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• tcp msl timeout implementation in linux

  - by iamrohitbanga

  The following is given in the book TCP IP Illustrated by Stevens Quiet Time Concept The 2MSL wait provides protection against delayed segments from an earlier incarnation of a connection from being interpreted as part of a new connection that uses the same local and foreign IP addresses and port numbers. But this works only if a host with connections in the 2MSL wait does not crash. What if a host with ports in the 2MSL wait crashes, reboots within MSL seconds, and immediately establishes new connections using the same local and foreign IP addresses and port numbers corresponding to the local ports that were in the 2MSL wait before the crash? In this scenario, delayed segments from the connections that existed before the crash can be misinterpreted as belonging to the new connections created after the reboot. This can happen regardless of how the initial sequence number is chosen after the reboot. To protect against this scenario, RFC 793 states that TCP should not create any connections for MSL seconds after rebooting. This is called the quiet time Few implementations abide by this since most hosts take longer than MSL seconds to reboot after a crash. Do operating systems wait for 2MSL seconds now after a reboot before initiating a TCP connection. The boot times are also less these days. Although the ports and sequence numbers are random but is this wait implemented in Linux? Also RFC 793 says that this wait is not required if history is maintained. Does linux maintain any history of used sequence numbers for connections to handle this case?

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• OSError : [Errno 38] Function not implemented - Django Celery implementation

  - by Jordan Messina

  I installed django-celery and I tried to start up the worker server but I get an OSError that a function isn't implemented. I'm running CentOS release 5.4 (Final) on a VPS: . broker -> amqp://guest@localhost:5672/ . queues -> . celery -> exchange:celery (direct) binding:celery . concurrency -> 4 . loader -> djcelery.loaders.DjangoLoader . logfile -> [stderr]@WARNING . events -> OFF . beat -> OFF [2010-07-22 17:10:01,364: WARNING/MainProcess] Traceback (most recent call last): [2010-07-22 17:10:01,364: WARNING/MainProcess] File "manage.py", line 11, in <module> [2010-07-22 17:10:01,364: WARNING/MainProcess] execute_manager(settings) [2010-07-22 17:10:01,364: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/django/core/management/__init__.py", line 438, in execute_manager [2010-07-22 17:10:01,364: WARNING/MainProcess] utility.execute() [2010-07-22 17:10:01,364: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/django/core/management/__init__.py", line 379, in execute [2010-07-22 17:10:01,365: WARNING/MainProcess] self.fetch_command(subcommand).run_from_argv(self.argv) [2010-07-22 17:10:01,365: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/django/core/management/base.py", line 191, in run_from_argv [2010-07-22 17:10:01,365: WARNING/MainProcess] self.execute(*args, **options.__dict__) [2010-07-22 17:10:01,365: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/django/core/management/base.py", line 218, in execute [2010-07-22 17:10:01,365: WARNING/MainProcess] output = self.handle(*args, **options) [2010-07-22 17:10:01,365: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/django_celery-2.0.0-py2.6.egg/djcelery/management/commands/celeryd.py", line 22, in handle [2010-07-22 17:10:01,366: WARNING/MainProcess] run_worker(**options) [2010-07-22 17:10:01,366: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/bin/celeryd.py", line 385, in run_worker [2010-07-22 17:10:01,366: WARNING/MainProcess] return Worker(**options).run() [2010-07-22 17:10:01,366: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/bin/celeryd.py", line 218, in run [2010-07-22 17:10:01,366: WARNING/MainProcess] self.run_worker() [2010-07-22 17:10:01,366: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/bin/celeryd.py", line 312, in run_worker [2010-07-22 17:10:01,367: WARNING/MainProcess] worker.start() [2010-07-22 17:10:01,367: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/worker/__init__.py", line 206, in start [2010-07-22 17:10:01,367: WARNING/MainProcess] component.start() [2010-07-22 17:10:01,367: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/concurrency/processes/__init__.py", line 54, in start [2010-07-22 17:10:01,367: WARNING/MainProcess] maxtasksperchild=self.maxtasksperchild) [2010-07-22 17:10:01,367: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/concurrency/processes/pool.py", line 448, in __init__ [2010-07-22 17:10:01,368: WARNING/MainProcess] self._setup_queues() [2010-07-22 17:10:01,368: WARNING/MainProcess] File "/usr/local/lib/python2.6/site-packages/celery-2.0.1-py2.6.egg/celery/concurrency/processes/pool.py", line 564, in _setup_queues [2010-07-22 17:10:01,368: WARNING/MainProcess] self._inqueue = SimpleQueue() [2010-07-22 17:10:01,368: WARNING/MainProcess] File "/usr/local/lib/python2.6/multiprocessing/queues.py", line 315, in __init__ [2010-07-22 17:10:01,368: WARNING/MainProcess] self._rlock = Lock() [2010-07-22 17:10:01,368: WARNING/MainProcess] File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line 117, in __init__ [2010-07-22 17:10:01,369: WARNING/MainProcess] SemLock.__init__(self, SEMAPHORE, 1, 1) [2010-07-22 17:10:01,369: WARNING/MainProcess] File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line 49, in __init__ [2010-07-22 17:10:01,369: WARNING/MainProcess] sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue) [2010-07-22 17:10:01,369: WARNING/MainProcess] OSError [2010-07-22 17:10:01,369: WARNING/MainProcess] : [2010-07-22 17:10:01,369: WARNING/MainProcess] [Errno 38] Function not implemented Am I just totally screwed and should use a new kernel that has this implemented or is there an easy way to resolve this?

