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• Long running transactions with Spring and Hibernate?

  - by jimbokun

  The underlying problem I want to solve is running a task that generates several temporary tables in MySQL, which need to stay around long enough to fetch results from Java after they are created. Because of the size of the data involved, the task must be completed in batches. Each batch is a call to a stored procedure called through JDBC. The entire process can take half an hour or more for a large data set. To ensure access to the temporary tables, I run the entire task, start to finish, in a single Spring transaction with a TransactionCallbackWithoutResult. Otherwise, I could get a different connection that does not have access to the temporary tables (this would happen occasionally before I wrapped everything in a transaction). This worked fine in my development environment. However, in production I got the following exception: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction This happened when a different task tried to access some of the same tables during the execution of my long running transaction. What confuses me is that the long running transaction only inserts or updates into temporary tables. All access to non-temporary tables are selects only. From what documentation I can find, the default Spring transaction isolation level should not cause MySQL to block in this case. So my first question, is this the right approach? Can I ensure that I repeatedly get the same connection through a Hibernate template without a long running transaction? If the long running transaction approach is the correct one, what should I check in terms of isolation levels? Is my understanding correct that the default isolation level in Spring/MySQL transactions should not lock tables that are only accessed through selects? What can I do to debug which tables are causing the conflict, and prevent those tables from being locked by the transaction?

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• How to hold payment in paygate for a while?

  - by Fero

  HI all, I have a query regarding holding the payment in PAYGATE PAYMENT GATEWAY. Here is the problem in brief. I am doing a website where the payment should be made only a certain members buy the product. For Example if there is an iPhone in my site, then that particular phone must be buy by certain quantities which given by admin. It may be done one by one user or a single user can buy all the quantities at a single time. In this case as a developer how can i able to hold the payment which received by user? Because i don't want to receive the payments until the certain quantities bought. Because if certain quantities were not buy i need to refund the money to their account. We don't like to do this process. That's why we are looking for holding the payment. Is it possible or what is the best way to solve this problem? Please let me know what is you professional opinion? thanks in advance... Please let me know what is you professional opinion?

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• Handling form from different view and passing form validation through session in django

  - by Mo J. Mughrabi

  I have a requirement here to build a comment-like app in my django project, the app has a view to receive a submitted form process it and return the errors to where ever it came from. I finally managed to get it to work, but I have doubt for the way am using it might be wrong since am passing the entire validated form in the session. below is the code comment/templatetags/comment.py @register.inclusion_tag('comment/form.html', takes_context=True) def comment_form(context, model, object_id, next): """ comment_form() is responsible for rendering the comment form """ # clear sessions from variable incase it was found content_type = ContentType.objects.get_for_model(model) try: request = context['request'] if request.session.get('comment_form', False): form = CommentForm(request.session['comment_form']) form.fields['content_type'].initial = 15 form.fields['object_id'].initial = 2 form.fields['next'].initial = next else: form = CommentForm(initial={ 'content_type' : content_type.id, 'object_id' : object_id, 'next' : next }) except Exception as e: logging.error(str(e)) form = None return { 'form' : form } comment/view.py def save_comment(request): """ save_comment: """ if request.method == 'POST': # clear sessions from variable incase it was found if request.session.get('comment_form', False): del request.session['comment_form'] form = CommentForm(request.POST) if form.is_valid(): obj = form.save(commit=False) if request.user.is_authenticated(): obj.created_by = request.user obj.save() messages.info(request, _('Your comment has been posted.')) return redirect(form.data.get('next')) else: request.session['comment_form'] = request.POST return redirect(form.data.get('next')) else: raise Http404 the usage is by loading the template tag and firing {% comment_form article article.id article.get_absolute_url %} my doubt is if am doing the correct approach or not by passing the validated form to the session. Would that be a problem? security risk? performance issues? Please advise Update In response to Pol question. The reason why I went with this approach is because comment form is handled in a separate app. In my scenario, I render objects such as article and all I do is invoke the templatetag to render the form. What would be an alternative approach for my case? You also shared with me the django comment app, which am aware of but the client am working with requires a lot of complex work to be done in the comment app thats why am working on a new one.

