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• Can an application affect TCP retransmits

  - by sipwiz

  I'm troubleshooting some communications issues and in the network traces I am occasionally coming across TCP sequence errors. One example I've got is: Server to Client: Seq=3174, Len=50 Client to Server: Ack=3224 Server to Client: Seq=3224, Len=50 Client to Server: Ack=3224 Server to Client: Seq=3274, Len=10 Client to Server: Ack=3224, SLE=3274, SRE=3284 Packets 4 & 5 are recorded in the trace (which is from a router in between the client and server) at almost exactly the same time so they most likely crossed in transit. The TCP session has got out of sync with the client missing the last two transmissions from the server. Those two packets should have been retransmitted but they weren't, the next log in the trace is a RST packet from the Client 24 seconds after packet 6. My question is related to what could be responsible for the failure to retransmit the server data from packets 3 & 5? I would assume that the retransmit would be at the operating system level but is there anyway the application could influence it and stop it being sent? A thread blocking or put to sleep or something like that?

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• Unable to get data from a WCF client

  - by Scott

  I am developing a DLL that will provide sychronized time stamps to multiple applications running on the same machine. The timestamps are altered in a thread that uses a high performance timer and a scalar to provide the appearance of moving faster than real-time. For obvious reasons I want only 1 instance of this time library, and I thought I could use WCF for the other processes to connect to this and poll for timestamps whenever they want. When I connect however I never get a valid time stamp, just an empty DateTime. I should point out that the library does work. The original implementation was a single DLL that each application incorporated and each one was synced using windows messages. I'm fairly sure it has something to do with how I'm setting up the WCF stuff, to which I am still pretty new. Here are the contract definitions: public interface ITimerCallbacks { [OperationContract(IsOneWay = true)] void TimerElapsed(String id); } [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ITimerCallbacks))] public interface ISimTime { [OperationContract] DateTime GetTime(); } Here is my class definition: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] public class SimTimeServer: ISimTime The host setup: // set up WCF interprocess comms host = new ServiceHost(typeof(SimTimeServer), new Uri[] { new Uri("net.pipe://localhost") }); host.AddServiceEndpoint(typeof(ISimTime), new NetNamedPipeBinding(), "SimTime"); host.Open(); and the implementation of the interface function server-side: public DateTime GetTime() { if (ThreadMutex.WaitOne(20)) { RetTime = CurrentTime; ThreadMutex.ReleaseMutex(); } return RetTime; } Lastly the client-side implementation: Callbacks myCallbacks = new Callbacks(); DuplexChannelFactory pipeFactory = new DuplexChannelFactory(myCallbacks, new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/SimTime")); ISimTime pipeProxy = pipeFactory.CreateChannel(); while (true) { string str = Console.ReadLine(); if (str.ToLower().Contains("get")) Console.WriteLine(pipeProxy.GetTime().ToString()); else if (str.ToLower().Contains("exit")) break; }

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• Using `<List>` when dealing with pointers in C#.

  - by Gorchestopher H

  How can I add an item to a list if that item is essentially a pointer and avoid changing every item in my list to the newest instance of that item? Here's what I mean: I am doing image processing, and there is a chance that I will need to deal with images that come in faster than I can process (for a short period of time). After this "burst" of images I will rely on the fact that I can process faster than the average image rate, and will "catch-up" eventually. So, what I want to do is put my images into a <List> when I acquire them, then if my processing thread isn't busy, I can take an image from that list and hand it over. My issue is that I am worried that since I am adding the image "Image1" to the list, then filling "Image1" with a new image (during the next image acquisition) I will be replacing the image stored in the list with the new image as well (as the image variable is actually just a pointer). So, my code looks a little like this: while (!exitcondition) { if(ImageAvailabe()) { Image1 = AcquireImage(); ImgList.Add(Image1); } if(ImgList.Count 0) { ProcessEngine.NewImage(ImgList[0]); ImgList.RemoveAt(0); } } Given the above, how can I ensure that: - I don't replace all items in the list every time Image1 is modified. - I don't need to pre-declare a number of images in order to do this kind of processing. - I don't create a memory devouring monster. Any advice is greatly appreciated.

