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• How to store a file on a server(web container) through a Java EE web application?

  - by Yatendra Goel

  I have developed a Java EE web application. This application allows a user to upload a file with the help of a browser. Once the user has uploaded his file, this application first stores the uploaded file on the server (on which it is running) and then processes it. At present, I am storing the file on the server as follows: try { FormFile formFile = programForm.getTheFile(); // formFile represents the uploaded file String path = getServlet().getServletContext().getRealPath("") + "/" + formFile.getFileName(); System.out.println(path); file = new File(path); outputStream = new FileOutputStream(file); outputStream.write(formFile.getFileData()); } where, the formFile represents the uploaded file. Now, the problem is that it is running fine on some servers but on some servers the getServlet().getServletContext().getRealPath("") is returning null so the final path that I am getting is null/filename and the file doesn't store on the server. When I checked the API for ServletContext.getRealPath() method, I found the following: public java.lang.String getRealPath(java.lang.String path) Returns a String containing the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext. The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns null if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a .war archive). So, Is there any other way by which I can store files on those servers also which is returning null for getServlet().getServletContext().getRealPath("")

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• order of onclick events

  - by NicoF

  I want to add a jquery click event to href's that already have an onclick event. In the example below the hard coded onclick event will get triggered first. How can I reverse that? <a class="whatever clickyGoal1" href="#" onclick="alert('trial game');">play trial</a> <br /> <a class="whatever clickyGoal2" href="#" onclick="alert('real game');">real trial</a> <p class="goal1"> </p> <p class="goal2"> </p> <script type="text/javascript"> $("a.clickyGoal1").click(function() { $("p.goal1").append("trial button click goal is fired");//example }); $("a.clickyGoal2").click(function() { $("p.goal2").append("real button click goal is fired"); //example }); </script>

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• Libraries and pseudocode for physical Dashboard/Status board

  - by dani

  OK, so I bought a 46" screen for the office yesterday, and with the imminent risk of being accused for setting up an "elaborate World Cup procrastination scheme", I'd better show my colleagues what it's meant for ;) Looking at my simple sketch, and at these great projects from which I was inspired, I would like to get some input on the following: Pseudocode for the skeleton: As some methods should be called every 24 hours ("Today's date in the heading"), others at 60 second intervals ("Twitter results"), what would be a good approach using JavaScript (jQuery) and PHP? EDIT: Alsciende: I can agree that #1 and #8 are too vague. Therefore I remove #8 and try to clarify #1: With "Pseudocode for the skeleton", I basically mean could this be done entirely using JavaScript timers and how would you set up the various timers? Library for Google Analytics: Which libraries support the Google Analytics API and can produce neat charts. Preferably HTML5, JavaScript-based like Protovis. Library for Twitter: Which libraries would you recommend for fetching twitter search results and latest tweets from profiles. Libraries for Typography/CSS/HTML5: Trying to learn some HTML5 etc. in the process, please advice on any other typography/css libraries that could be of relevance. Scraping/Parsing? I'll give you a concrete example: Trying to fetch today's menu from this restaurant's website, how would you go about? (it's in Swedish - but you get the point - sorry ;) ) Real-time stats? I'm using the WassUp-plugin for WordPress to track real-time visitors on our website. Other logging software (AWStats etc.) is probably also installed on the webserver. Any ideas on how to extract information from these and present in real-time on the dashboard? Browser choice? Which Browser and OS would you pick? Stable, Full-screen, HTML5.

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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• Simple continuously running XMPP client in python

