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Jython is an implementation of the high-level, dynamic, object-oriented
language Python written in 100% Pure Java, and seamlessly integrated with
the Java platform. It thus allows you to run Python on any Java platform.
/* Copyright (c) Jython Developers */
package org.python.modules._weakref;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.python.core.JyAttribute;
import org.python.core.Py;
import org.python.core.PyList;
import org.python.core.PyObject;
import org.python.core.PySystemState;
import org.python.util.Generic;
import org.python.modules.gc;
public class GlobalRef extends WeakReference implements ReferenceBackend {
/**
* This is a hook for JyNI to insert a native-objects-aware implementation
* of ReferenceBackend.
*/
public static ReferenceBackendFactory factory = null;
/**
* This reference's hashCode: The {@code System.identityHashCode} of the referent.
* Only used internally.
*/
private int hashCode;
/**
* The public hashCode for the Python AbstractReference wrapper. Derived from the
* referent's hashCode.
*/
private int pythonHashCode;
/** Whether {@link #pythonHashCode} was already determined. */
private boolean havePythonHashCode;
/**
* This boolean is set {@code true} when the callback is processed.
* If the reference is cleared it might potentially be restored until
* this boolean is set true. If weak reference restoring is activated (c.f.
* {@link gc#PRESERVE_WEAKREFS_ON_RESURRECTION}), {@link AbstractReference#get()}
* would block until a consistent state is reached (i.e. referent is
* non-{@code null} or {@code cleared == true}).
*
* @see gc#PRESERVE_WEAKREFS_ON_RESURRECTION
* @see AbstractReference#get()
*/
protected boolean cleared = false;
private List> references = new ArrayList<>();
private static ReferenceQueue referenceQueue = new ReferenceQueue<>();
private static volatile Thread reaperThread;
private static ReentrantReadWriteLock reaperLock = new ReentrantReadWriteLock();
private static ConcurrentMap objects = Generic.concurrentMap();
private static List delayedCallbacks;
/*
* Consider to make this protected, so use of newInstance is enforced.
*/
public GlobalRef(PyObject object) {
super(object, referenceQueue);
hashCode = System.identityHashCode(object);
}
public synchronized void add(AbstractReference ref) {
WeakReference r = new WeakReference<>(ref);
references.add(r);
}
private final AbstractReference getReferenceAt(int idx) {
WeakReference wref = references.get(idx);
return wref.get();
}
/**
* Search for a reusable reference. To be reused, it must be of the
* same class and it must not have a callback.
*/
public synchronized AbstractReference find(Class cls) {
for (int i = references.size() - 1; i >= 0; i--) {
AbstractReference r = getReferenceAt(i);
if (r == null) {
references.remove(i);
} else if (r.callback == null && r.getClass() == cls) {
return r;
}
}
return null;
}
/**
* Call each of the registered references.
*/
synchronized void call() {
if (!cleared) {
cleared = true;
for (int i = references.size() - 1; i >= 0; i--) {
AbstractReference r = getReferenceAt(i);
if (r == null) {
references.remove(i);
} else {
Thread pendingGet = (Thread) JyAttribute.getAttr(
r, JyAttribute.WEAKREF_PENDING_GET_ATTR);
if (pendingGet != null) {
pendingGet.interrupt();
}
r.call();
}
}
ReferenceBackend ref2 = objects.get(this);
if (ref2.isCleared()) {
objects.remove(this);
} else if (factory != null && ref2 != this) {
factory.notifyClear(ref2, this);
}
}
}
/**
* Call all callbacks that were enqueued via
* {@link #delayedCallback(GlobalRef)} method.
*
* @see #delayedCallback(GlobalRef)
*/
public static void processDelayedCallbacks() {
if (delayedCallbacks != null) {
synchronized (delayedCallbacks) {
for (GlobalRef gref: delayedCallbacks) {
gref.call();
}
delayedCallbacks.clear();
}
}
}
/**
* Stores the callback for later processing. This is needed if
* weak reference restoration (c.f.
* {@link gc#PRESERVE_WEAKREFS_ON_RESURRECTION})
* is active. In this case the callback is delayed until it was
* determined whether a resurrection restored the reference.