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• committing to a branch that's not checked out

  - by intuited

  I'm using git to version my home directories on a couple different machines. I'd like for them to each use separate branches and both pull from a common branch. So most commits should be made to that common branch, unless something specific to that machine is being committed, in which case the commit should go to the checked out, machine-specific branch. Switching branches is clearly not a very good option in this case. It's mentioned in this post that what I want to do is impossible, but I found that answer to be rather blunt and to perhaps not take into account the possibility of using the plumbing commands. Unfortunately I don't have enough reputation to comment on that thread. I rather suspect that there is some way to do this and am hoping to save myself an hour or few of questing for the answer by just asking you good folk. So is it possible to commit to a different branch without checking that branch out first? Ideally I'd like to use the index in the same way that git commit normally does.

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• How do I keep from running out of memory on graphics for an Android app?

  - by user279112

  I've been working on an Android app in Eclipse, and so far, my program hasn't really grown past midget size. However I've already run into an issue with an Out of Memory error. You see, I've been using graphics comprised solely of bitmaps and PNGs in this program, and recently, when I tried to add a little bit more functionality to the program (mainly including a few more bitmaps and causing an extra sprite to be created), it started crashing in the graphics thread's constructor - sprite's constructor. When I tracked the problem down, it turned out to be an Out of Memory error that is seemingly caused by adding too many picture files to the program and creating Drawables out of them. This would be a problem, as I really don't have that many picture resources worked into that program...maybe 20 or so. I haven't even started to include sound yet. These images aren't all that fancy. My questions are this: 1) Are programs for the Android phone really that limited on how much memory they can employ, or is it probably something other than the 20-30 resource pictures causing that error? 2) If the memory for Android apps is so awful it can't even handle 20-30 picture resources being loaded into Drawables that exist at the same time, then how in the world are you supposed to make decent graphics and sound for that thing? Thanks.

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• Where do I put the logic of my MFC program?

  - by Matthew

  I created an application core, in C++, that I've compiled into a static library in Visual Studio. I am now at the process of writing a GUI for it. I am using MFC to do this. I figured out how to map button presses to execute certain methods of my application core's main class (i.e. buttons to have it start and stop). The core class however, should always be sampling data from an external source every second or two. The GUI should then populate some fields after each sample is taken. I can't seem to find a spot in my MFC objects like CDialog that I can constantly check to see if my class has grabbed the data.. then if it has put that data into some of the text boxes. A friend suggested that I create a thread on the OnInit() routine that would take care of this, but that solution isn't really working for me. Is there no spot where I can put an if statement that keeps being called until the program quits? i.e. if( coreapp.dataSampleReady() ) { // put coreapp.dataItem1() in TextBox1 // set progress bar to coreapp.dataItem2() // etc. // reset dataSampleReady }

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• Bash script to insert code from one file at a specific location in another file?

  - by Kurtosis

  I have a fileA with a snippet of code, and I need a script to insert that snippet into fileB on the line after a specific pattern. I'm trying to make the accepted answer in this thread work, but it's not, and is not giving an error so not sure why not: sed -e '/pattern/r text2insert' filewithpattern Any suggestions? pattern (insert snippet on line after): def boot { also tried escaped pattern but no luck: def\ boot\ { def\ boot\ \{ fileA snippet: LiftRules.htmlProperties.default.set((r: Req) => new Html5Properties(r.userAgent)) fileB (Boot.scala): package bootstrap.liftweb import net.liftweb._ import util._ import Helpers._ import common._ import http._ import sitemap._ import Loc._ /** * A class that's instantiated early and run. It allows the application * to modify lift's environment */ class Boot { def boot { // where to search snippet LiftRules.addToPackages("code") // Build SiteMap val entries = List( Menu.i("Home") / "index", // the simple way to declare a menu // more complex because this menu allows anything in the // /static path to be visible Menu(Loc("Static", Link(List("static"), true, "/static/index"), "Static Content"))) // set the sitemap. Note if you don't want access control for // each page, just comment this line out. LiftRules.setSiteMap(SiteMap(entries:_*)) // Use jQuery 1.4 LiftRules.jsArtifacts = net.liftweb.http.js.jquery.JQuery14Artifacts //Show the spinny image when an Ajax call starts LiftRules.ajaxStart = Full(() => LiftRules.jsArtifacts.show("ajax-loader").cmd) // Make the spinny image go away when it ends LiftRules.ajaxEnd = Full(() => LiftRules.jsArtifacts.hide("ajax-loader").cmd) // Force the request to be UTF-8 LiftRules.early.append(_.setCharacterEncoding("UTF-8")) } }

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• How to add deploy.jar to classpath?

