twisted - locking threads when deferToThread is used

[Ladislav Andel]

Hi,
I'm writing an application which will be periodically testing servers.
I will have a global list of these servers(domain names) and need to do
few tasks.
1) DNS checks - I will use asynchronous twisted-names for it
- in case there is a difference comparing to the list it should update 
the list(then also in DB)
2) ICMP pings - should be also possible to do it asynchronously
3) Blocking function which will be pinging with SIP requests
- here I will use function deferToThread to make it non-blocking.

Questions:
1) How do I lock each thread when writing to a global list in twisted?
2) How will I put together all three results mentioned above in the 
global list
- is it by using function callLater ?
3) Could you help me with a rough skeleton of this application, please?

Thank you,
Lada