Simplify SliceExecutor and QueueSizeBasedExecutor (#12285)

The only behaviour that QueueSizeBasedExecutor overrides from SliceExecutor is when to execute on the caller thread. There is no need to override the whole invokeAll method for that. Instead, this commit introduces a shouldExecuteOnCallerThread method that can be overridden.

lucene/core/src/java/org/apache/lucene/search/QueueSizeBasedExecutor.java

@@ -17,7 +17,6 @@
 
 package org.apache.lucene.search;
 
-import java.util.Collection;
 import java.util.concurrent.ThreadPoolExecutor;
 
 /**
@@ -30,31 +29,15 @@ class QueueSizeBasedExecutor extends SliceExecutor {
 
   private final ThreadPoolExecutor threadPoolExecutor;
 
-  public QueueSizeBasedExecutor(ThreadPoolExecutor threadPoolExecutor) {
+  QueueSizeBasedExecutor(ThreadPoolExecutor threadPoolExecutor) {
     super(threadPoolExecutor);
     this.threadPoolExecutor = threadPoolExecutor;
   }
 
   @Override
-  public void invokeAll(Collection<? extends Runnable> tasks) {
-    int i = 0;
-
-    for (Runnable task : tasks) {
-      boolean shouldExecuteOnCallerThread = false;
-
-      // Execute last task on caller thread
-      if (i == tasks.size() - 1) {
-        shouldExecuteOnCallerThread = true;
-      }
-
-      if (threadPoolExecutor.getQueue().size()
-          >= (threadPoolExecutor.getMaximumPoolSize() * LIMITING_FACTOR)) {
-        shouldExecuteOnCallerThread = true;
-      }
-
-      processTask(task, shouldExecuteOnCallerThread);
-
-      ++i;
-    }
+  boolean shouldExecuteOnCallerThread(int index, int numTasks) {
+    return super.shouldExecuteOnCallerThread(index, numTasks)
+        || threadPoolExecutor.getQueue().size()
+            >= (threadPoolExecutor.getMaximumPoolSize() * LIMITING_FACTOR);
   }
 }

lucene/core/src/java/org/apache/lucene/search/SliceExecutor.java

@@ -18,6 +18,7 @@
 package org.apache.lucene.search;
 
 import java.util.Collection;
+import java.util.Objects;
 import java.util.concurrent.Executor;
 import java.util.concurrent.RejectedExecutionException;
 
@@ -28,54 +29,30 @@ import java.util.concurrent.RejectedExecutionException;
 class SliceExecutor {
   private final Executor executor;
 
-  public SliceExecutor(Executor executor) {
-    this.executor = executor;
-  }
-
-  public void invokeAll(Collection<? extends Runnable> tasks) {
-
-    if (tasks == null) {
-      throw new IllegalArgumentException("Tasks is null");
-    }
-
-    if (executor == null) {
-      throw new IllegalArgumentException("Executor is null");
+  SliceExecutor(Executor executor) {
+    this.executor = Objects.requireNonNull(executor, "Executor is null");
   }
 
+  final void invokeAll(Collection<? extends Runnable> tasks) {
     int i = 0;
-
     for (Runnable task : tasks) {
-      boolean shouldExecuteOnCallerThread = false;
-
-      // Execute last task on caller thread
-      if (i == tasks.size() - 1) {
-        shouldExecuteOnCallerThread = true;
-      }
-
-      processTask(task, shouldExecuteOnCallerThread);
-      ++i;
-    }
-    ;
-  }
-
-  // Helper method to execute a single task
-  protected void processTask(final Runnable task, final boolean shouldExecuteOnCallerThread) {
-    if (task == null) {
-      throw new IllegalArgumentException("Input is null");
-    }
-
-    if (!shouldExecuteOnCallerThread) {
+      if (shouldExecuteOnCallerThread(i, tasks.size())) {
+        task.run();
+      } else {
         try {
           executor.execute(task);
-
-        return;
         } catch (
             @SuppressWarnings("unused")
             RejectedExecutionException e) {
-        // Execute on caller thread
+          task.run();
+        }
+      }
+      ++i;
     }
   }
 
-    task.run();
+  boolean shouldExecuteOnCallerThread(int index, int numTasks) {
+    // Execute last task on caller thread
+    return index == numTasks - 1;
   }
 }

lucene/core/src/test/org/apache/lucene/search/TestIndexSearcher.java

@@ -453,20 +453,15 @@ public class TestIndexSearcher extends LuceneTestCase {
     }
   }
 
-  private class RandomBlockingSliceExecutor extends SliceExecutor {
+  private static class RandomBlockingSliceExecutor extends SliceExecutor {
 
-    public RandomBlockingSliceExecutor(Executor executor) {
+    RandomBlockingSliceExecutor(Executor executor) {
       super(executor);
     }
 
     @Override
-    public void invokeAll(Collection<? extends Runnable> tasks) {
-
-      for (Runnable task : tasks) {
-        boolean shouldExecuteOnCallerThread = random().nextBoolean();
-
-        processTask(task, shouldExecuteOnCallerThread);
-      }
+    boolean shouldExecuteOnCallerThread(int index, int numTasks) {
+      return random().nextBoolean();
     }
   }
 }