  - by tom

  I'm using python-xmpp to send jabber messages. Everything works fine except that every time I want to send messages (every 15 minutes) I need to reconnect to the jabber server, and in the meantime the sending client is offline and cannot receive messages. So I want to write a really simple, indefinitely running xmpp client, that is online the whole time and can send (and receive) messages when required. My trivial (non-working) approach: import time import xmpp class Jabber(object): def __init__(self): server = 'example.com' username = 'bot' passwd = 'password' self.client = xmpp.Client(server) self.client.connect(server=(server, 5222)) self.client.auth(username, passwd, 'bot') self.client.sendInitPresence() self.sleep() def sleep(self): self.awake = False delay = 1 while not self.awake: time.sleep(delay) def wake(self): self.awake = True def auth(self, jid): self.client.getRoster().Authorize(jid) self.sleep() def send(self, jid, msg): message = xmpp.Message(jid, msg) message.setAttr('type', 'chat') self.client.send(message) self.sleep() if __name__ == '__main__': j = Jabber() time.sleep(3) j.wake() j.send('[email protected]', 'hello world') time.sleep(30) The problem here seems to be that I cannot wake it up. My best guess is that I need some kind of concurrency. Is that true, and if so how would I best go about that? EDIT: After looking into all the options concerning concurrency, I decided to go with twisted and wokkel. If I could, I would delete this post.

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• python can't start a new thread

  - by Giorgos Komnino

  I am building a multi threading application. I have setup a threadPool. [ A Queue of size N and N Workers that get data from the queue] When all tasks are done I use tasks.join() where tasks is the queue . The application seems to run smoothly until suddently at some point (after 20 minutes in example) it terminates with the error thread.error: can't start new thread Any ideas? Edit: The threads are daemon Threads and the code is like: while True: t0 = time.time() keyword_statuses = DBSession.query(KeywordStatus).filter(KeywordStatus.status==0).options(joinedload(KeywordStatus.keyword)).with_lockmode("update").limit(100) if keyword_statuses.count() == 0: DBSession.commit() break for kw_status in keyword_statuses: kw_status.status = 1 DBSession.commit() t0 = time.time() w = SWorker(threads_no=32, network_server='http://192.168.1.242:8180/', keywords=keyword_statuses, cities=cities, saver=MySqlRawSave(DBSession), loglevel='debug') w.work() print 'finished' When the daemon threads are killed? When the application finishes or when the work() finishes? Look at the thread pool and the worker (it's from a recipe ) from Queue import Queue from threading import Thread, Event, current_thread import time event = Event() class Worker(Thread): """Thread executing tasks from a given tasks queue""" def __init__(self, tasks): Thread.__init__(self) self.tasks = tasks self.daemon = True self.start() def run(self): '''Start processing tasks from the queue''' while True: event.wait() #time.sleep(0.1) try: func, args, callback = self.tasks.get() except Exception, e: print str(e) return else: if callback is None: func(args) else: callback(func(args)) self.tasks.task_done() class ThreadPool: """Pool of threads consuming tasks from a queue""" def __init__(self, num_threads): self.tasks = Queue(num_threads) for _ in range(num_threads): Worker(self.tasks) def add_task(self, func, args=None, callback=None): ''''Add a task to the queue''' self.tasks.put((func, args, callback)) def wait_completion(self): '''Wait for completion of all the tasks in the queue''' self.tasks.join() def broadcast_block_event(self): '''blocks running threads''' event.clear() def broadcast_unblock_event(self): '''unblocks running threads''' event.set() def get_event(self): '''returns the event object''' return event

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• Is there something like a Filestorage class to store files in?

  - by nebukadnezzar

  Is there something like a class that might be used to store Files and directories in, just like the way Zip files might be used? Since I haven't found any "real" class to write Zip files (real class as in real class), It would be nice to be able to store Files and Directories in a container-like file. A perfect API would probably look like this: int main() { ContainerFile cntf("myContainer.cnt", ContainerFile::CREATE); cntf.addFile("data/some-interesting-stuff.txt"); cntf.addDirectory("data/foo/"); cntf.addDirectory("data/bar/", ContainerFile::RECURSIVE); cntf.close(); } ... I hope you get the Idea. Important Requirements are: The Library must be crossplatform anything *GPL is not acceptable in this case (MIT and BSD License are) I already played with the thought of creating an Implentation based on SQLite (and its ability to store binary blobs). Unfortunately, it seems impossible to store Directory structures in a SQLite Database, which makes it pretty much useless in this case. Is it useless to hope for such a class library?

