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  • how can I save/keep-in-sync an in-memory graph of objects with the database?

    - by Greg
    Question - What is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Background: That is say I have the classes Node and Relationship, and the application is building up a graph of related objects using these classes. There might be 1000 nodes with various relationships between them. The application needs to query the structure hence an in-memory approach is good for performance no doubt (e.g. traverse the graph from Node X to find the root parents) The graph does need to be persisted however into a database with tables NODES and RELATIONSHIPS. Therefore what is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Ideal requirements would include: build up changes in-memory and then 'save' afterwards (mandatory) when saving, apply updates to database in correct order to avoid hitting any database constraints (mandatory) keep persistence mechanism separate from model, for ease in changing persistence layer if needed, e.g. don't just wrap an ADO.net DataRow in the Node and Relationship classes (desirable) mechanism for doing optimistic locking (desirable) Or is the overhead of all this for a smallish application just not worth it and I should just hit the database each time for everything? (assuming the response times were acceptable) [would still like to avoid if not too much extra overhead to remain somewhat scalable re performance]

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  • CCAnimate/CCAnimation cause inconsistent setTexture behavior in cocos2d on iPhone

    - by chillid
    Hi, I have a character that goes through multiple states. The state changes are reflected by means of a sprite image (texture) change. The state change is triggered by a user tapping on the sprite. This works consistently and quite well. I then added an animation during State0. Now, when the user taps - setTexture gets executed to change the texture to reflect State1, however some of the times (unpredictable) it does not change the texture. The code flows as below: // 1. // Create the animation sequence CGRect frame1Rect = CGRectMake(0,32,32,32); CGRect frame2Rect = CGRectMake(32,32,32,32); CCTexture2D* texWithAnimation = [[CCTextureCache sharedTextureCache] addImage:@"Frames0_1_thinkNthickoutline32x32.png"]; id anim = [[[CCAnimation alloc] initWithName:@"Sports" delay:1/25.0] autorelease]; [anim addFrame:[CCSpriteFrame frameWithTexture:texWithAnimation rect:frame1Rect offset:ccp(0,0)]]; [anim addFrame:[CCSpriteFrame frameWithTexture:texWithAnimation rect:frame2Rect offset:ccp(0,0)]]; // Make the animation sequence repeat forever id myAction = [CCAnimate actionWithAnimation: anim restoreOriginalFrame:NO]; // 2. // Run the animation: sports = [[CCRepeatForever alloc] init]; [sports initWithAction:myAction]; [self.sprite runAction:sports]; // 3. stop action on state change and change texture: NSLog(@"Stopping action"); [sprite stopAction:sports]; NSLog(@"Changing texture for kCJSports"); [self setTexture: [[CCTextureCache sharedTextureCache] addImage:@"SportsOpen.png"]]; [self setTextureRect:CGRectMake(0,0,32,64)]; NSLog(@"Changed texture for kCJSports"); Note that all the NSLog lines get logged - and the texture RECT changes - but the image/texture changes only some of the times - fails for around 10-30% of times. Locking/threading/timing issue somewhere? My app (game) is single threaded and I only use the addImage and not the Async version. Any help much appreciated.

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  • How can I get the main thread to sleep while waiting for a delgate to be called?

    - by Erik B
    Consider a class with these methods: - (id) initWithFrame: (CGRect) frame { if (!(self = [super init])) return nil; webView = [[UIWebView alloc] initWithFrame:frame]; [webView setDelegate:self]; lock = [[NSConditionLock alloc] initWithCondition:LOCK_WAIT]; return self; } - (void) setHTML: (NSString *) html { [lock lockWhenCondition:LOCK_WAIT]; [webView loadHTMLString:html baseURL:nil]; [lock unlock]; } - (void)webViewDidFinishLoad:(UIWebView *)aWebView { [lock lockWhenCondition:LOCK_WAIT]; // Locking to be able to unlock and change the condition. [lock unlockWithCondition:LOCK_GO]; } - (NSString *) stringByEvaluatingJavaScriptFromString: (NSString *) jsCommand { [lock lockWhenCondition:LOCK_GO]; return [webView stringByEvaluatingJavaScriptFromString:jsCommand]; [lock unlock]; } Let's call this class SynchronousUIWebView. From the main thread I execute: webView = [[SynchronousUIWebView alloc] initWithFrame:frame]; [webView setHTML:html]; [webView stringByEvaluatingJavaScriptFromString:jsCommand]; The problem seems to be that the delegate is not called until I leave the current call stack, which I don't since I'm waiting for the delegate call to happen, aka deadlock. To me it seems like the delegate call is pushed to a queue that is called when the current call is done. So the question is can I modify this behavior? Note: The reason this is needed is that I can't execute the JavaScript until the HTML has loaded.

