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• Workflow engine BPMN, Drools, etc or ESB?

  - by Tom

  We currently have an application that is based on an in-house developed workflow engine with YAML based DSL. We are looking to move parts of it to Java. I have discovered a number of java solutions like Intalio, JBPM, Drools Expert, Drools Flow etc. They appear to be aimed at businesses where the business analyst creates the workflows using a graphical editor and submits them to the workflow engine. They seem geared towards ease of use for non-technical people rather than for developers with a focus on human interaction. The workflows tend to look like. Discover-a-file -\ -> join -> process-file -> move-file -> register-file Discover-some-metadata -/ If any step fails we need to retry it X times. We also need to be able to stop the system and be able to restart it and have it continue from where it was (durable). Some of our workflows can be defined by a set of goals we need to achieve so Jess's backwards rule chaining sounds interesting but it is not open source. It might be that what we are after is a Finite State Machine engine or just an Enterprise Service Bus and do everything as JMS queues. Is there a good open source workflow engine that is both standards-based but also geared towards developers. We don't particular want to use a graphical workflow designer or write reams of XML and it should ideally be in Java or language agnostic (makes REST/Soap calls to external services). Thanks, Tom

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• Generating all unique combinations for "drive ya nuts" puzzle

  - by Yuval A

  A while back I wrote a simple python program to brute-force the single solution for the drive ya nuts puzzle. The puzzle consists of 7 hexagons with the numbers 1-6 on them, and all pieces must be aligned so that each number is adjacent to the same number on the next piece. The puzzle has ~1.4G non-unique possibilities: you have 7! options to sort the pieces by order (for example, center=0, top=1, continuing in clockwise order...). After you sorted the pieces, you can rotate each piece in 6 ways (each piece is a hexagon), so you get 6**7 possible rotations for a given permutation of the 7 pieces. Totalling: 7!*(6**7)=~1.4G possibilities. The following python code generates these possible solutions: def rotations(p): for i in range(len(p)): yield p[i:] + p[:i] def permutations(l): if len(l)<=1: yield l else: for perm in permutations(l[1:]): for i in range(len(perm)+1): yield perm[:i] + l[0:1] + perm[i:] def constructs(l): for p in permutations(l): for c in product(*(rotations(x) for x in p)): yield c However, note that the puzzle has only ~0.2G unique possible solutions, as you must divide the total number of possibilities by 6 since each possible solution is equivalent to 5 other solutions (simply rotate the entire puzzle by 1/6 a turn). Is there a better way to generate only the unique possibilities for this puzzle?

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• Difficulties using custom control - RichTextEditor

  - by Chris

  I am working on a school project that uses ASP.NET. I found this TextEditor control ( http://blogs.msdn.com/kirti/archive/2007/11/10/rich-text-editor-is-here.aspx ) that I am trying to include but it isn't working. The error I am getting is: Error Rendering Control - TextEditor. An unhandled exception has occurred. Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index. I see this error when I go Design part of the editor. I just don't understand this error at all. Also I am a lil bit confused as there is no parameter called index. :( What I have done is reference the binary in my project and then on the page I am trying to use it have registered its namespace and assembly with this line: <%@ Register Assembly="RichTextEditor" Namespace="AjaxControls" TagPrefix="rtt" %> I then go ahead and try to add the control to the page with this line of code: <rtt:richtexteditor ID="TextEditor" Theme="Blue" runat="server" /> Any help would be much appreciated. I haven't done anything like add a custom control before.

