8253478: (se) epoll Selector should use eventfd for wakeup instead of pipe

Reviewed-by: alanb

Author: Brian Burkhalter

src/java.base/linux/classes/sun/nio/ch/EPollSelectorImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -58,9 +58,8 @@ class EPollSelectorImpl extends SelectorImpl {
     // address of poll array when polling with epoll_wait
     private final long pollArrayAddress;
 
-    // file descriptors used for interrupt
-    private final int fd0;
-    private final int fd1;
+    // eventfd object used for interrupt
+    private final EventFD eventfd;
 
     // maps file descriptor to selection key, synchronize on selector
     private final Map<Integer, SelectionKeyImpl> fdToKey = new HashMap<>();
@@ -80,17 +79,16 @@ class EPollSelectorImpl extends SelectorImpl {
         this.pollArrayAddress = EPoll.allocatePollArray(NUM_EPOLLEVENTS);
 
         try {
-            long fds = IOUtil.makePipe(false);
-            this.fd0 = (int) (fds >>> 32);
-            this.fd1 = (int) fds;
+            this.eventfd = new EventFD();
+            IOUtil.configureBlocking(IOUtil.newFD(eventfd.efd()), false);
         } catch (IOException ioe) {
             EPoll.freePollArray(pollArrayAddress);
             FileDispatcherImpl.closeIntFD(epfd);
             throw ioe;
         }
 
-        // register one end of the socket pair for wakeups
-        EPoll.ctl(epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);
+        // register the eventfd object for wakeups
+        EPoll.ctl(epfd, EPOLL_CTL_ADD, eventfd.efd(), EPOLLIN);
     }
 
     private void ensureOpen() {
@@ -188,7 +186,7 @@ private int processEvents(int numEntries, Consumer<SelectionKey> action)
         for (int i=0; i<numEntries; i++) {
             long event = EPoll.getEvent(pollArrayAddress, i);
             int fd = EPoll.getDescriptor(event);
-            if (fd == fd0) {
+            if (fd == eventfd.efd()) {
                 interrupted = true;
             } else {
                 SelectionKeyImpl ski = fdToKey.get(fd);
@@ -218,8 +216,7 @@ protected void implClose() throws IOException {
         FileDispatcherImpl.closeIntFD(epfd);
         EPoll.freePollArray(pollArrayAddress);
 
-        FileDispatcherImpl.closeIntFD(fd0);
-        FileDispatcherImpl.closeIntFD(fd1);
+        eventfd.close();
     }
 
     @Override
@@ -251,7 +248,7 @@ public Selector wakeup() {
         synchronized (interruptLock) {
             if (!interruptTriggered) {
                 try {
-                    IOUtil.write1(fd1, (byte)0);
+                    eventfd.set();
                 } catch (IOException ioe) {
                     throw new InternalError(ioe);
                 }
@@ -263,7 +260,7 @@ public Selector wakeup() {
 
     private void clearInterrupt() throws IOException {
         synchronized (interruptLock) {
-            IOUtil.drain(fd0);
+            eventfd.reset();
             interruptTriggered = false;
         }
     }

src/java.base/linux/classes/sun/nio/ch/EventFD.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package sun.nio.ch;
+
+import java.io.IOException;
+
+/*
+ * Provides access to the Linux eventfd object.
+ */
+final class EventFD {
+    private final int efd;
+
+    /**
+     * Creates a blocking eventfd object with initial value zero.
+     */
+    EventFD() throws IOException {
+        efd = eventfd0();
+    }
+
+    int efd() {
+        return efd;
+    }
+
+    void set() throws IOException {
+        set0(efd);
+    }
+
+    void reset() throws IOException {
+        IOUtil.drain(efd);
+    }
+
+    void close() throws IOException {
+        FileDispatcherImpl.closeIntFD(efd);
+    }
+
+    private static native int eventfd0() throws IOException;
+
+    /**
+     * Writes the value 1 to the eventfd object as a long in the
+     * native byte order of the platform.
+     *
+     * @param the integral eventfd file descriptor
+     * @return the number of bytes written; should equal 8
+     */
+    private static native int set0(int efd) throws IOException;
+
+    static {
+        IOUtil.load();
+    }
+}

src/java.base/linux/native/libnio/ch/EventFD.c

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+ #include <sys/eventfd.h>
+
+#include "jni.h"
+#include "jni_util.h"
+#include "jvm.h"
+#include "jlong.h"
+#include "nio.h"
+#include "nio_util.h"
+
+#include "sun_nio_ch_EventFD.h"
+
+JNIEXPORT jint JNICALL
+Java_sun_nio_ch_EventFD_eventfd0(JNIEnv *env, jclass klazz)
+{
+    int efd = eventfd((uint64_t)0, 0);
+    if (efd == -1) {
+        JNU_ThrowIOExceptionWithLastError(env, "eventfd failed");
+        return IOS_THROWN;
+    }
+    return efd;
+}
+
+JNIEXPORT jint JNICALL
+Java_sun_nio_ch_EventFD_set0(JNIEnv *env, jclass klazz, jint efd)
+{
+    long one = 1L;
+    return convertReturnVal(env, write(efd, (void*)&one, sizeof(long)),
+        JNI_FALSE);
+}

test/micro/org/openjdk/bench/java/nio/SelectorWakeup.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2014, Oracle America, Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ *  * Neither the name of Oracle nor the names of its contributors may be used
+ *    to endorse or promote products derived from this software without
+ *    specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.openjdk.bench.java.nio;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+
+import java.io.*;
+import java.net.*;
+import java.nio.*;
+import java.nio.channels.*;
+
+/**
+ * Benchmark for the Selector wakeup mechanism. Intended primarily for the
+ * epoll(7)-based implementation on Linux.
+ */
+@State(Scope.Thread)
+public class SelectorWakeup {
+    private Selector sel;
+
+    @Setup(Level.Iteration)
+    public void setup() throws IOException {
+        sel = Selector.open();
+    }
+
+    @Benchmark
+    public int test() throws IOException {
+        return sel.wakeup().select();
+    }
+}