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  • SQL Server: preventing dirty reads in a stored procedure

    - by pcampbell
    Consider a SQL Server database and its two stored procs: *1. A proc that performs 3 important things in a transaction: Create a customer, call a sproc to perform another insert, and conditionally insert a third record with the new identity. BEGIN TRAN INSERT INTO Customer(CustName) (@CustomerName) SELECT @NewID = SCOPE_IDENTITY() EXEC CreateNewCustomerAccount @NewID, @CustomerPhoneNumber IF @InvoiceTotal > 100000 INSERT INTO PreferredCust(InvoiceTotal, CustID) VALUES (@InvoiceTotal, @NewID) COMMIT TRAN *2. A stored proc which polls the Customer table for new entries that don't have a related PreferredCust entry. The client app performs the polling by calling this stored proc every 500ms. A problem has arisen where the polling stored procedure has found an entry in the Customer table, and returned it as part of its results. The problem was that it has picked up that record, I am assuming, as part of a dirty read. The record ended up having an entry in PreferredCust later, and ended up creating a problem downstream. Question How can you explicitly prevent dirty reads by that second stored proc? The environment is SQL Server 2005 with the default configuration out of the box. No other locking hits are given in either of these stored procedures.

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  • Thread Safety of C# List<T> for readers

    - by ILIA BROUDNO
    I am planning to create the list once in a static constructor and then have multiple instances of that class read it (and enumerate through it) concurrently without doing any locking. In this article http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx MS describes the issue of thread safety as follows: Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe. A List can support multiple readers concurrently, as long as the collection is not modified. Enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with one or more write accesses, the only way to ensure thread safety is to lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization. The "Enumerating through a collection is intrinsically not a thread-safe procedure." Statement is what worries me. Does this mean that it is thread safe for readers only scenario, but as long as you do not use enumeration? Or is it safe for my scenario?

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  • How can I share an entity framework model across website users

    - by richardmoss
    Hello, Currently my website is based around MVC and the Entity Framework running against a SQL Server 2005 database. So far, it has all been running very smoothly, and I really enjoy MVC and its slimmer more concise code (and no huge viewstates or soul destroying postbacks ;)) Recently I was working on upgrading the site to use a simple forum system, and this is where I started running into problems. When I was testing the site using two different browsers, if I created or replied to a post in one browser, the other browser couldn't see the post. At the moment, each visitor to the site gets their own copy of the entity model, which I store in their session data. Obviously this is the problem as updates to one model aren't getting carried to the other. As a test, I tried storing a single copy of the model which all visitors would access by assigning the model to a static variable. This worked, and both browsers could see each others modifications. However, it had its side effects. For example, if I fired up both browsers at the same time and the model was initialized, one browser would crash, and the other would work fine, despite me using a locking object so in theory one of them should have been delayed until the model was ready (of course I could have implemented this wrong ;)). Also, originally this site did use one model for all visitors and when it was live, it frequently shut down - killing the IIS application pool while it did. Now I'm not sure if this was related, but I don't really want to reintroduce whatever bug I had that caused this shut down. So, my question is a simple one really - what is the best way of either using the same model for all website users so they all see updates, or if they do have separate copies (which I imagine will have a performance impact in time) how can the models detect changes in the database and update themselves according. Thanks in advance for any advice! Regards; Richard Moss

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  • Synchronizing in SQL Replication works when manually syncing, but not automatically

