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  • Apple shortcuts in Ubuntu

    - by rcourtna
    Hi, I switch between a Mac and Ubuntu often. On my Ubuntu box, I use an Apple Aluminum keyboard. I'm interested in Apple's "command" key: ? (I'm not concerned about the hardware control keys) cmd-T opens a browser tab cmd-C, cmd-V for copy/paste, especially in a terminal window control-c maintains the same meaning in terminal (abort) Just switching the control & command keys in Ubuntu would almost get me there, except for the special behaviour of the keys a terminal (Terminal is my most frequently used app). Has it been done? edit: using Gnome, not KDE

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  • How to bypass Plesk's Loading Window

    - by Ehsan
    I'm in trouble with the loading window in Parallels Plesk control panel. it prevents any action before page completely loaded. It can be bypassed by unchecking "Prevent users from working with the control panel until interface screens are completely loaded" in the "Interface Preferences" in the each user's control panel, but I wanna to disable it for all accounts of the server. I haven't found any option in the panel to do it, is there any hack? or who knows where I can change it in the psa database? Hope to ask in a correct place. Thanks

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  • Using C# FindControl to find a user-control in the master page

    - by Jisaak
    So all I want to do is simply find a user control I load based on a drop down selection. I have the user control added but now I'm trying to find the control so I can access a couple properties off of it and I can't find the control for the life of me. I'm actually doing all of this in the master page and there is no code in the default.aspx page itself. Any help would be appreciated. MasterPage.aspx <body> <form id="form1" runat="server"> <div> <asp:ScriptManager runat="server"> </asp:ScriptManager> </div> <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="false" OnLoad="UpdatePanel2_Load"> <ContentTemplate> <div class="toolbar"> <div class="section"> <asp:DropDownList ID="ddlDesiredPage" runat="server" AutoPostBack="True" EnableViewState="True" OnSelectedIndexChanged="goToSelectedPage"> </asp:DropDownList> &nbsp; <asp:DropDownList ID="ddlDesiredPageSP" runat="server" AutoPostBack="True" EnableViewState="True" OnSelectedIndexChanged="goToSelectedPage"> </asp:DropDownList> <br /> <span class="toolbarText">Select a Page to Edit</span> </div> <div class="options"> <div class="toolbarButton"> <asp:LinkButton ID="lnkSave" CssClass="modal" runat="server" OnClick="lnkSave_Click"><span class="icon" id="saveIcon" title="Save"></span>Save</asp:LinkButton> </div> </div> </div> </ContentTemplate> <Triggers> </Triggers> </asp:UpdatePanel> <div id="contentContainer"> <asp:UpdatePanel ID="UpdatePanel1" runat="server" OnLoad="UpdatePanel1_Load" UpdateMode="Conditional" ChildrenAsTriggers="False"> <ContentTemplate> <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server"> </asp:ContentPlaceHolder> </ContentTemplate> <Triggers> <asp:AsyncPostBackTrigger ControlID="lnkHome" EventName="Click" /> <asp:AsyncPostBackTrigger ControlID="rdoTemplate" EventName="SelectedIndexChanged" /> </Triggers> </asp:UpdatePanel> </div> MasterPage.cs protected void goToSelectedPage(object sender, System.EventArgs e) { temp1 ct = this.Page.Master.LoadControl("temp1.ascx") as temp1; ct.ID = "TestMe"; this.UpdatePanel1.ContentTemplateContainer.Controls.Add(ct); } //This is where I CANNOT SEEM TO FIND THE CONTROL //////////////////////////////////////// protected void lnkSave_Click(object sender, System.EventArgs e) { UpdatePanel teest = this.FindControl("UpdatePanel1") as UpdatePanel; Control test2 = teest.ContentTemplateContainer.FindControl("ctl09") as Control; temp1 test3 = test2.FindControl("TestMe") as temp1; string maybe = test3.Col1TopTitle; } Here I don't understand what it's telling me. for "par" I get "ctl09" and I have no idea how I am supposed to find this control. temp1.ascx.cs protected void Page_Load(object sender, EventArgs e) { string ppp = this.ID; string par = this.Parent.ID; }

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  • wpf custom control problem

