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• Android Activity is displayed after user unlocks the screen

  - by Dave

  Hi, I was wondering if anyone understood how to make your application be displayed when you unlock the screen. I have an application where the user turns on a Bluetooth device, it connects to the phone, and the user should be presented with a UI. Having them hunt for the app or using the notification menu is not a workable option (too much work and not the obvious behavior). The problem is that: When the screen is unlocked: - you can popup the activity from the background service when Bluetooth connects to a device - User is happy because the UI is right there When the screen is locked: - The application gets started but is destroyed - User unlocks the phone and nothing is there but the homescreen One work around would be to disable the keyguard when the application gets woken up but the nuclear option is a pretty bad option. PS: I know the standard Android assumption is that you shouldn't do this. In the normal case this behavior is fine, but in this case I explicitly did something I want the phone to respond without adding more work for the user to do. As per Google's guidelines if you don't like this behavior there can be an option for you to turn this off or you can not use the application.

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• using text and ntext SQL Datatypes in RPG

  - by David Stratton

  I'll preface this with saying that I'm a .NET developer, and am NOT an RPG developer. I'm working with one of our RPG developers to come up with a solution, so any suggestions you provide will get passed to him. We have a scenario where we want our iSeries to read from a SQL Server database. One of the columns is a TEXT column. IN RPG, there is no equivalent data type to use for this. We've gone back and forth on this, and our current plan is to change course, and have our SQL Server write out a text file, which the iSeries can pick up and parse. This is, however, a last resort option, as the data in the file is sensitive, and we'd like to avoid the additional security overhead. We've already got the SQL Server locked down as tight as possible (one user only has read access to this, and that user is an iSeries user.) We don't want to have to worry about transferring files back and forth. However, at this point, we see no other option. We have no in-house Java developers, and need to do this in RPG. So I'm wondering if there are any RPG developers out there who have faced this situation and have any advice.

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• pthreads: reader/writer locks, upgrading read lock to write lock

  - by ScaryAardvark

  I'm using read/write locks on Linux and I've found that trying to upgrade a read locked object to a write lock deadlocks. i.e. // acquire the read lock in thread 1. pthread_rwlock_rdlock( &lock ); // make a decision to upgrade the lock in threads 1. pthread_rwlock_wrlock( &lock ); // this deadlocks as already hold read lock. I've read the man page and it's quite specific. The calling thread may deadlock if at the time the call is made it holds the read-write lock (whether a read or write lock). What is the best way to upgrade a read lock to a write lock in these circumstances.. I don't want to introduce a race on the variable I'm protecting. Presumably I can create another mutex to encompass the releasing of the read lock and the acquiring of the write lock but then I don't really see the use of read/write locks. I might as well simply use a normal mutex. Thx

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• Lucene.net create+lock errors in ASP.NET

  - by acidzombie24

  I have an issue with Lucene.net. It throws a lock exception. After poking around i notice these things. My code below works in an app bit when calling in Application_Start i get a NoSuchDirectoryException. Not closing the writer (as my code doesnt do below) i WILL get a LockObtainFailedException with the message Lock obtain timed out: SimpleFSLock@<FULL_PATH> from either app or asp.net These thread hinted when spawning threads they get less permissions then i do (but! my main thread has problems as well...) and one solution is to impersonate IIS. I am using visual studios 2010. I am not sure how full blown it is but my attempt to impersonate it failed. So my question is how do i have lucene create the directory and not throw an exception if dont close the writer for some reason (such as power going out)? http://stackoverflow.com/questions/2341163/why-is-my-lucene-index-getting-locked/2499285#2499285 http://stackoverflow.com/questions/1123517/lucene-net-and-i-o-threading-issue/1123981#1123981 static IndexWriter writer = null; static void lucene_init() { bool create = false; //I now use a full path. I still get NoSuchDirectoryException //string dirname = "LuceneIndex_z"; if (System.IO.Directory.Exists(dirname) == false) create = true; var directory = FSDirectory.GetDirectory(dirname); var analyzer = new StandardAnalyzer(); writer = new IndexWriter(directory, analyzer, create); }

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• Lucene.net create+lock errors in ASP.NET

