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• Specifying both multiple targets and multiple build files with ant or subant in 1.6

  - by Paul Marshall

  I'm trying to unify a build process, running one build to get multiple packages. My first shot at this is just having a central build script call <ant or <subant on each project's build.xml file. I'm using Ant 1.6, and I've run into a funny problem: either I use the <ant task, and I can specify multiple targets but not multiple build files, or I use the <subant task, and I can specify multiple build files but not multiple targets. I realize there's a few solutions here already: Just upgrade to Ant 1.7 already; <antcall can do multiple targets there. Edit the separate project build files to have a variety of top-level targets, so I can call each individual file with just one target, and use <antcall. Copy-paste a lot of <ant tasks, with a little help from <macrodef to help the sanity. Is there something I've missed, that will allow me to do what I want from this single central build.xml without a) editing individual project files, b) writing lots of repetitive code, or c) upgrading Ant, and that d) doesn't require editing every time I add a new project?

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• Get Function Pointer to function in a shared library I didn't directly load

  - by bdk

  My Linux application (A) links against a Third Party shared Library (B) which I don't have source code to. This library makes use of another third party shared library that I don't have source code to (C). I believe that (B) uses dlopen to access (C) instead of directly linking. My reasoning for this is that 'ldd' on (B) does not show (C) and objdump -X (B) shows references to dlopen/dlclose/dlsym. My requirement is that I need to in my code for (A) get a function pointer to a function foo() located in (C). Normally I'd use dlsym for this, but I need to pass it the handle returned from dlopen which I don't have since (B) does not expose this. - For the larger context: I need to modify the function in (C) such that everytime it calls its helper function bar() (also located in (C)), it also calls a function with the same signature located in (A) with the same parameters (Basically inject my code into the codepath of (C) foo()-bar(). I believe I've found a way to accomplish this using gdb, but in order to port my gdb command list, but I'm stuck on the step of getting the function pointer. I'm also open to alternatives to accomplish the same task rather than the exact problem as stated above Edit: After writing this I realized I can probably just do another dlopen on the file in my code and the symbols returned via dlsym on that handle should be the same as received via the original dlopen, If I'm reading the dlopen man page correctly. However I'm still interested in advice or assistance with the my larger context, If theres a better way to go about this

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• Ditching Django's models for Ajax/Web Services

  - by Igor Ganapolsky

  Recently I came across a problem at work that made me rethink Django's models. The app I am developing resides on a Linux server. Its a simple model/view/controller app that involves user interaction and updating data in the database. The problem is that this data resides in a MS SQL database on a Windows machine. So in order to use Django's models, I would have to leverage an ODBC driver on linux, and the use a python add-on like pyodbc. Well, let me tell you, setting up a reliable and functional ODBC connection on linux is no easy feat! So much so, that I spent several hours maneuvering this on my CentOS with no luck, and was left with frustration and lots of dumb system errors. In the meantime I have a deadline to meet, and suddenly the very agile and rapid Django application is a roadblock rather than a pleasure to work with. Someone on my team suggested writing this app in .NET. But there are a few problems with that: it won't be deployable on a linux machine, and I won't be able to work on it since I don't know ASP.net. Then a much better suggestion was made: keep the app in django, but instead of using models, do straight up ajax/web services calls in the template. And then it dawned on me - what a great idea. Django's models seem like a nuissance and hindrance in this case, and I can just have someone else write .Net services on their side, that I can call from my template. As a result my app will be leaner and more compact. So, I was wondering if you guys ever came across a similar dillema and what you decided to do about it.

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• How do i write tasks? (parallel code)

  - by acidzombie24

  I am impressed with intel thread building blocks. I like how i should write task and not thread code and i like how it works under the hood with my limited understanding (task are in a pool, there wont be 100 threads on 4cores, a task is not guaranteed to run because it isnt on its own thread and may be far into the pool. But it may be run with another related task so you cant do bad things like typical thread unsafe code). I wanted to know more about writing task. I like the 'Task-based Multithreading - How to Program for 100 cores' video here http://www.gdcvault.com/sponsor.php?sponsor_id=1 (currently second last link. WARNING it isnt 'great'). My fav part was 'solving the maze is better done in parallel' which is around the 48min mark (you can click the link on the left side. That part is really all you need to watch if any). However i like to see more code examples and some API of how to write task. Does anyone have a good resource? I have no idea how a class or pieces of code may look after pushing it onto a pool or how weird code may look when you need to make a copy of everything and how much of everything is pushed onto a pool.

