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• Fastest Method to Learn Web Design for a Developer

  - by hekevintran

  I am a Web developer and in my projects I have noticed that my weakest point is not being good at the front-end design. Relying on other designers can be annoying if they are not able to produce as quickly as I want. My perspective on HTML/CSS is that it is basically a big hack that amazingly works. There are too many CSS and browser specific bugs/quirks to learn and remember them all without spending extreme amounts of time trying to untangle everything. Is there a fast track route to getting CSS into my brain? I have looked at some CSS books, but to me they really read as long lists of how to render things correctly in IE6 and how to make corners rounded. (Seriously why does it require so many tricks to make a sharp corner round? On any platform but the Web this would be called a major oversight.) Does there exist something that does the analogous to CSS that jQuery does for JavaScript? Using jQuery you don't need to know JavaScript well to make things that work. I am not interested in learning why IE6 does things in weird ways because I don't care about supporting it at all. I am more interested in a method of learning how to use CSS to do what I want without spending hours and hours reading obscure blogs.

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• Gravatar XML-RPC request problem in Objective-C

  - by Erik

  Hi all, I'm trying to incorporate some Gravatar functionality using its XML-RPC API in an iPhone app I'm writing. I grabbed the Cocoa XML-RPC Framework by Eric Czarny (http://github.com/eczarny/xmlrpc) and it works well when I tested it with some of the Wordpress methods. However, when I try to use the Gravatar API, I always receive a response of "Error code: -9 Authentication error". I think I'm constructing the request correctly, but I've been wracking my brain and can't seem to figure it out. Maybe someone has some experience with this API or can see what I'm doing wrong. Here's the call: <?xml version="1.0"> <methodCall> <methodName>grav.addresses</methodName> <params> <param><value><string>PASSWORD_HERE</string></value></param> </params> </methodCall> Again, the Cocoa XML-RPC Framework worked like a dream with Wordpress, but it's choking on the Gravatar API for some reason. Thanks for your help.

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• How to update QStandartItemModel without freezing the main UI

  - by user1044002

  I'm starting to learn PyQt4 and have been stuck on something for a long time now and can't figure it out myself: Here is the concept: There is a TreeView with custom QStandartItemModel, which gets rebuild every couple of seconds, and can have a lot (hundreds at least) of entries, there also will be additional delegates for the different columns etc. It's fairly complex and the building time for even plain model, without delegates, goes up to .3 sec, which makes the TreeView to freeze. Please advice me for the best approach on solving this. I was thing of somehow building the model in different thread, and eventually sending it to the TreeView, where it would just perform setModel() with the new one, but couldn't make that work. here is some code that may illustrate the problem a bit: from PyQt4.QtCore import * from PyQt4.QtGui import * import sys, os, re, time app = QApplication(sys.argv) REFRESH = 1 class Reloader_Thread(QThread): def __init__(self, parent = None): QThread.__init__(self, parent) self.loaders = ['\\', '--', '|', '/', '--'] self.emit(SIGNAL('refresh')) def run(self): format = '|%d/%b/%Y %H:%M:%S| ' while True: self.emit(SIGNAL('refresh')) self.sleep(REFRESH) class Model(QStandardItemModel): def __init__(self, viewer=None): QStandardItemModel.__init__(self,None) self.build() def build(self): stTime = time.clock() newRows = [] for r in range(1000): row = [] for c in range(12): item = QStandardItem('%s %02d%02d' % (time.strftime('%H"%M\'%S'), r,c)) row.append(item) newRows.append(row) eTime = time.clock() - stTime outStr = 'Build %03f' % eTime format = '|%d/%b/%Y %H:%M:%S| ' stTime = time.clock() self.beginRemoveRows(QModelIndex(), 0, self.rowCount()) self.removeRows(0, self.rowCount()) self.endRemoveRows() eTime = time.clock() - stTime outStr += ', Remove %03f' % eTime stTime = time.clock() numNew = len(newRows) for r in range(numNew): self.appendRow(newRows[r]) eTime = time.clock() - stTime outStr += ', Set %03f' % eTime self.emit(SIGNAL('status'), outStr) self.reset() w = QWidget() w.setGeometry(200,200,800,600) hb = QVBoxLayout(w) tv = QTreeView() tvm = Model(tv) tv.setModel(tvm) sb = QStatusBar() reloader = Reloader_Thread() tvm.connect(tvm, SIGNAL('status'), sb.showMessage) reloader.connect(reloader, SIGNAL('refresh'), tvm.build) reloader.start() hb.addWidget(tv) hb.addWidget(sb) w.show() app.setStyle('plastique') app.processEvents(QEventLoop.AllEvents) app.aboutToQuit.connect(reloader.quit) app.exec_()

