我目前正在尝试使用Py4J执行以下操作:
这就是我在Java方面所拥有的东西:
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()
以下是尝试执行此脚本时发生的情况。首先,使用gateway = ClientServer(java_parameters=JavaParameters(), python_parameters=PythonParameters())
,两个测试都失败了:
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,如果我注释掉self.execfunc()
行,则测试1可以正常工作而不会出现错误。然而,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())
。当我保持self.execfunc()
注释时,测试2仍然在这里失败:
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适用于启用self.execfunc()
。
我的问题是:如何在self.execfunc()
调用时使用线程方法?这可能与Py4J有关吗?
编辑:为了使事情变得更加棘手,self.execfunc()
调用的Java命令应该在调用.notify()
的同一Java线程中运行。
答案 0 :(得分:2)
解决。结果很简单:
然后,Java将完全遵循预期的线程模型,即接收Python回调调用的Java命令在执行回调的同一Java线程中执行。
通过一个简单的Python函数,可以添加shutdown_when_done
方法,等待所有回调在退出之前回来。