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  • .NET List Thread-Safe Implementation Suggestion needed

    - by Bamboo
    .Net List class isn't thread safe. I hope to achieve the minimal lock needed and yet still fulfilling the requirement such that as for reading, phantom record is allowed, and for writing, they must be thread-safe so there won't be any lost updates. So I have something like public static List<string> list = new List<string>(); In Methods that have **List.Add**/**List.Remove** , I always lock to assure thread safety lock (lockHelper) { list.Add(obj); or list.Remove(obj); } In Methods that requires **List Reading** I don't care about phantom record so I go ahead to read without any locking. In this case. Return a bool by checking whether a string had been added. if (list.Count() != 0) { return list.Contains("some string") } All I did was locking write accesses, and allow read accesses to go through without any locking. Is my thread safety idea valid? I understand there is List size expansion. Will it be ok? My guess is that when a List is expanding, it may uses a temp. list. This is ok becasue the temp list size will always have a boundary, and .Net class is well implemented, ie. there shouldn't be any indexOutOfBound or circular reference problems when reading was caught in updates.

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  • When creating a library for a simple program, what must I do to protect others from its lack of thread safety?

    - by DeveloperDon
    When creating a library for a simple program, is it more cost effective to make it thread safe or is there a way to detect the program's use in a multithreaded program and ASSERT() or otherwise determine (preferably at compile or link time) that it may create problems. Related help for this question would be automated tool support for finding potential problems with thread safety, programming language features that enforce it,

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  • N processes and M types of processes - enter and exit cs

    - by sarit
    i was asked to write: enter function and exit function for the following case: there are N processes and M types of processes (NM) tere is a critical section in which all processes with the same type can enter. for example: if type A is in cs, type B cannot enter cs. but all processes with type A can enter. i can use only mutex and "type" which is the type of the process. deadlock is not allowed. do you think this is ok? shared: this.type = -1; mutex m, m1=1; enter{ down(m) if (this.type == process.type) up(m1) down(m1) this.type= process.type up(m) } exit { this.type = -1 up(m1) } thanks! (by the way, this is not HW... i have an exam and im solvig tests from previous years)

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  • Is there a straightforward way to have a ThreadStatic instance member?

    - by Dan Tao
    With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there some corresponding attribute that provides the same functionality, but for instance members? In other words, that allows me to have one instance of the object, per thread, per instance of the containing class?

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  • Is there a straightforward way to have a thread-local instance variable?

    - by Dan Tao
    With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there any straightforward way to declare a class member as thread-local, meaning, each class instance gets an object per thread?

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  • How to use CriticalSection - MFC?

    - by mapples
    I' am working on a small example and am a bit of curious using criticalsection in my example. What I'am doing is,I have a CStringArray(which has 10 elements added to it).I want to copy these 10 elements(string) to another CStringArray(am doing this to understand threading and Critical section),I have created 2 threads,Thread1 will copy the first 5 element to another CStringArray and Thread2 will copy the rest.Here two CStringArray are being used,I know only 1 thread can access it at a time.I wanted to know how this can be solved by using criticalsection or any other method. void CThreadingEx4Dlg::OnBnClickedOk() { // TODO: Add your control notification handler code here thread1 = AfxBeginThread((AFX_THREADPROC)MyThreadFunction1,this); thread2 = AfxBeginThread((AFX_THREADPROC)MyThreadFunction2,this); } UINT MyThreadFunction1(LPARAM lparam) { CThreadingEx4Dlg* pthis = (CThreadingEx4Dlg*)lparam; pthis->MyFunction(0,5); return 0; } UINT MyThreadFunction2(LPARAM lparam) { CThreadingEx4Dlg* pthis = (CThreadingEx4Dlg*)lparam; pthis->MyFunction(6,10); return 0; } void CThreadingEx4Dlg::MyFunction(int minCount,int maxCount) { for(int i=minCount;i<=maxCount;i++) { CString temp; temp = myArray.GetAt(i); myShiftArray.Add(temp); } }

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  • Does the Virtual PC XP Mode need safety measures?

    - by Ivo
    Does the Virtual PC XP-Mode (or any other virtualized mode) require safety measures, such as antivirus or a firewall? I'm just wondering if the XP-Mode would be a large security loophole, since it's so much more integrated into Windows 7. Actually I'm wondering the same for Portable Ubuntu, are their any safety measures I should undertake, so that I don't open a backdoor on my computer.

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  • I found two usb sticks on the ground. Now what?

    - by Stefano Borini
    As from subject. I want to see what's inside. I am seriously interested in finding the owner if possible and returning them, but I am worried it could be an attempt at social engineering. I own a macbook intel with OSX 10.6. It is a very important install. What would you do in my situation if you want to see the content without risks ? Any proposal welcome. Edit: I decided not to plug them in, and I brought them to the hotel reception. They will forward it to the police.

