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• Synergy 1.5 crash (OSX 10.6.8)

  - by Oliver

  THANKS FOR TAKING THE TIME TO READ THIS I recently installed Synergy 1.5 r2278 (for Mac OSX 10.6.8) and was using it fine for most of the day, then it decided to stop working (the only thing I changed systemwise was the screensaver - and then after it started crashing disabled it - to see if it would resolve). When I start Synergy (on the Mac - Client) it says: after about 5 seconds (and successfully connecting to the Server) "synergyc quit unexpectedly" Here is the crash log (w/ binery info removed - too long for post requirements) Process: synergyc [1026] Path: /Applications/Synergy.app/Contents/MacOS/synergyc Identifier: synergy Version: ??? (???) Code Type: X86 (Native) Parent Process: Synergy [1023] Date/Time: 2014-05-28 15:36:17.746 +0930 OS Version: Mac OS X 10.6.8 (10K549) Report Version: 6 Interval Since Last Report: 2144189 sec Crashes Since Last Report: 23 Per-App Interval Since Last Report: 10242 sec Per-App Crashes Since Last Report: 9 Anonymous UUID: 86D5A57C-13D4-470E-AC72-48ACDDDE5EB0 Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x0000000000000000, 0x0000000000000000 Crashed Thread: 5 Application Specific Information: abort() called Thread 0: Dispatch queue: com.apple.main-thread 0 libSystem.B.dylib 0x95cf3afa mach_msg_trap + 10 1 libSystem.B.dylib 0x95cf4267 mach_msg + 68 2 com.apple.CoreFoundation 0x95af02df __CFRunLoopRun + 2079 3 com.apple.CoreFoundation 0x95aef3c4 CFRunLoopRunSpecific + 452 4 com.apple.CoreFoundation 0x95aef1f1 CFRunLoopRunInMode + 97 5 com.apple.HIToolbox 0x93654e04 RunCurrentEventLoopInMode + 392 6 com.apple.HIToolbox 0x93654bb9 ReceiveNextEventCommon + 354 7 com.apple.HIToolbox 0x937dd137 ReceiveNextEvent + 83 8 synergyc 0x000356d0 COSXEventQueueBuffer::waitForEvent(double) + 48 9 synergyc 0x00010dd5 CEventQueue::getEvent(CEvent&, double) + 325 10 synergyc 0x00011fb0 CEventQueue::loop() + 272 11 synergyc 0x00044eb6 CClientApp::mainLoop() + 134 12 synergyc 0x0005c509 standardStartupStatic(int, char**) + 41 13 synergyc 0x000448a9 CClientApp::runInner(int, char**, ILogOutputter*, int (*)(int, char**)) + 137 14 synergyc 0x0005c4b0 CAppUtilUnix::run(int, char**) + 64 15 synergyc 0x000427df CApp::run(int, char**) + 63 16 synergyc 0x00006e65 main + 117 17 synergyc 0x00006dd9 start + 53 Thread 1: 0 libSystem.B.dylib 0x95d607da __sigwait + 10 1 libSystem.B.dylib 0x95d607b6 sigwait$UNIX2003 + 71 2 synergyc 0x00009583 CArchMultithreadPosix::threadSignalHandler(void*) + 67 3 libSystem.B.dylib 0x95d21259 _pthread_start + 345 4 libSystem.B.dylib 0x95d210de thread_start + 34 Thread 2: 0 libSystem.B.dylib 0x95d21aa2 __semwait_signal + 10 1 libSystem.B.dylib 0x95d2175e _pthread_cond_wait + 1191 2 libSystem.B.dylib 0x95d212b1 pthread_cond_timedwait$UNIX2003 + 72 3 synergyc 0x00009476 CArchMultithreadPosix::waitCondVar(CArchCondImpl*, CArchMutexImpl*, double) + 150 4 synergyc 0x0002b18f CCondVarBase::wait(double) const + 63 5 synergyc 0x0002ce68 CSocketMultiplexer::serviceThread(void*) + 136 6 synergyc 0x0002d698 TMethodJob<CSocketMultiplexer>::run() + 40 7 synergyc 0x0002b8f4 CThread::threadFunc(void*) + 132 8 synergyc 0x00008f30 CArchMultithreadPosix::doThreadFunc(CArchThreadImpl*) + 80 9 synergyc 0x0000902a CArchMultithreadPosix::threadFunc(void*) + 74 10 libSystem.B.dylib 0x95d21259 _pthread_start + 345 11 libSystem.B.dylib 0x95d210de thread_start + 34 Thread 3: Dispatch queue: com.apple.libdispatch-manager 0 libSystem.B.dylib 0x95d1a382 kevent + 10 1 libSystem.B.dylib 0x95d1aa9c _dispatch_mgr_invoke + 215 2 libSystem.B.dylib 0x95d19f59 _dispatch_queue_invoke + 163 3 libSystem.B.dylib 0x95d19cfe _dispatch_worker_thread2 + 240 4 libSystem.B.dylib 0x95d19781 _pthread_wqthread + 390 5 libSystem.B.dylib 0x95d195c6 start_wqthread + 30 Thread 4: 0 libSystem.B.dylib 0x95d19412 __workq_kernreturn + 10 1 libSystem.B.dylib 0x95d199a8 _pthread_wqthread + 941 2 libSystem.B.dylib 0x95d195c6 start_wqthread + 30 Thread 5 Crashed: 0 libSystem.B.dylib 0x95d610ee __semwait_signal_nocancel + 10 1 libSystem.B.dylib 0x95d60fd2 nanosleep$NOCANCEL$UNIX2003 + 166 2 libSystem.B.dylib 0x95ddbfb2 usleep$NOCANCEL$UNIX2003 + 61 3 libSystem.B.dylib 0x95dfd6f0 abort + 105 4 libSystem.B.dylib 0x95d79b1b _Unwind_Resume + 59 5 synergyc 0x00008fd1 CArchMultithreadPosix::doThreadFunc(CArchThreadImpl*) + 241 6 synergyc 0x0000902a CArchMultithreadPosix::threadFunc(void*) + 74 7 libSystem.B.dylib 0x95d21259 _pthread_start + 345 8 libSystem.B.dylib 0x95d210de thread_start + 34 Thread 5 crashed with X86 Thread State (32-bit): eax: 0x0000003c ebx: 0x95d60f39 ecx: 0xb0288a7c edx: 0x95d610ee edi: 0x00521950 esi: 0xb0288ad8 ebp: 0xb0288ab8 esp: 0xb0288a7c ss: 0x0000001f efl: 0x00000247 eip: 0x95d610ee cs: 0x00000007 ds: 0x0000001f es: 0x0000001f fs: 0x0000001f gs: 0x00000037 cr2: 0x002fe000 Model: MacBook2,1, BootROM MB21.00A5.B07, 2 processors, Intel Core 2 Duo, 2.16 GHz, 2 GB

