i = 0; for(int x = 0; x < parts_size_ / dims_ / dims_ * 25; x += 25) { for(int y = 0; y < parts_size_ / dims_ / dims_ * 25; y += 25) { parts_[i] = x; parts_[i+1] = y; i+=2; // Indentation hates me today .< How can I implement this for n-dimensions where 25 can be any number? The straight line part is because it seems to me logical that a line is a somewhat regular shape in 1D, as is a square in 2D, and a cube in 3D. It seems to me that it would follow that there would be similar shapes in this family that could be implemented for 4D and higher dimensions via a similar fill pattern. This is the shape I wish to set my array to represent.

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• C++ STL make_heap and pop_heap not working.

  - by Henrique

  I need to use a Heap, so i've searched about the STL one, but it doesn't seem to work, i wrote some code to explain what i mean: #include <stdio.h> #include <stdlib.h> #include <vector> #include <algorithm> struct data { int indice; int tamanho; }; bool comparator2(const data* a, const data* b) { return (a->tamanho < b->tamanho); } int main() { std::vector<data*> mesas; data x1, x2, x3, x4, x5; x1.indice = 1; x1.tamanho = 3; x2.indice = 2; x2.tamanho = 5; x3.indice = 3; x3.tamanho = 2; x4.indice = 4; x4.tamanho = 6; x5.indice = 5; x5.tamanho = 4; mesas.push_back(&x1); mesas.push_back(&x2); mesas.push_back(&x3); mesas.push_back(&x4); mesas.push_back(&x5); make_heap(mesas.begin(), mesas.end(), comparator2); for(int i = 0 ; i < 5 ; i++) { data* mesa = mesas.front(); pop_heap(mesas.begin(),mesas.end()); mesas.pop_back(); printf("%d, %d\n", mesa->indice, mesa->tamanho); } return 0; }; and this is what i get: 4, 6 2, 5 1, 3 3, 2 5, 4 So it's not working as a heap, as the maximum element on the vector is not being returned right. Or am i doing something wrong?

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• c permutation of a number

  - by Pkp

  I am writing a program for magic box. As the only way around it is brute force, I wrote a program to compute permutations of a given array using bells algorithm. I wrote in the lines similar to http://programminggeeks.com/c-code-for-permutation/. It does work for array of 3 and 4. It does not work for an arryay of 8 numbers (1,2,3,4,5,6,7,8). I see that the combination 1 2 3 4 5 6 7 8 gets repeated couple of times. Also there are other combinations that gets repeated. I see that certain combinations don't get displayed even. So could someone tell me what is wrong in the program below. Code: include<stdio.h> int len,numperm=1,count=0; display(int a[]){ int i; for(i=0;i<len;i++) printf("%d ",a[i]); printf("\n"); count++; } swap(int *a,int *b){ int temp; temp=*a; *a=*b; *b=temp; } no_of_perm(){ int x; for(x=1;x<=len;x++) numperm=numperm*x; } perm(int a[]){ int x,y; while(count < numperm){ for(x=0;x<len-1;x++){ swap(&a[x],&a[x+1]); display(a); } swap(&a[0],&a[1]); display(a); for(y=len-1;y>0;y--){ swap(&a[y],&a[y-1]); display(a); } swap(&a[len-1],&a[len-2]); display(a); } } main(int argc, char *argv[]){ if(argc<2){ printf("Error\n"); exit(0); } int i,*a=malloc(sizeof(int)*atoi(argv[1])); len=atoi(argv[1]); for(i=0;i<len;i++) a[i]=i+1; no_of_perm(); perm(a); }

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• Where can I find "canonical" sample programs that give quick refreshers for any given language? [on hold]

  - by acheong87

  Note to those close-voting this question: I understand this isn't a conventional programming question and I can agree with the reasoning that it's in the subjective domain (like best-of lists). In other ways though I think it's appropriate because, though it's not a "a specific programming problem," nor concerning "a software algorithm", nor (strictly) concerning "software tools commonly used by programmers", I think it is a "practical, answerable [problem that is] unique to the programming profession," and I think it is "based on an actual [problem I] face." I've been wanting this for some time now, because both approaches of (a) Googling for samples as I write every other line of code and (b) just winging it and seeing what errors crop up, distract me from coding efficiently. This note will be removed if the question gains popularity; this question will be deleted otherwise. I spend most of my time developing in C++, PHP, or Javascript, and every once in a while I have to do something in, say, VBA. In those times, it'd be convenient if I could just put up some sample code on a second monitor, something in between a cheat sheet (often too compact; and doesn't resemble anything that could actually compile/run), and a language reference (often too verbose, or segmented; requires extra steps to search or click through an index), so I can just glance at it and recall things, like how to loop through non-empty cells in a column. I think there's a hidden benefit to seeing formed code, that triggers the right spots in our brains to get back into a language we only need to brush up on. Similar in spirit is how http://ideone.com lets you click "Template" in any given language so you can get started without even doing a search. That template alone tells a lot, sometimes! Case-sensitivity, whitespace conventions, identifier conventions, the spelling of certain types, etc. I couldn't find a resource that pulled together such samples, so if there indeed doesn't exist such a repository, I was hoping this question would inspire professionals and experts to contribute links to the most useful sample code they've used for just this purpose: a keep-on-the-side, form-as-well-as-content, compilable/executable, reminder of a language's basic and oft-used features. Personally I am interested in seeing "samplers" for: VBA, Perl, Python, Java, C# (though for some of these autocompleters in Eclipse, Visual Studio, etc. help enough), awk, and sed. I'm tagging c++, php, and javascript because these are languages for which I'd best be able to evaluate whether proffered sample code matches what I had in mind.

