How and what you lock on depends upon what you’re doing. Let’s say that you’re working with a device of some kind – say a coffee maker. You might have a class that looks like this: public CoffeeMaker { private IntPtr _coffeeHandle; private Object _lock = new Object(); } In this case, you are protecting … Read more
Needed this answer myself and from the link provided by David Moye, decided on this and thought it might be of use to others with the same question: CREATE PROCEDURE … AS BEGIN BEGIN TRANSACTION — lock table “a” till end of transaction SELECT … FROM a WITH (TABLOCK, HOLDLOCK) WHERE … — do some … Read more
Just a wild guess here… but if the compiler let you lock on a value type, you would end up locking nothing at all… because each time you passed the value type to the lock, you would be passing a boxed copy of it; a different boxed copy. So the locks would be as if … Read more
MongoDB Locking is Different Locking in MongoDB does not work like locking in an RDBMS, so a bit of explanation is in order. In earlier versions of MongoDB, there was a single global reader/writer latch. Starting with MongoDB 2.2, there is a reader/writer latch for each database. The readers-writer latch The latch is multiple-reader, single-writer, … Read more
I would say the error lies in the object _bikes not being thread safe. As commented, somewhere there is a modify of the _bikes object that is not being lock’ed. It is a split second error where the variable bs is set up to a size X when the size of _bikes is measured. In … Read more
The difference lies in locking mechanism. PESSIMISTIC_READ lock means that dirty reads and non-repeatable reads are impossible when you have such a lock. If data should be changed it’s required to obtain PESSIMISTIC_WRITE lock PESSIMISTIC_WRITE lock guarantees that besides dirty and non-repeatable reads are impossible you can update data without obtaining additional locks(and possible deadlocks … Read more
Yes, NOLOCK will propagate to the tables used by the view definition (at least in SQL Server 2005). See Table Hints in MSDN: In SQL Server 2005, all lock hints are propagated to all the tables and views that are referenced in a view. Also, SQL Server performs the corresponding lock consistency checks. However, If … Read more
Handle should do the trick. Ever wondered which program has a particular file or directory open? Now you can find out. Handle is a utility that displays information about open handles for any process in the system. You can use it to see the programs that have a file open, or to see the object … Read more
All those answers I see are way too complicated. Why not simply use: public void executeInNamedLock(String lockName, Runnable runnable) { synchronized(lockName.intern()) { runnable.run(); } } The key point is the method intern: it ensures that the String returned is a global unique object, and so it can be used as a vm-instance-wide mutex. All interned … Read more
From MySQL 5.7 onwards, this is possible, but requires first enabling the mdl instrument in the performance_schema.setup_instruments table. You can do this temporarily (until the server is next restarted) by running: UPDATE performance_schema.setup_instruments SET enabled = ‘YES’ WHERE name=”wait/lock/metadata/sql/mdl”; Or permanently, by adding the following incantation to the [mysqld] section of your my.cnf file (or … Read more