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• PostgreSQL, Foreign Keys, Insert speed & Django

  - by Miles

  A few days ago, I ran into an unexpected performance problem with a pretty standard Django setup. For an upcoming feature, we have to regenerate a table hourly, containing about 100k rows of data, 9M on the disk, 10M indexes according to pgAdmin. The problem is that inserting them by whatever method literally takes ages, up to 3 minutes of 100% disk busy time. That's not something you want on a production site. It doesn't matter if the inserts were in a transaction, issued via plain insert, multi-row insert, COPY FROM or even INSERT INTO t1 SELECT * FROM t2. After noticing this isn't Django's fault, I followed a trial and error route, and hey, the problem disappeared after dropping all foreign keys! Instead of 3 minutes, the INSERT INTO SELECT FROM took less than a second to execute, which isn't too surprising for a table <= 20M on the disk. What is weird is that PostgreSQL manages to slow down inserts by 180x just by using 3 foreign keys. Oh, disk activity was pure writing, as everything is cached in RAM; only writes go to the disks. It looks like PostgreSQL is working very hard to touch every row in the referred tables, as 3MB/sec * 180s is way more data than the 20MB this new table takes on disk. No WAL for the 180s case, I was testing in psql directly, in Django, add ~50% overhead for WAL logging. Tried @commit_on_success, same slowness, I had even implemented multi row insert and COPY FROM with psycopg2. That's another weird thing, how can 10M worth of inserts generate 10x 16M log segments? Table layout: id serial primary, a bunch of int32, 3 foreign keys to small table, 198 rows, 16k on disk large table, 1.2M rows, 59 data + 89 index MB on disk large table, 2.2M rows, 198 + 210MB So, am I doomed to either drop the foreign keys manually or use the table in a very un-Django way by defining saving bla_id x3 and skip using models.ForeignKey? I'd love to hear about some magical antidote / pg setting to fix this.

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• Distributing a bundle of files across an extranet

  - by John Zwinck

  I want to be able to distribute bundles of files, about 500 MB per bundle, to all machines on a corporate "extranet" (which is basically a few LANs connected using various private mechanisms, including leased lines and VPN). The total number of hosts is roughly 100, and the goal is to get a copy of the bundle from one host onto all the other hosts reliably, quickly, and efficiently. One important issue is that some hosts are grouped together on single fast LANs in which case the network I/O should be done once from one group to the next and then within each group between all the peers. This is as opposed to a strict central server system where multiple hosts might each fetch the same bundle over a slow link, rather than once via the slow link and then between each other quickly. A new bundle will be produced every few days, and occasionally old bundles will be deleted (but that problem can be solved separately). The machines in question happen to run recent Linuxes, but bonus points will go to solutions which are at least somewhat cross-platform (in which case the bundle might differ per platform but maybe the same mechanism can be used). That's pretty much it. I'm not opposed to writing some code to handle this, but it would be preferable if it were one of bash, Python, Ruby, Lua, C, or C++.

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• Is it legal to extend the Class class?

  - by spiralganglion

  I've been writing a system that generates some templates, and then generates some objects based on those templates. I had the idea that the templates could be extensions of the Class class, but that resulted in some magnificent errors: VerifyError: Error #1107: The ABC data is corrupt, attempt to read out of bounds. What I'm wondering is if subclassing Class is even possible, if there is perhaps some case where doing this would be appropriate, and not just a gross misuse of OOP. I believe it should be possible, as ActionScript allows you to create variables of the Class type. This use is described in the LiveDocs entry for Class, yet I've seen no mentions of subclassing Class. Here's a pseudocode example: class Foo extends Class var a:Foo = new Foo(); trace(a is Class) // true, right? var b = new a(); I have no idea what the type of b would be. In summary: can you subclass the Class class? If so, how can you do it without errors, and what type are the instances of the instances of the Class subclass?