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• Is there a better way to refresh WebView?

  - by cdg

  Hi all. Ok. I have looked EVERYWHERE and my little brain just can't understand a better way to refresh an activity. Any suggestions that I can understand would be great. :) Here is the java code: package com.dge.dges; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.webkit.WebView; import android.widget.Button; public class dgeActivity extends Activity { WebView mWebView; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mWebView = (WebView) findViewById(R.id.webview); mWebView.getSettings(); mWebView.loadUrl("http://www.websitehere.php"); Button newButton = (Button)findViewById(R.id.new_button); newButton.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { Intent intent = new Intent(dgeActivity.this, dgeActivity.class); startActivity(intent); } }); } } And here is the main.xml <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/RelativeLayout" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#000000" > <WebView android:id="@+id/webview" android:layout_width="fill_parent" android:layout_height="wrap_content" android:scrollbars="none" /> <Button android:id="@+id/new_button" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_centerHorizontal="true" android:text="Refresh" /> </RelativeLayout> I don't like the idea of just re-stacking activity after activity. There has to be an easier way to refresh the webview. Please help. :)

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• how to match var/id to class

  - by circey

  Hi. I'm new to jquery and, in addition, I think I'm having a brain freeze. I have a number of links with different ids. I want to match the clicked link with a div with the corresponding class so the div will show/hide/toggle as appropriate. I have: <script type="text/javascript"> $(document).ready(function() { $('.folioBox').hide(); $('a.interface').click(function(){ var currentId = $(this).attr('id'); var currentBox = $('.folioBox .' + currentId); $(currentBox).toggle(400); }); }); </script> <a class="interface" id="apple">Apple flavor</a> <a class="interface" id="banana">Banana flavor</a> <a class="interface" id="cherry">Cherry flavor</a> <div class="folioBox apple">content</div> <div class="folioBox banana">content</div> <div class="folioBox cherry">content</div> I just can't get it to work and I can't figure out whether I would be best using match or find or filter. Some assistance would be much appreciated!

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• when updating location.hash in Chrome the jQuery animation "freezes" for a second

  - by ubunut

  I'm trying to create a sort of "virtual gallery". I'm using Coda Slider 2.0 & jQuery v1.4.2 It behaves perfectly in IE, FF & Safari, but Chrome seems to reload/hang for a second when setting location.hash. This causes the jQuery animation to freeze for a second :S Example: http://hardyernst.dk/gallery.html try clicking on the navigation links above the pictures. The jQuery code that is being executed when clicking a navigation link: $('#coda-nav-' + sliderCount + ' a').each(function(z) { // What happens when a nav link is clicked $(this).bind("click", function() { offset = -(panelWidth*z); navClicks++; $(this).addClass('current').parents('ul').find('a').not($(this)).removeClass('current'); alterPanelHeight(z); currentPanel = z + 1; $('.panel-container', slider).stop().animate({ left: offset }, settings.slideEaseDuration, settings.slideEaseFunction, function(){ if (!settings.crossLinking) { return false; } // Don't change the URL hash unless cross-linking is specified }); }); }); if I add return false; at the end of the function. The animation will slide smoothly :)... BUT as you might have guessed the location.hash value remains unchanged :( I have tried setting the location.hash earlier in the function alas it did not change the behavior in Chrome Would be immensely grateful for any help :) Regards Ubunut

