8080115: (fs) Crash in libgio when calling Files.probeContentType(path) from parallel threads

Make GnomeFileTypeDetector.probeGio() synchronized and add a regression test based on the test source included in JDK-8080115.

Reviewed-by: chegar

jdk/src/java.base/unix/classes/sun/nio/fs/GnomeFileTypeDetector.java

@@ -67,7 +67,7 @@ public class GnomeFileTypeDetector
 
     // GIO
     private static native boolean initializeGio();
-    private static native byte[] probeGio(long pathAddress);
+    private static synchronized native byte[] probeGio(long pathAddress);
 
     static {
         AccessController.doPrivileged(new PrivilegedAction<>() {

jdk/test/java/nio/file/Files/probeContentType/ParallelProbes.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2015, 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.
+ */
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+
+/* @test
+ * @summary Test probing content type simultaneously from multiple threads.
+ * @requires (os.family == "linux") | (os.family == "solaris")
+ * @run main/othervm ParallelProbes 10
+ */
+public class ParallelProbes {
+
+    private static final int REPEATS = 1000;
+
+    private int numThreads = 0;
+    private ArrayList<Thread> threads;
+
+    public ParallelProbes(int numThreads) {
+        System.out.println("Using <" + numThreads + "> threads.");
+        this.numThreads = numThreads;
+        this.threads = new ArrayList<Thread>(numThreads);
+    }
+
+    private Path createTmpFile() throws IOException {
+        final Path p = Files.createTempFile("prefix", ".json");
+        Files.write(p, "{\"test\"}".getBytes());
+        System.out.println("Write test file <" + p + ">");
+        return p;
+    }
+
+    private Runnable createRunnable(final Path p) {
+        Runnable r = new Runnable() {
+            public void run() {
+                for (int i = 0; i < REPEATS; i++) {
+                    try {
+                        System.out.println(Thread.currentThread().getName()
+                            + " -> " + Files.probeContentType(p));
+                    } catch (IOException ioException) {
+                        ioException.printStackTrace();
+                    }
+                }
+            }
+        };
+        return r;
+    }
+
+    public void start() throws IOException {
+        for (int i = 0; i < numThreads; i++) {
+            final Path p = createTmpFile();
+            Runnable r = createRunnable(p);
+            Thread thread = new Thread(r, "thread-" + i);
+            thread.start();
+            threads.add(thread);
+        }
+    }
+
+    public void join() {
+        for (Thread thread : threads) {
+            try {
+                thread.join();
+            } catch (InterruptedException e) {
+                // ignore it and proceed to the next one
+            }
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        ParallelProbes probes =
+            new ParallelProbes(args.length < 1 ? 1 : Integer.parseInt(args[0]));
+        probes.start();
+        probes.join();
+    }
+}