synchronization

问题 What is the difference between synchronized methods and synchronized statements ? If possible, please use an example to make it more clear. 回答1: A synchronized method locks the monitor associated with the instance of the class (ie 'this') or the class (if a static method) and prevents others from doing so until the return from the method. A synchronized block can lock any monitor (you tell it which) and can have a scope smaller than that of the encolsing method. Synchronized blocks are

问题 I'm designing a base class that, when inherited, will provide business functionality against a context in a multithreaded environment. Each instance may have long-running initialization operations, so I want to make the objects reusable. In order to do so, I need to be able to: Assign a context to one of these objects to allow it to do its work Prevent an object from being assigned a new context while it already has one Prevent certain members from being accessed while the object doesn't have

问题 Is there any way to check how many threads are waiting for a synchronized method to become unlocked? I would like to know when the thread calls a synchronized method: 1) How many threads are already waiting to call the method? 2) Once the method is called how long it needed to wait for the method to become unlocked? Solution: I solved this using stackers answer: public class LockedClass { public static int count; public static void measuringClass() throws IOException{ long startTime = System

问题 I've read this answer in the end of which the following's written: Anything that you can with volatile can be done with synchronized, but not vice versa. It's not clear. JLS 8.3.1.4 defines volatile fields as follows: A field may be declared volatile, in which case the Java Memory Model ensures that all threads see a consistent value for the variable (§17.4). So, the volatile fields are about memory visibility. Also, as far as I got from the answer I cited, reading and writing to volatile

问题 Is there any implementation of monitor on Windows? I didn't see any win32 API references Monitor. 回答1: Windows does not have a monitor implementation of its own. However, Vista introduced Condition Variables and Slim Reader/Writer locks, which can be used together to create a monitor implementation. 回答2: Yes it does. Windows has monitors and monitor functions: EnterCriticalSection is similar to POSIX pthread_mutex_lock (enters the monitor). LeaveCriticalSection is similar to POSIX pthread

问题 class MyService { public void a() { synchronized(somekey) { b(); } } @Transactional(propagation = Propagation.REQUIRES_NEW) public void b() { ...do DB works... } } My aim is 1 - get the key 2 - start transaction 3 - commit transaction 4 - release the key When i call a() method from outside, transaction doesn't work. Any suggestions ? Thanks. 回答1: Unless you're using code weaving, this can't work. The default way Spring handles transactions is through AOP proxies. The call to a transactional

问题 I created two threads and using a single instance of class called the static and non-static methods of that object. Ideally static methods need to be called using the class name and i did that too. I synchronized both the static and non-static methods on a private static member of the class whose methods the threads are calling. I noticed that the output was synchronized! My questions are: Static methods if synchronized using a synchronized block it usually requires the class instance, then

问题 I'm writing a fast multi-thread program, and I want to avoid syncronization (the function which would need to be syncronized must be called something like 5,000,000 times per second, so even a mutex would be too heavy). The scenario is: I have a single global instance of a class, and each thread can access it. In order to avoid syncronization, all the data inside the class is accessed read-only, except for a bunch of class members, which are then declared in TLS (with __thread or __declspec

问题 Specifically, can somebody tell me what is wrong with this piece of code. It should start the threads, so should print "Entering thread.." 5 times and then wait until notifyAll() is called. But, it randomly prints "Entering.." and "Done.." and still keeps waiting on others. public class ThreadTest implements Runnable { private int num; private static Object obj = new Object(); ThreadTest(int n) { num=n; } @Override public void run() { synchronized (obj) { try { System.out.println("Entering

问题 I have a trigger function: CREATE OR REPLACE FUNCTION "trigger_deleteUsers"() RETURNS trigger AS $BODY$ BEGIN INSERT INTO "DeletedEntities" ("uuidKey", "dateCreated", "dateModified", "dateSynced", "username", "entityName") VALUES (OLD."uuidKey", OLD."dateCreated", OLD."dateModified", "dateSynced", OLD."username", 'Users'); RETURN NULL; END; $BODY$ LANGUAGE plpgsql; CREATE TRIGGER "deleteUsers" AFTER DELETE ON "Users" FOR EACH ROW EXECUTE PROCEDURE "trigger_deleteUsers"(); This works for the