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• What's a good box to serve files on my local network, cross platform?

  - by rogpeppe

  I've installed CAT5e cable and gigabit switches in my house with the goal of having an "always-on" file server in the loft, accessible to both my macbook and my partner's Windows box. I'd like to find a solution which: uses minimal power. allows me to access as much disk bandwidth as possible. provides glitch-free file access to both MacOS and Windows. is as cheap as possible, while remaining reliable. Optional, but desirable extras: software or hardware RAID; open source solutions. A SheevaPlug with eSATA seems one possibility, but I'm sure there are any number of other good options.

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• How can you handle cross-cutting conerns in JAX-WS without Spring or AOP? Handlers?

  - by LES2

  I do have something more specific in mind, however: Each web service method needs to be wrapped with some boiler place code (cross cutting concern, yes, spring AOP would work great here but it either doesn't work or unapproved by gov't architecture group). A simple service call is as follows: @WebMethod... public Foo performFoo(...) { Object result = null; Object something = blah; try { soil(something); result = handlePerformFoo(...); } catch(Exception e) { throw translateException(e); } finally { wash(something); } return result; } protected abstract Foo handlePerformFoo(...); (I hope that's enough context). Basically, I would like a hook (that was in the same thread - like a method invocation interceptor) that could have a before() and after() that could could soil(something) and wash(something) around the method call for every freaking WebMethod. Can't use Spring AOP because my web services are not Spring managed beans :( HELP!!!!! Give advice! Please don't let me copy-paste that boiler plate 1 billion times (as I've been instructed to do). Regards, LES

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• Why would delaying a thread response fix view corruption?

  - by Beth S

  6 times out of 10 my very simple iPhone app is getting a corrupted display on launch or crashes randomly. But it behaves fine in the simulator. The display corruption looks like mis-colored fonts, out of place font text, wrong background colors, etc. I've found a strange work-around.. when my thread delays by 2 seconds before calling the "done" notification, everything works swimmingly. The thread reads a web page and the "done" notification loads up a PickerView with strings. So what gives? Can I not safely initiate a threaded task from viewDidLoad? - (void) loadWebPage:(NSString *)urlAddition { NSAutoreleasePool *subPool = [[NSAutoreleasePool alloc] init]; NSString *pageSource; NSError *err; NSString *urlString = [NSString stringWithString:@"http://server/%@", urlAddition]; pageSource = [NSString stringWithContentsOfURL:[NSURL URLWithString: urlString] encoding:NSUTF8StringEncoding error:&err]; [NSThread sleepForTimeInterval:2.0]; // THIS STOPS THE DISPLAY CORRUPTION [[NSNotificationCenter defaultCenter] postNotificationName:@"webDoneNotification" object:nil]; [subPool drain]; } - (void) webDoneNotification: (NSNotification *)pNotification { [mediaArray release]; mediaArray = [[NSArray arrayWithObjects: [NSString stringWithString:@"new pickerview text"], nil] retain]; [mediaPickerView reloadAllComponents]; [mediaPickerView selectRow:0 inComponent:0 animated:NO]; } - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { mediaArray = [[NSArray arrayWithObjects: [NSString stringWithString:@"init pickerview text"], nil] retain]; if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) { // Custom initialization } return self; } - (void)viewDidLoad { [super viewDidLoad]; myWebThread = [[WebThread alloc] initWithDelegate:self]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(webDoneNotification:) name:@"webDoneNotification" object:nil]; [myWebThread performSelectorInBackground:@selector(loadWebPage:) withObject:@""]; } Thanks! Update: Even a delay of 0.1 seconds is enough to completely fix the problem.

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• Cross browser's probelm to highlight option item as bold in form element "select".

  - by Vivek

  Hello All , I am facing one weird cross browsers problem i.e. I want to highlight some of the option items as bold by using CSS class in my form element "select". This all is working fine in firefox only but not in other browsers like safari , chrome and IE .Given below is the code. <html> <head> <title>MAke Heading Bold</title> <style type="text/css"> .mycss {font-weight:bold;} </style> </head> <body> <form name="myform"> <select name="myselect"> <option value="one">one</option> <option value="two" class="mycss">two</option> <option value="three" >Three </option> </select> </form> </body> </html> Please suggest me best possible solution for this . Thanks Vivek

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• What is an efficient strategy for multiple threads posting jobs and waiting for response from a single thread?

