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  • cancelPreviousPerformRequestWithTarget is not canceling my previously delayed thread started with pe

    - by jmurphy
    Hello, I've launched a delayed thread using performSelector but the user still has the ability to hit the back button on the current view causing dealloc to be called. When this happens my thread still seems to be called which causes my app to crash because the properties that thread is trying to write to have been released. To solve this I am trying to call cancelPreviousPerformRequestsWithTarget to cancel the previous request but it doesn't seem to be working. Below are some code snippets. - (void) viewDidLoad { [self performSelector:@selector(myStopUpdatingLocation) withObject:nil afterDelay:6]; } (void)viewWillDisappear:(BOOL)animated { [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(myStopUpdatingLocation) object:nil]; } Am I doing something incorrect here? The method myStopUpdatingLocation is defined in the same class that I'm calling the perform requests. A little more background. The function that I'm trying to implement is to find a users location, search google for some locations around that location and display several annotations on the map. On viewDidLoad I start updating the location with CLLocationManager. I've build in a timeout after 6 seconds if I don't get my desired accuracy within the timeout and I'm using a performSelector to do this. What can happen is the user clicks the back button in the view and this thread will still execute even though all my properties have been released causing a crash. Thanks in advance! James

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  • ADO.NET DataTable/DataRow Thread Safety

    - by Allen E. Scharfenberg
    Introduction A user reported to me this morning that he was having an issue with inconsistent results (namely, column values sometimes coming out null when they should not be) of some parallel execution code that we provide as part of an internal framework. This code has worked fine in the past and has not been tampered with lately, but it got me to thinking about the following snippet: Code Sample lock (ResultTable) { newRow = ResultTable.NewRow(); } newRow["Key"] = currentKey; foreach (KeyValuePair<string, object> output in outputs) { object resultValue = output.Value; newRow[output.Name] = resultValue != null ? resultValue : DBNull.Value; } lock (ResultTable) { ResultTable.Rows.Add(newRow); } (No guarantees that that compiles, hand-edited to mask proprietery information.) Explanation We have this cascading type of locking code other places in our system, and it works fine, but this is the first instance of cascading locking code that I have come across that interacts with ADO .NET. As we all know, members of framework objects are usually not thread safe (which is the case in this situation), but the cascading locking should ensure that we are not reading and writing to ResultTable.Rows concurrently. We are safe, right? Hypothesis Well, the cascading lock code does not ensure that we are not reading from or writing to ResultTable.Rows at the same time that we are assigning values to columns in the new row. What if ADO .NET uses some kind of buffer for assigning column values that is not thread safe--even when different object types are involved (DataTable vs. DataRow)? Has anyone run into anything like this before? I thought I would ask here at StackOverflow before beating my head against this for hours on end :) Conclusion Well, the consensus appears to be that changing the cascading lock to a full lock has resolved the issue. That is not the result that I expected, but the full lock version has not produced the issue after many, many, many tests. The lesson: be wary of cascading locks used on APIs that you do not control. Who knows what may be going on under the covers!

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  • different thread accessing MemoryStream

    - by Wayne
    There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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  • Terminal-based snake game: input thread manipulates output

    - by enlightened
    I'm writing a snake game for the terminal, i.e. output via print. The following works just fine: while status[snake_monad] do print to_string draw canvas, compose_all([ frame, specs, snake_to_hash(snake[snake_monad]) ]) turn! snake_monad, get_dir move! snake_monad, specs sleep 0.25 end But I don't want the turn!ing to block, of course. So I put it into a new Thread and let it loop: Thread.new do loop do turn! snake_monad, get_dir end end while status[snake_monad] do ... # no turn! here ... end Which also works logically (the snake is turning), but the output is somehow interspersed with newlines. As soon as I kill the input thread (^C) it looks normal again. So why and how does the thread have any effect on my output? And how do I work around this issue? (I don't know much about threads, even less about them in ruby. Input and output concurrently on the same terminal make the matter worse, I guess...) Also (not really important): Wanting my program as pure as possible, would it be somewhat easily possible to get the input non-blockingly while passing everything around? Thank you!