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• PHP array performance

  - by dfo

  Hi, this is my first question on Stackoverflow, please bear with me. I'm testing an algorithm for 2d bin packing and I've chosen PHP to mock it up as it's my bread-and-butter language nowadays. As you can see on http://themworks.com/pack_v0.2/oopack.php?ol=1 it works pretty well, but you need to wait around 10-20 seconds for 100 rectangles to pack. For some hard to handle sets it would hit the php's 30s runtime limit. I did some profiling and it shows that most of the time my script goes through different parts of a small 2d array with 0's and 1's in it. It either checks if certain cell equals to 0/1 or sets it to 0/1. It can do such operations million times and each times it takes few microseconds. I guess I could use an array of booleans in a statically typed language and things would be faster. Or even make an array of 1 bit values. I'm thinking of converting the whole thing to some compiled language. Is PHP just not good for it? If I do need to convert it to let's say C++, how good are the automatic converters? My script is just a lot of for loops with basic arrays and objects manipulations. Thank you! Edit. This function gets called more than any other. It reads few properties of a very simple object, and goes through a very small part of a smallish array to check if there's any element not equal to 0. function fits($bin, $file, $x, $y) { $flag = true; $xw = $x + $file->get_width();; $yh = $y + $file->get_height(); for ($i = $x; $i < $xw; $i++) { for ($j = $y; $j < $yh; $j++) { if ($bin[$i][$j] !== 0) { $flag = false; break; } } if (!$flag) break; } return $flag; }

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• How to generate a script for changing a column of varchar to xml type with data being converted?

  - by user1323981

  Initially I have a column (partner_email) of varchar.Now a recent change has come where it needs to be changed to be changed to the XML type but the previous records needs to be reserve into the new column. I have applied the below algorithm to accomplish the work /*********************************************************************** Purpose: To change the partner_email column from Varchar Type To Xml Type and convert the existing records from varchar to xml types. Programmers Notes: 1. Create a new Column by the name partner_email_temp of type XML into the Partner Table 2. Copy the Email contents from partner_email to partner_email_temp column after proper conversion N.B.~ The format will be <PartnerEmails> <Email>[email protected]</Email> <Email /> <Email /> </PartnerEmails> 3. Drop the exisitng partner_email 4. Rename partner_email_temp column to partner_email ***********************************************************************/ USE [Test] GO --===== Create a partner_email_temp column of type xml into the Partner table IF NOT EXISTS ( SELECT * FROM INFORMATION_SCHEMA.columns WHERE table_name = 'Partner' AND column_name = 'partner_email_temp' ) BEGIN ALTER TABLE [dbo].[Partner] ADD partner_email_temp XML NULL END GO --===== Copy the Email contents from partner_email to partner_email_temp column -- after proper conversion to xml type UPDATE [dbo].[Partner] SET partner_email_temp = CAST('<PartnerEmails><Email>' + REPLACE(partner_email, '&', '&amp;') + '</Email><Email></Email><Email></Email></PartnerEmails>' AS XML) GO --===== Drop the exisitng partner_email ALTER TABLE [dbo].[Partner] DROP COLUMN partner_email GO --===== Rename partner_email_temp column to partner_email Exec sp_RENAME 'Partner.partner_email_temp','partner_email','COLUMN' GO I works fine for the first time I ran. Now if I ran it for the next time, it am getting an error Msg 8116, Level 16, State 1, Line 4 Argument data type xml is invalid for argument 1 of replace function. Caution: Changing any part of an object name could break scripts and stored procedures. The intention is that, if the partner_email column is varchar, the script will change it to xml type and will convert all the data in xml format . If I ran it second time, it should ignore the statement. How to achieve this? I am trying in a different way DECLARE @columnDataType VARCHAR(50) SELECT @columnDataType = DATA_TYPE FROM INFORMATION_SCHEMA.columns WHERE table_name = 'Partner' AND column_name = 'partner_email' print @columnDataType IF (@columnDataType = 'varchar') BEGIN --===== Create a partner_email_temp column of type xml into the Partner table IF NOT EXISTS ( SELECT * FROM INFORMATION_SCHEMA.columns WHERE table_name = 'Partner' AND column_name = 'partner_email_temp' ) BEGIN ALTER TABLE [dbo].[Partner] ADD partner_email_temp XML NULL --===== Copy the Email contents from partner_email to partner_email_temp column -- after proper conversion to xml type UPDATE [dbo].[Partner] SET partner_email_temp = CAST('<PartnerEmails><Email>' + REPLACE(partner_email, '&', '&amp;') + '</Email><Email></Email><Email></Email></PartnerEmails>' AS XML) --===== Drop the exisitng partner_email ALTER TABLE [dbo].[Partner] DROP COLUMN partner_email --===== Rename partner_email_temp column to partner_email EXEC sp_RENAME 'Partner.partner_email_temp','partner_email','COLUMN' END END but getting error Msg 207, Level 16, State 1, Line 29 Invalid column name 'partner_email_temp'. Help needed

