Problem: Thread Safety

SAGE includes the C/C++ libraries listed below. For each library, determine whether or not (or to what extent) it is thread safe.

"Be careful if your application uses libraries or other objects that don't explicitly guarantee thread-safeness. When in doubt, assume that they are not thread-safe until proven otherwise. Thread-safeness: in a nutshell, refers an application's ability to execute multiple threads simultaneously without "clobbering" shared data or creating "race" conditions. For example, suppose that you use a library routine that accesses/modifies a global structure or location in memory. If two threads both call this routine it is possible that they may try to modify this global structure/memory location at the same time. If the routine does not employ some sort of synchronization constructs to prevent data corruption, then it is not thread-safe. The implication to users of external library routines is that if you aren't 100% certain the routine is thread-safe, then you take your chances with problems that could arise." -- from the pthreads tutorial

GMP: Arbitrary Precision Arithmetic Library

Mostly safe. See this web page.

GSL: Gnu Scientific Library

Yes, see this post.

MPFR: Arbitrary precision real arithmetic

NTL: Number theory C++ library

OpenSSL: Secure networking

PARI: Number theory calculator

"PARI is (more or less) thread-safe when compiled with --enable-tls" according to this post.

Singular: fast commutative and noncommutative algebra

Singular doesn't quite have a library mode yet. But it also includes various libraries.