  - by dma_k

  I am facing the problem: I need to add ${java.home}/lib/deploy.jar JAR file to classpath in the runtime (dynamically from java). The solution with Thread#setContextClassLoader(ClassLoader) (mentioned here) does not work because of this bug (if somebody can explain what is really a problem – you are welcome). The solution with -Xbootclasspath/a:"%JAVA_HOME%/jre/lib/deploy.jar" does not work well for me, because I want to have "pure executable jar" as a deliverable: no wrapping scripts please (more over %JAVA_HOME% may not be defined in user's environment in Windows for example, plus I need to write a script per platform) The solution with merging deploy.jar file into my deliverable works only if I make a build on Windows platform. Unfortunately, when the deliverable is produced on build server running on Linux, I got Linux-dependant JAR, which does not execute on Windows – it fails with the trace below. I have read How the Java Launcher Finds Classes and Java programming dynamics: Java classes and class loading articles but I've got no extra ideas, how to correctly handle this situation. Any advices or solutions are very welcomed. Trace: java.lang.NoClassDefFoundError: Could not initialize class com.sun.deploy.config.Config at com.sun.deploy.net.proxy.UserDefinedProxyConfig.getBrowserProxyInfo(UserDefinedProxyConfig.java:43) at com.sun.deploy.net.proxy.DynamicProxyManager.reset(DynamicProxyManager.java:235) at com.sun.deploy.net.proxy.DeployProxySelector.reset(DeployProxySelector.java:59) ... java.lang.NullPointerException at com.sun.deploy.net.proxy.DynamicProxyManager.getProxyList(DynamicProxyManager.java:63) at com.sun.deploy.net.proxy.DeployProxySelector.select(DeployProxySelector.java:166)

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• Python 3.3 Webserver restarting problems

  - by IPDGino

  I have made a simple webserver in python, and had some problems with it before as described here: Python (3.3) Webserver script with an interesting error In that question, the answer was to use a While True: loop so that any crashes or errors would be resolved instantly, because it would just start itself again. I've used this for a while, and still want to make the server restart itself every few minutes, but on Linux for some reason it won't work for me. On windows the code below works fine, but on linux it keeps saying Handler class up here ... ... class Server: def __init__(self): self.server_class = HTTPServer self.server_adress = ('MY IP GOES HERE, or localhost', 8080) global httpd httpd = self.server_class(self.server_adress, Handler) self.main() def main(self): if count > 1: global SERVER_UP_SINCE HOUR_CHECK = int(((count - 1) * RESTART_INTERVAL) / 60) SERVER_UPTIME = str(HOUR_CHECK) + " MINUTES" if HOUR_CHECK > 60: minutes = int(HOUR_CHECK % 60) hours = int(HOUR_CHECK // 60) SERVER_UPTIME = ("%s HOURS, %s MINUTES" % (str(hours), str(minutes))) SERVING_ON_ADDR = self.server_adress SERVER_UP_SINCE = str(SERVER_UP_SINCE) SERVER_RESTART_NUMBER = count - 1 print(""" SERVER INFO ------------------------------------- SERVER_UPTIME: %s SERVER_UP_SINCE: %s TOTAL_FILES_SERVED: %d SERVING_ON_ADDR: %s SERVER_RESTART_NUMBER: %s \n\nSERVER HAS RESTARTED """ % (SERVER_UPTIME, SERVER_UP_SINCE, TOTAL_FILES, SERVING_ON_ADDR, SERVER_RESTART_NUMBER)) else: print("SERVER_BOOT=1\nSERVER_ONLINE=TRUE\nRESTART_LOOP=TRUE\nSERVING_ON_ADDR:%s" % str(self.server_adress)) while True: try: httpd.serve_forever() except KeyboardInterrupt: print("Shutting down...") break httpd.shutdown() httpd.socket.close() raise(SystemExit) return def server_restart(): """If you want the restart timer to be longer, replace the number after the RESTART_INTERVAL variable""" global RESTART_INTERVAL RESTART_INTERVAL = 10 threading.Timer(RESTART_INTERVAL, server_restart).start() global count count = count + 1 instance = Server() if __name__ == "__main__": global SERVER_UP_SINCE SERVER_UP_SINCE = strftime("%d-%m-%Y %H:%M:%S", gmtime()) server_restart() Basically, I make a thread to restart it every 10 seconds (For testing purposes) and start the server. After ten seconds it will say File "/home/username/Desktop/Webserver/server.py", line 199, in __init__ httpd = self.server_class(self.server_adress, Handler) File "/usr/lib/python3.3/socketserver.py", line 430, in __init__ self.server_bind() File "/usr/lib/python3.3/http/server.py", line 135, in server_bind socketserver.TCPServer.server_bind(self) File "/usr/lib/python3.3/socketserver.py", line 441, in server_bind self.socket.bind(self.server_address) OSError: [Errno 98] Address already in use As you can see in the except KeyboardInterruption line, I tried everything to make the server stop, and the program stop, but it will NOT stop. But the thing I really want to know is how to make this server able to restart, without giving some wonky errors.

