Re: [Py4j-users] An issue in reflection?
Status: Beta
Brought to you by:
barthe
Menu
▾
▴
Re: [Py4j-users] An issue in reflection?
|
From: Jeremy <ken...@gm...> - 2014-05-16 23:35:37
|
Sorry for the delayed reply. Been busy, finally got time to work on my
project.
I looked at the Vector.java code and can see that it calls the Object
class method, equals().
So taking your suggestion, I added an equals(Object) method to the
interface (not necessary likely) and tried to implement something in the
implementing class in Python. Something like:
class equals(self, obj):
if self == obj:
return True
return False
But still got the same error. Tried adding in Python's global equal, and
that didn't work either. And even tried creating a UUID for each
EventListener, but that didn't work either. It just can't seem to find
the equals method. My final EventListener ended up looking like this.
class EventListener(object):
id = uuid.uuid4()
def onEvent(self, event):
pass
def equals(self, obj):
return __eq__(obj)
def __eq__(self, obj):
if obj == None:
return False
if obj.id == self.id:
return True
else:
return False
class Java:
implements = ['pctelelog.EventListener']
pass
My solution that seems to be working now has been to remove passing
around an interface and instead rename the interface EventCallback and
wrap it inside a new class (EventListener) and pass an object of that
class around. It works fine but I have a strange issue now, maybe I'm
doing it wrong.
Here's my new EventListener.java
public class EventListener implements EventCallback {
private EventCallback m_callback = null;
public EventListener() {
}
public EventListener(EventCallback callback) {
assert callback != null;
m_callback = callback;
}
public void setCallback(EventCallback callback) {
m_callback = callback;
}
public static EventListener createEventListener(EventCallback
callback) {
return new EventListener(callback);
}
@Override
public void onEvent(AbstractEvent event) {
m_callback.onEvent(event);
}
}
Here's the Python I use to get an instance of the class and then add it
to the listener pool:
(This method sits inside a PyQt Widget class.)
def initCallback(self, func):
callback = EventCallback()
callback.onEvent = self.onEvent
self.eventListener =
self.__gateway.jvm.pctelelog.EventListener(callback)
self.__gateway.entry_point.addEventListener(self.eventListener)
When I try to do it like that I get an error (Logger + Error):
Callback Server Starting
Socket listening on ('127.0.0.1', 25334)
Command to send: r
u
pctelelog
rj
e
Answer received: yp
Command to send: r
u
pctelelog.EventListener
rj
e
Answer received: ycpctelelog.EventListener
Traceback (most recent call last):
File
"/Users/Shared/eclipse/workspace/PCTeleLog-PyQt/pytelelog-pyqt/Launcher.py",
line 27, in <module>
Launcher()
File
"/Users/Shared/eclipse/workspace/PCTeleLog-PyQt/pytelelog-pyqt/Launcher.py",
line 23, in __init__
mainWindow = MainWindow(self.__gateway)
File
"/Users/Shared/eclipse/workspace/PCTeleLog-PyQt/pytelelog-pyqt/MainWindow.py",
line 25, in __init__
self.initCallback(self.onEvent)
File
"/Users/Shared/eclipse/workspace/PCTeleLog-PyQt/pytelelog-pyqt/MainWindow.py",
line 49, in initCallback
self.eventListener =
self.__gateway.jvm.pctelelog.EventListener(callback)
File "/usr/local/lib/python2.7/site-packages/py4j/java_gateway.py",
line 662, in __call__
args_command = ''.join([get_command_part(arg) for arg in args])
File "/usr/local/lib/python2.7/site-packages/py4j/protocol.py", line
261, in get_command_part
command_part = PYTHON_PROXY_TYPE + python_proxy_pool.put(parameter)
AttributeError: 'NoneType' object has no attribute 'put'
===
Now, if I change it around and instantiate with the void constructor and
set the callback with the setter. It works fine.
def initCallback(self, func):
callback = EventCallback()
callback.onEvent = self.onEvent
self.eventListener = self.__gateway.jvm.pctelelog.EventListener()
self.eventListener.setCallback(callback)
self.__gateway.entry_point.addEventListener(self.eventListener)
I'd rather do without the setter if there was a way to manage it. Any
idea what's going on?
Thanks!
On 5/7/14, 7:54 AM, Barthelemy Dagenais wrote:
> Hi!
>
> Thanks for using Py4J! I'll try to look at this issue more deeply
> during the weekend, but from the stack trace, it seems the Java side
> is sending a method call to the Python side and the Python side is
> replying with an exception:
>
> Error:
> py4j.protocol.Py4JJavaError: An error occurred while calling
> t.removeEventListener.
> : py4j.Py4JException: An exception was raised by the Python Proxy.
> Return Message: x
>
> Also, from the stack trace, it appears that when deleting the listener
> from the Java vector, the vector calls the "equals" method on the
> listener. This is the first time I have to deal with this scenario and
> I believe the equals method is delegated to the python side. Because
> it is not implemented, I believe this may be the cause of failure. A
> workaround might be to try to implement an "equals" method in your
> Python listener.
>
> Do you have logging enabled on the Python side? Any stack trace visible there?