  - by jakewins

  In java, what is an efficient solution to the following problem: I have multiple threads (10-20 or so) generating jobs ("Job Creators"), and a single thread capable of performing them ("The worker"). Once a job creator has posted a job, it should wait for the job to finish, yielding no result other than "it's done", before it keeps going. For sending the jobs to the worker thread, I think a ring buffer or similar standard fan-in setup would perhaps be a good approach? But for a Job Creator to find out that her job has been done, I'm not so sure.. The job creators could sleep, and the worker interrupt them when done.. Or each job creator could have an atomic boolean that it checks, and that the worker sets. I dunno, neither of those feel very nice. I'd like to do it with as few (none, if possible) locks as absolutely possible. So to be clear: What I'm looking for is speed, not necessarily simplicity. Does anyone have any suggestions? Links to reading about concurrency strategies would also be very welcome!

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• Why there is no scoped locks for multiple mutexes in C++0x or Boost.Thread?

  - by Vicente Botet Escriba

  C++0x thread library or Boost.thread define non-member variadic template function that lock all lock avoiding dead lock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); While this function avoid help to deadlock, the standard do not includes the associated scoped lock to write exception safe code. { std::lock(l1,l2); // do some thing // unlock li l2 exception safe } That means that we need to use other mechanism as try-catch block to make exception safe code or define our own scoped lock on multiple mutexes ourselves or even do that { std::lock(l1,l2); std::unique_lock lk1(l1, std::adopted); std::unique_lock lk2(l2, std::adopted); // do some thing // unlock li l2 on destruction of lk1 lk2 } Why the standard doesn't includes a scoped lock on multiple mutexes of the same type, as for example { std::array_unique_lock<std::mutex> lk(l1,l2); // do some thing // unlock l1 l2 on destruction of lk } or tuples of mutexes { std::tuple_unique_lock<std::mutex, std::recursive_mutex> lk(l1,l2); // do some thing // unlock l1 l2 on destruction of lk } Is there something wrong on the design?

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• What is preferred strategies for cross browser and multiple styled table in CSS?

  - by jitendra

  What is preferred strategies for cross browser and multiple styled table in CSS? in default css what should i predefined for <table>, td, th , thead, tbody, tfoot I have to work in a project there are so many tables with different color schemes and different type of alignment like in some table , i will need to horizontally align data of cell to right, sometime left, sometime right. same thing for vertical alignment, top, bottom and middle. some table will have thin border on row , some will have thick (same with column border). Some time i want to give different background color to particular row or column or in multiple row or column. So my question is: What code should i keep in css default for all tables and how to handle table with different style using ID and classes in multiple pages. I want to do every presentational thing with css. How to make ID classes for everything using semantic naming ? Which tags related to table can be useful? How to control whole tables styling from one css class?

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• How can you exclude a large number of records in a cross db query using LINQ2SQL?

  - by tap

  So here is my situation: I have a vendor supplied DB we cannot modify and a custom db that imports data from the vendor app and acts on it. Once records are imported form the vendor app, they cannot appear on the list of records to be imported. Also we only want to display the 250 most recent records that have not been imported. What I originally started with was select the list of ids that have been imported from the custom db, and then query the vendor db, using the list of ids in a .Where(x = !idList.Contains(x.Id)) clause on the remote query. This worked up until we broke 2100 records imported into the custom db, as 2100 is the limit on the number of parameters that can be passed into SQL. After finding out this was the actual problem and not the 'invalid buffer'/'severe error' ADO.Net reported, my solution was to remove the first 2000 ids in the remote query, and then remove the remaining records in the local query. Having to pull back a large number of irrelevant records, just to exclude them, so I can get the correct 250 records seems very inelegant. Is there a better way to do this, short of doing a cross db stored procedure? Thanks in advance.

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• Why onCreate() calling multiple times when i use Thread()?

  - by RajaReddy PolamReddy

  In my app i faced a problem with threads. i am using native code in my app. i try to load library and then calling native functions from the android code. 1. By using Threads() : PjsuaThread pjsuaThread = new PjsuaThread(); pjsuaThread.start(); thread code class PjsuaThread extends Thread { public void run() { if (pjsua_app.initApp() != 0) { // native function calling return; } else { } pjsua_app.startPjsua(ApjsuaActivity.CFG_FNAME); // native function calling finished = true; } When i use code like this, onCreate() function calling multiple times and able to load library and calling some functions properly, after some seconds onCreate calling again because of that it's crashing. 2. Using AsyncTask(): And also i used AsyncTask< for this requirement, it's crashing the application( crashing in lib code ). not able to open any functions class SipTask extends AsyncTask<Void, String, Void> { protected Void doInBackground(Void... args) { if (pjsua_app.initApp() != 0) { return null; } else { } pjsua_app.startPjsua(ApjsuaActivity.CFG_FNAME); finished = true; return null; } @Override protected void onPostExecute(Void result) { super.onPostExecute(result); Log.i(TAG, "On POst "); } } What is annoying is that in most cases it is not the missing library, it's tried to able to load the lib crashing in between. any one know the reason ?

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• How can I get back into my main processing thread?