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• CSS3 animations - how to make different animations to different elements on scroll

  - by DeanDeey

  I have a question about the doing CSS3 animations on scroll.. I found a code, that shows the DIV element after the user scrolls down: <script type="text/javascript"> $(document).ready(function() { /* Every time the window is scrolled ... */ $(window).scroll( function(){ /* Check the location of each desired element */ $('.hideme').each( function(i){ var bottom_of_object = $(this).position().top + $(this).outerHeight(); var bottom_of_window = $(window).scrollTop() + $(window).height(); /* If the object is completely visible in the window, fade it it */ if( bottom_of_window > bottom_of_object ){ $(this).animate({'opacity':'1'},500); } }); }); }); </script> I'm building a site, which one will have about 5 different boxes, which one will be shown when the user scrolls down to each box. But my question is, how i make the animation inside those boxes. Foe example: in each box there is title, content and images. How do i make all the elements appear after each other, because with this code all the class elements are shown at once. But i would like that if user scrolls down, first the tittle appears, then the content and at the end the images. And then when user scrolls to the next box, the same process repeat's itself. I use some CSS3 delays, but in this case i don't know how long will user take to scroll down. thanks!

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• Is there a language with native pass-by-reference/pass-by-name semantics, which could be used in mod

  - by Bubba88

  Hi! This is a reopened question. I look for a language and supporting platform for it, where the language could have pass-by-reference or pass-by-name semantics by default. I know the history a little, that there were Algol, Fortran and there still is C++ which could make it possible; but, basically, what I look for is something more modern and where the mentioned value pass methodology is preferred and by default (implicitly assumed). I ask this question, because, to my mind, some of the advantages of pass-by-ref/name seem kind of obvious. For example when it is used in a standalone agent, where copyiong of values is not necessary (to some extent) and performance wouldn't be downgraded much in that case. So, I could employ it in e.g. rich client app or some game-style or standalone service-kind application. The main advantage to me is the clear separation between identity of a symbol, and its current value. I mean when there is no reduntant copying, you know that you're working with the exact symbol/path you have queried/received. And intristing boxing of values will not interfere with the actual logic of program. I know that there is C# ref keyword, but it's something not so intristic, though acceptable. Equally, I realize that pass-by-reference semantics could be simulated in virtually any language (Java as an instant example) and so on.. not sure about pass by name :) What would you recommend - create a something like DSL for such needs wherever it be appropriate; or use some languages that I already know? Maybe, there is something that I'm missing? Thank you!

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• Redirecting to a Facelet is not working when extending FaceletViewHandler

  - by Abel Morelos

  I'm overriding the handleRenderResponse method defined in com.sun.facelets.FaceletViewHandler: protected void handleRenderException(FacesContext context, Exception ex) I'm overriding this method so I can redirect the user to a custom error page (which contain the desired look and feel and other stuff). This is the way I'm trying to String errorPage = "/error.xhtml"; String contextPath = context.getExternalContext().getRequestContextPath(); String errorPagePath = contextPath+errorPage; context.getExternalContext().redirect(errorPagePath); The previous code is what I'm using to perform the redirect to this custom error page. Anyway, when I perform the redirect I'm prompted with a download dialog (this is with Internet Explorer, in Firefox the page does not display properly or as I would expect). I tried changing "/error.xhtml" to "/error.jsf" but in that case I get a 404 error. Somehow I think that the XHTML file is not being handled to the Facelets ViewHandler after the redirect, if I open the downloaded xhtml file I can see that the EL expressions were not resolved and the the ui tags were not handled. I don't have problems with other pages in my application, only when doing the redirect programatically. Important data from my web.xml: facelets.VIEW_MAPPINGS is set to *.xhtml javax.faces.DEFAULT_SUFFIX is set to .xhtml servlet-mapping for the "Faces Servlet" is ".jsf" and "/faces/"

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• How should i organize authority code?