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  • OS X Lion: Emptying the trash takes "forever": is using rm -r safe?

    - by EOL
    Emptying my Trash in OS X Lion (non securely) is taking about three hours (about 1.5 million files, from a Time Machine backup). I had to stop the process a few times already, because I could not move my laptop with the external harddrive the files are on. This is also a problem because the Trash emptying is restarted from the very beginning each time I empty the Trash again (i.e., files are not deleted when the Trash emptying is aborted). I read that it is faster to use rm -rf on ~/.Trash, in this case. However, is this safe? (I am afraid that does OS X Lion performs tasks behind the scenes—which would explain its slowness—that rm -r does not, which could lead to problems in the future.)

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  • Tool to assist loading servers into a rack??

    - by MikeJ
    Is there any kind of tool to assist in loading an unloading servers? I realized that I lack both height and upper body strength to remove servers from the upper tiers of a rack? I could not find the name or type of equipment that folks are using to do this kind of work safely?

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  • I found two usb sticks on the ground. Now what ?

    - by Stefano Borini
    As from subject. I want to see what's inside. I am seriously interested in finding the owner if possible and returning them, but I am worried it could be an attempt at social engineering. I own a macbook intel with OSX 10.6. It is a very important install. What would you do in my situation if you want to see the content without risks ? Any proposal welcome. Edit: I decided not to plug them in, and I brought them to the hotel reception. They will forward it to the police.

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  • Moving an external hard drive while running

    - by user1108939
    I mean physically moving the drive around. I've never dealt with external hard drives before. Just plugged this wd mypassport to test the transfer rate. At one point I 'safely ejected' the drive. A minute later I decide to check the underside of the drive, not realizing the disk is still spinning. I lift the drive, rotating my writs about 70 degrees to the left... I hear a sequence of three high pitched sounds. I couldn't determine whether that was an indication beep by an internal security feature or the head scratching the plate (oh god...). Drive stops and usb power is disconnected. I reconnect it - it shows up fine - reads/writes. The drive was not reading/writing when i moved it. Did I damage my drive? Are these things that fragile? I thought them to be at least as durable as a standard 2.5" internal drive. Am I mistaken?

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  • How to get PHP command line to work with PDO?

    - by Sabya
    I want to work with PDO, through PHP command line. It works perfect through the PHP web API, but not through the command line. But when I execute the command: php test.php, it says unknown class PDO. I think it has something to do with the thread-safety difference. Because, when I execute the above command, the following warnings come: - F:\shema\htdocs>php test.php PHP Warning: PHP Startup: soap: Unable to initialize module Module compiled with module API=20060613, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: sockets: Unable to initialize module Module compiled with module API=20060613, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: mysql: Unable to initialize module Module compiled with module API=20060613, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: pdo_mysql: Unable to initialize module Module compiled with module API=20060613, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: pdo_pgsql: Unable to initialize module Module compiled with module API=20060613, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=1 These options need to match in Unknown on line 0 PHP Fatal error: Class 'PDO' not found in F:\shema\htdocs\test.php on line 2 PHP version: 5.2.9-2, downloaded from here. OS: Windows Vista If the problem is with the modules, where do I get the thread safe modules for those modules?

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  • C# thread with multiple parameters

    - by Lucas B
    Does anyone know how to pass multiple parameters into a Thread.Start routine? I thought of extending the class, but the C# Thread class is sealed. Here is what I think the code would look like: ... Thread standardTCPServerThread = new Thread(startSocketServerAsThread); standardServerThread.Start( orchestrator, initializeMemberBalance, arg, 60000); ... } static void startSocketServerAsThread(ServiceOrchestrator orchestrator, List<int> memberBalances, string arg, int port) { startSocketServer(orchestrator, memberBalances, arg, port); } Thank you in advance. BTW, I start a number of threads with different orchestrators, balances and ports. Please consider thread safety also.

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  • WCF methods sharing a dictionary

    - by YeomansLeo
    I'm creating a WCF Service Library and I have a question regarding thread-safety consuming a method inside this library, here is the full implementation that I have until now. namespace WCFConfiguration { [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall, ConcurrencyMode = ConcurrencyMode.Single)] public class ConfigurationService : IConfigurationService { ConcurrentDictionary<Tuple<string,string>, string> configurationDictionary = new ConcurrentDictionary<Tuple<string,string>, string>(); public void Configuration(IEnumerable<Configuration> configurationSet) { Tuple<string, string> lookupStrings; foreach (var config in configurationSet) { lookupStrings = new Tuple<string, string>(config.BoxType, config.Size); configurationDictionary.TryAdd(lookupStrings, config.RowNumber); } } public void ScanReceived(string boxType, string size, string packerId = null) { } } } Imagine that I have a 10 values in my configurationDictionary and many people want to query this dictionary consuming ScanReceived method, are those 10 values be shared for each of the clients that request ScanReceived? Do I need to change my ServiceBehavior? The Configuration method is only consumed by one person by the way.

