Is there a possibility to set priority to tasks which are executed by Executors? I've found some statements in JCIP about it's possible but I cannot find any example and I cannot find anything related in docs. From JCIP: An execution policy specifies the "what, where, when, and how" of task execution, including: ... ...
Does the following java code guarantee and exclusive lock on an unopened file in Windows? import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; public class Test { public static void main(String[] args) { File file = new File("mylog.log"); try { ...
I have a computing map (with soft values) that I am using to cache the results of an expensive computation. Now I have a situation where I know that a particular key is likely to be looked up within the next few seconds. That key is also more expensive to compute than most. I would like to compute the value in advance, in a minimum-pr...
What is the best way to share a file between two "writer" services in the same application? Edit: Sorry I should have given more details I guess. I have a Service that saves entries into a buffer. When the buffer gets full it writes all the entries to the file (and so on). Another Service running will come at some point and read the fi...
In a web service that I am working on, a user's data needs to be updated in the background - for example pulling down and storing their tweets. As there may be multiple servers performing these updates, I want to ensure that only one can update any single user's data at one time. Therefore, (I believe) I need a method of doing an atomic ...
Hi all, I'm writing a small multithreaded client-side python application that contains a small webserver (only serves page to the localhost) and a daemon. The webserver loads and puts data into a persistent "datastore", and the daemon processes this data, modifies it and adds some more. It should also takes care of the synchronization w...
What is the best way to restrict concurrent user access in any web application? Existing problem: We have different reports in our web application. if one user is accessing any report we must not allow other users to access the same report. How can we achieve this? Proposed solution: create singleton class which will hold the report...
Possible Duplicate: Ive heard i++ isnt thread safe, is ++i thread-safe? Hi all, Yesterday I did interesting investigation on behavior of ++ operator in multithreaded environment. I knew for a long time that this code is not thread safe: (C-like pseudocode) int i = 0; thread() { for (int j = 0;j < 1000000;j++) { ...
Hi, I have some code where i execute a several tasks using Executors and a Blocking Queue. The results have to be returned as an iterator because that is what the application that i work on expects. However, there is a 1:N relationship between the task and the results added to the queue, so i cannot use the ExecutorCompletionService. W...
I have already read the hibernate docs about concurrency and I think, I have understood the available locking methods, but I am not sure how I should implement the following scenario. Two clients F (fast) and S (slow) access the database and can modify the same objects. Now, one additional requirement: It is critical to the application...
I am developing a set of applications that all hit the same database, and concurrency has been one of the biggest issues I've had to deal with. I'm developing solutions to work around these issues, and I recently thought of using SQL queries instead of LINQ queries to update databases. Because SQL has pessimistic concurrency control, ...
Many people at SO adviced to dive into Java concurrency by reading Java Concurrency in Practice (JCIP), sometimes Doug Lea's book of 1999 is mentioned as well: http://stackoverflow.com/questions/1237980/java-5-concurrency-book-recommendations http://stackoverflow.com/questions/452391/recommended-books-on-concurrency-synchronization-mec...
I've noticed something very strange yesterday. It seems that two threads are entering two synchronized blocks locking on the same object at the same time. The class (MyClass) containing the relevant code looks similar to this: private static int[] myLock = new int[0]; protected static int methodA(final long handle, final byte[] so...
I want to test concurrency, and reliably replicate an issue that JMeter brought to my attention. What I want to do is set a unique identifier (currently the time in milliseconds with a counter appended) and increment the counter between loops but not between threads. The idea being that the number of threads I have set up is the number ...
I recently inherited a simple PHP application built on Piwi (http://www.piwiframework.de/default.html). Has anyone deployed this framework in a high-availability high-concurrency scenario? I was thinking about 5000 concurrent users (at least) with a 2-3 hour burst totaling about 15-50k unique sessions. I'm not asking if php can be scal...
I'm currently working on some concurrent code that would appear to have a few race conditions in it. I'm attempting to debug the code using my current IDE, Eclipse, but I'm not completely satisfied. In particular, a race condition is present for a variable such that without a break point on one of the methods accessing it (the one 'getti...
On CPUs like x86, which provide cache coherency, how is this useful from a practical perspective? I understand that the idea is to make memory updates done on one core immediately visible on all other cores. This is a useful property. However, one can't rely too heavily on it if not writing in assembly language, because the compiler c...
Few listings from JCIP already appeared here. Here is one more (orig. code): public class ThreadGate { private boolean isOpen; private int generation; public synchronized void close() { isOpen = false; } public synchronized void open() { ++generation; isOpen = true; notifyAll(); ...
When I click on link 1 and then, before the response was received, click on link 2 on the same page, I get a "Page Expired" error from Wicket. Is Wicket conceptional capable to do such a concurrent processing? Any ideas why Wicket loses the session (it seems to reside on tomcat though)? ...
I'm trying to make an actor 'go to sleep' waiting for another actors signal. I want to do something like: def act(){ loop{ //Should I use loop here too?? if(sleepy){ react{ //SLEEPING case "Wake Up"=> sleepy=false; //just to breack the react } }else{ ...