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  • Lock statement vs Monitor.Enter method.

    - by Vokinneberg
    I suppose it is an interesting code example. We have a class, let's call it Test with Finalize method. In Main method here is two code blocks where i am using lock statement and Monitor.Enter call. Also i have two instances of class Test here. The experiment is pretty simple - nulling Test variable within locking block and try to collect it manually with GC.Collect method call. So, to see the Finilaze call i am calling GC.WaitForPendingFinalizers method. Everything is very simple as you can see. By defenition of lock statement it's opens by compiler to try{...}finally{..} block with Minitor.Enter call inside of try block and Monitor.Exit in finally block. I've tryed to implement try-finally block manually. I've expected the same behaviour in both cases. in case of using lock and in case of unsing Monitor.Enter. But, surprize, surprize - it is different as you can see below. public class Test : IDisposable { private string name; public Test(string name) { this.name = name; } ~Test() { Console.WriteLine(string.Format("Finalizing class name {0}.", name)); } } class Program { static void Main(string[] args) { var test1 = new Test("Test1"); var test2 = new Test("Tesst2"); lock (test1) { test1 = null; Console.WriteLine("Manual collect 1."); GC.Collect(); GC.WaitForPendingFinalizers(); Console.WriteLine("Manual collect 2."); GC.Collect(); } var lockTaken = false; System.Threading.Monitor.Enter(test2, ref lockTaken); try { test2 = null; Console.WriteLine("Manual collect 3."); GC.Collect(); GC.WaitForPendingFinalizers(); Console.WriteLine("Manual collect 4."); GC.Collect(); } finally { System.Threading.Monitor.Exit(test2); } Console.ReadLine(); } } Output of this example is Manual collect 1. Manual collect 2. Manual collect 3. Finalizing class name Test2. Manual collect 4. And null reference exception in last finally block because test2 is null reference. I've was surprised and disasembly my code into IL. So, here is IL dump of Main method. .entrypoint .maxstack 2 .locals init ( [0] class ConsoleApplication2.Test test1, [1] class ConsoleApplication2.Test test2, [2] bool lockTaken, [3] bool <>s__LockTaken0, [4] class ConsoleApplication2.Test CS$2$0000, [5] bool CS$4$0001) L_0000: nop L_0001: ldstr "Test1" L_0006: newobj instance void ConsoleApplication2.Test::.ctor(string) L_000b: stloc.0 L_000c: ldstr "Tesst2" L_0011: newobj instance void ConsoleApplication2.Test::.ctor(string) L_0016: stloc.1 L_0017: ldc.i4.0 L_0018: stloc.3 L_0019: ldloc.0 L_001a: dup L_001b: stloc.s CS$2$0000 L_001d: ldloca.s <>s__LockTaken0 L_001f: call void [mscorlib]System.Threading.Monitor::Enter(object, bool&) L_0024: nop L_0025: nop L_0026: ldnull L_0027: stloc.0 L_0028: ldstr "Manual collect." L_002d: call void [mscorlib]System.Console::WriteLine(string) L_0032: nop L_0033: call void [mscorlib]System.GC::Collect() L_0038: nop L_0039: call void [mscorlib]System.GC::WaitForPendingFinalizers() L_003e: nop L_003f: ldstr "Manual collect." L_0044: call void [mscorlib]System.Console::WriteLine(string) L_0049: nop L_004a: call void [mscorlib]System.GC::Collect() L_004f: nop L_0050: nop L_0051: leave.s L_0066 L_0053: ldloc.3 L_0054: ldc.i4.0 L_0055: ceq L_0057: stloc.s CS$4$0001 L_0059: ldloc.s CS$4$0001 L_005b: brtrue.s L_0065 L_005d: ldloc.s CS$2$0000 L_005f: call void [mscorlib]System.Threading.Monitor::Exit(object) L_0064: nop L_0065: endfinally L_0066: nop L_0067: ldc.i4.0 L_0068: stloc.2 L_0069: ldloc.1 L_006a: ldloca.s lockTaken L_006c: call void [mscorlib]System.Threading.Monitor::Enter(object, bool&) L_0071: nop L_0072: nop L_0073: ldnull L_0074: stloc.1 L_0075: ldstr "Manual collect." L_007a: call void [mscorlib]System.Console::WriteLine(string) L_007f: nop L_0080: call void [mscorlib]System.GC::Collect() L_0085: nop L_0086: call void [mscorlib]System.GC::WaitForPendingFinalizers() L_008b: nop L_008c: ldstr "Manual collect." L_0091: call void [mscorlib]System.Console::WriteLine(string) L_0096: nop L_0097: call void [mscorlib]System.GC::Collect() L_009c: nop L_009d: nop L_009e: leave.s L_00aa L_00a0: nop L_00a1: ldloc.1 L_00a2: call void [mscorlib]System.Threading.Monitor::Exit(object) L_00a7: nop L_00a8: nop L_00a9: endfinally L_00aa: nop L_00ab: call string [mscorlib]System.Console::ReadLine() L_00b0: pop L_00b1: ret .try L_0019 to L_0053 finally handler L_0053 to L_0066 .try L_0072 to L_00a0 finally handler L_00a0 to L_00aa I does not see any difference between lock statement and Monitor.Enter call. So, why i steel have a reference to the instance of test1 in case of lock, and object is not collected by GC, but in case of using Monitor.Enter it is collected and finilized?