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• Minimal-change algorithm which maximises 'swapping'

  - by Kim Bastin

  This is a question on combinatorics from a non-mathematician, so please try to bear with me! Given an array of n distinct characters, I want to generate subsets of k characters in a minimal-change order, i.e. an order in which generation n+1 contains exactly one character that was not in generation n. That's not too hard in itself. However, I also want to maximise the number of cases in which the character that is swapped out in generation n+1 is the same character that was swapped in in generation n. To illustrate, for n=7, k=3: abc abd abe* abf* abg* afg aeg* adg* acg* acd ace* acf* aef adf* ade bde bdf bef bcf* bce bcd* bcg* bdg beg* bfg* cfg ceg* cdg* cde cdf* cef def deg dfg efg The asterisked strings indicate the case I want to maximise; e.g. the e that is new in generation 3, abe, replaces a d that was new in generation 2, abd. It doesn't seem possible to have this happen in every generation, but I want it to happen as often as possible. Typical array sizes that I use are 20-30 and subset sizes around 5-8. I'm using an odd language, Icon (or actually its derivative Unicon), so I don't expect anyone to post code that I can used directly. But I will be grateful for answers or hints in pseudo-code, and will do my best to translate C etc. Also, I have noticed that problems of this kind are often discussed in terms of arrays of integers, and I can certainly apply solutions posted in such terms to my own problem. Thanks Kim Bastin

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• Pros & Cons of Google App Engine

  - by Rishi

  Pros & Cons of Google App Engine [An Updated List 21st Aug 09] Help me Compile a List of all the Advantages & Disadvantages of Building an Application on the Google App Engine Pros: 1) No Need to buy Servers or Server Space (no maintenance). 2) Makes solving the problem of scaling much easier. Cons: 1) Locked into Google App Engine ?? 2)Developers have read-only access to the filesystem on App Engine. 3)App Engine can only execute code called from an HTTP request (except for scheduled background tasks). 4)Users may upload arbitrary Python modules, but only if they are pure-Python; C and Pyrex modules are not supported. 5)App Engine limits the maximum rows returned from an entity get to 1000 rows per Datastore call. 6)Java applications may only use a subset (The JRE Class White List) of the classes from the JRE standard edition. 7)Java applications cannot create new threads. Known Issues!! http://code.google.com/p/googleappengine/issues/list Hard limits Apps per developer - 10 Time per request - 30 sec Files per app - 3,000 HTTP response size - 10 MB Datastore item size - 1 MB Application code size - 150 MB Pro or Con? App Engine's infrastructure removes many of the system administration and development challenges of building applications to scale to millions of hits. Google handles deploying code to a cluster, monitoring, failover, and launching application instances as necessary. While other services let users install and configure nearly any *NIX compatible software, App Engine requires developers to use Python or Java as the programming language and a limited set of APIs. Current APIs allow storing and retrieving data from a BigTable non-relational database; making HTTP requests; sending e-mail; manipulating images; and caching. Most existing Web applications can't run on App Engine without modification, because they require a relational database.

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• In-document schema declarations and lxml

  - by shylent

  As per the official documentation of lxml, if one wants to validate a xml document against a xml schema document, one has to construct the XMLSchema object (basically, parse the schema document) construct the XMLParser, passing the XMLSchema object as its schema argument parse the actual xml document (instance document) using the constructed parser There can be variations, but the essense is pretty much the same no matter how you do it, - the schema is specified 'externally' (as opposed to specifying it inside the actual xml document). If you follow this procedure, the validation occurs, sure enough, but if I understand it correctly, that completely ignores the whole idea of the schemaLocation and noNamespaceSchemaLocation attributes from xsi. This introduces a whole bunch of limitations, starting with the fact, that you have to deal with instance<-schema relation all by yourself (either store it externally or write some hack to retrieve the schema location from the root element of the instance document), you can not validate the document using multiple schemata (say, when each schema governs its own namespace) and so on. So the question is: maybe I am missing something completely trivial or doing it wrong? Or are my statements about lxml's limitations regarding schema validation true? To recap, I'd like to be able to: have the parser use the schema location declarations in the instance document at parse/validation time use multiple schemata to validate a xml document declare schema locations on non-root elements (not of extreme importance) Maybe I should look for a different library? Although, that'd be a real shame, - lxml is a de-facto xml processing library for python and is regarded by everyone as the best one in terms of performace/features/convenience (and rightfully so, to a certain extent)

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• How to convert an InputStream to a DataHandler?

