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• Cache consistency & spawning a thread

  - by Dave Keck

  Background I've been reading through various books and articles to learn about processor caches, cache consistency, and memory barriers in the context of concurrent execution. So far though, I have been unable to determine whether a common coding practice of mine is safe in the strictest sense. Assumptions The following pseudo-code is executed on a two-processor machine: int sharedVar = 0; myThread() { print(sharedVar); } main() { sharedVar = 1; spawnThread(myThread); sleep(-1); } main() executes on processor 1 (P1), while myThread() executes on P2. Initially, sharedVar exists in the caches of both P1 and P2 with the initial value of 0 (due to some "warm-up code" that isn't shown above.) Question Strictly speaking – preferably without assuming any particular CPU – is myThread() guaranteed to print 1? With my newfound knowledge of processor caches, it seems entirely possible that at the time of the print() statement, P2 may not have received the invalidation request for sharedVar caused by P1's assignment in main(). Therefore, it seems possible that myThread() could print 0. References These are the related articles and books I've been reading. (It wouldn't allow me to format these as links because I'm a new user - sorry.) Shared Memory Consistency Models: A Tutorial hpl.hp.com/techreports/Compaq-DEC/WRL-95-7.pdf Memory Barriers: a Hardware View for Software Hackers rdrop.com/users/paulmck/scalability/paper/whymb.2009.04.05a.pdf Linux Kernel Memory Barriers kernel.org/doc/Documentation/memory-barriers.txt Computer Architecture: A Quantitative Approach amazon.com/Computer-Architecture-Quantitative-Approach-4th/dp/0123704901/ref=dp_ob_title_bk

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• junit assert in thread throws exception

  - by antony.trupe

  What am I doing wrong that an exception is thrown instead of showing a failure, or should I not have assertions inside threads? @Test public void testComplex() throws InterruptedException { int loops = 10; for (int i = 0; i < loops; i++) { final int j = i; new Thread() { @Override public void run() { ApiProxy.setEnvironmentForCurrentThread(env);//ignore this new CounterFactory().getCounter("test").increment();//ignore this too int count2 = new CounterFactory().getCounter("test").getCount();//ignore assertEquals(j, count2);//here be exceptions thrown. this is line 75 } }.start(); } Thread.sleep(5 * 1000); assertEquals(loops, new CounterFactory().getCounter("test").getCount()); } StackTrace Exception in thread "Thread-26" junit.framework.AssertionFailedError: expected:<5> but was:<6> at junit.framework.Assert.fail(Assert.java:47) at junit.framework.Assert.failNotEquals(Assert.java:277) at junit.framework.Assert.assertEquals(Assert.java:64) at junit.framework.Assert.assertEquals(Assert.java:195) at junit.framework.Assert.assertEquals(Assert.java:201) at com.bitdual.server.dao.ShardedCounterTest$3.run(ShardedCounterTest.java:77)

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• Can a standalone ruby script (windows and mac) reload and restart itself?

  - by user30997

  I have a master-workers architecture where the number of workers is growing on a weekly basis. I can no longer be expected to ssh or remote console into each machine to kill the worker, do a source control sync, and restart. I would like to be able to have the master place a message out on the network that tells each machine to sync and restart. That's where I hit a roadblock. If I were using any sane platform, I could just do: exec('ruby', __FILE__) ...and be done. However, I did the following test: p Process.pid sleep 1 exec('ruby', __FILE__) ...and on Windows, I get one ruby instance for each call to exec. None of them die until I hit ^C on the window in question. On every platform I tried this on, it is executing the new version of the file each time, which I have verified this by making simple edits to the test script while the test marched along. The reason I'm printing the pid is to double-check the behavior I'm seeing. On windows, I am getting a different pid with each execution - which I would expect, considering that I am seeing a new process in the task manager for each run. The mac is behaving correctly: the pid is the same for every system call and I have verified with dtrace that each run is trigging a call to the execve syscall. So, in short, is there a way to get a windows ruby script to restart its execution so it will be running any code - including itself - that has changed during its execution? Please note that this is not a rails application, though it does use activerecord.

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• Help passing reference to class subroutine in Perl.

