Java take() Method of LinkedBlockingQueue is stuck, even if the Queue should not be empty
I’m writing Code for a Network Application. Therefor I’m using a LinkedBlockingQueue to store incoming messaged until they are consumed. The following code runs in it’s own Thread and fills up the Queue:
while(true) { String msg = in.readLine(); if(msg == null) continue; recieveQueue.offer(msg); System.out.println("recieveQueue.offer() called at: " + System.currentTimeMillis() + " hash:" + recieveQueue.hashCode()); System.out.println("Server recieved: " + msg.replace("\n", "")); break; } Next I wrote a Method, which runs in the same "Main-Thread" (No extra Thread is created for this Method). It’s only called when the stored Elements have to be consumed. It looks like the following:
public String recieveMessage() { try { System.out.println("recieveQueue.take() called at: " + System.currentTimeMillis() + " hash:" + recieveQueue.hashCode()); return recieveQueue.take(); }catch(InterruptedException e) { e.printStackTrace(); return null; } } When running this Code I get the following output:
recieveQueue.offer() called at: 1594558123030 hash:2091496189 Server recieved: CONFIRMED recieveQueue.take() called at: 1594558123031 hash:2091496189 The hash verifies that I’m working on the same Queue, and as seen by the Time, recieveQueue.offer(msg) is definitely called before take() and so the Queue should contain a message. But the Program stops at the take() call. No Exceptions were thrown and there is no other point in the code where take() gets called. I waited for like 10 minutes but the take() call never finishes
Made few changes in your program.
Note: Please check in your code Consumer in while loop.
import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.BlockingQueue; public class Main { public static void main(String[] args) { BlockingQueue recieveQueue = new LinkedBlockingQueue<String>(10); new Thread(){ public void run(){ int count=0; while(true) { count++; String msg = "AAA:"+count; if(msg == null) continue; recieveQueue.offer(msg); System.out.println("recieveQueue.offer() called at: " + System.currentTimeMillis() + " hash:" + recieveQueue.hashCode()); System.out.println("Server recieved: " + msg.replace("\n", "")); } } }.start(); while(true){ try { System.out.println("recieveQueue.take() called at: " + System.currentTimeMillis() + " hash:" + recieveQueue.hashCode()); System.out.println("recieveQueue.take() : "+recieveQueue.take()); }catch(InterruptedException e) { e.printStackTrace(); } } } } 