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• Trouble Shoot JavaScript Function in IE

  - by CreativeNotice

  So this function works fine in geko and webkit browsers, but not IE7. I've busted my brain trying to spot the issue. Anything stick out for you? Basic premise is you pass in a data object (in this case a response from jQuery's $.getJSON) we check for a response code, set the notification's class, append a layer and show it to the user. Then reverse the process after a time limit. function userNotice(data){ // change class based on error code returned var myClass = ''; if(data.code == 200){ myClass='success'; } else if(data.code == 400){ myClass='error'; } else{ myClass='notice'; } // create message html, add to DOM, FadeIn var myNotice = '<div id="notice" class="ajaxMsg '+myClass+'">'+data.msg+'</div>'; $("body").append(myNotice); $("#notice").fadeIn('fast'); // fadeout and remove from DOM after delay var t = setTimeout(function(){ $("#notice").fadeOut('slow',function(){ $(this).remove(); }); },5000); }

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• Javascript/PHP and timezones

  - by James

  Hi, I'd like to be able to guess the user's timezone offset and whether or not daylight savings is being applied. Currently, the most definitive code that I've found for this is here: http://www.michaelapproved.com/articles/daylight-saving-time-dst-detect/ So this gives me the offset along with the DST indicator. Now, I want to use these in my PHP scripts in order to ouput the local date/time for the user....but what's best for this? I figure I have 2 options: a) Pick a random timezone which has the same offset and DST setting from the output of timezone_abbreviations_list(). Then call date_timezone_set() with this in order to apply the correct treatment to the time. b) Continue treating the date as UTC but just do some timestamp addition to add the appropriate number of hours on. My feeling is that option B is the best way. The reason for this is that with A, I could be using a timezone which although correct in terms of offset/dst, may have some obscur rules in place behind the scene that could give surprising results (I don't know of any but nonetheless I don't think I can rule it out). I'd then re-check the timezone using Javascript at the start of each session in order to capture when either the user's timezone changes (very unlikely) or they pass in to the DST period. Sorry for the brain dump - I'm really just after some sort of reassurance that the approaches above are valid. Thanks, James.

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• vb.net, How can I limit a textchanged event for a textbox to keyboard input only?

  - by Luay

  Hi everyone, Please allow me to explain what I have and what I am trying to achieve. I have a textbox (called txtb1) and a button under it (called btn_browse) on a winform in a vb.net project. When the user clicks the button a folder browser dialog appears. The user selects his desired folder and when he/she clicks 'ok' the dialog closes and the path of the folder selected appears in the textbox. I also want to store that value in a variable to be used somewhere else(the value will be copied to an xml file when the user clicks 'apply' on the form, but this has no effect nor is related to my problem). To achieve that I have the following code: Public myVar As String Private Sub btn_browse_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_browse.Click Dim f As New FolderBrowserDialog If f.ShowDialog() = DialogResult.OK Then txtb1.Text = f.SelectedPath End If myVar = txtb1.text f.Dispose() End Sub This part works with no problems. Now, what if the user either: 1- decides to enter the path manually rather than use the browse button. or, 2- after using the browse button and selecting the folder they decide to manually change the location In trying to solve this I added a textchanged event to the textbox as follows: Private Sub txtb1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtb1.TextChanged myVar = txtb1.Text End Sub However, this is not working. Apparently, and I don't know if this is relevant, when the user selects the desired folder using the browse button the textchanged event is also triggered. and when I click on the textbox (to give it focus) and press any keyboard key the application simply stops responding. So my questions are: am I going about this the right way? if my logic is flawed, could someone point me to how usually such a thing could be achieved? is it possible to limit the triggering events to only keyboard input as a way around this? I tried the keydown and keypress events but I am getting the freeze. I would be grateful for your help. Thanks

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• Liferay hook: filter url giving filterstart error and current url generates exception null