    - by Dominic Zukiewicz
    I'm using SQL Server 2005 to create a replication copy of the main databases, so that the reports can point to the replication copy instead of locking out our main databases. I have set up the 3 databases as publications and then 3 subscribers moving the transactions over to the subscribers, instantaneously I hope! What seems to be happening is that when using the "Insert Tracer" function, replication take publisher to distributor < 2 seconds, but to replicate to the subscribers can take over 7 minutes (and these are local databases on a SAN). This could be for 2 reasons: The SQL statements used to query the database are obtaining locks which are stopping the transactions updating the subscribers. The subscribers are just too busy for the replication to apply the changes. What seems to trouble me more, is that although the Replication Monitor / Insert Tracer are showing these statistics, if you use the "View Subscription Details" and then click Start, it will sync within seconds. My goal would be to have the data syncing (ideally) continuously, or every minute, perhaps I should reduce the batch size of the transactions? What am I doing wrong? [Note that the -Continuous flag is set!]

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  • What's the next steps for moving from appengine to full django?

    - by tomcritchlow
    Hey guys, I'm super new to programming and I've been using appengine to help me learn python and general coding. I'm getting better quickly and I'm loving it all the way :) Appengine was awesome for allowing me to just dive into writing my app and getting something live that works (see http://www.7bks.com/). But I'm realising that the longer I continue to learn on appengine the more I'm constraining myself and locking myself into a single system. I'd like to move to developing on full django (since django looks super cool!). What are my next steps? To give you a feel for my level of knowledge: I'm not a unix user I'm not familiar with command line controls (I still use appengine/python completely via the appengine SDK) I've never programmed in anything other than python, anywhere other than appengine I know the word SQL, but don't know what MySQL is really or how to use it. So, specifically: What are the skills I need to learn to get up and running with full django/python? If I'm going to host somewhere else I suppose I'll need to learn some sysadmin type skills (maybe even unix?). Is there anywhere that offers easy hosting (like appengine) but that supports django? I hear such great things about heroku I'm considering switching to RoR and going there I appreciate that I'm likely not quite ready to move away from appengine just yet but I'm a fiercely passionate learner (http://www.7bks.com/blog/179001) and would love it if I knew all the steps I needed to learn so I could set about learning them. At the moment, I don't even know what the steps are I need to learn! Thank you very much. Sorry this isn't a specific programming question but I've looked around and haven't found a good how-to for someone of my level of experience and I think others would appreciate a good roadmap for the things we need to learn to get up and running. Thanks, Tom PS - if anyone is in London and fancies showing me the ropes in person that would be super awesome :)

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  • Low-level Keyboard Hooks/SendInput with Winkey+L possible? (workstation lockout is intercepted in Vi

    - by Brian Jorgensen
    I work on a project called UAWKS (Unofficial Apple Wireless Keyboard Support) that helps Windows users use Apple's bluetooth keyboard. One of the main goals of UAWKS is to swap the Cmd key (which behaves as Winkey in Windows) with Ctrl, allowing users to do Cmd+C for copy, Cmd+T for new tab, etc. It is currently developed using AutoHotkey, which worked pretty well under Windows XP. However, on Vista and Windows 7, Cmd+L causes problems: Regardless of low-level keyboard hooks, Winkey+L is always intercepted by Windows and normally locks the workstation... You can disable workstation locking with this registry hack, but pressing Winkey+L still can't be rebound in AHK Pressing Winkey+L leaves Winkey in the Keydown state until the next (additional) Winkey Up. Simulating a Keyup event doesn't seem to work either! It seems that Winkey+L is a special chord that messes everything else up. I've looked through the AHK source code, and they try to address this problem in SendKey() in keyboard_mouse.cpp (near line 883 in v1.0.48.05), but it doesn't work. I wrote up my own low-level keyboard hook application in C#, and I see the same problem. Has anyone else run into this? Is there a workaround?

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  • What can a company possibly gain by making Android phones hard to root?

