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• How do you stop a user-instance of Sql Server? (Sql Express user instance database files locked, eve

  - by Bittercoder

  When using SQL Server Express 2005's User Instance feature with a connection string like this: <add name="Default" connectionString="Data Source=.\SQLExpress; AttachDbFilename=C:\My App\Data\MyApp.mdf; Initial Catalog=MyApp; User Instance=True; MultipleActiveResultSets=true; Trusted_Connection=Yes;" /> We find that we can't copy the database files MyApp.mdf and MyApp_Log.ldf (because they're locked) even after stopping the SqlExpress service, and have to resort to setting the SqlExpress service from automatic to manual startup mode, and then restarting the machine, before we can then copy the files. It was my understanding that stopping the SqlExpress service should stop all the user instances as well, which should release the locks on those files. But this does not seem to be the case - could anyone shed some light on how to stop a user instance, such that it's database files are no longer locked? Update OK, I stopped being lazy and fired up Process Explorer. Lock was held by sqlserver.exe - but there are two instances of sql server: sqlserver.exe PID: 4680 User Name: DefaultAppPool sqlserver.exe PID: 4644 User Name: NETWORK SERVICE The file is open by the sqlserver.exe instance with the PID: 4680 Stopping the "SQL Server (SQLEXPRESS)" service, killed off the process with PID: 4644, but left PID: 4680 alone. Seeing as the owner of the remaining process was DefaultAppPool, next thing I tried was stopping IIS (this database is being used from an ASP.Net application). Unfortunately this didn't kill the process off either. Manually killing off the remaining sql server process does remove the open file handle on the database files, allowing them to be copied/moved. Unfortunately I wish to copy/restore those files in some pre/post install tasks of a WiX installer - as such I was hoping there might be a way to achieve this by stopping a windows service, rather then having to shell out to kill all instances of sqlserver.exe as that poses some problems: Killing all the sqlserver.exe instances may have undesirable consequencies for users with other Sql Server instances on their machines. I can't restart those instances easily. Introduces additional complexities into the installer. Does anyone have any further thoughts on how to shutdown instances of sql server associated with a specific user instance?

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• Distributed Lock Service over MySql/GigaSpaces/Netapp

  - by ripper234

  Disclaimer: I already asked this question, but without the deployment requirement. I got an answer that got 3 upvotes, and when I edited the question to include the deployment requirement the answer then became irrelevant. The reason I'm resubmitting is because SO considers the original question 'answered', even though I got no meaningful upvoted answer. I opened a uservoice submission about this problem. The reason I reposted is so StackOverflow consider the original question answered, so it doesn't show up on the 'unanswered questions' tab. Which distributed lock service would you use? Requirements are: A mutual exclusion (lock) that can be seen from different processes/machines lock...release semantics Automatic lock release after a certain timeout - if lock holder dies, it will automatically be freed after X seconds Java implementation Easy deployment - must not require complicated deployment beyond either Netapp, MySql or GigaSpaces. Must play well with those products (especially GigaSpaces - this is why TerraCotta was ruled out). Nice to have: .Net implementation If it's free: Deadlock detection / mitigation I'm not interested in answers like "it can be done over a database", or "it can be done over JavaSpaces" - I know. Relevant answers should only contain a ready, out-of-the-box, proven implementation.

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• SQL Server Compact timed out waiting for a lock

  - by jankhana

  Hi all, I'm having an application in that i use Sql Compact 3.5 with VS2008. I'm running multiple threads in my application which contacts the compact database and accesses the row. It selects and deletes those rows in a fashion i.e selecting and giving to the application 5 rows and deleting those rows from the table. It works great with a single thread but if i use multiple threads i.e if 3 or more threads are running I get very often the TimeOut Error!!! I have increased the Time out property in the connection string but it didn't give me expected result. The error log is as follow: SQL Server Compact timed out waiting for a lock. The default lock time is 2000ms for devices and 5000ms for desktops. The default lock timeout can be increased in the connection string using the ssce: default lock timeout property. [ Session id = 5,Thread id = 4204,Process id = 4808,Table name = XXX,Conflict type = x lock (s blocks),Resource = TAB ] The Query that I use to retrieve is as follows: " select Top(5) * from TableName order by id; delete from TableName where id in(select top(5) id from TableName order by id); " Is there any way by which we can avoid this Time Out exception??????? The above query I un as a transaction in VS2008 one using SQLCECommand and the other using SqlCEDataAdapter. Any Idea!!!!!! Reply

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• Is SynchronizationContext.Post() threadsafe?