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• Atomic swap in GNU C++

  - by Steve

  I want to verify that my understanding is correct. This kind of thing is tricky so I'm almost sure I am missing something. I have a program consisting of a real-time thread and a non-real-time thread. I want the non-RT thread to be able to swap a pointer to memory that is used by the RT thread. From the docs, my understanding is that this can be accomplished in g++ with: // global Data *rt_data; Data *swap_data(Data *new_data) { #ifdef __GNUC__ // Atomic pointer swap. Data *old_d = __sync_lock_test_and_set(&rt_data, new_data); #else // Non-atomic, cross your fingers. Data *old_d = rt_data; rt_data = new_data; #endif return old_d; } This is the only place in the program (other than initial setup) where rt_data is modified. When rt_data is used in the real-time context, it is copied to a local pointer. For old_d, later on when it is sure that the old memory is not used, it will be freed in the non-RT thread. Is this correct? Do I need volatile anywhere? Are there other synchronization primitives I should be calling? By the way I am doing this in C++, although I'm interested in whether the answer differs for C. Thanks ahead of time.

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• Why PHPUnit test doesn't fail?

  - by JohnM2

  I have a test method which looks like that: $row = $this->GetRowFromUserTable($id); $this->asserLessThan(time(), time($row['last_update'])); When $row is null access to $row['last_update'] should trigger a NOTICE and this test should fail, but it doesn't. This code fails on first assert, so I know $db_row is null (fixture is the same): $row = $this->GetRowFromUserTable($id); $this->asserNotNull($row); $this->asserLessThan(time(), time($row['last_update'])); When I write this: $row = $this->GetRowFromUserTable($id); $this->assertEquals(E_ALL, error_reporting()); $this->asserLessThan(time(), time($row['last_update'])); it successes, so I am also sure that error_reproting is right and this situation must have something to do with PHPUnit. I use PHPUnit 3.5.6 I read this question: Can I make PHPUnit fail if the code throws a notice? but the answer suggests to use newer version of PHPUnit, but that answer is from 2009, so it's not it. EDIT: I use NetBeans IDE 6.9.1 to run my test.

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• How do I change the base class at runtime in C#?

  - by MatthewMartin

  I may be working on mission impossible here, but I seem to be getting close. I want to extend a ASP.NET control, and I want my code to be unit testable. Also, I'd like to be able to fake behaviors of a real Label (namely things like ID generation, etc), which a real Label can't do in an nUnit host. Here a working example that makes assertions on something that depends on a real base class and something that doesn't-- in a more realistic unit test, the test would depend on both --i.e. an ID existing and some custom behavior. Anyhow the code says it better than I can: public class LabelWrapper : Label //Runtime //public class LabelWrapper : FakeLabel //Unit Test time { private readonly LabelLogic logic= new LabelLogic(); public override string Text { get { return logic.ProcessGetText(base.Text); } set { base.Text=logic.ProcessSetText(value); } } } //Ugh, now I have to test FakeLabelWrapper public class FakeLabelWrapper : FakeLabel //Unit Test time { private readonly LabelLogic logic= new LabelLogic(); public override string Text { get { return logic.ProcessGetText(base.Text); } set { base.Text=logic.ProcessSetText(value); } } } [TestFixture] public class UnitTest { [Test] public void Test() { //Wish this was LabelWrapper label = new LabelWrapper(new FakeBase()) LabelWrapper label = new LabelWrapper(); //FakeLabelWrapper label = new FakeLabelWrapper(); label.Text = "ToUpper"; Assert.AreEqual("TOUPPER",label.Text); StringWriter stringWriter = new StringWriter(); HtmlTextWriter writer = new HtmlTextWriter(stringWriter); label.RenderControl(writer); Assert.AreEqual(1,label.ID); Assert.AreEqual("<span>TOUPPER</span>", stringWriter.ToString()); } } public class FakeLabel { virtual public string Text { get; set; } public void RenderControl(TextWriter writer) { writer.Write("<span>" + Text + "</span>"); } } //System Under Test internal class LabelLogic { internal string ProcessGetText(string value) { return value.ToUpper(); } internal string ProcessSetText(string value) { return value.ToUpper(); } }