    - by josika
    Hi! I have a problem, and I have not found the solution yet. I woud like to create a base custom control and use it in another custom control. The base control work fine when I use in a window, but when I use in the other custom control, the binding does not work. What's wrong with my code? Code: Model: public class ElementModel { public string Name { get; set; } public string FullName { get; set; } } The base control: public class ListControl : Control { static ListControl() { DefaultStyleKeyProperty.OverrideMetadata(typeof(ListControl), new FrameworkPropertyMetadata(typeof(ListControl))); } public ListControl() { SetValue(ElementListProperty, new List<ElementModel>()); } public static readonly DependencyProperty ElementListProperty = DependencyProperty.Register( "ElementList", typeof(List<ElementModel>), typeof(ListControl), new FrameworkPropertyMetadata(new List<ElementModel>()) ); public List<ElementModel> ElementList { get { return (List<ElementModel>)GetValue(ElementListProperty); } set { SetValue(ElementListProperty, value); } } } The Wrapper Control: public class ListWrapper : Control { static ListWrapper() { DefaultStyleKeyProperty.OverrideMetadata(typeof(ListWrapper), new FrameworkPropertyMetadata(typeof(ListWrapper))); } public ListWrapper() { SetValue(EMListProperty, new List<ElementModel>()); } public static readonly DependencyProperty EMListProperty = DependencyProperty.Register( "EMList", typeof(List<ElementModel>), typeof(ListWrapper), new FrameworkPropertyMetadata(new List<ElementModel>()) ); public List<ElementModel> EMList { get { return (List<ElementModel>)GetValue(EMListProperty); } set { SetValue(EMListProperty, value); } } } Generic.xaml <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:UIControl"> <Style TargetType="{x:Type local:ListControl}"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type local:ListControl}"> <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}"> <ListBox ItemsSource="{TemplateBinding ElementList}"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel> <Label Content="Name:"/> <TextBlock Text="{Binding Path=Name}" /> <Label Content="Full name:"/> <TextBlock Text="{Binding Path=FullName}" /> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> <Style TargetType="{x:Type local:ListWrapper}"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type local:ListWrapper}"> <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}"> <local:ListControl ElementList="{TemplateBinding EMList}" /> </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> If I put the controls in the window and binding properties, than the ListControl works fine and shows the elements, but the WrapperList does not. <Window x:Class="MainApplication.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ui="clr-namespace:UIControl;assembly=UIControl" Title="Window1" Height="304" Width="628"> <Grid> <ui:ListControl x:Name="listCtr" ElementList="{Binding Path=EList}" HorizontalAlignment="Left" Width="300" /> <ui:ListWrapper x:Name="listWrp" EMList="{Binding Path=EList}" HorizontalAlignment="Right" Width="300" Background="Gray"/> </Grid> Project archive

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  • Does the HTMLEditor control raise any client-side events?

    - by SAMIR BHOGAYTA
    The HTML Editor has three modes: Design, HTML Text and preview mode. Design mode is in an IFrame. HTML Text is prensented in a TextArea and preview mode is in another Iframe. The code rendered about these three modes is as below. iframe id="editor1_ctl02_ctl00" name="editor1_ctl02_ctl00" marginheight="0" marginwidth="0" frameborder="0" src="javascript:false;" style="height:100%;width:100%;display:none;border-width:0px;" /iframe textarea id="editor1_ctl02_ctl01" class="ajax__htmleditor_htmlpanel_default" style="height:100%;width:100%;display:none;" /textarea iframe id="editor1_ctl02_ctl02" name="editor1_ctl02_ctl02" marginheight="0" marginwidth="0" frameborder="0" src="javascript:false;" style="height:100%;width:100%;display:none;border-width:0px;" /iframe In design mode, we can use the following JavaScript to append a callback function in onKeypress event. script type="text/javascript" var count = 0; function pageLoad() { $get('editor1_ctl02_ctl00').contentWindow.document.body.onkeypress = function() { count++; $get('cc').innerHTML = "you input " + count + "charactors"; }; } /script As a same way, you can append another keypress event on TextArea and preview IFrame.