  - by pcorey

  I'm working on a java web application in which files will be stored in a database. Originally we retrieved files already in the DB by simply calling getBytes on our result set: byte[] bytes = resultSet.getBytes(1); ... This byte array was then converted into a DataHandler using the obvious constructor: dataHandler=new DataHandler(bytes,"application/octet-stream"); This worked great until we started trying to store and retrieve larger files. Dumping the entire file contents into a byte array and then building a DataHandler out of that simply requires too much memory. My immediate idea is to retrieve a stream of the data in the database with getBinaryStream and somehow convert that InputStream into a DataHandler in a memory-efficient way. Unfortunately it doesn't seem like there's a direct way to convert an InputStream into a DataHandler. Another idea I've been playing with is reading chunks of data from the InputStream and writing them to the OutputStream of the DataHandler. But... I can't find a way to create an "empty" DataHandler that returns a non-null OutputStream when I call getOutputStream... Has anyone done this? I'd appreciate any help you can give me or leads in the right direction.

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• x86 CMP Instruction Difference

  - by Pindatjuh

  Question What is the (non-trivial) difference between the following two x86 instructions? 39 /r CMP r/m32,r32 Compare r32 with r/m32 3B /r CMP r32,r/m32 Compare r/m32 with r32 Background I'm building a Java assembler, which will be used by my compiler's intermediate language to produce Windows-32 executables. Currently I have following code: final ModelBase mb = new ModelBase(); // create new memory model mb.addCode(new Compare(Register.ECX, Register.EAX)); // add code mb.addCode(new Compare(Register.EAX, Register.ECX)); // add code final FileOutputStream fos = new FileOutputStream(new File("test.exe")); mb.writeToFile(fos); fos.close(); To output a valid executable file, which contains two CMP instruction in a TEXT-section. The executable outputted to "text.exe" will do nothing interesting, but that's not the point. The class Compare is a wrapper around the CMP instruction. The above code produces (inspecting with OllyDbg): Address Hex dump Command 0040101F |. 3BC8 CMP ECX,EAX 00401021 |. 3BC1 CMP EAX,ECX The difference is subtle: if I use the 39 byte-opcode: Address Hex dump Command 0040101F |. 39C1 CMP ECX,EAX 00401021 |. 39C8 CMP EAX,ECX Which makes me wonder about their synonymity and why this even exists.

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• Debugging a release only flash problem

  - by Fire Lancer

  I've got an Adobe Flash 10 program that freezes in certain cases, however only when running under a release version of the flash player. With the debug version, the application works fine. What are the best approaches to debugging such issues? I considered installing the release player on my computer and trying to set some kind of non-graphical method of output up (I guess there's some way to write a log file or similar?), however I see no way to have both the release and debug versions installed anyway :( . EDIT: Ok I managed to replace my version of flash player with the release version, and no freeze...so what I know so far is: Flash: Debug Release Vista 32: works works XP PRO 32: works* freeze I gave them the debug players I had to test this Hmm, seeming less and less like an error in my code and more like a bug in the player (10.0.45.2 in all cases)... At the very least id like to see the callstack at the point it freezes. Is there some way to do that without requiring them to install various bits and pieces, e.g. by letting flash write out a log.txt or something with a "trace" like function I can insert in the code in question? EDIT2: I just gave the swf to another person with XP 32bit, same results :(

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• Vanilla WPF application hangs on one customer's machine

  - by Heinzi

  At a customer, one of our WPF applications started to hang. When trying to reproduce the problem with a minimal working example, I discovered that even the most basic (non-trivial) WPF application will hang on that machine. Example A: Create a new C# WPF project in Visual Studio 2008. Change nothing, compile it and run it on the customer's machine. It will run. Example B: Take Example A, and add a TextBlock to the main form Window1: <Window ...> <Grid> <TextBlock>Test</TextBlock> </Grid> </Window> Compile the application and run it on the customer's machine. It will hang: The title bar and the window border is visible, the inside is transparent and the window does not react to anything (cannot be moved or closed). The application must be shut down using the task manager. Obviously, this customer's WPF is broken. Is this a known issue, i.e., has anyone encountered it before and already knows how to solve it (e.g. reinstall .net 3.5 SP1, etc.)? The development machine is W7SP1, the customer's machine is XP (probably SP3, didn't check).

