using of fork() in multithreaded application

Hello,
On my NetBSD 10.1 I am trying to run multithreaded application where 
first are created several threads and then is called fork() from main 
thread.
Forked child then calls execvp() .
Passed command line (in argv argument) is "gcc", "-dumpversion".

Application freezes because it waits for finishing child and ps -auxd 
shows child process "(gcc)"
with flag zombie.

I have two questions:
Is safe using of fork() in NetBSD 10.1 in mutlithreaded application ?
Does NetBSD 10.1 support "set follow-fork-mode child" when used 
/usr/bin/gdb ? I can step through source code of forked child only 
on-two lines not more.

Peter