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• Spinlocks, How Much Useful Are They?

  - by unknown

  How often do you find yourself actually using spinlocks in your code? How common is it to come across a situation where using a busy loop actually outperforms the usage of locks? Personally, when I write some sort of code that requires thread safety, I tend to benchmark it with different synchronization primitives, and as far as it goes, it seems like using locks gives better performance than using spinlocks. No matter for how little time I actually hold the lock, the amount of contention I receive when using spinlocks is far greater than the amount I get from using locks (of course, I run my tests on a multiprocessor machine). I realize that it's more likely to come across a spinlock in "low-level" code, but I'm interested to know whether you find it useful in even a more high-level kind of programming?

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• Convert Byte Array into Bitset

  - by Unknown

  I have a byte array generated by a random number generator. I want to put this into the STL bitset. Unfortunately, it looks like Bitset only supports the following constructors: A string of 1's and 0's like "10101011" An unsigned long. (my byte array will be longer) The only solution I can think of now is to read the byte array bit by bit and make a string of 1's and 0's. Does anyone have a more efficient solution?

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• DatagGridViewColumn.DataPropertyName to an array element?

  - by unknown

  Hi there, I'm using a DataGridView binding its datasource to a List, and specifying the properties for each column. An example would be: DataGridViewTextBoxColumn colConcept = new DataGridViewTextBoxColumn(); DataGridViewCell cell4 = new DataGridViewTextBoxCell(); colConcept.CellTemplate = cell4; colConcept.Name = "concept"; colConcept.HeaderText = "Concept"; colConcept.DataPropertyName = "Concept"; colConcept.Width = 200; this.dataGridViewBills.Columns.Add(colConcept); {... assign other colums...} And finally this.dataGridViewBills.DataSource=billslist; //billslist is List<Bill> Obviously Class Bill has a Property called Concept, as well as one Property for each column. Well, now my problem, is that Bill should have and Array/List/whateverdynamicsizecontainer of strings called Years. Let's assume that every Bill will have the same Years.Count, but this only known at runtime.Thus, I can't specify properties like Bill.FirstYear to obtain Bill.Years[0], Bill.SecondYear to obtain Bills.Years[1]... etc... and bind it to each column. The idea, is that now I want to have a grid with dynamic number of colums (known at runtime), and each column filled with a string from the Bill.Years List. I can make a loop to add columns to the grid at runtime depending of Bill.Years.Count, but is possible to bind them to each of the strings that the Bill.Years List contains??? I'm not sure if I'm clear enough. The result ideally would be something like this, for 2 bills on the list, and 3 years for each bill: --------------------------------------GRID HEADER------------------------------- NAME CONCEPT YEAR1 YEAR2 YEAR3 --------------------------------------GRID VALUES------------------------------- Bill1 Bill1.Concept Bill1.Years[0] Bill1.Years[1] Bill1.Years[2] Bill2 Bill2.Concept Bill2.Years[0] Bill2.Years[1] Bill2.Years[2] I can always forget the datasource, and write each cell manually, as the MSFlexGrid used to like, but if possible, I would like to use the binding capabilities of the DataGridView. Any ideas? Thanks a lot.

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• Text message (SMS) verification for signups

  - by Unknown

  I have seen a disturbing trend where websites are starting to require verification sent to cellphones by text message (SMS). Gmail and Facebook are two of them. What I want to know are the following: Is it a good idea to start requiring cellphones instead of emails now? How do I do it on my own website? Edit Here are some of my new questions on the topic in response to the answers: I see that most of you are saying that SMS registrations is ok. But what about the people who don't have cell phones? And why is it accepted to give out your cell phone information freely? Do those big providers really pay per message to a gateway service? Is it not possible to set up a server with the correct SMS software, or at least buy a subscription directly instead of having a middleman?

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• OpenCV to use in memory buffers or file pointers

  - by The Unknown

  The two functions in openCV cvLoadImage and cvSaveImage accept file path's as arguments. For example, when saving a image it's cvSaveImage("/tmp/output.jpg", dstIpl) and it writes on the disk. Is there any way to feed this a buffer already in memory? So instead of a disk write, the output image will be in memory. I would also like to know this for both cvSaveImage and cvLoadImage (read and write to memory buffers). Thanks! My goal is to store the Encoded (jpeg) version of the file in Memory. Same goes to cvLoadImage, I want to load a jpeg that's in memory in to the IplImage format.

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• Java compilers or JVM languages that support goto?