  - by acidzombie24

  I have an issue with Lucene.net. It throws a lock exception. After poking around i notice these things. My code below works in an app bit when calling in Application_Start i get a NoSuchDirectoryException. Not closing the writer (as my code doesnt do below) i WILL get a LockObtainFailedException with the message Lock obtain timed out: SimpleFSLock@<FULL_PATH> from either app or asp.net These thread hinted when spawning threads they get less permissions then i do (but! my main thread has problems as well...) and one solution is to impersonate IIS. I am using visual studios 2010. I am not sure how full blown it is but my attempt to impersonate it failed. So my question is how do i have lucene create the directory and not throw an exception if dont close the writer for some reason (such as power going out)? http://stackoverflow.com/questions/2341163/why-is-my-lucene-index-getting-locked/2499285#2499285 http://stackoverflow.com/questions/1123517/lucene-net-and-i-o-threading-issue/1123981#1123981 static IndexWriter writer = null; static void lucene_init() { bool create = false; string dirname = "LuceneIndex_z"; if (System.IO.Directory.Exists(dirname) == false) create = true; var directory = FSDirectory.GetDirectory(dirname); var analyzer = new StandardAnalyzer(); writer = new IndexWriter(directory, analyzer, create); }

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• Axis2 attachments are vanishing in the response

  - by Shamik

  I am using axis2 to come up with a basic web service which will get the file name as parameter and produces a response SOAP packet which will have the file attached along with the SOAP. Here is the way I am creating the service code (its simple and inspired by Axis2 sample code) public String getFile(String name) throws IOException { MessageContext msgCtx = MessageContext.getCurrentMessageContext(); File file = new File (name); System.out.println("File = " + name); System.out.println("File exists = " + file.exists()); FileDataSource fileDataSource = new FileDataSource(file); System.out.println("fileDataSource = " + fileDataSource); DataHandler dataHandler = new DataHandler(fileDataSource); System.out.println("DataHandler = " + dataHandler); String attachmentID = msgCtx.addAttachment(dataHandler); System.out.println("attachment ID = " + attachmentID); return attachmentID; } Now The client side code - MessageContext response = mepClient .getMessageContext(WSDLConstants.MESSAGE_LABEL_IN_VALUE); SOAPBody body = response.getEnvelope().getBody(); OMElement element = body.getFirstElement().getFirstChildWithName( new QName("http://service.soapwithattachments.sample","return")); String attachementId = element.getText(); System.out.println("attachment id is " + attachementId); Attachments attachment = response.getAttachmentMap(); DataHandler dataHandler = attachment.getDataHandler(attachementId); Problem is that dataHandler is always null. Though I think at the server side, the file was read and attached along with the SOAP packet. Am I doing something wrong ? EDIT : I have put <parameter name="enableSwA" locked="false">true</parameter> in the axis2.xml file.

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• Password Cracking Windows Accounts

  - by Kevin

  At work we have laptops with encrypted harddrives. Most developers here (on occasion I have been guilty of it too) leave their laptops in hibernate mode when they take them home at night. Obviously, Windows (i.e. there is a program running in the background which does it for windows) must have a method to unencrypt the data on the drive, or it wouldn't be able to access it. That being said, I always thought that leaving a windows machine on in hibernate mode in a non-secure place (not at work on a lock) is a security threat, because someone could take the machine, leave it running, hack the windows accounts and use it to encrypt the data and steal the information. When I got to thinking about how I would go about breaking into the windows system without restarting it, I couldn't figure out if it was possible. I know it is possible to write a program to crack windows passwords once you have access to the appropriate file(s). But is it possible to execute a program from a locked Windows system that would do this? I don't know of a way to do it, but I am not a Windows expert. If so, is there a way to prevent it? I don't want to expose security vulnerabilities about how to do it, so I would ask that someone wouldn't post the necessary steps in details, but if someone could say something like "Yes, it's possible the USB drive allows arbitrary execution," that would be great! EDIT: The idea being with the encryption is that you can't reboot the system, because once you do, the disk encryption on the system requires a login before being able to start windows. With the machine being in hibernate, the system owner has already bypassed the encryption for the attacker, leaving windows as the only line of defense to protect the data.

