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• Parallel Tasking Concurrency with Dependencies on Python like GNU Make

  - by Brian Bruggeman

  I'm looking for a method or possibly a philosophical approach for how to do something like GNU Make within python. Currently, we utilize makefiles to execute processing because the makefiles are extremely good at parallel runs with changing single option: -j x. In addition, gnu make already has the dependency stacks built into it, so adding a secondary processor or the ability to process more threads just means updating that single option. I want that same power and flexibility in python, but I don't see it. As an example: all: dependency_a dependency_b dependency_c dependency_a: dependency_d stuff dependency_b: dependency_d stuff dependency_c: dependency_e stuff dependency_d: dependency_f stuff dependency_e: stuff dependency_f: stuff If we do a standard single thread operation (-j 1), the order of operation might be: dependency_f -> dependency_d -> dependency_a -> dependency_b -> dependency_e \ -> dependency_c For two threads (-j 2), we might see: 1: dependency_f -> dependency_d -> dependency_a -> dependency_b 2: dependency_e -> dependency_c Does anyone have any suggestions on either a package already built or an approach? I'm totally open, provided it's a pythonic solution/approach. Please and Thanks in advance!

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• Would an immutable keyword in Java be a good idea?

  - by berry120

  Generally speaking, the more I use immutable objects in Java the more I'm thinking they're a great idea. They've got lots of advantages from automatically being thread-safe to not needing to worry about cloning or copy constructors. This has got me thinking, would an "immutable" keyword go amiss? Obviously there's the disadvantages with adding another reserved word to the language, and I doubt it will actually happen primarily for the above reason - but ignoring that I can't really see many disadvantages. At present great care has to be taken to make sure objects are immutable, and even then a dodgy javadoc comment claiming a component object is immutable when it's in fact not can wreck the whole thing. There's also the argument that even basic objects like string aren't truly immutable because they're easily vunerable to reflection attacks. If we had an immutable keyword the compiler could surely recursively check and give an iron clad guarantee that all instances of a class were immutable, something that can't presently be done. Especially with concurrency becoming more and more used, I personally think it'd be good to add a keyword to this effect. But are there any disadvantages or implementation details I'm missing that makes this a bad idea?

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• Creating PowerShell Automatic Variables from C#

  - by Uros Calakovic

  I trying to make automatic variables available to Excel VBA (like ActiveSheet or ActiveCell) also available to PowerShell as 'automatic variables'. PowerShell engine is hosted in an Excel VSTO add-in and Excel.Application is available to it as Globals.ThisAddin.Application. I found this thread here on StackOverflow and started created PSVariable derived classes like: public class ActiveCell : PSVariable { public ActiveCell(string name) : base(name) { } public override object Value { get { return Globals.ThisAddIn.Application.ActiveCell; } } } public class ActiveSheet : PSVariable { public ActiveSheet(string name) : base(name) { } public override object Value { get { return Globals.ThisAddIn.Application.ActiveSheet; } } } and adding their instances to the current POwerShell session: runspace.SessionStateProxy.PSVariable.Set(new ActiveCell("ActiveCell")); runspace.SessionStateProxy.PSVariable.Set(new ActiveSheet("ActiveSheet")); This works and I am able to use those variables from PowerShell as $ActiveCell and $ActiveSheet (their value change as Excel active sheet or cell change). Then I read PSVariable documentation here and saw this: "There is no established scenario for deriving from this class. To programmatically create a shell variable, create an instance of this class and set it by using the PSVariableIntrinsics class." As I was deriving from PSVariable, I tried to use what was suggested: PSVariable activeCell = new PSVariable("ActiveCell"); activeCell.Value = Globals.ThisAddIn.Application.ActiveCell; runspace.SessionStateProxy.PSVariable.Set(activeCell); Using this, $ActiveCell appears in my PowerShell session, but its value doesn't change as I change the active cell in Excel. Is the above comment from PSVariable documentation something I should worry about, or I can continue creating PSVariable derived classes? Is there another way of making Excel globals available to PowerShell?

