[ML] Refactor inference request executor to leverage scheduled execution (#126858)

* Using threadpool schedule and fixing tests

* Update docs/changelog/126858.yaml

* Clean up

* change log

docs/changelog/126858.yaml

@@ -0,0 +1,6 @@
+pr: 126858
+summary: Leverage threadpool schedule for inference api to avoid long running thread
+area: Machine Learning
+type: bug
+issues:
+ - 126853

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/http/sender/RequestExecutorService.java

@@ -57,15 +57,6 @@ import static org.elasticsearch.xpack.inference.InferencePlugin.UTILITY_THREAD_P
  */
 public class RequestExecutorService implements RequestExecutor {
 
-    /**
-     * Provides dependency injection mainly for testing
-     */
-    interface Sleeper {
-        void sleep(TimeValue sleepTime) throws InterruptedException;
-    }
-
-    // default for tests
-    static final Sleeper DEFAULT_SLEEPER = sleepTime -> sleepTime.timeUnit().sleep(sleepTime.duration());
     // default for tests
     static final AdjustableCapacityBlockingQueue.QueueCreator<RejectableTask> DEFAULT_QUEUE_CREATOR =
         new AdjustableCapacityBlockingQueue.QueueCreator<>() {
@@ -118,7 +109,6 @@ public class RequestExecutorService implements RequestExecutor {
     private final Clock clock;
     private final AtomicBoolean shutdown = new AtomicBoolean(false);
     private final AdjustableCapacityBlockingQueue.QueueCreator<RejectableTask> queueCreator;
-    private final Sleeper sleeper;
     private final RateLimiterCreator rateLimiterCreator;
     private final AtomicReference<Scheduler.Cancellable> cancellableCleanupTask = new AtomicReference<>();
     private final AtomicBoolean started = new AtomicBoolean(false);
@@ -129,16 +119,7 @@ public class RequestExecutorService implements RequestExecutor {
         RequestExecutorServiceSettings settings,
         RequestSender requestSender
     ) {
-        this(
-            threadPool,
-            DEFAULT_QUEUE_CREATOR,
-            startupLatch,
-            settings,
-            requestSender,
-            Clock.systemUTC(),
-            DEFAULT_SLEEPER,
-            DEFAULT_RATE_LIMIT_CREATOR
-        );
+        this(threadPool, DEFAULT_QUEUE_CREATOR, startupLatch, settings, requestSender, Clock.systemUTC(), DEFAULT_RATE_LIMIT_CREATOR);
     }
 
     public RequestExecutorService(
@@ -148,7 +129,6 @@ public class RequestExecutorService implements RequestExecutor {
         RequestExecutorServiceSettings settings,
         RequestSender requestSender,
         Clock clock,
-        Sleeper sleeper,
         RateLimiterCreator rateLimiterCreator
     ) {
         this.threadPool = Objects.requireNonNull(threadPool);
@@ -157,7 +137,6 @@ public class RequestExecutorService implements RequestExecutor {
         this.requestSender = Objects.requireNonNull(requestSender);
         this.settings = Objects.requireNonNull(settings);
         this.clock = Objects.requireNonNull(clock);
-        this.sleeper = Objects.requireNonNull(sleeper);
         this.rateLimiterCreator = Objects.requireNonNull(rateLimiterCreator);
     }
 
@@ -213,15 +192,10 @@ public class RequestExecutorService implements RequestExecutor {
             startCleanupTask();
             signalStartInitiated();
 
-            while (isShutdown() == false) {
-                handleTasks();
-            }
-        } catch (InterruptedException e) {
-            Thread.currentThread().interrupt();
-        } finally {
-            shutdown();
-            notifyRequestsOfShutdown();
-            terminationLatch.countDown();
+            handleTasks();
+        } catch (Exception e) {
+            logger.warn("Failed to start request executor", e);
+            cleanup();
         }
     }
 
@@ -256,13 +230,44 @@ public class RequestExecutorService implements RequestExecutor {
         }
     }
 