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• How to improve the use of Delphi Frames

  - by Brian Frost

  I've used frames in Delphi for years, and they are one of the most powerful features of the VCL, but standard use of them seems to have some risk such as: It's easy to accidentally move or edit the frame sub-components on a frame's host form without realising that you are 'tweaking' with the frame - I know this does not affect the original frame code, but it's generally not what you would want. When working with the frame you are still exposed to its sub-components for visual editing, even when that frame is years old and should not be touched. So I got to thinking.... Is there a way of 'grouping' components such that their positions are 'locked'? This would be useful for finished forms as well as frames. Often other developers return code to me where only the form bounds have changed and even they did not intend any change. Is there any way of turning a frame and its components into a single Delphi component? If so, the frame internals would be completely hidden and its useability would increase further. I'm interested in any thoughts... Brian.

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• Troubleshooting a COM+ application deadlock

  - by Chris Karcher

  I'm trying to troubleshoot a COM+ application that deadlocks intermittently. The last time it locked up, I was able to take a usermode dump of the dllhost process and analyze it using WinDbg. After inspecting all the threads and locks, it all boils down to a critical section owned by this thread: ChildEBP RetAddr Args to Child 0deefd00 7c822114 77e6bb08 000004d4 00000000 ntdll!KiFastSystemCallRet 0deefd04 77e6bb08 000004d4 00000000 0deefd48 ntdll!ZwWaitForSingleObject+0xc 0deefd74 77e6ba72 000004d4 00002710 00000000 kernel32!WaitForSingleObjectEx+0xac 0deefd88 75bb22b9 000004d4 00002710 00000000 kernel32!WaitForSingleObject+0x12 0deeffb8 77e660b9 000a5cc0 00000000 00000000 comsvcs!PingThread+0xf6 0deeffec 00000000 75bb21f1 000a5cc0 00000000 kernel32!BaseThreadStart+0x34 The object it's waiting on is an event: 0:016> !handle 4d4 f Handle 000004d4 Type Event Attributes 0 GrantedAccess 0x1f0003: Delete,ReadControl,WriteDac,WriteOwner,Synch QueryState,ModifyState HandleCount 2 PointerCount 4 Name <none> No object specific information available As far as I can tell, the event never gets signaled, causing the thread to hang and hold up several other threads in the process. Does anyone have any suggestions for next steps in figuring out what's going on? Now, seeing as the method is called PingThread, is it possible that it's trying to ping another thread in the process that's already deadlocked? UPDATE This actually turned out to be a bug in the Oracle 10.2.0.1 client. Although, I'm still interested in ideas on how I could have figured this out without finding the bug in Oracle's bug database.

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• "Cannot open user default database" error with "User Instance=True"

  - by Keith

  I have a desktop application that uses Sql user instancing. This is my connection string: "Data Source=.\SqlExpress; AttachDbFilename=C:\path\file.mdf; Integrated Security=True; User Instance=True; Connect Timeout=100;" My application creates this DB, downloads a load of data into it from a web service and then does a lot of actions with it. The problem comes when I attempt to re-open the connection. I get a SqlException: "Cannot open user default database. Login failed. Login failed for user 'myDomain\myusername'." This error makes no sense in this context - I have no default database. I'm logging in to an instance created just for the current application, running separately from SqlExpress. There's no other way to connect to this DB. If I start the SqlExpress service and connect to the default instance it won't be visible. It only exists for this application. The file on disk is locked by the SqlExpress instance service running under the application. if I stop the app and restart it the connection works first time, but fails on re-opening. If I just stop the app I can delete the .mdf files and begin again, but it still crashes when I re-open the connection. As my app started the instance running as me my current user should have access to every DB in the instance. This doesn't happen for other users of the same code, which suggests that it's a SQL config issue. Does anyone have any idea what causes this and how to work around it?

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• Lost Update Anomaly in Sql Server Update Command

  - by Javed

  Hi, I am very much confused. I have a transaction in ReadCommitted Isolation level. Among other things I am also updating a counter value in it, something similar to below: Update tblCount set counter = counter + 1 My application is a desktop application and this transaction happens to occur quite frequently and concurrently. We recently noticed an error that sometimes the counter value doesn't get updated or is missed. We also insert one record on each counter update so we are sure that records have been inserted but somehow counter fails to update. This happens once in 2000 simulaneous transactions. I seriously doubt it is a lost update anomaly I am facing but if you look at the command above, it's just update the counter from its own value: if I have started a transaction and the transaction has reached this statement, it should have locked the row. This should not cause lost update, but it's happening somehow. Is the thing that this update command works in two parts? Like first it reads the counter value (during which it doesn't get the exclusive lock) and then writes the new calculated value (when it does get an exclusive lock)? Please help, I have got really confused.

