我目前正在尝试使用py4j：
进行以下操作- 在python中定义一种调用JVM方法的方法（" executor"）
- 定义python（"回调"）对象实现JVM接口
- 给定此回调对象构建一个JVM对象
- 调用此对象上的方法，该方法将在Java中产生新线程，在回调对象上调用回调，该回调将（在Python侧）执行" executor"方法
这是我在爪哇一侧所拥有的：
package javabridge.test;
public interface PythonCallback {
Object notify(Object source);
}
package javabridge.test;
public class ScheduledRunnable implements Runnable {
private PythonCallback callback;
public ScheduledRunnable(PythonCallback callback) {
this.callback = callback;
}
@Override
public void run() {
System.out.println("[ScheduledRunnable] run -> notify");
this.callback.notify(this);
}
}
package javabridge.test;
import py4j.GatewayServer;
public class Test {
private PythonCallback callback;
public Test(PythonCallback callback) {
this.callback = callback;
}
public void runSynchronous() {
System.out.println("[runSynchronous] run -> notify");
this.callback.notify(this);
}
public void runAsynchronous() {
System.out.println("[runAsynchronous] run -> spawn thread");
ScheduledRunnable runnable = new ScheduledRunnable(callback);
Thread t = new Thread(runnable);
t.start();
}
public static void main(String[] args) {
GatewayServer server = new GatewayServer();
server.start(true);
}
}
在Python方面，我有以下脚本：
from py4j.java_gateway import JavaGateway, java_import, get_field, CallbackServerParameters
from py4j.clientserver import ClientServer, JavaParameters, PythonParameters
gateway = JavaGateway(callback_server_parameters=CallbackServerParameters())
#gateway = ClientServer(java_parameters=JavaParameters(), python_parameters=PythonParameters())
java_import(gateway.jvm, 'javabridge.test.*')
class PythonCallbackImpl(object):
def __init__(self, execfunc):
self.execfunc = execfunc
def notify(self, obj):
print('[PythonCallbackImpl] notified from Java')
self.execfunc()
return 'dummy return value'
class Java:
implements = ["javabridge.test.PythonCallback"]
def simple_fun():
print('[simple_fun] called')
gateway.jvm.System.out.println("[simple_fun] Hello from python!")
# Test 1: Without threading
input('Ready to begin test 1')
python_callback = PythonCallbackImpl(simple_fun)
nothread_executor = gateway.jvm.Test(python_callback)
nothread_executor.runSynchronous()
# Test 2: With threading
input('Ready to begin test 2')
python_callback = PythonCallbackImpl(simple_fun)
nothread_executor = gateway.jvm.Test(python_callback)
nothread_executor.runAsynchronous()
gateway.shutdown()
这是试图执行此脚本的情况。首先，使用gateway = ClientServer(java_parameters=JavaParameters(), python_parameters=PythonParameters())，两个测试失败：
Test 1:
py4j.protocol.Py4JJavaError: An error occurred while calling o0.runSynchronous.
: py4j.Py4JException: Command Part is Empty or is the End of Command Part
at py4j.Protocol.getObject(Protocol.java:277)
at py4j.Protocol.getReturnValue(Protocol.java:458)
Test 2:
Exception in thread "Thread-4" py4j.Py4JException: Error while obtaining a new communication channel
at py4j.CallbackClient.getConnectionLock(CallbackClient.java:218)
at py4j.CallbackClient.sendCommand(CallbackClient.java:337)
at py4j.CallbackClient.sendCommand(CallbackClient.java:316)
但是，如果我评论self.execfunc()行，则测试1确实有效而不会增加错误。测试2仍然失败：
Exception in thread "Thread-5" py4j.Py4JException: Error while sending a command.
at py4j.CallbackClient.sendCommand(CallbackClient.java:357)
at py4j.CallbackClient.sendCommand(CallbackClient.java:316)
现在切换到gateway = JavaGateway(callback_server_parameters=CallbackServerParameters())。当我保留self.execfunc()评论时，测试2仍然失败：
Exception in thread "Thread-5" py4j.Py4JException: Error while sending a command.
at py4j.CallbackClient.sendCommand(CallbackClient.java:357)
at py4j.CallbackClient.sendCommand(CallbackClient.java:316)
但至少测试1确实可以与启用self.execfunc()一起使用。
我的问题是：如何将螺纹方法与self.execfunc()调用使用？PY4J？
编辑：为了使事情更加棘手， self.execfunc()调用的java命令应在调用.notify()的同一Java线程中运行。
已解决。原来很简单：
- 在Python侧和Java侧也使用Cliendererver！
- 请勿致电Gateway.shutdown（），因为这将在接收回调之前断开python（du！）
通过简单的Python函数，可以添加shutdown_when_done方法，该方法等待所有回调在退出之前返回。