Hi
We are using EJB3 and we've created an interceptor to check whether the user
has already sent a request or not.
if we noticed that the user has already sent a request then in this interceptor
we need to suspend that thread and wait till the former request being completed
otherwise the thread will proceed. This suspension should be applied if the
same user has already a request and for other users this is not the case.
in order to find whether or not a user has sent a request, each time a request
comes, we store its user id in a Map structure.
here is the body of our interceptor
|
| public class ConcurrectBankingTransaction {
|
| private static Map<Long,Condition> users = new
HashMap<Long,Condition>();
| private static final Lock lock = new ReentrantLock();
|
| @AroundInvoke
| public Object check(InvocationContext context) throws Throwable {
| Object result = null;
| if(context.getParameters() == null) {
| //TODO what....
| }
| Object obj = context.getParameters()[0];
| String cmSessionId = null;
| cmSessionId = ((BaseDto)obj).getCmSessionId();
| Long userId = null;
| if (cmSessionId == null) {
| if(obj instanceof LoginDto) {
| UserInfoDto entity = findUser((LoginDto) obj);
| if (entity != null) {
| userId = entity.getId();
| }else {
| //TODO what to do...
| }
| }else {
| //TODO what to do...
| }
| }else {
| try {
| userId =
(CurrentSessionData.getUserId(cmSessionId));
| } catch (ChannelManagerException e) {
| //TODO handle the exception here...
| e.printStackTrace();
| }
| }
|
| //acquires the lock
| lock.lock();
| try {
| if(contains(userId)) {
| final Condition inProcessTransaction =
getLockForUserId(userId);
| while (contains(userId)) {
| try {
| //this releases the lock and
causes the current thread to be waiting...
|
inProcessTransaction.await(2000, TimeUnit.MILLISECONDS);
| } catch (InterruptedException e) {
| // It's OK
| }
| }
| addUserId(userId,inProcessTransaction);
| }else {
| addUserId(userId,lock.newCondition());
| }
| }finally {
| lock.unlock();
| }
|
| try {
| result = context.proceed();
| }catch (Throwable e) {
| //any throwable supposed to be caught to release the
previous lock condition
| getLockForUserId(userId).signal();
| removeUserId(userId);
| throw e;
| }
|
| //notifying the condition to proceed the awaiting thread
| getLockForUserId(userId).signal();
| removeUserId(userId);
| return result;
| }
|
|
now, I am skeptical on the way this works. I just created this interceptor
based on information gathering through the internet and not sure that works
fine. Unfortunately, I can't create a situation in which we can test the system.
I have seen a CountDownLatch but I fear to use that because no knowledge I have
about that.
I appreciate if you can help me on this or if you have any other idea on how to
suspend other threads
thank you very much
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