  - by cyclotis04

  This is a pretty basic question, and I imagine that it is, but I can't find any definitive answer. Is SynchronizationContext.Post() threadsafe? I have a member variable which holds the main thread's context, and _context.Post() is being called from multiple threads. I imagine that Post() could be called simultaneously on the object. Should I do something like lock (_contextLock) _context.Post(myDelegate, myEventArgs); or is that unnecessary? Edit: MSDN states that "Any instance members are not guaranteed to be thread safe." Should I keep my lock(), then?

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• Is lock returned by ReentrantReadWriteLock equivalent to it's read and write locks?

  - by Todd

  Hello, I have been looking around for the answer to this, but no joy. In Java, is using the lock created by ReentrantReadWriteLock equivalent to getting the read and write locks as returned by readLock.lock() and writeLock.lock()? In other words, can I expect the read and write locks associated with the ReentrantReadWriteLock to be requested and held by synchronizing on the ReentrantReadWriteLock? My gut says "no" since any object can be used for synchronization. I wouldn't think that there would be special behavior for ReentrantReadWriteLock. However, special behavior is the corner case of which I may not be aware. Thanks, Todd

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• C++ Unlocking a std::mutex before calling std::unique_lock wait

  - by Sant Kadog

  I have a multithreaded application (using std::thread) with a manager (class Tree) that executes some piece of code on different subtrees (embedded struct SubTree) in parallel. The basic idea is that each instance of SubTree has a deque that store objects. If the deque is empty, the thread waits until a new element is inserted in the deque or the termination criteria is reached. One subtree can generate objects and push them in the deque of another subtree. For convenience, all my std::mutex, std::locks and std::variable_condition are stored in a struct called "locks". The class Tree creates some threads that run the following method (first attempt) : void Tree::launch(SubTree & st, Locks & locks ) { /* some code */ std::lock_guard<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem is that "deque_lock" is still locked while the thread is waiting. Hence no object can be added in the deque of the current thread by a concurrent one. So I turned the lock_guard into a unique_lock and managed the lock/unlock manually : void launch(SubTree & st, Locks & locks ) { /* some code */ std::unique_lock<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { deque_lock.unlock() ; // unlock the access to the deque to enable the other threads to add objects // DATA RACE : nothing must happen to the unprotected deque here !!!!!! // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem now, is that there is a data race, and I would like to make sure that the "wait" instruction is performed directly after the "deque_lock.unlock()" one. Would anyone know a way to create such a critical instruction sequence with the standard library ? Thanks in advance.

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• Removing file locks in Windows and Java

  - by Jack

  I have a Java program that opens a file using the RandomAccessFile class. I'd like to be able to rename that file while it is opened by Java. In Unix, this isn't a problem. Does anyone know how I can do this in Windows? Should I set Java to open it a certain way? Thanks in advance.

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• Remove another user's lock obtained with sp_getapplock on SQL Server

  - by joshperry

  We have a system that uses sp_getapplock to create an exclusive mutex any time someone opens an order in the GUI. This is used to prevent multiple people from making changes to an order simultaneously. Sometimes people will open an order and go home, leaving it open. This effectively blocks anyone from being able to make changes to the order. I then get emails, calls and end up doing a kill <spid> in enterprise manager. Obviously I've gotten sick of this and want to make a quick self-service webform. The main problem I've run into is that kill requires sysadmin privileges, which I do not want to give to the user that the our website runs as. I have tried sp_releaseapplock but this doesn't let you release another user's lock (even when calling it as a sysadmin). So, finally my question; does anyone know of an alternative method to release a lock that was obtained by another user using sp_getapplock?

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• Unlock a file with unlocker from a WinForms App?