-    private void handleTasks() throws InterruptedException {
-        var timeToWait = settings.getTaskPollFrequency();
-        for (var endpoint : rateLimitGroupings.values()) {
-            timeToWait = TimeValue.min(endpoint.executeEnqueuedTask(), timeToWait);
+    private void scheduleNextHandleTasks(TimeValue timeToWait) {
+        if (shutdown.get()) {
+            logger.debug("Shutdown requested while scheduling next handle task call, cleaning up");
+            cleanup();
+            return;
         }
 
-        sleeper.sleep(timeToWait);
+        threadPool.schedule(this::handleTasks, timeToWait, threadPool.executor(UTILITY_THREAD_POOL_NAME));
+    }
+
+    private void cleanup() {
+        try {
+            shutdown();
+            notifyRequestsOfShutdown();
+            terminationLatch.countDown();
+        } catch (Exception e) {
+            logger.warn("Encountered an error while cleaning up", e);
+        }
+    }
+
+    private void handleTasks() {
+        try {
+            if (shutdown.get()) {
+                logger.debug("Shutdown requested while handling tasks, cleaning up");
+                cleanup();
+                return;
+            }
+
+            var timeToWait = settings.getTaskPollFrequency();
+            for (var endpoint : rateLimitGroupings.values()) {
+                timeToWait = TimeValue.min(endpoint.executeEnqueuedTask(), timeToWait);
+            }
+
+            scheduleNextHandleTasks(timeToWait);
+        } catch (Exception e) {
+            logger.warn("Encountered an error while handling tasks", e);
+            cleanup();
+        }
     }
 
     private void notifyRequestsOfShutdown() {

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/external/http/sender/HttpRequestSenderTests.java

@@ -50,6 +50,7 @@ import static org.elasticsearch.xpack.inference.Utils.inferenceUtilityPool;
 import static org.elasticsearch.xpack.inference.Utils.mockClusterServiceEmpty;
 import static org.elasticsearch.xpack.inference.external.http.Utils.entityAsMap;
 import static org.elasticsearch.xpack.inference.external.http.Utils.getUrl;
+import static org.elasticsearch.xpack.inference.services.ServiceComponentsTests.createWithEmptySettings;
 import static org.elasticsearch.xpack.inference.services.elastic.ElasticInferenceService.ELASTIC_INFERENCE_SERVICE_IDENTIFIER;
 import static org.elasticsearch.xpack.inference.services.elastic.request.ElasticInferenceServiceRequestTests.randomElasticInferenceServiceRequestMetadata;
 import static org.elasticsearch.xpack.inference.services.openai.OpenAiUtils.ORGANIZATION_HEADER;
@@ -90,7 +91,7 @@ public class HttpRequestSenderTests extends ESTestCase {
     }
 
     public void testCreateSender_SendsRequestAndReceivesResponse() throws Exception {
-        var senderFactory = createSenderFactory(clientManager, threadRef);
+        var senderFactory = new HttpRequestSender.Factory(createWithEmptySettings(threadPool), clientManager, mockClusterServiceEmpty());
 
         try (var sender = createSender(senderFactory)) {
             sender.start();

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/external/http/sender/RequestExecutorServiceTests.java

@@ -51,7 +51,6 @@ import static org.hamcrest.Matchers.is;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.Mockito.doAnswer;
-import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
@@ -206,7 +205,7 @@ public class RequestExecutorServiceTests extends ESTestCase {
         assertFalse(thrownException.isExecutorShutdown());
     }
 
-    public void testTaskThrowsError_CallsOnFailure() {
+    public void testTaskThrowsError_CallsOnFailure() throws InterruptedException {
         var requestSender = mock(RetryingHttpSender.class);
 
         var service = createRequestExecutorService(null, requestSender);
@@ -229,6 +228,8 @@ public class RequestExecutorServiceTests extends ESTestCase {
         var thrownException = expectThrows(ElasticsearchException.class, () -> listener.actionGet(TIMEOUT));
         assertThat(thrownException.getMessage(), is(format("Failed to send request from inference entity id [%s]", "id")));
         assertThat(thrownException.getCause(), instanceOf(IllegalArgumentException.class));
+        service.awaitTermination(TIMEOUT.getSeconds(), TimeUnit.SECONDS);
+
         assertTrue(service.isTerminated());
     }
 
