Revamp the selector auto rebuild checker

- Count the number of select() calls made to wait until reaching at the expected dead line, and rebuild selectors if too many select() calls were made.

common/src/main/java/io/netty/util/concurrent/SingleThreadEventExecutor.java

@@ -352,26 +352,13 @@ public abstract class SingleThreadEventExecutor extends AbstractEventExecutor {
     /**
      * Returns the ammount of time left until the scheduled task with the closest dead line is executed.
      */
-    protected long delayNanos() {
+    protected long delayNanos(long currentTimeNanos) {
         ScheduledFutureTask<?> delayedTask = delayedTaskQueue.peek();
         if (delayedTask == null) {
             return SCHEDULE_PURGE_INTERVAL;
         }
 
-        return delayedTask.delayNanos();
-    }
-
-    /**
-     * Returns the ammount of time left until the scheduled task with the closest dead line is executed.
-     */
-    protected long delayMillis() {
-        long delayNanos = delayNanos();
-        long delayMillis = delayNanos / 1000000L;
-        if (delayNanos % 1000000L < 500000L) {
-            return delayMillis;
-        } else {
-            return delayMillis + 1;
-        }
+        return delayedTask.delayNanos(currentTimeNanos);
     }
 
     /**
@@ -763,6 +750,10 @@ public abstract class SingleThreadEventExecutor extends AbstractEventExecutor {
             return Math.max(0, deadlineNanos() - nanoTime());
         }
 
+        public long delayNanos(long currentTimeNanos) {
+            return Math.max(0, deadlineNanos() - (currentTimeNanos - START_TIME));
+        }
+
         @Override
         public long getDelay(TimeUnit unit) {
             return unit.convert(delayNanos(), TimeUnit.NANOSECONDS);

transport/src/main/java/io/netty/channel/nio/NioEventLoop.java

@@ -77,7 +77,7 @@ public final class NioEventLoop extends SingleThreadEventLoop {
             }
         }
 
-        int selectorAutoRebuildThreshold = SystemPropertyUtil.getInt("io.netty.selectorAutoRebuildThreshold", 16);
+        int selectorAutoRebuildThreshold = SystemPropertyUtil.getInt("io.netty.selectorAutoRebuildThreshold", 512);
         if (selectorAutoRebuildThreshold < MIN_PREMATURE_SELECTOR_RETURNS) {
             selectorAutoRebuildThreshold = 0;
         }
@@ -108,7 +108,6 @@ public final class NioEventLoop extends SingleThreadEventLoop {
     private volatile int ioRatio = 50;
     private int cancelledKeys;
     private boolean needsToSelectAgain;
-    private int prematureSelectorReturns;
 
     NioEventLoop(
             NioEventLoopGroup parent, ThreadFactory threadFactory, SelectorProvider selectorProvider) {
@@ -121,7 +120,6 @@ public final class NioEventLoop extends SingleThreadEventLoop {
     }
 
     private Selector openSelector() {
-        resetPrematureSelectorReturns();
         try {
             return provider.openSelector();
         } catch (IOException e) {
@@ -548,9 +546,7 @@ public final class NioEventLoop extends SingleThreadEventLoop {
 
     void selectNow() throws IOException {
         try {
-            if (selector.selectNow() != 0) {
-                resetPrematureSelectorReturns();
-            }
+            selector.selectNow();
         } finally {
             // restore wakup state if needed
             if (wakenUp.get()) {
@@ -561,48 +557,52 @@ public final class NioEventLoop extends SingleThreadEventLoop {
 
     private void select() throws IOException {
         Selector selector = this.selector;
-        long delayMillis = delayMillis();
         try {
-            if (delayMillis > 0) {
-                long startTimeNanos = System.nanoTime();
-                if (selector.select(delayMillis) == 0) {
-                    if (oldWakenUp || wakenUp.get() || hasTasks()) {
-                        // Waken up by user or the task queue has a pending task.
-                        return;
+            int selectCnt = 0;
+            long currentTimeNanos = System.nanoTime();
+            long selectDeadLineNanos = currentTimeNanos + delayNanos(currentTimeNanos);
+            for (;;) {
+                long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L;
+                if (timeoutMillis <= 0) {
+                    if (selectCnt == 0) {
+                        selector.selectNow();
+                        selectCnt = 1;
+                    }
+                    break;
                 }
 
-                    long delayNanos = delayNanos();
-                    if (delayNanos <= 0) {
-                        // Waken up to handle a delayed task.
-                        return;
+                int selectedKeys = selector.select(timeoutMillis);
+                selectCnt ++;
+
+                if (selectedKeys != 0 || oldWakenUp || wakenUp.get() || hasTasks()) {
+                    // Selected something,
+                    // waken up by user, or
+                    // the task queue has a pending task.
+                    break;
                 }
 
-                    if (System.nanoTime() - startTimeNanos < delayNanos >>> 1) {
-                        // Returned way before the specified timeout with no selected keys.
-                        // This may be because of the JDK /dev/epoll bug - increment the counter.
-                        prematureSelectorReturns ++;
                 if (SELECTOR_AUTO_REBUILD_THRESHOLD > 0 &&
-                            prematureSelectorReturns >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
+                        selectCnt >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
                     // The selector returned prematurely many times in a row.
                     // Rebuild the selector to work around the problem.
                     logger.warn(
                             "Selector.select() returned prematurely {} times in a row; rebuilding selector.",
-                                    prematureSelectorReturns);
+                            selectCnt);
 
                     rebuildSelector();
 
                     // Select again to populate selectedKeys.
                     selector.selectNow();
+                    selectCnt = 1;
+                    break;
                 }
-                    } else {
-                        resetPrematureSelectorReturns();
+
+                currentTimeNanos = System.nanoTime();
             }
-                } else {
-                    resetPrematureSelectorReturns();
-                }
-            } else {
-                if (selector.selectNow() != 0) {
-                    resetPrematureSelectorReturns();
+
+            if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS) {
+                if (logger.isDebugEnabled()) {
+                    logger.debug("Selector.select() returned prematurely {} times in a row.", selectCnt - 1);
                 }
             }
         } catch (CancelledKeyException e) {
@@ -616,21 +616,9 @@ public final class NioEventLoop extends SingleThreadEventLoop {
     private void selectAgain() {
         needsToSelectAgain = false;
         try {
-            if (selector.selectNow() != 0) {
-                resetPrematureSelectorReturns();
-            }
+            selector.selectNow();
         } catch (Throwable t) {
             logger.warn("Failed to update SelectionKeys.", t);
         }
     }
-
-    private void resetPrematureSelectorReturns() {
-        int prematureSelectorReturns = this.prematureSelectorReturns;
-        if (prematureSelectorReturns >= MIN_PREMATURE_SELECTOR_RETURNS) {
-            if (logger.isDebugEnabled()) {
-                logger.debug("Selector.select() returned prematurely {} times in a row.", prematureSelectorReturns);
-            }
-            this.prematureSelectorReturns = 0;
-        }
-    }
 }

transport/src/test/java/io/netty/channel/SingleThreadEventLoopTest.java

@@ -377,7 +377,7 @@ public class SingleThreadEventLoopTest {
         protected void run() {
             for (;;) {
                 try {
-                    Thread.sleep(TimeUnit.NANOSECONDS.toMillis(delayNanos()));
+                    Thread.sleep(TimeUnit.NANOSECONDS.toMillis(delayNanos(System.nanoTime())));
                 } catch (InterruptedException e) {
                     // Waken up by interruptThread()
                 }