Jep.close() does not close daemon thread? error: [Py_EndInterpreter: not the last thread]

[Xianda Ke]

Hi folks,

java code:

try(Jep jep = new Jep()) {
            jep.runScript("./src/main/python/thread_test.py");
        } catch (JepException e) {
            e.printStackTrace();
        }

}

python code:

import threading
import time
import sys
# import thread
def f1():
    for i in range(5):
        print ("f1...\n")
        sys.stdout.flush()
        time.sleep(1)

if __name__ == "__main__":

    t = threading.Thread(target=f1, args=())
    t.setDaemon(True)
    t.start()

    for t in threading.enumerate():
        print (t.getName())
        #if t.getName() != "MainThread":
            #t._Thread__stop()
            #t._stop()
    print (threading.enumerate())

When Jep.close() is called,  there is a fatal error:

Fatal Python error: Py_EndInterpreter: not the last thread.

it seems that pyembed_thread_close() should not call Py_EndInterpreter() before all the daemon threads are close.

    if (jepThread->tstate->interp == mainThreadState->interp) {

        PyThreadState_Clear(jepThread->tstate);

        PyThreadState_Swap(NULL);

        PyThreadState_Delete(jepThread->tstate);

    } else {

        Py_EndInterpreter(jepThread->tstate);

    }

[Ben Steffensmeier]

In general if you use any system resources, such as threads, from python using jep you are responsible for ensuring that they are cleaned up so I would recommend you add a wait before the close. I do not think jep should wait for all daemon threads because they may never complete causing a freeze Last time this issue was seen it was in a third party library and the thread would never complete without intervention. I do not like that this results in a fatal error, I will investigate further and see if we can detect this and throw a JepException and avoid the fatal error.

Ben

[Xianda Ke]

Thank Ben for the reply. 

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Ke, Xianda

[Nathan Jensen]

I opened a github issue for this.  https://github.com/ninia/jep/issues/161  At this time I'm not sure what release this will go into.

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Ke, Xianda

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