  - by acidzombie24

  I have users that fall into the following Not logged in Not Verified Verified Moderator Admin All code that only admin and moderators can access (like banning) is in ModeratorUser which inherits from verified which inherits from BaseUser. Some pages are accessible to all users such as public profiles. If a user is logged in he can leave a comment. To check this i use if (IsVerifiedUser). Now here is the problem. To avoid problems if a user is banned he is not recognized as a verified user. However in the rare case i need to know if he is verified i can use usertype & Verified. Should i not be doing this? I have a bunch of code in my VerifiedUser class and find i am moving tons of it to BaseUser. Is this something i help because a not logged in user can access the page? Should i handle the ban user in a different way and allow IsVerifiedUser to be true even if the user is banned?

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• How do I get started designing and implementing a script interface for my .NET application?

  - by Peter Mortensen

  How do I get started designing and implementing a script interface for my .NET application? There is VSTA (the .NET equivalent of VBA for COM), but as far as I understand I would have to pay a license fee for every installation of my application. It is an open source application so this will not work. There is also e.g. the embedding of interpreters (IronPython?), but I don't understand how this would allow exposing an "object model" (see below) to external (or internal) scripts. What is the scripting interface story in .NET? Is it somehow trivial in .NET to do this? Background: I have once designed and implemented a fairly involved script interface for a Macintosh application for acquisition and analysis of data from a mass spectrometer (Mac OS, System 7) and later a COM interface for a Windows application. Both were designed with an "object model" and classes (that can have properties). These are overloaded words, but in a scripting interface context object model is essentially a containment hiarchy of objects of specific classes. Classes have properties and lists of contained objects. E.g. like in the COM interfaces exposed in Microsoft Office applications, where the application object can be used to add to its list of documents (with the side effect of creating the GUI representation of a document). External scripts can create new objects in a container and navigate through the content of the hiarchy at any given time. In the Macintosh case scripts could be written in e.g. AppleScript or Frontier. On the Macintosh the implementation of a scripting interface was very complicated. Support for it in Metroworks' C++ class library (the name escapes me right now) made it much simpler.

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• Trying to convert existing production database table columns from enum to VARCHAR (Rails)

  - by dchua

  Hi everyone, I have a problem that needs me to convert my existing live production (I've duplicated the schema on my local development box, don't worry :)) table column types from enums to a string. Background: Basically, a previous developer left my codebase in absolute shit, migration versions are extremely out of date, and apparently he never used it after a certain point of time in development and now that I'm tasked with migrating a rails 1.2.6 app to 2.3.5, I can't get the tests to run properly on 2.3.5 because my table columns have ENUM column types and they convert to :string, :limit = 0 on my schema.rb which creates the problem of an invalid default value when doing a rake db:test:prepare, like in the case of: Mysql::Error: Invalid default value for 'own_vehicle': CREATE TABLE `lifestyles` (`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY, `member_id` int(11) DEFAULT 0 NOT NULL, `own_vehicle` varchar(0) DEFAULT 'Y' NOT NULL, `hobbies` text, `sports` text, `AStar_activities` text, `how_know_IRC` varchar(100), `IRC_referral` varchar(200), `IRC_others` varchar(100), `IRC_rdrive` varchar(30)) ENGINE=InnoDB I'm thinking of writing a migration task that looks through all the database tables for columns with enum and replace it with VARCHAR and I'm wondering if this is the right way to approach this problem. I'm also not very sure how to write it such that it would loop through my database tables and replace all ENUM colum_types with a VARCHAR. References [1] https://rails.lighthouseapp.com/projects/8994/tickets/997-dbschemadump-saves-enum-columns-as-varchar0-on-mysql [2] http://dev.rubyonrails.org/ticket/2832

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• How to distribute the android reusable code in a package?