@@ -361,7 +362,6 @@ public class RequestExecutorServiceTests extends ESTestCase {
             createRequestExecutorServiceSettingsEmpty(),
             requestSender,
             Clock.systemUTC(),
-            RequestExecutorService.DEFAULT_SLEEPER,
             RequestExecutorService.DEFAULT_RATE_LIMIT_CREATOR
         );
 
@@ -375,36 +375,7 @@ public class RequestExecutorServiceTests extends ESTestCase {
         });
         service.start();
 
-        assertTrue(service.isTerminated());
-    }
-
-    public void testSleep_ThrowingInterruptedException_TerminatesService() throws Exception {
-        @SuppressWarnings("unchecked")
-        BlockingQueue<RejectableTask> queue = mock(LinkedBlockingQueue.class);
-        var sleeper = mock(RequestExecutorService.Sleeper.class);
-        doThrow(new InterruptedException("failed")).when(sleeper).sleep(any());
-
-        var service = new RequestExecutorService(
-            threadPool,
-            mockQueueCreator(queue),
-            null,
-            createRequestExecutorServiceSettingsEmpty(),
-            mock(RetryingHttpSender.class),
-            Clock.systemUTC(),
-            sleeper,
-            RequestExecutorService.DEFAULT_RATE_LIMIT_CREATOR
-        );
-
-        Future<?> executorTermination = threadPool.generic().submit(() -> {
-            try {
-                service.start();
-            } catch (Exception e) {
-                fail(Strings.format("Failed to shutdown executor: %s", e));
-            }
-        });
-
-        executorTermination.get(TIMEOUT.millis(), TimeUnit.MILLISECONDS);
-
+        service.awaitTermination(TIMEOUT.getSeconds(), TimeUnit.SECONDS);
         assertTrue(service.isTerminated());
     }
 
@@ -581,7 +552,6 @@ public class RequestExecutorServiceTests extends ESTestCase {
             settings,
             requestSender,
             Clock.systemUTC(),
-            RequestExecutorService.DEFAULT_SLEEPER,
             rateLimiterCreator
         );
         var requestManager = RequestManagerTests.createMock(requestSender);
@@ -614,7 +584,6 @@ public class RequestExecutorServiceTests extends ESTestCase {
             settings,
             requestSender,
             Clock.systemUTC(),
-            RequestExecutorService.DEFAULT_SLEEPER,
             rateLimiterCreator
         );
         var requestManager = RequestManagerTests.createMock(requestSender);
@@ -626,11 +595,15 @@ public class RequestExecutorServiceTests extends ESTestCase {
 
         doAnswer(invocation -> {
             service.shutdown();
+            ActionListener<InferenceServiceResults> passedListener = invocation.getArgument(4);
+            passedListener.onResponse(null);
+
             return Void.TYPE;
         }).when(requestSender).send(any(), any(), any(), any(), any());
 
         service.start();
 
+        listener.actionGet(TIMEOUT);
         verify(requestSender, times(1)).send(any(), any(), any(), any(), any());
     }
 
@@ -648,7 +621,6 @@ public class RequestExecutorServiceTests extends ESTestCase {
             settings,
             requestSender,
             clock,
-            RequestExecutorService.DEFAULT_SLEEPER,
             RequestExecutorService.DEFAULT_RATE_LIMIT_CREATOR
         );
         var requestManager = RequestManagerTests.createMock(requestSender, "id1");
@@ -682,7 +654,6 @@ public class RequestExecutorServiceTests extends ESTestCase {
             settings,
             requestSender,
             Clock.systemUTC(),
-            RequestExecutorService.DEFAULT_SLEEPER,
             RequestExecutorService.DEFAULT_RATE_LIMIT_CREATOR
         );