task1627 fails despite correct output

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This problem concerns the fourth requirement: The run methods of all players who did not win (those who were interrupted) should display [getName() + ":lost"]. For example: [Gates:lost] Validation seems to be broken - the requirement is listed as failed even though the output is correct. Here's the complete output (via println):

Gates:Start game
Smith:Start game
Gates:Gather resources
Gates:Grow economy
Smith:Gather resources
Gates:Kill enemies
Gates:won!
Smith:lost
Jones:lost

This is exactly what the requirement says. I also tried several obvious variations (blank after the colon, exclamation mark at the end and so on) but to no avail. Can anyone help? Side note: Jones never gets to make a move because Gates's rate is five times as high and so Gates makes the final move before Jones even starts. If l let everyone make a move before the first delay then first requirement is listed as failed (even though it says 'at regular intervals', not 'after regular delays' - which looks like a classical fence post error). P.S: I had the sneaking suspicion that the issue might be breaking the loop on isWinnerFound instead of waiting for interruption; however, removing the break condition and adding gamer.interrupt() to the post-game loop did not change anything. P.P.S.: my intuition regarding the missing interrupt was correct insofar as the interruption is necessary for the timely ending of the game (i.e. for pulling the losers out of Thread.sleep(). However, this doesn't change anything with regard to the fourth requirement failing.

Three people play the game. Each player (Gamer) is characterized by two parameters: last name (name) and the actions-per-second (rating).
Display the actions taken and determine the winner and the losers.
Let's begin...
1. Figure out what the program does.
1.1. List<String> actions stores the sequence of actions performed by each player from 0 to the last.
1.2. isWinnerFound indicates whether the winner has been found.
1.3. The sleep method throws an InterruptedException and takes a long argument.
1.4. The players play independently of each other.
2. Implement the run method so that for each player:
2.1. At regular intervals (1000ms/rating), the actions specified in the actions list are displayed.
2.2. All text begins with the player's name (getName()), followed by a colon, and then the text itself.

Example:[Smith:Game start].

2.3. When a player has performed all of the actions in the actions list, he or she wins. Display [getName() + ":won!"].
2.4. When the winner is found, the game ends, and the remaining players have lost. For these players, display [getName() + ":lost"].

Don't display the square brackets ("[]").

Requirements:

At regular intervals (1000ms/rating), the Gamer class's run method should display the player's last name (getName()), followed by a colon, and then the text in OnlineGame.actions. Example: [Smith:Game start].
When all the game actions have been completed and the winner has not yet been found, the run method must set the flag OnlineGame.isWinnerFound to true (to inform the others that it is the winner).
If a player wins, his or her run method should display [getName() + ":won!"]. For example: [Jones:won!].
The run methods of all players who did not win (those who were interrupted) should display [getName() + ":lost"]. For example: [Gates:lost]
The run method must not throw an exception when it is interrupted.

package com.codegym.task.task16.task1627; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class Solution { public static void main(String[] args) throws InterruptedException { OnlineGame onlineGame = new OnlineGame(); onlineGame.start(); } public static class OnlineGame extends Thread { public static volatile boolean isWinnerFound = false; public static List<String> actions = new ArrayList<>(); static { actions.add("Start game"); actions.add("Gather resources"); actions.add("Grow economy"); actions.add("Kill enemies"); } protected Gamer gamer1 = new Gamer("Smith", 3); protected Gamer gamer2 = new Gamer("Jones", 1); protected Gamer gamer3 = new Gamer("Gates", 5); public void run() { gamer1.start(); gamer2.start(); gamer3.start(); while (!isWinnerFound) { } for (Gamer gamer : Arrays.asList(gamer1, gamer2, gamer3)) { try { gamer.interrupt(); gamer.join(); } catch (InterruptedException ignored) { } } } } public static class Gamer extends Thread { private int rating; public Gamer(String name, int rating) { super(name); this.rating = rating; } @Override public void run() { int delay = 1000 / rating; for (String action : OnlineGame.actions) { try { Thread.sleep(delay); } catch (InterruptedException ignored) { break; } if (OnlineGame.isWinnerFound) { break; } synchronized (Solution.class) { System.out.println(getName() + ":" + action); } } synchronized (Solution.class) { // synchronised for concurrent state manipulation boolean playerLost = OnlineGame.isWinnerFound; if (!playerLost) { OnlineGame.isWinnerFound = true; } // synchronised for concurrent output System.out.println(getName() + (playerLost ? ":lost" : ":won!")); } } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