  - by stephenmm

  I am trying to pass a routine to another subroutine within a Perl module. But when I pass the sub reference the passed in ref no longer has the object data. Maybe its not possible to do it this way. The line I have a question about is the "unless" lines below: sub get_flag_end { my $self = shift; return ( -e "$self->{file}" ); } sub wait_for_end { my $self = shift; my $timeout = shift; my $poll_interval = shift; # Is it even possible to pass the oject subroutine and retain the objects data? #unless ( $self->timeout( $timeout, $poll_interval, $self->get_flag_end ) ) { # does not work unless ( $self->timeout( $timeout, $poll_interval, \&get_flag_end ) ) { # call happens but members are empty die "!!!ERROR!!! Timed out while waiting for wait_for_end: timeout=$timeout, poll_interval=$poll_interval \n"; } } sub timeout { my $self = shift; my $timeout = shift; my $poll_interval = shift; my $test_condition = shift; until ($test_condition->() || $timeout <= 0) { $timeout -= $poll_interval; sleep $poll_interval; } return $timeout > 0; # condition was met before timeout } I know that I could change the "get_flag_end" routine to take the value as an argument to the subroutine but what if there was a bunch of stuff done in "get_flag_end" and I needed more members from the object. I simplified the code a bit to make it a little easier to follow.

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• BackgroundWorker might be causing my application to hang

  - by alexD

  I have a Form that uses a BackgroundWorker to execute a series of tests. I use the ProgressChanged event to send messages to the main thread, which then does all of the updates on the UI. I've combed through my code to make sure I'm not doing anything to the UI in the background worker. There are no while loops in my code and the BackgroundWorker has a finite execution time (measured in seconds or minutes). However, for some reason when I lock my computer, often times the application will be hung when I log back in. The thing is, the BackgroundWorker isn't even running when this happens. The reason I believe it is related to the BackgroundWorker though is because the form only hangs when the BackgroundWorker has been executed since the application was loaded (it only runs when given a certain user input). I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread..any modifications I make to them is done in the UI thread through the progressChanged event. I do use Thread.Sleep in my worker thread to execute tests at timed intervals (which involves sending messages over a TCP socket, which was not created in the worker thread). I am completely perplexed as to why my application might be hanging. I'm sure I'm doing something 'illegal' somewhere, I just don't know what.

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• Java swing hold buttons

  - by Simon Charette

  Hi, I'm trying to create a subclass of JButton or AbstractButton that would call specified .actionPerformed as long as the mouse is held down on the button. So far I was thinking of extending JButton, adding a mouse listener on creation (inside constructor) and calling actionPerformed while the mouse is down. So far i came up with that but I was wondwering if I was on the right track and if so, how to correctly implement the "held down" logic. package components; import java.awt.event.ActionEvent; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import javax.swing.Action; import javax.swing.Icon; import javax.swing.JButton; public class HoldButton extends JButton { private class HeldDownMouseListener implements MouseListener { private boolean mouseIsHeldDown; private HoldButton button; private long millis; public HeldDownMouseListener(HoldButton button, long millis) { this.button = button; this.millis = millis; } @Override public void mouseClicked(MouseEvent arg0) { } @Override public void mouseEntered(MouseEvent arg0) { } @Override public void mouseExited(MouseEvent arg0) { } @Override public void mousePressed(MouseEvent arg0) { mouseIsHeldDown = true; // This should be run in a sub thread? // while (mouseIsHeldDown) { // button.fireActionPerformed(new ActionEvent(button, ActionEvent.ACTION_PERFORMED, "heldDown")); // try { // Thread.sleep(millis); // } catch (InterruptedException e) { // e.printStackTrace(); // continue; // } // } } @Override public void mouseReleased(MouseEvent arg0) { mouseIsHeldDown = false; } } public HoldButton() { addHeldDownMouseListener(); } public HoldButton(Icon icon) { super(icon); addHeldDownMouseListener(); } public HoldButton(String text) { super(text); addHeldDownMouseListener(); } public HoldButton(Action a) { super(a); addHeldDownMouseListener(); } private void addHeldDownMouseListener() { addMouseListener(new HeldDownMouseListener(this, 300)); } } Thanks a lot for your time.