    - by Chinmay Kanchi
    As someone who recently got a HTC Hero, I had to jump through several hoops to get root access on the phone to install custom firmware. Now, Android is open-source and fairly easy to build and hack on an emulator. It seems to be against the spirit of open-source to lock down a phone so you can't hack the phone itself. Now, often, there are understandable (though not always justifiable) reasons for locking a device down. For example, it might have proprietary software on it or you might want to retain control of the platform. However, Android by its open-source nature makes such concerns moot. Everyone and their dog has access to the userland code, and HTC is forced by the GPL to release kernel sources for each of their devices. So, I fail to see any motivation for alienating the hackers, when there is no possible benefit (in my mind) to be had from doing this. Any idea why a company would want to do this? Is it just short-sightedness or am I missing possible commercial implications of this?

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  • Is something along the lines of nested memoization needed here?

    - by Daniel
    System.Transactions notoriously escalates transactions involving multiple connections to the same database to the DTC. The module and helper class, ConnectionContext, below are meant to prevent this by ensuring multiple connection requests for the same database return the same connection object. This is, in some sense, memoization, although there are multiple things being memoized and the second is dependent on the first. Is there some way to hide the synchronization and/or mutable state (perhaps using memoization) in this module, or perhaps rewrite it in a more functional style? (It may be worth nothing that there's no locking when getting the connection by connection string because Transaction.Current is ThreadStatic.) type ConnectionContext(connection:IDbConnection, ownsConnection) = member x.Connection = connection member x.OwnsConnection = ownsConnection interface IDisposable with member x.Dispose() = if ownsConnection then connection.Dispose() module ConnectionManager = let private _connections = new Dictionary<string, Dictionary<string, IDbConnection>>() let private getTid (t:Transaction) = t.TransactionInformation.LocalIdentifier let private removeConnection tid = let cl = _connections.[tid] for (KeyValue(_, con)) in cl do con.Close() lock _connections (fun () -> _connections.Remove(tid) |> ignore) let getConnection connectionString (openConnection:(unit -> IDbConnection)) = match Transaction.Current with | null -> new ConnectionContext(openConnection(), true) | current -> let tid = getTid current // get connections for the current transaction let connections = match _connections.TryGetValue(tid) with | true, cl -> cl | false, _ -> let cl = Dictionary<_,_>() lock _connections (fun () -> _connections.Add(tid, cl)) cl // find connection for this connection string let connection = match connections.TryGetValue(connectionString) with | true, con -> con | false, _ -> let initial = (connections.Count = 0) let con = openConnection() connections.Add(connectionString, con) // if this is the first connection for this transaction, register connections for cleanup if initial then current.TransactionCompleted.Add (fun args -> let id = getTid args.Transaction removeConnection id) con new ConnectionContext(connection, false)

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  • Entity Framework autoincrement key

    - by Tommy Ong
    I'm facing an issue of duplicated incremental field on a concurrency scenario. I'm using EF as the ORM tool, attempting to insert an entity with a field that acts as a incremental INT field. Basically this field is called "SequenceNumber", where each new record before insert, will read the database using MAX to get the last SequenceNumber, append +1 to it, and saves the changes. Between the getting of last SequenceNumber and Saving, that's where the concurrency is happening. I'm not using ID for SequenceNumber as it is not a unique constraint, and may reset on certain conditions such as monthly, yearly, etc. InvoiceNumber | SequenceNumber | DateCreated INV00001_08_14 | 1 | 25/08/2014 INV00001_08_14 | 1 | 25/08/2014 <= (concurrency is creating two SeqNo 1) INV00002_08_14 | 2 | 25/08/2014 INV00003_08_14 | 3 | 26/08/2014 INV00004_08_14 | 4 | 27/08/2014 INV00005_08_14 | 5 | 29/08/2014 INV00001_09_14 | 1 | 01/09/2014 <= (sequence number reset) Invoice number is formatted based on the SequenceNumber. After some research I've ended up with these possible solutions, but wanna know the best practice 1) Optimistic Concurrency, locking the table from any reads until the current transaction is completed (not fancy of this idea as I guess performance will be of a great impact?) 2) Create a Stored Procedure solely for this purpose, does select and insert on a single statement as such concurrency is at minimum (would prefer a EF based approach if possible)

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  • What C++ templates issue is going on with this error?