  - by Kaillash

  Hi, I have developed some reusable android component which is basically a class . This class has some resource dependencies e.g. some png drawables, some xml layouts etc. So this class referenced the auto-generated R file.I would like to distribute this code in a single package like jar file to other developers for use in their applications. I have read that the only possible solution is to distribute code together with all my resources, which others have to copy to their "res" folder (source). So I created a jar file having the class file (say MyClass which is in the package com.xyz.android.app) and resources and tried to use this in my new application. So I added the jar file to my new applications build path using add external jars option in eclipse and copied all the resources to my new application's res folder. (The activity class say MainActivity of my new application is in com.abc.myapplication package, just for the case if it may helpful) But when I run this new application there is java.lang.ClassCastException in the MyClass class. I tried to debug the application and then I found that in the MyClass class, there is "R cannot be resolved" problem. Then I changed MainActivity's package to com.xyz.android.app (which is not the way, other developers will be happy to do), But again the same problem. But When I just copy the source java file such that both MainActivity.java and MyClass.java are in com.xyz.android.app package then application runs fine. So if I need to distribute such that other users need not to bother these package naming things, how can I accomplish this? Please help !!

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• how to create trackballevent in android custom adapter?

  - by UMMA

  dear friends, i am using following code to create custom adapter for listview. now i want to use trackball click event in it but i dont know how to do that can any one help me out in creating ontracballevent in custom adapter? i have tried writing few lines but not able to solve it. public class EfficientAdapter extends BaseAdapter implements Filterable { private LayoutInflater mInflater; private Context context; int pos; public EfficientAdapter(Context context) { mInflater = LayoutInflater.from(context); this.context = context; } public View getView(final int position, View convertView, ViewGroup parent) { ViewHolder holder; convertView = mInflater.inflate(R.layout.adaptor_contentposts, null); convertView.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { //click functionality } }); MotionEvent event= MotionEvent.CREATOR.createFromParcel(null); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: //display click message } convertView.onTrackballEvent(event); return convertView; } class ViewHolder { TextView textLine; TextView textLine2; TextView PostedByAndPostedOn; ImageButton ImgButton; } @Override public Filter getFilter() { return null; } @Override public long getItemId(int position) { return 0; } @Override public int getCount() { return ad_id.length; } @Override public Object getItem(int position) { return ad_id[position]; } }

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• questions about name mangling in C++

  - by Tim

  I am trying to learn and understand name mangling in C++. Here are some questions: (1) From devx When a global function is overloaded, the generated mangled name for each overloaded version is unique. Name mangling is also applied to variables. Thus, a local variable and a global variable with the same user-given name still get distinct mangled names. Are there other examples that are using name mangling, besides overloading functions and same-name global and local variables ? (2) From Wiki The need arises where the language allows different entities to be named with the same identifier as long as they occupy a different namespace (where a namespace is typically defined by a module, class, or explicit namespace directive). I don't quite understand why name mangling is only applied to the cases when the identifiers belong to different namespaces, since overloading functions can be in the same namespace and same-name global and local variables can also be in the same space. How to understand this? Do variables with same name but in different scopes also use name mangling? (3) Does C have name mangling? If it does not, how can it deal with the case when some global and local variables have the same name? C does not have overloading functions, right? Thanks and regards!

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• On-Demand thumbnail creation with django and nginx

  - by sharjeel

  I want to generate thumbnails of images on the fly. My site is built with django and deployed using nginx which serves all the static content and communicates with django/apache using reverse proxy. Right now, for every image in my site, I generate all required sizes of thumbnails on-hand and deliver them when required. The problem is that whenever I change the size of a thumbnail, I have to regenerate all of them (and they are tons). However now I'd like to generate the thumbnail the first time it is accessed and later on nginx would deliver the same file over n over. If I delete that thumbnail file because of lesser accesses, it should get generated automatically the next time. Thumbnails in my case also have watermarks which require some computation logic of my application so a webserver thumbnail module might not work very well. The size of the thumbnail can be embedded in the URL. So http://www.example.com/thumbnail/abc_320x240.jpg gets the 320x240 size of the thumbnail. The approach I'm looking right now is to let nginx lookup the file and if it doesn't exist, forward the query to my django application which would create the thumbnail and send either the response or a redirect string. However I'm not sure about the concurrency issues and any other issues which might pop up later. What is the appropriate way to achieve this?

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• What's the best NAME for "quick" Category you add to a file?

