com.fasterxml.uuid.ext.LockedFile Maven / Gradle / Ivy
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/* JUG Java Uuid Generator
*
* Copyright (c) 2002- Tatu Saloranta, [email protected]
*
* Licensed under the License specified in the file LICENSE which is
* included with the source code.
* You may not use this file except in compliance with the License.
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.fasterxml.uuid.ext;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Utility class used by {@link FileBasedTimestampSynchronizer} to do
* actual file access and locking.
*
* Class stores simple timestamp values based on system time accessed
* using System.currentTimeMillis(). A single timestamp
* is stored into a file using {@link RandomAccessFile} in fully
* synchronized mode. Value is written in ISO-Latin (ISO-8859-1)
* encoding (superset of Ascii, 1 byte per char) as 16-digit hexadecimal
* number, surrounded by brackets. As such, file produced should
* always have exact size of 18 bytes. For extra robustness, slight
* variations in number of digits are accepeted, as are white space
* chars before and after bracketed value.
*/
class LockedFile
{
private static final Logger logger = LoggerFactory.getLogger(LockedFile.class);
/**
* Expected file length comes from hex-timestamp (16 digits),
* preamble "[0x",(3 chars) and trailer "]\r\n" (2 chars, linefeed
* to help debugging -- in some environments, missing trailing linefeed
* causes problems: also, 2-char linefeed to be compatible with all
* standard linefeeds on MacOS, Unix and Windows).
*/
final static int DEFAULT_LENGTH = 22;
final static long READ_ERROR = 0L;
// // // Configuration:
final File mFile;
// // // File state
RandomAccessFile mRAFile;
FileChannel mChannel;
FileLock mLock;
ByteBuffer mWriteBuffer = null;
/**
* Flag set if the original file (created before this instance was
* created) had size other than default size and needs to be
* truncated
*/
boolean mWeirdSize;
/**
* Marker used to ensure that the timestamps stored are monotonously
* increasing. Shouldn't really be needed, since caller should take
* care of it, but let's be bit paranoid here.
*/
long mLastTimestamp = 0L;
LockedFile(File f)
throws IOException
{
mFile = f;
RandomAccessFile raf = null;
FileChannel channel = null;
FileLock lock = null;
boolean ok = false;
try { // let's just use a single block to share cleanup code
raf = new RandomAccessFile(f, "rwd");
// Then lock them, if possible; if not, let's err out
channel = raf.getChannel();
if (channel == null) {
throw new IOException("Failed to access channel for '"+f+"'");
}
lock = channel.tryLock();
if (lock == null) {
throw new IOException("Failed to lock '"+f+"' (another JVM running UUIDGenerator?)");
}
ok = true;
} finally {
if (!ok) {
doDeactivate(f, raf, lock);
}
}
mRAFile = raf;
mChannel = channel;
mLock = lock;
}
public void deactivate()
{
RandomAccessFile raf = mRAFile;
mRAFile = null;
FileLock lock = mLock;
mLock = null;
doDeactivate(mFile, raf, lock);
}
public long readStamp()
{
int size;
try {
size = (int) mChannel.size();
} catch (IOException ioe) {
logger.error("Failed to read file size", ioe);
return READ_ERROR;
}
mWeirdSize = (size != DEFAULT_LENGTH);
// Let's check specifically empty files though
if (size == 0) {
logger.warn("Missing or empty file, can not read timestamp value");
return READ_ERROR;
}
// Let's also allow some slack... but just a bit
if (size > 100) {
size = 100;
}
byte[] data = new byte[size];
try {
mRAFile.readFully(data);
} catch (IOException ie) {
logger.error("(file '{}') Failed to read {} bytes", mFile, size, ie);
return READ_ERROR;
}
/* Ok, got data. Now, we could just directly parse the bytes (since
* it is single-byte encoding)... but for convenience, let's create
* the String (this is only called once per JVM session)
*/
char[] cdata = new char[size];
for (int i = 0; i < size; ++i) {
cdata[i] = (char) (data[i] & 0xFF);
}
String dataStr = new String(cdata);
// And let's trim leading (and trailing, who cares)
dataStr = dataStr.trim();
long result = -1;
String err = null;
if (!dataStr.startsWith("[0")
|| dataStr.length() < 3
|| Character.toLowerCase(dataStr.charAt(2)) != 'x') {
err = "does not start with '[0x' prefix";
} else {
int ix = dataStr.indexOf(']', 3);
if (ix <= 0) {
err = "does not end with ']' marker";
} else {
String hex = dataStr.substring(3, ix);
if (hex.length() > 16) {
err = "length of the (hex) timestamp too long; expected 16, had "+hex.length()+" ('"+hex+"')";
} else {
try {
result = Long.parseLong(hex, 16);
} catch (NumberFormatException nex) {
err = "does not contain a valid hex timestamp; got '"
+hex+"' (parse error: "+nex+")";
}
}
}
}
// Unsuccesful?
if (result < 0L) {
logger.error("(file '{}') Malformed timestamp file contents: {}", mFile, err);
return READ_ERROR;
}
mLastTimestamp = result;
return result;
}
final static String HEX_DIGITS = "0123456789abcdef";
public void writeStamp(long stamp)
throws IOException
{
// Let's do sanity check first:
if (stamp <= mLastTimestamp) {
/* same stamp is not dangerous, but pointless... so warning,
* not an error:
*/
if (stamp == mLastTimestamp) {
logger.warn("(file '{}') Trying to re-write existing timestamp ({})", mFile, stamp);
return;
}
throw new IOException(""+mFile+" trying to overwrite existing value ("+mLastTimestamp+") with an earlier timestamp ("+stamp+")");
}
//System.err.println("!!!! Syncing ["+mFile+"] with "+stamp+" !!!");
// Need to initialize the buffer?
if (mWriteBuffer == null) {
mWriteBuffer = ByteBuffer.allocate(DEFAULT_LENGTH);
mWriteBuffer.put(0, (byte) '[');
mWriteBuffer.put(1, (byte) '0');
mWriteBuffer.put(2, (byte) 'x');
mWriteBuffer.put(19, (byte) ']');
mWriteBuffer.put(20, (byte) '\r');
mWriteBuffer.put(21, (byte) '\n');
}
// Converting to hex is simple
for (int i = 18; i >= 3; --i) {
int val = (((int) stamp) & 0x0F);
mWriteBuffer.put(i, (byte) HEX_DIGITS.charAt(val));
stamp = (stamp >> 4);
}
// and off we go:
mWriteBuffer.position(0); // to make sure we always write it all
mChannel.write(mWriteBuffer, 0L);
if (mWeirdSize) {
mRAFile.setLength(DEFAULT_LENGTH);
mWeirdSize = false;
}
// This is probably not needed (as the random access file is supposedly synced)... but let's be safe:
mChannel.force(false);
// And that's it!
}
/*
//////////////////////////////////////////////////////////////
// Internal methods
//////////////////////////////////////////////////////////////
*/
protected static void doDeactivate(File f, RandomAccessFile raf,
FileLock lock)
{
if (lock != null) {
try {
lock.release();
} catch (Throwable t) {
logger.error("Failed to release lock (for file '{}')", f, t);
}
}
if (raf != null) {
try {
raf.close();
} catch (Throwable t) {
logger.error("Failed to close file '{}'", f, t);
}
}
}
}