  - by daveomcd

  I have an app that I'm accessing a remote website with NSURLConnection to run some code and then save out some XML files. I am then accessing those XML Files and parsing through them for information. The process works fine except that my User Interface isn't getting updated properly. I want to keep the user updated through my UILabel. I'm trying to update the text by using setBottomBarToUpdating:. It works the first time when I set it to "Processing Please Wait..."; however, in the connectionDidFinishLoading: it doesn't update. I'm thinking my NSURLConnection is running on a separate thread and my attempt with the dispatch_get_main_queue to update on the main thread isn't working. How can I alter my code to resolve this? Thanks! [If I need to include more information/code just let me know!] myFile.m NSLog(@"Refreshing..."); dispatch_sync( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ [self getResponse:@"http://mylocation/path/to/file.aspx"]; }); [self setBottomBarToUpdating:@"Processing Please Wait..."]; queue = dispatch_queue_create("updateQueue", DISPATCH_QUEUE_CONCURRENT); connectionDidFinishLoading: if ([response rangeOfString:@"Complete"].location == NSNotFound]) { // failed } else { //success dispatch_async(dispatch_get_main_queue(),^ { [self setBottomBarToUpdating:@"Updating Contacts..."]; }); [self updateFromXMLFile:@"http://thislocation.com/path/to/file.xml"]; dispatch_async(dispatch_get_main_queue(),^ { [self setBottomBarToUpdating:@"Updating Emails..."]; }); [self updateFromXMLFile:@"http://thislocation.com/path/to/file2.xml"]; }

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• Penetration testing with Nikto, unknown results found

  - by heldrida

  I've scanned my new webserver and I'm surprised to find that in the results there's programs that I never installed. This is a fresh new install of Ubuntu 12.04 and just installed Php 5.3, mysql, fail2ban, apache2, git, a few other things. Not sure if related, but I've got Wordpress installed but this doesn't have anything to do with myphpnuke does it? I'd like to understand why am I getting this results ? + OSVDB-27071: /phpimageview.php?pic=javascript:alert(8754): PHP Image View 1.0 is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + OSVDB-3931: /myphpnuke/links.php?op=search&query=[script]alert('Vulnerable);[/script]?query=: myphpnuke is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + OSVDB-3931: /myphpnuke/links.php?op=MostPopular&ratenum=[script]alert(document.cookie);[/script]&ratetype=percent: myphpnuke is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + /modules.php?op=modload&name=FAQ&file=index&myfaq=yes&id_cat=1&categories=%3Cimg%20src=javascript:alert(9456);%3E&parent_id=0: Post Nuke 0.7.2.3-Phoenix is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + /modules.php?letter=%22%3E%3Cimg%20src=javascript:alert(document.cookie);%3E&op=modload&name=Members_List&file=index: Post Nuke 0.7.2.3-Phoenix is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + OSVDB-4598: /members.asp?SF=%22;}alert('Vulnerable');function%20x(){v%20=%22: Web Wiz Forums ver. 7.01 and below is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. + OSVDB-2946: /forum_members.asp?find=%22;}alert(9823);function%20x(){v%20=%22: Web Wiz Forums ver. 7.01 and below is vulnerable to Cross Site Scripting (XSS). http://www.cert.org/advisories/CA-2000-02.html. Thanks for looking!

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• Qthread - trouble shutting down threads

  - by Bryan Greenway

  For the last few days, I've been trying out the new preferred approach for using QThreads without subclassing QThread. The trouble I'm having is when I try to shutdown a set of threads that I created. I regularly get a "Destroyed while thread is still running" message (if I'm running in Debug mode, I also get a Segmentation Fault dialog). My code is very simple, and I've tried to follow the examples that I've been able to find on the internet. My basic setup is as follows: I've a simple class that I want to run in a separate thread; in fact, I want to run 5 instances of this class, each in a separate thread. I have a simple dialog with a button to start each thread, and a button to stop each thread (10 buttons). When I click one of the "start" buttons, a new instance of the test class is created, a new QThread is created, a movetothread is called to get the test class object to the thread...also, since I have a couple of other members in the test class that need to move to the thread, I call movetothread a few additional times with these other items. Note that one of these items is a QUdpSocket, and although this may not make sense, I wanted to make sure that sockets could be moved to a separate thread in this fashion...I haven't tested the use of the socket in the thread at this point. Starting of the threads all seem to work fine. When I use the linux top command to see if the threads are created and running, they show up as expected. The problem occurs when I begin stopping the threads. I randomly (or it appears to be random) get the error described above. Class that is to run in separate thread: // Declaration class TestClass : public QObject { Q_OBJECT public: explicit TestClass(QObject *parent = 0); QTimer m_workTimer; QUdpSocket m_socket; Q_SIGNALS: void finished(); public Q_SLOTS: void start(); void stop(); void doWork(); }; // Implementation TestClass::TestClass(QObject *parent) : QObject(parent) { } void TestClass::start() { connect(&m_workTimer, SIGNAL(timeout()),this,SLOT(doWork())); m_workTimer.start(50); } void TestClass::stop() { m_workTimer.stop(); emit finished(); } void TestClass::doWork() { int j; for(int i = 0; i<10000; i++) { j = i; } } Inside my main app, code called to start the first thread (similar code exists for each of the other threads): mp_thread1 = new QThread(); mp_testClass1 = new TestClass(); mp_testClass1->moveToThread(mp_thread1); mp_testClass1->m_socket.moveToThread(mp_thread1); mp_testClass1->m_workTimer.moveToThread(mp_thread1); connect(mp_thread1, SIGNAL(started()), mp_testClass1, SLOT(start())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(quit())); connect(mp_testClass1, SIGNAL(finished()), mp_testClass1, SLOT(deleteLater())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(deleteLater())); connect(this,SIGNAL(stop1()),mp_testClass1,SLOT(stop())); mp_thread1->start(); Also inside my main app, this code is called when a stop button is clicked for a specific thread (in this case thread 1): emit stop1(); Sometimes it appears that threads are stopped and destroyed without issue. Other times, I get the error described above. Any guidance would be greatly appreciated. Thanks, Bryan

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• Parallelism in .NET – Part 4, Imperative Data Parallelism: Aggregation