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• Issue with Callback method and maintaining CultureInfo and ASP.Net HttpRuntime

  - by Little Larry Sellers

  Hi All, Here is my issue. I am working on an E-commerce solution that is deployed to multiple European countries. We persist all exceptions within the application to SQL Server and I have found that there are records in the DB that have a DateTime in the future! We define the culture in the web.config, for example pt-PT, and the format expected is DD-MM-YYYY. After debugging I found the issue with these 'future' records in the DB is because of Callback methods we use. For example, in our Caching architecture we use Callbacks, as such - CacheItemRemovedCallback ReloadCallBack = new CacheItemRemovedCallback(OnRefreshRequest); When I check the current threads CultureInfo, on these Callbacks it is en-US instead of pt-PT and also the HttpContext is null. If an exception occurs on the Callback our exception manager reports it as MM-DD-YYYY and thus it is persisted to SQL Server incorrectly. Unfortunately, in the exception manager code, we use DateTime.Now, which is fine if it is not a callback. I can't change this code to be culture specific due to it being shared across other verticals. So, why don't callbacks into ASP.Net maintain context? Is there any way to maintain it on this callback thread? What are the best practices here? Thanks.

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• ReaderWriterLockSlim and Pulse/Wait

  - by Jono

  Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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• Blackberry (Java) - Can't get KeyListener to work

  - by paullb

  I am trying to get the KeyListener working for Blackberry, but none of the Dialogs pop up indicating that a key has been pressed (see code below, each action has a dialog popup in them). Any ideas on what i might be doing wrong? public class CityInfo extends UiApplication implements KeyListener { static CityInfo application; public static void main(String[] args) { //create a new instance of the application //and start the application on the event thread application.enterEventDispatcher(); } public CityInfo() { //display a new screen application = new CityInfo(); pushScreen(new WorkflowDisplayScreen()); this.addKeyListener(this); } public boolean keyChar(char arg0, int arg1, int arg2) { // TODO Auto-generated method stub Dialog.alert("key pressed : " + arg0); return true; } public boolean keyDown(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyDown : " + keycode); return false; } public boolean keyRepeat(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyRepeat : " + keycode); return false; } public boolean keyStatus(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyStatus : " + keycode); return false; } public boolean keyUp(int keycode, int time) { Dialog.alert("keyUp : " + keycode); // TODO Auto-generated method stub return false; } } I also tried implementing keyChar on the MainScreen class but that did not yield any results either.