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• How can I scale movement physics functions to frames per second (in a game engine)?

  - by Richard

  I am working on a game in Javascript (HTML5 Canvas). I implemented a simple algorithm that allows an object to follow another object with basic physics mixed in (a force vector to drive the object in the right direction, and the velocity stacks momentum, but is slowed by a constant drag force). At the moment, I set it up as a rectangle following the mouse (x, y) coordinates. Here's the code: // rectangle x, y position var x = 400; // starting x position var y = 250; // starting y position var FPS = 60; // frames per second of the screen // physics variables: var velX = 0; // initial velocity at 0 (not moving) var velY = 0; // not moving var drag = 0.92; // drag force reduces velocity by 8% per frame var force = 0.35; // overall force applied to move the rectangle var angle = 0; // angle in which to move // called every frame (at 60 frames per second): function update(){ // calculate distance between mouse and rectangle var dx = mouseX - x; var dy = mouseY - y; // calculate angle between mouse and rectangle var angle = Math.atan(dy/dx); if(dx < 0) angle += Math.PI; else if(dy < 0) angle += 2*Math.PI; // calculate the force (on or off, depending on user input) var curForce; if(keys[32]) // SPACE bar curForce = force; // if pressed, use 0.35 as force else curForce = 0; // otherwise, force is 0 // increment velocty by the force, and scaled by drag for x and y velX += curForce * Math.cos(angle); velX *= drag; velY += curForce * Math.sin(angle); velY *= drag; // update x and y by their velocities x += velX; y += velY; And that works fine at 60 frames per second. Now, the tricky part: my question is, if I change this to a different framerate (say, 30 FPS), how can I modify the force and drag values to keep the movement constant? That is, right now my rectangle (whose position is dictated by the x and y variables) moves at a maximum speed of about 4 pixels per second, and accelerates to its max speed in about 1 second. BUT, if I change the framerate, it moves slower (e.g. 30 FPS accelerates to only 2 pixels per frame). So, how can I create an equation that takes FPS (frames per second) as input, and spits out correct "drag" and "force" values that will behave the same way in real time? I know it's a heavy question, but perhaps somebody with game design experience, or knowledge of programming physics can help. Thank you for your efforts. jsFiddle: http://jsfiddle.net/BadDB

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• Week in Geek: LastPass Rescues Xmarks Edition

