Avoid catch (Throwable t) in AmazonBedrockStreamingChatProcessor (#115715) (#115789)

`CompletableFuture.runAsync` implicitly catches all `Throwable`
instances thrown by the task, which includes `Error` instances that no
reasonable application should catch. Moreover, discarding the return
value from these methods means that any such `Error` will be ignored,
allowing the JVM to carry on running in an invalid state.

This commit replaces these trappy calls with more appropriate exception
handling.

Author: DaveCTurner

docs/changelog/115715.yaml

@@ -0,0 +1,5 @@
+pr: 115715
+summary: Avoid `catch (Throwable t)` in `AmazonBedrockStreamingChatProcessor`
+area: Machine Learning
+type: bug
+issues: []

x-pack/plugin/inference/src/main/java/module-info.java

@@ -33,6 +33,7 @@
     requires org.slf4j;
     requires software.amazon.awssdk.retries.api;
     requires org.reactivestreams;
+    requires org.elasticsearch.logging;
 
     exports org.elasticsearch.xpack.inference.action;
     exports org.elasticsearch.xpack.inference.registry;

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/external/amazonbedrock/AmazonBedrockStreamingChatProcessor.java

@@ -14,11 +14,12 @@
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.common.util.concurrent.EsExecutors;
 import org.elasticsearch.core.Strings;
+import org.elasticsearch.logging.LogManager;
+import org.elasticsearch.logging.Logger;
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.xpack.core.inference.results.StreamingChatCompletionResults;
 
 import java.util.ArrayDeque;
-import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Flow;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
@@ -27,6 +28,8 @@
 import static org.elasticsearch.xpack.inference.InferencePlugin.UTILITY_THREAD_POOL_NAME;
 
 class AmazonBedrockStreamingChatProcessor implements Flow.Processor<ConverseStreamOutput, StreamingChatCompletionResults.Results> {
+    private static final Logger logger = LogManager.getLogger(AmazonBedrockStreamingChatProcessor.class);
+
     private final AtomicReference<Throwable> error = new AtomicReference<>(null);
     private final AtomicLong demand = new AtomicLong(0);
     private final AtomicBoolean isDone = new AtomicBoolean(false);
@@ -75,13 +78,13 @@ public void onNext(ConverseStreamOutput item) {
 
     // this is always called from a netty thread maintained by the AWS SDK, we'll move it to our thread to process the response
     private void sendDownstreamOnAnotherThread(ContentBlockDeltaEvent event) {
-        CompletableFuture.runAsync(() -> {
+        runOnUtilityThreadPool(() -> {
             var text = event.delta().text();
             var result = new ArrayDeque<StreamingChatCompletionResults.Result>(1);
             result.offer(new StreamingChatCompletionResults.Result(text));
             var results = new StreamingChatCompletionResults.Results(result);
             downstream.onNext(results);
-        }, threadPool.executor(UTILITY_THREAD_POOL_NAME));
+        });
     }
 
     @Override
@@ -108,6 +111,14 @@ public void onComplete() {
         }
     }
 
+    private void runOnUtilityThreadPool(Runnable runnable) {
+        try {
+            threadPool.executor(UTILITY_THREAD_POOL_NAME).execute(runnable);
+        } catch (Exception e) {
+            logger.error(Strings.format("failed to fork [%s] to utility thread pool", runnable), e);
+        }
+    }
+
     private class StreamSubscription implements Flow.Subscription {
         @Override
         public void request(long n) {
@@ -142,7 +153,7 @@ private void requestOnMlThread(long n) {
             if (UTILITY_THREAD_POOL_NAME.equalsIgnoreCase(currentThreadPool)) {
                 upstream.request(n);
             } else {
-                CompletableFuture.runAsync(() -> upstream.request(n), threadPool.executor(UTILITY_THREAD_POOL_NAME));
+                runOnUtilityThreadPool(() -> upstream.request(n));
             }
         }