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  • Way to turn on keyboard's caps-lock light without actually turning on caps-lock?

    - by cksubs
    I'm writing a program that uses caps-lock as a toggle switch. It would be nice to set the LED of the key to show that my program is on or off, like the capslock key does naturally. I know that I could just SendInput('Capslock'); or whatever to actually turn caps-lock on and off. But my app is a typing program, and I don't want to have to deal with translating the all-caps keys that turning it on would give me into their lower/upper cases. I might go that route eventually, but not for this version. I would however be interested in just turning on the LED light WITHOUT actually turning on caps-lock. Is there any way to do that? Thank you.

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  • Acquiring Table Lock in Database - Interview Question

    - by harigm
    One of my interview Questions, if multiple users across the world are accessing the application, in which it uses a Table which has a Primary Key as Auto Increment Field. The Question how can you prevent the other user getting the Same Primary key when the other user is executing? My answer was I will obtain the Lock on the table and I will make the user to wait Until that user is released with the Primary key. But the Question How do you acquire the Table lock programmatically and implement this? If there are 1000 users coming every minute to the application, if you explicity hold the lock on the table, then the application will become slower? How do you manage this? Please suggest the possible answers for the above question

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  • Implementing a Mutex Lock in C

    - by Adam
    I'm trying to make a really mutex in C and for some reason I'm getting cases where two threads are getting the lock at the same time, which shouldn't be possible. Any ideas why it's not working? void mutexLock(mutex_t *mutexlock, pid_t owner) { int failure; while(mutexlock->mx_state == 0 || failure || mutexlock->mx_owner != owner) { failure = 1; if (mutexlock->mx_state == 0) { asm( "test:" "movl $0x01,%%eax\n\t" // move 1 to eax "xchg %%eax,%0\n\t" // try to set the lock bit "mov %%eax,%1\n\t" // export our result to a test var "test %%eax,%%eax\n\t" "jnz test\n\t" :"=r"(mutexlock->mx_state),"=r"(failure) :"r"(mutexlock->mx_state) :"%eax" ); } if (failure == 0) { mutexlock->mx_owner = owner; //test to see if we got the lock bit } } }

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  • How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

    - by Amir
    Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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  • Using accelerometer to detect iPad lock switch trigger?

    - by DevDevDev
    So for complicated reasons I am managing view rotations myself, and am only implementing UIDeviceOrientationPortrait as the autorotating orientation. Anyway, when one clicks the screen lock on the iPad, the device will rotate to UIDeviceOrientationPortrait, which will cause my code to rotate, which I do not want to happen. For instance of the user is holding the device in "landscape mode", i.e. I have already manually rotated the UI to landscape mode, and he/she clicks the screen lock, it will rotate the UI to portrait mode, even though the user did not move the device at all. So somehow I need a way to differentiate between rotations to portrait mode occuring from the screen lock, and those occuring from device rotation. As such, I would like somehow to use the accelerometer to detect whether or not the device was actually 'rotated' or whether the button was clicked. Thanks!

