How to check the status of service from which I am subscribing the update programmatically?

Did you manage to request the source directory as per your previous query?

If you did then you will note that part of the information received contains status i.e. the Service State and if it is Accepting Requests

MAP
MAP_ENTRY (Action.ADD) :
flags:
Key: IDN_RDF
Value:
	FILTER_LIST
	flags:
		FILTER_ENTRY 1 (Action.SET) :
		flags:
		ELEMENT_LIST
			ELEMENT_ENTRY Name: IDN_RDF
			ELEMENT_ENTRY Vendor: Reuters
			ELEMENT_ENTRY Capabilities:
		ARRAY
			ARRAY_ENTRY: 5
			ARRAY_ENTRY: 6
			....
			....
		FILTER_ENTRY 2 (Action.SET) :
		flags:
		ELEMENT_LIST
			ELEMENT_ENTRY ServiceState: 1
			ELEMENT_ENTRY AcceptingRequests: 1
MAP_ENTRY (Action.ADD) :
flags:
Key: ELEKTRON_DD
Value:
	FILTER_LIST
	flags:
		FILTER_ENTRY 1 (Action.SET) :
		flags:
		ELEMENT_LIST
			ELEMENT_ENTRY Name: ELEKTRON_DD
			ELEMENT_ENTRY Vendor: Reuters
			ELEMENT_ENTRY Capabilities:
		ARRAY
			ARRAY_ENTRY: 5
			ARRAY_ENTRY: 6
			ARRAY_ENTRY: 7
			....
			....
		FILTER_ENTRY 2 (Action.SET) :
		flags:
		ELEMENT_LIST
			ELEMENT_ENTRY ServiceState: 1
			ELEMENT_ENTRY AcceptingRequests: 1

In the above extract of the Source Directory you can see two services; IDN_RDF and ELEKTRON_DD and both ave ServiceState : 1 (UP) and AcceptingRequests : 1 (Yes)

You can get more details in the RDMUsageGuide.pdf file that comes with your RFA developer kit.

The other thing to note is that provided your source directory request is a streaming one (i.e. not a Snapshot request) then you would receive updates to the directory as and when a service state changes e.g. if a service goes down at later point in time..