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• Check if files in a directory are still being written in Windows Batch File

  - by FMFF

  Hello. Here's my batch file to parse a directory, and zip files of certain type REM Begin ------------------------ tasklist /FI "IMAGENAME eq 7za.exe" /FO CSV > search.log FOR /F %%A IN (search.log) DO IF %%~zA EQU 0 GOTO end for /f "delims=" %%A in ('dir C:\Temp\*.ps /b') do ( "C:\Program Files\7-Zip\cmdline\7za.exe" a -tzip -mx9 "C:\temp\Zip\%%A.zip" "C:\temp\%%A" Move "C:\temp\%%A" "C:\Temp\Archive" ) :end del search.log REM pause exit REM End --------------------------- This code works just fine for 90% of my needs. It will be deployed as a scheduled task. However, the *.ps files are rather large (minimum of 1GB) in real time cases. So the code is supposed to check if the incoming file is completely written and is not locked by the application that is writing it. I saw another example elsewhere, that suggested the following approach :TestFile ren c:\file.txt c:\file.txt if errorlevel 0 goto docopy sleep 5 goto TestFile :docopy However this example is good for a fixed file. How can I use that many labels and GoTo's inside a for loop without causing an infinite loop? Or is this code safe to be used in the For Loop? Thank you for any help.

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• WinForms Load Event / Static Initialization Strangeness

  - by Eric J.

  Background I'm troubleshooting an WinForms 2.0 program that's already been burned to CD for distribution to an internet-challenged target audience. Some users are experiencing a fatal error that I can reproduce locally. Reproducing the Error I get the fatal error when I log into my Vista box using a standard user that I just created, even if I run the program as administrator. I do not get the fatal error when I log in as local administrator. I'm not sure that being administrator is necessarily the trigger (since runas did not help). I have reproduced this half a dozen times under each account with consistent results. The faulty code Base.cs (base class for several user controls, only one of which is shown on first screen) private void BaseWindow_Load(object sender, EventArgs e) { // This message shown once in both cases MessageBox.Show("BaseWindow_Load for " + this.GetType().FullName); SkinManager.ApplySkin(this); } SkinManager.cs private static Skin skin = null; public static void ApplySkin(UserControl applyTo) { if (skin == null) { skin = new Skin(SkinsDirectory, "Default"); } } Skin.cs internal Skin(string skinPath, string skinName) { config = SkinConfig.Load(path); } SkinConfig.cs public static SkinConfig Load(string path) { // This message shown only once running as Admin but twice running as standard user System.Windows.Forms.MessageBox.Show("@1"); // !!! LOCK path HERE !!! } A user control loads on the first form, which triggers a call to SkinManager.ApplySkin, which checks if skin is null and, if so assigns it (without thread synchronization or recursion protection), which ultimately causes a file to be opened. When logged in as local admin, that sequence completes just fine. When logged in as my test standard user, ApplySkin is always called a second time while skin is still null, causing a second attempt to load, causing the file to be locked on the second attempt. The error handling is draconian at this point and the program terminates. The Question While this code can be easily fixed, I would like to understand why the error is happening only in some cases.

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• Delphi: Alternative to using Assign/ReadLn for text file reading