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• Time with and without OpenMP

  - by was

  I have a question.. I tried to improve a well known program algorithm in C, FOX algorithm for matrix multiplication.. relative link without openMP: (http://web.mst.edu/~ercal/387/MPI/ppmpi_c/chap07/fox.c). The initial program had only MPI and I tried to insert openMP in the matrix multiplication method, in order to improve the time of computation: (This program runs in a cluster and computers have 2 cores, thus I created 2 threads.) The problem is that there is no difference of time, with and without openMP. I observed that using openMP sometimes, time is equivalent or greater than the time without openMP. I tried to multiply two 600x600 matrices. void Local_matrix_multiply( LOCAL_MATRIX_T* local_A /* in */, LOCAL_MATRIX_T* local_B /* in */, LOCAL_MATRIX_T* local_C /* out */) { int i, j, k; chunk = CHUNKSIZE; // 100 #pragma omp parallel shared(local_A, local_B, local_C, chunk, nthreads) private(i,j,k,tid) num_threads(2) { /* tid = omp_get_thread_num(); if(tid == 0){ nthreads = omp_get_num_threads(); printf("O Pollaplasiamos pinakwn ksekina me %d threads\n", nthreads); } printf("Thread %d use the matrix: \n", tid); */ #pragma omp for schedule(static, chunk) for (i = 0; i < Order(local_A); i++) for (j = 0; j < Order(local_A); j++) for (k = 0; k < Order(local_B); k++) Entry(local_C,i,j) = Entry(local_C,i,j) + Entry(local_A,i,k)*Entry(local_B,k,j); } //end pragma omp parallel } /* Local_matrix_multiply */

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• Java: ResultSet exception - before start of result set

  - by Rosarch

  I'm having trouble getting data from a ResultSet object. Here is my code: String sql = "SELECT type FROM node WHERE nid = ?"; PreparedStatement prep = conn.prepareStatement(sql); int meetNID = Integer.parseInt(node.get(BoutField.field_meet_nid)); prep.setInt(1, meetNID); ResultSet result = prep.executeQuery(); result.beforeFirst(); String foundType = result.getString(1); if (! foundType.equals("meet")) { throw new IllegalArgumentException(String.format("Node %d must be of type 'meet', but was %s", meetNID, foundType)); } The error trace: Exception in thread "main" java.sql.SQLException: Before start of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1072) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:986) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:981) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:841) at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5656) at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5576) at nth.cumf3.nodeImport.Validator.validate(Validator.java:43) at nth.cumf3.nodeImport.Main.main(Main.java:38) What am I doing wrong here?

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• Generating a canonical path

  - by Joel

  Does any one know of any Java libraries I could use to generate canonical paths (basically remove back-references). I need something that will do the following: Raw Path - Canonical Path /../foo/ -> /foo /foo/ -> /foo /../../../ -> / /./foo/./ -> /foo //foo//bar -> /foo/bar //foo/../bar -> /bar etc... At the moment I lazily rely on using: new File("/", path).getCanonicalPath(); But this resolves the path against the actual file system, and is synchronised. java.lang.Thread.State: BLOCKED (on object monitor) at java.io.ExpiringCache.get(ExpiringCache.java:55) - waiting to lock <0x93a0d180> (a java.io.ExpiringCache) at java.io.UnixFileSystem.canonicalize(UnixFileSystem.java:137) at java.io.File.getCanonicalPath(File.java:559) The paths that I am canonicalising do not exist on my file system, so just the logic of the method will do me fine, thus not requiring any synchronisation. I'm hoping for a well tested library rather than having to write my own.

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• Sharing a COM port over TCP

  - by guinness

  What would be a simple design pattern for sharing a COM port over TCP to multiple clients? For example, a local GPS device that could transmit co-ordinates to remote hosts in realtime. So I need a program that would open the serial port and accept multiple TCP connections like: class Program { public static void Main(string[] args) { SerialPort sp = new SerialPort("COM4", 19200, Parity.None, 8, StopBits.One); Socket srv = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); srv.Bind(new IPEndPoint(IPAddress.Any, 8000)); srv.Listen(20); while (true) { Socket soc = srv.Accept(); new Connection(soc); } } } I would then need a class to handle the communication between connected clients, allowing them all to see the data and keeping it synchronized so client commands are received in sequence: class Connection { static object lck = new object(); static List<Connection> cons = new List<Connection>(); public Socket socket; public StreamReader reader; public StreamWriter writer; public Connection(Socket soc) { this.socket = soc; this.reader = new StreamReader(new NetworkStream(soc, false)); this.writer = new StreamWriter(new NetworkStream(soc, true)); new Thread(ClientLoop).Start(); } void ClientLoop() { lock (lck) { connections.Add(this); } while (true) { lock (lck) { string line = reader.ReadLine(); if (String.IsNullOrEmpty(line)) break; foreach (Connection con in cons) con.writer.WriteLine(line); } } lock (lck) { cons.Remove(this); socket.Close(); } } } The problem I'm struggling to resolve is how to facilitate communication between the SerialPort instance and the threads. I'm not certain that the above code is the best way forward, so does anybody have another solution (the simpler the better)?

