fixed bugs with thread functions not being re-entrant

fixed bugs with thread functions not being re-entrant

This change fixes potential problems with thread functions being
called several times in parallel (which may happen if the network
operations performed by these functions really take long). In these
cases, the thread's data structure (see previous commit) will not be
used exclusively anymore.

To fix this, the thread's data structure will be allocated separately
for each invocation of the corresponding thread function.