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• TransactionScope Prematurely Completed

  - by Chris

  I have a block of code that runs within a TransactionScope and within this block of code I make several calls to the DB. Selects, Updates, Creates, and Deletes, the whole gamut. When I execute my delete I execute it using an extension method of the SqlCommand that will automatically resubmit the query if it deadlocks as this query could potentially hit a deadlock. I believe the problem occurs when a deadlock is hit and the function tries to resubmit the query. This is the error I receive: The transaction associated with the current connection has completed but has not been disposed. The transaction must be disposed before the connection can be used to execute SQL statements. This is the simple code that executes the query (all of the code below executes within the using of the TransactionScope): using (sqlCommand.Connection = new SqlConnection(ConnectionStrings.App)) { sqlCommand.Connection.Open(); sqlCommand.ExecuteNonQueryWithDeadlockHandling(); } Here is the extension method that resubmits the deadlocked query: public static class SqlCommandExtender { private const int DEADLOCK_ERROR = 1205; private const int MAXIMUM_DEADLOCK_RETRIES = 5; private const int SLEEP_INCREMENT = 100; public static void ExecuteNonQueryWithDeadlockHandling(this SqlCommand sqlCommand) { int count = 0; SqlException deadlockException = null; do { if (count > 0) Thread.Sleep(count * SLEEP_INCREMENT); deadlockException = ExecuteNonQuery(sqlCommand); count++; } while (deadlockException != null && count < MAXIMUM_DEADLOCK_RETRIES); if (deadlockException != null) throw deadlockException; } private static SqlException ExecuteNonQuery(SqlCommand sqlCommand) { try { sqlCommand.ExecuteNonQuery(); } catch (SqlException exception) { if (exception.Number == DEADLOCK_ERROR) return exception; throw; } return null; } } The error occurs on the line that executes the nonquery: sqlCommand.ExecuteNonQuery();

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• JME: How to get the complete screen in WHITE without buttons, etc etc

  - by Sepala

  Please have a look at the following code /* * To change this template, choose Tools | Templates * and open the template in the editor. */ import javax.microedition.midlet.*; import javax.microedition.lcdui.*; /** */ public class Midlet extends MIDlet{ private Form f; private Display d; private Command start,stop; private Thread t; public Midlet() { t = new Thread(new TurnLightOn()); } public void startApp() { f = new Form("Back Light On"); d = Display.getDisplay(this); d.setCurrent(f); start = new Command("Turn On",Command.OK,0); stop = new Command("Turn Off",Command.OK,1); f.addCommand(start); f.setCommandListener(new Action()); } public void pauseApp() { } public void destroyApp(boolean unconditional) { this.notifyDestroyed(); } private class Action implements CommandListener { public void commandAction(Command c, Displayable dis) { f.append("Light is Turnning On"); t.start(); } } private class ActionOff implements CommandListener { public void commandAction(Command c, Displayable dis) { } } private class TurnLightOn implements Runnable { public void run() { f.append("Working"); for(int i=0;i<100;i++) { try { d.flashBacklight(200); d.vibrate(200); Thread.sleep(1000); } catch (InterruptedException ex) { ex.printStackTrace(); } } } } } First, Please note I am a 100% newbie to Java Mobile. In here, I am making the light on and vibrate on when user click the button. However, I really wanted to create a SOS application which turn the whole screen into white, and go to black, like that, in the thread. I guess I didn't achieve that by this app because even the lights are on, the buttons are still there. I tried to turn the "Form" color to "white" but it seems like JME has no "Color" class! Please help!

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• Java Scanner won't follow file

  - by Steve Renyolds

  Trying to tail / parse some log files. Entries start with a date then can span many lines. This works, but does not ever see new entries to file. File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } } Doesn't seem like Scanner's next() or hasNext() detects new entries to file. Any idea how else I can implement, basically, a tail -f with custom delimiter. ok - using Kelly's advise i'm checking & refreshing the scanner, this works. Thank you !! if anyone has improvement suggestions plz do! File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } Thread.sleep(50); if(bis.available() > 0){ src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); } }

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• 2 Mutually exclusive RadioButton "Lists"

  - by user72603

  I think this has to be THE most frustrating thing I've ever done in web forms. Yet one would think it would be the easiest of all things in the world to do. That is this: I need 2 separate lists of radiobuttons on my .aspx page. One set allows a customer to select an option. The other set does also but for a different purpose. But only one set can have a selected radiobutton. Ok I've tried this using 2 asp.net Radiobuttonlists controls on the same page. Got around the nasty bug with GroupName (asp.net assigns the control's uniqueID which prevents the groupname from ever working because now, 2 radiobuttonlists can't have the same groupname for all their radiobuttons because each radiobuttonlist has a different uniqueID thus the bug assigns the unique ID as the name attribute when the buttons are rendered. since the name sets are different, they are not mutually exclusive). Anyway, so I created that custom RadioButtonListcontrol and fixed that groupname problem. But when ended up happening is when I went to put 2 instances of my new custom radiobuttonlist control on my .aspx page, all was swell until I noticed that every time I checked for radiobuttonlist1.SelectedValue or radiobuttonlist2.SelectedValue (did not matter which I was checking) the value always spit back string.empty and i was not able to figure out why (see http://forums.asp.net/t/1401117.aspx). Ok onto the third try tonight and into the break of dawn (no sleep). I tried to instead just scrap trying to use 2 custom radiobuttonlists altogether because of that string.empty issue and try to spit out 2 sets of radiobuttonlists via using 2 asp.net repeaters and a standard input HTML tag inside. Got that working. Ok but the 2 lists still are not mutually exclusive. I can select a value in the first set of radiobuttons from repeater1 and same goes for repeater2. I cannot for the life of me get the "sets" to be mutually exclusive sets of radiobuttons.

