true if the file was created, false if
* the file already existed
- * @throws IOException
+ * @throws java.io.IOException
+ * @deprecated use {@link #createNewFileAtomic(File)} instead
* @since 4.5
*/
+ @Deprecated
public boolean createNewFile(File path) throws IOException {
return path.createNewFile();
}
+ /**
+ * A token representing a file created by
+ * {@link #createNewFileAtomic(File)}. The token must be retained until the
+ * file has been deleted in order to guarantee that the unique file was
+ * created atomically. As soon as the file is no longer needed the lock
+ * token must be closed.
+ *
+ * @since 4.7
+ */
+ public static class LockToken implements Closeable {
+ private boolean isCreated;
+
+ private Optionalfalse
+ *
+ * @param path
+ * the file to be created
+ * @return LockToken this token must be closed after the created file was
+ * deleted
+ * @throws IOException
+ * @since 4.7
+ */
+ public LockToken createNewFileAtomic(File path) throws IOException {
+ return new LockToken(path.createNewFile(), Optional.empty());
+ }
+
/**
* See {@link FileUtils#relativizePath(String, String, String, boolean)}.
*
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
index 76aa69776..607e07860 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java
@@ -52,14 +52,19 @@ import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.PosixFilePermission;
+import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
+import java.util.Optional;
import java.util.Set;
+import java.util.UUID;
+import org.eclipse.jgit.annotations.Nullable;
import org.eclipse.jgit.api.errors.JGitInternalException;
import org.eclipse.jgit.errors.CommandFailedException;
import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.ConfigConstants;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.Repository;
@@ -360,9 +365,12 @@ public class FS_POSIX extends FS {
* multiple clients manage to create the same lock file nlink would be
* greater than 2 showing the error.
*
- * @see https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html
+ * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
+ *
+ * @deprecated use {@link FS_POSIX#createNewFileAtomic(File)} instead
* @since 4.5
*/
+ @Deprecated
public boolean createNewFile(File lock) throws IOException {
if (!lock.createNewFile()) {
return false;
@@ -371,22 +379,94 @@ public class FS_POSIX extends FS {
return true;
}
Path lockPath = lock.toPath();
- Path link = Files.createLink(Paths.get(lock.getAbsolutePath() + ".lnk"), //$NON-NLS-1$
- lockPath);
+ Path link = null;
try {
+ link = Files.createLink(
+ Paths.get(lock.getAbsolutePath() + ".lnk"), //$NON-NLS-1$
+ lockPath);
Integer nlink = (Integer) (Files.getAttribute(lockPath,
"unix:nlink")); //$NON-NLS-1$
- if (nlink != 2) {
+ if (nlink > 2) {
LOG.warn("nlink of link to lock file {0} was not 2 but {1}", //$NON-NLS-1$
lock.getPath(), nlink);
return false;
+ } else if (nlink < 2) {
+ supportsUnixNLink = false;
}
return true;
} catch (UnsupportedOperationException | IllegalArgumentException e) {
supportsUnixNLink = false;
return true;
} finally {
- Files.delete(link);
+ if (link != null) {
+ Files.delete(link);
+ }
}
}
+
+ /**
+ * {@inheritDoc}
+ * + * An implementation of the File#createNewFile() semantics which can create + * a unique file atomically also on NFS. If the config option + * {@code core.supportsAtomicCreateNewFile = true} (which is the default) + * then simply File#createNewFile() is called. + * + * But if {@code core.supportsAtomicCreateNewFile = false} then after + * successful creation of the lock file a hard link to that lock file is + * created and the attribute nlink of the lock file is checked to be 2. If + * multiple clients manage to create the same lock file nlink would be + * greater than 2 showing the error. The hard link needs to be retained + * until the corresponding file is no longer needed in order to prevent that + * another process can create the same file concurrently using another NFS + * client which might not yet see the file due to caching. + * + * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html" + * @param file + * the unique file to be created atomically + * @return LockToken this lock token must be held until the file is no + * longer needed + * @throws IOException + * @since 5.0 + */ + @Override + public LockToken createNewFileAtomic(File file) throws IOException { + if (!file.createNewFile()) { + return token(false, null); + } + if (supportsAtomicCreateNewFile() || !supportsUnixNLink) { + return token(true, null); + } + Path link = null; + Path path = file.toPath(); + try { + link = Files.createLink(Paths.get(uniqueLinkPath(file)), path); + Integer nlink = (Integer) (Files.getAttribute(path, + "unix:nlink")); //$NON-NLS-1$ + if (nlink.intValue() > 2) { + LOG.warn(MessageFormat.format( + JGitText.get().failedAtomicFileCreation, path, nlink)); + return token(false, link); + } else if (nlink.intValue() < 2) { + supportsUnixNLink = false; + } + return token(true, link); + } catch (UnsupportedOperationException | IllegalArgumentException e) { + supportsUnixNLink = false; + return token(true, link); + } + } + + private static LockToken token(boolean created, @Nullable Path p) { + return ((p != null) && Files.exists(p)) + ? new LockToken(created, Optional.of(p)) + : new LockToken(created, Optional.empty()); + } + + private static String uniqueLinkPath(File file) { + UUID id = UUID.randomUUID(); + return file.getAbsolutePath() + "." //$NON-NLS-1$ + + Long.toHexString(id.getMostSignificantBits()) + + Long.toHexString(id.getLeastSignificantBits()); + } }