locking

Is it possible to lock exclusively entire table with JPA in database agnostic way (without using native queries for instance)? So far I saw only EntityManager.lock(*) but this locks only given record. I don't think this is supported by JPA natively - you always lock single entity or every entity which is a result from a query. Inserts are always allowed as they are new entities. You may either use native query to trigger a lock using SQL supported by your DB server, or you need to lock your insert programmatically. By programmatically I mean that you need to acquire a lock before every insert.

You can see an interesting table at this link. http://norvig.com/21-days.html#answers The table described, Mutex lock/unlock 25 nanosec fetch from main memory 100 nanosec Nanosec? I surprised because mutex lock is faster than fetch data from memory . If so, what mutex lock exactly do? And what does Mutex lock mean at the table? Andrew Savinykh The article you linked does not mentioned the architecture, but judging by mentions of L1 and L2 cache it's Intel. If this is so, then I think that by mutex they meant LOCK instruction. In this respect this post seems relevant: Intel 64 and IA-32 |

I was reading this MSDN article on lockless thread syncing . The article seems to infer that as long as you enter a lock before accessing shared variables, then those variables will be up to date (in .Net 2.0 at least). I got to thinking how this was possible? A lock in .Net is just some arbitrary object that all threads check before accessing memory, but the lock itself has no knowledge of the memory locations that are being accessed. If I have a thread updating a variable, or even a whole chunk of memory, How are those updates guaranteed to be flushed from CPU caches when entering / exiting

On enabling the +XX:PrintSafePointStatistics , I see a dump on the stdout in the following format. Can anyone please help me interpret the column names or the JVM guide which explains this properly? The JVM specification guide does not seem to be covering the meaning of the headers and its explanation at all. @400000005175823c18c9d534 16762.525: GenCollectForAllocation [ 973 0 0 ] [ 0 0 0 5 53 ] 0 @400000005175823c18c9f08c 16762.586: CMS_Initial_Mark [ 973 0 1 ] [ 0 0 0 4 24 ] 0 @400000005175823c18ca0414 16774.619: GenCollectForAllocation [ 975 0 0 ] [ 0 0 0 5 77 ] 0 @400000005175823c18ca0be4

While I understand that JavaScript is inherently single-threaded and generally frowns upon such things, I am wondering if there is any way to get a WebWorker to wait until some data is made available from the main thread without destroying the call stack of the WebWorker. As this is for a fun project, I can use new technologies and things that won't reliably run on older browsers, and I don't mind esoteric hacks as long as they work. Some other solutions that I have thought about: Continuously poll LocalStorage in a loop until there is data at a predetermined key. This would seem to work

I'd like to access a SQLite database from 2 different threads, thereby using 2 different connections to the database. Both threads will mainly perform reads from the DB and will write to the DB only occasionally. If I feel the odds are against both threads writing to the DB at the same time, should I feel safe that I should not have any issues in this scenario ? SQLite is threadsafe and, with recent versions, you can share a single connection among threads. That said, the SQLite FAQ states "Threads Are Evil" (I don't think they mean this in the context of SQLite, but as a general statement).

I am very new to C# and I wanted to ask if I have this situation in MULTI THREADS (pseudo code): public class ClassA { ClassB c = new ClassB(); public void someMethod() { c.myVar = 1; // Some other stuff c.myVar = 0; } } public class ClassB { internal int myVar; public void MethodA() { if(myVar = 1) myVar = 0; } } If someMethod() and MethodA() can be active in separate threads, then MethodA() could evaluate the if statement as true; but before it sets myVar = 0 , someMethod() sets myVar = 0 making it incorrect to have set myVar to 0 in MethodA() !! Basically, how do I lock myVar : can I lock{}