>
> Btw, you should subscribe to the mailing list, it would be easier to
> manage the replies :-)
>
> Bart
>
> On Tue, May 6, 2014 at 7:58 PM, Jeremy <ken...@gm...> wrote:
>> So I'm trying to use Py4j to let a UI talk to a Java server. The java
>> server uses 3 threads (entry-point, server socket, client-event
>> dispatch). The python UI registers an event call back listener and that
>> listener eventually gets dumped into a Vector. I had some initial
>> trouble getting the addEventListener() working but fixed it (somehow).
>> But now any calls to removeEventListener() don't work.
>>
>> My first guess was something to do with different instances of the
>> object when Vector does the lookup, but I'm not sure. I don't understand
>> relfection concepts well enough and the Py->Java (callback) thing seems
>> to suggest I should be fine since the original eventlistener hasn't been
>> garbage collected yet. If you have any insight that would be great.
>>
>> Error:
>> py4j.protocol.Py4JJavaError: An error occurred while calling
>> t.removeEventListener.
>> : py4j.Py4JException: An exception was raised by the Python Proxy.
>> Return Message: x
>> at py4j.Protocol.getReturnValue(Protocol.java:417)
>> at
>> py4j.reflection.PythonProxyHandler.invoke(PythonProxyHandler.java:113)
>> at com.sun.proxy.$Proxy0.equals(Unknown Source)
>> at java.util.Vector.indexOf(Vector.java:404)
>> at java.util.Vector.indexOf(Vector.java:378)
>> at java.util.Vector.removeElement(Vector.java:637)
>> at java.util.Vector.remove(Vector.java:795)
>> at
>> pctelelog.EventOperatorThread.removeEventListener(EventOperatorThread.java:20)
>> at pctelelog.ServerThread.removeEventListener(ServerThread.java:16)
>> at pctelelog.Launcher.removeEventListener(Launcher.java:17)
>> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>> at
>> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
>>
>> This code is a stripped down version of the development version but both
>> are generating the same error.
>>
>> package pctelelog;
>>
>> public class Event {
>> public String testData = "test";
>> }
>>
>> ===
>>
>> package pctelelog;
>>
>> public interface EventListener {
>> public void onEvent(Event event);
>> }
>>
>> ===
>>
>> package pctelelog;
>>
>> import java.util.Vector;
>>
>> public class EventOperatorThread extends Thread {
>>
>> private Vector<EventListener> m_listeners = new
>> Vector<EventListener>();
>>
>> public void run() {
>> while(true) {}
>> }
>>
>> public synchronized void addEventListener(EventListener listener) {
>> System.out.println("ADD");
>> m_listeners.add(listener);
>> }
>>
>> public synchronized void removeEventListener(EventListener listener) {
>> System.out.println("REMOVE");
>> m_listeners.remove(listener);
>> }
>> }
>>
>> ===
>>
>> package pctelelog;
>>
>> public class ServerThread extends Thread {
>>
>> private EventOperatorThread m_operator = new EventOperatorThread();
>>
>> public void run() {
>> m_operator.start();
>> while(true) {}
>> }
>>
>> public synchronized void addEventListener(EventListener listener) {
>> m_operator.addEventListener(listener);
>> }
>> public synchronized void removeEventListener(EventListener listener) {
>> m_operator.removeEventListener(listener);
>> }
>>
>> }
>>
>> ===
>>
>> package pctelelog;
>>
>> import py4j.GatewayServer;
>>
>> public class Launcher {
>> private ServerThread m_server = new ServerThread();
>>
>> public Launcher() {
>> m_server.start();
>> System.out.println("Server started.");
>> }
>>
>> public void addEventListener(EventListener listener) {
>> m_server.addEventListener(listener);
>> }
>> public void removeEventListener(EventListener listener) {
>> m_server.removeEventListener(listener);
>> }
>>
>> public static void main(String[] args) {
>> GatewayServer gateway = new GatewayServer(new Launcher());
>> gateway.start();
>> }
>> }
>>
>> ===
>>
>> from py4j.java_gateway import JavaGateway, GatewayClient
>>
>> class EventListener(object):
>>
>> def onEvent(self, event):
>> print event.testData;
>>
>> class Java:
>> implements = ['pctelelog.EventListener']
>>
>> class Launcher:
>>
>> def __init__(self):
>> self.__gateway = JavaGateway(start_callback_server=True)
>> listener = EventListener()
>> self.__gateway.entry_point.addEventListener(listener)
>> self.__gateway.entry_point.removeEventListener(listener)
>>
>> if __name__ == '__main__':
>> Launcher()
>> pass
>>
>>
>> ------------------------------------------------------------------------------
>> Is your legacy SCM system holding you back? Join Perforce May 7 to find out:
>> • 3 signs your SCM is hindering your productivity
>> • Requirements for releasing software faster
>> • Expert tips and advice for migrating your SCM now
>> http://p.sf.net/sfu/perforce
>> _______________________________________________
>> Py4j-users mailing list
>> Py4...@li...
>> https://lists.sourceforge.net/lists/listinfo/py4j-users
|