  - by Reed

  In the article on simple data parallelism, I described how to perform an operation on an entire collection of elements in parallel.  Often, this is not adequate, as the parallel operation is going to be performing some form of aggregation. Simple examples of this might include taking the sum of the results of processing a function on each element in the collection, or finding the minimum of the collection given some criteria.  This can be done using the techniques described in simple data parallelism, however, special care needs to be taken into account to synchronize the shared data appropriately.  The Task Parallel Library has tools to assist in this synchronization. The main issue with aggregation when parallelizing a routine is that you need to handle synchronization of data.  Since multiple threads will need to write to a shared portion of data.  Suppose, for example, that we wanted to parallelize a simple loop that looked for the minimum value within a dataset: double min = double.MaxValue; foreach(var item in collection) { double value = item.PerformComputation(); min = System.Math.Min(min, value); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This seems like a good candidate for parallelization, but there is a problem here.  If we just wrap this into a call to Parallel.ForEach, we’ll introduce a critical race condition, and get the wrong answer.  Let’s look at what happens here: // Buggy code! Do not use! double min = double.MaxValue; Parallel.ForEach(collection, item => { double value = item.PerformComputation(); min = System.Math.Min(min, value); }); This code has a fatal flaw: min will be checked, then set, by multiple threads simultaneously.  Two threads may perform the check at the same time, and set the wrong value for min.  Say we get a value of 1 in thread 1, and a value of 2 in thread 2, and these two elements are the first two to run.  If both hit the min check line at the same time, both will determine that min should change, to 1 and 2 respectively.  If element 1 happens to set the variable first, then element 2 sets the min variable, we’ll detect a min value of 2 instead of 1.  This can lead to wrong answers. Unfortunately, fixing this, with the Parallel.ForEach call we’re using, would require adding locking.  We would need to rewrite this like: // Safe, but slow double min = double.MaxValue; // Make a "lock" object object syncObject = new object(); Parallel.ForEach(collection, item => { double value = item.PerformComputation(); lock(syncObject) min = System.Math.Min(min, value); }); This will potentially add a huge amount of overhead to our calculation.  Since we can potentially block while waiting on the lock for every single iteration, we will most likely slow this down to where it is actually quite a bit slower than our serial implementation.  The problem is the lock statement – any time you use lock(object), you’re almost assuring reduced performance in a parallel situation.  This leads to two observations I’ll make: When parallelizing a routine, try to avoid locks. That being said: Always add any and all required synchronization to avoid race conditions. These two observations tend to be opposing forces – we often need to synchronize our algorithms, but we also want to avoid the synchronization when possible.  Looking at our routine, there is no way to directly avoid this lock, since each element is potentially being run on a separate thread, and this lock is necessary in order for our routine to function correctly every time. However, this isn’t the only way to design this routine to implement this algorithm.  Realize that, although our collection may have thousands or even millions of elements, we have a limited number of Processing Elements (PE).  Processing Element is the standard term for a hardware element which can process and execute instructions.  This typically is a core in your processor, but many modern systems have multiple hardware execution threads per core.  The Task Parallel Library will not execute the work for each item in the collection as a separate work item. Instead, when Parallel.ForEach executes, it will partition the collection into larger “chunks” which get processed on different threads via the ThreadPool.  This helps reduce the threading overhead, and help the overall speed.  In general, the Parallel class will only use one thread per PE in the system. Given the fact that there are typically fewer threads than work items, we can rethink our algorithm design.  We can parallelize our algorithm more effectively by approaching it differently.  Because the basic aggregation we are doing here (Min) is communitive, we do not need to perform this in a given order.  We knew this to be true already – otherwise, we wouldn’t have been able to parallelize this routine in the first place.  With this in mind, we can treat each thread’s work independently, allowing each thread to serially process many elements with no locking, then, after all the threads are complete, “merge” together the results. This can be accomplished via a different set of overloads in the Parallel class: Parallel.ForEach<TSource,TLocal>.  The idea behind these overloads is to allow each thread to begin by initializing some local state (TLocal).  The thread will then process an entire set of items in the source collection, providing that state to the delegate which processes an individual item.  Finally, at the end, a separate delegate is run which allows you to handle merging that local state into your final results. To rewriting our routine using Parallel.ForEach<TSource,TLocal>, we need to provide three delegates instead of one.  The most basic version of this function is declared as: public static ParallelLoopResult ForEach<TSource, TLocal>( IEnumerable<TSource> source, Func<TLocal> localInit, Func<TSource, ParallelLoopState, TLocal, TLocal> body, Action<TLocal> localFinally ) The first delegate (the localInit argument) is defined as Func<TLocal>.  This delegate initializes our local state.  It should return some object we can use to track the results of a single thread’s operations. The second delegate (the body argument) is where our main processing occurs, although now, instead of being an Action<T>, we actually provide a Func<TSource, ParallelLoopState, TLocal, TLocal> delegate.  This delegate will receive three arguments: our original element from the collection (TSource), a ParallelLoopState which we can use for early termination, and the instance of our local state we created (TLocal).  It should do whatever processing you wish to occur per element, then return the value of the local state after processing is completed. The third delegate (the localFinally argument) is defined as Action<TLocal>.  This delegate is passed our local state after it’s been processed by all of the elements this thread will handle.  This is where you can merge your final results together.  This may require synchronization, but now, instead of synchronizing once per element (potentially millions of times), you’ll only have to synchronize once per thread, which is an ideal situation. Now that I’ve explained how this works, lets look at the code: // Safe, and fast! double min = double.MaxValue; // Make a "lock" object object syncObject = new object(); Parallel.ForEach( collection, // First, we provide a local state initialization delegate. () => double.MaxValue, // Next, we supply the body, which takes the original item, loop state, // and local state, and returns a new local state (item, loopState, localState) => { double value = item.PerformComputation(); return System.Math.Min(localState, value); }, // Finally, we provide an Action<TLocal>, to "merge" results together localState => { // This requires locking, but it's only once per used thread lock(syncObj) min = System.Math.Min(min, localState); } ); Although this is a bit more complicated than the previous version, it is now both thread-safe, and has minimal locking.  This same approach can be used by Parallel.For, although now, it’s Parallel.For<TLocal>.  When working with Parallel.For<TLocal>, you use the same triplet of delegates, with the same purpose and results. Also, many times, you can completely avoid locking by using a method of the Interlocked class to perform the final aggregation in an atomic operation.  The MSDN example demonstrating this same technique using Parallel.For uses the Interlocked class instead of a lock, since they are doing a sum operation on a long variable, which is possible via Interlocked.Add. By taking advantage of local state, we can use the Parallel class methods to parallelize algorithms such as aggregation, which, at first, may seem like poor candidates for parallelization.  Doing so requires careful consideration, and often requires a slight redesign of the algorithm, but the performance gains can be significant if handled in a way to avoid excessive synchronization.

