Styjun

I am trying to use dash for live monitoring of JBeans attributes. When using dcc.Interval program closes automatically after first POST /_dash-update-component try.

• Python 3.6


• Dash 1.0.2

I connected to Jconsole. Referring to Jbean attributes and extracting values works. It even works when I launch dash app for first time, but then when Interval is triggered dash program closes.

• JBean tested - works fine


• Dash code tested - it extracts n_intervals just fine

Steps:

1. JMX FUNCTIONS MODULE

import jpype as jpype
from jpype import java
from jpype import javax
import sys, os
import pandas as pd
import datetime

#JMX CONNECTION FUNCTION:

def jmx_connect(HOST, USER, PORT, PASS):
 URL = 'service:jmx:rmi:///jndi/rmi://'+HOST+':'+PORT+'/jmxrmi'
 jpype.startJVM(jpype.get_default_jvm_path())
 jhash = java.util.HashMap()
 jarray=jpype.JArray(java.lang.String)([USER,PASS])
 jhash.put(javax.management.remote.JMXConnector.CREDENTIALS, jarray);
 jmxurl = javax.management.remote.JMXServiceURL(URL)
 jmxsoc = javax.management.remote.JMXConnectorFactory.connect(jmxurl,jhash)
 connection = jmxsoc.getMBeanServerConnection();
 return connection

#Enter login details HERE:
HOST = 
USER = 
PORT = 
PASS = 

#initializing connection with my login details
connection = jmx_connect(HOST, USER, PORT, PASS)


#Thread Count function to extract number of active threads:
#THREAD COUNT
def jmx_ThreadCount():
 object="java.lang:type=Threading"
 attribute= "ThreadCount"
 attr = connection.getAttribute(javax.management.ObjectName(object),attribute)
 return attr

2. DASH MODULE

from TEST_jvmRun import * #this is import of my JVM functions
import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
import plotly.graph_objs as go

app = dash.Dash()

app.layout = html.Div([
 html.H1(id='live-update-text'),
 dcc.Interval(id='interval-component', interval=10000, n_intervals=0)
])

@app.callback(Output('live-update-text', 'children'),
 [Input('interval-component', 'n_intervals')])
def update_current_delay(n): 
 #return f"counter: n"
 return f"WORKING, trial: n ; jmx_ThreadCount()" 

if __name__ == '__main__':
 app.run_server()

a) ACTUAL RESULTS

--- command line output:

C:Usersm011472DocumentsPython ScriptsWeb>cd "c:Usersm011472DocumentsPython ScriptsWeb" && cmd /C "set "PYTHONIOENCODING=UTF-8" && set "PYTHONUNBUFFERED=1" && C:Python36python.exe C:Usersm011472.vscodeextensionsms-python.python-2018.4.0pythonFilesPythonToolsvisualstudio_py_launcher.py "c:Usersm011472DocumentsPython ScriptsWeb" 53564 34806ad9-833a-4524-8cd6-18ca4aa74f14 RedirectOutput,RedirectOutput "c:Usersm011472DocumentsPython ScriptsWebTEST_dashboard.py" "
 * Serving Flask app "TEST_dashboard" (lazy loading) * Environment: production WARNING: Do not use the development server in a production environment.
 Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)
127.0.0.1 - - [28/Mar/2019 14:57:02] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [28/Mar/2019 14:57:03] "GET /_dash-layout HTTP/1.1" 200 -
127.0.0.1 - - [28/Mar/2019 14:57:03] "GET /_dash-dependencies HTTP/1.1" 200 -
127.0.0.1 - - [28/Mar/2019 14:57:03] "POST /_dash-update-component HTTP/1.1" 200 -

C:Usersm011472DocumentsPython ScriptsWeb>

--- dashboard output:

WORKING, trial: 0 ; 418

b) EXPECTED RESULTS

--- command line output:

Program should execute POST every 10 sec and never end

--- DASHBOARD OUTPUT:

Numbers should be updated each 10 sec

WORKING, trial: 0 ; XXX (any number)
WORKING, trial: 1 ; XXY
WORKING, trial: 2 ; XXZ

Should someone be interested - I found partial solution. Issue caused by dcc.Interval because it creates new thread at each interval and JMX call requires JVM instance to be attached to current thread.

1. Added jpype.attachThreadToJVM()

def jmx_ThreadCount():
 print("State=", jpype.isThreadAttachedToJVM())
 if not jpype.isThreadAttachedToJVM():
 print ("Needs to attach...")
 jpype.attachThreadToJVM()
 print ("Check Attached=", jpype.isThreadAttachedToJVM()) 
 object="java.lang:type=Threading"
 attribute= "ThreadCount"
 attr = connection.getAttribute(javax.management.ObjectName(object),attribute)
 return attr

Now the question is: how do I prevent dcc.Interval from creating new thread at each interval?