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  • ConcurrentDictionary and updating values

    - by rboarman
    Hello, After searching via Google and coming up empty, I decided to ask the gurus here on StackOverflow. I am trying to update entries in a ConcurrentDictionary something like this: class Class1 { public int Counter { get; set; } } class Test { private ConcurrentDictionary<int, Class1> dict = new ConcurrentDictionary<int, Class1>(); public void TestIt() { foreach (var foo in dict) { foo.Value.Counter = foo.Value.Counter + 1; // Simplified example } } } Essentially I need to iterate over the dictionary and update a field on each Value. I understand from the documentation that I need to avoid using the Value property. Instead I think I need to use TryUpdate except that I don’t want to replace my whole object. Instead, I want to update a field on the object. After reading this: http://blogs.msdn.com/b/pfxteam/archive/2010/01/08/9945809.aspx Perhaps I need to use AddOrUpdate and simply do nothing in the add delegate. Does anyone have any insight as to how to do this? Thank you, Rick

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  • Locking Cache Key without Locking the entire Cache

    - by Gandalf
    I have servlets that caches user information rather then retrieving it from the user store on every request (shared Ehcache). The issue I have is that if a client is multi-threaded and they make more then one simultaneous request, before they have been authenticated, then I get this in my log: Retrieving User [Bob] Retrieving User [Bob] Retrieving User [Bob] Returned [Bob] ...caching Returned [Bob] ...caching Returned [Bob] ...caching What I would want is that the first request would call the user service, while the other two requests get blocked - and when the first request returns, and then caches the object, the other two requests go through: Retrieving User [Bob] blocking... blocking... Returned [Bob] ...caching [Bob] found in cache [Bob] found in cache I've thought about locking on the String "Bob" (because due to interning it's always the same object right?). Would that work? And if so how do I keep track of the keys that actually exist in the cache and build a locking mechanism around them that would then return the valid object once it's retrieved. Thanks.

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  • Java ReentrantReadWriteLocks - how to safely acquire write lock?

    - by Andrzej Doyle
    I am using in my code at the moment a ReentrantReadWriteLock to synchronize access over a tree-like structure. This structure is large, and read by many threads at once with occasional modifications to small parts of it - so it seems to fit the read-write idiom well. I understand that with this particular class, one cannot elevate a read lock to a write lock, so as per the Javadocs one must release the read lock before obtaining the write lock. I've used this pattern successfully in non-reentrant contexts before. What I'm finding however is that I cannot reliably acquire the write lock without blocking forever. Since the read lock is reentrant and I am actually using it as such, the simple code lock.getReadLock().unlock(); lock.getWriteLock().lock() can block if I have acquired the readlock reentrantly. Each call to unlock just reduces the hold count, and the lock is only actually released when the hold count hits zero. EDIT to clarify this, as I don't think I explained it too well initially - I am aware that there is no built-in lock escalation in this class, and that I have to simply release the read lock and obtain the write lock. My problem is/was that regardless of what other threads are doing, calling getReadLock().unlock() may not actually release this thread's hold on the lock if it acquired it reentrantly, in which case the call to getWriteLock().lock() will block forever as this thread still has a hold on the read lock and thus blocks itself. For example, this code snippet will never reach the println statement, even when run singlethreaded with no other threads accessing the lock: final ReadWriteLock lock = new ReentrantReadWriteLock(); lock.getReadLock().lock(); // In real code we would go call other methods that end up calling back and // thus locking again lock.getReadLock().lock(); // Now we do some stuff and realise we need to write so try to escalate the // lock as per the Javadocs and the above description lock.getReadLock().unlock(); // Does not actually release the lock lock.getWriteLock().lock(); // Blocks as some thread (this one!) holds read lock System.out.println("Will never get here"); So I ask, is there a nice idiom to handle this situation? Specifically, when a thread that holds a read lock (possibly reentrantly) discovers that it needs to do some writing, and thus wants to "suspend" its own read lock in order to pick up the write lock (blocking as required on other threads to release their holds on the read lock), and then "pick up" its hold on the read lock in the same state afterwards? Since this ReadWriteLock implementation was specifically designed to be reentrant, surely there is some sensible way to elevate a read lock to a write lock when the locks may be acquired reentrantly? This is the critical part that means the naive approach does not work.

