concurrency

问题 How can I implement class CaseInsensitiveConcurrentMap<V> implements ConcurrentMap<String , V> which works just like ConcurrentHashMap<String , V> except that the keys are compared case-insensitively? The keys should not be converted to lowercase or uppercase. Note that Collections.synchronizedMap(new TreeMap<String, new MyCaseInsensitiveComparator()) is no solution as it allows no concurrency and misses the additional methods. Creating a String-like class with case-insensitive equals and

问题 I am trying to understand the concept of synchronized blocks in java. As of the documents that I have read, I understood that if we acquire a lock ( synchronized block using an instance variable ) then we cannot acquire a synchronized lock on same object in that class. But when I tried practically using the following snippet I found that my understanding is going wrong. I.e I am able to acquire lock (synchronized block on same instance variable) in two different methods at the same time. When

问题 I am learning hibernate optimistic lock mechanism and I haven't found answer on my question in user guide Let's say we have entity like this: @Entity class Employee{ @Version Long versionField; List<Employee> subordinates; ... } And somewhere we have following code: Employee sub = .... Emplyee emp = readEmploye(); emp.getSubordinates().add(sub); Can I control of version incrementation at this case ? 回答1: By default no. Since you're not changing the entity, but rather other entities that are

问题 I am learning hibernate optimistic lock mechanism and I haven't found answer on my question in user guide Let's say we have entity like this: @Entity class Employee{ @Version Long versionField; List<Employee> subordinates; ... } And somewhere we have following code: Employee sub = .... Emplyee emp = readEmploye(); emp.getSubordinates().add(sub); Can I control of version incrementation at this case ? 回答1: By default no. Since you're not changing the entity, but rather other entities that are

问题 I have a few function calls that return Flowable object. I have to call this function multiple times and this function is doing some network calls. I want to do all these calls concurrently. Below is the code. Interface containing the function public Interface XYZDownstreamService { Flowable<String> getData(Request request); } Below is the Caller public List<String> getDataFromDownstreamForRequests(List<Request> requests, XYZDownstreamService service) { List<String> dataFromDownstream = Lists

问题 I have the following case where attachDirty saveOrUpdate() always tries to persist the entities when the transactional annotated method is called in burst. Is there a way to avoid this primary key constraint violation exception? I thought that saveOrUpdate() would persist if the entity is not yet created and update it otherwise. I used this ..orUpdate() instead of persist() as a way to handle these bursts. There is no data corruption actually. Because the first saveOrUpdate() does save 1

问题 There is a SynchronousProducer interface, that supports two operations: public interface SynchronousProducer<ITEM> { /** * Produces the next item. * * @return produced item */ ITEM next(); /** * Tells if there are more items available. * * @return true if there is more items, false otherwise */ boolean hasNext(); } Consumer asks the producer if there are more items available and if none goes into a shutdown sequence. Now follows the issue. At the moment there is a for-loop cycle that acts as

问题 Lets say we have some kind of pub/sub protocol. When someone is connecting and subscribing, we can save channel in Map, List or ChannelGroup: @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { super.channelActive(ctx); log.debug("Client connected: {}", ctx.channel().remoteAddress()); clients.add(ctx); } After that, when some message has come or some event has happened, I can notify clients: @Override public void channelRead(ChannelHandlerContext ctx, Object msg)

问题 I’m working on a stateful and websocket server on Node. We require a piece of read-only data that is important for the biz logic and save it in Node’s global scope, and recently we have to invalidate this require cache and re-require to allow changes of this piece of data at runtime. My question is should we worry simply reassigning the global variable the result of the re-require would cause issues between concurrent connections which read this single copy of data at different phases? Thanks

问题 Java 8 environment. run tasks using CompletableFuture.allOf() concurrently and then get each result from each thread and then combine all results into one combinedResult and return it. In the below code, to get the result ( = List<Student> ) it doesn't have to be the code between I. and II. They say I need to use join() but didn't work I also got some allOf() from Java 8 CompletableFuture.allOf(...) with Collection or List and other links, but nothing works for me. I think I miss some very