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• How to poll a file in /sys

  - by Bjoern

  Hi, I am stuck reading a file in /sys/ which contains the light intensity in Lux of the ambient light sensor on my Nokia N900 phone. See thread on talk.maemo.org here I tried to use pyinotify to poll the file but this looks some kind of wrong to me since the file is alway "process_IN_OPEN", "process_IN_ACCESS" and "process_IN_CLOSE_NOWRITE" I basically want to get the changes ASAP and if something changed trigger an event, execute a class... Here's the code I tried, which works, but not as I expected (I was hoping for process_IN_MODIFY to be triggered): #!/usr/bin/env python # -*- coding: utf-8 -*- # import os, time, pyinotify import pyinotify ambient_sensor = '/sys/class/i2c-adapter/i2c-2/2-0029/lux' wm = pyinotify.WatchManager() # Watch Manager mask = pyinotify.ALL_EVENTS def action(self, the_event): value = open(the_event.pathname, 'r').read().strip() return value class EventHandler(pyinotify.ProcessEvent): def process_IN_ACCESS(self, event): print "ACCESS event:", action(self, event) def process_IN_ATTRIB(self, event): print "ATTRIB event:", action(self, event) def process_IN_CLOSE_NOWRITE(self, event): print "CLOSE_NOWRITE event:", action(self, event) def process_IN_CLOSE_WRITE(self, event): print "CLOSE_WRITE event:", action(self, event) def process_IN_CREATE(self, event): print "CREATE event:", action(self, event) def process_IN_DELETE(self, event): print "DELETE event:", action(self, event) def process_IN_MODIFY(self, event): print "MODIFY event:", action(self, event) def process_IN_OPEN(self, event): print "OPEN event:", action(self, event) #log.setLevel(10) notifier = pyinotify.ThreadedNotifier(wm, EventHandler()) notifier.start() wdd = wm.add_watch(ambient_sensor, mask) wdd time.sleep(5) notifier.stop() Thanks for any hints, suggestions and examples Kind regards Bjoern

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• How to open AsyncTask from a Thread

  - by Abhishek

  In my application I have created a SplashScreen that will b shown for 5 Seconds and after that it executes an if else case depending upon the values stored in the Preference file. If Preference file contains values then the AsyncTask code will run else the Login form will load. When i try to run my application. The thread is going to the Login form with the help of intent but when it comes to AsyncTask my application shows a force close error message. This is my SplashScreen code: public class SplashScreen extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.splashscreen); Thread timer = new Thread() { public void run() { try { sleep(5000); } catch(InterruptedException e) { e.printStackTrace(); } finally { if(GoGolfPref.getEmail(SplashScreen.this)!=null && GoGolfPref.getPass(SplashScreen.this)!=null) { new LoadingScreen(SplashScreen.this, SplashScreen.this).execute("login_page", Login.url+GoGolfPref.getEmail(SplashScreen.this)+"/"+GoGolfPref.getPass(SplashScreen.this)); } else { Intent in = new Intent(SplashScreen.this, Login.class); startActivity(in); finish(); } } } }; timer.start(); } } This is the error I am getting: 08-29 07:25:58.040: E/AndroidRuntime(2365): FATAL EXCEPTION: Thread-10 08-29 07:25:58.040: E/AndroidRuntime(2365): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.os.Handler.<init>(Handler.java:121) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.Dialog.<init>(Dialog.java:101) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.AlertDialog.<init>(AlertDialog.java:63) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.ProgressDialog.<init>(ProgressDialog.java:80) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.ProgressDialog.<init>(ProgressDialog.java:76) 08-29 07:25:58.040: E/AndroidRuntime(2365): at com.pnf.gogolf.LoadingScreen.<init>(LoadingScreen.java:130) 08-29 07:25:58.040: E/AndroidRuntime(2365): at com.pnf.gogolf.SplashScreen$1.run(SplashScreen.java:32) How to get this working? Thanks in advance...