  - by unknown

  Is there a java compiler flag that allows me to use goto as a valid construct? If not, are there any third-party java compilers that supports goto? If not, are there any other languages that support goto while at the same time can easily call methods written in Java? The reason is I'm making a language that is implemented in Java. Gotos are an important part of my language; I want to be able to compile it to native or JVM bytecode, although it has to be able to easily use Java libraries (ie. C supports goto, but to use it I'd have to rewrite the libraries in C). I want to generate C or Java, etc source files, and not bytecode or machine code. I'm using a third-party compiler to do that.

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• How does Gmail do comet on Opera?

  - by Unknown

  I would like to know how Gmail (or anyone else) does comet on Opera. Here is what I know so far from my experiments. It doesn't use the event-source tag which is broken in Opera 10.51. It doesn't use iframe which displays a spinning throbber and a busy mouse cursor. It doesn't use responseText on xmlhttprequest when readyState = 3 which is known to be broken on Opera. I tried seeing how it was done in mibbit and etherpad, and I found that they both use long-polling.

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• How to stop GHC from generating intermediate files?

  - by unknown

  When compiling a haskell source file via ghc --make foo.hs GHC always leaves behind a variety of intermediate files other than foo.exe. These are foo.hi and foo.o. I often end up having to delete the .hi and .o files to avoid cluttering up the folders. Is there a command line option for GHC not to leave behind its intermediate files? (When asked on #haskell, the best answer I got was ghc --make foo.hs && rm foo.hi foo.o.

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• Strange beep when using cout

  - by Unknown

  Hello everyone, today when I was working on some code of mine I came across a beeping sound when printing a buffer to the screen. Here's the mysterious character that produces the beep: '' I don't know if you can see it, but my computer beeps when I try to print it like this: cout<<(char)7<<endl; Another point of interest is that the 'beep' doesn't originate from my on board beeper, but from my headphone/speaker Is this just my computer or there something wrong with the cout function? EDIT: But then why does printing this character produce the beep sound? does that mean that I could send other such characters through the cout function to produce different effects?

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• How to (legitimately) access files after putting self into chrooted sandbox?

  - by unknown google user

  Changing a Linux C++ program which gives the user limited file access. Thus the program chroots itself to a sandbox with the files the user can get at. All worked well. Now, however, the program needs to access some files for its own needs (not the user's) but they are outside the sandbox. I know chroot allows access to files opened before the chroot but in this case the needed files could a few among many hundreds so it is obviously impractical to open them all just for the couple that might be required. Is there any way to get at the files?

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• throw exception

  - by Unknown

  Why can't you throw an InterruptedException in the following way: try { System.in.wait(5) //Just an example } catch (InterruptedException exception) { exception.printStackTrace(); //On this next line I am confused as to why it will not let me throw the exception throw exception; } I went to http://java24hours.com, but it didn't tell me why I couldn't throw an InterruptedException. If anyone knows why, PLEASE tell me! I'm desperate! :S

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• Python interpreter with Linux Screen

  - by Unknown

  I was working with Python with a Linux terminal screen. When I typed: help(somefunction) It printed the appropriate output, but then my screen was stuck, and at the bottom of the terminal was "(end)". How do I get unstuck? Thanks in advance.

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• Get e-mail Contacts from exchange 2007 in C#

  - by unknown (google)

  Is anybody know how to pull contact list from Microsoft Exchange 2007 using c#?

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• Please explain syntax rules and scope for "typedef"

  - by unknown google user

  What are the rules? OTOH the simple case seems to imply the new type is the last thing on a line. Like here Uchar is the new type. typedef unsigned char Uchar; But a function pointer is completely different. Here the new type is pFunc: typedef int (*pFunc) (int); I can't think of any other examples offhand but I have come across some very confusing usages. So are there rules or are people just suppose to know from experience that this is how it is done because they have seen it done this way before? ALSO: What is the scope of a typedef. Thanks to everyone.

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• initialise a var in scala

  - by user unknown

  I have a class where I like to initialize my var by reading a configfile, which produces intermediate objects/vals, which I would like to group and hide in a method. Here is the bare minimum of the problem - I call the ctor with a param i, in reality a File to parse, and the init-method generates the String s, in reality more complicated than here, with a lot of intermediate objects being created: class Foo (val i: Int) { var s : String; def init () { s = "" + i } init () } This will produce the error: class Foo needs to be abstract, since variable s is not defined. In this example it is easy to solve by setting the String to "": var s = "";, but in reality the object is more complex than String, without an apropriate Null-implementation. I know, I can use an Option, which works for more complicated things than String too: var s : Option [String] = None def init () { s = Some ("" + i) } or I can dispense with my methodcall. Using an Option will force me to write Some over and over again, without much benefit, since there is no need for a None else than to initialize it that way I thought I could. Is there another way to achieve my goal?

