Since this question was asked in 2010, there has been real simplification in how to do simple multithreading with Python with map and pool. The code below comes from an article/blog post that you should definitely check out (no affiliation) – Parallelism in one line: A Better Model for Day to Day Threading Tasks. I’ll … Read more
You’re probably looking forwith (updlock, holdlock). This will make a select grab an exclusive lock, which is required for updates, instead of a shared lock. The holdlock hint tells SQL Server to keep the lock until the transaction ends. FROM TABLE_ITEM with (updlock, holdlock)
This is partly because an AtomicInteger is not a general purpose replacement for an Integer. The java.util.concurrent.atomic package summary states: Atomic classes are not general purpose replacements for java.lang.Integer and related classes. They do not define methods such as hashCode and compareTo. (Because atomic variables are expected to be mutated, they are poor choices for … Read more
Yes, you are right, the user delegates are not synchronized by ConcurrentDictionary. If you need those synchronized it is your responsibility. The MSDN itself says: Also, although all methods of ConcurrentDictionary are thread-safe, not all methods are atomic, specifically GetOrAdd and AddOrUpdate. The user delegate that is passed to these methods is invoked outside of … Read more
When you use NSPrivateQueueConcurrencyType you need to do anything that touches that context or any object belonging to that context inside the -performBlock: method. Your code above is illegal since you’re passing those objects back to the main queue. The new API helps you in solving this, though: You create one context that’s associated with … Read more
I just ran into a similar scenario (“I am interested in a fast Add and Contains and Remove”) and implemented this sucker: using System.Collections.Generic; using System.Threading; namespace BlahBlah.Utilities { public class ConcurrentHashSet<T> : IDisposable { private readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion); private readonly HashSet<T> _hashSet = new HashSet<T>(); #region Implementation of ICollection<T> …ish public … Read more
No, a temp table is limited to the scope of your database connection. You can use the temp table in subsequent calls to the procedure during the same database connection, but other connections cannot access it. They can create a table by the same name, but each temp table will be independent. Temp tables go … Read more
I recommend you go over Using tables as Queues. Properly implemented queues can handle thousands of concurrent users and service as high as 1/2 Million enqueue/dequeue operations per minute. Until SQL Server 2005 the solution was cumbersome and involved a mixing a SELECT and an UPDATE in a single transaction and give just the right … Read more
The main difference between AtomicBoolean and volatile from a practical point of view is that the compare-and-set operation isn’t atomic with volatile variables. volatile boolean b; void foo() { if( b ) { //Here another thread might have already changed the value of b to false b = false; } } But seeing as all … Read more
The API docs for the java.util.concurrent package states the following: […] Additionally, classes are provided only for those types that are commonly useful in intended applications. For example, there is no atomic class for representing byte. In those infrequent cases where you would like to do so, you can use an AtomicInteger to hold byte … Read more