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  • If array is thread safe, what the issue with this function?

    - by Ajay Sharma
    I am totally lost with the things that is happening with my code.It make me to think & get clear with Array's thread Safe concept. Is NSMutableArray OR NSMutableDictionary Thread Safe ? While my code is under execution, the values for the MainArray get's changes although, that has been added to Array. Please try to execute this code, onyour system its very much easy.I am not able to get out of this Trap. It is the function where it is returning Array. What I am Looking to do is : -(Array) (Main Array) --(Dictionary) with Key Value (Multiple Dictionary in Main Array) ----- Above dictionary has 9 Arrays in it. This is the structure I am developing for Array.But even before #define TILE_ROWS 3 #define TILE_COLUMNS 3 #define TILE_COUNT (TILE_ROWS * TILE_COLUMNS) -(NSArray *)FillDataInArray:(int)counter { NSMutableArray *temprecord = [[NSMutableArray alloc] init]; for(int i = 0; i <counter;i++) { if([temprecord count]<=TILE_COUNT) { NSMutableDictionary *d1 = [[NSMutableDictionary alloc]init]; [d1 setValue:[NSString stringWithFormat:@"%d/2011",i+1] forKey:@"serial_data"]; [d1 setValue:@"Friday 13 Sep 12:00 AM" forKey:@"date_data"]; [d1 setValue:@"Description Details " forKey:@"details_data"]; [d1 setValue:@"Subject Line" forKey:@"subject_data"]; [temprecord addObject:d1]; d1= nil; [d1 release]; if([temprecord count]==TILE_COUNT) { NSMutableDictionary *holderKey = [[NSMutableDictionary alloc]initWithObjectsAndKeys:temprecord,[NSString stringWithFormat:@"%d",[casesListArray count]+1],nil]; [self.casesListArray addObject:holderKey]; [holderKey release]; holderKey =nil; [temprecord removeAllObjects]; } } else { [temprecord removeAllObjects]; NSMutableDictionary *d1 = [[NSMutableDictionary alloc]init]; [d1 setValue:[NSString stringWithFormat:@"%d/2011",i+1] forKey:@"serial_data"]; [d1 setValue:@"Friday 13 Sep 12:00 AM" forKey:@"date_data"]; [d1 setValue:@"Description Details " forKey:@"details_data"]; [d1 setValue:@"Subject Line" forKey:@"subject_data"]; [temprecord addObject:d1]; d1= nil; [d1 release]; } } return temprecord; [temprecord release]; } What is the problem with this Code ? Every time there are 9 records in Array, it just replaces the whole Array value instead of just for specific key Value.

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  • What image processing Library should I use

    - by Swippen
    I have been reading What is the best image manipulation library? And tried a few libraries and are now looking for inputs on what is the best for our need. I will start by describing our current setting and problems. We have a system that needs to resize and crop a large amount of images from big original images. We handle 50 000+ images every day on 2 powerfull servers. Today we use ImageGlue from WebSupergoo but we don't like it at all, it is slow and hangs the service now and then (Its in another unanswered stack overflow question). We have a threaded windows service that uses Microsoft ThreadPool to resize as much as possible on the 8 core machines. I have tried AForge and it went very well it was loads faster and never crashed or anything. But I had problems with quality on a few images. This due to what algorithms I used ofc so can be tweaked. But want to widen our eyes to see if thats the right way to go. so: It needs to be c# .net and run in a windows service. (Since we wont change the rest of the service only image handling) It needs to handle threaded environment well. We have a great need of it being fast since today its too slow. But we also want good quality and small filesize since the images are later displayed on webpage with loads of visitors and needs good quality. So we have a lot of demands on ability to get god quality at a fast pace, and also secondary keep filesizes lowered even if that can be adjusted with compression a bit. Any comments or suggestions on what library to use?

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  • Are indivisible operations still indivisible on multiprocessor and multicore systems?

