I need to post-process result of CompletableFuture.supplyAsync execution to get intermediate result. My code looks following In a result I’m facing with java.util.concurrent.CompletionException: java.lang.IllegalMonitorStateException on .thenAccept(resultPerBatch -> { line Seems like I’m using …
Tag: locking
Java Thread Race, Code messes up after changing System.out.println
I am having issues with my program printing out only one winner and still allowing the other threads to finish the race while printing their time. When I take out the System.out.println line it messes everything up and I have no idea how and why it is possible. I am using the Runnable and lock statements and …
What is the purpose of fairness parameter in REENTRANT LOCK in JAVA?
I found the following text while going through Java doc of Reentrant lock: fairness of locks does not guarantee fairness of thread scheduling. Thus, one of many threads using a fair lock may obtain it multiple times in succession while other active threads are not progressing and not currently holding the loc…
Try-finally with lock when no exception is thrown
In the java manual it says that it is recommended to use try-finally when using lock() and unlock(), but this is also necessary when an exception is never thrown in the try block? for example: Answer Adding it always is a reasonable advice: For a beginner, because they may not be aware of all the ways excepti…
How can I guarantee a thread is safely unlocking a lock upon termination, while all methods already handle it?
A server project, might run for very long time and create many threads. In the following code I ask myself do i have to protect the lock somehow in addition to an overall try catch in method setData(MyData data): note: assuming its thread-safe, i am not really familiar with other reasons or natural disasters …
Execute query with MySQL GET_LOCK function in Hibernate
My application uses Hibernate as ORM. I am trying to execute few mysql locking function within my application like GET_LOCK, IS_FREE_LOCK, RELEASE_LOCK (https://dev.mysql.com/doc/refman/5.6/en/locking-functions.html). However I am running into following issue: Here is my Dao code: I am not sure how to execute…
Implementing a resource read/write lock in Java
I’m trying to implement a simple read/write lock for a resource accessed concurrently by multiple threads. The workers randomly try reading or writing to a shared object. When a read lock is set, workers should not be able to write until the lock is released. When a write lock is set, read and write are…
Mutex Locks vs Peterson’s Algorithm?
Do mutex locks ensure bounded waiting condition ? Is it possible if two threads are trying to get hold of a lock, but only one process (just by luck) gets it again and again. Since Peterson’s Algorithm ensures bounded waiting, is it better to use that instead of mutex locks ? Answer It is possible to ha…
How to avoid two different threads read the same rows from DB (Hibernate and Oracle 10g)
Let’s suppose I got two different threads, T1 and T2, accessing concurrently the same database and fetching data from the same table. Now on thread startup I need to fetch data from the table and store the rows into a collection, that I will then use to perform some work elsewhere. I don’t want th…
JPA PessimisticLockScope.NORMAL and locking “relationships”
I am studying JPA Documentation and encountered the following lines: Entity relationships for which the locked entity contains the foreign key will also be locked, but not the state of the referenced entities (unless those entities are explicitly locked). Element collections and relationships for which the en…