locking

问题 i want to add an item into a global list every 2 seconds in one thread, and save the list into database before empty it every 3 seconds in another thread. i create two local varibles to monitor the total added items and total saveditems, they should be equal every 6 senconds,but it is not. here is my code: import datetime import psutil,os,time from threading import * class AddToList(Thread): totalAdded=0 def run(self): lock=RLock() lock.acquire() while True: entryList.append("AddToList at "

问题 I work with multethreading bug. Now I see that for some reason lock isn't executed even once but is locked. I have the next class: public sealed class Foo { private readonly object _lock = new object(); private static ulong _inCnt = 0; public void SomeMethod(ulong poo) { lock (_lock) { _inCnt++; ... [some code] } } } I paused all threads in the VS, inspected all of them and see that there is only one thread in the SomeMethod and it is waiting for lock (_lock) to be freed (_inCnt = 0) . I

问题 I've read this topic, and this blog article about try with resources locks, as the question popped in my head. But actually, what I'd rather like would be a try with lock , I mean without lock instantiation. It would release us from the verbose lock.lock(); try { //Do some synchronized actions throwing Exception } finally { //unlock even if Exception is thrown lock.unlock(); } Would rather look like : ? implements Unlockable lock ; ... try(lock) //implicitly calls lock.lock() { //Do some

问题 http://www.codeproject.com/Articles/28785/Thread-synchronization-Wait-and-Pulse-demystified Queues: The ready queue is the collection of threads that are waiting for a particular lock. The Monitor.Wait methods introduce another queue: the waiting queue. This is required as waiting for a Pulse is distinct from waiting to acquire a lock. Like the ready queue, the waiting queue is FIFO. Recommended pattern: These queues can lead to unexpected behaviour. When a Pulse occurs, the head of the

问题 In production environments where Django is running on Apache or with multiple Gunicorn workers, it runs the risk of concurrency issues. As such, I was pretty surprised to find that Django's ORM doesn't explicitly support table/row locking. It supports transactions very handedly, but that only solves half of the concurrency problem. With a MySQL backend, what is the correct way to perform locking in Django? Or is there something else at play in Django's framework that makes them unnecessary?

问题 1)Is there a pragma or any way to know the current lock state of sqlite db?. 2)Also, Is there a way to know if any other process is using the DB?. 回答1: Regarding #1: No, because the answer you got would be immediately stale (that is if you got an answer of "no the database isn't locked", someone else could come along and immediately lock it, leaving you with bad info). The correct approach is to simply try your operation (optionally with a timeout) and see if it succeeds. 回答2: No pragma, but

问题 Checkstyle reports this code as "The double-checked locking idiom is broken", but I don't think that my code actually is affected by the problems with double-checked locking. The code is supposed to create a row in a database if a row with that id doesn't exist. It runs in a multi-threaded environment and I want to avoid the primary-key-exists SQL-exceptions. The pseudo-code: private void createRow(int id) { Row row = dao().fetch(id); if (row == null) { synchronized (TestClass.class) { row =

问题 I'd like to lock specified row(s) in my table exclusively, so no reads no updates allowed until the actual transaction completes. To do this, I've created a helper class in my database repository: public void PessimisticMyEntityHandler(Action<IEnumerable<MyEntity>> fieldUpdater, string sql, params object[] parameters) { using (var scope = new System.Transactions.TransactionScope()) { fieldUpdater(DbContext.Set<MyEntity>().SqlQuery(sql, parameters)); scope.Complete(); } } Here is my test code.

问题 Normally when I ask for a thread dump, the symptoms of a poorly performing system are easily explained; i.e. normally I would be able to see that a number of threads are clearly waiting on a monitor which has been acquired but not released by another. In this case, I have a lot of threads waiting for a monitor (0x965ad100), but none appears to have that monitor in the first place. The threads in question can be identified with this signature: waiting to lock <0x965ad100> (a uk.gov.dti.og.fox

问题 I have read a lot about the dangers of double checked locking and I would try hard to stay away of it, but with that said I think they make a very interesting read. I was reading this article of Joe Duffy about implementing singleton with double checked locking: http://www.bluebytesoftware.com/blog/PermaLink,guid,543d89ad-8d57-4a51-b7c9-a821e3992bf6.aspx And the (variant of) solution he seemed to propose is this: class Singleton { private static object slock = new object(); private static