libdpf/thirdparty/portable-snippets/once

Once

This is a simple abstraction for a once which will choose from a few different back-ends:

• If C11 threads are available, use call_once().
• On Windows, use InitOnceExecuteOnce()
• If PTHREAD_ONCE_INIT is defined (i.e., if <pthread.h> has been included prior to including once.h), use pthread_once().
• Use [atomic.h](../atomic).