  - by Asian Angel

  This week we learned how to breathe new life into an aging Windows Mobile 6.x device, use filters in Photoshop, backup and move VirtualBox machines, use the BitDefender Rescue CD to clean an infected PC, and had fun setting up a pirates theme on our computers. Photo by _nash. Weekly Feature Do you love using the Faenza icon set on your Ubuntu system but feel that there are a few much needed icons missing (or you desire a different version of a particular icon)? Then you may want to take a look at the Faenza Variants icon pack. The icons are available in the following sizes: 16px, 22px, 32px, 48px and scalable sizes. Photo by Asian Angel. Faenza Variants Random Geek Links Another week with extra link goodness to help keep you on top of the news. Photo by Asian Angel. LastPass acquires Xmarks, premium service announced Xmarks announced that it has been acquired by LastPass, a cross-platform password management service. This also means that Xmarks is now in transition from a “free” to a “freemium” business model. WikiLeaks reappears on European Net domains WikiLeaks has re-emerged on a Swiss Internet domain followed by domains in Germany, Finland, and the Netherlands, sidestepping a move that had in effect taken the controversial site off the Internet. Iran: Yes, Stuxnet hurt our nuclear program The Stuxnet worm got some big play from Iranian President Mahmoud Ahmadinejad, who acknowledged that the malware dinged his nuclear program. More Windows Rogues than Just AV – Fake Defragmenter Check Disk Don’t think for a second that rogues are limited to scareware, because as so-called products such as “System Defragmenter”, “Scan Disk” “Check Disk” prove, they’re not. Internet Explorer’s Protected Mode can be bypassed Researchers from Verizon Business have now described a way of bypassing Protected Mode in IE 7 and 8 in order to gain access to user accounts. Can you really see who viewed your Facebook profile? Rogue application spreads virally Once again, a rogue application is spreading virally between Facebook users pretending to offer you a way of seeing who has viewed your profile. More holes in Palm’s WebOS Researchers Orlando Barrera and Daniel Herrera, who both work for security firm SecTheory, have discovered a gaping security hole in Palm’s WebOS smartphone operating system. Next-gen banking Trojans hit APAC With the proliferation of banking Trojans, Web and smartphone users of online banking services have to be on constant alert to avoid falling prey to fraud schemes, warned Etay Maor, project manager for RSA Fraud Action. AVG update cripples 64-bit computers A signature update automatically deployed by the AVG virus scanner Thursday has crippled numerous computers. Article includes link to forums to fix computers affected after a restart. Congress moves to outlaw ‘mystery charges’ for Web shoppers Legislation that makes it illegal for Web merchants and so-called post-transaction marketers to charge credit cards without the card owners’ say-so came closer to becoming law this week. Ballmer Set to “Look Into” Windows Home Server Drive Extender Fiasco Tuesday’s announcement from Microsoft regarding the removal of Drive Extender from Windows Home Server has sent shock waves across the web. Google tweaks search recipe to ding scam artists Google has changed its search algorithm to penalize sites deemed to provide an “extremely poor user experience” following a New York Times story on a merchant who justified abusive behavior towards customers as a search-engine optimization tactic. Geek Video of the Week Watch as our two friends debate back and forth about the early adoption of new technology through multiple time periods (Stone Age to the far future). Will our reluctant friend finally succumb to the temptation? Photo by CollegeHumor. Early Adopters Through History Random TinyHacker Links Fix Issues in Windows 7 Using Reliability Monitor Learn how to analyze Windows 7 errors and then fix them using the built-in reliability monitor. Learn About IE Tab Groups Tab groups is a useful feature in IE 8. Here’s a detailed guide to what it is all about. Google’s Book Helps You Learn About Browsers and Web A cool new online book by the Google Chrome team on browsers and the web. TrustPort Internet Security 2011 – Good Security from a Less Known Provider TrustPort is not exactly a well-known provider of security solutions. At least not in the consumer space. This review tests in detail their latest offering. How the World is Using Cell phones An infographic showing the shocking demographics of cell phone use. Super User Questions See the great answers to these questions from Super User. I am unable to access my C drive. It says it is unable to display current owner. List of Windows special directories/shortcuts like ‘%TEMP%’ Is using multiple passes for wiping a disk really necessary? How can I view two files side by side in Notepad++ Is there any tool that automatically puts screenshots to my Dropbox? How-To Geek Weekly Article Recap Look through our hottest articles from this past week at How-To Geek. How to Create a Software RAID Array in Windows 7 9 Alternatives for Windows Home Server’s Drive Extender Why Doesn’t Disk Cleanup Delete Everything from the Temp Folder? Ask the Readers: How Much Do You Customize Your Operating System? How to Upload Really Large Files to SkyDrive, Dropbox, or Email One Year Ago on How-To Geek Enjoy reading through these awesome articles from one year ago. How To Upgrade from Vista to Windows 7 Home Premium Edition How To Fix No Aero Transparency in Windows 7 Troubleshoot Startup Problems with Startup Repair Tool in Windows 7 & Vista Rename the Guest Account in Windows 7 for Enhanced Security Disable Error Reporting in XP, Vista, and Windows 7 The Geek Note That wraps things up here for this week. Regardless of the weather wherever you may be, we hope that you have an opportunity to get outside and have some fun! Remember to keep sending those great tips in to us at [email protected]. Photo by Tony the Misfit. Latest Features How-To Geek ETC The How-To Geek Guide to Learning Photoshop, Part 8: Filters Get the Complete Android Guide eBook for Only 99 Cents [Update: Expired] Improve Digital Photography by Calibrating Your Monitor The How-To Geek Guide to Learning Photoshop, Part 7: Design and Typography How to Choose What to Back Up on Your Linux Home Server How To Harmonize Your Dual-Boot Setup for Windows and Ubuntu Hang in There Scrat! – Ice Age Wallpaper How Do You Know When You’ve Passed Geek and Headed to Nerd? On The Tip – A Lamborghini Theme for Chrome and Iron What if Wile E. Coyote and the Road Runner were Human? [Video] Peaceful Winter Cabin Wallpaper Store Tabs for Later Viewing in Opera with Tab Vault

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• Parallelism in .NET – Part 10, Cancellation in PLINQ and the Parallel class