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• Offline Mapping API

  - by Aaron M

  Are there any services available that allow me to manipulate maps in an offline setting? I am working on a project that requires me to take a map and based on features on the map, generate a game world. I have looked at a few of the API's for different providers: Google, ms, etc. The API's I looked seem to be strictly showing a user a map. I am looking for something that allows me to create a derivative of a map (the Gameworld), that will never be seen by the public, and is only used by the game engine. However one caveat is that I would like to be able to link the derivative created for use by the game engine, with something I can show the user. As an example. Think of a cross country racing sim. Users cannot control the vehicles directly in this game, they can only control the cars setup, driver, etc. I create a gameworld from a map. The gameworld data (driver position, etc) is overlayed onto a real map. A race might last several days. The only interaction users have with the real map is viewing their position on the map, and where they are in relation to the others. I don't want to violate the terms of the API here. I read Googles API TOS, and it seems to me that creating the gameworld would violdate their TOS. The features I really need are the following The ability to locate a specific place on the map by lat/long The ability/rights to grab those maps and save them as an image file temporarily for processing The ability/rights to store a gameworld that is based on the real map The ability to show a user a map with an overlay (this is optional. I can use googles API, or any other one that supports lat/long.)

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• How can I set the name of the class xml by constructor?

  - by spderosso

  Hi, I want to be able to do something like this: @Root(name="events") class XMLEvents { @ElementList(inline=true) ArrayList<XMLEvent> events = Lists.newArrayList(); XMLEvents(){ ... events.add(new XMLEvent(time, type, professorP)); events.add(new XMLEvent(time, type, student)); events.add(new XMLEvent(time, type, course)); ... } } The XMLEvent class to go something like: class XMLEvent { @Root(name="professor") XMLEvent(DateTime time, LogType type, Professor p){ ... } @Root(name="student") XMLEvent(DateTime time, LogType type, Student st){ ... } @Root(name="course") XMLEvent(DateTime time, LogType type, Course c){ ... } } For the output to be: <events> <professor> ... </professor> <student> ... </student> <course> ... </course> </events> So depending on the constructor I call to create a new XMLEvent the root name to which is mapped is different. Is this even possible? Of course the past example was just to transmit what I need. Putting the @Root annotation there didn't change anything Thanks!

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• why do we need advanced knowledge of mathematics & physics for programming?

  - by Sumeet

  Guys, I have been very good in mathematics and physics in my schools and colleges. Right now I am a programmer. Even in the colleges I have to engrossed my self into computers and programming things all the time. As I used to like it very much. But I have always felt the lack of advanced mathematics and physics in all the work I have done (Programs). Programming never asked me any advanced mathematics and physics knowledge in what I was very good. It always ask u some optimized loops, and different programming technologies which has never been covered in advanced mathematics and physics. Even at the time of selection in big College , such a kind of advanced knowledge is required. Time by time I got out of touch of all that facts and concepts (advanced mathematics and physics). And now after, 5 years in job I found it hard to resolve Differentiations and integrations from Trigonometry. Which sometimes make me feel like I have wasted time in those concepts because they are never used. (At that time I knew that I am going to be a programmer) If one need to be a programmer why do all this advanced knowledge is required. One can go with elementry knowledge a bit more. You never got to think like scientists and R&D person in your Schols and colleges for being a programmer? Just think and let me know your thoughts. I must be wrong somewhere in what I think , but not able to figure that out..? Regards Sumeet

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• Can the Subversion client (svn) derefence symbolic links as if they were files?

  - by Ryan B. Lynch

  I have a directory on a Linux system that mostly contains symlinks to files on a different filesystem. I'd like to add the directory to a Subversion repository, dereferencing the symlinks in the process (treating them as the files they point to, rather than links). Generally, I'd like to be able to handle any working-copy operations with this behavior, but the 'svn add' command is where it starts, I think. The SVN client utility doesn't appear to have any options related to symlink dereferencing in the working copy. I didn't find any references to this in the manual (http://svnbook.red-bean.com/en/1.5/index.html), either. I found a poster on the SVN users mailing list who asked the same question but never received an answer, here: http://markmail.org/message/ngchfnzlmm43yj7h (That poster ended up using hard links instead of symlinks. That technique is not an option, in my case, because the real underlying files reside on a separate filesystem.) I'm using Subversion v1.6.1 on Fedora 11. For what it's worth, I know that there are alternative tools/techniques that could help approximate this behavior, but which I have to discard for various reasons. I've already considered [and dust-binned] these possibilities: - a "union" mount, merging all of the the directories containing the real files, with the SVN working-copy directory as the "top" layer in the union; - copying/moving the real files to the same filesystem as the SVN working-copy, and using hardlinks instead of symlinks; - non-SVN version control systems. These were all neat ideas, and I'm sure they are good solutions to other problems, but they won't work given the constraints of this environment and situation.