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• Java abstract visitor - guarantueed to succeed? If so, why?

  - by disown

  I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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• Issue reading in a cell from Excel with Apache POI

  - by Nick

  I am trying to use Apache POI to read in old (pre-2007 and XLS) Excel files. My program goes to the end of the rows and iterates back up until it finds something that's not either null or empty. Then it iterates back up a few times and grabs those cells. This program works just fine reading in XLSX and XLS files made in Office 2010. I get the following error message: Exception in thread "main" java.lang.NumberFormatException: empty String at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source) at java.lang.Double.parseDouble(Unknown Source) at the line: num = Double.parseDouble(str); from the code: str = cell.toString(); if (str != "" || str != null) { System.out.println("Cell is a string"); num = Double.parseDouble(str); } else { System.out.println("Cell is numeric."); num = cell.getNumericCellValue(); } where the cell is the last cell in the document that's not empty or null. When I try to print the first cell that's not empty or null, it prints nothing, so I think I'm not accessing it correctly.

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• Is there a better way to write named-pipes in F#?

  - by Niran

  Hi I am new to F#. I am trying to communicate with java from F# using named pipe. The code below works but I am not sure if there is a better way to do this (I know the infinite loop is a bad idea but this is just a proof of concept) if anyone have any idea to improve this code please post your comments. Thanks in advance Niran open System.IO open System.IO.Pipes exception OuterError of string let continueLooping = true while continueLooping do let pipeServer = new NamedPipeServerStream("testpipe", PipeDirection.InOut, 4) printfn "[F#] NamedPipeServerStream thread created." //wait for connection printfn "[F#] Wait for a client to connect" pipeServer.WaitForConnection() printfn "[F#] Client connected." try // Stream for the request. let sr = new StreamReader(pipeServer) // Stream for the response. let sw = new StreamWriter(pipeServer) sw.AutoFlush <- true; // Read request from the stream. let echo = sr.ReadLine(); printfn "[F#] Request message: %s" echo // Write response to the stream. sw.WriteLine("[F#]: " + echo) pipeServer.Disconnect() with | OuterError(str) -> printfn "[F#]ERROR: %s" str printfn "[F#] Client Closing." pipeServer.Close()

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• python on apache - getting 404

  - by Kirby

  I edited this question after i found a solution... i need to understand why the solution worked instead of my method? This is likely to be a silly question. I tried searching other questions that are related... but to no avail. i am running Apache/2.2.11 (Ubuntu) DAV/2 SVN/1.5.4 PHP/5.2.6-3ubuntu4.5 with Suhosin-Patch mod_python/3.3.1 Python/2.6.2 i have a script called test.py #! /usr/bin/python print "Content-Type: text/html" # HTML is following print # blank line, end of headers print "hello world" running it as an executable works... /var/www$ ./test.py Content-Type: text/html hello world when i run http://localhost/test.py i get a 404 error. What am i missing? i used this resource to enable python parsing on apache. http://ubuntuforums.org/showthread.php?t=91101 From that same thread... the following code worked.. why? #!/usr/bin/python import sys import time def index(req): # Following line causes error to be sent to browser # rather than to log file (great for debug!) sys.stderr = sys.stdout #print "Content-type: text/html\n" #print """ blah1 = """<html> <head><title>A page from Python</title></head> <body> <h4>This page is generated by a Python script!</h4> The current date and time is """ now = time.gmtime() displaytime = time.strftime("%A %d %B %Y, %X",now) #print displaytime, blah1 += displaytime #print """ blah1 += """ <hr> Well House Consultants demonstration </body> </html> """ return blah1

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• Java Applet - ArrayIndexOutOfBoundsException (pt 2)