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• iPhone app: How to implement in-app purchased game levels

  - by Wonderflonium

  So, I understand that it's possible to set up in-app purchases for iPhone apps to purchase non-consumables like game levels. I understand the logic behind the purchase part, but what I don't understand is, how can I deliver the new game level. For example: I build an app that contains the first level and they purchase additional levels. Is it better to build all the other levels into the app and whenever they purchase the app, it unlocks it with a plist entry or something? That doesn't seem very update-able to me. Every time I come up with a new level, I'd have to update the app. So, what I don't understand then, is what is how do I package up a level and download it as a separate entity that can accessed by the game? Would the level just be some XML with images in a ZIP folder or something? How does the level get added to the game? What are best practices for this type of thing? I Googled and have found NOTHING about this. I'm a little bit confused by the concept and any help would be appreciated. I'm not looking for someone to write the game for me, I just need pointed in the right direction so I can develop it on my own.

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• Windows could not start the Apache2 on Local Computer - problem

  - by vaske

  During the installation of Apache2 I got the following message into cmd window: Installing the Apache2.2 service The Apache2.2 service is successfully installed. Testing httpd.conf.... Errors reported here must be corrected before the service can be started. httpd.exe: Could not reliably determine the server's fully qualified domain name , using 192.168.1.3 for ServerName (OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. : make_sock: could not bind to address 0.0.0.0:80 no listening sockets available, shutting down Unable to open logs Note the errors or messages above, and press the key to exit. 24... and after installing everything look fine, but it isn't. If I try to start service I got the following message: Windows could not start the Apache2 on Local Computer. For more information, review the System Event Log. If this is a non-Micorsoft service, contact the service vendor, and refer to service-specific error code 1. Apach2 version is 2.2.9 Does anyone have the same problem, or could help me.

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• Is there a GUI that I can use to create XML documents based on my schema?

  - by David Conlisk

  Hi all, I want to create a simple graphical user interface to allow non-technical users to create an XML file without having to manually edit the XML source. Ideally I'd like a drag and drop interface, but failing that, anything really. The contents of the XML file are similar to an encoded flow chart of a binary tree, so maybe something like Visio, with a save as xml option? Here's a quick sample of the XML output that is required: <?xml version="1.0" encoding="utf-8"?> <steps> <step id="1" type="prompt"> <prompt> Welcome. </prompt> <next>1.1</next> </step> <step id="1.1" type="question"> <prompt> Do you have what you need? </prompt> <yes>1.2</yes> <no>1.1.1</no> </step> ... </steps> Are there any existing tools out there that you can recommend for this purpose? Ideally open-source or with a free personal license, but I'm interested in hearing about all options. Thanks, David

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• python protobufs - avoid the install step ?

  - by orion elenzil

  i'm writing a small python utility which will be consumed by moderately non-technical users and which needs to interface w/ some protobufs. ideally, i would like the only prerequisites to using this on a local machine to be: have python installed * have an SVN checkout of the repository * run a simple bash script to build the local proto .py definitions * run "python myutility" i'm running into trouble around importing descriptor_pb2.py, tho. i've seen Why do I see "cannot import name descriptor_pb2" error when using Google Protocol Buffers? , but would like to avoid adding the additional prerequisite of having run the proto SDK installer. i've modified the bash script to also generate descriptor_pb2.py in the local heirarchy, which works for the first level of imports from my other _pb2.py files, but it looks like descriptor_pb2.py itself tries to import descriptor_pb2 can't find it: $ python myutility.py Traceback (most recent call last): File "myutility.py", line 4, in <module> import protos.myProto_pb2 File "/myPath/protos/myProto_pb2.py", line 8, in <module> from google.protobuf import descriptor_pb2 File "/myPath/google/protobuf/descriptor_pb2.py", line 8, in <module> from google.protobuf import descriptor_pb2 ImportError: cannot import name descriptor_pb2 my local folder looks like: * myutility.py * google/ * protobuf/ * descriptor.py * descriptor_pb2.py * protos * myProto_ob2.py also, i'm a python n00b, so it's possible i'm overlooking something obvious. tia, orion