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• Tricky MySQL Query for messaging system in Rails - Please Help

  - by ole_berlin

  Hi, I'm writing a facebook style messaging system for a Rails App and I'm having trouble selecting the Messages for the inbox (with will_paginate). The messages are organized in threads, in the inbox the most recent message of a thread will appear with a link to it's thread. The thread is organized via a parent_id 1-n relationship with itself. So far I'm using something like this: class Message < ActiveRecord::Base belongs_to :sender, :class_name => 'User', :foreign_key => "sender_id" belongs_to :recipient, :class_name => 'User', :foreign_key => "recipient_id" has_many :children, :class_name => "Message", :foreign_key => "parent_id" belongs_to :thread, :class_name => "Message", :foreign_key => "parent_id" end class MessagesController < ApplicationController def inbox @messages = current_user.received_messages.paginate :page => params[:page], :per_page => 10, :order => "created_at DESC" end end That gives me all the messages, but for one thread the thread itself and the most recent message will appear (and not only the most recent message). I can also not use the GROUP BY clause, because for the thread itself (the parent so to say) the parent_id = nil of course. Anyone got an idea on how to solve this in an elegant way? I already thought about adding the parent_id to the parent itself and then group by parent_id, but I'm not sure if that works. Thanks

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• "Session is Closed!" - NHibernate

  - by Alexis Abril

  This is in a web application environment: An initial request is able to successfully complete, however any additional requests return a "Session is Closed" response from the NHibernate framework. I'm using a HttpModule approach with the following code: public class MyHttpModule : IHttpModule { public void Init(HttpApplication context) { context.EndRequest += ApplicationEndRequest; context.BeginRequest += ApplicationBeginRequest; } public void ApplicationBeginRequest(object sender, EventArgs e) { CurrentSessionContext.Bind(SessionFactory.Instance.OpenSession()); } public void ApplicationEndRequest(object sender, EventArgs e) { ISession currentSession = CurrentSessionContext.Unbind( SessionFactory.Instance); currentSession.Dispose(); } public void Dispose() { } } SessionFactory.Instance is my singleton implementation, using FluentNHibernate to return an ISessionFactory object. In my repository class, I attempt to use the following syntax: public class MyObjectRepository : IMyObjectRepository { public MyObject GetByID(int id) { using (ISession session = SessionFactory.Instance.GetCurrentSession()) return session.Get<MyObject>(id); } } This allows code in the application to be called as such: IMyObjectRepository repo = new MyObjectRepository(); MyObject obj = repo.GetByID(1); I have a suspicion my repository code is to blame, but I'm not 100% sure on the actual implementation I should be using. I found a similar issue on SO here. I too am using WebSessionContext in my implementation, however, no solution was provided other than writing a custom SessionManager. For simple CRUD operations, is a custom session provider required apart from the built in tools(ie WebSessionContext)?

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• How can I print the argument value that caused Exception in Java?

  - by Sanoj

  I am writing a parser for csv-files, and sometimes I get NumberFormatException. Is there an easy way to print the argument value that caused the exception? For the moment do I have many try-catch blocks that look like this: String ean; String price; try { builder.ean(Long.parseLong(ean)); } catch (NumberFormatException e) { System.out.println("EAN: " + ean); e.printStackTrace(); } try { builder.price(new BigDecimal(price)); } catch (NumberFormatException e) { System.out.println("Price: " + price); e.printStackTrace(); } I would like to be able to write something like: try { builder.ean(Long.parseLong(ean)); } catch (NumberFormatException e) { e.printMethod(); // Long.parseLong() e.printArgument(); // should print the string ean "99013241.23" e.printStackTrace(); } Is there any way that I at least can improve my code? And do this kind of printing/logging more programmatically?

