/*
* Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
* Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Git Development Community nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.spearce.jgit.lib;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
/**
* 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 final File ref;
private final File lck;
private FileLock fLck;
private boolean haveLck;
private FileOutputStream os;
private boolean needStatInformation;
private long commitLastModified;
/**
* Create a new lock for any file.
*
* @param f
* the file that will be locked.
*/
public LockFile(final File f) {
ref = f;
lck = new File(ref.getParentFile(), ref.getName() + ".lock");
}
/**
* 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 IOException
* the temporary output file could not be created. The caller
* does not hold the lock.
*/
public boolean lock() throws IOException {
lck.getParentFile().mkdirs();
if (lck.createNewFile()) {
haveLck = true;
try {
os = new FileOutputStream(lck);
try {
fLck = os.getChannel().tryLock();
if (fLck == null)
throw new OverlappingFileLockException();
} catch (OverlappingFileLockException ofle) {
// We cannot use unlock() here as this file is not
// held by us, but we thought we created it. We must
// not delete it, as it belongs to some other process.
//
haveLck = false;
try {
os.close();
} catch (IOException ioe) {
// Fail by returning haveLck = false.
}
os = null;
}
} catch (IOException ioe) {
unlock();
throw ioe;
}
}
return haveLck;
}
/**
* 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 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();
return true;
}
/**
* 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 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 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 {
final FileInputStream fis = new FileInputStream(ref);
try {
final byte[] buf = new byte[2048];
int r;
while ((r = fis.read(buf)) >= 0)
os.write(buf, 0, r);
} finally {
fis.close();
}
} catch (FileNotFoundException fnfe) {
// Don't worry about a file that doesn't exist yet, it
// conceptually has no current content to copy.
//
} catch (IOException ioe) {
unlock();
throw ioe;
} catch (RuntimeException ioe) {
unlock();
throw ioe;
} catch (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 IOException
* the temporary file could not be written. The lock is released
* before throwing the underlying IO exception to the caller.
* @throws RuntimeException
* the temporary file could not be written. The lock is released
* before throwing the underlying exception to the caller.
*/
public void write(final ObjectId id) throws IOException {
requireLock();
try {
final BufferedOutputStream b;
b = new BufferedOutputStream(os, Constants.OBJECT_ID_LENGTH * 2 + 1);
id.copyTo(b);
b.write('\n');
b.flush();
fLck.release();
b.close();
os = null;
} catch (IOException ioe) {
unlock();
throw ioe;
} catch (RuntimeException ioe) {
unlock();
throw ioe;
} catch (Error ioe) {
unlock();
throw ioe;
}
}
/**
* 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 IOException
* the temporary file could not be written. The lock is released
* before throwing the underlying IO exception to the caller.
* @throws RuntimeException
* the temporary file could not be written. The lock is released
* before throwing the underlying exception to the caller.
*/
public void write(final byte[] content) throws IOException {
requireLock();
try {
os.write(content);
os.flush();
fLck.release();
os.close();
os = null;
} catch (IOException ioe) {
unlock();
throw ioe;
} catch (RuntimeException ioe) {
unlock();
throw ioe;
} catch (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();
return new OutputStream() {
@Override
public void write(final byte[] b, final int o, final int n)
throws IOException {
os.write(b, o, n);
}
@Override
public void write(final byte[] b) throws IOException {
os.write(b);
}
@Override
public void write(final int b) throws IOException {
os.write(b);
}
@Override
public void flush() throws IOException {
os.flush();
}
@Override
public void close() throws IOException {
try {
os.flush();
fLck.release();
os.close();
os = null;
} catch (IOException ioe) {
unlock();
throw ioe;
} catch (RuntimeException ioe) {
unlock();
throw ioe;
} catch (Error ioe) {
unlock();
throw ioe;
}
}
};
}
private void requireLock() {
if (os == null) {
unlock();
throw new IllegalStateException("Lock on " + ref + " not held.");
}
}
/**
* Request that {@link #commit()} remember modification time.
*
* @param on
* true if the commit method must remember the modification time.
*/
public void setNeedStatInformation(final boolean on) {
needStatInformation = on;
}
/**
* 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 IllegalStateException
* the lock is not held.
*/
public boolean commit() {
if (os != null) {
unlock();
throw new IllegalStateException("Lock on " + ref + " not closed.");
}
saveStatInformation();
if (lck.renameTo(ref))
return true;
if (!ref.exists() || ref.delete())
if (lck.renameTo(ref))
return true;
unlock();
return false;
}
private void saveStatInformation() {
if (needStatInformation)
commitLastModified = lck.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 long getCommitLastModified() {
return commitLastModified;
}
/**
* Unlock this file and abort this change.
* <p>
* The temporary file (if created) is deleted before returning.
*/
public void unlock() {
if (os != null) {
if (fLck != null) {
try {
fLck.release();
} catch (IOException ioe) {
// Huh?
}
fLck = null;
}
try {
os.close();
} catch (IOException ioe) {
// Ignore this
}
os = null;
}
if (haveLck) {
haveLck = false;
lck.delete();
}
}
@Override
public String toString() {
return "LockFile[" + lck + ", haveLck=" + haveLck + "]";
}
}