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  • Oracle global lock across process

    - by Jimm
    I would like to synchronize access to a particular insert. Hence, if multiple applications execute this "one" insert, the inserts should happen one at a time. The reason behind synchronization is that there should only be ONE instance of this entity. If multiple applications try to insert the same entity,only one should succeed and others should fail. One option considered was to create a composite unique key, that would uniquely identify the entity and rely on unique constraint. For some reasons, the dba department rejected this idea. Other option that came to my mind was to create a stored proc for the insert and if the stored proc can obtain a global lock, then multiple applications invoking the same stored proc, though in their seperate database sessions, it is expected that the stored proc can obtain a global lock and hence serialize the inserts. My question is it possible to for a stored proc in oracle version 10/11, to obtain such a lock and any pointers to documentation would be helpful.

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  • is it possible to lock oracle 10g database table with C#/(ADO?).NET 2.0

    - by matti
    I have a table that contains a maximum value that needs to be get and set by multiple programs. How can I lock the table for a while when old value is got and new is updated in C#? In other words: string sql = "lock table MaxValueTable in exclusive mode"; using (DbCommand cmd = cnctn.CreateCommand()) { cmd.CommandText = sql; // execute command somehow!! } maxValue = GetMaxValue(); SetMaxValue(maxValue + X); sql = "lock table MaxValueTable in share mode"; using (DbCommand cmd = cnctn.CreateCommand()) { cmd.CommandText = sql; // execute command somehow!! } -BR: Matti

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  • net c# lock statement in data access layer

    - by Pedro Rivera
    I saw a code where they have the data access layer like this: public class CustomerDA{ private static readonly object _sync = new object(); private static readonly CustomerDA _mutex = new CustomerDA(); private CustomerDA(){ } public CustomerDA GetInstance(){ lock(_sync){ return _mutex; } } public DataSet GetCustomers(){ //database SELECT //return a DataSet } public int UpdateCustomer(some parameters){ //update some user } } public class CustomerBO{ public DataSet GetCustomers(){ //some bussiness logic return CustomerDA.GetInstance().GetCustomers(); } } I was using it, but start thinking... "and what if had to build a facebook like application where there are hundreds of thousands of concurrent users? would I be blocking each user from doing his things until the previous user ends his database stuff? and for the Update method, is it useful to LOCK THREADS in the app when database engines already manage concurrency at database server level?" Then I started to think about moving the lock to the GetCustomers and UpdateCustomer methods, but think again: "is it useful at all?"

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  • innodb lock wait timeout

    - by shantanuo
    As per the documentation link given below: When a lock wait timeout occurs, the current statement is not executed. The current transaction is not rolled back. (Until MySQL 5.0.13 InnoDB rolled back the entire transaction if a lock wait timeout happened. You can restore this behavior by starting the server with the --innodb_rollback_on_timeout option, available as of MySQL 5.0.32. http://dev.mysql.com/doc/refman/5.0/en/innodb-parameters.html#sysvar_innodb_lock_wait_timeout Does it mean that when a lock wait timeout occurs, it compromises the transactional integrity? "roollback on timeout" was the default behaviour till 5.0.13 and I guess that was the correct way to handle such situations. Does anyone think that this should be the default behaviour and the user should not be asked to add a parameter for a functionality that is taken for granted?

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  • Timer applications running under lock on Windows Phone 7

    - by cpedros
    Under the current Windows Phone 7 Application Certification Requirements (pdf) applications running under lock must "stop any ... active timers" (section 6.3.1). However looking out on Marketplace there are a number of timer/stopwatch apps claiming to run under lock and also allow lock to be disabled in their settings. How are these apps certified or is there some loosening on the restrictions by Microsoft if the app allows the user to make that decision? Also some of these apps also suggest they continue even when the app is exited or when the device off. Is it the case that they are not truly running under these circumstances, i.e. the timers either start where they left off when reactivated, or perhaps use the OS time to work out the time elapsed between tombstoning and reactivation? In these circumstance I also presume it is not possible for the app to notify the user when the timer completes?

