Uses better approach #313

This uses CompleteableFutures instead of a recurring Bukkit task to
check if collections have been removed. This is a much more reliable way
to do it because it will complete when all the tasks are done and not
before.

src/main/java/world/bentobox/level/calculators/IslandLevelCalculator.java

@@ -608,42 +608,32 @@ public class IslandLevelCalculator {
                 // Done
                 pipeliner.getInProcessQueue().remove(this);
                 // Chunk finished
-                // This was the last chunk
-                handleStackedBlocks();
-                handleChests();
-                long checkTime = System.currentTimeMillis();
-                finishTask = Bukkit.getScheduler().runTaskTimer(addon.getPlugin(), () -> {
-                    // Check every half second if all the chests and stacks have been cleared
-                    if ((chestBlocks.isEmpty() && stackedBlocks.isEmpty())
-                            || System.currentTimeMillis() - checkTime > MAX_AMOUNT) {
+                // This was the last chunk. Handle stacked blocks, then chests and exit
+                handleStackedBlocks().thenCompose(v -> handleChests()).thenRun(() -> {
                     this.tidyUp();
                     this.getR().complete(getResults());
-                        finishTask.cancel();
-                    }
-                }, 0, 10L);
-
+                });
             }
         });
     }
 
-    private void handleChests() {
-        Iterator<Chunk> it = chestBlocks.iterator();
-        while (it.hasNext()) {
-            Chunk v = it.next();
-            Util.getChunkAtAsync(v.getWorld(), v.getX(), v.getZ()).thenAccept(c -> {
+    private CompletableFuture<Void> handleChests() {
+        List<CompletableFuture<Void>> futures = new ArrayList<>();
+        for (Chunk v : chestBlocks) {
+            CompletableFuture<Void> future = Util.getChunkAtAsync(v.getWorld(), v.getX(), v.getZ()).thenAccept(c -> {
                 scanChests(c);
-                it.remove();
             });
+            futures.add(future);
         }
+        // Return a CompletableFuture that completes when all futures are done
+        return CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]));
     }
 
-    private void handleStackedBlocks() {
+    private CompletableFuture<Void> handleStackedBlocks() {
         // Deal with any stacked blocks
-    List<Location> toRemove = new ArrayList<>();
-    Iterator<Location> it = stackedBlocks.iterator();
-    while (it.hasNext()) {
-        Location v = it.next();
-        Util.getChunkAtAsync(v).thenAccept(c -> {
+        List<CompletableFuture<Void>> futures = new ArrayList<>();
+        for (Location v : stackedBlocks) {
+            CompletableFuture<Void> future = Util.getChunkAtAsync(v).thenAccept(c -> {
                 Block stackedBlock = v.getBlock();
                 boolean belowSeaLevel = seaHeight > 0 && v.getBlockY() <= seaHeight;
                 if (WildStackerAPI.getWildStacker().getSystemManager().isStackedBarrel(stackedBlock)) {
@@ -658,17 +648,12 @@ public class IslandLevelCalculator {
                         checkBlock(stackedBlock.getType(), belowSeaLevel);
                     }
                 }
-            synchronized (toRemove) {
-                toRemove.add(v);
-            }
             });
+            futures.add(future);
         }
+        // Return a CompletableFuture that completes when all futures are done
+        return CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]));
 
-    // Wait for all asynchronous tasks to complete before removing elements
-    // Remove the elements collected in toRemove
-    synchronized (toRemove) {
-        stackedBlocks.removeAll(toRemove);
-    }
     }
 
 }