  - by Joe Blow

  So the other day I was sick of typing out repetetive addTarget:action:forControlEvents:s, and macros are only entertaining for so long, so I did this: @implementation UIControl (xx) -(void)addTarget:(id)target action:(SEL)action { [self addTarget:target action:action forControlEvents:UIControlEventTouchUpInside]; } @end *and simply added it at the top of the .m file in question. Works great of course, but notice the "xx".* What's the best thing to NAME a "quick" Category like this? Annoyingly, it appears you can not leave the xx blank - it would then become an "Extension" (which, incidentally, I don't understand at all). I was thinking maybe: a single underscore the name of the class again identically "quick" perhaps the name of the class in this file (as in "quick extra routines for UIControl in CherryBomb") - so it would be UIControl(CherryBomb), ie, remind you that these extra routines are handy for CherryBomb "x" your or your company's initials (use the same "quick" Category name everywhere) "ThisTextNeverUsedAnywhere" By the way, I've been assuming that Categories only happen in the files that see them (CherryBomb.m in the example) - they do not from then on apply app-wide. ie they only apply where you include the header file (UIControl+NattyStuff) or in the "quick" case only in the file to which one adds the text. (By the way ... it appears you do not actually need to include an interface for such a Category, i.e. you can omit... //you can actually get away without these lines... //#import <UIKit/UIControl.h> //@interface UIControl (x) //-(void)addTarget:(id)target action:(SEL)action; //@end ... that part and it works fine.) For people who love Categories, and who doesn't, what's the answer to this troubling question? What should you name a "quick" Category where the name is never going to be referenced again and is irrelevant? Is "_" a solution?

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• How can I superimpose modified loess lines on a ggplot2 qplot?

  - by briandk

  Background Right now, I'm creating a multiple-predictor linear model and generating diagnostic plots to assess regression assumptions. (It's for a multiple regression analysis stats class that I'm loving at the moment :-) My textbook (Cohen, Cohen, West, and Aiken 2003) recommends plotting each predictor against the residuals to make sure that: The residuals don't systematically covary with the predictor The residuals are homoscedastic with respect to each predictor in the model On point (2), my textbook has this to say: Some statistical packages allow the analyst to plot lowess fit lines at the mean of the residuals (0-line), 1 standard deviation above the mean, and 1 standard deviation below the mean of the residuals....In the present case {their example}, the two lines {mean + 1sd and mean - 1sd} remain roughly parallel to the lowess {0} line, consistent with the interpretation that the variance of the residuals does not change as a function of X. (p. 131) How can I modify loess lines? I know how to generate a scatterplot with a "0-line,": # First, I'll make a simple linear model and get its diagnostic stats library(ggplot2) data(cars) mod <- fortify(lm(speed ~ dist, data = cars)) attach(mod) str(mod) # Now I want to make sure the residuals are homoscedastic qplot (x = dist, y = .resid, data = mod) + geom_smooth(se = FALSE) # "se = FALSE" Removes the standard error bands But does anyone know how I can use ggplot2 and qplot to generate plots where the 0-line, "mean + 1sd" AND "mean - 1sd" lines would be superimposed? Is that a weird/complex question to be asking?

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• PHP Regex to match lines with all-caps with occaisional hyphens.

  - by Yaaqov

  I'm trying to to convert an existing PHP Regular Expression match case to apply to a slightly different style of document. Here's the original style of the document: **FOODS - TYPE A** ___________________________________ **PRODUCT** 1) Mi Pueblito Queso Fresco Authentic Mexican Style Fresh Cheese; 2) La Fe String Cheese **CODE** Sell by date going back to February 1, 2009 And the successfully-running PHP Regex match code that only returns "true" if the line is surrounded by asterisks, and stores each side of the "-" as $m[1] and $m[2], respectively. if ( preg_match('#^\*\*([^-]+)(?:-(.*))?\*\*$#', $line, $m) ) { // only for **header - subheader** $m[2] is set. if ( isset($m[2]) ) { return array(TYPE_HEADER, array(trim($m[1]), trim($m[2]))); } else { return array(TYPE_KEY, array($m[1])); } } So, for line 1: $m[1] = "FOODS" AND $m[2] = "TYPE A"; Line 2 would be skipped; Line 3: $m[1] = "PRODUCT", etc. The question: How would I re-write the above regex match if the headers did not have the asterisks, but still was all-caps, and was at least 4 characters long? For example: FOODS - TYPE A ___________________________________ PRODUCT 1) Mi Pueblito Queso Fresco Authentic Mexican Style Fresh Cheese; 2) La Fe String Cheese CODE Sell by date going back to February 1, 2009 Thank you.