  - by Ian Boyd

  i want to process a text file line by line. In the olden days i loaded the file into a StringList: slFile := TStringList.Create(); slFile.LoadFromFile(filename); for i := 0 to slFile.Count-1 do begin oneLine := slFile.Strings[i]; //process the line end; Problem with that is once the file gets to be a few hundred megabytes, i have to allocate a huge chunk of memory; when really i only need enough memory to hold one line at a time. (Plus, you can't really indicate progress when you the system is locked up loading the file in step 1). The i tried using the native, and recommended, file I/O routines provided by Delphi: var f: TextFile; begin Assign(filename, f); while ReadLn(f, oneLine) do begin //process the line end; Problem withAssign is that there is no option to read the file without locking (i.e. fmShareDenyNone). The former stringlist example doesn't support no-lock either, unless you change it to LoadFromStream: slFile := TStringList.Create; stream := TFileStream.Create(filename, fmOpenRead or fmShareDenyNone); slFile.LoadFromStream(stream); stream.Free; for i := 0 to slFile.Count-1 do begin oneLine := slFile.Strings[i]; //process the line end; So now even though i've gained no locks being held, i'm back to loading the entire file into memory. Is there some alternative to Assign/ReadLn, where i can read a file line-by-line, without taking a sharing lock? i'd rather not get directly into Win32 CreateFile/ReadFile, and having to deal with allocating buffers and detecting CR, LF, CRLF's. i thought about memory mapped files, but there's the difficulty if the entire file doesn't fit (map) into virtual memory, and having to maps views (pieces) of the file at a time. Starts to get ugly. i just want Assign with fmShareDenyNone!

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• How can I make a server log file available via my ASP.NET MVC website?

  - by Gary McGill

  I have an ASP.NET MVC website that works in tandem with a Windows Service that processes file uploads. For easy maintenance of the site, I'd like the log file for the Windows Service to be accessible (to me, only) via the website, so that I can hit http://myserver/logs/myservice to view the contents of the log file. How can I do that? At a guess, I could either have the service write its log file in a "Logs" folder at the top level of the site, or I could leave it where it is and set up a virtual directory to point to it. Which of these is better - or is there another, better way? Wherever the file is stored, I can see that there's going to be another problem. I tried out the first option (Logs folder in my website), but when I try to access the file via HTTP I get an error: The process cannot access the file 'foo' because it is being used by another process. Now, I know from experience that my service keeps the file locked for writing while it's running, but that I can still open the file in Notepad to view the current contents. (I'm surprised that IIS insists on write access, if that's what's happening). How can I get around that? Do I really have to write a handler to read the file and serve it to the browser myself? Or can I fix this with configuration or somesuch? PS. I'm using IIS7 if that helps.

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• Writing to a log4net FileAppender with multiple threads performance problems

  - by Wayne

  TickZoom is a very high performance app which uses it's own parallelization library and multiple O/S threads for smooth utilization of multi-core computers. The app hits a bottleneck where users need to write information to a LogAppender from separate O/S threads. The FileAppender uses the MinimalLock feature so that each thread can lock and write to the file and then release it for the next thread to write. If MinimalLock gets disabled, log4net reports errors about the file being already locked by another process (thread). A better way for log4net to do this would be to have a single thread that takes care of writing to the FileAppender and any other threads simply add their messages to a queue. In that way, MinimalLock could be disabled to greatly improve performance of logging. Additionally, the application does a lot of CPU intensive work so it will also improve performance to use a separate thread for writing to the file so the CPU never waits on the I/O to complete. So the question is, does log4net already offer this feature? If so, how do you do enable threaded writing to a file? Is there another, more advanced appender, perhaps? If not, then since log4net is already wrapped in the platform, that makes it possible to implement a separate thread and queue for this purpose in the TickZoom code. Sincerely, Wayne

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• Keymap issues with NX from Mac OS X Lion

  - by Andy

  I tried to answer the question from Mark: Keymap issues with NX from Mac OS X Lion to Ubuntu However, it is locked so I figured I would post a new question / answer. I have been trying to answer this for a few days now because I have no issues when connecting through NX Client (technically OpenNX) to FreeNX server from an iMac (with Lion), but if I try to connect with a Macbook Pro I get horrible keyboard binding issues. The fix that is working for me is to go into: ~/.nx/config/HOST.nxs and change: <option key="Current keyboard" value="false"/> <option key="Custom keyboard layout" value="empty"/> <option key="Grab keyboard" value="false"/> I have tried this on three NX Servers and all are fixed. Hope it helps or gets you closer. Always check in the ~/.nx/temp/ for the sshlog and see if --keyboard="empty/empty" instead of "pc105/en" because the Mac is really pc104. 9:05:35: startsession --session="HOST" --type="unix-gnome" --cache="8M" --images="32M" --link="adsl" --geometry="2556\ x1396" --screeninfo="2560x1440x32+render" --keyboard="empty/empty" --backingstore="1" --encryption="1" --composite="1" --\ shmem="1" --shpix="1" --streaming="1" --samba="0" --cups="0" --nodelay="1" --defer="0" --client="macosx" --media="0" --st\ rict="0" --aux="1"

