synchronization

public class counting { private static int counter = 0; public void boolean counterCheck(){ counter++; if(counter==10) counter=0; } } Method counterCheck can be accessed by multiple threads in my application. I know that static variables are not thread safe. I would appreciate if someone can help me with example or give me reason why I have to synchronize method or block. What will happen if I don't synchronize? This is not thread safe, AND this pattern of updating a count from multiple threads is probably the #1 way to achieve negative scaling (it runs slower when you add more threads) of a

In a Cocoa app, I have a setup like this: The main thread (M) can submit requests to a some background "producer" thread (B) to get some work done, say the result of a computation on item X. A different background thread (C) shortly thereafter might want the results of computing item X, and want those results synchronously. Thread C could just re-do the work synchronously itself, but if thread B happens to be in the middle of computing item X already, I would like thread C to block and get the results from B. The results of the computation are findable on disk, so the data passing is not the

When one must synchronize programs (shell scripts) via file system, I have found an flock -based solution to be recommended (should also work on NFS ). The canonical example for usage from within a script (from http://linux.die.net/man/1/flock ) is: ( flock -s 200 # ... commands executed under lock ... ) 200>/var/lock/mylockfile I don't quite get why this whole construct ensures atomicity. In particular, I am wondering in which order flock -s 200 and 200>/var/lock/mylockfile are executed when e.g. bash executes these lines of code. Is this order guaranteed/deterministic? The way I understand

I'm wondering if there's a package or model that will help me solve this scenario. Let's say I have 3 threads and a bunch of objects A,B,C,D,E,F T1 needs locks A,B T2 needs locks B,C,D T3 needs locks E,F In this scenario, it'd be ok if T1 & T3 ran simultaneously. Also, T2 & T3 can run simultaneously. But T1 & T2 should never run simultaneously. Also, note that Threads can obtain an arbitrary number of locks, not just 2. (I saw an elegant solution to this problem with a fixed number of locks but not sure I can apply it here.) Obviously, I'd like each thread to acquire all the needed locks at

Problem I'm building a postgres database for a few hundred thousand products. I will set-up an index (Solr or maybe ElasticSearch) to improve query times for complex search queries. The point now is how to let the index synchronized with the database? In the past I had a kind of application that polled the database periodically to check for updates that should be done, but I would have an outdated index state time (from the database update to the index update pull). I would prefer a solution in which the database would notify my application (java application) that something has been changed

I have been trying to solve a problem involving thread communication using wait() and notify(). Basically i have 2 threads T1 and T2 and i want them to be executed in the following order T1 , T2, T1, T2 ..... How can i achieve that? Actual Problem: There are 2 threads T1 - which prints odd numbers (say 1 - 100) and T2 - which prints even numbers (1 - 100). Now, the output should be 1, 2, 3, 4 , 5 , .... 100 You describe a Producer-Consumer pattern. It's java implementations described in numerous java books including M.Grand "Patterns in Java. Volume I" and "Java 2: The Complete Reference" by

I need to keep synchronized two folder on different host in Windows. I really think that something already done exists but I did not find anything (SyncToys is not an option), do you have something to suggest me? Requirements are: running as a service sync over a network shared path (ie \\myhost\myfolder ) syllogism I would say use rsync with task scheduler to accomplish what you're wanting. There are several ports of rsync to windows, you might check out the following: DeltaCopy cwrsync After a long search, I found SuperFlexible . Maybe that's the answer - and it doesn't cost much. Real Time