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• Linux software RAID 10 implementation

  - by fabrik

  Hello there! I don't want to force anybody to make it on behalf of me but trust me: i've looked hundreds of sites and i can't find a good starting point for this. I have 4x500Gb HDD's which i want to set up in RAID 10. The most promising description is here, but it's a little old and unclear for me, above all i prefer Debian over Ubuntu (i know there are slight or no differences). Is it possible to build RAID 10 with Debian's installer or i need to build RAID 1 first in the installer then use mdadm later? What is the best practice for building software RAID 10 under Linux (Debian)? Thanks for your time, fabrik

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• Can someone correct me about Windows 2008 DFS implementation

  - by cwheeler33

  I have 2 two Windows 2003 file servers using DoubleTake at the moment. They are in an 2003 AD domain. And each server has it's own disk set. It is time to replace the servers... I want to use Windows 2008 64bit Ent. I was thinking of using DFS-R to replace DoubleTake. The part I'm not sure about is clustering. Do I need to have shared storage if each server has a copy of the data? I want to have the data available to the same share name, so maybe I don't fully understand how DFS is set up. I currently have about 6TB of data. I expect to grow by 3TB a year on these file servers. Any resources/books that could teach me would be good to know as well.

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• Help with proposed iSCSI SAN VMware implementation.

  - by obsidian

  We have four (with plans to grow to four more) Dell servers with 6 NICs. They are running VMware ESXi 4.1. We would like to connect all of them to an Openfiler iSCSI SAN via HP ProCurve 1810G switches. Based on the design below, is there anything I should be concerned about or anything unusual that I should look out for when making the iSCSI network configurations on the servers, switches and OpenFiler? Should I bond the connections on the servers or simply setup them up for failover? The primary goal is to maximize IOPS. Thanks in advance.

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• SMTP Client implementation [on hold]

  - by orif

  I'm implementing SMTP client. What should the client do once it already sent the "." at the end of the mail, but didn't receive "250 Ok"? This is how the conversation between the client and server look like: Server Response: 220 www.sample.com ESMTP Postfix Client Sending : HELO domain.com Server Response: 250 Hello domain.com Client Sending : MAIL FROM: <[email protected]> Server Response: 250 Ok Client Sending : RCPT TO: <[email protected]> Server Response: 250 Ok Client Sending : DATA Server Response: 354 End data with <CR><LF>.<CR><LF> Client Sending : Subject: Example Message Client Sending : From: [email protected] Client Sending : To: [email protected] Client Sending : Client Sending : TEST MAIL Client Sending : Client Sending : . Server Response: 250 Ok: queued as 23411 Client Sending : QUIT I'm not sure what should I do if the client sends "." and doesn't receive the 250 Ok - because of possible network error. Was the "." sent or not? Should the client resend the mail - and - maybe - duplicate the item, or not - and risk in losing an important mail item? Thank you.

