We don't really take good advantage of the parallelism anyway (though
it is very useful if you want to make 10000 messages, we don't do that
often). If we decide we need that functionality, we can figure out
what the right way is to do threads with this stuff.
(imported from commit 98aa4b54fab6fd437b7c7ac0c3c7e658d2f8cb33)
Tim Abbott
Kevin Mehall
Leo Franchi