  - by Reed

  Many routines are parallelized because they are long running processes.  When writing an algorithm that will run for a long period of time, its typically a good practice to allow that routine to be cancelled.  I previously discussed terminating a parallel loop from within, but have not demonstrated how a routine can be cancelled from the caller’s perspective.  Cancellation in PLINQ and the Task Parallel Library is handled through a new, unified cooperative cancellation model introduced with .NET 4.0. Cancellation in .NET 4 is based around a new, lightweight struct called CancellationToken.  A CancellationToken is a small, thread-safe value type which is generated via a CancellationTokenSource.  There are many goals which led to this design.  For our purposes, we will focus on a couple of specific design decisions: Cancellation is cooperative.  A calling method can request a cancellation, but it’s up to the processing routine to terminate – it is not forced. Cancellation is consistent.  A single method call requests a cancellation on every copied CancellationToken in the routine. Let’s begin by looking at how we can cancel a PLINQ query.  Supposed we wanted to provide the option to cancel our query from Part 6: double min = collection .AsParallel() .Min(item => item.PerformComputation()); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would rewrite this to allow for cancellation by adding a call to ParallelEnumerable.WithCancellation as follows: var cts = new CancellationTokenSource(); // Pass cts here to a routine that could, // in parallel, request a cancellation try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation()); } catch (OperationCanceledException e) { // Query was cancelled before it finished } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, if the user calls cts.Cancel() before the PLINQ query completes, the query will stop processing, and an OperationCanceledException will be raised.  Be aware, however, that cancellation will not be instantaneous.  When cts.Cancel() is called, the query will only stop after the current item.PerformComputation() elements all finish processing.  cts.Cancel() will prevent PLINQ from scheduling a new task for a new element, but will not stop items which are currently being processed.  This goes back to the first goal I mentioned – Cancellation is cooperative.  Here, we’re requesting the cancellation, but it’s up to PLINQ to terminate. If we wanted to allow cancellation to occur within our routine, we would need to change our routine to accept a CancellationToken, and modify it to handle this specific case: public void PerformComputation(CancellationToken token) { for (int i=0; i<this.iterations; ++i) { // Add a check to see if we've been canceled // If a cancel was requested, we'll throw here token.ThrowIfCancellationRequested(); // Do our processing now this.RunIteration(i); } } With this overload of PerformComputation, each internal iteration checks to see if a cancellation request was made, and will throw an OperationCanceledException at that point, instead of waiting until the method returns.  This is good, since it allows us, as developers, to plan for cancellation, and terminate our routine in a clean, safe state. This is handled by changing our PLINQ query to: try { double min = collection .AsParallel() .WithCancellation(cts.Token) .Min(item => item.PerformComputation(cts.Token)); } catch (OperationCanceledException e) { // Query was cancelled before it finished } PLINQ is very good about handling this exception, as well.  There is a very good chance that multiple items will raise this exception, since the entire purpose of PLINQ is to have multiple items be processed concurrently.  PLINQ will take all of the OperationCanceledException instances raised within these methods, and merge them into a single OperationCanceledException in the call stack.  This is done internally because we added the call to ParallelEnumerable.WithCancellation. If, however, a different exception is raised by any of the elements, the OperationCanceledException as well as the other Exception will be merged into a single AggregateException. The Task Parallel Library uses the same cancellation model, as well.  Here, we supply our CancellationToken as part of the configuration.  The ParallelOptions class contains a property for the CancellationToken.  This allows us to cancel a Parallel.For or Parallel.ForEach routine in a very similar manner to our PLINQ query.  As an example, we could rewrite our Parallel.ForEach loop from Part 2 to support cancellation by changing it to: try { var cts = new CancellationTokenSource(); var options = new ParallelOptions() { CancellationToken = cts.Token }; Parallel.ForEach(customers, options, customer => { // Run some process that takes some time... DateTime lastContact = theStore.GetLastContact(customer); TimeSpan timeSinceContact = DateTime.Now - lastContact; // Check for cancellation here options.CancellationToken.ThrowIfCancellationRequested(); // If it's been more than two weeks, send an email, and update... if (timeSinceContact.Days > 14) { theStore.EmailCustomer(customer); customer.LastEmailContact = DateTime.Now; } }); } catch (OperationCanceledException e) { // The loop was cancelled } Notice that here we use the same approach taken in PLINQ.  The Task Parallel Library will automatically handle our cancellation in the same manner as PLINQ, providing a clean, unified model for cancellation of any parallel routine.  The TPL performs the same aggregation of the cancellation exceptions as PLINQ, as well, which is why a single exception handler for OperationCanceledException will cleanly handle this scenario.  This works because we’re using the same CancellationToken provided in the ParallelOptions.  If a different exception was thrown by one thread, or a CancellationToken from a different CancellationTokenSource was used to raise our exception, we would instead receive all of our individual exceptions merged into one AggregateException.