  - by netadictos

  I am trying to unlock a file from a C# program, using unlocker. In my UI, I put a button to unlock the file the app couldn't delete. When the user pushes the button, I want unlocker (the famous app) to be opened. I have read about in the Unlocker web, and there is some explanations about the commandline to use but nothing works. I write the following code but nothing happens: "c:\Program Files\unlocker\unlocker.exe" -L "PATHFORTHEFILE.doc" Nothing happens. I have tried without parameters and with -LU. Any idea? Something more efficient than unlocker to integrate it with software?

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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 this a correct Interlocked synchronization design?

  - by Dan Bryant

  I have a system that takes Samples. I have multiple client threads in the application that are interested in these Samples, but the actual process of taking a Sample can only occur in one context. It's fast enough that it's okay for it to block the calling process until Sampling is done, but slow enough that I don't want multiple threads piling up requests. I came up with this design (stripped down to minimal details): public class Sample { private static Sample _lastSample; private static int _isSampling; public static Sample TakeSample(AutomationManager automation) { //Only start sampling if not already sampling in some other context if (Interlocked.CompareExchange(ref _isSampling, 0, 1) == 0) { try { Sample sample = new Sample(); sample.PerformSampling(automation); _lastSample = sample; } finally { //We're done sampling _isSampling = 0; } } return _lastSample; } private void PerformSampling(AutomationManager automation) { //Lots of stuff going on that shouldn't be run in more than one context at the same time } } Is this safe for use in the scenario I described?

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• Is lock() type-cast safe?

  - by Andy

  public class A { } public class B:A { } void foo() { A a = new B(); B b = a as B; } for a given instance setup, will lock(a) be equivalent to lock(b) ?

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• How to identify what locked PL/SQL package (Oracle 10.0.4.2)?

  - by Roman Kagan

  I was trying to recompile PL/SQL package and no avail. because something obtained the lock and that wasn't released for long time. As soon as I kill all sessions I was able to recompile but encounter the same behavior (i.e. locked package) and I wonder what tools are avail to identify what could of obtain it and never release it? This happen on (Oracle 10.0.4.2). Greatly appreciate for your help.

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• What is the best way to apply rowlevel writelock in T-SQL? Best Practices And Samples Please

  - by Kerem Kusmezer

  What is the best way to apply rowlevel writelock in T-SQL? Best Practices And Samples Please

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• Obtain Update Table Lock at start of Stored Procedure in SQL Server

  - by Jim Hurne

  I'm writing a SQL Server stored procedure in which I want to lock a table for update before executing the body of the stored procedure. I don't want to prevent other processes from reading the table, but I do want to prevent other processes updating the table. Here is my first attempt: CREATE PROCEDURE someProcedure BEGIN SET TRANSACTION ISOLATION LEVEL READ COMITTED BEGIN TRANSANCTION SELECT COUNT(*) FROM TheTable WITH (UPDLOCK, TABLOCK) -- Pause procedure so that we can view the locks with sp_lock WAITFOR DELAY '00:15' -- Do stuff COMMIT END When I execute the stored procedure, and invoke sp_lock, I see that the table is indeed locked. However, it's locked with an Exclusive lock instead of an update lock: spid | dbid | ObjId | IndId | Type | Resource | Mode | Status ------------------------------------------------------------------ 63 | 10 | 233208031 | 0 | TAB | | X | GRANT How can I get an update (U) lock instead?

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• Using Entity Framework for SQL Compact Edition 3.5 does not respect mode=exclusive property of conne

  - by AJ

  I am using SQL Server Compact 3.5 edition with Entity Framework and I want to have exclusive lock on the database as documented here http://msdn.microsoft.com/en-us/library/ms171817.aspx. However when you pass this in a connection string to Entity Framework it does not respect this at all. An example of the connection string as following private static readonly string _ConnectionStringFormat = @"metadata=res://*/Model.csdl|res://*/Model.ssdl|res://*/Model.msl; provider=System.Data.SqlServerCe.3.5; provider connection string='Data Source={0};Mode=Exclusive'"; If anyone has come across this issue before and have found out how to resolve this, then please let me know. Thanks Aj

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• Error opening streamreader because file is used by another process

  - by Geri Langlois

  I am developing an application to read an excel spreadsheet, validate the data and then map it to a sql table. The process is to read the file via a streamreader, validate the data, manually make corrections to the excel spreadsheet, validate again -- repeat this process until all data validates. If the excel spreadsheet is open, then when I attempt to read the data via a streamreader I get an error, "The process cannot access the file ... because it is being used by another process." Is there a way to remove the lock or otherwise read the data into a streamreader without having to open and close excel each time?