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• How can I get penetration depth from Minkowski Portal Refinement / Xenocollide?

  - by Raven Dreamer

  I recently got an implementation of Minkowski Portal Refinement (MPR) successfully detecting collision. Even better, my implementation returns a good estimate (local minimum) direction for the minimum penetration depth. So I took a stab at adjusting the algorithm to return the penetration depth in an arbitrary direction, and was modestly successful - my altered method works splendidly for face-edge collision resolution! What it doesn't currently do, is correctly provide the minimum penetration depth for edge-edge scenarios, such as the case on the right: What I perceive to be happening, is that my current method returns the minimum penetration depth to the nearest vertex - which works fine when the collision is actually occurring on the plane of that vertex, but not when the collision happens along an edge. Is there a way I can alter my method to return the penetration depth to the point of collision, rather than the nearest vertex? Here's the method that's supposed to return the minimum penetration distance along a specific direction: public static Vector3 CalcMinDistance(List<Vector3> shape1, List<Vector3> shape2, Vector3 dir) { //holding variables Vector3 n = Vector3.zero; Vector3 swap = Vector3.zero; // v0 = center of Minkowski sum v0 = Vector3.zero; // Avoid case where centers overlap -- any direction is fine in this case //if (v0 == Vector3.zero) return Vector3.zero; //always pass in a valid direction. // v1 = support in direction of origin n = -dir; //get the differnce of the minkowski sum Vector3 v11 = GetSupport(shape1, -n); Vector3 v12 = GetSupport(shape2, n); v1 = v12 - v11; //if the support point is not in the direction of the origin if (v1.Dot(n) <= 0) { //Debug.Log("Could find no points this direction"); return Vector3.zero; } // v2 - support perpendicular to v1,v0 n = v1.Cross(v0); if (n == Vector3.zero) { //v1 and v0 are parallel, which means //the direction leads directly to an endpoint n = v1 - v0; //shortest distance is just n //Debug.Log("2 point return"); return n; } //get the new support point Vector3 v21 = GetSupport(shape1, -n); Vector3 v22 = GetSupport(shape2, n); v2 = v22 - v21; if (v2.Dot(n) <= 0) { //can't reach the origin in this direction, ergo, no collision //Debug.Log("Could not reach edge?"); return Vector2.zero; } // Determine whether origin is on + or - side of plane (v1,v0,v2) //tests linesegments v0v1 and v0v2 n = (v1 - v0).Cross(v2 - v0); float dist = n.Dot(v0); // If the origin is on the - side of the plane, reverse the direction of the plane if (dist > 0) { //swap the winding order of v1 and v2 swap = v1; v1 = v2; v2 = swap; //swap the winding order of v11 and v12 swap = v12; v12 = v11; v11 = swap; //swap the winding order of v11 and v12 swap = v22; v22 = v21; v21 = swap; //and swap the plane normal n = -n; } /// // Phase One: Identify a portal while (true) { // Obtain the support point in a direction perpendicular to the existing plane // Note: This point is guaranteed to lie off the plane Vector3 v31 = GetSupport(shape1, -n); Vector3 v32 = GetSupport(shape2, n); v3 = v32 - v31; if (v3.Dot(n) <= 0) { //can't enclose the origin within our tetrahedron //Debug.Log("Could not reach edge after portal?"); return Vector3.zero; } // If origin is outside (v1,v0,v3), then eliminate v2 and loop if (v1.Cross(v3).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v2 = v3; v21 = v31; v22 = v32; n = (v1 - v0).Cross(v3 - v0); continue; } // If origin is outside (v3,v0,v2), then eliminate v1 and loop if (v3.Cross(v2).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v1 = v3; v11 = v31; v12 = v32; n = (v3 - v0).Cross(v2 - v0); continue; } bool hit = false; /// // Phase Two: Refine the portal int phase2 = 0; // We are now inside of a wedge... while (phase2 < 20) { phase2++; // Compute normal of the wedge face n = (v2 - v1).Cross(v3 - v1); n.Normalize(); // Compute distance from origin to wedge face float d = n.Dot(v1); // If the origin is inside the wedge, we have a hit if (d > 0 ) { //Debug.Log("Do plane test here"); float T = n.Dot(v2) / n.Dot(dir); Vector3 pointInPlane = (dir * T); return pointInPlane; } // Find the support point in the direction of the wedge face Vector3 v41 = GetSupport(shape1, -n); Vector3 v42 = GetSupport(shape2, n); v4 = v42 - v41; float delta = (v4 - v3).Dot(n); float separation = -(v4.Dot(n)); if (delta <= kCollideEpsilon || separation >= 0) { //Debug.Log("Non-convergance detected"); //Debug.Log("Do plane test here"); return Vector3.zero; } // Compute the tetrahedron dividing face (v4,v0,v1) float d1 = v4.Cross(v1).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v2) float d2 = v4.Cross(v2).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v3) float d3 = v4.Cross(v3).Dot(v0); if (d1 < 0) { if (d2 < 0) { // Inside d1 & inside d2 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } else { // Inside d1 & outside d2 ==> eliminate v3 v3 = v4; v31 = v41; v32 = v42; } } else { if (d3 < 0) { // Outside d1 & inside d3 ==> eliminate v2 v2 = v4; v21 = v41; v22 = v42; } else { // Outside d1 & outside d3 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } } } return Vector3.zero; } }