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• Dependency Injection into your Singleton

  - by Langali

  I have a singleton that has a spring injected Dao (simplified below): public class MyService<T> implements Service<T> { private final Map<String, T> objects; private static MyService instance; MyDao myDao; public void set MyDao(MyDao myDao) { this. myDao = myDao; } private MyService() { this.objects = Collections.synchronizedMap(new HashMap<String, T>()); // start a background thread that runs for ever } public static synchronized MyService getInstance() { if(instance == null) { instance = new MyService(); } return instance; } public void doSomething() { myDao.persist(objects); } } My spring config will probably look like this: <bean id="service" class="MyService" factory-method="getInstance"/> But this will instantiate the MyService during startup. Is there a programmatic way to do a dependency injection of MyDao into MyService, but not have spring manage the MyService? Basically I want to be able to do this from my code: MyService.getInstance().doSomething(); while having spring inject the MyDao for me.

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• How important is the programming language when you choose a new job?

  - by Luhmann

  We are currently hiring at the company where I work, and here the codebase is in VB.Net. We are worried that we miss out on a lot of brilliant programmers, who would never ever consider working with VB.Net. My own background is Java and C#, and I was somewhat sceptical as to whether it would work out with VB, as - to be honest - i didn't care much for VB. After a month or so, I was completely fluent in VB, and a few months later i discovered to my surprise, that I actually like VB. I still code my free time projects in C# and Boo though. So my question is firstly, how important is language for you, when you choose a new programming job? Lets say if its a great company, salary is good, and generally an attractive work-place. Would you say no to the perfect job, if the language wasn't your preferred dialect? VB or C# is one thing, but how about Java or C# etc. Secondly if the best developers won't join your company because of your language or platform, would you consider changing, to get the right people? (This is not a language bashing thread, so please no religious language wars) NB: This is Community Wiki

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• How to use Comparator in Java to sort

  - by Dan

  I learned how to use the comparable but I'm having difficulty with the Comparator. I am having a error in my code: Exception in thread "main" java.lang.ClassCastException: New.People cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at New.TestPeople.main(TestPeople.java:18) Here is my code: import java.util.Comparator; public class People implements Comparator{ private int id; private String info; private double price; public People(int newid, String newinfo, double newprice){ setid(newid); setinfo(newinfo); setprice(newprice); } public int getid() { return id; } public void setid(int id) { this.id = id; } public String getinfo() { return info; } public void setinfo(String info) { this.info = info; } public double getprice() { return price; } public void setprice(double price) { this.price = price; } public int compare(Object obj1, Object obj2) { Integer p1 = ((People)obj1).getid(); Integer p2 = ((People)obj2).getid(); if (p1 p2 ){ return 1; } else if (p1 < p2){ return -1; } else return 0; } } import java.util.ArrayList; import java.util.Collections; public class TestPeople { public static void main(String[] args) { ArrayList peps = new ArrayList(); peps.add(new People(123, "M", 14.25)); peps.add(new People(234, "M", 6.21)); peps.add(new People(362, "F", 9.23)); peps.add(new People(111, "M", 65.99)); peps.add(new People(535, "F", 9.23)); Collections.sort(peps); for(int i=0;i I believe it has to do something with the casting in the compare method but I was playing around with it and still could not find the solution

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• http_access.log on WebSphere 6.1.0.29

  - by DavidG

  I am running WebSphere 6.1.0.29 and I need to track the requests being made to an Enterprise Application. Previously I did this by routing the requests through a proxy server, but I need to repeat the exercise and I figure there must be a simpler way. Does anyone know how to enable HTTP access logging? I have been through the console an thought I had enabled http_access.log and http_error.log via: Application servers server1 HTTP error and NCSA access logging (where 'server1' is the application server) I've enabled the service at startup, and ticked the boxes to enable access logging and error logging - however... nothing has happened. I have restarted the server, restarted the Enterprise apps and even did a "find . -name" for the log files - but they don't seem to be anywhere on the system. I saw on a JavaRanch thread someone suggested writing a custom filter for requests in an application, but this seems like wild overkill - plus I am doing the logs to test a pre-built binary, so I don't want to mess with the code. Anyone have any ideas/suggestions? Help! :-)

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• why does entity framework+mysql provider enumeration returns partial results with no exceptions