    - by Steve314
    As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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  • VB.NET 2.0 - StackOverflowException when using Thread Safe calls to Windows Forms Controls

    - by LamdaComplex
    I have a Windows Forms app that, unfortunately, must make calls to controls from a second thread. I've been using the thread-safe pattern described on the http://msdn.microsoft.com/en-us/library/ms171728.aspx. Which has worked great in the past. The specific problem I am having now: I have a WebBrowser control and I'm attempting to invoke the WebBrowser.Navigate() method using this Thread-Safe pattern and as a result I am getting StackOverflow exceptions. Here is the Thread-Safe Navigate method I've written. Private Delegate Sub NavigateControlCallback(ByRef wb As WebBrowser, ByVal url As String) Private Sub AsyncNavigate(ByRef wb As WebBrowser, ByVal URL As String) Try If wb.InvokeRequired Then Dim callback As New NavigateControlCallback(AddressOf AsyncNavigate) callback(wb, url) Else wb.Navigate(url) End If Catch ex As Exception End Try End Sub Is there a Thread-Safe way to interact with WinForms components without the side effect of these StackOverflowExceptions?

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  • How do I refactor this IEnumerable<T> to be thread-safe?

    - by DayOne
    I am looking at Skeet's AtomicEnumerable but I'm not sure how to integrate it into my current IEnumerable exmaple below (http://msmvps.com/blogs/jon_skeet/archive/2009/10/23/iterating-atomically.aspx) Basically I want to foreach my blahs type in a thread-safe way. thanks public sealed class Blahs : IEnumerable<string> { private readonly IList<string> _data = new List<string>() { "blah1", "blah2", "blah3" }; public IEnumerator<string> GetEnumerator() { return _data.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } }

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  • Safest LAMP encrypt method

    - by Adam Kiss
    Hello, what is PHP's safest encrypt/decrypt method, in use with MySQL - to store let's say passwords? Of course, not for portal purposes. I want to do little password (domain/mysql/ftp...) storage for whole team online, but I don't want really to endanger our clients' bussinesses. Hash can't be used for obvious reasons (Doesn't really make sense to run rainbow tables every time :D). Any idea?

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  • Is it okay to pass injected EntityManagers to EJB bean's helper classes and use it?

    - by Zwei steinen
    We have some JavaEE5 stateless EJB bean that passes the injected EntityManager to its helpers. Is this safe? It has worked well until now, but I found out some Oracle document that states its implementation of EntityManager is thread-safe. Now I wonder whether the reason we did not have issues until now, was only because the implementation we were using happened to be thread-safe (we use Oracle). @Stateless class SomeBean { @PersistenceContext private EntityManager em; private SomeHelper helper; @PostConstruct public void init(){ helper = new SomeHelper(em); } @Override public void business(){ helper.doSomethingWithEm(); } } Actually it makes sense.. If EntityManager is thread-unsafe, a container would have to do inercept business() this.em = newEntityManager(); business(); which will not propagate to its helper classes. If so, what is the best practice in this kind of a situation? Passing EntityManagerFactory instead of EntityManager?

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  • Efficient implementation of threads in the given scenario

    - by shadeMe
    I've got a winforms application that is set up in the following manner: 2 buttons, a textbox, a collection K, function X and another function, Y. Function X parses a large database and enumerates some of its data in the global collection. Button 1 calls function X. Function Y walks through the above collection and prints out the data in the textbox. Button 2 calls function Y. I'd like to call function X through a worker thread in such a way that: The form remains responsive to user input. This comes intrinsically from the use of a separate thread. There is never more than a single instance of function X running at any point in time. K can be accessed by both functions at all times. What would be the most efficient implementation of the above environment ?

