RE2 is a fast, safe, thread-friendly alternative to backtracking regular
expression engines like those used in PCRE, Perl, and Python.
It is a C++ library.
RE2 uses automata theory  to guarantee that regular expression searches run in
time linear in the size of the input. RE2 implements memory limits, so that
searches can be constrained to a fixed amount of memory. RE2 is engineered to
use a small fixed C++ stack footprint no matter what inputs or regular
expressions it must process; thus RE2 is useful in multithreaded environments
where thread stacks cannot grow arbitrarily large.

WWW: https://github.com/google/re2