  - by Freddy Rios

  I'm trying to make sense of a situation I have using entity framework on .net 3.5 sp1 + MySQL 6.1.2.0 as the provider. It involves the following code: Response.Write("Products: " + plist.Count() + "<br />"); var total = 0; foreach (var p in plist) { //... some actions total++; //... other actions } Response.Write("Total Products Checked: " + total + "<br />"); Basically the total products is varying on each run, and it isn't matching the full total in plist. Its varies widely, from ~ 1/5th to half. There isn't any control flow code inside the foreach i.e. no break, continue, try/catch, conditions around total++, anything that could affect the count. As confirmation, there are other totals captured inside the loop related to the actions, and those match the lower and higher total runs. I don't find any reason to the above, other than something in entity framework or the mysql provider that causes it to end the foreach when retrieving an item. The body of the foreach can have some good variation in time, as the actions involve file & network access, my best shot at the time is that when the .net code takes beyond certain threshold there is some type of timeout in the underlying framework/provider and instead of causing an exception it is silently reporting no more items for enumeration. Can anyone give some light in the above scenario and/or confirm if the entity framework/mysql provider has the above behavior? Update: I can't reproduce the behavior by using Thread.Sleep in a simple foreach in a test project, not sure where else to look for this weird behavior :(.

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• Hide Image Title in Slimbox

  - by Stephen

  My issue is a lot like this solved thread, except I'm using Slimbox 2: http://stackoverflow.com/questions/940994/hide-image-title-tool-tip-popup-on-mouse-rollover-or-hover When you hover over an image, the "Title" attribute pops up. I need HTML in my image title in Slimbox. So, of course, when you're hovering, the "Title" attribute shows all the HTML code. The code works perfectly when you're viewing the image in Slimbox so no problems there. I just need the Title attribute to be hidden/modified not to show this HTML code. I tried to change Q.title in slimbox.js to something else (like captionname). Then changed the HTML to call for: <a href="images/team/large.jpg" title="Joe Smith" captionname="URL" rel="lightbox-team"><img src="images/team/small.jpg" class ="headline" border="1" hspace="2" /></a> "Joe Smith" displays as the Title but when you view the image in Slimbox, captionname does not come up at all and neither does the Title. It's just blank where it should be. What do I need to modify in slimbox2.js to make this work?

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• ExecutorSerrvice memory leak on exception

  - by TofuBeer

  I am having a hard time tracking this down since the profiler keeps crashing (hotspot error). Before I go too deep into figuring it out I'd like to know if I really have a problem or not :-) I have a few thread pools created via: Executors.newFixedThreadPool(10); The threads connect to different web sites and, on occasion, I get connection refused and wind up throwing an exception. When I later on call Future.get() to get the result it will then catch the ExecutionException that wraps the exception that was thrown when the connection could not be made. The program uses a fairly constant amount of memory up until the point in time that the exceptions get thrown (they tend to happen in batches when a particular site is overloaded). After that point the memory again remains constant but at a higher level. So my question is along the lines of is the memory behaviour (reported by "top" on Unix) expected because the exceptions just triggered something or do I probably have an actual leak that I'll need to track down? Additionally when Future.get() throws an exception is there anything else I need to do besides catch the exception (such as call Future.cancel() on it)?

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• What's a reasonable way to mutate a primitive variable from an anonymous Java class?

  - by Steve

  I would like to write the following code: boolean found = false; search(new SearchCallback() { @Override void onFound(Object o) { found = true; } }); Obviously this is not allowed, since found needs to be final. I can't make found a member field for thread-safety reasons. What is the best alternative? One workaround is to define final class MutableReference<T> { private T value; MutableReference(T value) { this.value = value; } T get() { return value; } void set(T value) { this.value = value; } } but this ends up taking a lot of space when formatted properly, and I'd rather not reinvent the wheel if at all possible. I could use a List<Boolean> with a single element (either mutating that element, or else emptying the list) or even a Boolean[1]. But everything seems to smell funny, since none of the options are being used as they were intended. What is a reasonable way to do this?