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  • C# struct with object as data member

    - by source-energy
    As we know, in C# structs are passed by value, not by reference. So if I have a struct with the following data members: private struct MessageBox { // data members private DateTime dm_DateTimeStamp; // a struct type private TimeSpan dm_TimeSpanInterval; // also a struct private ulong dm_MessageID; // System.Int64 type, struct private String dm_strMessage; // an object (hence a reference is stored here) // more methods, properties, etc ... } So when a MessageBox is passed as a parameter, a COPY is made on the stack, right? What does that mean in terms of how the data members are copied? The first two are struct types, so copies should be made of DateTime and TimeSpan. The third type is a primitive, so it's also copied. But what about the dm_strMessage, which is a reference to an object? When it's copied, another reference to the same String is created, right? The object itself resides in the heap, and is NOT copied (there is only one instance of it on the heap.) So now we have to references to the same object of type String. If the two references are accessed from different threads, it's conceivable that the String object could be corrupted by being modified from two different directions simultaneously. The MSDN documentation says that System.String is thread safe. Does that mean that the String class has a built-in mechanism to prevent an object being corrupted in exactly the type of situation described here? I'm trying to figure out if my MessageBox struct has any potential flaws / pitfalls being a structure vs. a class. Thanks for any input. Source.Energy.

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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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  • How to find out where a thread lock happend?

    - by SchlaWiener
    One of our company's Windows Forms application had a strange problem for several month. The app worked very reliable for most of our customers but on some PC's (mostly with a wireless lan connection) the app sometimes just didn't respond anymore. (You click on the UI and windows ask you to wait or kill the app). I wasn't able to track down the problem for a long time but now I figured out what happend. The app had this line of code // don't blame me for this. Wasn't my code :D Control.CheckForIllegalCrossThreadCalls = false and used some background threads to modify the controls. No I found a way to reproduce the application stopping responding bug on my dev machine and tracked it down to a line where I actually used Invoke() to run a task in the main thread. Me.Invoke(MyDelegate, arg1, arg2) Obviously there was a thread lock somewhere. After removing the Control.CheckForIllegalCrossThreadCalls = false statement and refactoring the whole programm to use Invoke() if modifying a control from a background thread, the problem is (hopefully) gone. However, I am wondering if there is a way to find such bugs without debugging every line of code (Even if I break into debugger after the app stops responding I can't tell what happend last, because the IDE didn't jump to the Invoke() statement) In other words: If my apps hangs how can I figure out which line of code has been executed last? Maybe even on the customers PC. I know VS2010 offers some backwards debugging feature, maybe that would be a solution, but currently I am using VS2008.

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  • ReaderWriterLockSlim question.

    - by Kamarey
    There are lots written about the ReaderWriterLockSlim class which allows multiple read and a single write. All of these (at least that I had found) tell how to use it without much explanation why and how it works. The standard code sample is: lock.EnterUpgradeableReadLock(); try { if (test if write is required) { lock.EnterWriteLock(); try { change the resourse here. } finally { lock.ExitWriteLock(); } } } finally { lock.ExitUpgradeableReadLock(); } The question is: if upgradeable lock permits only a single thread to enter its section, why I should call EnterWriteLock method within? What will happen if I don't? Or what will happen if instead of EnterUpgradeableReadLock I will call EnterWriteLock and will write to a resource without using upgradeable lock at all?

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  • What is wrong with locking non-static fields? What is the correct way to lock a particular instance?

    - by smartcaveman
    Why is it considered bad practice to lock non-static fields? And, if I am not locking non-static fields, then how do I lock an instance method without locking the method on all other instances of the same or derived class? I wrote an example to make my question more clear. public abstract class BaseClass { private readonly object NonStaticLockObject = new object(); private static readonly object StaticLockObject = new object(); protected void DoThreadSafeAction<T>(Action<T> action) where T: BaseClass { var derived = this as T; if(derived == null) { throw new Exception(); } lock(NonStaticLockObject) { action(derived); } } } public class DerivedClass :BaseClass { private readonly Queue<object> _queue; public void Enqueue(object obj) { DoThreadSafeAction<DerivedClass>(x=>x._queue.Enqueue(obj)); } } If I make the lock on the StaticLockObject, then the DoThreadSafeAction method will be locked for all instances of all classes that derive from BaseClass and that is not what I want. I want to make sure that no other threads can call a method on a particular instance of an object while it is locked.