    - by WilliamKF
    Running gcc v3.4.6 on the Botan v1.8.8 I get the following compile time error building my application after successfully building Botan and running its self test: ../../src/Botan-1.8.8/build/include/botan/secmem.h: In member function `Botan::MemoryVector<T>& Botan::MemoryVector<T>::operator=(const Botan::MemoryRegion<T>&)': ../../src/Botan-1.8.8/build/include/botan/secmem.h:310: error: missing template arguments before '(' token What is this compiler error telling me? Here is a snippet of secmem.h that includes line 130: [...] /** * This class represents variable length buffers that do not * make use of memory locking. */ template<typename T> class MemoryVector : public MemoryRegion<T> { public: /** * Copy the contents of another buffer into this buffer. * @param in the buffer to copy the contents from * @return a reference to *this */ MemoryVector<T>& operator=(const MemoryRegion<T>& in) { if(this != &in) set(in); return (*this); } // This is line 130! [...]

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  • How many users are sufficient to make a heavy load for web application

    - by galymzhan
    I have a web application, which has been suffering high load recent days. The application runs on single server which has 8-core Intel CPU and 4gb of RAM. Software: Drupal 5 (Apache 2, PHP5, MySQL5) running on Debian. After reaching 500 authenticated and 200 anonymous users (simultaneous), the application drastically decreases its performance up to total failure. The biggest load comes from authenticated users, who perform activities, causing insert/update/deletes on db. I think mysql is a bottleneck. Is it normal to slow down on such number of users? EDIT: I forgot to mention that I did some kind of profiling. I runned commands top, htop and they showed me that all memory was being used by MySQL! After some time MySQL starts to perform terribly slow, site goes down, and we have to restart/stop apache to reduce load. Administrators said that there was about 200 active mysql connections at that moment. The worst point is that we need to solve this ASAP, I can't do deep profiling analysis/code refactoring, so I'm considering 2 ways: my tables are MyIsam, I heard they use table-level locking which is very slow, is it right? could I change it to Innodb without worry? what if I take MySQL, and move it to dedicated machine with a lot of RAM?

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  • ZeroMQ REQ/REP on ipc:// and concurrency

    - by Metiu
    I implemented a JSON-RPC server using a REQ/REP 0MQ ipc:// socket and I'm experiencing strange behavior which I suspect is due to the fact that the ipc:// underlying unix socket is not a real socket, but rather a single pipe. From the documentation, one has to enforce strict zmq_send()/zmq_recv() alternation, otherwise the out-of-order zmq_send() will return an error. However, I expected the enforcement to be per-client, not per-socket. Of course with a Unix socket there is just one pipeline from multiple clients to the server, so the server won't know who it is talking with. Two clients could zmq_send() simultaneously and the server would see this as an alternation violation. The sequence could be: ClientA: zmq_send() ClientB: zmq_send() : will it block until the other send/receive completes? will it return -1? (I suspect it will with ipc:// due to inherent low-level problems, but with TCP it could distinguish the two clients) ClientA: zmq_recv() ClientB: zmq_recv() so what about tcp:// sockets? Will it work concurrently? Should I use some other locking mechanism to work around this?

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  • Nginx , Apache , Mysql , Memcache with server 4G ram. How optimize to enoigh of memory?

    - by TomSawyer
    i have 1 dedicated server with Nginx proxy for Apache. Memcache, mysql, 4G Ram. These day, my visitor on my site wasn't increased, but my server get overload always in some specified time. (9AM - 15PM) Ram in use is increased second by second to full. that's moment, my server will get overload. i have to kill all apache , mysql service and reboot it to get free memory. and it'll full again. that's the terrible circle. here is my ram in use at the moment 160(nginx) 220(apache) 512(memcache) 924(mysql) here's process number 4(nginx) 14(apache) 5(memcache) 20(mysql) and here's my my.cnf config. someone can help me to optimize it? [mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock user=mysql skip-locking skip-networking skip-name-resolve # enable log-slow-queries log-slow-queries = /var/log/mysql-slow-queries.log long_query_time=3 max_connections=200 wait_timeout=64 connect_timeout = 10 interactive_timeout = 25 thread_stack = 512K max_allowed_packet=16M table_cache=1500 read_buffer_size=4M join_buffer_size=4M sort_buffer_size=4M read_rnd_buffer_size = 4M max_heap_table_size=256M tmp_table_size=256M thread_cache=256 query_cache_type=1 query_cache_limit=4M query_cache_size=16M thread_concurrency=8 myisam_sort_buffer_size=128M # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 [mysqldump] quick max_allowed_packet=16M [mysql] no-auto-rehash [isamchk] key_buffer=256M sort_buffer=256M read_buffer=64M write_buffer=64M [myisamchk] key_buffer=256M sort_buffer=256M read_buffer=64M write_buffer=64M [mysqlhotcopy] interactive-timeout [mysql.server] user=mysql basedir=/var/lib [mysqld_safe] log-error=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid