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• Strange Values in SYS.DM_TRAN_LOCKS table RESOURCE_ASSOCIATED_ENTITY_ID column

  - by AJM

  I’ve been trying to understand some strange values in the RESOURCE_ASSOCIATED_ENTITY_ID column of SYS.DM_TRAN_LOCKS when RESOURCE_TYPE is “OBJECT”. Although these should be object Ids, I cannot determine what object they actually refer to. I’ve tried everything I can think of, including querying all system tables with columns of type INT and BIGINT to see if I can find the value. No luck. The funny values actually appear in SYS.DM_TRAN_LOCKS, SYS.SYSLOCKINFO and SP_LOCK.

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• Determine which process (b)locks a file, programmatically (under Windows >= XP)

  - by fred-hh

  How to programmatically determine from a process P, which other process P' has a lock on a file, that prevents P from recreating that file ? I know there are tools to do that, but how do they achieve that ? (Context: a batch program that runs overnight fails because of a locked file. Running an admin tool the next day may be too late to get useful information. So it would be nice if the batch program itself was able to determine the culprit.) EDIT: Added complexity: the file resides on a DFS and P' might not run on the same machine as P (but maybe does). But a solution that works locally would be a good beginning.

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• File Locked by Services (after service code reading the text file)

  - by rvpals

  I have a windows services written in C# .NET. The service is running on a internal timer, every time the interval hits, it will go and try to read this log file into a String. My issue is every time the log file is read, the service seem to lock the log file. The lock on that log file will continue until I stop the windows service. At the same time the service is checking the log file, the same log file needs to be continuously updated by another program. If the file lock is on, the other program could not update the log file. Here is the code I use to read the text log file. private string ReadtextFile(string filename) { string res = ""; try { System.IO.FileStream fs = new System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read); System.IO.StreamReader sr = new System.IO.StreamReader(fs); res = sr.ReadToEnd(); sr.Close(); fs.Close(); } catch (System.Exception ex) { HandleEx(ex); } return res; } Thank you.

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• Blackberry Keyboard Lock timeout

  - by Vernon

  I want this blackberry 9700 to "fully lock" as soon as I click the icon for the "Keyboard Lock" application. Currently I have to wait 5 to 7 seconds for the screen to go dark after each time I click the "Keyboard Lock" icon. During that time if something touches the touch pad, then the 5-7 second timer resets and you have to wait another 5 to 7 seconds for the screen to go dark and "fully lock" After it finally goes dark, touching the touch pad does not reset the timer. At that point it is "fully locked" and requires a key to be pressed. How can I get it to "fully lock" as soon as the lock icon is clicked? I want the screen to go dark immediately, and for it to require a key press to request an unlock. I have tried Options - Screen/Keyboard - Backlight Timeout ... etc ... none of that reduces the timeout for the "Keyboard Lock" application. And there does not seem to be an option screen for the "Keyboard Lock" application, that I can find. NOTE: This is occurring with BlackBerry 9700 v5.0.0.330 (Platform 5.1.0.91)

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• Using SQL dB column as a lock for concurrent operations in Entity Framework