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  • Is boost shared_ptr <XXX> thread safe?

    - by sxingfeng
    I have a question about boost :: shared_ptr. There are lots of thread. class CResource { xxxxxx } class CResourceBase { public: void SetResource(shared_ptr<CResource> res) { m_Res = res; } shared_ptr<CResource> GetResource() { return m_Res; } private: shared_ptr<CResource> m_Res; } CResourceBase base; //---------------------------------------------- Thread A: while (true) { ...... shared_ptr<CResource> nowResource = base.GetResource(); nowResource.doSomeThing(); ... } Thread B: shared_ptr<CResource> nowResource; base.SetResource(nowResource); ... //----------------------------------------------------------- If thread A do not care the nowResource is the newest . Will this part of code have problem? I mean when ThreadB do not SetResource completely, Thread A get a wrong smart point by GetResource? Another question : what does thread-safe mean? If I do not care about whether the resource is newest, will the shared_ptr nowResource crash the program when the nowResource is released or will the problem destroy the shared_point?

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  • Read -> change -> save. Thread safe.

    - by Pavel Alexeev
    This code should automatically connect players when they enter a game. But the problem is when two users try to connect at the same time - in this case 2nd user can easily overwrite changes made by 1st user ('room_1' variable). How could I make it thread safe? def join(userId): users = memcache.get('room_1') users.append(userId) memcache.set('room_1', users) return users I'm using Google App Engine (python) and going to implement simple game-server for exchanging peers given by Adobe Stratus.

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  • DOM Storage and locks

    - by user535759
    Since DOM storage and its equivalencies persist in between tabs and windows, I've thought about using it for message passing. The problem is that fetch and store are different operations, and therefore not atomic. I have models that rely on UUID generation, conflict resolutions, and beaconing to do the small subset of what I need to do, but my real question is this: Since the local storage is a shared memory resource, what are the locking mechanisms available for mutual access?

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  • Best practices about creating a generic object dictionary in C#? Is this bad?

    - by JimDaniel
    For clarity I am using C# 3.5/Asp.Net MVC 2 Here is what I have done: I wanted the ability to add/remove functionality to an object at run-time. So I simply added a generic object dictionary to my class like this: public Dictionary<int, object> Components { get; set; } Then I can add/remove any kind of .Net object into this dictionary at run-time. To insert an object I do something like this: var tag = new Tag(); myObject.Components.Add((int)Types.Components.Tag, tag); Then to retrieve I just do this: if(myObject.Components.ContainsKey((int)Types.Components.Tag)) { var tag = myObject.Components[(int)Types.Components.Tag] as Tag; if(tag != null) { //do stuff } } Somehow I feel sneaky doing this. It works okay, but I am wondering what you guys think about it as a best practice. Thanks for your input, Daniel

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  • MMGR Questions, code use and thread-saftey

    - by chadb
    1) Is MMGR thread safe? 2) I was hoping someone could help me understand some code. I am looking at something where a macro is used, but I don't understand the macro. I know it contains a function call and an if check, however, the function is a void function. How does wrapping "(m_setOwner (FILE,_LINE_,FUNCTION),false)" ever change return types? #define someMacro (m_setOwner(__FILE__,__LINE__,__FUNCTION__),false) ? NULL : new ... void m_setOwner(const char *file, const unsigned int line, const char *func); 3) What is the point of the reservoir? 4) On line 770 ("void *operator new(size_t reportedSize)" there is the line "// ANSI says: allocation requests of 0 bytes will still return a valid value" Who/what is ANSI in this context? Do they mean the standards? 5) This is more of C++ standards, but where does "reportedSize" come from for "void *operator new(size_t reportedSize)"? 6) Is this the code that is actually doing the allocation needed? "au-actualAddress = malloc(au-actualSize);"

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  • Does Interlocked guarantee visibility to other threads in C# or do I still have to use volatile?