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  • Updating fields of values in a ConcurrentDictionary

    - by rboarman
    I am trying to update entries in a ConcurrentDictionary something like this: class Class1 { public int Counter { get; set; } } class Test { private ConcurrentDictionary<int, Class1> dict = new ConcurrentDictionary<int, Class1>(); public void TestIt() { foreach (var foo in dict) { foo.Value.Counter = foo.Value.Counter + 1; // Simplified example } } } Essentially I need to iterate over the dictionary and update a field on each Value. I understand from the documentation that I need to avoid using the Value property. Instead I think I need to use TryUpdate except that I don’t want to replace my whole object. Instead, I want to update a field on the object. After reading this blog entry on the PFX team blog: Perhaps I need to use AddOrUpdate and simply do nothing in the add delegate. Does anyone have any insight as to how to do this?

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  • Android 2.1 GoogleMaps ItemizedOverlay ConcurrentModificationException

    - by Soumya Simanta
    Hi, I cannot figure out the origin of the ConcurrentModificationException. In my activity I'm calling updateMapOverlay(). I'm also calling updateMapOverlay() inside another Thread (a TimerTask) that is invoked on regular intervals. I'm taking the appropriate locks when invoking updateMapOverlay() from both the threads. Is this problem being caused because I'm invoking updateMapOverlay from inside a non-UI thread (i.e., TimerTask). Has anyone else faced a similar issue ? private void updateMapOverlay() { this.itemizedOverlay.refreshItems(createOverlayItemsList()); List<Overlay> overlays = mapView.getOverlays(); overlays.clear(); overlays.add(cotItemizedOverlay); this.mapview.invalidate(); } Thanks. Exception: W/dalvikvm(10641): threadid=3: thread exiting with uncaught exception (group=0x4001b180) E/AndroidRuntime(10641): Uncaught handler: thread main exiting due to uncaught exception E/AndroidRuntime(10641): java.util.ConcurrentModificationException E/AndroidRuntime(10641): at java.util.AbstractList$SimpleListIterator.next(AbstractList.java:64) E/AndroidRuntime(10641): at com.google.android.maps.OverlayBundle.draw(OverlayBundle.java:41) E/AndroidRuntime(10641): at com.google.android.maps.MapView.onDraw(MapView.java:494) E/AndroidRuntime(10641): at android.view.View.draw(View.java:6535) E/AndroidRuntime(10641): at android.view.ViewGroup.drawChild(ViewGroup.java:1531) E/AndroidRuntime(10641): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime(10641): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime(10641): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime(10641): at android.view.View.draw(View.java:6538) E/AndroidRuntime(10641): at android.widget.FrameLayout.draw(FrameLayout.java:352) E/AndroidRuntime(10641): at android.view.ViewGroup.drawChild(ViewGroup.java:1531) E/AndroidRuntime(10641): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime(10641): at android.view.ViewGroup.drawChild(ViewGroup.java:1529) E/AndroidRuntime(10641): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258) E/AndroidRuntime(10641): at android.view.View.draw(View.java:6538) E/AndroidRuntime(10641): at android.widget.FrameLayout.draw(FrameLayout.java:352) E/AndroidRuntime(10641): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1830) E/AndroidRuntime(10641): at android.view.ViewRoot.draw(ViewRoot.java:1349) E/AndroidRuntime(10641): at android.view.ViewRoot.performTraversals(ViewRoot.java:1114) E/AndroidRuntime(10641): at android.view.ViewRoot.handleMessage(ViewRoot.java:1633) E/AndroidRuntime(10641): at android.os.Handler.dispatchMessage(Handler.java:99) E/AndroidRuntime(10641): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime(10641): at android.app.ActivityThread.main(ActivityThread.java:4363) E/AndroidRuntime(10641): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime(10641): at java.lang.reflect.Method.invoke(Method.java:521) E/AndroidRuntime(10641): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) E/AndroidRuntime(10641): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) E/AndroidRuntime(10641): at dalvik.system.NativeStart.main(Native Method) I/Process ( 95): Sending signal. PID: 10641 SIG: 3

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  • Can I query DOM Document with xpath expression from multiple threads safely?

