Prevent unexpected native controller output hanging the process

qa/no-bootstrap-tests/src/test/java/org/elasticsearch/bootstrap/SpawnerNoBootstrapTests.java

@@ -91,7 +91,7 @@ public void testNoControllerSpawn() throws IOException {
                 "has.native.controller", "false");
 
         try (Spawner spawner = new Spawner()) {
-            spawner.spawnNativeControllers(environment);
+            spawner.spawnNativeControllers(environment, false);
             assertThat(spawner.getProcesses(), hasSize(0));
         }
     }
@@ -149,7 +149,7 @@ private void assertControllerSpawns(final Function<Environment, Path> pluginsDir
             "has.native.controller", "false");
 
         Spawner spawner = new Spawner();
-        spawner.spawnNativeControllers(environment);
+        spawner.spawnNativeControllers(environment, false);
 
         List<Process> processes = spawner.getProcesses();
 
@@ -196,7 +196,7 @@ public void testControllerSpawnWithIncorrectDescriptor() throws IOException {
         Spawner spawner = new Spawner();
         IllegalArgumentException e = expectThrows(
                 IllegalArgumentException.class,
-                () -> spawner.spawnNativeControllers(environment));
+                () -> spawner.spawnNativeControllers(environment, false));
         assertThat(
                 e.getMessage(),
                 equalTo("module [test_plugin] does not have permission to fork native controller"));
@@ -217,10 +217,10 @@ public void testSpawnerHandlingOfDesktopServicesStoreFiles() throws IOException
         final Spawner spawner = new Spawner();
         if (Constants.MAC_OS_X) {
             // if the spawner were not skipping the Desktop Services Store files on macOS this would explode
-            spawner.spawnNativeControllers(environment);
+            spawner.spawnNativeControllers(environment, false);
         } else {
             // we do not ignore these files on non-macOS systems
-            final FileSystemException e = expectThrows(FileSystemException.class, () -> spawner.spawnNativeControllers(environment));
+            final FileSystemException e = expectThrows(FileSystemException.class, () -> spawner.spawnNativeControllers(environment, false));
             if (Constants.WINDOWS) {
                 assertThat(e, instanceOf(NoSuchFileException.class));
             } else {

server/src/main/java/org/elasticsearch/bootstrap/Bootstrap.java

@@ -168,7 +168,7 @@ private void setup(boolean addShutdownHook, Environment environment) throws Boot
         Settings settings = environment.settings();
 
         try {
-            spawner.spawnNativeControllers(environment);
+            spawner.spawnNativeControllers(environment, true);
         } catch (IOException e) {
             throw new BootstrapException(e);
         }

server/src/main/java/org/elasticsearch/bootstrap/Spawner.java

@@ -55,10 +55,12 @@ public void close() throws IOException {
     /**
      * Spawns the native controllers for each module.
      *
-     * @param environment the node environment
+     * @param environment The node environment
+     * @param inheritIo   Should the stdout and stderr of the spawned process inherit the
+     *                    stdout and stderr of the JVM spawning it?
      * @throws IOException if an I/O error occurs reading the module or spawning a native process
      */
-    void spawnNativeControllers(final Environment environment) throws IOException {
+    void spawnNativeControllers(final Environment environment, final boolean inheritIo) throws IOException {
         if (!spawned.compareAndSet(false, true)) {
             throw new IllegalStateException("native controllers already spawned");
         }
@@ -83,7 +85,7 @@ void spawnNativeControllers(final Environment environment) throws IOException {
                     modules.getFileName());
                 throw new IllegalArgumentException(message);
             }
-            final Process process = spawnNativeController(spawnPath, environment.tmpFile());
+            final Process process = spawnNativeController(spawnPath, environment.tmpFile(), inheritIo);
             processes.add(process);
         }
     }
@@ -92,7 +94,7 @@ void spawnNativeControllers(final Environment environment) throws IOException {
      * Attempt to spawn the controller daemon for a given module. The spawned process will remain connected to this JVM via its stdin,
      * stdout, and stderr streams, but the references to these streams are not available to code outside this package.
      */
-    private Process spawnNativeController(final Path spawnPath, final Path tmpPath) throws IOException {
+    private Process spawnNativeController(final Path spawnPath, final Path tmpPath, final boolean inheritIo) throws IOException {
         final String command;
         if (Constants.WINDOWS) {
             /*
@@ -114,6 +116,14 @@ private Process spawnNativeController(final Path spawnPath, final Path tmpPath)
         pb.environment().clear();
         pb.environment().put("TMPDIR", tmpPath.toString());
 
+        // The process _shouldn't_ write any output via its stdout or stderr, but if it does then
+        // it will block if nothing is reading that output. To avoid this we can inherit the
+        // JVM's stdout and stderr (which are redirected to files in standard installations).
+        if (inheritIo) {
+            pb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
+            pb.redirectError(ProcessBuilder.Redirect.INHERIT);
+        }
+
         // the output stream of the process object corresponds to the daemon's stdin
         return pb.start();
     }