LockFile.java
/*
* Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
* Copyright (C) 2006-2021, Shawn O. Pearce <spearce@spearce.org> and others
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0 which is available at
* https://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.eclipse.jgit.internal.storage.file;
import static org.eclipse.jgit.lib.Constants.LOCK_SUFFIX;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FilenameFilter;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.StandardCopyOption;
import java.nio.file.attribute.FileTime;
import java.text.MessageFormat;
import java.time.Instant;
import java.util.concurrent.TimeUnit;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.util.FS;
import org.eclipse.jgit.util.FS.LockToken;
import org.eclipse.jgit.util.FileUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Git style file locking and replacement.
* <p>
* To modify a ref file Git tries to use an atomic update approach: we write the
* new data into a brand new file, then rename it in place over the old name.
* This way we can just delete the temporary file if anything goes wrong, and
* nothing has been damaged. To coordinate access from multiple processes at
* once Git tries to atomically create the new temporary file under a well-known
* name.
*/
public class LockFile {
private static final Logger LOG = LoggerFactory.getLogger(LockFile.class);
/**
* Unlock the given file.
* <p>
* This method can be used for recovering from a thrown
* {@link org.eclipse.jgit.errors.LockFailedException} . This method does
* not validate that the lock is or is not currently held before attempting
* to unlock it.
*
* @param file
* a {@link java.io.File} object.
* @return true if unlocked, false if unlocking failed
*/
public static boolean unlock(File file) {
final File lockFile = getLockFile(file);
final int flags = FileUtils.RETRY | FileUtils.SKIP_MISSING;
try {
FileUtils.delete(lockFile, flags);
} catch (IOException ignored) {
// Ignore and return whether lock file still exists
}
return !lockFile.exists();
}
/**
* Get the lock file corresponding to the given file.
*
* @param file
* @return lock file
*/
static File getLockFile(File file) {
return new File(file.getParentFile(),
file.getName() + LOCK_SUFFIX);
}
/** Filter to skip over active lock files when listing a directory. */
static final FilenameFilter FILTER = (File dir,
String name) -> !name.endsWith(LOCK_SUFFIX);
private final File ref;
private final File lck;
private boolean haveLck;
private FileOutputStream os;
private boolean needSnapshot;
private boolean fsync;
private boolean isAppend;
private boolean written;
private boolean snapshotNoConfig;
private FileSnapshot commitSnapshot;
private LockToken token;
/**
* Create a new lock for any file.
*
* @param f
* the file that will be locked.
*/
public LockFile(File f) {
ref = f;
lck = getLockFile(ref);
}
/**
* Try to establish the lock.
*
* @return true if the lock is now held by the caller; false if it is held
* by someone else.
* @throws java.io.IOException
* the temporary output file could not be created. The caller
* does not hold the lock.
*/
public boolean lock() throws IOException {
if (haveLck) {
throw new IllegalStateException(
MessageFormat.format(JGitText.get().lockAlreadyHeld, ref));
}
FileUtils.mkdirs(lck.getParentFile(), true);
try {
token = FS.DETECTED.createNewFileAtomic(lck);
} catch (IOException e) {
LOG.error(JGitText.get().failedCreateLockFile, lck, e);
throw e;
}
boolean obtainedLock = token.isCreated();
if (obtainedLock) {
haveLck = true;
isAppend = false;
written = false;
} else {
closeToken();
}
return obtainedLock;
}
/**
* Try to establish the lock for appending.
*
* @return true if the lock is now held by the caller; false if it is held
* by someone else.
* @throws java.io.IOException
* the temporary output file could not be created. The caller
* does not hold the lock.
*/
public boolean lockForAppend() throws IOException {
if (!lock()) {
return false;
}
copyCurrentContent();
isAppend = true;
written = false;
return true;
}
// For tests only
boolean isLocked() {
return haveLck;
}
private FileOutputStream getStream() throws IOException {
return new FileOutputStream(lck, isAppend);
}
/**
* Copy the current file content into the temporary file.
* <p>
* This method saves the current file content by inserting it into the
* temporary file, so that the caller can safely append rather than replace
* the primary file.
* <p>
* This method does nothing if the current file does not exist, or exists
* but is empty.
*
* @throws java.io.IOException
* the temporary file could not be written, or a read error
* occurred while reading from the current file. The lock is
* released before throwing the underlying IO exception to the
* caller.
* @throws java.lang.RuntimeException
* the temporary file could not be written. The lock is released
* before throwing the underlying exception to the caller.