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• Should I learn Haskell or F# if I already know OCaml?

  - by Unknown

  I am wondering if I should continue to learn OCaml or switch to F# or Haskell. Here are the criteria I am most interested in: Longevity Which language will last longer? I don't want to learn something that might be abandoned in a couple years by users and developers. Will Inria, Microsoft, University of Glasgow continue to support their respective compilers for the long run? Practicality Articles like this make me afraid to use Haskell. A hash table is the best structure for fast retrieval. Haskell proponents in there suggest using Data.Map which is a binary tree. I don't like being tied to a bulky .NET framework unless the benefits are large. I want to be able to develop more than just parsers and math programs. Well Designed I like my languages to be consistent. Please support your opinion with logical arguments and citations from articles. Thank you.

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• Make datalist into 3 x 3

  - by unknown

  This is my code behind for products page. The prodblem is that my datalist will fill in new items whenever I add a new object in the website. So may I know how to add the codes in so that I can make the datalist into 3x3. Thanks. Code behind Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim Product As New Product Dim DataSet As New DataSet Dim pds As New PagedDataSource DataSet = Product.GetProduct Session("Dataset") = DataSet pds.PageSize = 4 pds.AllowPaging = True pds.CurrentPageIndex = 1 Session("Page") = pds If Not Page.IsPostBack Then UpdateDatabind() End If End Sub Sub UpdateDatabind() Dim DataSet As DataSet = Session("DataSet") If DataSet.Tables(0).Rows.Count > 0 Then pds.DataSource = DataSet.Tables(0).DefaultView Session("Page") = pds dlProducts.DataSource = DataSet.Tables(0).DefaultView dlProducts.DataBind() lblCount.Text = DataSet.Tables(0).Rows.Count End If End Sub Private Sub dlProducts_UpdateCommand(source As Object, e As System.Web.UI.WebControls.DataListCommandEventArgs) Handles dlProducts.UpdateCommand dlProducts.DataBind() End Sub Public Sub PrevNext_Command(source As Object, e As CommandEventArgs) Dim pds As PagedDataSource = Session("Page") Dim CurrentPage = pds.CurrentPageIndex If e.CommandName = "Previous" Then If CurrentPage < 1 Or CurrentPage = pds.IsFirstPage Then CurrentPage = 1 Else CurrentPage -= 1 End If UpdateDatabind() ElseIf e.CommandName = "Next" Then If CurrentPage > pds.PageCount Or CurrentPage = pds.IsLastPage Then CurrentPage = CurrentPage Else CurrentPage += 1 End If UpdateDatabind() End If Response.Redirect("Products.aspx?PageIndex=" & CurrentPage) End Sub this is my code for product.vb Public Function GetProduct() As DataSet Dim strConn As String strConn = ConfigurationManager.ConnectionStrings("HomeFurnitureConnectionString").ToString Dim conn As New SqlConnection(strConn) Dim strSql As String 'strSql = "SELECT * FROM Product p INNER JOIN ProductDetail pd ON p.ProdID = pd.ProdID " & _ ' "WHERE pd.PdColor = (SELECT min(PdColor) FROM ProductDetail as pd1 WHERE pd1.ProdID = p.ProdID)" Dim cmd As New SqlCommand(strSql, conn) Dim ds As New DataSet Dim da As New SqlDataAdapter(cmd) conn.Open() da.Fill(ds) conn.Close() Return ds End Function

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• power and modulo on the fly for big numbers