  - by jack

  I'm trying to make an autologinfilter in Eclipse using a liferay hook. Now I've added the: <filter> <filter-name>myautologinfilter</filter-name> <filter-class>bla.bla.xyz</filter-class> </filter> <filter-mapping> <filter-name>myautologinfilter</filter-name> <url-pattern>/c/login/myurl</url-pattern> </filter-mapping> To the liferay hook's web.xml. In the liferay-hook.xml I added: portal.properties And in that hook.xml I added: auto.login.hooks=bla.bla.xyz bla.bla.xyz implements AutoLogin, but for now it's pretty gutted: @Override public String[] login(HttpServletRequest request, HttpServletResponse response) throws AutoLoginException { Object parameters = request.getAttribute("javax.servlet.forward.query_string"); Map<String, String> x = parserClass.parsing(parameters.toString()); System.out.println("voornaam: " + geparsdeParameters.get("tokenvalue1")); try { return null; } catch (Exception e) { throw new AutoLoginException(e); } } Since the hook doesn't start when I add the filtering I removed it and just tried: http://localhost:8080/c/portal/login?tokenvalue1=55 but when I check my tomcat I see: Error XYZ Url: url myUsedUrl exception null Also I tried adding some util classes but I got: classnotfoundexceptions. Is there anything specific I have to do when I add extra classes in a hook? Any advice/input would be appreciated. Or someone's ear I could lend so I could mail them a little bit so I could pick their brain a bit would be really appreciated since I don't know anyone who programs for liferay.

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• Filling SWT table object using a separated thread class ...

  - by erlord

  Hi all I've got a code snippet by the swt team that does exactly what I need. However, there is a part I want to separate into another class, in particular, the whole inline stuff. In response to my former question, it has been suggested that Callable should be used in order to implement threaded objects. It is suggested to make use of an implementation of runnable or better callable, since I do need some kind of return. However, I don't get it. My problems are: In the original code, within the inline implementation of the method run, some of the parents objects are called. How would I do this when the thread is separated? Pass the object via the C'tor's parameter? In the original code, another runnable object is nested within the runnable implementation. What is it good for? How to implement this when having separated the code? Furthermore, this nested runnable again calls objects created by the main method. Please, have mercy with me, but I am still quite a beginner and my brain is near collapsing :-( All I want is to separate all the threaded stuff into another class and make the program do just the same thing as it already does. Help please! Again thank you very much in advance for any useful suggestions, hints, examples etc... Regs Me

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• Is it possible to unstick a remote IIS ASP server after an exception hangs the session?

  - by user89691

  I have been coding an app in classic ASP that accesses 2 Access databases. I had a page I was working on throw an exception, which is normal during development and causes no lasting problems. This time however, after the exception any attempt to open either of the databases would freeze the session with an infinite script timeout. If I delete the session cookie I an able to access ASP pages again until I try to open the database again. The database that was open when the exception was thrown is left open. There is a LDB lock file and I can't rename or delete either the LDB or MDB file, though I can download the MDB file with FTP. The 2nd access database is not open but any attempt to read this also hangs the session. Accessing HTML pages is fine. The site is hosted with Hostway and they are not interested ("Coding problem = Your problem" even though it leaves my site dead in the water, I suspect until the next reboot, whenever that might be). Here is the dump from the relevant ASP page that threw the exception: Active Server Pages error 'ASP 0115' Unexpected error /translatestats.asp A trappable error (C0000005) occurred in an external object. The script cannot continue running. Active Server Pages error 'ASP 0240' Script Engine Exception /translatestats.asp A ScriptEngine threw exception 'C0000005' in 'IActiveScript::Close()' from 'CActiveScriptEngine::FinalRelease()'. Is there any way I can unstick the site / force close the database remotely ?

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• Refresh a Div that has a Google ad inside it

  - by Abs

  Hello all, I have a div that holds a google ad. My website is mostly AJAX and there is no need for a browser refresh. That means my ads will not refresh either, which isnt ideal, a user staring at one ad all day. So I wanted a way to refresh a particular div on a page. I found many solutions but they didnt work. For example, using JQuery's html function: $("#ads").html("google ad script here"); This managed to refresh the whole page no idea how. I can also make an AJAX request to a HTML page that contains the google ad but I am guessing it will have the same effect as the above attempt. I do not want to use iFrames. Is there any other option open to me? My pea brain can not think of anymore. :) Thanks you for any help. EDIT: It is allowed since I will be initiating the refresh only when a user clicks a link. A prime example is Yahoo Mail - their new AJAX mailbox uses this same method, when a user clicks a link then a new ad is shown.

