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Add file access synchronization to prevent conflicting tile updates

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This commit is contained in:
Mike Primm 2011-05-31 21:20:23 -05:00
parent 5dbb69f2fe
commit c48d06eec1
5 changed files with 135 additions and 2 deletions
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105
src/main/java/org/dynmap/utils/FileLockManager.java Normal file
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@ -0,0 +1,105 @@
package org.dynmap.utils;
import java.io.File;
import java.util.HashMap;
import org.dynmap.Log;
/**
* Implements soft-locks for prevent concurrency issues with file updates
*/
public class FileLockManager {
private static Object lock = new Object();
private static HashMap<String, Integer> filelocks = new HashMap<String, Integer>();
private static final Integer WRITELOCK = new Integer(-1);
/**
* Get write lock on file - exclusive lock, no other writers or readers
* @throws InterruptedException
*/
public static void getWriteLock(File f) {
String fn = f.getPath();
synchronized(lock) {
boolean got_lock = false;
while(!got_lock) {
Integer lockcnt = filelocks.get(fn); /* Get lock count */
if(lockcnt != null) { /* If any locks, can't get write lock */
try {
lock.wait();
} catch (InterruptedException ix) {
Log.severe("getWriteLock(" + fn + ") interrupted");
}
}
else {
filelocks.put(fn, WRITELOCK);
got_lock = true;
}
}
}
//Log.info("getWriteLock(" + f + ")");
}
/**
* Release write lock
*/
public static void releaseWriteLock(File f) {
String fn = f.getPath();
synchronized(lock) {
Integer lockcnt = filelocks.get(fn); /* Get lock count */
if(lockcnt == null)
Log.severe("releaseWriteLock(" + fn + ") on unlocked file");
else if(lockcnt.equals(WRITELOCK)) {
filelocks.remove(fn); /* Remove lock */
lock.notifyAll(); /* Wake up folks waiting for locks */
}
else
Log.severe("releaseWriteLock(" + fn + ") on read-locked file");
}
//Log.info("releaseWriteLock(" + f + ")");
}
/**
* Get read lock on file - multiple readers allowed, blocks writers
*/
public static void getReadLock(File f) {
String fn = f.getPath();
synchronized(lock) {
boolean got_lock = false;
while(!got_lock) {
Integer lockcnt = filelocks.get(fn); /* Get lock count */
if(lockcnt == null) {
filelocks.put(fn, Integer.valueOf(1)); /* First lock */
got_lock = true;
}
else if(!lockcnt.equals(WRITELOCK)) { /* Other read locks */
filelocks.put(fn, Integer.valueOf(lockcnt+1));
got_lock = true;
}
else { /* Write lock in place */
try {
lock.wait();
} catch (InterruptedException ix) {
Log.severe("getReadLock(" + fn + ") interrupted");
}
}
}
}
//Log.info("getReadLock(" + f + ")");
}
/**
* Release read lock
*/
public static void releaseReadLock(File f) {
String fn = f.getPath();
synchronized(lock) {
Integer lockcnt = filelocks.get(fn); /* Get lock count */
if(lockcnt == null)
Log.severe("releaseReadLock(" + fn + ") on unlocked file");
else if(lockcnt.equals(WRITELOCK))
Log.severe("releaseReadLock(" + fn + ") on write-locked file");
else if(lockcnt > 1) {
filelocks.put(fn, Integer.valueOf(lockcnt-1));
}
else {
filelocks.remove(fn); /* Remove lock */
lock.notifyAll(); /* Wake up folks waiting for locks */
}
}
//Log.info("releaseReadLock(" + f + ")");
}
}