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• What's the pattern for a JSONP method that was initiated from a jQuery plugin?

  - by michielvoo

  I'm writing a jQuery plugin to render data retrieved from another domain in an element on the page. I follow the typical pattern for my jQuery plugin: $(selector).Plugin(options); In the plugin I get external data using jQuery.getScript(url, [success]). The external data source allows me to define the name of a method and it will wrap the data in a call to that method (JSONP): $.getScript("http://www.example.com/data?callback=global_callback", instance_callback); This effectively results in: <script type="text/javascript"> global_callback(data); </script> The scope of global_callback limits what the Plugin instance can do with the data. And the global_callback method has no knowledge of the selector or options that the plugin was instantiated with. I was thinking that global_callback would just store the data, and the plugin would retrieve the data in instance_callback. But I need to make sure that instance_callback will retrieve the correct data, I foresee a problem with multiple instances of the Plugin. How can I handle this? Thanks!

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• Simulating mouse clicks on Mac OS X does not work for some applications.

  - by Thomi

  I'm writing an application for Mac OS X 10.6 and later in C++. One part of the application needs to simulate mouse movement and mouse clicks. I do this currently by posting CGEvent objects using CGEventPost(kCGHIDEventTap, event);. This works, for the most part - I can simulate mouse movement and clicks just fine, but it seems to fail in some areas. For example: In Mozilla Firefox and Safari, I can click on all the menus, but cannot click on a link within a website. When I try, the link is highlighted, but the browser never follows the link. However, I can right-click on a link, select "open link in new tab", and everything works as expected. Solved - creating the mouse event using CGEventCreateMouseEvent(...) makes the event work within web browser. I can click on the "Dashboard" icon to brink up the dashboard, but I cannot click on the "i" button on any of the dashboard widgets. Similarly, clicking on any of the search results from the spotlight search widget doesn't work either. This inconsistency is along application boundaries. What might be the cause?

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• Rapid calls to fread crashes the application

  - by Slynk

  I'm writing a function to load a wave file and, in the process, split the data into 2 separate buffers if it's stereo. The program gets to i = 18 and crashes during the left channel fread pass. (You can ignore the couts, they are just there for debugging.) Maybe I should load the file in one pass and use memmove to fill the buffers? if(params.channels == 2){ params.leftChannelData = new unsigned char[params.dataSize/2]; params.rightChannelData = new unsigned char[params.dataSize/2]; bool isLeft = true; int offset = 0; const int stride = sizeof(BYTE) * (params.bitsPerSample/8); for(int i = 0; i < params.dataSize; i += stride) { std::cout << "i = " << i << " "; if(isLeft){ std::cout << "Before Left Channel, "; fread(params.leftChannelData+offset, sizeof(BYTE), stride, file + i); std::cout << "After Left Channel, "; } else{ std::cout << "Before Right Channel, "; fread(params.rightChannelData+offset, sizeof(BYTE), stride, file + i); std::cout << "After Right Channel, "; offset += stride; std::cout << "After offset incr.\n"; } isLeft != isLeft; } } else { params.leftChannelData = new unsigned char[params.dataSize]; fread(params.leftChannelData, sizeof(BYTE), params.dataSize, file); }

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• How to perform a binary search on IList<T>?

  - by Daniel Brückner

  Simple question - given an IList<T> how do you perform a binary search without writing the method yourself and without copying the data to a type with build-in binary search support. My current status is the following. List<T>.BinarySearch() is not a member of IList<T> There is no equivalent of the ArrayList.Adapter() method for List<T> IList<T> does not inherit from IList, hence using ArrayList.Adapter() is not possible I tend to believe that is not possible with build-in methods, but I cannot believe that such a basic method is missing from the BCL/FCL. If it is not possible, who can give the shortest, fastest, smartest, or most beatiful binary search implementation for IList<T>? UPDATE We all know that a list must be sorted before using binary search, hence you can assume that it is. But I assume (but did not verify) it is the same problem with sort - how do you sort IList<T>? CONCLUSION There seems to be no build-in binary search for IList<T>. One can use First() and OrderBy() LINQ methods to search and sort, but it will likly have a performance hit. Implementing it yourself (as an extension method) seems the best you can do.