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• MySQL query does not return any data

  - by Alex L

  Hi, I need to retrieve data from a specific time period. The query works fine until I specify the time period. Is there something wrong with the way I specify time period? I know there are many entries within that time-frame. This query returns empty: SELECT stop_times.stop_id, STR_TO_DATE(stop_times.arrival_time, '%H:%i:%s') as stopTime, routes.route_short_name, routes.route_long_name, trips.trip_headsign FROM trips JOIN stop_times ON trips.trip_id = stop_times.trip_id JOIN routes ON routes.route_id = trips.route_id WHERE stop_times.stop_id = 5508 HAVING stopTime BETWEEN DATE_SUB(stopTime,INTERVAL 1 MINUTE) AND DATE_ADD(stopTime,INTERVAL 20 MINUTE); Here is it's EXPLAIN: +----+-------------+------------+--------+------------------+---------+---------+-------------------------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+--------+------------------+---------+---------+-------------------------------+------+-------------+ | 1 | SIMPLE | stop_times | ref | trip_id,stop_id | stop_id | 5 | const | 605 | Using where | | 1 | SIMPLE | trips | eq_ref | PRIMARY,route_id | PRIMARY | 4 | wmata_gtfs.stop_times.trip_id | 1 | | | 1 | SIMPLE | routes | eq_ref | PRIMARY | PRIMARY | 4 | wmata_gtfs.trips.route_id | 1 | | +----+-------------+------------+--------+------------------+---------+---------+-------------------------------+------+-------------+ 3 rows in set (0.00 sec) The query works if I remove the HAVING clause (don't specify time range). Returns: +---------+----------+------------------+-----------------+---------------+ | stop_id | stopTime | route_short_name | route_long_name | trip_headsign | +---------+----------+------------------+-----------------+---------------+ | 5508 | 06:31:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 06:57:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 07:23:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 07:49:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 08:15:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 08:41:00 | "80" | "" | "FORT TOTTEN" | | 5508 | 09:08:00 | "80" | "" | "FORT TOTTEN" | I am using Google Transit format Data loaded into MySQL. The query is supposed to provide stop times and bus routes for a given bus stop. For a bus stop, I am trying to get: Route Name Bus Name Bus Direction (headsign) Stop time The results should be limited only to buses times from 1 min ago to 20 min from now. Please let me know if you could help.

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• How to index a table with a Type 2 slowly changing dimension for optimal performance

  - by The Lazy DBA

  Suppose you have a table with a Type 2 slowly-changing dimension. Let's express this table as follows, with the following columns: * [Key] * [Value1] * ... * [ValueN] * [StartDate] * [ExpiryDate] In this example, let's suppose that [StartDate] is effectively the date in which the values for a given [Key] become known to the system. So our primary key would be composed of both [StartDate] and [Key]. When a new set of values arrives for a given [Key], we assign [ExpiryDate] to some pre-defined high surrogate value such as '12/31/9999'. We then set the existing "most recent" records for that [Key] to have an [ExpiryDate] that is equal to the [StartDate] of the new value. A simple update based on a join. So if we always wanted to get the most recent records for a given [Key], we know we could create a clustered index that is: * [ExpiryDate] ASC * [Key] ASC Although the keyspace may be very wide (say, a million keys), we can minimize the number of pages between reads by initially ordering them by [ExpiryDate]. And since we know the most recent record for a given key will always have an [ExpiryDate] of '12/31/9999', we can use that to our advantage. However... what if we want to get a point-in-time snapshot of all [Key]s at a given time? Theoretically, the entirety of the keyspace isn't all being updated at the same time. Therefore for a given point-in-time, the window between [StartDate] and [ExpiryDate] is variable, so ordering by either [StartDate] or [ExpiryDate] would never yield a result in which all the records you're looking for are contiguous. Granted, you can immediately throw out all records in which the [StartDate] is greater than your defined point-in-time. In essence, in a typical RDBMS, what indexing strategy affords the best way to minimize the number of reads to retrieve the values for all keys for a given point-in-time? I realize I can at least maximize IO by partitioning the table by [Key], however this certainly isn't ideal. Alternatively, is there a different type of slowly-changing-dimension that solves this problem in a more performant manner?