  - by Dan

  Hi there, I fixed my previous problem. But now when on my tile map... if I try to go 9 tiles to the RIGHT, and on trying to get to the 9th tile.... I will get this error: Exception in thread "AWT-EventQueue-1" java.lang.ArrayIndexOutOfBoundsException: 8 at tileGen.blocked(tileGen.java:125) at tileGen.keyPressed(tileGen.java:58) at java.awt.Component.processKeyEvent(Component.java:6221) at java.awt.Component.processEvent(Component.java:6040) at java.awt.Container.processEvent(Container.java:2041) at java.awt.Component.dispatchEventImpl(Component.java:4630) at java.awt.Container.dispatchEventImpl(Container.java:2099) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1850) at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:712) at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:990) at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:855) at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:676) at java.awt.Component.dispatchEventImpl(Component.java:4502) at java.awt.Container.dispatchEventImpl(Container.java:2099) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.EventQueue.dispatchEvent(EventQueue.java:599) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) Here is code: http://www.so.pastebin.com/hYkpQf13 I have tried many solutions, all of which have failed. Maybe someone here can I help me? Thank you.

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• Filp route value in asp.net mvc routes

  - by Herman

  Hi all, I am new to asp.net mvc, so please bear with me. We have the following route dictionary setup. routes.MapRoute( "Default", // Route name "{language}/{controller}/{action}/{id}", // URL with parameters new { language = "en", controller = "Home", action = "Index", id = "" } // Parameter defaults ); for any given page in our app, we to render a link to the a french version of the same page. For example, the page: http://www.example.com/en/home should have link on that page that points to http://www.example.com/fr/home Now I have the following UrlHelper extension method public static string FilpLanguage(this UrlHelper urlHelper) { var data = urlHelper.RequestContext.RouteData; if (System.Threading.Thread.CurrentThread.CurrentCulture == CultureInfo.GetCultureInfoByIetfLanguageTag("en-CA")) data.Values["language"] = "fr"; else data.Values["language"] = "en"; return urlHelper.RouteUrl(data.Values.Where(item => item.Value != null)); } However, calling FilpLanguage on www.example.com/en/home will return the following URL: www.example.com/en/home?current=[,] Am I missing something here? where did the current parameter come from? Thanks in advance.

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• CreateThread() fails on 64 bit Windows, works on 32 bit Windows. Why?

  - by Stephen Kellett

  Operating System: Windows XP 64 bit, SP2. I have an unusual problem. I am porting some code from 32 bit to 64 bit. The 32 bit code works just fine. But when I call CreateThread() for the 64 bit version the call fails. I have three places where this fails. 2 call CreateThread(). 1 calls beginthreadex() which calls CreateThread(). All three calls fail with error code 0x3E6, "Invalid access to memory location". The problem is all the input parameters are correct. HANDLE h; DWORD threadID; h = CreateThread(0, // default security 0, // default stack size myThreadFunc, // valid function to call myParam, // my param 0, // no flags, start thread immediately &threadID); All three calls to CreateThread() are made from a DLL I've injected into the target program at the start of the program execution (this is before the program has got to the start of main()/WinMain()). If I call CreateThread() from the target program (same params) via say a menu, it works. Same parameters etc. Bizarre. If I pass NULL instead of &threadID, it still fails. If I pass NULL as myParam, it still fails. I'm not calling CreateThread from inside DllMain(), so that isn't the problem. I'm confused and searching on Google etc hasn't shown any relevant answers. If anyone has seen this before or has any ideas, please let me know. Thanks for reading.

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• Updating an application OTA

  - by Bostjan

  I'm developing an application that will be available from a website (market probably as well). The problem I'm having at the moment is how to handle the updates to the app. I know how to check the version against the current one and I know if I need to update it. Question is...how? Is there a way I can download an APK from the website and start the install process? The user will have to confirm of course, but I just want to be able to start it for him. At the moment I'm doing this: private void doUpgrade() { // TODO Auto-generated method stub Builder builder = new AlertDialog.Builder(this); builder.setTitle(getString(R.string.upgrade)); builder.setIcon(R.drawable.help); builder.setMessage(getString(R.string.needUpgrade)); builder.setPositiveButton(getString(R.string.ok), new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub Map<String, String> data = new HashMap<String, String>(); try { HttpResponse re = Registration.doPost("http://www.android-town.com/appRelease/AndroidTown.apk",data); int statusCode = re.getStatusLine().getStatusCode(); closeApp(); } catch (ClientProtocolException e) { e.printStackTrace(); Toast.makeText(getApplicationContext(), getString(R.string.noURLAccess), Toast.LENGTH_SHORT).show(); closeApp(); } catch (IOException e) { e.printStackTrace(); Toast.makeText(getApplicationContext(), getString(R.string.noURLAccess), Toast.LENGTH_SHORT).show(); closeApp(); } } }); builder.setNegativeButton(getString(R.string.cancel), new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub dialog.cancel(); closeApp(); } }); builder.show(); } But it doesn't really do anything...should I open a webView with the URL? A new runnable thread? Any other way? Please help :) Cheers

