java.util.concurrent

I am writing an application which will return a HashMap to user. User will get reference to this MAP. On the backend, I will be running some threads which will update the Map. What I have done so far? I have made all the backend threads so share a common channel to update the MAP. So at backend I am sure that concurrent write operation will not be an issue. Issues I am having If user tries to update the MAP and simultaneously MAP is being updated at backend --> Concurrent write operation problem. If use tries to read something from MAP and simultaneously MAP is being updated at backend -->

If we use an ExecutorCompletionService we can submit a series of tasks as Callable s and get the result interacting with the CompletionService as a queue . But there is also the invokeAll of ExecutorService that accepts a Collection of tasks and we get a list of Future to retrieve the results. As far as I can tell, there is no benefit in using one or over the other (except that we avoid a for loop using an invokeAll that we would have to submit the tasks to the CompletionService ) and essentially they are the same idea with a slight difference. So why are there 2 different ways to submit a

This question already has an answer here: How to understand happens-before consistent 4 answers While reading Java docs on Memory Consistency errors. I find points related to two actions that creates happen - before relationship: When a statement invokes Thread.start() , every statement that has a happens-before relationship with that statement also has a happens-before relationship with every statement executed by the new thread. The effects of the code that led up to the creation of the new thread are visible to the new thread. When a thread terminates and causes a Thread.join() in another

I have spent a while learning the topic of Scala execution contexts, underlying threading models and concurrency. Can you explain in what ways does scala.concurrent.blocking "adjust the runtime behavior" and "may improve performance or avoid deadlocks" as described in the scaladoc ? In the documentation , it is presented as a means to await api that doesn't implement Awaitable. (Perhaps also just long running computation should be wrapped?). What is it that it actually does? Following through the source doesn't easily betray its secrets. blocking is meant to act as a hint to the

One of the four major changes brought to java 6 with regards to improving the performance of intrinsic locks is Adapative Spinning technique. What exactly is adaptive spinning? Is it a combination of spinlocks and mutex lock? Can someone explain in an easy to understand way the usefulness of this strategy which by default is available from JDK6 onwards. What exactly is adaptive spinning? To quote from this Java 6 performance page : Adaptive spinning is an optimization technique where a two-phase spin-then-block strategy is used by threads attempting a contended synchronized enter operation.

How will you execute Three threads sequentially? For eg. Thread1, Thread2, Thread3. It is not possible to pass the reference of one Thread to the other and invoke from the run() method. So code should be like this: Thread1.start(); Thread2.start(); Thread3.start(); and out put should be Printing Thread1 Printing Thread2 Printing Thread3 This can be possible by using ThreadPoolExecutor and using a blocking queue but even that is not an acceptable answer. Use ExecutorService in java.util.concurrent package. More precisely use Executors.newSingleThreadExecutor(); You could use Executors