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• Could Python's logging SMTP Handler be freezing my thread for 2 minutes?

  - by Oddthinking

  A rather confusing sequence of events happened, according to my log-file, and I am about to put a lot of the blame on the Python logger, which is a bold claim. I thought I should get some second opinions about whether what I am saying could be true. I am trying to explain why there is are several large gaps in my log file (around two minutes at a time) during stressful periods for my application when it is missing deadlines. I am using Python's logging module on a remote server, and have set-up, with a configuration file, for all logs of severity of ERROR or higher to be emailed to me. Typically, only one error will be sent at a time, but during periods of sustained problems, I might get a dozen in a minute - annoying, but nothing that should stress SMTP. I believe that, after a short spurt of such messages, the Python logging system (or perhaps the SMTP system it is sitting on) is encountering errors or congestion. The call to Python's log is then BLOCKING for two minutes, causing my thread to miss its deadlines. (I was smart enough to move the logging until after the critical path of the application - so I don't care if logging takes me a few seconds, but two minutes is far too long.) This seems like a rather awkward architecture (for both a logging system that can freeze up, and for an SMTP system (Ubuntu, sendmail) that cannot handle dozens of emails in a minute**), so this surprises me, but it exactly fits the symptoms. Has anyone had any experience with this? Can anyone describe how to stop it from blocking? ** EDIT: I actually counted. A little under 4000 short emails in two hours. So far more than I suggested, sorry. But enough to over-fill a Sendmail's buffers?

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• How to restrain one's self from the overwhelming urge to rewrite everything?

  - by Scott Saad

  Setup Have you ever had the experience of going into a piece of code to make a seemingly simple change and then realizing that you've just stepped into a wasteland that deserves some serious attention? This usually gets followed up with an official FREAK OUT moment, where the overwhelming feeling of rewriting everything in sight starts to creep up. It's important to note that this bad code does not necessarily come from others as it may indeed be something we've written or contributed to in the past. Problem It's obvious that there is some serious code rot, horrible architecture, etc. that needs to be dealt with. The real problem, as it relates to this question, is that it's not the right time to rewrite the code. There could be many reasons for this: Currently in the middle of a release cycle, therefore any changes should be minimal. It's 2:00 AM in the morning, and the brain is starting to shut down. It could have seemingly adverse affects on the schedule. The rabbit hole could go much deeper than our eyes are able to see at this time. etc... Question So how should we balance the duty of continuously improving the code, while also being a responsible developer? How do we refrain from contributing to the broken window theory, while also being aware of actions and the potential recklessness they may cause? Update Great answers! For the most part, there seems to be two schools of thought: Don't resist the urge as it's a good one to have. Don't give in to the temptation as it will burn you to the ground. It would be interesting to know if more people feel any balance exists.

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• MySQL Query That Can Pull the Data I am Seeking?

  - by Amy

  On the project I am working on, I am stuck with the table structure from Hades. Two things to keep in mind: I can't change the table structure right now. I'm stuck with it for the time being. The queries are dynamically generated and not hard coded. So, while I am asking for a query that can pull this data, what I am really working toward is an algorithm that will generate the query I need. Hopefully, I can explain the problem without making your eyes glaze over and your brain implode. We have an instance table that looks (simplified) along these lines: Instances InstanceID active 1 Y 2 Y 3 Y 4 N 5 Y 6 Y Then, there are multiple data tables along these lines: Table1 InstanceID field1 reference_field2 1 John 5 2 Sally NULL 3 Fred 6 4 Joe NULL Table2 InstanceID field3 5 1 6 1 Table3 InstanceID fieldID field4 5 1 Howard 5 2 James 6 2 Betty Please note that reference_field2 in Table1 contains a reference to another instance. Field3 in Table2 is a bit more complicated. It contains a fieldID for Table 3. What I need is a query that will get me a list as follows: InstanceID field1 field4 1 John Howard 2 Sally 3 Fred The problem is, in the query I currently have, I do not get Fred because there is no entry in Table3 for fieldID 1 and InstanceID 6. So, the very best list I have been able to get thus far is InstanceID field1 field4 1 John Howard 2 Sally In essence, if there is an entry in Table1 for Field 2, and there is not an entry in Table 3 that has the instanceID contained in field2 and the field ID contained in field3, I don't get the data from field1. I have looked at joins till I'm blue in the face, and I can't see a way to handle the case when table3 has no entry.