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• How do I enumerate all monitors in Windows 7?

  - by Jon Tackabury

  I am trying to enumerate all the monitors in Windows 7, and according to MSDN, using the QueryDisplayConfig method is the correct way to do this. All of this code works fine, and returns a couple of arrays, one with paths and one with modes. However, it doesn't have the same monitor ID's as Windows. I am trying to build an array of all the monitors that appear in the Windows 7 "Screen Resolution" dialog. The paths collection return far too many items, and I'm not sure how to tell if it's a valid non-active monitor. Any help would be much appreciated. UINT32 PathArraySize = 0; UINT32 ModeArraySize = 0; DISPLAYCONFIG_PATH_INFO* PathArray; DISPLAYCONFIG_MODE_INFO* ModeArray; GetDisplayConfigBufferSizes( QDC_ALL_PATHS, &PathArraySize, &ModeArraySize); PathArray = (DISPLAYCONFIG_PATH_INFO*)malloc( PathArraySize * sizeof(DISPLAYCONFIG_PATH_INFO)); memset(PathArray, 0, PathArraySize * sizeof(DISPLAYCONFIG_PATH_INFO)); ModeArray = (DISPLAYCONFIG_MODE_INFO*)malloc( ModeArraySize * sizeof(DISPLAYCONFIG_MODE_INFO)); memset(ModeArray, 0, ModeArraySize * sizeof(DISPLAYCONFIG_MODE_INFO)); LONG rtn = QueryDisplayConfig( QDC_ALL_PATHS, &PathArraySize, PathArray, &ModeArraySize, ModeArray, NULL);

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• Android : Customizing tabs on state : How do I make a selector a drawable

  - by Chrispix

  I know how to put the icon on each tab, that is no problem. I also ran across this : Stack Overflow thread on pretty much same thing I followed one of the links from that question, and found this Pretty much, it said use a selector defined in the xml, sure, did that. But there is no id associated w/ it so I am not sure how to get the selector function as a drawable so I can use it as the icon for the tabs. Maybe I am going about this the wrong way.. But this is what I have, and obviously missing something. <selector android:id="@+id/myselector" xmlns:android="http://schemas.android.com/apk/res/android"> <!-- Non focused states --> <item android:state_focused="false" android:state_selected="false" android:state_pressed="false" android:drawable="@drawable/darklogo" /> <item android:state_focused="false" android:state_selected="true" android:state_pressed="false" android:drawable="@drawable/lightlogo" /> <!-- Focused states --> <item android:state_focused="true" android:state_selected="false" android:state_pressed="false" android:drawable="@drawable/lightlogo" /> <item android:state_focused="true" android:state_selected="true" android:state_pressed="false" android:drawable="@drawable/lightlogo" /> <!-- Pressed --> <item android:state_pressed="true" android:drawable="@drawable/lightlogo" /> </selector> In my code, an example tab is generated using : host.addTab(host.newTabSpec("three") .setIndicator("map",drawables) .setContent(new Intent(this, Map.class))); Right now drawables is just a reference to an drawable image resource. How do I make the selector a drawable? * This is my question *

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• NSKeyedArchiver on NSArray has large size overhead