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• Java-Eclipse-Spring 3.1 - the fastest way to get familiar with this set

  - by Leron

  I, know almost all of you at some point of your life as a programmer get to the point where you know (more or less) different technologies/languages/IDEs and a times come when you want to get things together and start using them once - more efficient and second - more closely to the real life situation where in fact just knowing Java, or some experience with Eclipse doesn't mean nothing, and what makes you a programmer worth something is the ability to work with the combination of 2 or more combinations. Having this in mind here is my question - what do you think is the optimal way of getting into Java+Eclipse+Spring3.1 world. I've read, and I've read a lot. I started writing real code but almost every step is discovering the wheel again and again, wondering how to do thing you know are some what trivial, but you've missed that one article where this topic was discussed and so on. I don't mind for paying for a good tutorial like for example, after a bit of research I decided that instead of losing a lot of time getting the different parts together I'd rather pay for the videos in http://knpuniversity.com/screencast/starting-in-symfony2-tutorial and save myself a lot of time (I hope) and get as fast as possible to writing a real code instead of wondering what do what and so on. But I find it much more difficult to find such sources of info especially when you want something more specific as me and that's the reason to ask this question. I know a lot of you go through the hard way, and I won't give up if I have to do the same, but to be honest I really hope to get post with good tutorials on the subject (paid or not) because in my situation time is literally money. Thanks Leron

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• Why Enumerable.Range is faster than a direct yield loop?

  - by Morgan Cheng

  Below code is checking performance of three different ways to do same solution. public static void Main(string[] args) { // for loop { Stopwatch sw = Stopwatch.StartNew(); int accumulator = 0; for (int i = 1; i <= 100000000; ++i) { accumulator += i; } sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, accumulator); } //Enumerable.Range { Stopwatch sw = Stopwatch.StartNew(); var ret = Enumerable.Range(1, 100000000).Aggregate(0, (accumulator, n) => accumulator + n); sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, ret); } //self-made IEnumerable<int> { Stopwatch sw = Stopwatch.StartNew(); var ret = GetIntRange(1, 100000000).Aggregate(0, (accumulator, n) => accumulator + n); sw.Stop(); Console.WriteLine("time = {0}; result = {1}", sw.ElapsedMilliseconds, ret); } } private static IEnumerable<int> GetIntRange(int start, int count) { int end = start + count; for (int i = start; i < end; ++i) { yield return i; } } } The result is like this: time = 306; result = 987459712 time = 1301; result = 987459712 time = 2860; result = 987459712 It is not surprising that "for loop" is faster than the other two solutions, because Enumerable.Aggregate takes more method invocations. However, it really surprises that "Enumerable.Range" is faster than the "self-made IEnumerable". I thought that Enumerable.Range will take more overhead than the simple GetIntRange method. What is the possible reason for this?

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• How to build a simulation of a login hardware token in .Net

  - by Michel

  Hi, i have a hardware token for remote login to some citrix environment. When i click the button on the device, i get an id and i can use that to login to the citrix farm. I can click the button as much as i like, and every time a new code gets generated, and they all work. Now i want to secure my private website likewise, but not with the hardware token, but with a 'token app' on my phone. So i run an app on my phone, generate a key, and use that to (partly) authenticate myself on the server. But here's the point: i don't know how it works! How can i generate 1, 2 or 100 keys at one time which i can see (on the server) are all valid, but without the server and the phone app having contact (the hardware token also is an 'offline' solution). Can you help me with a hint how i would do this? This is what i thought of so far: the phone app and the server app know (hardcoded) the same encryption key. The phone app encrypts the current time. The server app decrypts the string to the current time and if the diff between that time and the actual server time is less than 10 minutes it's an ok. Difficult for other users to fake a key, but encryption gives such nasty strings to enter, and the hardware token gives me nice things like 'H554TU8' And this is probably not how the real hardware token works, because the server and the phone app must 'know' the same encryption key. Michel

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• Reasonably faster way to traverse a directory tree in Python?