*
* @see gc#PRESERVE_WEAKREFS_ON_RESURRECTION
* @see gc#FORCE_DELAYED_WEAKREF_CALLBACKS
*/
private static void delayedCallback(GlobalRef cl) {
if (delayedCallbacks == null) {
delayedCallbacks = new ArrayList<>();
}
synchronized (delayedCallbacks) {
delayedCallbacks.add(cl);
}
}
public static boolean hasDelayedCallbacks() {
return delayedCallbacks != null && !delayedCallbacks.isEmpty();
}
public boolean isCleared() {
return cleared;
}
synchronized public int count() {
for (int i = references.size() - 1; i >= 0; i--) {
AbstractReference r = getReferenceAt(i);
if (r == null) {
references.remove(i);
}
}
return references.size();
}
synchronized public PyList refs() {
List list = new ArrayList<>();
for (int i = references.size() - 1; i >= 0; i--) {
AbstractReference r = getReferenceAt(i);
if (r == null) {
references.remove(i);
} else {
list.add(r);
}
}
return new PyList(list);
}
/**
* Returns null if nothing is changed. If a factory exists
* and produces a result different from {@code this}, this
* result is returned. Also, this result is then installed
* in all weak-references, in the referent's JyAttribute and
* in the objects-map to act as a proxy for this GlobalRef,
* which will still serve as a backend for the proxy. This
* method is most likely used exclusively by JyNI.
*/
synchronized protected ReferenceBackend retryFactory() {
if (factory == null) {
return null;
}
ReferenceBackend result = factory.makeBackend(this, null);
if (result != this) {
objects.put(this, result);
for (int i = references.size() - 1; i >= 0; i--) {
AbstractReference r = getReferenceAt(i);
if (r == null) {
references.remove(i);
} else {
r.gref = result;
}
}
PyObject referent = result.get();
JyAttribute.setAttr(referent, JyAttribute.WEAK_REF_ATTR, result);
return result;
}
return null;
}
/**
* Create a new tracked {@code ReferenceBackend}.
* If no {@code ReferenceBackendFactory} is registered, it actually
* returns a {@code GlobalRef}.
*
* @param object a {@link org.python.core.PyObject} to reference
* @return a new tracked {@code ReferenceBackend}
*/
public static ReferenceBackend newInstance(PyObject object) {
createReaperThreadIfAbsent();
GlobalRef newRef = new GlobalRef(object);
/*
* Note: Before factory was introduced, the following used to be
* objects.putIfAbsent(newRef, newRef), which is an atomic
* operation and was used to prevent multiple threads from
* creating multiple GlobalRefs for the same referent. With
* factory we cannot use objects.putIfAbsent any more, so
* we use a synchronized block instead. (Maybe objects could
* now be replaced by an ordinary map rather than concurrent.)
*/
synchronized (objects) {
ReferenceBackend ref = objects.get(newRef);
if (ref == null) {
ref = factory == null ? newRef : factory.makeBackend(newRef, object);
objects.put(newRef, ref);
JyAttribute.setAttr(object, JyAttribute.WEAK_REF_ATTR, ref);
} else {
// We clear the not-needed GlobalRef so that it won't
// pop up in ref-reaper thread's activity.
newRef.clear();
newRef.cleared = true;
}
return ref;
}
}
/**
* Restores this weak reference to its former referent.
* This actually means that a fresh {@code GlobalRef} is created
* and inserted into all adjacent
* {@link org.python.modules._weakref.AbstractReference}s. The
* current {@code GlobalRef} is disbanded.
* If the given {@link org.python.core.PyObject} is not the former
* referent of this weak reference, an
* {@link java.lang.IllegalArgumentException} is thrown.
*
* @throws java.lang.IllegalArgumentException if {@code formerReferent} is not
* the actual former referent.