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• .NET Backgroundworker - Is there no way to let exceptions pass back normally to main thread?

  - by Greg

  Hi, QUESTION: Re use of .NET Backgroundworker, is there not a way to let exceptions pass back normally to main thread? BACKGROUND: Currently in my WinForms application I have generic exception handle that goes along the lines of, if (a) a custom app exception then present to user, but don't exit program, and (b) if other exception then present and then exit application The above is nice as I can just throw the appropriate exception anywhere in the application and the presentation/handling is handled generically

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• Dynamic changes to thread stack size in Solaris 9 ?

  - by Satya

  Hello, I am looking for a configurable / tunable on Solaris 9 through which I can change the default thread stack size without recompiling the code to use "pthread_attr_setstacksize" For example on HPUX 11.11 / 11.23 the environment variable "PTHREAD_DEFAULT_STACK_SIZE" can be exported (available via HPUX patches PHCO_38307 / PHCO_38955 ) - Is there a equivalent Solaris 9 way to achieve the same ? Thanks! Satya

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• Fulltext search for django : Mysql not so bad ? (vs sphinx, xapian)

  - by Eric

  I am studying fulltext search engines for django. It must be simple to install, fast indexing, fast index update, not blocking while indexing, fast search. After reading many web pages, I put in short list : Mysql MYISAM fulltext, djapian/python-xapian, and django-sphinx I did not choose lucene because it seems complex, nor haystack as it has less features than djapian/django-sphinx (like fields weighting). Then I made some benchmarks, to do so, I collected many free books on the net to generate a database table with 1 485 000 records (id,title,body), each record is about 600 bytes long. From the database, I also generated a list of 100 000 existing words and shuffled them to create a search list. For the tests, I made 2 runs on my laptop (4Go RAM, Dual core 2.0Ghz): the first one, just after a server reboot to clear all caches, the second is done juste after in order to test how good are cached results. Here are the "home made" benchmark results : 1485000 records with Title (150 bytes) and body (450 bytes) Mysql 5.0.75/Ubuntu 9.04 Fulltext : ========================================================================== Full indexing : 7m14.146s 1 thread, 1000 searchs with single word randomly taken from database : First run : 0:01:11.553524 next run : 0:00:00.168508 Mysql 5.5.4 m3/Ubuntu 9.04 Fulltext : ========================================================================== Full indexing : 6m08.154s 1 thread, 1000 searchs with single word randomly taken from database : First run : 0:01:11.553524 next run : 0:00:00.168508 1 thread, 100000 searchs with single word randomly taken from database : First run : 9m09s next run : 5m38s 1 thread, 10000 random strings (random strings should not be found in database) : just after the 100000 search test : 0:00:15.007353 1 thread, boolean search : 1000 x (+word1 +word2) First run : 0:00:21.205404 next run : 0:00:00.145098 Djapian Fulltext : ========================================================================== Full indexing : 84m7.601s 1 thread, 1000 searchs with single word randomly taken from database with prefetch : First run : 0:02:28.085680 next run : 0:00:14.300236 python-xapian Fulltext : ========================================================================== 1 thread, 1000 searchs with single word randomly taken from database : First run : 0:01:26.402084 next run : 0:00:00.695092 django-sphinx Fulltext : ========================================================================== Full indexing : 1m25.957s 1 thread, 1000 searchs with single word randomly taken from database : First run : 0:01:30.073001 next run : 0:00:05.203294 1 thread, 100000 searchs with single word randomly taken from database : First run : 12m48s next run : 9m45s 1 thread, 10000 random strings (random strings should not be found in database) : just after the 100000 search test : 0:00:23.535319 1 thread, boolean search : 1000 x (word1 word2) First run : 0:00:20.856486 next run : 0:00:03.005416 As you can see, Mysql is not so bad at all for fulltext search. In addition, its query cache is very efficient. Mysql seems to me a good choice as there is nothing to install (I need just to write a small script to synchronize an Innodb production table to a MyISAM search table) and as I do not really need advanced search feature like stemming etc... Here is the question : What do you think about Mysql fulltext search engine vs sphinx and xapian ?