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• Simplest distributed persistent key/value store that supports primary key range queries

  - by StaxMan

  I am looking for a properly distributed (i.e. not just sharded) and persisted (not bounded by available memory on single node, or cluster of nodes) key/value ("nosql") store that does support range queries by primary key. So far closest such system is Cassandra, which does above. However, it adds support for other features that are not essential for me. So while I like it (and will consider using it of course), I am trying to figure out if there might be other mature projects that implement what I need. Specifically, for me the only aspect of value I need is to access it as a blob. For key, however, I need range queries (as in, access values ordered, limited by start and/or end values). While values can have structures, there is no need to use that structure for anything on server side (can do client-side data binding, flexible value/content types etc). For added bonus, Cassandra style storage (journaled, all sequential writes) seems quite optimal for my use case. To help filter out answers, I have investigated some alternatives within general domain like: Voldemort (key/value, but no ordering) and CouchDB (just sharded, more batch-oriented); and am aware of systems that are not quite distributed while otherwise qualifying (bdb variants, tokyo cabinet itself (not sure if Tyrant might qualify), redis (in-memory store only)).

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• UpdateModel not working consistently for me if a ddl gets hidden by jQuery

  - by awrigley

  Hi My jQuery code hides a ddl under certain circumstances. When this is the case, after submitting the form, using the UpdateModel doesn't seem to work consistently. My code in the controller: // POST: /IllnessDetail/Edit [AcceptVerbs(HttpVerbs.Post)] public ActionResult Edit(IllnessDetail ill) { IllnessDetailFormViewModel mfv = new IllnessDetailFormViewModel(ill); if (ModelState.IsValid) { try { IllnessDetail sick = idr.GetLatestIllnessDetailByUsername(User.Identity.Name); UpdateModel(sick); idr.Save(); return RedirectToAction("Current", "IllnessDetail"); } catch { ModelState.AddRuleViolations(mfv.IllnessDetail.GetRuleViolations()); } } return View(new IllnessDetailFormViewModel(ill)); } I have only just started with MVC, and working under a deadline, so am still hazy as to how UpdateModel works. Debugging seems to reveal that the correct value is passed in to the action method: public ActionResult Edit(IllnessDetail ill) And the correct value is put into sick in the following line: IllnessDetailFormViewModel mfv = new IllnessDetailFormViewModel(ill); However, when all is said, done and returned to the client, what displays is the value of: sick.IdInfectiousAgent instead of the value of: ill.IdInfectiousAgent The only reason I can think of is that the ddlInfectiousAgent has been hidden by jQuery. Or am I barking up the wrong lamp post? Andrew

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• How do I abort a socket.recv() from another thread in python?

  - by Samuel Skånberg

  I have a main thread that waits for connection. It spawns client threads that will echo the response from the client (telnet in this case). But say that I want to close down all sockets and all threads after some time, like after 1 connection. How would I do? If I do clientSocket.close() from the main thread, it won't stop doing the recv. It will only stop if I first send something through telnet, then it will fail doing further sends and recvs. My code look like this: # Echo server program import socket from threading import Thread import time class ClientThread(Thread): def __init__(self, clientSocket): Thread.__init__(self) self.clientSocket = clientSocket def run(self): while 1: try: # It will hang here, even if I do close on the socket data = self.clientSocket.recv(1024) print "Got data: ", data self.clientSocket.send(data) except: break self.clientSocket.close() HOST = '' PORT = 6000 serverSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) serverSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) serverSocket.bind((HOST, PORT)) serverSocket.listen(1) clientSocket, addr = serverSocket.accept() print 'Got a new connection from: ', addr clientThread = ClientThread(clientSocket) clientThread.start() time.sleep(1) # This won't make the recv in the clientThread to stop immediately, # nor will it generate an exception clientSocket.close()