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• Getting all objects with a certain element inside a collection of strings with criteria API.

  - by Jens Jansson

  Hey. I'm trying to build a Hibernate Criteria query to find entities that have a specific element inside a collection. We can take as an example a Book -object that looks like this: public class Book { private Long id; private String title; private Set<String> authors = new HashSet<String>(); } The entity is mapped like this: <class name="Book" table="Book"> <id name="id" column="BOOK_ID"> <generator class="native"/> </id> <property name="title"/> <set name="authors" table="Book_Authors"> <key column="BOOK_ID"/> <element type="string" column="AUTHORS"/> </set> </class> Now I would like to find out which books are written by Matt. With pure SQL I can do a query like this: String author = "Matt"; String query = "SELECT * FROM Book " + "WHERE BOOK_ID IN " + "(SELECT BOOK_ID FROM Book_Authors " + "WHERE authors = :author )"; List<Book> result = session.createSQLQuery(query) .addEntity(Book.class) .setParameter("author", author) .list(); This works all good and well, and I get out all books that Matt has been a part of writing. The project I work in, however, uses the Criteria API instead of raw SQL, and I haven't found a way to express the same query in that form. I've taken a look on the Restrictions API and the closest I've found is Restions.in(propertyName, collection) but that works the other way around (one value in object, many values to match against). Any ideas?

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• Is it possible to use SqlGeography with Linq to Sql?

  - by cofiem

  I've been having quite a few problems trying to use Microsoft.SqlServer.Types.SqlGeography. I know full well that support for this in Ling to Sql is not great. I've tried numerous ways, beginning with what would the expected way (Database type of geography, CLR type of SqlGeography). This produces the NotSupportedException, which is widely discussed via blogs. I've then gone down the path of treating the geography column as a varbinary(max), as geography is a UDT stored as binary. This seems to work fine (with some binary reading and writing extension methods). However, I'm now running into a rather obscure issue, which does not seem to have happened to many other people. System.InvalidCastException: Unable to cast object of type 'Microsoft.SqlServer.Types.SqlGeography' to type 'System.Byte[]'. This error is thrown from an ObjectMaterializer when iterating through a query. It seems to only occur when the tables containing geography columns are included in a query implicitly (ie. using the EntityRef<> properties to do joins). System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext() My question: If I'm retrieving the geography column as varbinary(max), I might expect the reverse error: can't cast byte[] to SqlGeography. That I would understand. This I don't. I do have some properies on the partial LINQ to SQL classes that hide the binary conversion... could those be the issue? Any help appreciated, and I know there's probably not enough information.

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• Is nested synchronized block necessary?

  - by Dan

  I am writing a multithreaded program and I have a method that has a nested synchronized blocks and I was wondering if I need the inner sync or if just the outer sync is good enough. public class Tester { private BlockingQueue<Ticket> q = new LinkedBlockingQueue<>(); private ArrayList<Long> list = new ArrayList<>(); public void acceptTicket(Ticket p) { try { synchronized (q) { q.put(p); synchronized (list) { if (list.size() < 5) { list.add(p.getSize()); } else { list.remove(0); list.add(p.getSize()); } } } } catch (InterruptedException ex) { Logger.getLogger(Consumer.class.getName()).log(Level.SEVERE, null, ex); } } } EDIT: This isn't a complete class as I am still working on it. But essentially I am trying to emulate a ticket machine. The ticket machine maintains a list of tickets in the BlockingQueue q. Whenever a client adds a ticket to the machine, the machine also keeps track of the price of the last 5 tickets (ArrayList list)

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• how to create trackballevent in android custom adapter?