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• Parallelism in .NET – Part 18, Task Continuations with Multiple Tasks

  - by Reed

  In my introduction to Task continuations I demonstrated how the Task class provides a more expressive alternative to traditional callbacks.  Task continuations provide a much cleaner syntax to traditional callbacks, but there are other reasons to switch to using continuations… Task continuations provide a clean syntax, and a very simple, elegant means of synchronizing asynchronous method results with the user interface.  In addition, continuations provide a very simple, elegant means of working with collections of tasks. Prior to .NET 4, working with multiple related asynchronous method calls was very tricky.  If, for example, we wanted to run two asynchronous operations, followed by a single method call which we wanted to run when the first two methods completed, we’d have to program all of the handling ourselves.  We would likely need to take some approach such as using a shared callback which synchronized against a common variable, or using a WaitHandle shared within the callbacks to allow one to wait for the second.  Although this could be accomplished easily enough, it requires manually placing this handling into every algorithm which requires this form of blocking.  This is error prone, difficult, and can easily lead to subtle bugs. Similar to how the Task class static methods providing a way to block until multiple tasks have completed, TaskFactory contains static methods which allow a continuation to be scheduled upon the completion of multiple tasks: TaskFactory.ContinueWhenAll. This allows you to easily specify a single delegate to run when a collection of tasks has completed.  For example, suppose we have a class which fetches data from the network.  This can be a long running operation, and potentially fail in certain situations, such as a server being down.  As a result, we have three separate servers which we will “query” for our information.  Now, suppose we want to grab data from all three servers, and verify that the results are the same from all three. With traditional asynchronous programming in .NET, this would require using three separate callbacks, and managing the synchronization between the various operations ourselves.  The Task and TaskFactory classes simplify this for us, allowing us to write: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAll( new[] {server1, server2, server3 }, (tasks) => { // Propogate exceptions (see below) Task.WaitAll(tasks); return this.CompareTaskResults( tasks[0].Result, tasks[1].Result, tasks[2].Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This is clean, simple, and elegant.  The one complication is the Task.WaitAll(tasks); statement. Although the continuation will not complete until all three tasks (server1, server2, and server3) have completed, there is a potential snag.  If the networkClass.GetResults method fails, and raises an exception, we want to make sure to handle it cleanly.  By using Task.WaitAll, any exceptions raised within any of our original tasks will get wrapped into a single AggregateException by the WaitAll method, providing us a simplified means of handling the exceptions.  If we wait on the continuation, we can trap this AggregateException, and handle it cleanly.  Without this line, it’s possible that an exception could remain uncaught and unhandled by a task, which later might trigger a nasty UnobservedTaskException.  This would happen any time two of our original tasks failed. Just as we can schedule a continuation to occur when an entire collection of tasks has completed, we can just as easily setup a continuation to run when any single task within a collection completes.  If, for example, we didn’t need to compare the results of all three network locations, but only use one, we could still schedule three tasks.  We could then have our completion logic work on the first task which completed, and ignore the others.  This is done via TaskFactory.ContinueWhenAny: var server1 = Task.Factory.StartNew( () => networkClass.GetResults(firstServer) ); var server2 = Task.Factory.StartNew( () => networkClass.GetResults(secondServer) ); var server3 = Task.Factory.StartNew( () => networkClass.GetResults(thirdServer) ); var result = Task.Factory.ContinueWhenAny( new[] {server1, server2, server3 }, (firstTask) => { return this.ProcessTaskResult(firstTask.Result); }); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Here, instead of working with all three tasks, we’re just using the first task which finishes.  This is very useful, as it allows us to easily work with results of multiple operations, and “throw away” the others.  However, you must take care when using ContinueWhenAny to properly handle exceptions.  At some point, you should always wait on each task (or use the Task.Result property) in order to propogate any exceptions raised from within the task.  Failing to do so can lead to an UnobservedTaskException.

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• Interesting things – Twitter annotations and your phone as a web server