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• Rails running multiple delayed_job - lock tables

  - by pepernik

  Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

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• Very weird C file-handling anomaly

  - by KáGé

  Hello, I got a very weird issue that I cant figure out in my school project, which is the simulation of a simple filesystem in a human-readable textfile. Unfortunately I don't yet have enough time to translate the comments in my code or make it less gibberish, so if you are bothered by that, you don't have to help, I understand. See the code HERE. Now in drive.h, at line 574 is this part: i = getline(); #ifdef DEBUG printf("Free space in all found at %d.\n\n", i); if(drive.disk != NULL){ printf("Disk OK\n\n"); } #endif //write in data state = seekline(i); Before this it finds place for the allocation database entry in the ALL sector (see the "image files" in the mounts folder, this issue was tested on mount_30.efs-dbf), then gets the line with i = getline() fine (getline is in lglobal.h, line 39), but after that any file manipulation (in this case seekline's fseek, but if I comment that out, then the first fprintf after that) crashes the program straight away. I think the file gets somehow corrupted (though the Disk OK message appears) but can't figure out how. I've tried putting i = getline(); into comment, but it didn't make any difference. I've also tried asking at local programming forums but they didn't really help either. The last few lines of the output before it crashes: Dir written. (drive.h line 562) Seekline entered: 268 (called at drive.h line 564) Getline entered. (called at drive.h line 574) Line got: 268. Free space in all found at 268. (drive.h line 576) Seekline entered: 268 (called at drive.h line 582, note that this exact call was run successfully less than 20 lines back. This one should set the pointer to the beginning of the line it is currently in) After this it crashes. Does anyone has any idea of what causes this and how could I fix it? Thank you.

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• substitution cypher with different alphabet length

  - by seanizer

  I would like to implement a simple substitution cypher to mask private ids in URLs I know how my IDs will look like (combination of upperchase ascii, digits and underscore), and they will be rather long, as they are composed keys. I would like to use a longer alphabet to shorten the resulting codes (I'd like to use upper and lower case ascii letters, digits and nothing else). So my incoming alphabet would be [A-Z0-9_] (37 chars) and my outgoing alphabet would be [A-Za-z0-9] (62 chars) so a compression of almost 50% would be available. let's say my URLs look like this: /my/page/GFZHFFFZFZTFZTF_24_F34 and I want them to look like this instead: /my/page/Ft32zfegZFV5 Obviously both arrays would be shuffled to bring some random order in. This does not have to be secure. if someone figures it out: fine, but I don't want the scheme to be obvious. My desired solution would be to convert the string to an integer representation of radix 37, convert the radix to 62 and use the second alphabet to write out that number. is there any sample code available that does something similar? Integer.parseInt ( http://java.sun.com/javase/6/docs/api/java/lang/Integer.html#parseInt%28java.lang.String,%20int%29 ) has some similar logic, but it is hard-coded to use standard digit behavior Any hints? I am using java to implement this but code or pseudo-code in any other language is of course also helpful

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• Message queue proxy in Python + Twisted