    - by Dan
    I plan to use dom4j DOM Document as a static cache in an application where multiples threads can query the document. Taking into the account that the document itself will never change, is it safe to query it from multiple threads? I wrote the following code to test it, but I am not sure that it actually does prove that operation is safe? package test.concurrent_dom; import org.dom4j.Document; import org.dom4j.DocumentException; import org.dom4j.DocumentHelper; import org.dom4j.Element; import org.dom4j.Node; /** * Hello world! * */ public class App extends Thread { private static final String xml = "<Session>" + "<child1 attribute1=\"attribute1value\" attribute2=\"attribute2value\">" + "ChildText1</child1>" + "<child2 attribute1=\"attribute1value\" attribute2=\"attribute2value\">" + "ChildText2</child2>" + "<child3 attribute1=\"attribute1value\" attribute2=\"attribute2value\">" + "ChildText3</child3>" + "</Session>"; private static Document document; private static Element root; public static void main( String[] args ) throws DocumentException { document = DocumentHelper.parseText(xml); root = document.getRootElement(); Thread t1 = new Thread(){ public void run(){ while(true){ try { sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } Node n1 = root.selectSingleNode("/Session/child1"); if(!n1.getText().equals("ChildText1")){ System.out.println("WRONG!"); } } } }; Thread t2 = new Thread(){ public void run(){ while(true){ try { sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } Node n1 = root.selectSingleNode("/Session/child2"); if(!n1.getText().equals("ChildText2")){ System.out.println("WRONG!"); } } } }; Thread t3 = new Thread(){ public void run(){ while(true){ try { sleep(3); } catch (InterruptedException e) { e.printStackTrace(); } Node n1 = root.selectSingleNode("/Session/child3"); if(!n1.getText().equals("ChildText3")){ System.out.println("WRONG!"); } } } }; t1.start(); t2.start(); t3.start(); System.out.println( "Hello World!" ); } }

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  • Cannot use READPAST in snapshot isolation mode

    - by Marcus
    I have a process which is called from multiple threads which does the following: Start transaction Select unit of work from work table with by finding the next row where IsProcessed=0 with hints (UPDLOCK, HOLDLOCK, READPAST) Process the unit of work (C# and SQL stored procedures) Commit the transaction The idea of this is that a thread dips into the pool for the "next" piece of work, and processes it, and the locks are there to ensure that a single piece of work is not processed twice. (the order doesn't matter). All this has been working fine for months. Until today that is, when I happened to realise that despite enabling snapshot isolation and making it the default at the database level, the actual transaction creation code was manually setting an isolation level of "ReadCommitted". I duly changed that to "Snapshot", and of course immediately received the "You can only specify the READPAST lock in the READ COMMITTED or REPEATABLE READ" error message. Oops! The main reason for locking the row was to "mark the row" in such a way that the "mark" would be removed when the transaction that applied the mark was committed and the lock seemed to be the best way to do this, since this table isn't read otherwise except by these threads. If I were to use the IsProcessed flag as the lock, then presumably I would need to do the update first, and then select the row I just updated, but I would need to employ the NOLOCK flag to know whether any other thread had set the flag on a row. All sounds a bit messy. The easiest option would be to abandon the snapshot isolation mode altogether, but the design of step #3 requires it. Any bright ideas on the best way to resolve this problem? Thanks Marcus

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  • Multithreading/Parallel Processing in PHP

    - by manyxcxi
    I have a PHP script that will generate a report using PHPExcel from data queried from a MySQL DB. Currently, it is linear in processing in that it gets the data back from MySQL, reads in the Excel template, writes the data to the template, then outputs it. I have optimized the code to the point that the data is only iterated over once, and there is very little processing done on the PHP side. The query returns hundreds of lines in less than .001 seconds, so it is running fast enough. After some timing I have found my bottlenecks to be (surprise, surprise) reading the template and writing the output. I would like to do this: Spawn a thread/process to read the template Spawn a thread/process to fetch the data Return back to parent thread - Parent thread will wait until both are complete Proceed on as normal My main questions are is this possible, is it worth it? If yes to both, how would you tackle it? Also, it is PHP 5 on CentOS

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  • Do the ‘up to date’ guarantees for values of Java's final fields extend to indirect references?

    - by mattbh
    The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed? I'm looking for clarification of the semantics of the Java Memory Model and language spec, rather than alternative solutions like synchronization. My dream answer would be a yes or no, with a reference to the relevant text.