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• @selector and return value

  - by user320926

  The idea it's very easy, i have an http download class, this class must support the http authentication but it's basically a background thread so i would like to avoid to prompt directly to the screen, i would like to use a delegate method to require from outside of the class, like a viewController. But i don't know if is possible or if i have to use a different syntax. This class use this delegate protocol: //Updater.h @protocol Updater <NSObject> -(NSDictionary *)authRequired; @optional -(void)statusUpdate:(NSString *)newStatus; -(void)downloadProgress:(int)percentage; @end @interface Updater : NSThread { ... } This is the call to the delegate method: //Updater.m // This check always fails :( if ([self.delegate respondsToSelector:@selector(authRequired:)]) { auth = [delegate authRequired]; } This is the implementation of the delegate method //rootViewController.m -(NSDictionary *)authRequired; { // TODO: some kind of popup or modal view NSMutableDictionary *ret=[[NSMutableDictionary alloc] init]; [ret setObject:@"utente" forKey:@"user"]; [ret setObject:@"password" forKey:@"pass"]; return ret; }

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• I am not able to kill a child process using TerminateProcess

  - by user1681210

  I have a problem to kill a child process using TerminateProcess. I call to this function and the process still there (in the Task Manager) This piece of code is called many times launching the same program.exe many times and these process are there in the task manager which i think is not good. sorry, I am quiet new in c++ I will really appreciate any help. thanks a lot!! the code is the following: STARTUPINFO childProcStartupInfo; memset( &childProcStartupInfo, 0, sizeof(childProcStartupInfo)); childProcStartupInfo.cb = sizeof(childProcStartupInfo); childProcStartupInfo.hStdInput = hFromParent; // stdin childProcStartupInfo.hStdOutput = hToParent; // stdout childProcStartupInfo.hStdError = hToParentDup; // stderr childProcStartupInfo.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW; childProcStartupInfo.wShowWindow = SW_HIDE; PROCESS_INFORMATION childProcInfo; /* for CreateProcess call */ bOk = CreateProcess( NULL, // filename pCmdLine, // full command line for child NULL, // process security descriptor */ NULL, // thread security descriptor */ TRUE, // inherit handles? Also use if STARTF_USESTDHANDLES */ 0, // creation flags */ NULL, // inherited environment address */ NULL, // startup dir; NULL = start in current */ &childProcStartupInfo, // pointer to startup info (input) */ &childProcInfo); // pointer to process info (output) */ CloseHandle( hFromParent ); CloseHandle( hToParent ); CloseHandle( hToParentDup ); CloseHandle( childProcInfo.hThread); CloseHandle( childProcInfo.hProcess); TerminateProcess( childProcInfo.hProcess ,0); //this is not working, the process thanks

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• Why is BorderLayout calling setSize() and setBounds()?

  - by ags

  I'm trying to get my head around proper use of the different LayoutManagers to make my GUI design skills more efficient and effective. For me, that usually requires a detailed understanding of what is going on under the hood. I've found some good discussion of the interaction and consequences of a Container using BorderLayout containing a Container using FlowLayout. I understand it for the most part, but wanted to confirm my mental model and to do so I am looking at the code for BorderLayout. In the code snippet below taken from BorderLayout.layoutContainer(), note the calls to the child Component's setSize() method followed by setBounds(). Looking at the source for these methods of Component, setSize() actually calls setBounds() with the current values for Component.x and Component.y. Why is this done (and not entirely redudant?) Doesn't the setBounds() call completely overwrite the results of the setSize() call? if ((c=getChild(NORTH,ltr)) != null) { c.setSize(right - left, c.height); Dimension d = c.getPreferredSize(); c.setBounds(left, top, right - left, d.height); top += d.height + vgap; } I'm also tring to understand where/when the child Component's size is initially set (before the LayoutManager.layoutContainer() method is called). Finally, this post itself raises a "meta-question": in a situation like this, where the source is available elsewhere, is the accepteed protocol to include the entire method? Or some other way to make it easier for folks to participate in the thread? Thanks.