*/
public void copyCurrentContent() throws IOException {
requireLock();
try (FileOutputStream out = getStream()) {
try (FileInputStream fis = new FileInputStream(ref)) {
if (fsync) {
FileChannel in = fis.getChannel();
long pos = 0;
long cnt = in.size();
while (0 < cnt) {
long r = out.getChannel().transferFrom(in, pos, cnt);
pos += r;
cnt -= r;
}
} else {
final byte[] buf = new byte[2048];
int r;
while ((r = fis.read(buf)) >= 0) {
out.write(buf, 0, r);
}
}
} catch (FileNotFoundException fnfe) {
if (ref.exists()) {
throw fnfe;
}
// Don't worry about a file that doesn't exist yet, it
// conceptually has no current content to copy.
}
} catch (IOException | RuntimeException | Error ioe) {
unlock();
throw ioe;
}
}
/**
* Write an ObjectId and LF to the temporary file.
*
* @param id
* the id to store in the file. The id will be written in hex,
* followed by a sole LF.
* @throws java.io.IOException
* the temporary file could not be written. The lock is released
* before throwing the underlying IO exception to the caller.
* @throws java.lang.RuntimeException
* the temporary file could not be written. The lock is released
* before throwing the underlying exception to the caller.
*/
public void write(ObjectId id) throws IOException {
byte[] buf = new byte[Constants.OBJECT_ID_STRING_LENGTH + 1];
id.copyTo(buf, 0);
buf[Constants.OBJECT_ID_STRING_LENGTH] = '\n';
write(buf);
}
/**
* Write arbitrary data to the temporary file.
*
* @param content
* the bytes to store in the temporary file. No additional bytes
* are added, so if the file must end with an LF it must appear
* at the end of the byte array.
* @throws java.io.IOException
* the temporary file could not be written. The lock is released
* before throwing the underlying IO exception to the caller.
* @throws java.lang.RuntimeException
* the temporary file could not be written. The lock is released
* before throwing the underlying exception to the caller.
*/
public void write(byte[] content) throws IOException {
requireLock();
try (FileOutputStream out = getStream()) {
if (written) {
throw new IOException(MessageFormat
.format(JGitText.get().lockStreamClosed, ref));
}
if (fsync) {
FileChannel fc = out.getChannel();
ByteBuffer buf = ByteBuffer.wrap(content);
while (0 < buf.remaining()) {
fc.write(buf);
}
fc.force(true);
} else {
out.write(content);
}
written = true;
} catch (IOException | RuntimeException | Error ioe) {
unlock();
throw ioe;
}
}
/**
* Obtain the direct output stream for this lock.
* <p>
* The stream may only be accessed once, and only after {@link #lock()} has
* been successfully invoked and returned true. Callers must close the
* stream prior to calling {@link #commit()} to commit the change.
*
* @return a stream to write to the new file. The stream is unbuffered.
*/
public OutputStream getOutputStream() {
requireLock();
if (written || os != null) {
throw new IllegalStateException(MessageFormat
.format(JGitText.get().lockStreamMultiple, ref));
}
return new OutputStream() {
private OutputStream out;
private boolean closed;
private OutputStream get() throws IOException {
if (written) {
throw new IOException(MessageFormat
.format(JGitText.get().lockStreamMultiple, ref));
}
if (out == null) {
os = getStream();
if (fsync) {
out = Channels.newOutputStream(os.getChannel());
} else {
out = os;
}
}
return out;
}
@Override
public void write(byte[] b, int o, int n) throws IOException {
get().write(b, o, n);
}
@Override
public void write(byte[] b) throws IOException {
get().write(b);
}
@Override
public void write(int b) throws IOException {
get().write(b);
}
@Override
public void close() throws IOException {
if (closed) {
return;
}
closed = true;
try {
if (written) {
throw new IOException(MessageFormat
.format(JGitText.get().lockStreamClosed, ref));
}
if (out != null) {
if (fsync) {
os.getChannel().force(true);
}
out.close();
os = null;
}
written = true;
} catch (IOException | RuntimeException | Error ioe) {
unlock();
throw ioe;
}
}
};
}
void requireLock() {
if (!haveLck) {
unlock();
throw new IllegalStateException(MessageFormat.format(JGitText.get().lockOnNotHeld, ref));
}
}
/**
* Request that {@link #commit()} remember modification time.
* <p>
* This is an alias for {@code setNeedSnapshot(true)}.
*
* @param on
* true if the commit method must remember the modification time.
*/
public void setNeedStatInformation(boolean on) {
setNeedSnapshot(on);
}
/**
* Request that {@link #commit()} remember the
* {@link org.eclipse.jgit.internal.storage.file.FileSnapshot}.