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  • Java LockSupport Memory Consistency

    - by Lachlan
    Java 6 API question. Does calling LockSupport.unpark(thread) have a happens-before relationship to the return from LockSupport.park in the just-unparked thread? I strongly suspect the answer is yes, but the Javadoc doesn't seem to mention it explicitly.

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  • atomic writes to ehcache

    - by Jacques René Mesrine
    Context I am storing a java.util.List inside ehcache. Key(String) --> List<UserDetail> The ordered List contains a Top 10 ranking of my most active users. Problem Concurrent 3rd party clients might be requesting for this list. I have a requirement to be as current as possible with regards to the ranking. Thus if the ranking is changed due the activities of users, the ordered List in the cache must not be left stale for very long. Once I've recalculated a new List, I want to replace the one in cache immediately. Consider a busy scenario whereby multiple concurrent clients are requesting for the ranking; how can I replace the cache item in an fashion such that: Clients can continue to pull a possibly stale snapshot. They should never get a null value. There will only be 1 server thread that writes to the cache.

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  • Java AtomicInteger: what are the differences between compareAndSet and weakCompareAndSet?

    - by WizardOfOdds
    (note that this question is not about CAS, it's about the "May fail spuriously" Javadoc). The only difference in the Javadoc between these two methods from the AtomicInteger class is that the weakCompareAndSet contains the comment: "May fail spuriously". Now unless my eyes are cheated by some spell, both method do look to be doing exactly the same: public final boolean compareAndSet(int expect, int update) { return unsafe.compareAndSwapInt(this, valueOffset, expect, update); } /* ... * May fail spuriously. */ public final boolean weakCompareAndSet(int expect, int update) { return unsafe.compareAndSwapInt(this, valueOffset, expect, update); } So I realize that "May" doesn't mean "Must" but then why don't we all start adding this to our codebase: public void doIt() { a(); } /** * May fail spuriously */ public void weakDoIt() { a(); } I'm really confused with that weakCompareAndSet() that appears to do the same as the compareAndSet() yet that "may fail spuriously" while the other can't. Apparently the "weak" and the "spurious fail" are in a way related to "happens-before" ordering but I'm still very confused by these two AtomicInteger (and AtomicLong etc.) methods: because apparently they call exactly the same unsafe.compareAndSwapInt method. I'm particularly confused in that AtomicInteger got introduced in Java 1.5, so after the Java Memory Model change (so it is obviously not something that could "fail spuriously in 1.4" but whose behavior changed to "shall not fail spuriously in 1.5").

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  • Java Memory Model: reordering and concurrent locks

    - by Steffen Heil
    Hi The java meomry model mandates that synchronize blocks that synchronize on the same monitor enforce a before-after-realtion on the variables modified within those blocks. Example: // in thread A synchronized( lock ) { x = true; } // in thread B synchronized( lock ) { System.out.println( x ); } In this case it is garanteed that thread B will see x==true as long as thread A already passed that synchronized-block. Now I am in the process to rewrite lots of code to use the more flexible (and said to be faster) locks in java.util.concurrent, especially the ReentrantReadWriteLock. So the example looks like this: // in thread A synchronized( lock ) { lock.writeLock().lock(); x = true; lock.writeLock().unlock(); } // in thread B synchronized( lock ) { lock.readLock().lock(); System.out.println( x ); lock.readLock().unlock(); } However, I have not seen any hints within the memory model specification that such locks also imply the nessessary ordering. Looking into the implementation it seems to rely on the access to volatile variables inside AbstractQueuedSynchronizer (for the sun implementation at least). However this is not part of any specification and moreover access to non-volatile variables is not really condsidered covered by the memory barrier given by these variables, is it? So, here are my questions: Is it safe to assume the same ordering as with the "old" synchronized blocks? Is this documented somewhere? Is accessing any volatile variable a memory barrier for any other variable? Regards, Steffen

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  • How to use Castle Windsor with ASP.Net web forms?