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• Database implementation question?

  - by gundam

  consider a disk with a sector size of 512 bytes, 2000 tracks/surface, 50 sectors/track, 5 doubled sided platters, average seek time is 10 msec. Assume a block size of 1024-byte is selected. Assume a file that contains 100,000 records of 100-byte each is to be stored on the disk, and NONE of the reocd can be spanned 2 blocks. How many blocks are needed to store the entire file?? If the file is arranged sequentially on disk, how many surfaces are required?? Now, i have calculated that 10,000 blocks are needed to store 100,000 records. But i am not sure how to find out the answer of the surfaces required. I only calculated the capacity of track is 25KB and capacity of surface is 50,000 KB But I don't know how to calculate the number of surfaces... Could anyone help me how to get the answer? Thanks a lot!!

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• Cisco ASA 5505 - InterVLAN NAT Exemptions Implementation not working

  - by Brandon Bearden

  Short version is we cannot communicate between our subnets. We have a Cisco ASA 5505 we are using for our network router. We have a Netgear L3 switch behind that with 10 vlans. Each VLAN is on its own subnet. (10.0.10.x/24, 10.0.11.x/24, etc) So ASA Switch Hosts We have PAT for each subnet to our outside interface. Each subnet NATs out properly. I have NAT exemption enabled for 2 of the subnets (eventually I will need all, but am just testing at the moment). Config is here: http://pastebin.com/pDsG7hsh I have tried multiple ways for the NAT exemption to allow all traffic from our inside VLANS. At this point in time I am trying to get "Engineering" to communicate with all hosts on "AuthUser". I can ping some hosts, but not as many as if I am directly on the interface. I can reach a port 80 service, but not 443. I cannot access anything via hostname or NetBIOS. What am I missing to allow higher security level interfaces to fully communicate with lower security level interfaces? Thx!

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• Database implementation question? [closed]

  - by gundam

  consider a disk with a sector size of 512 bytes, 2000 tracks/surface, 50 sectors/track, 5 doubled sided platters, average seek time is 10 msec. Assume a block size of 1024-byte is selected. Assume a file that contains 100,000 records of 100-byte each is to be stored on the disk, and NONE of the reocd can be spanned 2 blocks. How many blocks are needed to store the entire file?? If the file is arranged sequentially on disk, how many surfaces are required?? Now, i have calculated that 10,000 blocks are needed to store 100,000 records. But i am not sure how to find out the answer of the surfaces required. I only calculated the capacity of track is 25KB and capacity of surface is 50,000 KB But I don't know how to calculate the number of surfaces... Could anyone help me how to get the answer? Thanks a lot!!

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• How to improve the builder pattern?

  - by tangens

  Motivation Recently I searched for a way to initialize a complex object without passing a lot of parameter to the constructor. I tried it with the builder pattern, but I don't like the fact, that I'm not able to check at compile time if I really set all needed values. Traditional builder pattern When I use the builder pattern to create my Complex object, the creation is more "typesafe", because it's easier to see what an argument is used for: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) ... .build(); But now I have the problem, that I can easily miss an important parameter. I can check for it inside the build() method, but that is only at runtime. At compile time there is nothing that warns me, if I missed something. Enhanced builder pattern Now my idea was to create a builder, that "reminds" me if I missed a needed parameter. My first try looks like this: public class Complex { private String m_first; private String m_second; private String m_third; private Complex() {} public static class ComplexBuilder { private Complex m_complex; public ComplexBuilder() { m_complex = new Complex(); } public Builder2 setFirst( String first ) { m_complex.m_first = first; return new Builder2(); } public class Builder2 { private Builder2() {} Builder3 setSecond( String second ) { m_complex.m_second = second; return new Builder3(); } } public class Builder3 { private Builder3() {} Builder4 setThird( String third ) { m_complex.m_third = third; return new Builder4(); } } public class Builder4 { private Builder4() {} Complex build() { return m_complex; } } } } As you can see, each setter of the builder class returns a different internal builder class. Each internal builder class provides exactly one setter method and the last one provides only a build() method. Now the construction of an object again looks like this: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) .build(); ...but there is no way to forget a needed parameter. The compiler wouldn't accept it. Optional parameters If I had optional parameters, I would use the last internal builder class Builder4 to set them like a "traditional" builder does, returning itself. Questions Is this a well known pattern? Does it have a special name? Do you see any pitfalls? Do you have any ideas to improve the implementation - in the sense of fewer lines of code?