  - by redguy

  I'm using NSKeyedArchiver in Mac OS X program which generates data for iPhone application. I found out that by default, resulting archives are much bigger than I expected. Example: NSMutableArray * ar = [NSMutableArray arrayWithCapacity:10]; for (int i = 0; i < 100000; i++) { NSString * s = [NSString stringWithFormat:@"item%06d", i]; [ar addObject:s]; } [NSKeyedArchiver archiveRootObject:ar toFile: @"NSKeyedArchiver.test"]; This stores 10 * 100000 = 1M bytes of useful data, yet the size of the resulting file is almost three megabytes. The overhead seems to be growing with number of items in the array. In this case, for 1000 items, the file was about 22k. "file" reports that it is a "Apple binary property list" (not the XML format). Is there an simple way to prevent this huge overhead? I wanted to use the NSKeyedArchiver for the simplicity it provides. I can write data to my own, non-generic, binary format, but that's not very elegant. Also, aggregating the data into large chunks and feeding these to the NSKeyedArchiver should work, but again, that kinda beats the point of using simple&easy&ready to use archiver. Am I missing some method call or usage pattern that would reduce this overhead?

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• SQLiteDataAdapter Fill exception C# ADO.NET

  - by Lirik

  I'm trying to use the OleDb CSV parser to load some data from a CSV file and insert it into a SQLite database, but I get an exception with the OleDbAdapter.Fill method and it's frustrating: An unhandled exception of type 'System.Data.ConstraintException' occurred in System.Data.dll Additional information: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. Here is the source code: public void InsertData(String csvFileName, String tableName) { String dir = Path.GetDirectoryName(csvFileName); String name = Path.GetFileName(csvFileName); using (OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + dir + @";Extended Properties=""Text;HDR=No;FMT=Delimited""")) { conn.Open(); using (OleDbDataAdapter adapter = new OleDbDataAdapter("SELECT * FROM " + name, conn)) { QuoteDataSet ds = new QuoteDataSet(); adapter.Fill(ds, tableName); // <-- Exception here InsertData(ds, tableName); // <-- Inserts the data into the my SQLite db } } } class Program { static void Main(string[] args) { SQLiteDatabase target = new SQLiteDatabase(); string csvFileName = "D:\\Innovations\\Finch\\dev\\DataFeed\\YahooTagsInfo.csv"; string tableName = "Tags"; target.InsertData(csvFileName, tableName); Console.ReadKey(); } } The "YahooTagsInfo.csv" file looks like this: tagId,tagName,description,colName,dataType,realTime 1,s,Symbol,symbol,VARCHAR,FALSE 2,c8,After Hours Change,afterhours,DOUBLE,TRUE 3,g3,Annualized Gain,annualizedGain,DOUBLE,FALSE 4,a,Ask,ask,DOUBLE,FALSE 5,a5,Ask Size,askSize,DOUBLE,FALSE 6,a2,Average Daily Volume,avgDailyVolume,DOUBLE,FALSE 7,b,Bid,bid,DOUBLE,FALSE 8,b6,Bid Size,bidSize,DOUBLE,FALSE 9,b4,Book Value,bookValue,DOUBLE,FALSE I've tried the following: Removing the first line in the CSV file so it doesn't confuse it for real data. Changing the TRUE/FALSE realTime flag to 1/0. I've tried 1 and 2 together (i.e. removed the first line and changed the flag). None of these things helped... One constraint is that the tagId is supposed to be unique. Here is what the table look like in design view: Can anybody help me figure out what is the problem here?