  - by user unknown

  I raise some basis b to the power p and take the modulo m of that. Let's assume b=55170 or 55172 and m=3043839241 (which happens to be the square of 55171). The linux-calculator bc gives the results (we need this for control): echo "p=5606;b=55171;m=b*b;((b-1)^p)%m;((b+1)^p)%m" | bc 2734550616 309288627 Now calculating 55170^5606 gives a somewhat large number, but since I have to do a modulooperation, I can circumvent the usage of BigInt, I thought, because of: (a*b) % c == ((a%c) * (b%c))%c i.e. (9*7) % 5 == ((9%5) * (7%5))%5 => 63 % 5 == (4 * 2) %5 => 3 == 8 % 5 ... and a^d = a^(b+c) = a^b * a^c, therefore I can divide b+c by 2, which gives, for even or odd ds d/2 and d-(d/2), so for 8^5 I can calculate 8^2 * 8^3. So my (defective) method, which always cut's off the divisor on the fly looks like that: def powMod (b: Long, pot: Int, mod: Long) : Long = { if (pot == 1) b % mod else { val pot2 = pot/2 val pm1 = powMod (b, pot, mod) val pm2 = powMod (b, pot-pot2, mod) (pm1 * pm2) % mod } } and feeded with some values, powMod (55170, 5606, 3043839241L) res2: Long = 1885539617 powMod (55172, 5606, 3043839241L) res4: Long = 309288627 As we can see, the second result is exactly the same as the one above, but the first one looks quiet different. I'm doing a lot of such calculations, and they seem to be accurate as long as they stay in the range of Int, but I can't see any error. Using a BigInt works as well, but is way too slow: def calc2 (n: Int, pri: Long) = { val p: BigInt = pri val p3 = p * p val p1 = (p-1).pow (n) % (p3) val p2 = (p+1).pow (n) % (p3) print ("p1: " + p1 + " p2: " + p2) } calc2 (5606, 55171) p1: 2734550616 p2: 309288627 (same result as with bc) Can somebody see the error in powMod?

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• Database for Large number of 1kB data chunks (MySQL?)

  - by The Unknown

  I have a very large dataset, each item in the dataset being roughly 1kB in size. The data needs to be queried rapidly by many applications distributed over a network. The dataset has more than a million items (so 500 million+ 1kB data chunks). What would be the best method to storing this dataset (need to allow adding more items, and reading them rapidly, but never modifying already added data)? Would using a MySQL DB using the binary blob format be appropriate? Or should each of these be stored as files on a file system? edit: the number is 1 million items now, but needs to be able to scale to well over 500 million items easily.

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• how to access jquery internal data?

  - by Unknown

  As you may or may not be aware as of jQuery 1.7 the whole event system was rewritten from the ground up. The codebase is much faster and with the new .on() method there is a lot of uniformity to wiring up event handlers. One used to be able to access the internal events data and investiate what events are registered on any given element, but recently this internal information has been hidden based on the following scenario... It seems that the "private" data is ALWAYS stored on the .data(jQuery.expando) - For "objects" where the deletion of the object should also delete its caches this makes some sense. In the realm of nodes however, I think we should store these "private" members in a separate (private) cache so that they don't pollute the object returned by $.fn.data()" Although I agree with the above change to hide the internal data, I have found having access to this information can be helpful for debugging and unit testing. What was the new way of getting the internal jquery event object in jQuery 1.7?

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• Any reason NOT to slap the 'synchronized' keyword everywhere?

  - by unknown

  In my java project, almost every non-static method I've written is synchronized. I've decided to fix up some code today, by removing most of the synchronized keywords. Right there I created several threading issues that took quite a while to fix, with no increase in performance. In the end I reverted everything. I don't see anyone else writing code with "synchronized" everywhere. So is there any reason I shouldn't have "synchronized" everywhere? What if I don't care too much about performance (ie. the method isn't called more than once every few seconds)?

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• Nginx: Rewrite rule for subfolder

  - by gryzzly

  Hello, I have a subdomain where I want to keep projects I am working on, in order to show these projects to clients. Here is the configuraion file from /etc/nginx/sites-available/projects: server { listen 80; server_name projects.example.com; access_log /var/log/nginx/projects.example.com.access.log; error_log /var/log/nginx/projects.example.com.error.log; location / { root /var/www/projects; index index.html index.htm index.php; } location /example2.com { root /var/www/projects/example2.com; auth_basic "Stealth mode"; auth_basic_user_file /var/www/projects/example2.com/htpasswd; } location /example3.com/ { index index.php; if (-f $request_filename) { break; } if (!-f $request_filename) { rewrite ^/example3\.com/(.*)$ /example3\.com/index.php?id=$1 last; break; } } location ~ \.php { root /var/www/mprojects; fastcgi_pass 127.0.0.1:9000; fastcgi_index index.php; fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name; include /etc/nginx/fastcgi_params; } } I want to be able to place different php engines (wordpress, getsimple etc.) in subfolders. These engines have different querry parameters (id, q, url etc.) so in order to make preety URLs work I have to make a rewrite. However, above doesn't work. This is the response I get: Warning: Unknown: Filename cannot be empty in Unknown on line 0 Fatal error: Unknown: Failed opening required '' (include_path='.:/usr/local/lib/php') in Unknown on line 0 If I take out "location /example3.com/" rule, then everything works but with no preety URLs. Please help. The configuration is based on this post: http://stackoverflow.com/questions/2119736/cakephp-in-a-subdirectory-using-nginx-rewrite-rules I am using Ubuntu 9.10 and nginx/0.7.62 with php-fpm.

