thrift: ThriftServer: make nextWorkerId_ atomic
thrift: ThriftServer: make nextWorkerId_ atomic

Summary:

we use it in one single place:

return internalFactory_->newThread([=](){
CHECK(!server_->serverChannel_);
auto id = nextWorkerId_++;

Let's not race on this.

Test Plan: n/a

Reviewed By: philipp@fb.com, robot9@fb.com

Subscribers: trunkagent, alandau, bmatheny, mshneer

FB internal diff: D1659587

Tasks: 5538418

Signature: t1:1659587:1415147539:628914eaf39f06f7d023e59862661c08bd080648

HankFaan/fbthrift,maxwell-demon/fbthrift,uber/fbthrift,Orvid/fbthrift,jesboat/fbthrift,soumith/fbthrift,getyourguide/fbthrift,uber/fbthrift,maxwell-demon/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,maxwell-demon/fbthrift,LinusU/fbthrift,guker/fbthrift,project-zerus/fbthrift,project-zerus/fbthrift,kangkot/fbthrift,soumith/fbthrift,fengshao0907/fbthrift,raphaelamorim/fbthrift,chjp2046/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,uber/fbthrift,HankFaan/fbthrift,sinjar666/fbthrift,HankFaan/fbthrift,raphaelamorim/fbthrift,raphaelamorim/fbthrift,chjp2046/fbthrift,jesboat/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,HankFaan/fbthrift,getyourguide/fbthrift,facebook/fbthrift,chjp2046/fbthrift,jesboat/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,facebook/fbthrift,fengshao0907/fbthrift,kangkot/fbthrift,maxwell-demon/fbthrift,SergeyMakarenko/fbthrift,maxwell-demon/fbthrift,jesboat/fbthrift,Orvid/fbthrift,project-zerus/fbthrift,guker/fbthrift,Orvid/fbthrift,uber/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,project-zerus/fbthrift,raphaelamorim/fbthrift,LinusU/fbthrift,LinusU/fbthrift,facebook/fbthrift,sinjar666/fbthrift,soumith/fbthrift,kangkot/fbthrift,sinjar666/fbthrift,jesboat/fbthrift,fengshao0907/fbthrift,sinjar666/fbthrift,HankFaan/fbthrift,chjp2046/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,jesboat/fbthrift,HankFaan/fbthrift,Orvid/fbthrift,soumith/fbthrift,soumith/fbthrift,raphaelamorim/fbthrift,guker/fbthrift,kangkot/fbthrift,kangkot/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,uber/fbthrift,raphaelamorim/fbthrift,LinusU/fbthrift,soumith/fbthrift,guker/fbthrift,maxwell-demon/fbthrift,SergeyMakarenko/fbthrift,sinjar666/fbthrift,project-zerus/fbthrift,sinjar666/fbthrift,soumith/fbthrift,chjp2046/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,guker/fbthrift,Orvid/fbthrift,sinjar666/fbthrift,uber/fbthrift,uber/fbthrift,kangkot/fbthrift,jesboat/fbthrift,jesboat/fbthrift,chjp2046/fbthrift,project-zerus/fbthrift,chjp2046/fbthrift,guker/fbthrift,sinjar666/fbthrift,chjp2046/fbthrift,chjp2046/fbthrift,sinjar666/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,kangkot/fbthrift,uber/fbthrift,HankFaan/fbthrift,sinjar666/fbthrift,facebook/fbthrift,project-zerus/fbthrift,Orvid/fbthrift,guker/fbthrift,maxwell-demon/fbthrift,soumith/fbthrift,guker/fbthrift,facebook/fbthrift,HankFaan/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,chjp2046/fbthrift,getyourguide/fbthrift,uber/fbthrift,uber/fbthrift,jesboat/fbthrift,guker/fbthrift,getyourguide/fbthrift,raphaelamorim/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,LinusU/fbthrift,facebook/fbthrift,Orvid/fbthrift,jesboat/fbthrift,Orvid/fbthrift,project-zerus/fbthrift,Orvid/fbthrift,LinusU/fbthrift,fengshao0907/fbthrift,project-zerus/fbthrift,LinusU/fbthrift,raphaelamorim/fbthrift,raphaelamorim/fbthrift,HankFaan/fbthrift,kangkot/fbthrift,raphaelamorim/fbthrift,maxwell-demon/fbthrift,SergeyMakarenko/fbthrift,kangkot/fbthrift,sinjar666/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,HankFaan/fbthrift,getyourguide/fbthrift,chjp2046/fbthrift,facebook/fbthrift,jesboat/fbthrift,soumith/fbthrift,kangkot/fbthrift,kangkot/fbthrift,SergeyMakarenko/fbthrift,raphaelamorim/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,guker/fbthrift,fengshao0907/fbthrift,guker/fbthrift,soumith/fbthrift,jesboat/fbthrift,soumith/fbthrift