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• Graceful termination of NSApplication with Core Data and Grand Central Dispatch (GCD)

  - by Vincent Mac

  I have an Cocoa Application (Mac OS X SDK 10.7) that is performing some processes via Grand Central Dispatch (GCD). These processes are manipulating some Core Data NSManagedObjects (non-document-based) in a manner that I believe is thread safe (creating a new managedObjectContext for use in this thread). The problem I have is when the user tries to quit the application while the dispatch queue is still running. The NSApplication delegate is being called before actually quitting. - (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender I get an error "Could not merge changes." Which is somewhat expected since there are still operations being performed through the different managedObjectContext. I am then presented with the NSAlert from the template that is generated with a core data application. In the Threading Programming Guide there is a section called "Be Aware of Thread Behaviors at Quit Time" which alludes to using replyToApplicationShouldTerminate: method. I'm having a little trouble implementing this. What I would like is for my application to complete processing the queued items and then terminate without presenting an error message to the user. It would also be helpful to update the view or use a sheet to let the user know that the app is performing some action and will terminate when the action is complete. Where and how would I implement this behavior?

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• Create a VPN with Python

  - by user213060

  I want to make a device "tunnel box" that you plug an input ethernet line, and an output ethernet line, and all the traffic that goes through it gets modified in a special way. This is similar to how a firewall, IDS, VPN, or similar boxes are connected inline in a network. I think you can just assume that I am writing a custom VPN in Python for the purpose of this question: LAN computer <--\ LAN computer <---> [LAN switch] <--> ["tunnel box"] <--> [internet modem] <--> LAN computer <--/ My question is, what is a good way to program this "tunnel box" from python? My application needs to see TCP flows at the network layer, not as individual ethernet frames. Non-TCP/IP traffic such as ICPM and other types should just be passed through. Example Twisted-like Code for my "tunnel box" tunnel appliance: from my_code import special_data_conversion_function class StreamInterceptor(twisted.Protocol): def dataReceived(self,data): data=special_data_conversion_function(data) self.outbound_connection.send(data) My initial guesses: TUN/TAP with twisted.pair.tuntap.py - Problem: This seems to only work at the ethernet frame level, not like my example? Socks proxy - Problem: Not transparent as in my diagram. Programs have to be specifically setup for it. Thanks!

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• "Work stealing" vs. "Work shrugging (tm)"?

  - by John

  Why is it that I can find lots of information on "work stealing" and nothing on a "work shrugging(tm)" as a load-balancing strategy? I am surprised because work-stealing seems to me to have an inherent weakness when implementating efficient fine-grained load-balancing. Vis:- Relying on consumer processors to implement distribution (by actively stealing) begs the question of what these processors do when they find no work? None of the work-stealing references and implementations I have come across so far address this issue satisfactorarily for me. They either:- 1) Manage not to disclose what they do with idle processors! [Cilk] (?anyone know?) 2) Have all idle processors sleep and wake periodically and scatter messages to the four winds to see if any work has arrived [e.g. JAWS] (= way too latent & inefficient for me). 3) Assume that it is acceptable to have processors "spinning" looking for work ( = non-starter for me!) Unless anyone thinks there is a solution for this I will move on to consider a "Work Shrugging(tm)" strategy. Having the task-producing processor distribute excess load seems to me inherently capable of a much more efficient implementation. However a quick google didn't show up anything under the heading of "Work Shrugging" so any pointers to prior-art would be welcome. tx Tags I would have added if I was allowed to [work-stealing]

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• How to route all subdomains to a single host using mDNS?

  - by John Mee

  I have a development webserver hosting as "myhost.local" which is found using Bonjour/mDNS. The server is running avahi-daemon. The webserver also wants to handle any subdomains of itself. Eg "cat.myhost.local" and "dog.myhost.local" and "guppy.myhost.local". Given that myhost.local is on a dynamic ip address from dhcp, is there still a way to route all requests for the subdomains to myhost.local? I'm starting to think it not currently possible... http://marc.info/?l=freedesktop-avahi&m=119561596630960&w=2 You can do this with the /etc/avahi/hosts file. Alternatively you can use avahi-publish-host-name. No, he cannot. Since he wants to define an alias, not a new hostname. I.e. he only wants to register an A RR, no reverse PTR RR. But if you stick something into /etc/avahi/hosts then it registers both, and detects a collision if the PTR RR is non-unique, which would be the case for an alias.

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• is delete p where p is a pointer to array a memory leak ?

