I’ve read from this article that: …Synchronized blocks also guarantee that all variables accessed inside the synchronized block will be read in from main memory, and when the thread exits the synchronized block, all updated variables will be flushed back to main memory again, regardless of whether…
Tag: concurrency
Java happens-before relationship?
Consider the following code. Thread A calls run(), then another thread B calls test() and there shouldn’t be any happens-before relationship. I know it is not guaranteed that thread B sees the changes which thread A made. But is it possible that the output of this program is: Answer Yes, it’s poss…
Is it necessary to make `AtomicBoolean` also `volatile`?
My understanding: Declaring a variable volatile guarantees the visibility for other threads about writes to that variable. Essentially, every write to volatile variable happens-before subsequent reads. I understand the atomicity of AtomicBoolean.compareAndSet() and how it provides the atomicity of read+write …
Is it possible to implement a semaphore that avails permits in timed intervals?
I’m trying to implement a program that allows a maximum of 5 customers to enter a store at once. They move around (one block at a time, max 1 customer per block) and then exit. The problem I’m facing …
How to run async bash command in java?
I’m trying to run an async bash command from a java file and wait for it to finish before I continue the java code execution. At this moment I’ve tried using Callable like so: and I call it like so: Thanks!!! Answer An easier way is to use Java 9+ .onExit(): If you want to block anyway, use .waitF…
How to ensure uniqueness when elasticsearch is inserted in multithreading？
We have some documents of elasticsearch . The uniqueness of the document is determined by some fields together, how to ensure uniqueness when java multi-threading determines whether it exists and is inserted. I didn’t know what good method I had before, so I wrote a method: I guess if it exists, if it d…
Spring Kafka, manual commiting in different threads
Good day collegues. I am using Spring Kafka 2.2.5 I have a listener: I do some operations and if they are succes i use Acknowledge interface to commit offset. I have a problem. While calculations are taking place in the created thread, the listener reads the message from the same offset again. Because of this…
Why should Tomcat’s PersistentValve not be used where there may be concurrent requests per session?
In the class comments at the top of PersistentValve there is a usage constraint: Why is this constraint here? Perusing the code I see three reasons: Concurrent requests for the same session on different Tomcat instances may be subject to “last write wins” and thus potential loss of session data. C…
How to take items from queue in chunks?
I have mulitple producer threads that add objects to a shared queue concurrently. I want to create a singlethread consumer that reads from that shared queue for further data processing (database batch insert). Problem: I want to only take the data from the queue in chunks for better performance during batch i…
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…