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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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• Using open2300 with Ubuntu

  - by Gawain

  Hello, I am currently running Ubuntu 8.10 and have been trying to use Open2300 to read data from a Lacrosse WS-2310 weather station and report it to the WUnderground server. The program compiles fine but when I try to run it, it does one of two things: usually it pauses for about 4 minutes, then prints "could not reset" to the screen. But sometimes it just hangs forever. It seems like my computer is unable to communicate with the weather station. I have set the serial port as /dev/ttyS0 in the open2300.conf file and i have also tried /dev/ttyS1, /dev/ttyS2, etc with the same result. As far as I can tell, there are no other settings regarding how Open2300 communicates with the device. Is my serial port locked somehow? It could be something as simple as an incorrect configuration for my serial port or something, but I would have no idea how to check that or change the configuration. Any help would be greatly appreciated. thanks, Gawain EDIT: I tried some tests that i found online and everything seems to be working with my serial port... gawain@gawain:~$ ls -l /dev/ttyS* crw-rw---- 1 root dialout 4, 64 2009-07-09 10:01 /dev/ttyS0 crw-rw---- 1 root dialout 4, 65 2009-07-09 08:56 /dev/ttyS1 crw-rw---- 1 root dialout 4, 66 2009-07-09 08:56 /dev/ttyS2 crw-rw---- 1 root dialout 4, 67 2009-07-09 08:56 /dev/ttyS3 gawain@gawain:~$ setserial -a /dev/ttyS0 /dev/ttyS0, Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4 Baud_base: 115200, close_delay: 50, divisor: 0 closing_wait: 3000 Flags: spd_normal skip_test gawain@gawain:~$ setserial -g /dev/ttyS* /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4 /dev/ttyS1, UART: 8250, Port: 0xd028, IRQ: 18 /dev/ttyS2, UART: 8250, Port: 0xd040, IRQ: 18 /dev/ttyS3, UART: 8250, Port: 0xd050, IRQ: 18 gawain@gawain:~$ echo 12345 > /dev/ttyS0 gawain@gawain:~$ dmesg | tail -3 [ 144.424259] ppdev0: unregistered pardevice [ 145.692199] ppdev0: registered pardevice [ 145.740052] ppdev0: unregistered pardevice I also tried changing the serial port name to /dev/ttys0 (with a lowercase S) and in that case it gave me a different error, "Unable to open serial device." This suggests to me that it is able to open /dev/ttyS0 but something else is preventing it from reading the weather station. Any ideas? thanks.

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• SQLite on iPhone - Techniques for tracking down multithreading-related bugs

  - by Jasarien

  Hey guys, I'm working with an Objective-C wrapper around SQLite that I didn't write, and documentation is sparse... It's not FMDB. The people writing this wrapper weren't aware of FMDB when writing this code. It seems that the code is suffering from a bug where database connections are being accessed from multiple threads -- which according to the SQLite documentation won't work if the if SQLite is compiled with SQLITE_THREADSAFE 2. I have tested the libsqlite3.dylib provided as part of the iPhone SDK and seen that it is compiled in this manner, using the sqlite_threadsafe() routine. Using the provided sqlite library, the code regularly hits SQLITE_BUSY and SQLITE_LOCKED return codes when performing routines. To combat this, I added some code to wait a couple of milliseconds and try again, with a maximum retry count of 50. The code didn't contain any retry logic prior to this. Now when a sqlite call returns SQLITE_BUSY or SQLITE_LOCKED, the retry loop is invoked and the retry returns SQLITE_MISUSE. Not good. Grasping at straws, I replaced the provided sqlite library with a version compiled by myself setting SQLITE_THREADSAFE to 1 - which according to the documentation means sqlite is safe to be used in a multithreaded environment, effectively serialising all of the operations. It incurs a performance hit, that which I haven't measured, but it ridded the app of the SQLITE_MISUSE happening and seemed to not need the retry logic as it never hit a busy or locked state. What I would rather do is fix the problem of accessing a single db connection from multiple threads, but I can't for the life of me find where it's occurring. So if anyone has any tips on locating multithreaded bugs I would be extremely appreciative. Thanks in advance.