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• HttpURLConnection: What is the minimum best-practice implementation?

  - by stormin986

  I've come across a lot of HttpURLConnection examples that are nothing more than openConnection(), getInputStream(), and then they just read the buffer and are done. It's simple but seems like it's not the best implementation ... it handles no problems. I don't yet know much about http, so I keep thinking I have everything covered until a new problem arises. I'm currently experiencing a similar problem to this one. Most times I try to read the same resource a second time (from a different HttpURLConnection object, after I .disconnect()'ed the previous one), the response code returns as -1 (but no exception is thrown!!). Before I knew to check the response code, I was baffled since I was throwing no exceptions. So, is there a minimum 'best practice' HttpURLConnection implementation? What are notable exceptions to handle? Request code checking? Any other error checks? What connection parameters do and don't need to be set (like doInput / doOutput, are these even necessary? Some examples have em, some don't). Etc. I realize this is kind of a broad question but I think it has potential to be a very useful resource if many of the common use cases and FAQs are addressed in one central place. This seems like the kind of thing a community wiki would be good for...

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• Implementation of any Hamiltonian Path Problem algorithm

  - by Julien

  Hi all ! Here is my problem : I have an array of points, the points have three properties : the "x" and "y" coordinates, and a sequence number "n". The "x" and "y" are defined for all the points, the "n" are not. You can access and write them calling points[i]-x, points[i]-y, points[i]-n. i.e. : points[i]->n = var var = points[i]->n So the title maybe ruined the surprise, but I'm looking for a possible implementation of a solution to the Hamiltonian path problem : I need to set the "n" number of each point, so that the sequence is the shortest path (not cycle, the edges have to be disjoint) that goes exactly once through each point. I looked for a solution and I found The Bellman Ford Algorithm but I think it doesn't work since the problem doesn't specify that it has to go through all of the points is it correct ? If it is, does somebody has another algorithm and the implementation ? If the Bellman Ford Algorithm works, how would I implement it ? Thanks a lot, Julien

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• Small-o(n^2) implementation of Polynomial Multiplication

  - by AlanTuring

  I'm having a little trouble with this problem that is listed at the back of my book, i'm currently in the middle of test prep but i can't seem to locate anything regarding this in the book. Anyone got an idea? A real polynomial of degree n is a function of the form f(x)=a(n)x^n+?+a1x+a0, where an,…,a1,a0 are real numbers. In computational situations, such a polynomial is represented by a sequence of its coefficients (a0,a1,…,an). Assuming that any two real numbers can be added/multiplied in O(1) time, design an o(n^2)-time algorithm to compute, given two real polynomials f(x) and g(x) both of degree n, the product h(x)=f(x)g(x). Your algorithm should **not** be based on the Fast Fourier Transform (FFT) technique. Please note it needs to be small-o(n^2), which means it complexity must be sub-quadratic. The obvious solution that i have been finding is indeed the FFT, but of course i can't use that. There is another method that i have found called convolution, where if you take polynomial A to be a signal and polynomial B to be a filter. A passed through B yields a shifted signal that has been "smoothed" by A and the resultant is A*B. This is supposed to work in O(n log n) time. Of course i am completely unsure of implementation. If anyone has any ideas of how to achieve a small-o(n^2) implementation please do share, thanks.