*
* @param on
* true if the commit method must remember the FileSnapshot.
*/
public void setNeedSnapshot(boolean on) {
needSnapshot = on;
}
/**
* Request that {@link #commit()} remember the
* {@link org.eclipse.jgit.internal.storage.file.FileSnapshot} without using
* config file to get filesystem timestamp resolution.
* This method should be invoked before the file is accessed.
* It is used by FileBasedConfig to avoid endless recursion.
*
* @param on
* true if the commit method must remember the FileSnapshot.
*/
public void setNeedSnapshotNoConfig(boolean on) {
needSnapshot = on;
snapshotNoConfig = on;
}
/**
* Request that {@link #commit()} force dirty data to the drive.
*
* @param on
* true if dirty data should be forced to the drive.
*/
public void setFSync(boolean on) {
fsync = on;
}
/**
* Wait until the lock file information differs from the old file.
* <p>
* This method tests the last modification date. If both are the same, this
* method sleeps until it can force the new lock file's modification date to
* be later than the target file.
*
* @throws java.lang.InterruptedException
* the thread was interrupted before the last modified date of
* the lock file was different from the last modified date of
* the target file.
*/
public void waitForStatChange() throws InterruptedException {
FileSnapshot o = FileSnapshot.save(ref);
FileSnapshot n = FileSnapshot.save(lck);
long fsTimeResolution = FS.getFileStoreAttributes(lck.toPath())
.getFsTimestampResolution().toNanos();
while (o.equals(n)) {
TimeUnit.NANOSECONDS.sleep(fsTimeResolution);
try {
Files.setLastModifiedTime(lck.toPath(),
FileTime.from(Instant.now()));
} catch (IOException e) {
n.waitUntilNotRacy();
}
n = FileSnapshot.save(lck);
}
}
/**
* Commit this change and release the lock.
* <p>
* If this method fails (returns false) the lock is still released.
*
* @return true if the commit was successful and the file contains the new
* data; false if the commit failed and the file remains with the
* old data.
* @throws java.lang.IllegalStateException
* the lock is not held.
*/
public boolean commit() {
if (os != null) {
unlock();
throw new IllegalStateException(MessageFormat.format(JGitText.get().lockOnNotClosed, ref));
}
saveStatInformation();
try {
FileUtils.rename(lck, ref, StandardCopyOption.ATOMIC_MOVE);
haveLck = false;
isAppend = false;
written = false;
closeToken();
return true;
} catch (IOException e) {
unlock();
return false;
}
}
private void closeToken() {
if (token != null) {
token.close();
token = null;
}
}
private void saveStatInformation() {
if (needSnapshot) {
commitSnapshot = snapshotNoConfig ?
// don't use config in this snapshot to avoid endless recursion
FileSnapshot.saveNoConfig(lck)
: FileSnapshot.save(lck);
}
}
/**
* Get the modification time of the output file when it was committed.
*
* @return modification time of the lock file right before we committed it.
* @deprecated use {@link #getCommitLastModifiedInstant()} instead
*/
@Deprecated
public long getCommitLastModified() {
return commitSnapshot.lastModified();
}
/**
* Get the modification time of the output file when it was committed.
*
* @return modification time of the lock file right before we committed it.
*/
public Instant getCommitLastModifiedInstant() {
return commitSnapshot.lastModifiedInstant();
}
/**
* Get the {@link FileSnapshot} just before commit.
*
* @return get the {@link FileSnapshot} just before commit.
*/
public FileSnapshot getCommitSnapshot() {
return commitSnapshot;
}
/**
* Update the commit snapshot {@link #getCommitSnapshot()} before commit.
* <p>
* This may be necessary if you need time stamp before commit occurs, e.g
* while writing the index.
*/
public void createCommitSnapshot() {
saveStatInformation();
}
/**
* Unlock this file and abort this change.
* <p>
* The temporary file (if created) is deleted before returning.
*/
public void unlock() {
if (os != null) {
try {
os.close();
} catch (IOException e) {
LOG.error(MessageFormat
.format(JGitText.get().unlockLockFileFailed, lck), e);
}
os = null;
}
if (haveLck) {
haveLck = false;
try {
FileUtils.delete(lck, FileUtils.RETRY);
} catch (IOException e) {
LOG.error(MessageFormat
.format(JGitText.get().unlockLockFileFailed, lck), e);
} finally {
closeToken();
}
}
isAppend = false;
written = false;
}
/** {@inheritDoc} */
@SuppressWarnings("nls")
@Override
public String toString() {
return "LockFile[" + lck + ", haveLck=" + haveLck + "]";
}
}