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• Lightweight spinlocks built from GCC atomic operations?

  - by Thomas

  I'd like to minimize synchronization and write lock-free code when possible in a project of mine. When absolutely necessary I'd love to substitute light-weight spinlocks built from atomic operations for pthread and win32 mutex locks. My understanding is that these are system calls underneath and could cause a context switch (which may be unnecessary for very quick critical sections where simply spinning a few times would be preferable). The atomic operations I'm referring to are well documented here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Atomic-Builtins.html Here is an example to illustrate what I'm talking about. Imagine a RB-tree with multiple readers and writers possible. RBTree::exists() is read-only and thread safe, RBTree::insert() would require exclusive access by a single writer (and no readers) to be safe. Some code: class IntSetTest { private: unsigned short lock; RBTree<int>* myset; public: // ... void add_number(int n) { // Aquire once locked==false (atomic) while (__sync_bool_compare_and_swap(&lock, 0, 0xffff) == false); // Perform a thread-unsafe operation on the set myset->insert(n); // Unlock (atomic) __sync_bool_compare_and_swap(&lock, 0xffff, 0); } bool check_number(int n) { // Increment once the lock is below 0xffff u16 savedlock = lock; while (savedlock == 0xffff || __sync_bool_compare_and_swap(&lock, savedlock, savedlock+1) == false) savedlock = lock; // Perform read-only operation bool exists = tree->exists(n); // Decrement savedlock = lock; while (__sync_bool_compare_and_swap(&lock, savedlock, savedlock-1) == false) savedlock = lock; return exists; } }; (lets assume it need not be exception-safe) Is this code indeed thread-safe? Are there any pros/cons to this idea? Any advice? Is the use of spinlocks like this a bad idea if the threads are not truly concurrent? Thanks in advance. ;)

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• Seam unit test can't connect to JBoss4.0.5GA

  - by user240423

  Does anybody know how to connect with JBoss4.0.5GA in Seam2.2.0GA unit test? I'm using Seam2.2.0GA with the embeded JBoss to run the unit test, the module needs to call old JBoss server (EJB2, because the vendor locked in JCA has to deploy on old JBoss). it's typical seam test case, and I can't get it connect to JBoss4.0.5GA by using jbossall-client.jar from JBoss4.0.5GA. so far I tested the embeded JBoss can only working with JBoss5.X server. with JBoss4.2.3GA, it report: [testng] java.rmi.MarshalException: Failed to communicate. Problem during marshalling/unmarshalling; nested exception is: [testng] java.net.SocketException: end of file [testng] at org.jboss.remoting.transport.socket.SocketClientInvoker.handleException(SocketClientInvoker.java:122) [testng] at org.jboss.remoting.transport.socket.MicroSocketClientInvoker.transport(MicroSocketClientInvoker.java:679) [testng] at org.jboss.remoting.MicroRemoteClientInvoker.invoke(MicroRemoteClientInvoker.java:122) [testng] at org.jboss.remoting.Client.invoke(Client.java:1634) [testng] at org.jboss.remoting.Client.invoke(Client.java:548) This is the best result I could get (JBoss5.1.0GA jbossall-client.jar call JBoss4.2.3GA server in the embeded JBoss env), here is the ant script: <testng classpathref="build.test.classpath" outputDir="${target.test-reports.dir}" haltOnfailure="true"> <jvmarg line="-Dsun.lang.ClassLoader.allowArraySyntax=true" /> <jvmarg line="-Dorg.jboss.j2ee.Serialization=true" /> <!-- <jvmarg line="-Djboss.remoting.pre_2_0_compatible=true" /> --> <jvmarg line="-Djboss.jndi.url=jnp://localhost:1099" /> <xmlfileset dir="src/test/java" includes="${ant.project.name}-testsuite.xml" /> </testng> Can anybody help?

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• How to Write to a User.Config file through ConfigurationManager?