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• Subsonic in a VS2008 Add-In woes

  - by Michael Smit

  Hi, I am writing a VS2008 add-in that connects to a remote database blah blah. I am having a problem with the app.config in this project. When I use SubSonic in my code, it moans that is cannot find the SubSonicServer section. This is because the .config file cannot be found. This appears to a problem with paths as the add-in is a DLL running in the context of VS2008 and the working directory is C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE. Is there a way to get the app.config to deploy properly with the application so my add-in (and SubSonic) can find what it needs in the .config file, or is there a way to get SubSonic to work without the need for the .config? I am very experienced in SubSonic projects now, but only winforms, web, web service, and WPF applications. This is the first time I have tried to use SubSonic in a VS2008 Add-In project. I also have AppSettings in the config file which the ConfigurationManager cannot read because it cannot see the .config file. 2AM now and brain is tired of trying to figure this one out. Hopefully there is an answer when I wake up :) TIA

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• SSH traffic over openvpn freezes under weird circumstances

  - by user289581

  I have an openvpn (version 2.1_rc15 at both ends) connection setup between two gentoo boxes using shared keys. it works fine for the most part. I use mysql, http, ftp, scp over the vpn with no problems. But when I ssh from the client to the server over the vpn, weird things happen. I can login, i can execute some commands. But if i try to run an ncurses application like top, or i try to cat a file, the connection will stall and I'll have to sever the ssh session. I can, for example, execute "echo blah; echo .; echo blah" and it will output the three lines of text over the ssh session fine. But if i execute "cat /etc/motd" the session will freeze the moment I press enter. While it seems like a terminal emulation problem it makes no sense why using the vpn would affect the ability for ssh to render things correctly. I am at a loss to explain why everything else works, including scp, but ssh just breaks over the vpn. Any thoughts ?

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• Java problem with multiple threads when executing a runnable jar file

  - by Spi1988

  I have developed a Java Swing application, which uses the SwingWorker class to perform some long running tasks. When the application is run from the IDE (Netbeans), I can start multiple long running tasks simultaneously without any problem. I created a runnable jar file for the application, in order to be able to run it from outside the IDE. The application when run from this jar file works well with the only exception that it doesn't allow me to start 2 long running tasks simultaneously. When I start the first task (assume it takes 2 minitues to complete), every thing works fine, the UI does not freeze (it never freezes). However, when I try to run another task (assume it takes just 10 seconds, therefore it should finish before the first task) while the first task has not yet completed, nothing seems to happen. In reality, the second task would have started, and also finished its processing, however its results are only displayed once the first task completes. I dunno why this is happening. Is there some restriction on the number of threads which could run simultaneously on the JVM? Are there any jvm arguments which i could try to solve this problem. I hope i explained my problem well. Thanks in advance, Peter Bartolo

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• how useful is Turing completeness? are neural nets turing complete?