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  • Thread mutex behaviour

    - by Alberteddu
    Hi there, I'm learning C. I'm writing an application with multiple threads; I know that when a variable is shared between two or more threads, it is better to lock/unlock using a mutex to avoid deadlock and inconsistency of variables. This is very clear when I want to change or view one variable. int i = 0; /** Global */ static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /** Thread 1. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); /** Thread 2. */ pthread_mutex_lock(&mutex); i++; pthread_mutex_unlock(&mutex); This is correct, I think. The variable i, at the end of the executions, contains the integer 2. Anyway, there are some situations in which I don't know exactly where to put the two function calls. For example, suppose you have a function obtain(), which returns a global variable. I need to call that function from within the two threads. I have also two other threads that call the function set(), defined with a few arguments; this function will set the same global variable. The two functions are necessary when you need to do something before getting/setting the var. /** (0) */ /** Thread 1, or 2, or 3... */ if(obtain() == something) { if(obtain() == somethingElse) { // Do this, sometimes obtain() and sometimes set(random number) (1) } else { // Do that, just obtain(). (2) } } else { // Do this and do that (3) // If # of thread * 3 > 10, then set(3*10) For example. (4) } /** (5) */ Where I have to lock, and where I have to unlock? The situation can be, I think, even more complex. I will appreciate an exhaustive answer. Thank you in advance. —Alberto

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  • Creating Thread in Win32

    - by Dave18
    Does ThreadFunc() gets called two times here? sometimes I notice a single call and sometimes none at all. #include <windows.h> #include <stdio.h> DWORD WINAPI ThreadFunc(LPVOID); int main() { HANDLE hThread; DWORD threadld; hThread = CreateThread(NULL, 0, ThreadFunc, 0, 0, &threadld ); printf("Thread is running\n"); } DWORD WINAPI ThreadFunc(LPVOID p) { printf("In ThreadFunc\n"); return 0; } Output 1 Thread is running In ThreadFunc In ThreadFunc Press any key to continue . . . Output 2 Thread is running In ThreadFunc Press any key to continue . . . Output 3 Thread is running Press any key to continue . . .

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  • Strange thread behavior in Perl

    - by Zaid
    Tom Christiansen's example code (à la perlthrtut) is a recursive, threaded implementation of finding and printing all prime numbers between 3 and 1000. Below is a mildly adapted version of the script #!/usr/bin/perl # adapted from prime-pthread, courtesy of Tom Christiansen use strict; use warnings; use threads; use Thread::Queue; sub check_prime { my ($upstream,$cur_prime) = @_; my $child; my $downstream = Thread::Queue->new; while (my $num = $upstream->dequeue) { next unless ($num % $cur_prime); if ($child) { $downstream->enqueue($num); } else { $child = threads->create(\&check_prime, $downstream, $num); if ($child) { print "This is thread ",$child->tid,". Found prime: $num\n"; } else { warn "Sorry. Ran out of threads.\n"; last; } } } if ($child) { $downstream->enqueue(undef); $child->join; } } my $stream = Thread::Queue->new(3..shift,undef); check_prime($stream,2); When run on my machine (under ActiveState & Win32), the code was capable of spawning only 118 threads (last prime number found: 653) before terminating with a 'Sorry. Ran out of threads' warning. In trying to figure out why I was limited to the number of threads I could create, I replaced the use threads; line with use threads (stack_size => 1);. The resultant code happily dealt with churning out 2000+ threads. Can anyone explain this behavior?

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  • how to slove error when using thread?

    - by ChandreshKanetiya
    I have following error msg in console when using NSThread "Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now..." I have submit my sample code here - (void)viewDidLoad { appDeleg = (NewAshley_MedisonAppDelegate *)[[UIApplication sharedApplication] delegate]; [[self tblView1] setRowHeight:80.0]; [super viewDidLoad]; self.title = @"Under Ground"; [UIApplication sharedApplication].networkActivityIndicatorVisible = YES; [NSThread detachNewThreadSelector:@selector(CallParser) toTarget:self withObject:nil]; } -(void)CallParser { Parsing *parsing = [[Parsing alloc] init]; [parsing DownloadAndParseUnderground]; [parsing release]; [self Update_View]; //[myIndicator stopAnimating]; [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; } here "DownloadAndParseUnderground" is the method of downloding data from the rss feed and -(void) Update_View{ [self.tblView1 reloadData]; } when Update_View method is called the tableView reload Data and in the cellForRowAtIndexPath create error and not display custom cell - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; CustomTableviewCell *cell = (CustomTableviewCell *) [tblView1 dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { [[NSBundle mainBundle] loadNibNamed:@"customCell" owner:self options:nil]; cell = objCustCell; objCustCell = nil; }

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  • Will VS2010 work with Visual Source Safe 2005?