  - by Josh G

  I'm trying to persist user settings to a configuration file using ConfigurationManager. I want to scope these settings to the user only, because application changes can't be saved on Vista/Win 7 without admin privileges. This seems to get me the user's configuration, which appears to be saved here in Win 7 ([Drive]:\Users\[Username]\AppData\Local\[ApplicationName]\[AssemblyName][hash]\[Version\) Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal); Whenever I try to save any changes at all to this config I get this exception: InnerException: System.InvalidOperationException Message="ConfigurationSection properties cannot be edited when locked." Source="System.Configuration" StackTrace: at System.Configuration.SectionInformation.VerifyIsEditable() at System.Configuration.MgmtConfigurationRecord.GetConfigDefinitionUpdates(Boolean requireUpdates, ConfigurationSaveMode saveMode, Boolean forceSaveAll, ConfigDefinitionUpdates& definitionUpdates, ArrayList& configSourceUpdates) I have tried adding a custom ConfigurationSection to this config. I have tried adding to the AppSettingsSection. Whenever I call config.Save() it throws the exception above. Any ideas? I tried using the ApplicationSettingsBase class through the Project-Settings designer, but it doesn't appear that you can save custom types with this. I want similar functionality with the ability to save custom types. Thanks.

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• PHP sessions causing Apache to hang indefinitely

  - by Kmaid

  The problem is that every so often a page that writes to a Session will cause apache to hang forever for a particular session. Once this error occurs for one user any further modifications to any session of any user will cause the website to hang for this user. This problem has been my sole focus for days. I have a development VPS running Windows 2003 and default latest version of XAMPP using the standard PHP session handler. The code in question actually runs on two other machines perfectly normally so although my common sense says it’s a web server configuration issue but at this point I am willing to try anything. On further investigation there are no errors in the Apache, PHP or System event log. Resources are abundant and there is no “AJAX shit storm” or more than a couple writes to a session per page. I have also implemented session_write_close() wherever possible to try and help elevate the problem. I have checked the session’s directory which is set to “C:\windows\Temp” and found that once a user enters this hanging phase that the corresponding session file is exclusively locked and the only way to resolve this is to stop Apache and wait a few moments for the files to become unlocked and delete them. I am not wondering if deletion is required. The Sessions themselves only contain 4 bits of information. ShoppingCartID, UserID, UserLevel and Refering URL and are alphanumerical with an occasional slash. My PHP.INI’s session section is configured like this: session.save_handler = files session.save_path = "C:\WINDOWS\Temp" session.use_cookies = 1 session.name = PHPSESSID session.auto_start = 0 session.cookie_lifetime = 0 session.cookie_path = / session.cookie_domain = session.cookie_httponly = session.serialize_handler = php session.gc_probability = 1 session.gc_divisor = 100 session.gc_maxlifetime = 1440 session.bug_compat_42 = 1 session.bug_compat_warn = 1 session.referer_check = session.entropy_length = 0 session.entropy_file = session.cache_limiter = nocache session.cache_expire = 180 session.use_trans_sid = 0 session.hash_function = 0 session.hash_bits_per_character = 4 I have tried everything I can think of and the whole problem is now a blur to me. Any ideas would be appreciated and thanks for your time reading this :)

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• Design considerations for temporarily transforming a player into an animal in a role playing game

  - by mikedev

  I am working on a role playing game for fun and to practice design patterns. I would like players to be able to transform themselves into different animals. For example, a Druid might be able to shape shift into a cheetah. Right now I'm planning on using the decorator pattern to do this but my question is - how do I make it so that when a druid is in the cheetah form, they can only access skills for the cheetah? In other words, they should not be able to access their normal Druid skills. Using the decorator pattern it appears that even in the cheetah form my druid will be able to access their normal druid skills. class Druid : Character { // many cool druid skills and spells void LightHeal(Character target) { } } abstract class CharacterDecorator : Character { Character DecoratedCharacter; } class CheetahForm : CharacterDecorator { Character DecoratedCharacter; public CheetahForm(Character decoratedCharacter) { DecoratedCharacter= decoratedCharacter; } // many cool cheetah related skills void CheetahRun() { // let player move very fast } } now using the classes Druid myDruid = new Druid(); myDruid.LightHeal(myDruid); // casting light heal here is fine myDruid = new CheetahForm(myDruid); myDruid.LightHeal(myDruid); // casting here should not be allowed Hmmmm...now that I think about it, will myDruid be unable to us the Druid class spells/skills unless the class is down-casted? But even if that's the case, is there a better way to ensure that myDruid at this point is locked out from all Druid related spells/skills until it is cast back to a Druid (since currently it's in CheetahForm)

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