First of, please think long and hard if you really want to disable the Home button or any other button for that matter (e.g. the Back button), this is not something that should be done (at least most of the times, this is a bad design). I can speak only for myself, but if I … Read more
The following code should do the job, it is cross-platform and runs on Python 2.4-3.2. I tested it on Windows, OS X and Linux. from tendo import singleton me = singleton.SingleInstance() # will sys.exit(-1) if other instance is running The latest code version is available singleton.py. Please file bugs here. You can install tend using … Read more
Found an article titled “MYSQL WITH NOLOCK” https://web.archive.org/web/20100814144042/http://sqldba.org/articles/22-mysql-with-nolock.aspx in MS SQL Server you would do the following: SELECT * FROM TABLE_NAME WITH (nolock) and the MYSQL equivalent is SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED ; SELECT * FROM TABLE_NAME ; SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ ; EDIT Michael Mior suggested the following … Read more
Worst (won’t actually work) Change the access modifier of counter to public volatile As other people have mentioned, this on its own isn’t actually safe at all. The point of volatile is that multiple threads running on multiple CPUs can and will cache data and re-order instructions. If it is not volatile, and CPU A … Read more
Can anyone tell me the advantage of the synchronized method over the synchronized block with an example? Thanks. There is not a clear advantage of using synchronized method over the block. Perhaps the only one ( but I wouldn’t call it an advantage ) is you don’t need to include the object reference this. Method: … Read more
A good resource for understanding why volatile is needed comes from the JCIP book. Wikipedia has a decent explanation of that material as well. The real problem is that Thread A may assign a memory space for instance before it is finished constructing instance. Thread B will see that assignment and try to use it. … Read more
What about the “JFDI” pattern? BEGIN TRY INSERT etc END TRY BEGIN CATCH IF ERROR_NUMBER() <> 2627 RAISERROR etc END CATCH Seriously, this is quickest and the most concurrent without locks, especially at high volumes. What if the UPDLOCK is escalated and the whole table is locked? Read lesson 4: Lesson 4: When developing the … Read more
It is bad form to use this in lock statements because it is generally out of your control who else might be locking on that object. In order to properly plan parallel operations, special care should be taken to consider possible deadlock situations, and having an unknown number of lock entry points hinders this. For … Read more
Optimistic Locking is a strategy where you read a record, take note of a version number (other methods to do this involve dates, timestamps or checksums/hashes) and check that the version hasn’t changed before you write the record back. When you write the record back you filter the update on the version to make sure … Read more
What is the advantage of using this type of object to lock? Why would there be an advantage to a specific type of lock object? As the manual states: Best practice is to define a private object to lock on, or a private static object variable to protect data common to all instances. Can I … Read more