Change Event Subscription in Java

# 7 years ago
TCS_GMRT	Hi Team, We think there is a problem with the change event subscription in Java. I will try to explain in short: Pain Area: Repeated change event response received from a Java Tango DS. Background: There are two Java Tango DS, "Test_Sub1" and "Test_Sub2", Test_Sub1 has a scalar attribute named "test_Sub1". Scenario: Test_Sub2 is going to subscribe a change event on attribute of Test_Sub1, "test_Sub1". Case 1: Test_Sub1 Java Tango DS is started first and then Test_Sub2 Tango DS is started. Case 1 Findings: In this case, the subscription from Test_Sub2 on an attribute, test_Sub1 of Test_Sub1, successfully happens for the first time. After which, any change in the attribute value of test_Sub1 at Test_Sub1 creates a change event at Test_Sub2, as it is subscribed to that attribute. No problem in Case 1. Works as expected. Case 2: Test_Sub2 Java Tango DS is started first and then after some time (say 2 mins) Test_Sub1 Tango DS is started. Case 2 Findings: In this case, the subscription from Test_Sub2 on an attribute, test_Sub1 of Test_Sub1, does not happen for the first time, as Test_Sub1 is still not running. Referring to "The TANGO Control System Manual Version 9.2", Chapter 4.6.5.2.1 on Page 41, Second last paragraph starting with "The stateless flag = false …….", in this case, 2, the stateless flag is set to true, so it will keep on trying every 10 secs, till it does not actually subscribe to the attribute. Ideally, once the Test_Sub1 is up and running, the subscription will happen and the subscription thread should stop as it's attributes will be available on Tango bus. However, it is seen that the subscription thread does not stop and keeps on subscribing every 10 secs thereafter, and therefore creating repeated change events, every 10 secs. Additional Information: Tango Version: 9.2.2 OS: Ubuntu 16.04 (64 bit) We can discuss this scenario in detail if required. Need help in getting this issues verified and fixed. Regards, TCS_GMRT

# 7 years ago

Hi Team,

We think there is a problem with the change event subscription in Java. I will try to explain in short:

Pain Area:
Repeated change event response received from a Java Tango DS.

Background:
There are two Java Tango DS, "Test_Sub1" and "Test_Sub2", Test_Sub1 has a scalar attribute named "test_Sub1".

Scenario:
Test_Sub2 is going to subscribe a change event on attribute of Test_Sub1, "test_Sub1".

Case 1: Test_Sub1 Java Tango DS is started first and then Test_Sub2 Tango DS is started.

Case 1 Findings: In this case, the subscription from Test_Sub2 on an attribute, test_Sub1 of Test_Sub1, successfully happens for the first time. After which, any change in the attribute value of test_Sub1 at Test_Sub1 creates a change event at Test_Sub2, as it is subscribed to that attribute.

No problem in Case 1. Works as expected.

Case 2: Test_Sub2 Java Tango DS is started first and then after some time (say 2 mins) Test_Sub1 Tango DS is started.

Case 2 Findings: In this case, the subscription from Test_Sub2 on an attribute, test_Sub1 of Test_Sub1, does not happen for the first time, as Test_Sub1 is still not running. Referring to "The TANGO Control System Manual Version 9.2", Chapter 4.6.5.2.1 on Page 41, Second last paragraph starting with "The stateless flag = false …….", in this case, 2, the stateless flag is set to true, so it will keep on trying every 10 secs, till it does not actually subscribe to the attribute. Ideally, once the Test_Sub1 is up and running, the subscription will happen and the subscription thread should stop as it's attributes will be available on Tango bus. However, it is seen that the subscription thread does not stop and keeps on subscribing every 10 secs thereafter, and therefore creating repeated change events, every 10 secs.

Additional Information:
Tango Version: 9.2.2
OS: Ubuntu 16.04 (64 bit)

We can discuss this scenario in detail if required.
Need help in getting this issues verified and fixed.

Regards,
TCS_GMRT

# 7 years ago
Pascal	Hi I can reproduce your scenario. I will try to fix it soon. Regards Pascal

# 7 years ago
TCS_GMRT	Thanks, Pascal for promptly working on it. Regards, TCS_GMRT Edited 7 years ago

# 7 years ago
Pascal	Hi It has been fixed in new JTango jar file available at JTango-9.3.2-shaded.jar Regards Pascal