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• ScrollView content async downloading problem

  - by Newbee

  Hi! I have UIScrollView with lots of UIImageView inside. In the loadView method I assign some temporary image for each of subview UIImageView images and starts several threads to async download images from internet. Each thread downloads and assign images as follows: NSData *data = [NSData dataWithContentsOfURL:URL]; UIImage *img = [UIImage imageWithData:data]; img_view.image = img; Here is the problem - I expects picture will changed after each image downloaded by I can see only temporary images until all images will downloads. UIScrollView still interact while images downloads - I can scroll temporary images inside it and see scrollers and nothing blocks run loop, but downloaded images doesn't updates.. What I tried to do: Call sleep() in the download thread -- not helps. Call setNeedsDisplay for each ImageView inside ScrollView and for ScrollView -- not helps. What's wrong ? Thanks. Update. I tried some experiments with number of threads and number of images to download. Now I'm sure -- images redraws only when thread finished. For example - if I load 100 images with one thread -- picture updates one time after all images downloads. If I increase number of threads to 10 -- picture updates 10 times -- 10 images appears per update. One more update. I fixed problem by staring new thread from the downloading threads each time one image downloaded and exit current thread (instead of download several images in one thread in the cycle and exit thread only when all downloaded). Obviously it's not a good solution and there must be right approach.

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• python VTE Terminal weirdness

  - by mykhal

  i'm trying to use the terminal from python VTE binding (python-vte from debian squeeze) as a virtual terminal emulator (just for ANSI/control chars text processing) in interactive python console, everything looks (almost) all right: >>> import vte >>> term = vte.Terminal() >>> term.feed("a\nb") >>> print repr(term.get_text(lambda *a: True).rstrip()) 'a\n b' however, launching this code (little modified) as python script, different result is yielded: $ python vte_wiredness_1.py '' strangely enough, pasting the code back into the (new) interactive python session also yields empty string: >>> import vte >>> term = vte.Terminal() >>> term.feed("a\nb") >>> print repr(term.get_text(lambda *a: True).rstrip()) '' >>> first thing caming on my mind was that the only difference between the two cases is the timing - there had to be some delay before get_text. unfortunately, preluding get_text with some seconds sleep did not help then i thought it has something to do with X window environment. but the results are the same pure linux console (with some warning on missing graphics). i wonder what causes such an unpredictable behavior (interactive console - pasted vs typed, and it's not the delay.. ant the interactive console has nothing to do with the vte terminal object.. i guess) can someone explain what is happening? is it possible to use the VTE Term such way? that the "b" letter in the output is preceded by the space, is another strangeness (all consecutive lines are preceded by more spaces.. looks like I have to send carriage return before the string.) (the lambda *a: True get_text method argument i'm using is a dummy callback, it's is some SlotSelectedCallback.. for its explanation i'd be grateful as well :) )

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• Testing Async downloads with ASIHTTPRequest

  - by Baishampayan Ghose

  I am writing a simple library using ASIHTTPRequest where I am fetching URLs in an async manner. My problem is that the main function that I have written to test my lib exits before the async calls are finished. I am very new to Obj C and iPhone development, can anyone suggest a good way to wait before all the requests are finished in the main function? Currently, my main function looks like this - int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; IBGApp *ibgapp = [[IBGApp alloc] init]; IBGLib *ibgl = [[IBGLib alloc] initWithUsername:@"joe" andPassword:@"xxx"]; // The two method calls below download URLs async. [ibgl downloadURL:@"http://yahoo.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [ibgl downloadURL:@"http://google.com/" withRequestDelegate:ibgapp andRequestSelector:@selector(logData:)]; [pool release]; return 0; // I reach here before the async calls are done. } So what is the best way to wait till the async calls are done? I tried putting sleep, but obviously doesn't work.

