👀 Views: 73 💬 Answers: 1 📅 Created: 2025-06-01

java multithreading nio Java

I've been banging my head against this for hours. I'm refactoring my project and I'm sure I'm missing something obvious here, but I'm encountering an issue when trying to write to a file using `FileChannel` in a multi-threaded environment in Java 11... I have multiple threads that are attempting to write to different parts of the same file, but I'm seeing inconsistent behavior. Sometimes, the written data appears corrupted or incomplete. Here’s a simplified version of my code: ```java import java.io.RandomAccessFile; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class FileWriterExample { public static void main(String[] args) throws Exception { RandomAccessFile file = new RandomAccessFile("output.txt", "rw"); FileChannel channel = file.getChannel(); Runnable writeTask = () -> { ByteBuffer buffer = ByteBuffer.allocate(1024); buffer.put("Hello from thread ".getBytes()); buffer.flip(); try { channel.write(buffer); } catch (IOException e) { e.printStackTrace(); } }; Thread thread1 = new Thread(writeTask); Thread thread2 = new Thread(writeTask); thread1.start(); thread2.start(); thread1.join(); thread2.join(); channel.close(); file.close(); } } ``` While both threads are attempting to write to the file, I notice that the output is not what I expect. Instead of seeing "Hello from thread 1" and "Hello from thread 2" clearly separated, I'm getting mixed outputs like "Hello from thread 1Hello from thread 2" or sometimes even partial messages. I’ve tried synchronizing the write operation by wrapping the `channel.write(buffer)` call in a synchronized block, but it caused the performance to drop significantly. Is there a better way to handle this? Should I be using a lock or a different approach to ensure each thread writes correctly without blocking each other too much? Any suggestions would be greatly appreciated! My development environment is macOS. Any help would be greatly appreciated! I'm working on a API that needs to handle this. Any help would be greatly appreciated! For context: I'm using Java on Linux. I'd be grateful for any help. I'm using Java stable in this project. Any pointers in the right direction?