  - by jamiet

  I overheard/read a couple of things today that really made me, data junkie that I am, take a step back and think, “Hmmm, yeah, that could be really interesting” and I wanted to make a note of them here so that (a) I could bring them to the attention of anyone that happens to read this and (b) I can maybe come back here in a few years and see if either of these have come to fruition. Your phone as a web server While listening to Jon Udell’s (twitter) “Interviews with Innovators Podcast” today in which he interviewed Herbert Van de Sompel (twitter) about his Momento project. During the interview Jon and Herbert made the following remarks: Jon: [some people] really had this vision of a web of servers, the notion that every node on the internet, every connected entity, is potentially a server and a client…we can see where we’re getting to a point where these endpoint devices we have in our pockets are going to be massively capable and it may be in the not too distant future that significant chunks of the web archive will be cached all over the place including on your own machine… Herbert: wasn’t it Opera who at one point turned your browser into a server? That really got my brain ticking. We all carry a mobile phone with us and therefore we all potentially carry a mobile web server with us as well and to my mind the only thing really stopping that from happening is the capabilities of the phone hardware, the capabilities of the network infrastructure and the will to just bloody do it. Certainly all the standards required for addressing a web server on a phone already exist (to this uninitiated observer DNS and IPv6 seem to solve that problem) so why not? I tweeted about the idea and Rory Street answered back with “why would you want a phone to be a web server?”: Its a fair question and one that I would like to try and answer. Mobile phones are increasingly becoming our window onto the world as we use them to upload messages to Twitter, record our location on FourSquare or interact with our friends on Facebook but in each of these cases some other service is acting as our intermediary; to see what I’m thinking you have to go via Twitter, to see where I am you have to go to FourSquare (I’m using ‘I’ liberally, I don’t actually use FourSquare before you ask). Why should this have to be the case? Why can’t that data be decentralised? Why can’t we be masters of our own data universe? If my phone acted as a web server then I could expose all of that information without needing those intermediary services. I see a time when we can pass around URLs such as the following: http://jamiesphone.net/location/current - Where is Jamie right now? http://jamiesphone.net/location/2010-04-21 – Where was Jamie on 21st April 2010? http://jamiesphone.net/thoughts/current – What’s on Jamie’s mind right now? http://jamiesphone.net/blog – What documents is Jamie sharing with me? http://jamiesphone.net/calendar/next7days – Where is Jamie planning to be over the next 7 days? and those URLs get served off of the phone in our pockets. If we govern that data then we can control who has access to it and (crucially) how long its available for. Want to wipe yourself off the face of the web? its pretty easy if you’re in control of all the data – just turn your phone off. None of this exists today but I look forward to a time when it does. Opera really were onto something last June when they announced Opera Unite (admittedly Unite only works because Opera provide an intermediary DNS-alike system – it isn’t totally decentralised). Opening up Twitter annotations Last week Twitter held their first developer conference called Chirp where they announced an upcoming new feature called ‘Twitter Annotations’; in short this will allow us to attach metadata to a Tweet thus enhancing the tweet itself. Think of it as a richer version of hashtags. To think of it another way Twitter are turning their data into a humongous Entity-Attribute-Value or triple-tuple store. That alone has huge implications both for the web and Twitter as a whole – the ability to enrich that 140 characters data and thus make it more useful is indeed compelling however today I stumbled upon a blog post from Eugene Mandel entitled Tweet Annotations – a Way to a Metadata Marketplace? where he proposed the idea of allowing tweets to have metadata added by people other than the person who tweeted the original tweet. This idea really fascinated me especially when I read some of the potential uses that Eugene and his commenters suggested. They included: Amazon could attach an ISBN to a tweet that mentions a book. Specialist clients apps for book lovers could be built up around this metadata. Advertisers could pay to place adverts in metadata. The revenue generated from those adverts could be shared with the tweeter or people who add the metadata. Granted, allowing anyone to add metadata to a tweet has the potential to create a spam problem the like of which we haven’t even envisaged but spam hasn’t halted the growth of the web and neither should it halt the growth of data annotations either. The original tweeter should of course be able to determine who can add metadata and whether it should be moderated. As Eugene says himself: Opening publishing tweet annotations to anyone will open the way to a marketplace of metadata where client developers, data mining companies and advertisers can add new meaning to Twitter and build innovative businesses. What Eugene and his followers did not mention is what I think is potentially the most fascinating use of opening up annotations. Google’s success today is built on their page rank algorithm that measures the validity of a web page by the number of incoming links to it and the page rank of the sites containing those links – its a system built on reputation. Twitter annotations could open up a new paradigm however – let’s call it People rank- where reputation can be measured by the metadata that people choose to apply to links and the websites containing those links. Its not hard to see why Google and Microsoft have paid big bucks to get access to the Twitter firehose! Neither of these features, phones as a web server or the ability to add annotations to other people’s tweets, exist today but I strongly believe that they could dramatically enhance the web as we know it today. I hope to look back on this blog post in a few years in the knowledge that these ideas have been put into place. @Jamiet Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• How can I get penetration depth from Minkowski Portal Refinement / Xenocollide?