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• Google Web Toolkit Asynchronous Call from a Service Implementation

  - by Thor Thurn

  I'm writing a simple Google Web Toolkit service which acts as a proxy, which will basically exist to allow the client to make a POST to a different server. The client essentially uses this service to request an HTTP call. The service has only one asynchronous method call, called ajax(), which should just forward the server response. My code for implementing the call looks like this: class ProxyServiceImpl extends RemoteServiceServlet implements ProxyService { @Override public Response ajax(String data) { RequestBuilder rb = /*make a request builder*/ RequestCallback rc = new RequestCallback() { @Override public void onResponseReceived(Response response) { /* Forward this response back to the client as the return value of the ajax method... somehow... */ } }; rb.sendRequest(data, requestCallback); return /* The response above... except I can't */; } } You can see the basic form of my problem, of course. The ajax() method is used asynchronously, but GWT decides to be smart and hide that from the dumb old developer, so they can just write normal Java code without callbacks. GWT services basically just do magic instead of accepting a callback parameter. The trouble arises, then, because GWT is hiding the callback object from me. I'm trying to make my own asynchronous call from the service implementation, but I can't, because GWT services assume that you behave synchronously in service implementations. How can I work around this and make an asynchronous call from my service method implementation?

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• Defining an implementation independent version of the global object in JavaScript

  - by Aadit M Shah

  I'm trying to define the global object in JavaScript in a single line as follows: var global = this.global || this; The above statement is in the global scope. Hence in browsers the this pointer is an alias for the window object. Assuming that it's the first line of JavaScript to be executed in the context of the current web page, the value of global will always be the same as that of the this pointer or the window object. In CommonJS implementations, such as RingoJS and node.js the this pointer points to the current ModuleScope. However, we can access the global object through the property global defined on the ModuleScope. Hence we can access it via the this.global property. Hence this code snippet works in all browsers and in at least RingoJS and node.js, but I have not tested other CommomJS implementations. Thus I would like to know if this code will not yield correct results when run on any other CommonJS implementation, and if so how I may fix it. Eventually, I intend to use it in a lambda expression for my implementation independent JavaScript framework as follows (idea from jQuery): (function (global) { // javascript framework })(this.global || this);

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• .Net Remoting: Serialize Object and implementation

  - by flogo

  Hi, In my scenario there is a client-side assembly that contains a class (Task). This class implements an interface (ITask) that is known on the server. I'm trying to send a Task object from client to server without copying the assembly of the client manually to the server. If I just serialize the task object, the server obviously complains about the missing assembly. I then tried to serialze typeof(Task).Assembly but could not derserialize it on the server. Next I tried to File.ReadAllBytes(typeof(Task).Assembly.Location) and saved it to a temporary file on the server, which threw an exception on Assembly.LoadFrom(@".\temporary.dll"); Why am I doing this? Java RMI has a neat feature to request the implementation of an object that is received through remoting but is stil "unkown" (this JVM doesn't have the *.class file). This can be used for a compute server that just knows the interface of a "task" containing a run() method and downloads the implementation of this method on demand. This way the server doesn't have to be changed for new tasks. I'm trying to achieve something like this in .Net.

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• Design issue in Iphone Dev - Generic implementation for Game Bonuses

  - by Idan

  So, I thought consulting you guys about my design, cause I sense there might be a better way of doing it. I need to implement game bonuses mechanism in my app. Currently there are 9 bonuses available, each one is based of different param of the MainGame Object. What I had in mind was at app startup to initialize 9 objects of GameBonus while each one will have different SEL (shouldBonus) which will be responsible for checking if the bonus is valid. So, every end of game I will just run over the bonuses array and call the isBonusValid() function with the MainGame object(which is different after every game). How's that sound ? The only issue I have currently, is that I need to make sure that if some bonuses are accepted some other won't (inner stuff)... any advice how to do that and still maintain generic implementation ? @interface GameBonus : NSObject { int bonusId; NSString* name; NSString* description; UIImage* img; SEL shouldBonus; } @implementation GameBonus -(BOOL) isBonusValid(MainGame*)mainGame { [self shouldBonus:mainGame]; } @end

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• Unable to step into interface implementation configured by unity application block