  - by Sid

  We have a long running user operation that is handled by a pool of worker processes. Data input and output is from Azure SQL. The master Azure SQL table structure columns are approximated to [UserId, col1, col2, ... , col N, beingProcessed, lastTimeProcessed ] beingProcessed is boolean and lastTimeProcessed is DateTime. The logic in every worker role is: public void WorkerRoleMain() { while(true) { try { dbContext db = new dbContext(); // Read foreach (UserProfile user in db.UserProfile .Where(u => DateTime.UtcNow.Subtract(u.lastTimeProcessed) > TimeSpan.FromHours(24) & u.beingProcessed == false)) { user.beingProcessed = true; // Modify db.SaveChanges(); // Write // Do some long drawn processing here ... ... ... user.lastTimeProcessed = DateTime.UtcNow; user.beingProcessed = false; db.SaveChanges(); } } catch(Exception ex) { LogException(ex); Sleep(TimeSpan.FromMinutes(5)); } } // while () } With multiple workers processing as above (each with their own Entity Framework layer), in essence beingProcessed is being used a lock for MutEx purposes Question: How can I deal with concurrency issues on the beingProcessed "lock" itself based on the above load? I think read-modify-write operation on the beingProcessed needs to be atomic but I'm open to other strategies. Open to other code refinements too.

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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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• Is this a valid pattern for raising events in C#?

  - by Will Vousden

  Update: For the benefit of anyone reading this, since .NET 4, the lock is unnecessary due to changes in synchronization of auto-generated events, so I just use this now: public static void Raise<T>(this EventHandler<T> handler, object sender, T e) where T : EventArgs { if (handler != null) { handlerCopy(sender, e); } } And to raise it: SomeEvent.Raise(this, new FooEventArgs()); Having been reading one of Jon Skeet's articles on multithreading, I've tried to encapsulate the approach he advocates to raising an event in an extension method like so (with a similar generic version): public static void Raise(this EventHandler handler, object @lock, object sender, EventArgs e) { EventHandler handlerCopy; lock (@lock) { handlerCopy = handler; } if (handlerCopy != null) { handlerCopy(sender, e); } } This can then be called like so: protected virtual void OnSomeEvent(EventArgs e) { this.someEvent.Raise(this.eventLock, this, e); } Are there any problems with doing this? Also, I'm a little confused about the necessity of the lock in the first place. As I understand it, the delegate is copied in the example in the article to avoid the possibility of it changing (and becoming null) between the null check and the delegate call. However, I was under the impression that access/assignment of this kind is atomic, so why is the lock necessary? Update: With regards to Mark Simpson's comment below, I threw together a test: static class Program { private static Action foo; private static Action bar; private static Action test; static void Main(string[] args) { foo = () => Console.WriteLine("Foo"); bar = () => Console.WriteLine("Bar"); test += foo; test += bar; test.Test(); Console.ReadKey(true); } public static void Test(this Action action) { action(); test -= foo; Console.WriteLine(); action(); } } This outputs: Foo Bar Foo Bar This illustrates that the delegate parameter to the method (action) does not mirror the argument that was passed into it (test), which is kind of expected, I guess. My question is will this affect the validity of the lock in the context of my Raise extension method? Update: Here is the code I'm now using. It's not quite as elegant as I'd have liked, but it seems to work: public static void Raise<T>(this object sender, ref EventHandler<T> handler, object eventLock, T e) where T : EventArgs { EventHandler<T> copy; lock (eventLock) { copy = handler; } if (copy != null) { copy(sender, e); } }

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• Can shared memory be read and validated without mutexes?

  - by Bribles

  On Linux I'm using shmget and shmat to setup a shared memory segment that one process will write to and one or more processes will read from. The data that is being shared is a few megabytes in size and when updated is completely rewritten; it's never partially updated. I have my shared memory segment laid out as follows: ------------------------- | t0 | actual data | t1 | ------------------------- where t0 and t1 are copies of the time when the writer began its update (with enough precision such that successive updates are guaranteed to have differing times). The writer first writes to t1, then copies in the data, then writes to t0. The reader on the other hand reads t0, then the data, then t1. If the reader gets the same value for t0 and t1 then it considers the data consistent and valid, if not, it tries again. Does this procedure ensure that if the reader thinks the data is valid then it actually is? Do I need to worry about out-of-order execution (OOE)? If so, would the reader using memcpy to get the entire shared memory segment overcome the OOE issues on the reader side? (This assumes that memcpy performs it's copy linearly and ascending through the address space. Is that assumption valid?)

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