  - by Raven Dreamer

  I recently got an implementation of Minkowski Portal Refinement (MPR) successfully detecting collision. Even better, my implementation returns a good estimate (local minimum) direction for the minimum penetration depth. So I took a stab at adjusting the algorithm to return the penetration depth in an arbitrary direction, and was modestly successful - my altered method works splendidly for face-edge collision resolution! What it doesn't currently do, is correctly provide the minimum penetration depth for edge-edge scenarios, such as the case on the right: What I perceive to be happening, is that my current method returns the minimum penetration depth to the nearest vertex - which works fine when the collision is actually occurring on the plane of that vertex, but not when the collision happens along an edge. Is there a way I can alter my method to return the penetration depth to the point of collision, rather than the nearest vertex? Here's the method that's supposed to return the minimum penetration distance along a specific direction: public static Vector3 CalcMinDistance(List<Vector3> shape1, List<Vector3> shape2, Vector3 dir) { //holding variables Vector3 n = Vector3.zero; Vector3 swap = Vector3.zero; // v0 = center of Minkowski sum v0 = Vector3.zero; // Avoid case where centers overlap -- any direction is fine in this case //if (v0 == Vector3.zero) return Vector3.zero; //always pass in a valid direction. // v1 = support in direction of origin n = -dir; //get the differnce of the minkowski sum Vector3 v11 = GetSupport(shape1, -n); Vector3 v12 = GetSupport(shape2, n); v1 = v12 - v11; //if the support point is not in the direction of the origin if (v1.Dot(n) <= 0) { //Debug.Log("Could find no points this direction"); return Vector3.zero; } // v2 - support perpendicular to v1,v0 n = v1.Cross(v0); if (n == Vector3.zero) { //v1 and v0 are parallel, which means //the direction leads directly to an endpoint n = v1 - v0; //shortest distance is just n //Debug.Log("2 point return"); return n; } //get the new support point Vector3 v21 = GetSupport(shape1, -n); Vector3 v22 = GetSupport(shape2, n); v2 = v22 - v21; if (v2.Dot(n) <= 0) { //can't reach the origin in this direction, ergo, no collision //Debug.Log("Could not reach edge?"); return Vector2.zero; } // Determine whether origin is on + or - side of plane (v1,v0,v2) //tests linesegments v0v1 and v0v2 n = (v1 - v0).Cross(v2 - v0); float dist = n.Dot(v0); // If the origin is on the - side of the plane, reverse the direction of the plane if (dist > 0) { //swap the winding order of v1 and v2 swap = v1; v1 = v2; v2 = swap; //swap the winding order of v11 and v12 swap = v12; v12 = v11; v11 = swap; //swap the winding order of v11 and v12 swap = v22; v22 = v21; v21 = swap; //and swap the plane normal n = -n; } /// // Phase One: Identify a portal while (true) { // Obtain the support point in a direction perpendicular to the existing plane // Note: This point is guaranteed to lie off the plane Vector3 v31 = GetSupport(shape1, -n); Vector3 v32 = GetSupport(shape2, n); v3 = v32 - v31; if (v3.Dot(n) <= 0) { //can't enclose the origin within our tetrahedron //Debug.Log("Could not reach edge after portal?"); return Vector3.zero; } // If origin is outside (v1,v0,v3), then eliminate v2 and loop if (v1.Cross(v3).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v2 = v3; v21 = v31; v22 = v32; n = (v1 - v0).Cross(v3 - v0); continue; } // If origin is outside (v3,v0,v2), then eliminate v1 and loop if (v3.Cross(v2).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v1 = v3; v11 = v31; v12 = v32; n = (v3 - v0).Cross(v2 - v0); continue; } bool hit = false; /// // Phase Two: Refine the portal int phase2 = 0; // We are now inside of a wedge... while (phase2 < 20) { phase2++; // Compute normal of the wedge face n = (v2 - v1).Cross(v3 - v1); n.Normalize(); // Compute distance from origin to wedge face float d = n.Dot(v1); // If the origin is inside the wedge, we have a hit if (d > 0 ) { //Debug.Log("Do plane test here"); float T = n.Dot(v2) / n.Dot(dir); Vector3 pointInPlane = (dir * T); return pointInPlane; } // Find the support point in the direction of the wedge face Vector3 v41 = GetSupport(shape1, -n); Vector3 v42 = GetSupport(shape2, n); v4 = v42 - v41; float delta = (v4 - v3).Dot(n); float separation = -(v4.Dot(n)); if (delta <= kCollideEpsilon || separation >= 0) { //Debug.Log("Non-convergance detected"); //Debug.Log("Do plane test here"); return Vector3.zero; } // Compute the tetrahedron dividing face (v4,v0,v1) float d1 = v4.Cross(v1).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v2) float d2 = v4.Cross(v2).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v3) float d3 = v4.Cross(v3).Dot(v0); if (d1 < 0) { if (d2 < 0) { // Inside d1 & inside d2 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } else { // Inside d1 & outside d2 ==> eliminate v3 v3 = v4; v31 = v41; v32 = v42; } } else { if (d3 < 0) { // Outside d1 & inside d3 ==> eliminate v2 v2 = v4; v21 = v41; v22 = v42; } else { // Outside d1 & outside d3 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } } } return Vector3.zero; } }

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