5 June 2021, 17:55

The point of the task is not to match the output. If that was the case then this would be equal to what you did:

System.out.println("Gates:Start game");
System.out.println("Smith:Start game");
System.out.println("Gates:Gather resources");
System.out.println("Gates:Grow economy");
System.out.println("Smith:Gather resources");
System.out.println("Gates:Kill enemies");
System.out.println("Gates:won!");
System.out.println("Smith:lost");
System.out.println("Jones:lost");

The point is to do what the directions say within the bounds that are given. The big problem with your code is that there were changes outside the bounds of the program. The task says that you are to implement the run() method of the Gamer class. However there is a modification in the run() method of the OnlineGame class:

for (Gamer gamer : Arrays.asList(gamer1, gamer2, gamer3)) {
   try {
      gamer.interrupt();
      gamer.join();
   } catch (InterruptedException ignored) {}
}

This code now changes what the program does and validation won't be able to complete. Be sure to put the default code back and be sure that you don't change code like this in the future. That may be the only problem with your code, however if you still are not passing consider that the task has two outcomes of the Gamer classes run() method: 1) either the run method is allowed to loop through all the tasks in the List at the specified delays; or 2) an InterruptedException is thrown The results of those two outcomes would be outputs of: 1) Player has won; or 2) Player has lost The task is no more complicated than this. My run method was 10 lines of code and didn't use synchronized.

DarthGizka

Level 24 , Wittenberg, Germany

5 June 2021, 19:43

Thanks for the explanation, but I'm still confused about exactly which of the documented requirements my code fails to fulfil. The argument with the println series is somewhat facetious, since my code runs according to spec even if you modify the parameters (e.g. the player ratings). The gamer.join() in OnlineGamer.run() is there to prevent the loss of the losing players' messages when execution falls off the end of main() (in which case all the extra threads get automatically killed due to ExitProcess() being called). The synchronisation is there for two reasons. (1) As far as I could find out, there is no guarantee against concurrent println output interleaving. The fact the println output *happens* to not interleave seems to be generally regarded as an unguaranteed implementation detail. (2) isWinnerFound needs to be both tested and set (first past the post wins). Synchronisation is strictly necessary here unless the variable is changed to integer so that interlocked functions can be used (in Java that would be AtomicInteger). But the latter would also mean changes to OnlineGame.run(), which you said were intended (but not documented) to be prohibited. I'm doing these exercises in order to learn how to do things right, so I'm not skimping on synchronisation simply because I can get away with it virtually all of the time in a setting like this. I know how bloody darn difficult it often is to write tests that can reliably prove the presence of insufficient synchronisation and other threading errors. I know this because I often find it difficult to write regression tests that can reliably uncover *known* concurrency bugs within the given time budget (usually 100 ms or 1.0 s per test), even when the tests run at raised priority in tight loops, with all cores of the CPU at their disposal, in a language where I have tight control over the generated machine instructions (C++, Delphi).

Guadalupe Gagnon

Level 37 , Tampa, United States

6 June 2021, 01:38

You have to remember that this course is a beginners course and not an advanced course. Also the validation system cannot test an infinite amount of solutions, codegym staff could spend an entire year trying to anticipate the solutions people would submit and still not be able to get every single one. The code that you submit will not be broken down by a panel of human judges who decide if it does what it is supposed to do but by a computer with static tests. You have to make a decision. either code to pass the validation system or code to solve the task at your ability level.

Guadalupe Gagnon

Level 37 , Tampa, United States

6 June 2021, 01:39

also, i understand the the code you added in the OnlineGame, however like I said above making changes where you are not supposed to will cause the validation to fail 90% of the time.

DarthGizka

Level 24 , Wittenberg, Germany

6 June 2021, 06:14

Thank you for your patience! I reset the task and started over, and this time I managed to solve the problem: it seems that the validation code expects losing players to wait for being interrupted before they print their "lost" messages. This is needlessly brittle and such a requirement should be stated explicitly in the task description (or better, just make someone fix the broken validation code).