Use available processor number for default thread count in consumer work service

The current value is available processors times 2, which may be overkill
nowadays. The commit also allows using the rabbitmq.amqp.client.availableProcessors
system property value, which is convenient as it's configuration-based (no code
changes required).

Fixes #730

Author: acogoluegnes

src/main/java/com/rabbitmq/client/impl/ConsumerWorkService.java

@@ -1,4 +1,4 @@
-// Copyright (c) 2007-2020 VMware, Inc. or its affiliates.  All rights reserved.
+// Copyright (c) 2007-2022 VMware, Inc. or its affiliates.  All rights reserved.
 //
 // This software, the RabbitMQ Java client library, is triple-licensed under the
 // Mozilla Public License 2.0 ("MPL"), the GNU General Public License version 2
@@ -22,19 +22,26 @@
 import java.util.concurrent.ThreadFactory;
 
 import com.rabbitmq.client.Channel;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 final public class ConsumerWorkService {
+    private static final Logger LOGGER = LoggerFactory.getLogger(ConsumerWorkService.class);
     private static final int MAX_RUNNABLE_BLOCK_SIZE = 16;
-    private static final int DEFAULT_NUM_THREADS = Runtime.getRuntime().availableProcessors() * 2;
+    private static final int DEFAULT_NUM_THREADS = Math.max(1, Utils.availableProcessors());
     private final ExecutorService executor;
     private final boolean privateExecutor;
     private final WorkPool<Channel, Runnable> workPool;
     private final int shutdownTimeout;
 
     public ConsumerWorkService(ExecutorService executor, ThreadFactory threadFactory, int queueingTimeout, int shutdownTimeout) {
         this.privateExecutor = (executor == null);
-        this.executor = (executor == null) ? Executors.newFixedThreadPool(DEFAULT_NUM_THREADS, threadFactory)
-                                           : executor;
+        if (executor == null) {
+            LOGGER.debug("Creating executor service with {} thread(s) for consumer work service", DEFAULT_NUM_THREADS);
+            this.executor = Executors.newFixedThreadPool(DEFAULT_NUM_THREADS, threadFactory);
+        } else {
+            this.executor = executor;
+        }
         this.workPool = new WorkPool<>(queueingTimeout);
         this.shutdownTimeout = shutdownTimeout;
     }

src/main/java/com/rabbitmq/client/impl/Utils.java

@@ -0,0 +1,31 @@
+// Copyright (c) 2022 VMware, Inc. or its affiliates.  All rights reserved.
+//
+// This software, the RabbitMQ Java client library, is triple-licensed under the
+// Mozilla Public License 2.0 ("MPL"), the GNU General Public License version 2
+// ("GPL") and the Apache License version 2 ("ASL"). For the MPL, please see
+// LICENSE-MPL-RabbitMQ. For the GPL, please see LICENSE-GPL2.  For the ASL,
+// please see LICENSE-APACHE2.
+//
+// This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND,
+// either express or implied. See the LICENSE file for specific language governing
+// rights and limitations of this software.
+//
+// If you have any questions regarding licensing, please contact us at
+// [email protected].
+
+package com.rabbitmq.client.impl;
+
+final class Utils {
+
+  private static final int AVAILABLE_PROCESSORS =
+      Integer.parseInt(
+          System.getProperty(
+              "rabbitmq.amqp.client.availableProcessors",
+              String.valueOf(Runtime.getRuntime().availableProcessors())));
+
+  static int availableProcessors() {
+    return AVAILABLE_PROCESSORS;
+  }
+
+  private Utils() {}
+}