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• Unexpected behavior of IntentService

  - by kknight

  I used IntentService in my code instead of Service because IntentService creates a thread for me in onHandleIntent(Intent intent), so I don't have to create a Thead myself in the code of my service. I expected that two intents to the same IntentSerivce will execute in parallel because a thread is generated in IntentService for each invent. But my code turned out that the two intents executed in sequential way. This is my IntentService code: public class UpdateService extends IntentService { public static final String TAG = "HelloTestIntentService"; public UpdateService() { super("News UpdateService"); } protected void onHandleIntent(Intent intent) { String userAction = intent .getStringExtra("userAction"); Log.v(TAG, "" + new Date() + ", In onHandleIntent for userAction = " + userAction + ", thread id = " + Thread.currentThread().getId()); if ("1".equals(userAction)) { try { Thread.sleep(20 * 1000); } catch (InterruptedException e) { Log.e(TAG, "error", e); } Log.v(TAG, "" + new Date() + ", This thread is waked up."); } } } And the code call the service is below: public class HelloTest extends Activity { //@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Intent selectIntent = new Intent(this, UpdateService.class); selectIntent.putExtra("userAction", "1"); this.startService(selectIntent); selectIntent = new Intent(this, UpdateService.class); selectIntent.putExtra("userAction", "2"); this.startService(selectIntent); } } I saw this log message in the log: V/HelloTestIntentService( 848): Wed May 05 14:59:37 PDT 2010, In onHandleIntent for userAction = 1, thread id = 8 D/dalvikvm( 609): GC freed 941 objects / 55672 bytes in 99ms V/HelloTestIntentService( 848): Wed May 05 15:00:00 PDT 2010, This thread is waked up. V/HelloTestIntentService( 848): Wed May 05 15:00:00 PDT 2010, In onHandleIntent for userAction = 2, thread id = 8 I/ActivityManager( 568): Stopping service: com.example.android/.UpdateService The log shows that the second intent waited the first intent to finish and they are in the same thread. It there anything I misunderstood of IntentService. To make two service intents execute in parallel, do I have to replace IntentService with service and start a thread myself in the service code? Thanks.

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• Is it allowed to load Swing classes in non-EDT thread?

  - by ddimitrov

  After the introduction of Java Memory Model, the Swing guidelines were changed to state that any Swing components need to be instantiated on the EDT in order to avoid non-published instance state. What I could not find anywhere is whether the classloading is also mandated to be on the EDT or can we pre-load key Swing classes in a background thread? Is there any official statement from Sun/Oracle on this? Are there any classes that are known to hold non-threadsafe static state, hence need to be loaded on EDT?

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• Call HttpWebRequest in another thread as UI with Task class - avoid to dispose object created in Task scope

  - by John

  I would like call HttpWebRequest on another thread as UI, because I must make 200 request or server and downloaded image. My scenation is that I make a request on server, create image and return image. This I make in another thread. I use Task class, but it call automaticaly Dispose method on all object created in task scope. So I return null object from this method. public BitmapImage CreateAvatar(Uri imageUri, int sex) { if (imageUri == null) return CreateDefaultAvatar(sex); BitmapImage image = null; new Task(() => { var request = WebRequest.Create(imageUri); var response = request.GetResponse(); using (var stream = response.GetResponseStream()) { Byte[] buffer = new Byte[response.ContentLength]; int offset = 0, actuallyRead = 0; do { actuallyRead = stream.Read(buffer, offset, buffer.Length - offset); offset += actuallyRead; } while (actuallyRead > 0); image = new BitmapImage { CreateOptions = BitmapCreateOptions.None, CacheOption = BitmapCacheOption.OnLoad }; image.BeginInit(); image.StreamSource = new MemoryStream(buffer); image.EndInit(); image.Freeze(); } }).Start(); return image; } How avoid it? Thank Mr. Jon Skeet try this: private Stream GetImageStream(Uri imageUri) { Byte[] buffer = null; //new Task(() => //{ var request = WebRequest.Create(imageUri); var response = request.GetResponse(); using (var stream = response.GetResponseStream()) { buffer= new Byte[response.ContentLength]; int offset = 0, actuallyRead = 0; do { actuallyRead = stream.Read(buffer, offset, buffer.Length - offset); offset += actuallyRead; } while (actuallyRead > 0); } //}).Start(); return new MemoryStream(buffer); } It return object which is null a than try this: private Stream GetImageStream(Uri imageUri) { Byte[] buffer = null; new Task(() => { var request = WebRequest.Create(imageUri); var response = request.GetResponse(); using (var stream = response.GetResponseStream()) { buffer= new Byte[response.ContentLength]; int offset = 0, actuallyRead = 0; do { actuallyRead = stream.Read(buffer, offset, buffer.Length - offset); offset += actuallyRead; } while (actuallyRead > 0); } }).Start(); return new MemoryStream(buffer); } Method above return null

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• How to find the current state of a thread in the scheduler strucure in windows.

  - by Renjith G

  Hi all, I want to know the current state(SUSPENDED/READY/RUNNING/WAITING state ) of a thread which has been created by CreateThread() api. How can I find it out? My developement environment is Visual studio 2008 Expresss edition also language is C/C++ /renjith g

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• Exception in thread "main" java.lang.OutOfMemoryError, How to find and fix??

  - by or.nomore

  hey, I'm trying to programming a crossword creator. using a given dictionary txt file and a given pattern txt file. The basic idea is using DFS algorithm. the problem begin when the dictionary file is v-e-r-y big (about 50000 words). then i recive the : Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded i know that there is a part in my program that waists memory, but i don't know where it is, how to find it and how to fix it

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• Why do some JVM/Linux Kernels show each java thread as a process and other not? How can I determine

  - by Jherico

  I have two machines, one running 2.4.18 and one running 2.4.20. Both run Java 1.5 build 13. On one machine (2.4.18), each thread shows up as a separate process in the ps output, and on the other the whole JVM shows up as one process. What is the distinguishing factor and can I control it?

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• Does an asynchronous call always create/call a new thread?

  - by Ted Smith

  Does asynchronous call always create a new thread? Example: If Javascript is single threaded then how can it do an async postback? Is it actually blocking until it gets a callback? If so, is this really an async call?

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