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  • Performing time consuming operation on STL container within a lock

    - by Ashley
    I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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  • Lock thread using somthing other than a object

    - by Scott Chamberlain
    when using a lock does the thing you are locking on have to be a object. For example is this legal static DateTime NextCleanup = DateTime.Now; const TimeSpan CleanupInterval = new TimeSpan(1, 0, 0); private static void DoCleanup() { lock ((object)NextCleanup) { if (NextCleanup < DateTime.Now) { NextCleanup = DateTime.Now.Add(CleanupInterval); System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(cleanupThread)); } } return; } EDIT-- From reading SLaks' responce I know the above code would be not valid but would this be? static MyClass myClass = new MyClass(); private static void DoCleanup() { lock (myClass) { // } return; }

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  • Why boost::recursive_mutex is not working as expected?

    - by Kjir
    I have a custom class that uses boost mutexes and locks like this (only relevant parts): template<class T> class FFTBuf { public: FFTBuf(); [...] void lock(); void unlock(); private: T *_dst; int _siglen; int _processed_sums; int _expected_sums; int _assigned_sources; bool _written; boost::recursive_mutex _mut; boost::unique_lock<boost::recursive_mutex> _lock; }; template<class T> FFTBuf<T>::FFTBuf() : _dst(NULL), _siglen(0), _expected_sums(1), _processed_sums(0), _assigned_sources(0), _written(false), _lock(_mut, boost::defer_lock_t()) { } template<class T> void FFTBuf<T>::lock() { std::cerr << "Locking" << std::endl; _lock.lock(); std::cerr << "Locked" << std::endl; } template<class T> void FFTBuf<T>::unlock() { std::cerr << "Unlocking" << std::endl; _lock.unlock(); } If I try to lock more than once the object from the same thread, I get an exception (lock_error): #include "fft_buf.hpp" int main( void ) { FFTBuf<int> b( 256 ); b.lock(); b.lock(); b.unlock(); b.unlock(); return 0; } This is the output: sb@dex $ ./src/test Locking Locked Locking terminate called after throwing an instance of 'boost::lock_error' what(): boost::lock_error zsh: abort ./src/test Why is this happening? Am I understanding some concept incorrectly?

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  • Lock a mutex multiple times in the same thread

    - by Megacan
    Hi, I'm developing an application on an embedded linux OS (uClinux) and I need to be able to lock the mutex more than once (by the same thread). I have a mutex and a mutexattr defined and initialized as follows: pthread_mutexattr_t waiting_barcode_mutexattr; pthread_mutex_t waiting_barcode_mutex; pthread_mutexattr_init(&waiting_barcode_mutexattr); pthread_mutexattr_settype(&waiting_barcode_mutexattr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init(&waiting_barcode_mutex, &waiting_barcode_mutexattr); But when I try to acquire the lock twice it blocks on the second lock: pthread_mutex_lock(&waiting_barcode_mutex); pthread_mutex_lock(&waiting_barcode_mutex); Am I initializing it wrong or is there a better way of accomplishing the same? Thanks in advance.

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  • What are programmers made to do in spare time in jobs?

    - by Shashank Jain
    Well, with no prior job experience I am completely ignorant of how things happen at software companies. I want to know what programmers are made to do when there is nothing to do? Lets consider Facebook or twitter. Now it is quite improbable that Facebook people have something or other feature in mind to be implemented. So software developers are quite expected to have some time when there is nothing to do. Are they free to do anything in this?