  - by Eli

  following a discussion in a software meeting I setup to find out if deleting an dynamically allocated primitive array with plain delete will cause a memory leak. I have written this tiny program and compiled with visual studio 2008 running on windows XP: #include "stdafx.h" #include "Windows.h" const unsigned long BLOCK_SIZE = 1024*100000; int _tmain() { for (unsigned int i =0; i < 1024*1000; i++) { int* p = new int[1024*100000]; for (int j =0;j<BLOCK_SIZE;j++) p[j]= j % 2; Sleep(1000); delete p; } } I than monitored the memory consumption of my application using task manager, surprisingly the memory was allocated and freed correctly, allocated memory did not steadily increase as was expected I've modified my test program to allocate a non primitive type array : #include "stdafx.h" #include "Windows.h" struct aStruct { aStruct() : i(1), j(0) {} int i; char j; } NonePrimitive; const unsigned long BLOCK_SIZE = 1024*100000; int _tmain() { for (unsigned int i =0; i < 1024*100000; i++) { aStruct* p = new aStruct[1024*100000]; Sleep(1000); delete p; } } after running for for 10 minutes there was no meaningful increase in memory I compiled the project with warning level 4 and got no warnings. is it possible that the visual studio run time keep track of the allocated objects types so there is no different between delete and delete[] in that environment ?

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• Graph limitations - Should I use Decorator?

  - by Nick Wiggill

  I have a functional AdjacencyListGraph class that adheres to a defined interface GraphStructure. In order to layer limitations on this (eg. acyclic, non-null, unique vertex data etc.), I can see two possible routes, each making use of the GraphStructure interface: Create a single class ("ControlledGraph") that has a set of bitflags specifying various possible limitations. Handle all limitations in this class. Update the class if new limitation requirements become apparent. Use the decorator pattern (DI, essentially) to create a separate class implementation for each individual limitation that a client class may wish to use. The benefit here is that we are adhering to the Single Responsibility Principle. I would lean toward the latter, but by Jove!, I hate the decorator Pattern. It is the epitome of clutter, IMO. Truthfully it all depends on how many decorators might be applied in the worst case -- in mine so far, the count is seven (the number of discrete limitations I've recognised at this stage). The other problem with decorator is that I'm going to have to do interface method wrapping in every... single... decorator class. Bah. Which would you go for, if either? Or, if you can suggest some more elegant solution, that would be welcome. EDIT: It occurs to me that using the proposed ControlledGraph class with the strategy pattern may help here... some sort of template method / functors setup, with individual bits applying separate controls in the various graph-canonical interface methods. Or am I losing the plot?

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• Python: Seeing all files in Hex.

  - by Recursion

  I am writing a python script which looks at common computer files and examines them for similar bytes, words, double word's. Though I need/want to see the files in Hex, ande cannot really seem to get python to open a simple file in python. I have tried codecs.open with hex as the encoding, but when I operate on the file descriptor it always spits back File "main.py", line 41, in <module> main() File "main.py", line 38, in main process_file(sys.argv[1]) File "main.py", line 27, in process_file seeker(line.rstrip("\n")) File "main.py", line 15, in seeker for unit in f.read(2): File "/usr/lib/python2.6/codecs.py", line 666, in read return self.reader.read(size) File "/usr/lib/python2.6/codecs.py", line 472, in read newchars, decodedbytes = self.decode(data, self.errors) File "/usr/lib/python2.6/encodings/hex_codec.py", line 50, in decode return hex_decode(input,errors) File "/usr/lib/python2.6/encodings/hex_codec.py", line 42, in hex_decode output = binascii.a2b_hex(input) TypeError: Non-hexadecimal digit found def seeker(_file): f = codecs.open(_file, "rb", "hex") for LINE in f.read(): print LINE f.close() I really just want to see files, and operate on them as if it was in a hex editor like xxd. Also is it possible to read a file in increments of maybe a word at a time. No this is not homework.

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