[#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

@@ -51,7 +51,8 @@ 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;
 
@@ -61,7 +62,13 @@ final class EpollEventLoop extends SingleThreadEventLoop {
 
     EpollEventLoop(EventLoopGroup parent, Executor executor, int maxEvents) {
         super(parent, executor, false);
+        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

@@ -46,14 +46,19 @@ public final class EpollEventLoopGroup extends MultithreadEventLoopGroup {
     /**
      * Create a new instance using the specified number of threads and the given {@link ThreadFactory}.
      */
+    @SuppressWarnings("deprecation")
     public EpollEventLoopGroup(int nThreads, ThreadFactory threadFactory) {
-        this(nThreads, threadFactory, 128);
+        this(nThreads, threadFactory, 0);
     }
 
     /**
      * Create a new instance using the specified number of threads, the given {@link ThreadFactory} and the given
      * maximal amount of epoll events to handle per epollWait(...).
+     *
+     * @deprecated  Use {@link #EpollEventLoopGroup(int)}, {@link #EpollEventLoopGroup(int)} or
+     *              {@link #EpollEventLoopGroup(int, ThreadFactory)}
      */
+    @Deprecated
     public EpollEventLoopGroup(int nThreads, ThreadFactory threadFactory, int maxEventsAtOnce) {
         super(nThreads, threadFactory, maxEventsAtOnce);
     }