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• Memcached session manager in Azure: Connection gets forcibly closed

  - by Edgar Pérez

  I am using Memcached Session Manager to handle Tomcat sessions in non-sticky mode. My deployment in Azure consists of a Worker Role with two instances which connect to an Azure VM running my Memcached server. Everything works pretty well, my session is persisted and retrieved by any of the two instances transparently. The problem arises when the session is idle for about 4 minutes; everything points out that the Azure Loadbalancer is closing the spymemcached connection to the VM after some period of inactivity. My MSM configuration is this: <Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager" memcachedNodes="n1:my-azure-vm.cloudapp.net:11211" sticky="false" sessionBackupAsync="false" sessionBackupTimeout="10000" lockingMode="uriPattern:/path1|/path2" requestUriIgnorePattern=".*\.(ico|png|gif|jpg|css|js|ttf|eot|svg|woff)$" transcoderFactoryClass="de.javakaffee.web.msm.serializer.kryo.KryoTranscoderFactory" customConverter="de.javakaffee.web.msm.serializer.kryo.HibernateCollectionsSerializerFactory"/> The stacktrace printed by the spymemcached client is this: INFO net.spy.memcached.MemcachedConnection: Reconnecting due to exception on {QA sa=/10.194.132.206:13000, #Rops=1, #Wops=0, #iq=0, topRop=net.spy.memcached.protocol.binary.StoreOperationImpl@1d95da8, topWop=null, toWrite=0, interested=1} java.io.IOException: An existing connection was forcibly closed by the remote host at sun.nio.ch.SocketDispatcher.read0(Native Method) at sun.nio.ch.SocketDispatcher.read(Unknown Source) at sun.nio.ch.IOUtil.readIntoNativeBuffer(Unknown Source) at sun.nio.ch.IOUtil.read(Unknown Source) at sun.nio.ch.SocketChannelImpl.read(Unknown Source) at net.spy.memcached.MemcachedConnection.handleReads (MemcachedConnection.java:303) at net.spy.memcached.MemcachedConnection.handleIO (MemcachedConnection.java:264) at net.spy.memcached.MemcachedConnection.handleIO (MemcachedConnection.java:184) at net.spy.memcached.MemcachedClient.run(MemcachedClient.java:1298) Given this idle time limitation in Azure, is there any other way to make MSM work in the azure cloud?

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• Hudson plugin problem

  - by user27644

  Hi. I've created almost the same plugin as JobTypeColumn. There is only one difference - it shows job description instead of job type. But after i can't add this column to my list view. I have an NullPointerException after i edited my config.xml manually. java.lang.NullPointerException at hudson.model.Descriptor.newInstancesFromHeteroList(Descriptor.java:626) at hudson.util.DescribableList.rebuildHetero(DescribableList.java:164) at hudson.model.ListView.submit(ListView.java:262) at hudson.model.View.doConfigSubmit(View.java:484) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:185) at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:101) at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:54) at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:74) at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492) at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:180) at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:30) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:492) at org.kohsuke.stapler.Stapler.invoke(Stapler.java:408) at org.kohsuke.stapler.Stapler.service(Stapler.java:117) at javax.servlet.http.HttpServlet.service(HttpServlet.java:45) at winstone.ServletConfiguration.execute(ServletConfiguration.java:249) at winstone.RequestDispatcher.forward(RequestDispatcher.java:335) at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:378) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:94) at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:304) at org.jvnet.hudson.plugins.monitoring.HudsonMonitoringFilter.doFilter(HudsonMonitoringFilter.java:31) at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:97) at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:86) at winstone.FilterConfiguration.execute(FilterConfiguration.java:195) at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368) at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47) at winstone.FilterConfiguration.execute(FilterConfiguration.java:195) at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368) at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84) at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76) at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164) at winstone.FilterConfiguration.execute(FilterConfiguration.java:195) at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:368) at winstone.RequestDispatcher.forward(RequestDispatcher.java:333) at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:244) at winstone.RequestHandlerThread.run(RequestHandlerThread.java:150) at java.lang.Thread.run(Unknown Source)

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