SHMEMX Features and Constants

SHMEMX_MALLOC_NO_BARRIER

This is a hint for shmem_malloc_with_hints which provides users with a way to bypass the barrier that occurs from within a shmem_malloc. This hint optimizes applications that have successive shmem_malloc calls where a barrier between each call may be unnecessary and expensive. OpenSHMEM still requires a barrier between memory allocation and symmetric data manipulation, so synchronization is required after a sequence of allocations passing the SHMEMX_MALLOC_NO_BARRIER hint. This synchronization could be a regular shmem_malloc, shmem_barrier_all, or shmem_sync_all depending on the use-case.