*/
public synchronized void restore(PyObject formerReferent) {
/* This method is synchronized to avoid concurrent invocation of call(). */
ReferenceBackend formerBackend = (ReferenceBackend)
JyAttribute.getAttr(formerReferent, JyAttribute.WEAK_REF_ATTR);
ReferenceBackend proxy = objects.get(this);
if (formerBackend != this && formerBackend != proxy) {
throw new IllegalArgumentException(
"Argument is not former referent of this GlobalRef.");
}
if (delayedCallbacks != null) {
synchronized (delayedCallbacks) {
delayedCallbacks.remove(this);
}
}
clear();
createReaperThreadIfAbsent();
GlobalRef restore = new GlobalRef(formerReferent);
if (proxy != this && factory != null) {
factory.updateBackend(proxy, restore);
} else {
JyAttribute.setAttr(formerReferent, JyAttribute.WEAK_REF_ATTR, restore);
}
restore.references = references;
objects.remove(this);
objects.put(restore, proxy == this ? restore : proxy);
AbstractReference aref;
for (int i = references.size() - 1; i >= 0; i--) {
aref = getReferenceAt(i);
if (aref == null) {
references.remove(i);
} else {
if (this == proxy) {
aref.gref = restore;
}
Thread pendingGet = (Thread) JyAttribute.getAttr(
aref, JyAttribute.WEAKREF_PENDING_GET_ATTR);
if (pendingGet != null) {
pendingGet.interrupt();
}
}
}
/* We must clear the old global ref to avoid processing of the
* callback in spite of restore (might happen because of bad timing).
* (The remove from delayed callback list might happen before
* the insert.) However we can only set cleared = true after
* all gref-variables were updated, otherwise some refs might
* break. To avoid callback-processing in the unsafe state
* between these actions, this method is synchronized (as is call()).
*/
cleared = true;
}
private static void createReaperThreadIfAbsent() {
reaperLock.readLock().lock();
try {
if (reaperThread == null || !reaperThread.isAlive()) {
reaperLock.readLock().unlock();
reaperLock.writeLock().lock();
try {
if (reaperThread == null || !reaperThread.isAlive()) {
initReaperThread();
}
} finally {
reaperLock.readLock().lock();
reaperLock.writeLock().unlock();
}
}
} finally {
reaperLock.readLock().unlock();
}
}
/**
* Return the number of references to the specified
* {@link org.python.core.PyObject}.
*
* @param object a PyObject
* @return an int reference count
*/
public static int getCount(PyObject object) {
ReferenceBackend ref = objects.get(new GlobalRef(object));
return ref == null ? 0 : ref.count();
}
/**
* Return a list of references to the specified
* {@link org.python.core.PyObject}.
*
* @param object a {@link org.python.core.PyObject}
* @return a {@link org.python.core.PyList} of references. May be empty.
*/
public static PyList getRefs(PyObject object) {
ReferenceBackend ref = objects.get(new GlobalRef(object));
return ref == null ? new PyList() : ref.refs();
}
/**
* Allow {@code GlobalRef}s to be used as hashtable-keys.
*/
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof GlobalRef)) {
return false;
}
Object t = this.get();
Object u = ((GlobalRef)o).get();
if ((t == null) || (u == null)) {
return false;
}
if (t == u) {
return true;
}
// Don't consult the objects' equals (__eq__) method, it can't be trusted
return false;
}
/**
* Allows {@code GlobalRef} to be used as hashtable-keys.
*
* @return a hashCode {@code int}-value
*/
public int hashCode() {
return hashCode;
}
/**
* The publicly used {@code hashCode}, for the
* {@link org.python.modules._weakref.AbstractReference}
* wrapper.
*
* @return a hashCode {@code int}-value
*/
public int pythonHashCode() {
if (havePythonHashCode) {
return pythonHashCode;
}
Object referent = get();
if (referent == null) {
throw Py.TypeError("weak object has gone away");
}
pythonHashCode = referent.hashCode();
havePythonHashCode = true;
return pythonHashCode;
}
private static void initReaperThread() {
RefReaper reaper = new RefReaper();
PySystemState systemState = Py.getSystemState();
systemState.registerCloser(reaper);
reaperThread = new Thread(reaper, "weakref reaper");
reaperThread.setDaemon(true);
reaperThread.start();
}
private static class RefReaper implements Runnable, Callable {
private volatile boolean exit = false;
private Thread thread;
public void collect() throws InterruptedException {
GlobalRef gr = (GlobalRef) referenceQueue.remove();
if (!gc.delayedWeakrefCallbacksEnabled()) {
gr.call();
} else {
delayedCallback(gr);
}
}
@Override
public void run() {
// Store the actual reaper thread so that when PySystemState.cleanup()
// is called this thread can be interrupted and die.
this.thread = Thread.currentThread();
while (true) {
try {
collect();
} catch (InterruptedException exc) {
// Is cleanup time so break out and die.
if (exit) {
break;
}
}
}
}
@Override
public Void call() throws Exception {
this.exit = true;
if (thread != null && thread.isAlive()) {
this.thread.interrupt();
this.thread = null;
}
return null;
}
}
}