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• Java: design for using many executors services and only few threads

  - by Guillaume

  I need to run in parallel multiple threads to perform some tests. My 'test engine' will have n tests to perform, each one doing k sub-tests. Each test result is stored for a later usage. So I have n*k processes that can be ran concurrently. I'm trying to figure how to use the java concurrent tools efficiently. Right now I have an executor service at test level and n executor service at sub test level. I create my list of Callables for the test level. Each test callable will then create another list of callables for the subtest level. When invoked a test callable will subsequently invoke all subtest callables test 1 subtest a1 subtest ...1 subtest k1 test n subtest a2 subtest ...2 subtest k2 call sequence: test manager create test 1 callable test1 callable create subtest a1 to k1 testn callable create subtest an to kn test manager invoke all test callables test1 callable invoke all subtest a1 to k1 testn callable invoke all subtest an to kn This is working fine, but I have a lot of new treads that are created. I can not share executor service since I need to call 'shutdown' on the executors. My idea to fix this problem is to provide the same fixed size thread pool to each executor service. Do you think it is a good design ? Do I miss something more appropriate/simple for doing this ?

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• Why does instanceof seem to work in a static generic function sometimes?

  - by michael

  Greetings. This is my first post in this site. I thought that because of type erasure, one could not expect the following code to compile, and indeed, it did not compile on an earlier version of Eclipse. My understanding was that instanceof was a run-time operator and could not know about the generic type which would be, by run-time, compiled away: public static <E extends Comparable<? super E>> void SampleForQuestion(E e) { if ( !(e instanceof String) ) System.out.println("I am not a String"); else System.out.println("I am a String"); } However, I was surprised to see that one of your threads actually included some code like this in an answer, and my latest Eclipse (Galileo on Windows with JVM 1.6 rev 20) is perfectly happy with it -- and it works, too. (I did notice that someone said it worked on Eclipse but not in another IDE/JDK in that thread, but don't remember the specifics.) Can someone explain why it works, and more importantly, because I have to guide my students, whether it should be expected to work in the future. Thank you. (I hope the code formatting comes through correctly - it looks indented correctly from my perspective and there are no tabs.)

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• Why won't WPF databindings show text when ToString() has a collaborating object?

  - by Jay

  In a simple form, I bind to a number of different objects -- some go in listboxes; some in textblocks. A couple of these objects have collaborating objects upon which the ToString() method calls when doing its work -- typically a formatter of some kind. When I step through the code I see that when the databinding is being set up, ToString() is called the collaborating object is not null and returns the expected result when inspected in the debugger, the objects return the expected result from ToString() BUT the text does not show up in the form. The only common thread I see is that these use a collaborating object, whereas the other bindings that show up as expected simply work from properties and methods of the containing object. If this is confusing, here is the gist in code: public class ThisThingWorks { private SomeObject some_object; public ThisThingWorks(SomeObject s) { some_object = s; } public override string ToString() { return some_object.name; } } public class ThisDoesntWork { private Formatter formatter; private SomeObject some_object; public ThisDoesntWork(SomeObject o, Formatter f) { formatter = f; some_object = o; } public override string ToString() { return formatter.Format(some_object.name); } } Again, let me reiterate -- the ToString() method works in every other context -- but when I bind to the object in WPF and expect it to display the result of ToString(), I get nothing. Update: The issue seems to be what I see as a buggy behaviour in the TextBlock binding. If I bind the Text property to a property of the DataContext that is declared as an interface type, ToString() is never called. If I change the property declaration to an implementation of the interface, it works as expected. Other controls, like Label work fine when binding the Content property to a DataContext property declared as either the implementation or the interface. Because this is so far removed from the title and content of this question, I've created a new question here: http://stackoverflow.com/questions/2917878/why-doesnt-textblock-databinding-call-tostring-on-a-property-whose-compile-tim

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• How to display a busy message over a wpf screen

  - by dave

  Hey, I have a WPF application based on Prism4. When performing slow operations, I want to show a busy screen. I will have a large number of screens, so I'm trying to build a single solution into the framework rather than adding the busy indicator to each screen. These long running operations run in a background thread. This allows the UI to be updated (good) but does not stop the user from using the UI (bad). What I'd like to do is overlay a control with a spinning dial sort of thing and have that control cover the entire screen (the old HTML trick with DIVs). When the app is busy, the control would display thus block any further interaction as well as showing the spinny thing. To set this up, I thought I could just have my app screen in a canvas along with the spinny thing (with a greater ZIndex) then just make the spinny thing visible as required. This, however, is getting hard. Canvases do not seem well set up for this and I think I might be barking up the wrong tree. I would appreciate any help. Thanks.