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  • Why are we as an industry not more technically critical of our peers? [closed]

    - by Jarrod Roberson
    For example: I still see people in 2011 writing blog posts and tutorials that promote setting the Java CLASSPATH at the OS environment level. I see people writing C and C++ tutorials dated 2009 and newer and the first lines of code are void main(). These are examples, I am not looking for specific answers to the above questions, but to why the culture of accepting sub-par knowledge in the industry is so rampant. I see people posting these same type of empirically wrong suggestions as answers on www.stackoverflow.com and they get lots of up votes and practically no down votes! The ones that get lots of down votes are usually from answering a question that wasn't asked because of lack of reading for comprehension skills, and not incorrect answers per se. Is our industry that ignorant as a whole, I can understand the internet in general being lazy, apathetic and un-informed but our industry should be more on top of things like this and way more critical of people that are promoting bad habits and out-dated techniques and information. If we are really an engineering discipline, why aren't people held to a higher standard as they are in other engineering disciplines? I want to know why people accept bad advice, poor practices as the norm and are not more critical of their peers in the software industry.?

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  • Android threading and database locking

    - by Sena Gbeckor-Kove
    Hi, We are using AsyncTasks to access database tables and cursors. Unfortunately we are seeing occasional exceptions regarding the database being locked. E/SQLiteOpenHelper(15963): Couldn't open iviewnews.db for writing (will try read-only): E/SQLiteOpenHelper(15963): android.database.sqlite.SQLiteException: database is locked E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:1637) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1587) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:638) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:659) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:652) E/SQLiteOpenHelper(15963): at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:482) E/SQLiteOpenHelper(15963): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158) E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.initData(IViewNewsTopStoryWidget.java:73) E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.updateNewsWidgets(IViewNewsTopStoryWidget.java:121) E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:338) E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:1) E/SQLiteOpenHelper(15963): at android.os.AsyncTask$2.call(AsyncTask.java:185) E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256) E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask.run(FutureTask.java:122) E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648) E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673) E/SQLiteOpenHelper(15963): at java.lang.Thread.run(Thread.java:1060) Does anybody have a general example for code which writes to a database from a different thread than the one reading and how can we ensure thread safety. One suggestion I've had is to use a ContentProvider, as this would handle the access of the database from multiple threads. I am going to look at this, but is this the recommended method of handling such a problem? It seems rather heavyweight considering we're talking about in front or behind Thanks in advance.

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  • Impossible to be const-correct when combining data and it's lock?

    - by Graeme
    I've been looking at ways to combine a piece of data which will be accessed by multiple threads alongside the lock provisioned for thread-safety. I think I've got to a point where I don't think its possible to do this whilst maintaining const-correctness. Take the following class for example: template <typename TType, typename TMutex> class basic_lockable_type { public: typedef TMutex lock_type; public: template <typename... TArgs> explicit basic_lockable_type(TArgs&&... args) : TType(std::forward<TArgs...>(args)...) {} TType& data() { return data_; } const TType& data() const { return data_; } void lock() { mutex_.lock(); } void unlock() { mutex_.unlock(); } private: TType data_; mutable TMutex mutex_; }; typedef basic_lockable_type<std::vector<int>, std::mutex> vector_with_lock; In this I try to combine the data and lock, marking mutex_ as mutable. Unfortunately this isn't enough as I see it because when used, vector_with_lock would have to be marked as mutable in order for a read operation to be performed from a const function which isn't entirely correct (data_ should be mutable from a const). void print_values() const { std::lock_guard<vector_with_lock>(values_); for(const int val : values_) { std::cout << val << std::endl; } } vector_with_lock values_; Can anyone see anyway around this such that const-correctness is maintained whilst combining data and lock? Also, have I made any incorrect assumptions here?

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  • What exactly is a reentrant function?