  - by Sridhar Ratnakumar

  Assuming that the given directory tree is of reasonable size: say an open source project like Twisted or Python, what is the fastest way to traverse and iterate over the absolute path of all files/directories inside that directory? I want to do this from within Python (subprocess is allowed). os.path.walk is slow. So I tried ls -lR and tree -fi. For a project with about 8337 files (including tmp, pyc, test, .svn files): $ time tree -fi > /dev/null real 0m0.170s user 0m0.044s sys 0m0.123s $ time ls -lR > /dev/null real 0m0.292s user 0m0.138s sys 0m0.152s $ time find . > /dev/null real 0m0.074s user 0m0.017s sys 0m0.056s $ tree appears to be faster than ls -lR (though ls -R is faster than tree, but it does not give full paths). find is the fastest. Can anyone think of a faster and/or better approach? On Windows, I may simply ship a 32-bit binary tree.exe or ls.exe if necessary. Update 1: Added find

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• Android ArrayList<Location> passing between activities

  - by squixy

  I have simple class Track, which stores information about route: import java.io.Serializable; import java.util.ArrayList; import java.util.Date; import android.location.Location; public class Track implements Serializable { private static final long serialVersionUID = -5317697499269650204L; private Date date; private String name; private int time; private double distance, speed; private ArrayList<Location> route; public Track(String name, int time, double distance, ArrayList<Location> route) { this.date = new Date(); this.name = name; this.time = time; this.distance = distance; this.speed = distance / (time / 3600.); this.route = route; } public String getDate() { return String.format("Date: %1$td-%1$tb-%1$tY%nTime: %1$tH:%1$tM:%1$tS", date); } public String getName() { return name; } public int getTime() { return time; } public double getDistance() { return distance; } public float getSpeed() { return (float) speed; } public ArrayList<Location> getRoute() { return route; } @Override public String toString() { return String.format("Name: %s%nDate: %2$td-%2$tb-%2$tY%nTime: %2$tH:%2$tM:%2$tS", name, date); } } And I'm passing it from one activity to another: Intent showTrackIntent = new Intent(TabSavedActivity.this, ShowTrackActivity.class); showTrackIntent.putExtra("track", adapter.getItem(position)); startActivity(showTrackIntent); Where (Track object is element on ListView). I get error during passing Track object: java.lang.RuntimeException: Parcelable encountered IOException writing serializable object (name = classes.Track) What is happening?

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• PHP strtotime without leap-years

  - by Christian Sciberras

  With regards to this thread, I've developed a partial solution: function strtosecs($time,$now=null){ static $LEAPDIFF=86400; $time=strtotime($time,$now); return $time-((date('Y',$time)-1968)/4*$LEAPDIFF); } The function is supposed to get the number of seconds given a string without checking leap-years. It does this calculating the number of leap-years 1970 [(year-1986)/4], multiplying it by the difference in seconds between a leap-year and a normal year (which in the end, it's just the number of seconds in a day). Finally, I simply remove all those excess leap-year seconds from the calculated time. Here's some examples of the inputs/outputs: // test code echo strtosecs('+20 years',0).'=>'.(strtosecs('+20 years',0)/31536000); echo strtosecs('+1 years',0).'=>'.(strtosecs('+1 years',0)/31536000); // test output 630676800 => 19.998630136986 31471200 => 0.99794520547945 You will probably ask why am I doing a division on the output? It's to test it out; 31536000 is the number of seconds in a year, so that 19.99... should be 20 and 0.99... should be a 1. Sure, I could round it all and get "correct" answer, but I'm worried about the inaccuracies.

