locking

问题 I've a table which is something like a list of URL I want to visit. The table is not referenced nor references other tables. What my application do is: select some rows from the list of URL start a cycle on them start a transacion visit the url elaborate it start a sub-transaction check if the results are already in the first two tables (select) if not, save it (insert) commit the sub-transaction start a sub-transaction check if the results are already in another table (select) if not, save

问题 So I just read about redlock. What I understood is that it needs 3 independent machines to work. By independent they mean that all the machines are masters and there is no replication amongst them, which means they are serving different types of data. So why would I need to lock a key present in three independent redis instances acting as masters ? What are the use cases where I would need to use redlock ? 回答1: So why would I need to lock a key present in three independent redis instances

问题 Is there anyway to lock on the object equality instead of referential equality in Scala/Java e.g. def run[A](id: A) = id.synchronized { println(s"Processing $id") Thread.sleep(5000) println(s"Done processing $id") } Seq(1, 1, 2, 3, 1).par.foreach(run) I want this to print something like: Processing 3 Processing 1 Processing 2 // 5 seconds later Done processing 1 Done processing 2 Done processing 3 Processing 1 // 5 seconds later Done processing 1 Processing 1 // 5 seconds later Done

问题 I have the following situation: A table ( MyTable ) should be processed (updates/inserts/deletes etc) by a batch process (a call to a myplsql() procedure). During myplsql execution no one should touch MyTable - so MyTable is locked in exclusive mode by myplsql . Now MyTable has a number of on insert , on update , on delete triggers defined but those are not needed while performing batch processing - moreover they slow down the batch process extremely. So the solution is to disable the

问题 I am using the java properties file construct. At the beginning I read it to populate a dialog, but I also give the users the ability to change the values in the dialog and click save. This causes me to call the setProperty method of the properties file. Now, since this webapp can exist over multiple browsers, all changing the same file, I want to be able to "lock" the properties file whenever I am in the "save" method. How can I accomplish this? I've seen similar questions refering to

问题 Question is a follow up to this. The SQL in question was UPDATE stats SET visits = (visits+1) And the question is, for the purpose of performance, does it matter if you lock all rows in stats in comparison to locking the table stats ? Or, if the database uses a page-lock rather than a table/row lock? 回答1: There is no predicate on this. Any self respecting DB engine should work this out and realise all rows need updated. Generally, don't second guess the DB engine: performance is subjectively

问题 I've been on this site a while and I've found so many helpful solutions to the problems I've encountered as I build my first python program. I'm hopeful you guys can help me once again. I am trying to launch a variable number of multiprocesses, with each one taking a small piece of a list to scan. I have been tinkering with queues, but when I implement them, they always add a sizable amount of time to my loop. I am looking to maximize my speed while protecting my Titles.txt from erroneous

问题 I am working on an Android Application where I need to access the different lock screens(e.g.- pin lock,pattern lock etc.) and also able to change it using my application upon some event. I have searched a lot over it but so far I am stuck. Please if anyone can help me out with this problem. Thanks 回答1: See if this page helps:Android Settings You should be able to access the inner elements if you watch the logcat output keenly. Still I am not sure whether you will be able to set a patter or

问题 As far as I understand when you give a user an exclusive lock to a file via flock($handle, LOCK_EX) you stop others from writing to the file until it is released. However is it still possible for others to open a shared lock to read from the file? e,g, flock($handle, LOCK_SH) . This is for a flatfile database system and I want people to be able to still query the database if someone is writing to it, but stop multiple people writing to it at once. 回答1: File reads using "file_get_contents"

问题 While this question is about the MemoryCache class, I can imagine the same need with a Dictionary or ConcurrentDictionary.GetOrAdd where the valueFactory -lambda is also a lengthy operation. In essence I want to synchronize/lock threads on a per-item base. I know MemoryCache is thread safe, but still, checking if an item exists and add the item when it doesn't exist, still needs to be synchronized. Consider this sample code: public class MyCache { private static readonly MemoryCache cache =