Unsafe future fix check

UnsafePlainActionFuture would allow any threads to do unsafe
completes when using the one-arg constructor, fixed.

server/src/main/java/org/elasticsearch/action/support/UnsafePlainActionFuture.java

@@ -25,12 +25,19 @@ public class UnsafePlainActionFuture<T> extends PlainActionFuture<T> {
     private final String unsafeExecutor;
     private final String unsafeExecutor2;
 
+    /**
+     * Allow the single executor passed to be used unsafely.
+     */
     public UnsafePlainActionFuture(String unsafeExecutor) {
-        this(unsafeExecutor, null);
+        this(unsafeExecutor, "__none__");
     }
 
+    /**
+     * Allow both executors passed to be used unsafely.
+     */
     public UnsafePlainActionFuture(String unsafeExecutor, String unsafeExecutor2) {
         Objects.requireNonNull(unsafeExecutor);
+        Objects.requireNonNull(unsafeExecutor2);
         this.unsafeExecutor = unsafeExecutor;
         this.unsafeExecutor2 = unsafeExecutor2;
     }
@@ -39,7 +46,6 @@ public UnsafePlainActionFuture(String unsafeExecutor, String unsafeExecutor2) {
     boolean allowedExecutors(Thread thread1, Thread thread2) {
         return super.allowedExecutors(thread1, thread2)
             || unsafeExecutor.equals(EsExecutors.executorName(thread1))
-            || unsafeExecutor2 == null
             || unsafeExecutor2.equals(EsExecutors.executorName(thread1));
     }
 }

server/src/test/java/org/elasticsearch/action/support/UnsafePlainActionFutureTests.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.action.support;
+
+import org.elasticsearch.common.util.concurrent.EsExecutors;
+import org.elasticsearch.test.ESTestCase;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class UnsafePlainActionFutureTests extends ESTestCase {
+
+    public void testOneArg() {
+        String unsafeExecutorName = "unsafe-executor";
+        String otherExecutorName = "other-executor";
+        UnsafePlainActionFuture<?> future = new UnsafePlainActionFuture<Void>(unsafeExecutorName);
+        Thread other1 = getThread(otherExecutorName);
+        Thread other2 = getThread(otherExecutorName);
+        assertFalse(future.allowedExecutors(other1, other2));
+        Thread unsafe1 = getThread(unsafeExecutorName);
+        Thread unsafe2 = getThread(unsafeExecutorName);
+        assertTrue(future.allowedExecutors(unsafe1, unsafe2));
+
+        assertTrue(future.allowedExecutors(unsafe1, other1));
+    }
+
+    public void testTwoArg() {
+        String unsafeExecutorName1 = "unsafe-executor-1";
+        String unsafeExecutorName2 = "unsafe-executor-2";
+        String otherExecutorName = "other-executor";
+        UnsafePlainActionFuture<?> future = new UnsafePlainActionFuture<Void>(unsafeExecutorName1, unsafeExecutorName2);
+        Thread other1 = getThread(otherExecutorName);
+        Thread other2 = getThread(otherExecutorName);
+        assertFalse(future.allowedExecutors(other1, other2));
+        Thread unsafe1Thread1 = getThread(unsafeExecutorName1);
+        Thread unsafe2Thread1 = getThread(unsafeExecutorName2);
+        Thread unsafe1Thread2 = getThread(unsafeExecutorName1);
+        Thread unsafe2Thread2 = getThread(unsafeExecutorName2);
+        assertTrue(future.allowedExecutors(unsafe1Thread1, unsafe1Thread2));
+        assertTrue(future.allowedExecutors(unsafe2Thread1, unsafe2Thread2));
+
+        assertTrue(future.allowedExecutors(unsafe1Thread1, unsafe2Thread2));
+        assertTrue(future.allowedExecutors(unsafe2Thread1, other1));
+        assertTrue(future.allowedExecutors(other1, unsafe2Thread2));
+    }
+
+    private static Thread getThread(String executorName) {
+        Thread t = new Thread("[" + executorName + "][]");
+        assertThat(EsExecutors.executorName(t), equalTo(executorName));
+        return t;
+    }
+}