    - by DanH
    Until I can convince others to convert over to Team Foundation Server 2010 (TFS2010), I'm still going to use Visual Source Safe 2005 (VSS2005). I will be upgrade to Visual Studio 2010 (VS2010) soon. What do I need to get VS2010 to work with VSS2005? I understand there is a patch for VSS.

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  • Web Safe Area (optimal resolution) for web app design

    - by M.A.X
    I'm in the process of designing a new web app and I'm wondering for what 'web safe area' should I optimize the app layout and design. I did some investigation and thinking on my own but wanted to share this to see what the general opinion is. Here is what I found: Optimal Display Resolution: w3schools web stats seems to be the most referenced source (however they state that these are results from their site and is biased towards tech savvy users) http://www.w3counter.com/globalstats.php (aggregate data from something like 15,000 different sites that use their tracking services) StatCounter Global Stats Display Resolution (Stats are based on aggregate data collected by StatCounter on a sample exceeding 15 billion pageviews per month collected from across the StatCounter network of more than 3 million websites) NetMarketShare Screen Resolutions (marketshare.hitslink.com) (a web analytics consulting firm, they get data from browsers of site visitors to their on-demand network of live stats customers. The data is compiled from approximately 160 million visitors per month) Display Resolution Summary: There is a bit of variation between the above sources but in general as of Jan 2011 looks like 1024x768 is about 20%, while ~85% have a higher resolution of at least 1280x768 (1280x800 is the most common of these with 15-20% of total web, depending on the source; 1280x1024 and 1366x768 follow behind with 9-14% of the share). My guess would be that the higher resolution values will be even more common if we filter on North America, and even higher if we filter on N.American corporate users (unfortunately I couldn't find any free geographically filtered statistics). Another point to note is that the 1024x768 desktop user population is likely lower than the aforementioned 20%, seeing as the iPad (1024x768 native display) is likely propping up those number. My recommendation would be to optimize around the 1280x768 constraint (*note: 1280x768 is actually a relatively rare resolution, but I think it's a valid constraint range considering that 1366x768 is relatively common and 1280 is the most common horizontal resolution). Browser + OS Constraints: To further add to the constraints we have to subtract the space taken up by the browser (assuming IE, which is the most space consuming) and the OS (assuming WinXP-Win7): Win7 has the biggest taskbar footprint at a height of 40px (XP's and Vista's is 30px) The default IE8 view uses up 25px at the bottom of the screen with the status bar and a further 120px at the top of the screen with the windows title bar and the browser UI (assuming the default 'favorites' toolbar is present, it would instead be 91px without the favorites toolbar). Assuming no scrollbar, we also loose a total of 4px horizontally for the window outline. This means that we are left with 583px of vertical space and 1276px of horizontal. In other words, a Web Safe Area of 1276 x 583 Is this a correct line of thinking? I tried to Google some design best practices but most still talk about designing around 1024x768 which seems to be quickly disappearing. Any help on this would be greatly appreciated! Thanks.

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  • Is django orm & templates thread safe?

    - by Piotr Czapla
    I'm using django orm and templates to create a background service that is ran as management command. Do you know if django is thread safe? I'd like to use threads to speed up processing. The processing is blocked by I/O not CPU so I don't care about performance hit caused by GIL.

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  • is it safe to call "plink.exe" in an application

    - by EBAGHAKI
    i want to use "plink.exe -u username -pw securepassword" on my windows visual c++ program. will username and password remain safe while calling this command? I mean can a hacker steal or sniff the username and password? (consider hacker can't get to the password directly from the exe file)

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  • why is there {Raw,Safe,}Configparser in Python 3

    - by Tshepang
    Am surprised there's 3 different forms: RawConfigParser, SafeConfigParser and ConfigParser. I read the differences but why isn't everyone using SafeConfigParser, since it seems, well, safe? I can understand that in the case for Python 2 that the other two were kept for backward compatibility.

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  • Is this technically thread safe despite being mutable?

    - by Finbarr
    Yes, the private member variable bar should be final right? But actually, in this instance, it is an atomic operation to simply read the value of an int. So is this technically thread safe? class foo { private int bar; public foo(int bar) { this.bar = bar; } public int getBar() { return bar; } } // assume infinite number of threads repeatedly calling getBar on the same instance of foo.

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