[#3378] Automatically increase number of possible handled events

Motivation:

At the moment the max number of events that can be handled per epoll wakup was set during construction.

Modifications:

- Automatically increase the max number of events to handle

Result:

Better performance when a lot of events need to be handled without adjusting the code.

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoop.java

@@ -52,7 +52,8 @@ final class EpollEventLoop extends SingleThreadEventLoop {
     private final int epollFd;
     private final int eventFd;
     private final IntObjectMap<AbstractEpollChannel> ids = new IntObjectHashMap<AbstractEpollChannel>();
-    private final long[] events;
+    private final boolean allowGrowing;
+    private long[] events;
 
     private int id;
 
@@ -62,7 +63,13 @@ final class EpollEventLoop extends SingleThreadEventLoop {
 
     EpollEventLoop(EventLoopGroup parent, Executor executor, int maxEvents) {
         super(parent, executor, false);
-        events = new long[maxEvents];
+        if (maxEvents == 0) {
+            allowGrowing = true;
+            events = new long[128];
+        } else {
+            allowGrowing = false;
+            events = new long[maxEvents];
+        }
         boolean success = false;
         int epollFd = -1;
         int eventFd = -1;
@@ -268,7 +275,10 @@ final class EpollEventLoop extends SingleThreadEventLoop {
                 final long ioTime = System.nanoTime() - ioStartTime;
                 runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
             }
-
+            if (allowGrowing && ready == events.length) {
+                // double the size of the array as we needed the whole space for the events
+                events = new long[events.length << 1];
+            }
             if (isShuttingDown()) {
                 closeAll();
                 if (confirmShutdown()) {

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollEventLoopGroup.java

@@ -62,8 +62,9 @@ public final class EpollEventLoopGroup extends MultithreadEventLoopGroup {
      *                      {@code executor} to lie very close together.
      * @param executor  the {@link Executor} to use, or {@code null} if the default should be used.
      */
+    @SuppressWarnings("deprecation")
     public EpollEventLoopGroup(int nEventLoops, Executor executor) {
-        this(nEventLoops, executor, 128);
+        this(nEventLoops, executor, 0);
     }
 
     /**
@@ -75,8 +76,9 @@ public final class EpollEventLoopGroup extends MultithreadEventLoopGroup {
      * @param executorServiceFactory   the {@link ExecutorServiceFactory} to use, or {@code null} if the
      *                                 default should be used.
      */
+    @SuppressWarnings("deprecation")
     public EpollEventLoopGroup(int nEventLoops, ExecutorServiceFactory executorServiceFactory) {
-        this(nEventLoops, executorServiceFactory, 128);
+        this(nEventLoops, executorServiceFactory, 0);
     }
 
     /**
@@ -87,7 +89,11 @@ public final class EpollEventLoopGroup extends MultithreadEventLoopGroup {
      *                      {@code executor} to lie very close together.
      * @param executor   the {@link Executor} to use, or {@code null} if the default should be used.
      * @param maxEventsAtOnce   the maximum number of epoll events to handle per epollWait(...).
+     *
+     * @deprecated  Use {@link #EpollEventLoopGroup(int)}, {@link #EpollEventLoopGroup(int)} or
+     *              {@link #EpollEventLoopGroup(int, Executor)}
      */
+    @Deprecated
     public EpollEventLoopGroup(int nEventLoops, Executor executor, int maxEventsAtOnce) {
         super(nEventLoops, executor, maxEventsAtOnce);
     }
@@ -101,7 +107,11 @@ public final class EpollEventLoopGroup extends MultithreadEventLoopGroup {
      * @param executorServiceFactory   the {@link ExecutorServiceFactory} to use, or {@code null} if the default
      *                                 should be used.
      * @param maxEventsAtOnce   the maximum number of epoll events to handle per epollWait(...).
+     *
+     * @deprecated  Use {@link #EpollEventLoopGroup(int)}, {@link #EpollEventLoopGroup(int)} or
+     *              {@link #EpollEventLoopGroup(int, ExecutorServiceFactory)}
      */
+    @Deprecated
     public EpollEventLoopGroup(int nEventLoops, ExecutorServiceFactory executorServiceFactory, int maxEventsAtOnce) {
         super(nEventLoops, executorServiceFactory, maxEventsAtOnce);
     }