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• proper use of volatile keyword

  - by luke

  I think i have a pretty good idea about the volatile keyword in java, but i'm thinking about re-factoring some code and i thought it would be a good idea to use it. i have a class that is basically working as a DB Cache. it holds a bunch of objects that it has read from a database, serves requests for those objects, and then occasionally refreshes the database (based on a timeout). Heres the skeleton public class Cache { private HashMap mappings =....; private long last_update_time; private void loadMappingsFromDB() { //.... } private void checkLoad() { if(System.currentTimeMillis() - last_update_time > TIMEOUT) loadMappingsFromDB(); } public Data get(ID id) { checkLoad(); //.. look it up } } So the concern is that loadMappingsFromDB could be a high latency operation and thats not acceptable, So initially i thought that i could spin up a thread on cache startup and then just have it sleep and then update the cache in the background. But then i would need to synchronize my class (or the map). and then i would just be trading an occasional big pause for making every cache access slower. Then i thought why not use volatile i could define the map reference as volatile private volatile HashMap mappings =....; and then in get (or anywhere else that uses the mappings variable) i would just make a local copy of the reference: public Data get(ID id) { HashMap local = mappings; //.. look it up using local } and then the background thread would just load into a temp table and then swap the references in the class HashMap tmp; //load tmp from DB mappings = tmp;//swap variables forcing write barrier Does this approach make sense? and is it actually thread-safe?

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• Displaying progressbar using threading in win 32 applicaition!

  - by kiddo

  In my application I have a simple module were I will read files for some process that will take few seconds..so I thought of displaying a progress bar(using worker thread) while the files are in progress.I have created a thread (code shown below) and also I designed a dialog window with progress control.I used the function MyThreadFunction below to display the progressbar but it just shows only one time and disappears,I am not sure how to make it work.I tried my best inspite of the fact that I am new to threading. reading files void ReadMyFiles() { for(int i = 0; i < fileCount ; fileCount++) { CWinThread* myThread = AfxBeginThread((AFX_THREADPROC)MyThreadFunction,NULL); tempState = *(checkState + index); if(tempCheckState == NOCHECKBOX) { //my operations } else//CHECKED or UNCHECKED { //myoperation } myThread->PostThreadMessage(WM_QUIT,NULL,NULL); } } thread functions UINT MyThreadFunction(LPARAM lparam) { HWND dialogWnd = CreateWindowEx(0,WC_DIALOG,L"Proccessing...",WS_OVERLAPPEDWINDOW|WS_VISIBLE, 600,300,280,120,NULL,NULL,NULL,NULL); HWND pBarWnd = CreateWindowEx(NULL,PROGRESS_CLASS,NULL,WS_CHILD|WS_VISIBLE|PBS_MARQUEE,40,20,200,20, dialogWnd,(HMENU)IDD_PROGRESS,NULL,NULL); MSG msg; PostMessage( pBarWnd, PBM_SETRANGE, 0, MAKELPARAM( 0, 100 ) ); PostMessage(pBarWnd,PBM_SETPOS,0,0); while(PeekMessage(&msg,NULL,NULL,NULL,PM_NOREMOVE)) { if(msg.message == WM_QUIT) { DestroyWindow(dialogWnd); return 1; } AfxGetThread()->PumpMessage(); Sleep(40); } return 1; }

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• Better way of looping to detect change.

  - by Dremation

  As of now I'm using a while(true) method to detect changes in memory. The problem with this is it's kill the applications performance. I have a list of 30 pointers that need checked as rapidly as possible for changes, without sacrificing a huge performance loss. Anyone have ideas on this? memScan = new Thread(ScanMem); public static void ScanMem() { int i = addy.Length; while (true) { Thread.Sleep(30000); //I do this to cut down on cpu usage for (int j = 0; j < i; j++) { string[] values = addy[j].Split(new char[] { Convert.ToChar(",") }); //MessageBox.Show(values[2]); try { if (Memory.Scanner.getIntFromMem(hwnd, (IntPtr)Convert.ToInt32(values[0], 16), 32).ToString() != values[1].ToString()) { //Ok, it changed lets do our work //work if (Globals.Working) return; SomeFunction("Results: " + values[2].ToString(), "Memory"); Globals.Working = true; }//end if }//end try catch { } }//end for }//end while }//end void

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• Ajax long polling (comet) + php on lighttpd v1.4.22 multiple instances problem.

  - by fibonacci

  Hi, I am new to this site, so I really hope I will provide all the necessary information regarding my question. I've been trying to create a "new message arrived notification" using long polling. Currently I am initiating the polling request by window.onLoad event of each page in my site. On the server side I have an infinite loop: while(1){ if(NewMessageArrived($current_user))break; sleep(10); } echo $newMessageCount; On the client side I have the following (simplified) ajax functions: poll_new_messages(){ xmlhttp=GetXmlHttpObject(); //... xmlhttp.onreadystatechange=got_new_message_count; //... xmlhttp.send(); } got_new_message_count(){ if (xmlhttp.readyState==4){ updateMessageCount(xmlhttp.responseText); //... poll_new_messages(); } } The problem is that with each page load, the above loop starts again. The result is multiple infinite loops for each user that eventually make my server hang. *The NewMessageArived() function queries MySQL DB for new unread messages. *At the beginning of the php script I run start_session() in order to obtain the $current_user value. I am currently the only user of this site so it is easy for me to debug this behavior by writing time() to a file inside this loop. What I see is that the file is being written more often than once in 10 seconds, but it starts only when I go from page to page. Please let me know if any additional information might help. Thank you.