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  • Boost threading/mutexs, why does this work?

    - by Flamewires
    Code: #include <iostream> #include "stdafx.h" #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> using namespace std; boost::mutex mut; double results[10]; void doubler(int x) { //boost::mutex::scoped_lock lck(mut); results[x] = x*2; } int _tmain(int argc, _TCHAR* argv[]) { boost::thread_group thds; for (int x = 10; x>0; x--) { boost::thread *Thread = new boost::thread(&doubler, x); thds.add_thread(Thread); } thds.join_all(); for (int x = 0; x<10; x++) { cout << results[x] << endl; } return 0; } Output: 0 2 4 6 8 10 12 14 16 18 Press any key to continue . . . So...my question is why does this work(as far as i can tell, i ran it about 20 times), producing the above output, even with the locking commented out? I thought the general idea was: in each thread: calculate 2*x copy results to CPU register(s) store calculation in correct part of array copy results back to main(shared) memory I would think that under all but perfect conditions this would result in some part of the results array having 0 values. Is it only copying the required double of the array to a cpu register? Or is it just too short of a calculation to get preempted before it writes the result back to ram? Thanks.

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  • Hibernate Exception Fixed By Alt+Tab

    - by Lee Theobald
    Hi all, I've got a very curious problem in Hibernate that I would like some opinions on. In my code if I do the following: Go to page A Click a link on page A to be taken to page B Click on data item on page B Exception thrown I get an error telling me: failed to lazily initialize a collection of role: XYZ, no session or session was closed Fair enough. But when I do the same thing but add an alt+tab in the middle, everything is fine. E.g. Go to page A Click a link on page A to be taken to page B Hit ALt+Tab to switch to another application Hit ALt+Tab to switch back to the web browser Click on data item on page B Everything is fine. I'm a little confused as to how switching focus from my application makes it act as I want it to. Does anyone have any light to shine on the subject? I don't think it's a locking issue as even if I do the second set of steps quicker than the first, still no error. It's a Seam application using Hibernate 3.3.2.GA & 3.4.0.GA.

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  • How can I make hundreds of simultaneously running processes communicate with a database through one

    - by Olfan
    Long speech short: How can I make hundreds of simultaneously running processes communicate with a database through one or few permanent sessions? The whole story: I once built a number crunching engine that handles vast amounts of large data files by forking off one child after another giving each a small number of files to work on. File locking, progress monitoring and result propagation happen in an Oracle database which all (sub-)processes access at various times using an application-specific module which encapsulates DBI. This worked well at first, but now with higher volumes of input data, the number of database sessions (one per child, and they can be very short-lived) constantly being opened and closed is becoming an issue. I now want to centralise database access so that there are only one or few fixed database sessions which handle all database access for all the (sub-)processes. The presence of the database abstraction module should make the changes easy because the function calls in the worker instances can stay the same. My problem is that I cannot think of a suitable way to enhance said module in order to establish communication between all the processes and the database connector(s). I thought of message queueing, but couldn't come up with a way of connecting a large herd of requestors with one or few database connectors in a way so that bidirectional communication is possible (for collecting the query result). An asynchronous approach could help here in that all requests are written to the same queue and the database connector servicing the request will "call back" to submit the result. But my mind fails me in generating an image clear enough so that I can paint into code. Threading instead of forking might have given me an easier start, but this would now require massive changes to the code base that I'm not prepared to do to a live system. The more I think of it, the more the base idea looks like a pre-forked web server to me only that it doesn't serve web pages but database queries. Any ideas on what to dig into, and where? Sample (pseudo) code to inspire me, links to possibly related articles, ready solutions on CPAN maybe?