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  • Paper-free Customer Engagement

    - by Michael Snow
    v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} 12.00 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-family:"Calibri","sans-serif"; mso-ascii- mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi- mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Appropriate repost from our friends at the AIIM blog: Digital Landfill -- John Mancini, supporting our mission of enabling customer engagement through better technology choices.  ---------- My wife didn't even give me a card for #wpfd - and they say husbands are bad at remembering anniversaries Well, today is the third World Paper Free Day.  I just got off the Tweet Jam, and there was a host of ideas for getting rid of -- or at least reducing -- paper. When we first started talking about "paper-free" most of the reasons raised to pursue this direction were "green" reasons.  I'm glad to see that the thinking has moved on to questions about how getting rid of paper and digitizing processes helps improve customer engagement.  And the bottom line.  And process responsiveness.  Not that the "green" reasons have gone away, but it's nice to see a maturation in the BUSINESS reasons to get rid of paper. Our World Paper Free Handbook (do not, do not, do not print it!) looks at how less paper in the workplace delivers significant benefits. Key findings show eliminating paper from processes can improve the responsiveness of customer service by 300 percent. Removing paper from business processes and moving content to PCs and tablets has the added advantage of helping companies adopt mobile-enable processes and eliminate elapsed time, lost forms, poor data and re-keying. To effectively mobile-enable processes and reduce reliance on paper, data should be captured as close to the point of origination as possible, which makes information easily available to whomever needs it, wherever they are, in the shortest time possible. This handbook summarizes the value of automating manual, paper-based processes. It then goes a step beyond to provide actionable steps that will set you on the path to productivity, profitability, and, yes, less paper.  Get your copy today and send the link around to your peers and colleagues.  Here's the link; please share it! http://www.aiim.org/Research-and-Publications/Research/AIIM-White-Papers/WPFD-Revolution-Handbook And don't miss out on the real world discussions about increasing engagement with WebCenter in new webinars being offered over the next couple of weeks:  October 30, 2012:  ResCare Solves Content Lifecycle Challenges with Oracle WebCenter November 1, 2012: WebCenter Content for Applications: Streamline Processes with Oracle WebCenter Content Management for Human Resources Applications Available On-Demand:  Using Oracle WebCenter to Content-Enable Your Business Applications

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  • web service host [closed]

    - by elyashiv
    I'm looking for a place to host a cloud service that well manage data from a App I'm developing. The service I need doesn't have any UI (accessed completely through the App software), and well work on only small requests - but hopefully quite a lot of them. I'm looking for something free that well give me the best - in storage and request handling. No specific language, but preferably one of the following: Python, C#, Java. (in this order).

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  • Windows 7 Group Policy to display message for login tries left before account lock

    - by Vivek
    My requirement is to display the the remaining count left on the login screen when user trying to login using Windows 7 OS before account lock in case user enter invalid password. I am having Active Directory on Windows 2008 R2 server. I set the maximum Lockout count = 5 in GPO policy. Example: If user try login first 1 attempt is failed, next time enter password and login shold show message for remaining attemps left.( my case count 4 left) Please let me know as this is urgent for me.

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  • X window (or whole linux system) replace Caps Lock with ESC *and* Control

    - by gcb
    on windows there are several key maps applications that replaces Caps lock with ESC on a single 'press and relase' and with a Control signal if hold and another key is pressed. Is there any way to do something similar on linux? Ideally on the whole system, but if it is only for X window it is fine too. i'm currently writting scripts with the xautomation package tools. but i guess there is already a better way to do that via configurations.

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  • Amazon EC2 Ami recommendations for free tier?

    - by Console
    Amazon web services recently introduced a free tier, where you basically get free stuff to try out AWS and run tiny sites and projects. Basically it's free as long as you remain below a certain limit of bandwidth, disk storage etc. Since going over the limits can quickly become quite expensive (for a hobbyist) I would like some recommendations or suggestions about which AMI's I can run on the free tier, for the purpose of trying out Ruby on Rails and/or Django.

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  • clients auto-lock feature for inactvity timeout not working

    - by Swaminathan Shanmugam
    In our sbs 2003 domain environment, the clients' pc's inactive for default period will be locked out automatically and only Ctrl+ Alt + Del & client password combination will unlock the client's pcs. Recently around 9 months before, all our client's pc's joined the new sbs 2011 but (usually all are locking with Win+L key combination manually)the auto lock feature is not working from the beginning onwards. Now only I am brought up with this issue by clients. Please help me set that option!

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  • Location of lock screen

    - by ICTdesk.net
    Does anybody know if it is possible to change a setting so that the Windows XP Lock Screen is not centered, but let's say in right or left top/down corner or maybe even a give x or y coordinate?

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