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• Java library class to handle scheduled execution of "callbacks"?

  - by Hanno Fietz

  My program has a component - dubbed the Scheduler - that lets other components register points in time at which they want to be called back. This should work much like the Unix cron service, i. e. you tell the Scheduler "notify me at ten minutes past every full hour". I realize there are no real callbacks in Java. Here's my approach, is there a library which already does this stuff? Feel free to suggest improvements, too. Register call to Scheduler passes: a time specification containing hour, minute, second, year month, dom, dow, where each item may be unspecified, meaning "execute it every hour / minute etc." (just like crontabs) an object containing data that will tell the calling object what to do when it is notified by the Scheduler. The Scheduler does not process this data, just stores it and passes it back upon notification. a reference to the calling object Upon startup, or after a new registration request, the Scheduler starts with a Calendar object of the current system time and checks if there are any entries in the database that match this point in time. If there are, they are executed and the process starts over. If there aren't, the time in the Calendar object is incremented by one second and the entreis are rechecked. This repeats until there is one entry or more that match(es). (Discrete Event Simulation) The Scheduler will then remember that timestamp, sleep and wake every second to check if it is already there. If it happens to wake up and the time has already passed, it starts over, likewise if the time has come and the jobs have been executed. Edit: Thanks for pointing me to Quartz. I'm looking for something much smaller, however.

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• Should I expect Comet to be this slow?

  - by Chad Johnson

  I have the following in a Rails controller: def poll records = [] start_time = Time.now.to_i while records.length == 0 do records = Something.uncached{Something.find(:all, :conditions => { :some_condition => false})} if records.length > 0 break end sleep 1 if Time.now.to_i - start_time >= 20 break end end responseData = [] records.each do |record| responseData << { 'something' => record.some_value } # Flag message as received. record.some_condition = true record.save end render :text => responseData.to_json end and then I have Javascript performing an AJAX request. The request sits there for 20 seconds or until the controller method finds a record in the database, waiting. That works. function poll() { $.ajax({ url: '/my_controller/poll', type: 'GET', dataType: 'json', cache: false, data: 'time=' + new Date().getTime(), success: function(response) { // show response here }, complete: function() { poll(); }, error: function() { alert('error'); poll(); } }); } When I have 5 - 10 tabs open in my browser, my web application becomes super slow. Is this to be expected? Or is there some obvious improvement(s) I can make?

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• Winsock tcp/ip Socket listening but connection refused, race condition?

  - by Wayne

  Hello folks. This involves two automated unit tests which each start up a tcp/ip server that creates a non-blocking socket then bind()s and listen()s in a loop on select() for a client that connects and downloads some data. The catch is that they work perfectly when run separately but when run as a test suite, the second test client will fail to connect with WSACONNREFUSED... UNLESS there is a Thread.Sleep() of several seconds between them??!!! Interestingly, there is retry loop every 1 second for connecting after any failure. So the second test loops for a while until timeout after 10 minutes. During that time, netstat -na shows the correct port number is in the LISTEN state for the server socket. So if it is in the listen state? Why won't it accept the connection? In the code, there are log messages that show the select NEVER even gets a socket ready to read (which means ready to accept a connection when it applies to a listening socket). Obviously the problem must be related to some race condition between finishing one test which means close() and shutdown() on each end of the socket, and the start up of the next. This wouldn't be so bad if the retry logic allowed it to connect eventually after a couple of seconds. However it seems to get "gummed up" and won't even retry. However, for some strange reason the listening socket SAYS it's in the LISTEN state even through keeps refusing connections. So that means it's the Windoze O/S which is actually catching the SYN packet and returning a RST packet (which means "Connection Refused"). The only other time I ever saw this error was when the code had a problem that caused hundreds of sockets to get stuck in TIME_WAIT state. But that's not the case here. netstat shows only about a dozen sockets with only 1 or 2 in TIME_WAIT at any given moment. Please help.