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• Building static (but complicated) lookup table using templates.

  - by MarkD

  I am currently in the process of optimizing a numerical analysis code. Within the code, there is a 200x150 element lookup table (currently a static std::vector < std::vector < double ) that is constructed at the beginning of every run. The construction of the lookup table is actually quite complex- the values in the lookup table are constructed using an iterative secant method on a complicated set of equations. Currently, for a simulation, the construction of the lookup table is 20% of the run time (run times are on the order of 25 second, lookup table construction takes 5 seconds). While 5-seconds might not seem to be a lot, when running our MC simulations, where we are running 50k+ simulations, it suddenly becomes a big chunk of time. Along with some other ideas, one thing that has been floated- can we construct this lookup table using templates at compile time? The table itself never changes. Hard-coding a large array isn't a maintainable solution (the equations that go into generating the table are constantly being tweaked), but it seems that if the table can be generated at compile time, it would give us the best of both worlds (easily maintainable, no overhead during runtime). So, I propose the following (much simplified) scenario. Lets say you wanted to generate a static array (use whatever container suits you best- 2D c array, vector of vectors, etc..) at compile time. You have a function defined- double f(int row, int col); where the return value is the entry in the table, row is the lookup table row, and col is the lookup table column. Is it possible to generate this static array at compile time using templates, and how?

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• Convincing why testing is good

  - by FireAphis

  Hello, In my team of real-time-embedded C/C++ developers, most people don't have any culture of testing their code beyond the casual manual sanity checks. I personally strongly believe in advantages of autonomous automatic tests, but when I try to convince I get some reappearing arguments like: We will spend more time on writing the tests than writing the code. It takes a lot of effort to maintain the tests. Our code is spaghetti; no way we can unit-test it. Our requirement are not sealed – we’ll have to rewrite all the tests every time the requirements are changed. Now, I'd gladly hear any convincing tips and advises, but what I am really looking for are references to researches, articles, books or serious surveys that show (preferably in numbers) how testing is worth the effort. Something like "We in IBM/Microsoft/Google, surveying 3475 active projects, found out that putting 50% more development time into testing decreased by 75% the time spent on fixing bugs" or "after half a year, the time needed to write code with test was only marginally longer than what used to take without tests". Any ideas? P.S.: I'm adding C++ tag too in case someone has a specific experience with convincing this, usually elitist, type of developers :-)

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• Why does this Haskell code produce the "infinite type" error?

  - by Charlie Flowers

  I am new to Haskell and facing a "cannot construct infinite type" error that I cannot make sense of. In fact, beyond that, I have not been able to find a good explanation of what this error even means, so if you could go beyond my basic question and explain the "infinite type" error, I'd really appreciate it. Here's the code: intersperse :: a -> [[a]] -> [a] -- intersperse '*' ["foo","bar","baz","quux"] -- should produce the following: -- "foo*bar*baz*quux" -- intersperse -99 [ [1,2,3],[4,5,6],[7,8,9]] -- should produce the following: -- [1,2,3,-99,4,5,6,-99,7,8,9] intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:y:xs) = x:s:y:intersperse s xs And here's the error trying to load it into the interpreter: Prelude :load ./chapter.3.ending.real.world.haskell.exercises.hs [1 of 1] Compiling Main ( chapter.3.ending.real.world.haskell.exercises.hs, interpreted ) chapter.3.ending.real.world.haskell.exercises.hs:147:0: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `intersperse' Failed, modules loaded: none. Thanks. EDIT: Thanks to the responses, I have corrected the code and I also have a general guideline for dealing with the "infinite type" error in Haskell: Corrected code intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:xs) = x ++ s:intersperse s xs What the problem was: My type signature states that the second parameter to intersperse is a list of lists. Therefore, when I pattern matched against "s (x:y:xs)", x and y became lists. And yet I was treating x and y as elements, not lists. Guideline for dealing with the "infinite type" error: Most of the time, when you get this error, you have forgotten the types of the various variables you're dealing with, and you have attempted to use a variable as if it were some other type than what it is. Look carefully at what type everything is versus how you're using it, and this will usually uncover the problem.

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