  - by Rahul

  I have configured a set of interface implementations with EntLib. unity block. The constructor of implementation classes work fine as soon as I run the application: 1. The interface to implement when I run the application the cctor runs fine, which shows that unity resolution was successful: But when I try to call a method of this class, the code just passes through without actually invoking the function of the implemented class: Edit: Added on June 11, 2012 Following is the Unity Configuration I have. (This is all the unity configuration I am doing) public class UnityControllerFactory : DefaultControllerFactory { private static readonly IUnityContainer container; private static UnityControllerFactory factory = null; static UnityControllerFactory() { container = new UnityContainer(); UnityConfigurationSection section = (UnityConfigurationSection)ConfigurationManager.GetSection("unity"); section.Configure(container); factory = new UnityControllerFactory(); } public static UnityControllerFactory GetControllerFactory() { return factory; } protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType) { return container.Resolve(controllerType) as IController; } } I am unable to step into this code and the implementation simply skips out without executing anything. What is wrong here?

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• Array indexOf implementation for Internet Explorer

  - by Daemon

  There are plenty of solutions on how to get the indexOf implementation into the Array prototype so that it works under Internet Explorer, however I've stumbled upon an issue that doesn't seem to be addressed anywhere I've looked so far. Using the pretty well agreed upon implementation at MDC, I have the following code that's being problematic now: // indexOf support for IE (from MDC) if (!Array.prototype.indexOf) { Array.prototype.indexOf = function(elt /*, from*/) { var len = this.length >>> 0; var from = Number(arguments[1]) || 0; from = (from < 0) ? Math.ceil(from) : Math.floor(from); if (from < 0) from += len; for (; from < len; from++) { if (from in this && this[from] === elt) return from; } return -1; }; } var i = [1,2,3,4]; for (j in i) { alert(i[j]); } I am expecting to receive 4 alerts, each one containing one of the elements of the array. In Firefox and Chrome, that's exactly what I see, however in IE8 I get an additional alert containing the indexOf function code. What can be done to avoid this?

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• Simple App Engine Sessions Implementation

  - by raz0r

  Here is a very basic class for handling sessions on App Engine: """Lightweight implementation of cookie-based sessions for Google App Engine. Classes: Session """ import os import random import Cookie from google.appengine.api import memcache _COOKIE_NAME = 'app-sid' _COOKIE_PATH = '/' _SESSION_EXPIRE_TIME = 180 * 60 class Session(object): """Cookie-based session implementation using Memcached.""" def __init__(self): self.sid = None self.key = None self.session = None cookie_str = os.environ.get('HTTP_COOKIE', '') self.cookie = Cookie.SimpleCookie() self.cookie.load(cookie_str) if self.cookie.get(_COOKIE_NAME): self.sid = self.cookie[_COOKIE_NAME].value self.key = 'session-' + self.sid self.session = memcache.get(self.key) if self.session: self._update_memcache() else: self.sid = str(random.random())[5:] + str(random.random())[5:] self.key = 'session-' + self.sid self.session = dict() memcache.add(self.key, self.session, _SESSION_EXPIRE_TIME) self.cookie[_COOKIE_NAME] = self.sid self.cookie[_COOKIE_NAME]['path'] = _COOKIE_PATH print self.cookie def __len__(self): return len(self.session) def __getitem__(self, key): if key in self.session: return self.session[key] raise KeyError(str(key)) def __setitem__(self, key, value): self.session[key] = value self._update_memcache() def __delitem__(self, key): if key in self.session: del self.session[key] self._update_memcache() return None raise KeyError(str(key)) def __contains__(self, item): try: i = self.__getitem__(item) except KeyError: return False return True def _update_memcache(self): memcache.replace(self.key, self.session, _SESSION_EXPIRE_TIME) I would like some advices on how to improve the code for better security. Note: In the production version it will also save a copy of the session in the datastore. Note': I know there are much more complete implementations available online though I would like to learn more about this subject so please don't answer the question with "use that" or "use the other" library.

