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package com.sun.jdo.spi.persistence.utility;
import java.util.ResourceBundle;
import com.sun.jdo.spi.persistence.utility.logging.Logger;
import org.glassfish.persistence.common.I18NHelper;
/** Implements a simple semaphore.
*
* @author Dave Bristor
* @author Marina Vatkina
*/
// db13166: I would rather we use Doug Lea's stuff, but don't want to
// introduce that magnitude of change at this point in time.
public class SemaphoreImpl implements Semaphore {
/** Where to log messages about locking operations
*/
private static final Logger _logger = LogHelperUtility.getLogger();
/** For logging, indicates on whose behalf locking is done.
*/
private final String _owner;
/** Synchronizes the lock.
*/
private final Object _lock = new Object();
/** Thread which holds the lock.
*/
private Thread _holder = null;
/** Semaphore counter.
*/
private int _counter = 0;
/**
* I18N message handler
*/
private final static ResourceBundle messages =
I18NHelper.loadBundle(SemaphoreImpl.class);
public SemaphoreImpl(String owner) {
_owner = owner;
}
/** Acquire a lock.
*/
public void acquire() {
boolean debug = _logger.isLoggable(Logger.FINEST);
if (debug) {
Object[] items = new Object[] {_owner, Thread.currentThread(),new Integer(_counter)};
_logger.finest("utility.semaphoreimpl.acquire",items); // NOI18N
}
synchronized (_lock) {
//
// If the current thread already holds this lock, we simply
// update the count and return.
//
if (Thread.currentThread() == _holder) {
_counter++;
} else {
while (_counter > 0) {
try {
// wait for the lock to be released
_lock.wait();
} catch (InterruptedException e) {
}
}
_holder = Thread.currentThread();
_counter++;
if (debug) {
Object[] items = new Object[] {_owner, Thread.currentThread(),new Integer(_counter)};
_logger.finest("utility.semaphoreimpl.gotlock",items); // NOI18N
}
}
}
}
/** Release a lock.
*/
public void release() {
boolean debug = _logger.isLoggable(Logger.FINEST);
if (debug) {
Object[] items = new Object[] {_owner, Thread.currentThread(),new Integer(_counter)};
_logger.finest("utility.semaphoreimpl.release",items); // NOI18N
}
synchronized (_lock) {
//
// If the current thread already holds this lock, we simply
// update the count and return.
//
if (Thread.currentThread() == _holder) {
if (--_counter == 0) {
_holder = null;
_lock.notify();
}
} else {
throw new IllegalMonitorStateException(
I18NHelper.getMessage(messages,
"utility.semaphoreimpl.wrongthread", // NOI18N
new Object[] {_owner, Thread.currentThread()}));
}
}
}
}