  - by UMMA

  dear friends, i am using following code to create custom adapter for listview. now i want to use trackball click event in it but i dont know how to do that can any one help me out in creating ontracballevent in custom adapter? i have tried writing few lines but not able to solve it. public class EfficientAdapter extends BaseAdapter implements Filterable { private LayoutInflater mInflater; private Context context; int pos; public EfficientAdapter(Context context) { mInflater = LayoutInflater.from(context); this.context = context; } public View getView(final int position, View convertView, ViewGroup parent) { ViewHolder holder; convertView = mInflater.inflate(R.layout.adaptor_contentposts, null); convertView.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { //click functionality } }); MotionEvent event= MotionEvent.CREATOR.createFromParcel(null); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: //display click message } convertView.onTrackballEvent(event); return convertView; } class ViewHolder { TextView textLine; TextView textLine2; TextView PostedByAndPostedOn; ImageButton ImgButton; } @Override public Filter getFilter() { return null; } @Override public long getItemId(int position) { return 0; } @Override public int getCount() { return ad_id.length; } @Override public Object getItem(int position) { return ad_id[position]; } }

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• No transperancy in Bitmap loading from MemoryStream

  - by Jogi Joseph George

  Please see the C# code. When i am writing a Bitmap to a file and read from the file, i am getting the transperancy correctly. using (Bitmap bmp = new Bitmap(2, 2)) { Color col = Color.FromArgb(1, 2, 3, 4); bmp.SetPixel(0, 0, col); bmp.Save("J.bmp"); } using (Bitmap bmp = new Bitmap("J.bmp")) { Color col = bmp.GetPixel(0, 0); // ------------------------------ // Here col.A is 1. This is right. // ------------------------------ } But if I write the Bitmap to a MemoryStream and read from that MemoryStream, the transperancy has been removed. All Alpha values become 255. MemoryStream ms = new MemoryStream(); using (Bitmap bmp = new Bitmap(2, 2)) { Color col = Color.FromArgb(1, 2, 3, 4); bmp.SetPixel(0, 0, col); bmp.Save(ms, ImageFormat.Bmp); } using (Bitmap bmp = new Bitmap(ms)) { Color col = bmp.GetPixel(0, 0); // ------------------------------ // But here col.A is 255. Why? i am expecting 1 here. // ------------------------------ } I wish to save the Bitmap to a MemoryStream and read it back with transperancy. Could you please help me?

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• I seek a PDF paginator

  - by Cameron Laird

  More precisely, I need software that will allow me to consume existing PDF instances, decorate them with page numbers, or page-number-like writing, then write them back to the filesystem. I'll happily pay for an application, or program it myself. I almost certainly require the software run under Linux (Ubuntu, more specifically). iText comes close. iText certainly can read existing PDF instances. While iText is, for this purpose, only a library, and requires me to program a tiny amount to specify where on the page the numbers should appear, I'm happy to do that. I hesitate with iText only because the latest iText license is a headache at certain government agencies (in practice, I'd probably request and pay for a special license), and because, over the last few years, I've observed cases where iText doesn't appear to keep up with the standard, that is, it has more troubles than I expect reading PDFs observed "in the wild". Similarly, every other possibility I know has at least one difficulty: ReportLab would likely require a disproportionate licensing fee for the small value it provides in this situation, and so on. This application requires no particular sophistication with Unicode, fonts, ... I recognize there are plenty of executables and libraries that do some or all of what I require. I welcome any tips on software that is reliable, generally current with PDF practice, flexible/programmable/configurable/..., and "automatable". In the absence of any new insight, I'll likely go with a specific open-source library I don't want to mention now for which I've already contracted enhancements, or perhaps revisit iText.

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• Advantages/Disadvantages of AIR vs Flex/Web

  - by Lizzan

  Hi all, I'm tasked with writing an application for placing and connecting objects (sort of like a room planner where you can place furniture). I've made a demo using Flash Builder 4 and built it for AIR as a desktop app. Now the client wants the full app, but they and I am unsure whether to continue building it as an AIR app or transform it to a web application using Flex. I tried making a simple conversion of the AIR app to a web app, and most things worked but not all. The things that don't work seem to be simple bugs, though, not complete lack of capability. The capabilities that I'm going to need (except for the modelling) are: Printing of the finished image + a list of the furniture that has been placed A way to save and retrieve finished plans A way to export the list of furniture to Excel format Handling a whole slew of data about the different objects Only the printing has been implemented so far, and seems to work in the web app as well. What advantages/disadvantages are there with the two approaches? Are any of the capabilities I need much worse (or even impossible) to implement in either approach?

