8282947: JFR: Dump on shutdown live-locks in some conditions

Reviewed-by: phh
Backport-of: 63eb0b7e8606dd9cd145e92eeeb744ff5b7be569

Author: Jiří Vaněk

jdk/src/share/classes/jdk/jfr/internal/ChunksChannel.java

@@ -96,10 +96,13 @@ public long transferTo(FileChannel out) throws IOException {
                 assert current != null;
 
                 long rem = current.getSize();
-
                 while (rem > 0) {
                     long n = Math.min(rem, 1024 * 1024);
                     long w = out.transferFrom(channel, pos, n);
+                    // Prevent endless loop
+                    if (w == 0) {
+                        return out.size();
+                    }
                     pos += w;
                     rem -= w;
                 }
@@ -111,7 +114,7 @@ public long transferTo(FileChannel out) throws IOException {
                 current = null;
             }
             if (!nextChannel()) {
-                return pos;
+                return out.size();
             }
         }
     }

jdk/src/share/classes/jdk/jfr/internal/PlatformRecording.java

@@ -682,8 +682,12 @@ public void dumpStopped(WriteableUserPath userPath) throws IOException {
         synchronized (recorder) {
                 userPath.doPriviligedIO(() -> {
                     try (ChunksChannel cc = new ChunksChannel(chunks); FileChannel fc = FileChannel.open(userPath.getReal(), StandardOpenOption.WRITE, StandardOpenOption.APPEND)) {
-                        cc.transferTo(fc);
-                        fc.force(true);
+                        long bytes = cc.transferTo(fc);
+                        Logger.log(LogTag.JFR, LogLevel.INFO, "Transferred " + bytes + " bytes from the disk repository");
+                        // No need to force if no data was transferred, which avoids IOException when device is /dev/null
+                        if (bytes != 0) {
+                            fc.force(true);
+                        }
                     }
                     return null;
                 });

jdk/test/jdk/jfr/api/recording/dump/TestDumpDevNull.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2022, 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.
+ *
+ * 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 jdk.jfr.api.recording.dump;
+
+import java.io.File;
+
+import jdk.jfr.Recording;
+
+/**
+ * @test
+ * @summary Tests that it's possible to dump to /dev/null without a livelock
+ * @key jfr
+ *
+ * @library /lib /
+ * @run main/othervm jdk.jfr.api.recording.dump.TestDumpDevNull
+ */
+public class TestDumpDevNull {
+
+    public static void main(String[] args) throws Exception {
+        try (Recording r1 = new Recording()) {
+            r1.setDestination(new File("/dev/null").toPath());
+            r1.start();
+            // Force a chunk rotation which ensures that jdk.jfr.internal.ChunkChannel
+            // invokes FileChannel::transferFrom(ReadableByteChannel, position, count) twice.
+            // FileChannel will return 0 the second time because position exceeds
+            // FileChannel::size(), which is always 0 for /dev/null
+            // Without proper handling of return value 0, the ChunkChannel will spin indefinitely.
+            try (Recording r2 = new Recording()) {
+                r2.start();
+            }
+        }
+    }
+}