How do you fix a Thread Join() that is stuck
java, multithreading
Solution
You are invoking `jointhreads` inside thread you want to join, so `T1` is basicly waiting for `T1` (itself) to terminate but that will never happen.
You should invoke `jointrheads` in your main thread, so the application will wait until all worker threads will finish their job
Problem
I am new to multi-threading and I am simply getting hands on practice by trying to print a 14000 size String Arraylist using threads. I am not considering efficiency nor even usefulness for that matter; I just want to understand the threading concept. My output has been extremely faulty and I have tried all kinds of synchronizes and other failed attempts. I came across a tool called join at the moment, however my program doesn't exit and stays running. I debugged the code and the program simply gets stuck on the first thread join and I can't think of any reason or solution to remedy the problem. The way I approached the problem is by creating 4 threads to split the task of the printing.Then I would wait until all threads were complete and use the join right before closing the output file. ``` public class Threadprinting implements Runnable{ private static List<String> list; private Thread T1,T2,T3,T4; public void printinput(List<String> store){ list=new ArrayList<String>(store); Threadprinting threadprinting=new Threadprinting(); Threadprinting.generatethreads(); } public void generatethreads() { T1=new Thread(this,"t1"); T1.start(); T2=new Thread(this,"t2"); T2.start(); T3=new Thread(this,"t3"); T3.start(); T4=new Thread(this,"t4"); T4.start(); } public void run(){ try { PrintWriter out = new PrintWriter(new FileWriter("Output.txt")); switch (Thread.currentThread().getName()) { case "t1": System.out.println("Thread "+ Thread.currentThread().getName() + " is running"); for (int i = 0; i < list.size() / 4; i++) { out.println((list.get(i))); } break; case "t2": System.out.println("Thread "+ Thread.currentThread().getName() + " is running"); for (int i = list.size() / 4; i < list.size() / 2; i++) { out.println((list.get(i))); } break; case "t3": System.out.println("Thread "+Thread.currentThread().getName()+" is running"); for (int i = list.size()/2; i < list.size()/4+list.size()/2; i++) { out.println((list.get(i))); } break; case "t4": System.out.println("Thread "+Thread.currentThread().getName()+" is running"); for (int i = list.size()/4+list.size()/2; i < list.size(); i++) { out.println((list.get(i))); } break; default: System.out.println("filler"); break; } jointhreads(); out.close(); } catch(IOException e){ System.out.println("problem came from here"); } } ``` Specifically: ``` private void jointhreads() { try { T1.join(); T2.join(); T3.join(); T4.join(); } catch (InterruptedException e) { System.out.println("the joins failed"); } } ``` } The program fails to terminate and stays running at T1.join according to the debugger.