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• Can threads safely read variables set by VCL events?

  - by Tom1952

  Is it safe for a thread to READ a variable set by a Delphi VCL event? When a user clicks on a VCL TCheckbox, the main thread sets a boolean to the checkbox's Checked state. CheckboxState := CheckBox1.Checked; At any time, a thread reads that variable if CheckBoxState then ... It doesn't matter if the thread "misses" a change to the boolean, because the thread checks the variable in a loop as it does other things. So it will see the state change eventually... Is this safe? Or do I need special code? Is surrounding the read and write of the variable (in the thread and main thread respectively) with critical code calls necessary and sufficient? As I said, it doesn't matter if the thread gets the "wrong" value, but I keep thinking that there might be a low-level problem if one thread tries to read a variable while the main thread is in the middle of writing it, or vice versa. My question is similar to this one: http://stackoverflow.com/questions/1353096/cross-thread-reading-of-a-variable. (Also related to my previous question: http://stackoverflow.com/questions/2449183/using-entercriticalsection-in-thread-to-update-vcl-label)

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• Java Random Slowdowns on Mac OS cont'd

  - by javajustice

  I asked this question a few weeks ago, but I'm still having the problem and I have some new hints. The original question is here: http://stackoverflow.com/questions/1651887/java-random-slowdowns-on-mac-os Basically, I have a java application that splits a job into independent pieces and runs them in separate threads. The threads have no synchronization or shared memory items. The only resources they do share are data files on the hard disk, with each thread having an open file channel. Most of the time it runs very fast, but occasionally it will run very slow for no apparent reason. If I attach a CPU profiler to it, then it will start running quickly again. If I take a CPU snapshot, it says its spending most of its time in "self time" in a function that doesn't do anything except check a few (unshared unsynchronized) booleans. I don't know how this could be accurate because 1, it makes no sense, and 2, attaching the profiler seems to knock the threads out of whatever mode they're in and fix the problem. Also, regardless of whether it runs fast or slow, it always finishes and gives the same output, and it never dips in total cpu usage (in this case ~1500%), implying that the threads aren't getting blocked. I have tried different garbage collectors, different sizings the parts of the memory space, writing data output to non-raid drives, and putting all data output in threads separate the main worker threads. Does anyone have any idea what kind of problem this could be? Could it be the operating system (OS X 10.6.2) ? I have not been able to duplicate it on a windows machine, but I don't have one with a similar hardware configuration.

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• Blackberry invalidate field not causing a repaint

  - by Michaela

  I'm writing a Blackberry app. I have a custom list field where I can select an item in the list which pushes the edit screen onto the stack. I edit the item and save, and when I pop that screen off so I am back on my list screen, I want to view the update I just made reflected in the list. I have done this on other screens which just had LabelFields and it worked fine. However, with the list screen, calling invalidate() seems to do nothing. I know the value has saved correctly through print lines, and I see the paint() method in the listfield is getting called. But the only way I can get the list field to update is to delete it from the screen and re-add it. That seems wrong. What am I doing wrong? public class ListTasksScreen extends MainScreen{ private TaskList tasks; private CustomListField taskListField; public ListTasksScreen (TaskList tasks){ super(); this.tasks = tasks; Vector incompleteTasks = tasks.getIncompleteTasks(); taskListField = new CustomListField(incompleteTasks, tasks); add(taskListField); } public void updateTaskList(TaskList t) { Vector incompleteTasks = t.getIncompleteTasks(); taskListField= new TaskListField(incompletetTasks, t); //I just want to call taskListField.invalidate() here. //the only thing that seems to work is deleting taskListField //and re-adding this.delete(taskListField); add(taskListField); } }

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• Technical choices in unmarshaling hash-consed data

  - by Pascal Cuoq

  There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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