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  • I have a fucntion that create histogram of each Bitmap. How can i create another 3 histograms for R.G.B of each Bitmap?

    - by Daniel Lip
    This is the histogram function im using today and if im not worng it's creating an histogram by Gray color. What i want is another fucntion that will return me 3 histograms of each Bitmap: The first histogram will be of the Red color of the bitmap the second for the Green color and the last one for the Blue color. public static long[] GetHistogram(Bitmap b) { long[] myHistogram = new long[256]; BitmapData bmData = null; try { //Lock it fixed with 32bpp bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb); int scanline = bmData.Stride; System.IntPtr Scan0 = bmData.Scan0; unsafe { byte* p = (byte*)(void*)Scan0; int nWidth = b.Width; int nHeight = b.Height; for (int y = 0; y < nHeight; y++) { for (int x = 0; x < nWidth; x++) { long Temp = 0; Temp += p[0]; // p[0] - blue, p[1] - green , p[2]-red Temp += p[1]; Temp += p[2]; Temp = (int)Temp / 3; myHistogram[Temp]++; //we do not need to use any offset, we always can increment by pixelsize when //locking in 32bppArgb - mode p += 4; } } } b.UnlockBits(bmData); } catch { try { b.UnlockBits(bmData); } catch { } } return myHistogram; } How may i do it ?

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  • inconsistent setTexture behavior in cocos2d on iPhone after using CCAnimate/CCAnimation

    - by chillid
    Hi, I have a character that goes through multiple states. The state changes are reflected by means of a sprite image (texture) change. The state change is triggered by a user tapping on the sprite. This works consistently and quite well. I then added an animation during State0. Now, when the user taps - setTexture gets executed to change the texture to reflect State1, however some of the times (unpredictable) it does not change the texture. The code flows as below: // 1. // Create the animation sequence CGRect frame1Rect = CGRectMake(0,32,32,32); CGRect frame2Rect = CGRectMake(32,32,32,32); CCTexture2D* texWithAnimation = [[CCTextureCache sharedTextureCache] addImage:@"Frames0_1_thinkNthickoutline32x32.png"]; id anim = [[[CCAnimation alloc] initWithName:@"Sports" delay:1/25.0] autorelease]; [anim addFrame:[CCSpriteFrame frameWithTexture:texWithAnimation rect:frame1Rect offset:ccp(0,0)]]; [anim addFrame:[CCSpriteFrame frameWithTexture:texWithAnimation rect:frame2Rect offset:ccp(0,0)]]; // Make the animation sequence repeat forever id myAction = [CCAnimate actionWithAnimation: anim restoreOriginalFrame:NO]; // 2. // Run the animation: sports = [[CCRepeatForever alloc] init]; [sports initWithAction:myAction]; [self.sprite runAction:sports]; // 3. stop action on state change and change texture: NSLog(@"Stopping action"); [sprite stopAction:sports]; NSLog(@"Changing texture for kCJSports"); [self setTexture: [[CCTextureCache sharedTextureCache] addImage:@"SportsOpen.png"]]; [self setTextureRect:CGRectMake(0,0,32,64)]; NSLog(@"Changed texture for kCJSports"); Note that all the NSLog lines get logged - and the texture RECT changes - but the image/texture changes only some of the times - fails for around 10-30% of times. Locking/threading/timing issue somewhere? My app (game) is single threaded and I only use the addImage and not the Async version. Any help much appreciated.

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  • Test the sequentiality of a column with a single SQL query

    - by LauriE
    Hey, I have a table that contains sets of sequential datasets, like that: ID set_ID some_column n 1 'set-1' 'aaaaaaaaaa' 1 2 'set-1' 'bbbbbbbbbb' 2 3 'set-1' 'cccccccccc' 3 4 'set-2' 'dddddddddd' 1 5 'set-2' 'eeeeeeeeee' 2 6 'set-3' 'ffffffffff' 2 7 'set-3' 'gggggggggg' 1 At the end of a transaction that makes several types of modifications to those rows, I would like to ensure that within a single set, all the values of "n" are still sequential (rollback otherwise). They do not need to be in the same order according to the PK, just sequential, like 1-2-3 or 3-1-2, but not like 1-3-4. Due to the fact that there might be thousands of rows within a single set I would prefer to do it in the db to avoid the overhead of fetching the data just for verification after making some small changes. Also there is the issue of concurrency. The way locking in InnoDB (repeatable read) works (as I understand) is that if I have an index on "n" then InnoDB also locks the "gaps" between values. If I combine set_ID and n to a single index, would that eliminate the problem of phantom rows appearing? Looks to me like a common problem. Any brilliant ideas? Thanks! Note: using MySQL + InnoDB