  - by gasper_k

  Hi, I want to implement a lightweight Message Queue proxy. It's job is to receive messages from a web application (PHP) and send them to the Message Queue server asynchronously. The reason for this proxy is that the MQ isn't always avaliable and is sometimes lagging, or even down, but I want to make sure the messages are delivered, and the web application returns immediately. So, PHP would send the message to the MQ proxy running on the same host. That proxy would save the messages to SQLite for persistence, in case of crashes. At the same time it would send the messages from SQLite to the MQ in batches when the connection is available, and delete them from SQLite. Now, the way I understand, there are these components in this service: message listener (listens to the messages from PHP and writes them to a Incoming Queue) DB flusher (reads messages from the Incoming Queue and saves them to a database; due to SQLite single-threadedness) MQ connection handler (keeps the connection to the MQ server online by reconnecting) message sender (collects messages from SQlite db and sends them to the MQ server, then removes them from db) I was thinking of using Twisted for #1 (TCPServer), but I'm having problem with integrating it with other points, which aren't event-driven. Intuition tells me that each of these points should be running in a separate thread, because all are IO-bound and independent of each other, but I could easily put them in a single thread. Even though, I couldn't find any good and clear (to me) examples on how to implement this worker thread aside of Twisted's main loop. The example I've started with is the chatserver.py, which uses service.Application and internet.TCPServer objects. If I start my own thread prior to creating TCPServer service, it runs a few times, but the it stops and never runs again. I'm not sure, why this is happening, but it's probably because I don't use threads with Twisted correctly. Any suggestions on how to implement a separate worker thread and keep Twisted? Do you have any alternative architectures in mind?

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• Passing IDisposable objects through constructor chains

  - by Matt Enright

  I've got a small hierarchy of objects that in general gets constructed from data in a Stream, but for some particular subclasses, can be synthesized from a simpler argument list. In chaining the constructors from the subclasses, I'm running into an issue with ensuring the disposal of the synthesized stream that the base class constructor needs. Its not escaped me that the use of IDisposable objects this way is possibly just dirty pool (plz advise?) for reasons I've not considered, but, this issue aside, it seems fairly straightforward (and good encapsulation). Codes: abstract class Node { protected Node (Stream raw) { // calculate/generate some base class properties } } class FilesystemNode : Node { public FilesystemNode (FileStream fs) : base (fs) { // all good here; disposing of fs not our responsibility } } class CompositeNode : Node { public CompositeNode (IEnumerable some_stuff) : base (GenerateRaw (some_stuff)) { // rogue stream from GenerateRaw now loose in the wild! } static Stream GenerateRaw (IEnumerable some_stuff) { var content = new MemoryStream (); // molest elements of some_stuff into proper format, write to stream content.Seek (0, SeekOrigin.Begin); return content; } } I realize that not disposing of a MemoryStream is not exactly a world-stopping case of bad CLR citizenship, but it still gives me the heebie-jeebies (not to mention that I may not always be using a MemoryStream for other subtypes). It's not in scope, so I can't explicitly Dispose () it later in the constructor, and adding a using statement in GenerateRaw () is self-defeating since I need the stream returned. Is there a better way to do this? Preemptive strikes: yes, the properties calculated in the Node constructor should be part of the base class, and should not be calculated by (or accessible in) the subclasses I won't require that a stream be passed into CompositeNode (its format should be irrelevant to the caller) The previous iteration had the value calculation in the base class as a separate protected method, which I then just called at the end of each subtype constructor, moved the body of GenerateRaw () into a using statement in the body of the CompositeNode constructor. But the repetition of requiring that call for each constructor and not being able to guarantee that it be run for every subtype ever (a Node is not a Node, semantically, without these properties initialized) gave me heebie-jeebies far worse than the (potential) resource leak here does.

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• Tablet interface for the physically disabled?

  - by Glenn

  My sister has Cerebral Palsy, which in her case means she has only gross motor control and her speech is slurred. Implications should be obvious: traditional computer/phone/tablet interfaces won't work for her and she can't speak clearly enough for speech recognition software to help her at all. She enjoys reading but has difficulty holding the book and/or turning a page. There are a few options for helping her use a computer, but nothing for tablets or eReaders. That's where you come in. I would like to make (or buy, if such a thing exists) a better interface to an Android tablet that would work for someone with little to no physical dexterity or speech ability. I'd also be interested in work on the Kindle or iPad, but I'm most familiar with Android so I'm starting there. I know Android has Bluetooth capability. Is it possible to interface a joystick to control the Android device? By "control", I mean the entire operating system - selecting an app, launching it, controlling the menus, etc. I want to give her control over the whole thing, not just a specific app. On a PC this can be accomplished by creating a generic USB HID interface and an arcade joystick to move the mouse over the screen and click on thigns. Is it possible to do something like that in Android? Any help you can offer would be greatly appreciated. Thanks!

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