  - by Albert

  While reading some papers about the Turing completeness of recurrent neural nets (for example: Turing computability with neural nets, Hava T. Siegelmann and Eduardo D. Sontag, 1991), I got the feeling that the proof which was given there was not really that practical. For example the referenced paper needs a neural network which neuron activity must be of infinity exactness (to reliable represent any rational number). Other proofs need a neural network of infinite size. Clearly, that is not really that practical. But I started to wonder now if it does make sense at all to ask for Turing completeness. By the strict definition, no computer system nowadays is Turing complete because none of them will be able to simulate the infinite tape. Interestingly, programming language specification leaves it most often open if they are turing complete or not. It all boils down to the question if they will always be able to allocate more memory and if the function call stack size is infinite. Most specification don't really specify this. Of course all available implementations are limited here, so all practical implementations of programming languages are not Turing complete. So, what you can say is that all computer systems are just equally powerful as finite state machines and not more. And that brings me to the question: How useful is the term Turing complete at all? And back to neural nets: For any practical implementation of a neural net (including our own brain), they will not be able to represent an infinite number of states, i.e. by the strict definition of Turing completeness, they are not Turing complete. So does the question if neural nets are Turing complete make sense at all? The question if they are as powerful as finite state machines was answered already much earlier (1954 by Minsky, the answer of course: yes) and also seems easier to answer. I.e., at least in theory, that was already the proof that they are as powerful as any computer.

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• How should I avoid memoization causing bugs in Ruby?

  - by Andrew Grimm

  Is there a consensus on how to avoid memoization causing bugs due to mutable state? In this example, a cached result had its state mutated, and therefore gave the wrong result the second time it was called. class Greeter def initialize @greeting_cache = {} end def expensive_greeting_calculation(formality) case formality when :casual then "Hi" when :formal then "Hello" end end def greeting(formality) unless @greeting_cache.has_key?(formality) @greeting_cache[formality] = expensive_greeting_calculation(formality) end @greeting_cache[formality] end end def memoization_mutator greeter = Greeter.new first_person = "Bob" # Mildly contrived in this case, # but you could encounter this in more complex scenarios puts(greeter.greeting(:casual) << " " << first_person) # => Hi Bob second_person = "Sue" puts(greeter.greeting(:casual) << " " << second_person) # => Hi Bob Sue end memoization_mutator Approaches I can see to avoid this are: greeting could return a dup or clone of @greeting_cache[formality] greeting could freeze the result of @greeting_cache[formality]. That'd cause an exception to be raised when memoization_mutator appends strings to it. Check all code that uses the result of greeting to ensure none of it does any mutating of the string. Is there a consensus on the best approach? Is the only disadvantage of doing (1) or (2) decreased performance? (I also suspect freezing an object may not work fully if it has references to other objects) Side note: this problem doesn't affect the main application of memoization: as Fixnums are immutable, calculating Fibonacci sequences doesn't have problems with mutable state. :)

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• Select * from 'many to many' SQL relationship

  - by Rampant Creative Group

  I'm still learning SQL and my brain is having a hard time with this one. Say I have 3 tables: teams players and teams_players as my link table All I want to do is run a query to get each team and the players on them. I tried this: SELECT * FROM teams INNER JOIN teams_players ON teams.id = teams_players.team_id INNER JOIN players ON teams_players.player_id = players.id But it returned a separate row for each player on each team. Is JOIN the right way to do it or should I be doing something else? ----------------------------------------- Edit Ok, so from what I'm hearing, this isn't necessarily a bad way to do it. I'll just have to group the data by team while I'm doing my loop. I have not yet tried the modified SQL statements provided, but I will today and get back to you. To answer the question about structure - I guess I wasn't thinking about the returned row structure which is part of what lead to my confusion. In this particular case, each team is limited to 4 players (or less) so I guess the structure that would be helpful to me is something like the following: teams.id, teams.name, players.id, players.name, players.id, players.name, players.id, players.name, players.id, players.name, 1 Team ABC 1 Jim 2 Bob 3 Ned 4 Roy 2 Team XYZ 2 Bob 3 Ned 5 Ralph 6 Tom

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• Question about making Asynchronous call in C# (WPF) to COM object