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• Using sigprocmask to implement locks

  - by EpsilonVector

  I'm implementing user threads in Linux kernel 2.4, and I'm using ualarm to invoke context switches between the threads. We have a requirement that our thread library's functions should be uninterruptable, so I looked into blocking signals and learned that using sigprocmask is the standard way to do this. However, it looks like I need to do quite a lot to implement this: sigset_t new_set, old_set; sigemptyset(&new_set); sigaddset(&new_set, SIGALRM); sigprocmask(SIG_BLOCK, &new_set, &old_set); This blocks SIGALARM but it does this with 3 function invocations! A lot can happen in the time it takes for these functions to run, including the signal being sent. The best idea I had to mitigate this was temporarily disabling ualarm, like this: sigset_t new_set, old_set; time=ualarm(0,0); sigemptyset(&new_set); sigaddset(&new_set, SIGALRM); sigprocmask(SIG_BLOCK, &new_set, &old_set); ualarm(time, 0); Which is fine except that this feels verbose. Isn't there a better way to do this?

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• iPhone --- 3DES Encryption returns "wrong" results?

  - by Jan Gressmann

  Hello fellow developers, I have some serious trouble with a CommonCrypto function. There are two existing applications for BlackBerry and Windows Mobile, both use Triple-DES encryption with ECB mode for data exchange. On either the encrypted results are the same. Now I want to implent the 3DES encryption into our iPhone application, so I went straight for CommonCrypto: http://www.opensource.apple.com/source/CommonCrypto/CommonCrypto-32207/CommonCrypto/CommonCryptor.h I get some results if I use CBC mode, but they do not correspond with the results of Java or C#. Anyway, I want to use ECB mode, but I don't get this working at all - there is a parameter error showing up... This is my call for the ECB mode... I stripped it a little bit: const void *vplainText; plainTextBufferSize = [@"Hello World!" length]; bufferPtrSize = (plainTextBufferSize + kCCBlockSize3DES) & ~(kCCBlockSize3DES - 1); plainText = (const void *) [@"Hello World!" UTF8String]; NSString *key = @"abcdeabcdeabcdeabcdeabcd"; ccStatus = CCCrypt(kCCEncrypt, kCCAlgorithm3DES, kCCOptionECBMode, key, kCCKeySize3DES, nil, // iv, not used with ECB plainText, plainTextBufferSize, (void *)bufferPtr, // output bufferPtrSize, &movedBytes); t is more or less the code from here: http://discussions.apple.com/thread.jspa?messageID=9017515 But as already mentioned, I get a parameter error each time... When I use kCCOptionPKCS7Padding instead of kCCOptionECBMode and set the same initialization vector in C# and my iPhone code, the iPhone gives me different results. Is there a mistake by getting my output from the bufferPtr? Currently I get the encrypted stuff this way: NSData *myData = [NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes]; result = [[NSString alloc] initWithData:myData encoding:NSISOLatin1StringEncoding]; It seems I almost tried every setting twice, different encodings and so on... where is my error?

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• NullPointerException on Activity Testing Tutorial

  - by Bendik

  Hello, I am currently trying the activity testing tutorial (Found here), and have a problem. It seems that whenever I try to call something inside the UIThread, I get a java.lang.NullPointerException. public void testSpinnerUI() { mActivity.runOnUiThread( new Runnable() { public void run() { mSpinner.requestFocus(); } }); } This gives me: Incomplete: java.lang.NullPointerException and nothing else. I have tried this on two different samples now, with the same result. I tried with a try/catch clause around the mSpinner.requestFocus() call, and it seems that mSpinner is null inside the thread. I have set it properly up with the setUp() function found in the same sample, and a quick assertNotNull( mSpinner ) shows me that mSpinner is in fact not null after the setUp() function. What can be the cause of this? EDIT; ok, some more testing has been done. It seems that the application that is being tested resets between each test. This essentially makes me have to reinstantiate all variables between each test. Is this normal?

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