3.8 Reentrancy

MPIR is reentrant and thread-safe, with some exceptions:

• If configured with --enable-alloca=malloc-notreentrant (or with --enable-alloca=notreentrant when alloca is not available), then naturally MPIR is not reentrant.
• mpf_set_default_prec and mpf_init use a global variable for the selected precision. mpf_init2 can be used instead, and in the C++ interface an explicit precision to the mpf_class constructor.
• mp_set_memory_functions uses global variables to store the selected memory allocation functions.
• If the memory allocation functions set by a call to mp_set_memory_functions (or malloc and friends by default) are not reentrant, then MPIR will not be reentrant either.
• If the standard I/O functions such as fwrite are not reentrant then the MPIR I/O functions using them will not be reentrant either.
• It’s safe for two threads to read from the same MPIR variable simultaneously, but it’s not safe for one to read while the another might be writing, nor for two threads to write simultaneously. It’s not safe for two threads to generate a random number from the same gmp_randstate_t simultaneously, since this involves an update of that variable.