org.python.modules._io.Closer Maven / Gradle / Ivy
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/* Copyright (c)2012 Jython Developers */
package org.python.modules._io;
import java.lang.ref.WeakReference;
import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicBoolean;
import org.python.core.PyObject;
import org.python.core.PySystemState;
/**
* A class to take responsibility for closing a stream on JVM shutdown. On creation a Closer adds
* itself to a list that will be run by PySystemState on shutdown and it maintains a reference to
* its client PyIOBase. The client (assuming it kept a reference to the Closer) may dismiss the
* closer at any time: normally this will be when the client stream is closed directly, or
* implicitly through {@link PyIOBase#__exit__(PyObject, PyObject, PyObject)}. A possibility is that
* the JVM exits before an close() is called. In that case, {@link Closer#call()} will
* be called, and the Closer will call the client's close operation.
*
* In case the close operation is overridden so that it does not dismiss the closer, it is useful to
* have the client's finalize dismiss the closer. If not, the Closer will remain registered and this
* will keep the PyIOBase object alive in the JVM, which is mostly harmless.
*/
/*
* Adapted from PyFile, but significantly different to call the overridden close operation of the
* client itself, rather than just the underlying file.
*/
class Closer implements Callable {
/** The client in need of closing. */
private final WeakReference client;
/** Interpreter state that will call {@link #call()} on shutdown. */
protected PySystemState sys;
private AtomicBoolean dismissed = new AtomicBoolean(); //Defaults to false
public Closer(C toClose, PySystemState sys) {
this.client = new WeakReference(toClose);
this.sys = sys;
sys.registerCloser(this);
}
/**
* Tell the Closer that its services are no longer required. This unhooks it from the shutdown
* list. Repeated calls are allowed but only the first has any effect.
*/
public void dismiss() {
if (dismissed.compareAndSet(false, true)) {
sys.unregisterCloser(this);
}
}
/**
* Called as part of a shutdown process. If the client is still (weakly) reachable, invoke its
* "close" method.
*/
@Override
public Void call() {
// This will prevent repeated work and dismiss() manipulating the list of closers
if (dismissed.compareAndSet(false, true)) {
// Call close on the client (if it still exists)
C toClose = client.get();
if (toClose != null) {
toClose.invoke("close");
}
}
return null;
}
}