    - by Lirik
    I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Interlocked. This is needed in scenarios where other libraries, interfaces or hardware can access your variable and update it anytime, or need the most recent version. Does Interlocked guarantee visibility of the atomic operation to all threads, or do I still have to use the volatile keyword on the value in order to guarantee visibility of the change? Here is my example: public class CountDownLatch { private volatile int m_remain; // <--- do I need the volatile keyword there since I'm using Interlocked? private EventWaitHandle m_event; public CountDownLatch (int count) { Reset(count); } public void Reset(int count) { if (count < 0) throw new ArgumentOutOfRangeException(); m_remain = count; m_event = new ManualResetEvent(false); if (m_remain == 0) { m_event.Set(); } } public void Signal() { // The last thread to signal also sets the event. if (Interlocked.Decrement(ref m_remain) == 0) m_event.Set(); } public void Wait() { m_event.WaitOne(); } }

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  • How to write a "thread safe" function in C ?

    - by Andrei Ciobanu
    Hello I am writing some data structures in C, and I've realized that their associated functions aren't thread safe. The i am writing code uses only standard C, and I want to achieve some sort of 'synchronization'. I was thinking to do something like this: enum sync_e { TRUE, FALSE }; typedef enum sync_e sync; struct list_s { //Other stuff struct list_node_s *head; struct list_node_s *tail; enum sync_e locked; }; typedef struct list_s list; , to include a "boolean" field in the list structure that indicates the structures state: locked, unlocked. For example an insertion function will be rewritten this way: int list_insert_next(list* l, list_node *e, int x){ while(l->locked == TRUE){ /* Wait */ } l->locked = TRUE; /* Insert element */ /* -------------- */ l->locked = FALSE; return (0); } While operating on the list the 'locked' field will be set to TRUE, not allowing any other alterations. After operation completes the 'locked' field will be again set to 'TRUE'. Is this approach good ? Do you know other approaches (using only standard C).

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  • Can the lock function be used to implement thread-safe enumeration?

    - by Daniel
    I'm working on a thread-safe collection that uses Dictionary as a backing store. In C# you can do the following: private IEnumerable<KeyValuePair<K, V>> Enumerate() { if (_synchronize) { lock (_locker) { foreach (var entry in _dict) yield return entry; } } else { foreach (var entry in _dict) yield return entry; } } The only way I've found to do this in F# is using Monitor, e.g.: let enumerate() = if synchronize then seq { System.Threading.Monitor.Enter(locker) try for entry in dict -> entry finally System.Threading.Monitor.Exit(locker) } else seq { for entry in dict -> entry } Can this be done using the lock function? Or, is there a better way to do this in general? I don't think returning a copy of the collection for iteration will work because I need absolute synchronization.

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  • Execute a block of database querys

    - by Nightmare
    I have the following task to complete: In my program a have a block of database querys or questions. I want to execute these questions and wait for the result of all questions or catch an error if one question fails! My Question object looks like this (simplified): public class DbQuestion(String sql) { [...] } [...] //The answer is just a holder for custom data... public void SetAnswer(DbAnswer answer) { //Store the answer in the question and fire a event to the listeners this.OnAnswered(EventArgs.Empty); } [...] public void SetError() { //Signal an Error in this query! this.OnError(EventArgs.Empty); } So every question fired to the database has a listener that waits for the parsed result. Now I want to fire some questions asynchronous to the database (max. 5 or so) and fire an event with the data from all questions or an error if only one question throws one! Which is the best or a good way to accomplish this task? Can I really execute more then one question parallel and stop all my work when one question throws an error? I think I need some inspiration on this... Just a note: I´m working with .NET framework 2.0

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  • efficient thread-safe singleton in C++

    - by user168715
    The usual pattern for a singleton class is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) inst = new Foo(...); return *inst; } However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread. One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) { pthread_mutex_lock(&mutex); if(inst == NULL) inst = new Foo(...); pthread_mutex_unlock(&mutex); } return *inst; } Is this the right way to do it, or are there any pitfalls I should be aware of? For instance, are there any static initialization order problems that might occur, i.e. is inst always guaranteed to be NULL the first time getInst is called?

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