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• Hibernate NamingStrategy implementation that maintains state between calls

  - by Robert Petermeier

  Hi, I'm working on a project where we use Hibernate and JBoss 5.1. We need our entity classes to be mapped to Oracle tables that follow a certain naming convention. I'd like to avoid having to specify each table and column name in annotations. Therefore, I'm currently considering implementing a custom implementation of org.hibernate.cfg.NamingStrategy. The SQL naming conventions require the name of columns to have a suffix that is equivalent to a prefix of the table name. If there is a table "T100_RESOURCE", the ID column would have to be named "RES_ID_T100". In order to implement this in a NamingStrategy, the implementation would have to maintain state, i.e. the current class name it is creating the mappings for. It would rely on Hibernate to always call classToTableName() before propertyToColumnName() and to determine all column names by calling propertyToColumnName() before the next call to classToTableName() Is it safe to do that or are there situations where Hibernate will mix things up? I am not thinking of problems through multiple threads here (which can be solved by keeping the last class name in a ThreadLocal) but also of Hibernate deliberately calling this out of order in certain circumstances. For example Hibernate asking for mappings of three properties of class A, then one of class B, then again more attributes of class A.

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• Elegant and 'correct' multiton implementation in Objective C?

  - by submachine

  Would you call this implementation of a multiton in objective-c 'elegant'? I have programmatically 'disallowed' use of alloc and allocWithZone: because the decision to allocate or not allocate memory needs to be done based on a key. I know for sure that I need to work with only two instances, so I'm using 'switch-case' instead of a map. #import "Multiton.h" static Multiton *firstInstance = nil; static Multiton *secondInstance = nil; @implementation Multiton + (Multiton *) sharedInstanceForDirection:(char)direction { return [[self allocWithKey:direction] init]; } + (id) allocWithKey:(char)key { return [self allocWithZone:nil andKey:key]; } + (id)allocWithZone:(NSZone *)zone andKey:(char)key { Multiton **sharedInstance; @synchronized(self) { switch (key) { case KEY_1: sharedInstance = &firstInstance; break; case KEY_2: sharedInstance = &secondInstance; break; default: [NSException raise:NSInvalidArgumentException format:@"Invalid key"]; break; } if (*sharedInstance == nil) *sharedInstance = [super allocWithZone:zone]; } return *sharedInstance; } + (id) allocWithZone:(NSZone *)zone { //Do not allow use of alloc and allocWithZone [NSException raise:NSObjectInaccessibleException format:@"Use allocWithZone:andKey: or allocWithKey:"]; return nil; } - (id) copyWithZone:(NSZone *)zone { return self; } - (id) retain { return self; } - (unsigned) retainCount { return NSUIntegerMax; } - (void) release { return; } - (id) autorelease { return self; } - (id) init { [super init]; return self; } PS: I've not tried out if this works as yet, but its compiling cleanly :)

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• Common methods/implementation across multiple WCF Services

  - by Rob

  I'm looking at implementing some WCF Services as part of an API for 3rd parties to access data within a product I work on. There are currently a set of services exposed as "classic" .net Web Services and I need to emulate the behaviour of these, at least in part. The existing services all have an AcquireAuthenticationToken method that takes a set of parameters (username, password, etc) and return a session token (represented as a GUID), which is then passed in on calls to any other method (There's also a ReleaseAuthenticationToken method, no guesses needed as to what that does!). What I want to do is implement multiple WCF services, such as: ProductData UserData and have both of these services share a common implementation of Acquire/Release. From the base project that is created by VS2k8, it would appear I will start with, per service: public class ServiceName : IServiceName { } public interface IServiceName { } Therefore my questions would be: Will WCF tolerate me adding a base class to this, public class ServiceName : ServiceBase, IServiceName, or does the fact that there's an interface involved mean that won't work? If "No it won't work" to Question 1, could I change IServiceName so it extends another interface, IServiceBase, thus forcing the presence of Acquire/Release methods, but then having to supply the implementation in each service. Are 1 and 2 both really bad ideas and there's actually a much better solution that, knowing next to nothing about WCF, I just haven't thought of?