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  • how can i make sure only a single record is inserted when multiple apache threads are trying to acce

    - by Ed Gl
    I have a web service (xmlrpc service to be exact) that handles among other things writing data into the database. Here's the scenario: I often receive requests to either update or insert a record. What I would do is this: If the record already exists, append to the record, If not, create a new record The issue is that there are certain times I would get a 'burst' of requests, which spawns several apache threads to handle the request. These 'bursts' would come within less than milliseconds of each other. I now have several threads performing #1 and #2. Often two threads would would 'pass' number #1 and actually create two duplicate records (except for the primary key). I'd like to use some locking mechanism to prevent other threads from accessing the table while the other thread finishes its work. I'm just afraid of using it because if something happens I don't want to leave the table locked. Is there a solid way of handling this? I'm open to using locks if I can do it properly. Thanks,

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  • .NET Application with SQL Server CE Database

    - by blu
    I just started using SQL Server CE 3.5 in my WinForms Application (C# in VS 2008 SP1). I've noticed a couple of interesting things I'd like some input on: 1. Copying of sdf file to bin My sdf file is located inside of an Infrastructure project that houses my repository implementations. When the application is first debugged the sdf was copied to debug\bin. This is where all future reads/writes operate. At some point when this is deployed the file will go into a data folder using Click Once, but during development where should I be putting this sdf? Is having it in the bin typical, or are there any other recommendations? 2. Updating sdf It appears that writing to the sdf file does not immediately update the database. I am using Linq-to-SQL and am calling SubmitChanges, but on read the values are not returned. However if I close the application and re-open it the added value is there. Is there an additional flush step I need to take? What is causing this, file locking, buffering, something else? Update 3. Unit Tests I have an MS test project, and the sdf file is not being copied to the correct output directory. I have the settings: Build Action: Content Copy to Output Directory: Copy Always The message is: System.Data.SqlServerCe.SqlCeException: The database file cannot be found. Check the path to the database. I appreciate any guidance on these questions, thanks. If there is a tutorial other than what is on MSDN that you know about that would be great too. Working with CE is proving to be a difficult task and I welcome any help I can find.

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  • How should I lock the table in this VB6 / Access application?

    - by Brian Hooper
    I'm working on a VB6 application using an Access database. The application writes messages to a log table from time to time. Several instances of the application may be running simultaneously and to distinguish them they each have their own run number. The run number is deduced from the log table thus... Set record_set = New ADODB.Recordset query_string = "SELECT MAX(RUN_NUMBER) + 1 AS NEW_RUN_NUMBER FROM ERROR_LOG" record_set.CursorLocation = adUseClient record_set.Open query_string, database_connection, adOpenStatic, , adCmdText record_set.MoveLast If IsNull(record_set.Fields("NEW_RUN_NUMBER")) Then run_number = 0 Else run_number = record_set.Fields("NEW_RUN_NUMBER") End If command_string = "INSERT INTO ERROR_LOG (RUN_NUMBER, SEVERITY, MESSAGE) " & _ " VALUES (" & Str$(run_number) & ", " & _ " " & Str$(SEVERITY_INFORMATION) & ", " & _ " 'Run Started'); " database_connection.Execute command_string Obviously there is a small gap between the calculation of the run number and the appearance of the new row in the database, and to prevent another instance getting access between the two operations I'd like to lock the table; something along the lines of SET TRANSACTION READ WRITE RESERVING ERROR_LOG FOR PROTECTED WRITE; How should I go about doing this? Would locking the recordset do any good (the row in the record set doesn't match any particular row in the database)?

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