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• Orphan IBM JVM process

  - by Nicholas Key

  Hi people, I have this issue about orphan IBM JVM process being created in the process tree: For example: C:\Program Files\IBM\WebSphere\AppServer\bin>wsadmin -lang jython -f "C:\Hello.py" Hello.py has the simple implementation: import time i = 0 while (1): i = i + 1 print "Hello World " + str(i) time.sleep(3.0) My machine has such JVM information: C:\Program Files\WebSphere\java\bin>java -verbose:sizes -version -Xmca32K RAM class segment increment -Xmco128K ROM class segment increment -Xmns0K initial new space size -Xmnx0K maximum new space size -Xms4M initial memory size -Xmos4M initial old space size -Xmox1624995K maximum old space size -Xmx1624995K memory maximum -Xmr16K remembered set size -Xlp4K large page size available large page sizes: 4K 4M -Xmso256K operating system thread stack size -Xiss2K java thread stack initial size -Xssi16K java thread stack increment -Xss256K java thread stack maximum size java version "1.6.0" Java(TM) SE Runtime Environment (build pwi3260sr6ifix-20091015_01(SR6+152211+155930+156106)) IBM J9 VM (build 2.4, JRE 1.6.0 IBM J9 2.4 Windows Server 2003 x86-32 jvmwi3260sr6-20091001_43491 (JIT enabled, AOT enabled) J9VM - 20091001_043491 JIT - r9_20090902_1330ifx1 GC - 20090817_AA) JCL - 20091006_01 While the program is running, I tried to kill it and subsequently I found an orphan IBM JVM process in the process tree. Is there a way to fix this issue? Why is there an orphan process in the first place? Is there something wrong with my code? I really don't believe that my simplistic code is wrongly implemented. Any suggestions?

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• Serial: write() throttling?

  - by damian

  Hi everyone, I'm working on a project sending serial data to control animation of LED lights, which need to stay in sync with a sound engine. There seems to be a large serial write buffer (OSX (POSIX) + FTDI chipset usb serial device), so without manually restricting the transmission rate, the animation system can get several seconds ahead of the serial transmission. Currently I'm manually restricting the serial write speed to the baudrate (8N1 = 10 bytes serial frame per 8 bytes data, 19200 bps serial - 1920 bytes per second max), but I am having a problem with the sound drifting out of sync over time - it starts fine, but after 10 minutes there's a noticeable (100ms+) lag between the sound and the lights. This is the code that's restricting the serial write speed (called once per animation frame, 'elapsed' is the duration of the current frame, 'baudrate' is the bps (19200)): void BufferedSerial::update( float elapsed ) { baud_timer += elapsed; if ( bytes_written > 1024 ) { // maintain baudrate float time_should_have_taken = (float(bytes_written)*10)/float(baudrate); float time_actually_took = baud_timer; // sleep if we have > 20ms lag between serial transmit and our write calls if ( time_should_have_taken-time_actually_took > 0.02f ) { float sleep_time = time_should_have_taken - time_actually_took; int sleep_time_us = sleep_time*1000.0f*1000.0f; //printf("BufferedSerial::update sleeping %i ms\n", sleep_time_us/1000 ); delayUs( sleep_time_us ); // subtract 128 bytes bytes_written -= 128; // subtract the time it should have taken to write 128 bytes baud_timer -= (float(128)*10)/float(baudrate); } } } Clearly there's something wrong, somewhere. A much better approach would be to be able to determine the number of bytes currently in the transmit queue, and try and keep that below a fixed threshold. Any advice appreciated.

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• MsSql Server high Resource Waits and Head Blocker

  - by MartinHN

  Hi I have a MS SQL Server 2008 Standard installation running a database for a webshop. The current size of the database is 2.5 GB. Running on Windows 2008 Standard. Dual Intel Xeon X5355 @ 2.00 GHz. 4 GB RAM. When I open the Activity Monitor, I see that I have a Wait Time (ms/sec) of 5000 in the "Other" category. In the Processes list, all connections from the webshop, the Head Blocker value is 1. I see every day that when I try to access the website, it can take 20-30 secs before it even starts to "work". I know that it is not network latency. (I have a 301 redirect from the same server that is executed instantly). When the first request has been served, it seems as if it's not a sleep anymore and every subsequent request is served instantly with the speed of light. The problem was worse two weeks ago, until I changed every query to include WITH (NOLOCK). But I still experience the problem, and the Wait times in the Activity Monitor is about the same. The largest table (Images) has 32764 rows (448576 KB). Some tables exceed 300000 rows, thought they're much smaller in size than the Images table. I have the default clustered index for every primary key column, only. Any ideas?

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