    - by eSKay
    Most of the times, the definition of reentrance is quoted from Wikipedia: A computer program or routine is described as reentrant if it can be safely called again before its previous invocation has been completed (i.e it can be safely executed concurrently). To be reentrant, a computer program or routine: Must hold no static (or global) non-constant data. Must not return the address to static (or global) non-constant data. Must work only on the data provided to it by the caller. Must not rely on locks to singleton resources. Must not modify its own code (unless executing in its own unique thread storage) Must not call non-reentrant computer programs or routines. How is safely defined? If a program can be safely executed concurrently, does it always mean that it is reentrant? What exactly is the common thread between the six points mentioned that I should keep in mind while checking my code for reentrant capabilities? Also, Are all recursive functions reentrant? Are all thread-safe functions reentrant? Are all recursive and thread-safe functions reentrant? While writing this question, one thing comes to mind: Are the terms like reentrance and thread safety absolute at all i.e. do they have fixed concrete definations? For, if they are not, this question is not very meaningful. Thanks!

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  • Is locking on the requested object a bad idea?

    - by Quick Joe Smith
    Most advice on thread safety involves some variation of the following pattern: public class Thing { private static readonly object padlock = new object(); private string stuff, andNonsense; public string Stuff { get { lock (Thing.padlock) { if (this.stuff == null) this.stuff = "Threadsafe!"; } return this.stuff; } } public string AndNonsense { get { lock (Thing.padlock) { if (this.andNonsense == null) this.andNonsense = "Also threadsafe!"; } return this.andNonsense; } } // Rest of class... } In cases where the get operations are expensive and unrelated, a single locking object is unsuitable because a call to Stuff would block all calls to AndNonsense, degrading performance. And rather than create a lock object for each call, wouldn't it be better to acquire the lock on the member itself (assuming it is not something that implements SyncRoot or somesuch for that purpose? For example: public string Stuff { get { lock (this.stuff) { // Pretend that this is a very expensive operation. if (this.stuff == null) this.stuff = "Still threadsafe and good?"; } return this.stuff; } } Strangely, I have never seen this approach recommended or warned against. Am I missing something obvious?

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  • Multiple locking task (threading)

    - by Archeg
    I need to implement the class that should perform locking mechanism in our framework. We have several threads and they are numbered 0,1,2,3.... We have a static class called ResourceHandler, that should lock these threads on given objects. The requirement is that n Lock() invokes should be realeased by m Release() invokes, where n = [0..] and m = [0..]. So no matter how many locks was performed on single object, only one Release call is enough to unlock all. Even further if o object is not locked, Release call should perform nothing. Also we need to know what objects are locked on what threads. I have this implementation: public class ResourceHandler { private readonly Dictionary<int, List<object>> _locks = new Dictionary<int, List<object>>(); public static ResourceHandler Instance {/* Singleton */} public virtual void Lock(int threadNumber, object obj) { Monitor.Enter(obj); if (!_locks.ContainsKey(threadNumber)) {_locks.Add(new List<object>());} _locks[threadNumber].Add(obj); } public virtual void Release(int threadNumber, object obj) { // Check whether we have threadN in _lock and skip if not var count = _locks[threadNumber].Count(x => x == obj); _locks[threadNumber].RemoveAll(x => x == obj); for (int i=0; i<count; i++) { Monitor.Exit(obj); } } // ..... } Actually what I am worried here about is thread-safety. I'm actually not sure, is it thread-safe or not, and it's a real pain to fix that. Am I doing the task correctly and how can I ensure that this is thread-safe?

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  • May volatile be in user defined types to help writing thread-safe code

    - by David Rodríguez - dribeas
    I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into failing to accept code that could be not thread safe. In the article the keyword is used more like a required_thread_safety tag than the actual intended use of volatile. Is this (ab)use of volatile appropriate? What possible gotchas may be hidden in the approach? The first thing that comes to mind is added confusion: volatile is not related to thread safety, but by lack of a better tool I could accept it. Basic simplification of the article: If you declare a variable volatile, only volatile member methods can be called on it, so the compiler will block calling code to other methods. Declaring an std::vector instance as volatile will block all uses of the class. Adding a wrapper in the shape of a locking pointer that performs a const_cast to release the volatile requirement, any access through the locking pointer will be allowed. Stealing from the article: template <typename T> class LockingPtr { public: // Constructors/destructors LockingPtr(volatile T& obj, Mutex& mtx) : pObj_(const_cast<T*>(&obj)), pMtx_(&mtx) { mtx.Lock(); } ~LockingPtr() { pMtx_->Unlock(); } // Pointer behavior T& operator*() { return *pObj_; } T* operator->() { return pObj_; } private: T* pObj_; Mutex* pMtx_; LockingPtr(const LockingPtr&); LockingPtr& operator=(const LockingPtr&); }; class SyncBuf { public: void Thread1() { LockingPtr<BufT> lpBuf(buffer_, mtx_); BufT::iterator i = lpBuf->begin(); for (; i != lpBuf->end(); ++i) { // ... use *i ... } } void Thread2(); private: typedef vector<char> BufT; volatile BufT buffer_; Mutex mtx_; // controls access to buffer_ };

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