/*
* Copyright 2004-2023 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
* Iso8601:
* Initial Developer: Robert Rathsack (firstName dot lastName at gmx dot de)
*/
package org.h2.util;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
/**
* A phantom reference to watch for unclosed objects.
*/
public class CloseWatcher extends PhantomReference<Object> {
/**
* The queue (might be set to null at any time).
*/
private static final ReferenceQueue<Object> queue = new ReferenceQueue<>();
/**
* The reference set. Must keep it, otherwise the references are garbage
* collected first and thus never enqueued.
*/
private static final Set<CloseWatcher> refs = Collections.synchronizedSet(new HashSet<>());
/**
* The stack trace of when the object was created. It is converted to a
* string early on to avoid classloader problems (a classloader can't be
* garbage collected if there is a static reference to one of its classes).
*/
private String openStackTrace;
/**
* The closeable object.
*/
private AutoCloseable closeable;
public CloseWatcher(Object referent, ReferenceQueue<Object> q,
AutoCloseable closeable) {
super(referent, q);
this.closeable = closeable;
}
/**
* Check for an collected object.
*
* @return the first watcher
*/
public static CloseWatcher pollUnclosed() {
while (true) {
CloseWatcher cw = (CloseWatcher) queue.poll();
if (cw == null) {
return null;
}
if (refs != null) {
refs.remove(cw);
}
if (cw.closeable != null) {
return cw;
}
}
}
/**
* Register an object. Before calling this method, pollUnclosed() should be
* called in a loop to remove old references.
*
* @param o the object
* @param closeable the object to close
* @param stackTrace whether the stack trace should be registered (this is
* relatively slow)
* @return the close watcher
*/
public static CloseWatcher register(Object o, AutoCloseable closeable, boolean stackTrace) {
CloseWatcher cw = new CloseWatcher(o, queue, closeable);
if (stackTrace) {
Exception e = new Exception("Open Stack Trace");
StringWriter s = new StringWriter();
e.printStackTrace(new PrintWriter(s));
cw.openStackTrace = s.toString();
}
refs.add(cw);
return cw;
}
/**
* Unregister an object, so it is no longer tracked.
*
* @param w the reference
*/
public static void unregister(CloseWatcher w) {
w.closeable = null;
refs.remove(w);
}
/**
* Get the open stack trace or null if none.
*
* @return the open stack trace
*/
public String getOpenStackTrace() {
return openStackTrace;
}
public AutoCloseable getCloseable() {
return closeable;
}
}