Introduced Thread Pool Optimizations (#1394)

fixes #1392

Signed-off-by: Amit Kumar Mondal <admin@amitinside.com>

Author: amitjoy

com.zsmartsystems.zigbee/src/main/java/com/zsmartsystems/zigbee/ZigBeeExecutors.java

@@ -7,11 +7,16 @@
  */
 package com.zsmartsystems.zigbee;
 
+import static java.util.concurrent.TimeUnit.SECONDS;
+
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.slf4j.Logger;
@@ -28,6 +33,13 @@ public class ZigBeeExecutors {
 
     private static Logger logger = LoggerFactory.getLogger(ZigBeeExecutors.class);
 
+    private static final int THREAD_POOL_CORE_THREADS_SIZE = 1;
+    private static final int THREAD_POOL_KEEP_ALIVE_TIME_IN_SECONDS = 60;
+    
+    private ZigBeeExecutors() {
+        throw new IllegalAccessError("Cannot be instantiated");
+    }
+
     /**
      * Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they
      * are available, and uses the provided ThreadFactory to create new threads when needed.
@@ -59,7 +71,10 @@ public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize,
         // as we cancel a lot we want to get rid of cancelled tasks
         // even with the penalty of the clean up overhead
         scheduledThreadPool.setRemoveOnCancelPolicy(true);
-
+        scheduledThreadPool.setKeepAliveTime(THREAD_POOL_KEEP_ALIVE_TIME_IN_SECONDS, SECONDS);
+        if (corePoolSize > 1) {
+            scheduledThreadPool.allowCoreThreadTimeOut(true);
+        }
         return scheduledThreadPool;
     }
 
@@ -76,9 +91,7 @@ public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize,
      */
     public static ScheduledExecutorService newSingleThreadScheduledExecutor(String name) {
         // reuse our custom method which configures removal of cancelled tasks
-        ScheduledExecutorService singleThreadScheduledExecutor = newScheduledThreadPool(1, name);
-
-        return singleThreadScheduledExecutor;
+        return newScheduledThreadPool(1, name);
     }
 
     /**
@@ -94,7 +107,18 @@ public static ScheduledExecutorService newSingleThreadScheduledExecutor(String n
      * @return the newly created thread pool
      */
     public static ExecutorService newFixedThreadPool(int nThreads, String name) {
-        return Executors.newFixedThreadPool(nThreads, new ThreadFactoryWithNamePrefix(name));
+        // @formatter:off
+        ThreadPoolExecutor executor =  new ThreadPoolExecutor(THREAD_POOL_CORE_THREADS_SIZE,
+                                                              nThreads,
+                                                              THREAD_POOL_KEEP_ALIVE_TIME_IN_SECONDS,
+                                                              SECONDS,
+                                                              new LinkedBlockingQueue<>(),
+                                                              new ThreadFactoryWithNamePrefix(name));
+        // @formatter:on
+        if (nThreads > 1) {
+            executor.allowCoreThreadTimeOut(true);
+        }
+        return executor;
     }
 
     /**