Assuming you compile with CC -Kthread, the generated code from the compiler is thread safe. This includes static local variables with dynamic initialization expressions, which require special guards in this case.

Assuming you also link with CC -Kthread, the language support runtime routines are thread safe. This means that things like exception handling, new/delete, and static init/ctor/dtor processing all work correctly in the presence of threads.

The C++ Standard Library is also safe for multithreaded applications. This means that: all internal data structures in the library are protected against simultaneous access; simultaneous access to distinct containers is safe; and simultaneous read-only access to a shared container is safe. Simultaneous access to a shared container with at least one thread writing, however, must be protected by the application through the use of mutual exclusion primitives.