Use FileChannel.open to touch file and set mtime to now

Use options
- StandardOpenOption.CREATE to create touched file if not existing
- StandardOpenOption.SYNC to enforce synch of data and meta data changes
- StandardOpenOption.WRITE

Also set mtime explicitly in FileUtils#touch to the current system time.
This should fix that the previous implementation didn't work on
- locally cached Windows network share (CSC-CACHE filesystem) mapped as
a drive
- nfsv4 mounts on Linux
and that it didn't create unborn file like Linux command "touch".
Apache common's and Guava's touch() use the same approach.

Immediately after creating the probe file used to measure timestamp
resolution touch it. This ensures we always use the local system clock
when measuring filesystem timestamp resolution. This should prevent that
clock skew could influence the measured timestamp resolution in case of
a mounted network filesystem.

Bug: 548598
Change-Id: Iaeaf5967963f582395a195aa637b8188bfadac60
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

3 files changed, 11 insertions, 5 deletions

diff --git a/org.eclipse.jgit/.settings/.api_filters b/org.eclipse.jgit/.settings/.api_filters
index d313e92a05..5f58e7e457 100644
--- a/org.eclipse.jgit/.settings/.api_filters
+++ b/org.eclipse.jgit/.settings/.api_filters
@@ -153,7 +153,7 @@
     <resource path="src/org/eclipse/jgit/util/FileUtils.java" type="org.eclipse.jgit.util.FileUtils">
         <filter id="1142947843">
             <message_arguments>
-                <message_argument value="5.2.3"/>
+                <message_argument value="5.1.8"/>
                 <message_argument value="touch(Path)"/>
             </message_arguments>
         </filter>
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
index 687c7a4fdd..64dbf58233 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
@@ -294,6 +294,8 @@ public abstract class FS {
 			Path probe = dir.resolve(".probe-" + UUID.randomUUID()); //$NON-NLS-1$
 			try {
 				Files.createFile(probe);
+				// ensure we always use the local system clock
+				FileUtils.touch(probe);
 				long wait = 512;
 				long start = System.nanoTime();
 				FileTime t1 = Files.getLastModifiedTime(probe);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
index 9bba6ca8a3..9650602fea 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FileUtils.java
@@ -49,7 +49,7 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 
 import java.io.File;
 import java.io.IOException;
-import java.io.OutputStream;
+import java.nio.channels.FileChannel;
 import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.CopyOption;
 import java.nio.file.Files;
@@ -57,6 +57,7 @@ import java.nio.file.InvalidPathException;
 import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
+import java.nio.file.StandardOpenOption;
 import java.nio.file.attribute.BasicFileAttributeView;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.nio.file.attribute.FileTime;
@@ -66,6 +67,7 @@ import java.nio.file.attribute.PosixFilePermission;
 import java.text.MessageFormat;
 import java.text.Normalizer;
 import java.text.Normalizer.Form;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
@@ -916,11 +918,13 @@ public class FileUtils {
 	 * @param f
 	 *            the file to touch
 	 * @throws IOException
-	 * @since 5.2.3
+	 * @since 5.1.8
 	 */
 	public static void touch(Path f) throws IOException {
-		try (OutputStream fos = Files.newOutputStream(f)) {
-			// touch the file
+		try (FileChannel fc = FileChannel.open(f, StandardOpenOption.CREATE,
+				StandardOpenOption.APPEND, StandardOpenOption.SYNC)) {
+			// touch
 		}
+		Files.setLastModifiedTime(f, FileTime.from(Instant.now()));
 	}
 }