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• java bubblesort with acm dialog

  - by qzar

  Hi, the program gives following exception: Exception in thread "main" java.lang.NullPointerException at myclasses.BubbleSort.run(BubbleSort.java:42) at acm.program.Program.runHook(Program.java:1519) at acm.program.Program.startRun(Program.java:1508) at acm.program.Program.start(Program.java:729) at myclasses.BubbleSort.main(BubbleSort.java:49) what is wrong? thank you very much! package myclasses; import acm.program.DialogProgram; public class BubbleSort extends DialogProgram { int[] array; public int[] getArray() { return array; } public void setArray(int[] array) { this.array = array; } void swap(int firstPos, int secondPos) { int temp = array[firstPos]; array[firstPos] = array[secondPos]; array[secondPos] = temp; } public void bubblesort() { int i, j, k; for (i = 1; i < array.length; i++) { j = i; k = array[i]; while (j > 0 && array[j - 1] > k) { array[j] = array[j - 1]; --j; } array[j] = k; } } public void run() { BubbleSort a = new BubbleSort(); a.setArray(new int[] {1, 3, 5, 7, 6, 2}); a.bubblesort(); StringBuffer sb = new StringBuffer(a.array.length * 2); for (int i = 0; i < getArray().length; i++) sb.append(getArray()[i]).append(" "); println(sb); } public static void main(String[] args) { new BubbleSort().start(args); } }

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• Using JavaMail to send a mail containing Unicode characters

  - by NoozNooz42

  I'm successfully sending emails through GMail's SMTP servers using the following piece of code: Properties props = new Properties(); props.put("mail.smtp.host", "smtp.gmail.com"); props.put("mail.smtp.socketFactory.port", "465"); props.put("mail.smtp.socketFactory.class","javax.net.ssl.SSLSocketFactory"); props.put("mail.smtp.auth", "true"); props.put("mail.smtp.port", "465"); props.put("mail.smtp.ssl", "true"); props.put("mail.smtp.starttls.enable","true"); props.put("mail.smtp.timeout", "5000"); props.put("mail.smtp.connectiontimeout", "5000"); // Do NOT use Session.getDefaultInstance but Session.getInstance // See: http://forums.sun.com/thread.jspa?threadID=5301696 final Session session = Session.getInstance( props, new javax.mail.Authenticator() { protected PasswordAuthentication getPasswordAuthentication() { return new PasswordAuthentication( USER, PWD ); } }); try { final Message message = new MimeMessage(session); message.setFrom( new InternetAddress( USER ) ); message.setRecipients( Message.RecipientType.TO, InternetAddress.parse( TO ) ); message.setSubject( emailSubject ); message.setText( emailContent ); Transport.send(message); emailSent = true; } catch ( final MessagingException e ) { e.printStackTrace(); } where emailContent is a String that does contain Unicode characters (like the euro symbol). When the email arrives (in another GMail account), the euro symbol has been converted to the ASCII '?' question mark. I don't know much about emails: can email use any character encoding? What should I modify in the code above so that an encoding allowing Unicode characters is used?

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• Checking if a console application is still running using the Process class

  - by Ced

  I'm making an application that will monitor the state of another process and restart it when it stops responding, exits, or throws an error. However, I'm having trouble to make it reliably check if the process (Being a C++ Console window) has stopped responding. My code looks like this: public void monitorserver() { while (true) { server.StartInfo = new ProcessStartInfo(textbox_srcdsexe.Text, startstring); server.Start(); log("server started"); log("Monitor started."); while (server.Responding) { if (server.HasExited) { log("server exitted, Restarting."); break; } log("server is running: " + server.Responding.ToString()); Thread.Sleep(1000); } log("Server stopped responding, terminating.."); try { server.Kill(); } catch (Exception) { } } } The application I'm monitoring is Valve's Source Dedicated Server, running Garry's Mod, and I'm over stressing the physics engine to simulate it stopping responding. However, this never triggers the process class recognizing it as 'stopped responding'. I know there are ways to directly query the source server using their own protocol, but i'd like to keep it simple and universal (So that i can maybe use it for different applications in the future). Any help appreciated

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• Fastest inline-assembly spinlock

  - by sigvardsen

  I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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• How to improve multi-threaded access to Cache (custom implementation)

  - by Andy

  I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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