    - by Xian
    I am trying to wire up dependency injection with Windsor to standard asp.net web forms. I think I have achieved this using a HttpModule and a CustomAttribute (code shown below), although the solution seems a little clunky and was wondering if there is a better supported solution out of the box with Windsor? There are several files all shown together here // index.aspx.cs public partial class IndexPage : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { Logger.Write("page loading"); } [Inject] public ILogger Logger { get; set; } } // WindsorHttpModule.cs public class WindsorHttpModule : IHttpModule { private HttpApplication _application; private IoCProvider _iocProvider; public void Init(HttpApplication context) { _application = context; _iocProvider = context as IoCProvider; if(_iocProvider == null) { throw new InvalidOperationException("Application must implement IoCProvider"); } _application.PreRequestHandlerExecute += InitiateWindsor; } private void InitiateWindsor(object sender, System.EventArgs e) { Page currentPage = _application.Context.CurrentHandler as Page; if(currentPage != null) { InjectPropertiesOn(currentPage); currentPage.InitComplete += delegate { InjectUserControls(currentPage); }; } } private void InjectUserControls(Control parent) { if(parent.Controls != null) { foreach (Control control in parent.Controls) { if(control is UserControl) { InjectPropertiesOn(control); } InjectUserControls(control); } } } private void InjectPropertiesOn(object currentPage) { PropertyInfo[] properties = currentPage.GetType().GetProperties(); foreach(PropertyInfo property in properties) { object[] attributes = property.GetCustomAttributes(typeof (InjectAttribute), false); if(attributes != null && attributes.Length > 0) { object valueToInject = _iocProvider.Container.Resolve(property.PropertyType); property.SetValue(currentPage, valueToInject, null); } } } } // Global.asax.cs public class Global : System.Web.HttpApplication, IoCProvider { private IWindsorContainer _container; public override void Init() { base.Init(); InitializeIoC(); } private void InitializeIoC() { _container = new WindsorContainer(); _container.AddComponent<ILogger, Logger>(); } public IWindsorContainer Container { get { return _container; } } } public interface IoCProvider { IWindsorContainer Container { get; } }

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  • How is spin lock implemented under the hood?

    - by httpinterpret
    This is a lock that can be held by only one thread of execution at a time. An attempt to acquire the lock by another thread of execution makes the latter loop until the lock is released. How does it handle the case when two threads try to acquire the lock exactly the same time? I think this question also applies to various of other mutex implementation.

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  • Lost Update Anomaly in Sql Server Update Command

    - by Javed
    Hi, I am very much confused. I have a transaction in ReadCommitted Isolation level. Among other things I am also updating a counter value in it, something similar to below: Update tblCount set counter = counter + 1 My application is a desktop application and this transaction happens to occur quite frequently and concurrently. We recently noticed an error that sometimes the counter value doesn't get updated or is missed. We also insert one record on each counter update so we are sure that records have been inserted but somehow counter fails to update. This happens once in 2000 simulaneous transactions. I seriously doubt it is a lost update anomaly I am facing but if you look at the command above, it's just update the counter from its own value: if I have started a transaction and the transaction has reached this statement, it should have locked the row. This should not cause lost update, but it's happening somehow. Is the thing that this update command works in two parts? Like first it reads the counter value (during which it doesn't get the exclusive lock) and then writes the new calculated value (when it does get an exclusive lock)? Please help, I have got really confused.

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  • Java 1.4 singleton containing a mutable field

    - by Philippe
    Hi, I'm working on a legacy Java 1.4 project, and I have a factory that instantiates a csv file parser as a singleton. In my csv file parser, however, I have a HashSet that will store objects created from each line of my CSV file. All that will be used by a web application, and users will be uploading CSV files, possibly concurrently. Now my question is : what is the best way to prevent my list of objects to be modified by 2 users ? So far, I'm doing the following : final class MyParser { private File csvFile = null; private static Set myObjects = Collections.synchronizedSet(new HashSet); public synchronized void setFile(File file) { this.csvFile = file; } public void parse() FileReader fr = null; try { fr = new FileReader(csvFile); synchronized(myObjects) { myObjects.clear(); while(...) { // foreach line of my CSV, create a "MyObject" myObjects.add(new MyObject(...)); } } } catch (Exception e) { //... } } } Should I leave the lock only on the myObjects Set, or should I declare the whole parse() method as synchronized ? Also, how should I synchronize - both - the setting of the csvFile and the parsing ? I feel like my actual design is broken because threads could modify the csv file several times while a possibly long parse process is running. I hope I'm being clear enough, because myself am a bit confused on those multi-synchronization issues. Thanks ;-)

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