  - by Andrew

  Hi, Sorry to ask such a basic question but I seem to have a brain freeze on this one! I'm calling a COM (ATL) object from my WPF project. The COM method might take a long time to complete. I thought I'd try and call it asychronously. I have a few demo lines that show the problem. private void checkBox1_Checked(object sender, RoutedEventArgs e) { //DoSomeWork(); AsyncDoWork caller = new AsyncDoWork(DoSomeWork); IAsyncResult result = caller.BeginInvoke(null, null); } private delegate void AsyncDoWork(); private void DoSomeWork() { _Server.DoWork(); } The ATL method DoWork is very exciting. It is: STDMETHODIMP CSimpleObject::DoWork(void) { Sleep(5000); return S_OK; } I had expectations that running this way would result in the checkbox being checked right away (instead of in 5 seconds) and me being able to move the WPF gui around the screen. I can't - for 5 seconds. What am I doing wrong? I'm sure it's something pretty simple. Delegate signature wrong? Thanks.

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• Errors when creating a custom Querable object with MVC and Subsonic pagedlist

  - by minus4

  hiya, i have the following code but when i try and create a new IQuerable i get an error that the interface cannot be implemented, if i take away the new i get a not implemented exception, have had to jump back and work on some old ASP classic sites for past month and for the life of me i can not wake my brain up into C# mode. Could you please have a look at below and give me some clues on where i'm going wrong: The code is to create a list of priceItems, but instead of a categoryID (int) i am going to be showing the name as string. public ActionResult ViewPriceItems(int? page) { var crm = 0; page = GetPage(page); // try and create items2 IQueryable<ViewPriceItemsModel> items2 = new IQueryable<ViewPriceItemsModel>(); // the data to be paged,but unmodified var olditems = PriceItem.All().OrderBy(x => x.PriceItemID); foreach (var item in olditems) { // set category as the name not the ID for easier reading items2.Concat(new [] {new ViewPriceItemsModel {ID = item.PriceItemID, Name = item.PriceItem_Name, Category = PriceCategory.SingleOrDefault( x => x.PriceCategoryID == item.PriceItem_PriceCategory_ID).PriceCategory_Name, Display = item.PriceItems_DisplayMethod}}); } crm = olditems.Count() / MaxResultsPerPage; ViewData["numtpages"] = crm; ViewData["curtpage"] = page + 1; // return a paged result set return View(new PagedList<ViewPriceItemsModel>(items2, page ?? 0, MaxResultsPerPage)); } many thanks

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• How do I model teams and gameplay in this scorekeeping application?

  - by Eric Hill

  I'm writing a scorekeeping application for card game that has a few possibly-interesting constraints. The application accepts user registrations for players, then lets them check-in to a particular game (modeled as Event). After the final player registers, the app should generate teams, singles or doubles, depending on the preference of the person running the game and some validations (can't do doubles if there's an odd number checked in). There are @event.teams.count rounds in the game. To sum up: An event consists of `@event.teams.count` rounds; Teams can have 1 or more players Events have n or n/2 teams (depending on whether it's singles or doubles) Users will be members of different teams at different events Currently I have a rat's nest of associations: class User < ActiveRecord::Base has_many :teams, :through => :players has_many :events, :through => :teams class Event < ActiveRecord::Base has_many :rounds has_many :teams has_many :players, :through => :teams class Player < ActiveRecord::Base belongs_to :user belongs_to :team end class Team < ActiveRecord::Base has_many :players belongs_to :event end class Round < ActiveRecord::Base belongs_to :event belongs_to :user end The sticky part is team generation. I have basically a "start game" button that should freeze the registrations and pair up teams either singly or doubly, and render to Round#new so that the first (and subsequent) matches can be scored. Currently I'm implementing this as a check on Round#new that calls Event#generate_teams and displays the view: # Event#generate_teams def generate_teams # User has_many :events, :through => :registrations # self.doubles is a boolean denoting 2 players per team registrations.in_groups_of(self.doubles ? 2 : 1, nil).each do |side| self.teams << Player.create(self,side) end end Which doesn't work. Should there maybe be a Game model that ties everything together rather than (my current method) defining the game as an abstraction via the relationships between Events, Users, and Rounds (and Teams and Players and etc.)? My head is swimming.

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