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• Implementing a Version check between an Abstract class and it's implementation

  - by Michael Stum

  I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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• OpenGL render vs. own Phong Illumination Implementation

  - by Myx

  Hello: I have implemented a Phong Illumination Scheme using a camera that's centered at (0,0,0) and looking directly at the sphere primitive. The following are the relevant contents of the scene file that is used to view the scene using OpenGL as well as to render the scene using my own implementation: ambient 0 1 0 dir_light 1 1 1 -3 -4 -5 # A red sphere with 0.5 green ambiance, centered at (0,0,0) with radius 1 material 0 0.5 0 1 0 0 1 0 0 0 0 0 0 0 0 10 1 0 sphere 0 0 0 0 1 The resulting image produced by OpenGL. The image that my rendering application produces. As you can see, there are various differences between the two: The specular highlight on my image is smaller than the one in OpenGL. The diffuse surface seems to not diffuse in the correct way, resulting in the yellow region to be unneccessarily large in my image, whereas in OpenGL there's a nice dark green region closer to the bottom of the sphere The color produced by OpenGL is much darker than the one in my image. Those are the most prominent three differences that I see. The following is my implementation of the Phong illumination: R3Rgb Phong(R3Scene *scene, R3Ray *ray, R3Intersection *intersection) { R3Rgb radiance; if(intersection->hit == 0) { radiance = scene->background; return radiance; } R3Vector normal = intersection->normal; R3Rgb Kd = intersection->node->material->kd; R3Rgb Ks = intersection->node->material->ks; // obtain ambient term R3Rgb intensity_ambient = intersection->node->material->ka*scene->ambient; // obtain emissive term R3Rgb intensity_emission = intersection->node->material->emission; // for each light in the scene, obtain calculate the diffuse and specular terms R3Rgb intensity_diffuse(0,0,0,1); R3Rgb intensity_specular(0,0,0,1); for(unsigned int i = 0; i < scene->lights.size(); i++) { R3Light *light = scene->Light(i); R3Rgb light_color = LightIntensity(scene->Light(i), intersection->position); R3Vector light_vector = -LightDirection(scene->Light(i), intersection->position); // calculate diffuse reflection intensity_diffuse += Kd*normal.Dot(light_vector)*light_color; // calculate specular reflection R3Vector reflection_vector = 2.*normal.Dot(light_vector)*normal-light_vector; reflection_vector.Normalize(); R3Vector viewing_vector = ray->Start() - intersection->position; viewing_vector.Normalize(); double n = intersection->node->material->shininess; intensity_specular += Ks*pow(max(0.,viewing_vector.Dot(reflection_vector)),n)*light_color; } radiance = intensity_emission+intensity_ambient+intensity_diffuse+intensity_specular; return radiance; } Here are the related LightIntensity(...) and LightDirection(...) functions: R3Vector LightDirection(R3Light *light, R3Point position) { R3Vector light_direction; switch(light->type) { case R3_DIRECTIONAL_LIGHT: light_direction = light->direction; break; case R3_POINT_LIGHT: light_direction = position-light->position; break; case R3_SPOT_LIGHT: light_direction = position-light->position; break; } light_direction.Normalize(); return light_direction; } R3Rgb LightIntensity(R3Light *light, R3Point position) { R3Rgb light_intensity; double distance; double denominator; if(light->type != R3_DIRECTIONAL_LIGHT) { distance = (position-light->position).Length(); denominator = light->constant_attenuation + light->linear_attenuation*distance + light->quadratic_attenuation*distance*distance; } switch(light->type) { case R3_DIRECTIONAL_LIGHT: light_intensity = light->color; break; case R3_POINT_LIGHT: light_intensity = light->color/denominator; break; case R3_SPOT_LIGHT: R3Vector from_light_to_point = position - light->position; light_intensity = light->color*( pow(light->direction.Dot(from_light_to_point), light->angle_attenuation)); break; } return light_intensity; } I would greatly appreciate any suggestions as to any implementation errors that are apparent. I am wondering if the differences could be occurring simply because of the gamma values used for display by OpenGL and the default gamma value for my display. I also know that OpenGL (or at least tha parts that I was provided) can't cast shadows on objects. Not that this is relevant for the point in question, but it just leads me to wonder if it's simply display and capability differences between OpenGL and what I am trying to do. Thank you for your help.

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