InnoDB is missing futex support on some platforms

In MDEV-20612, MDEV-24142 and related tasks, the InnoDB synchronization primitives were rewritten. On Linux, Microsoft Windows, and OpenBSD, we make use of futex-like system calls. (On Microsoft Windows, srw_mutex and srw_lock are simple wrappers of SRWLOCK; on other platforms they are implemented with futexes.)

According to https://shift.click/blog/futex-like-apis/ there are a few more platforms that we should be able to support:

• FreeBSD: _umtx_op (UMTX_OP_WAIT_UINT_PRIVATE, UMTX_OP_WAKE_PRIVATE)
• DragonflyBSD: umtx_sleep, umtx_wakeup
• Apple macOS: __ulock_wait, __ulock_wake

When futex support is missing, we will fall back to the SUX_LOCK_GENERIC implementation that is based on native mutexes, condition variables and native rw-locks when available. Not only will this increase the memory footprint, but lock_sys_t::hash_latch::release() could be a scalability bottleneck, because it uses a single mutex and condition variable to ‘emulate’ futex so that we can avoid increasing the memory footprint of lock_sys.rec_hash.

To be determined: Are any futex-like operations available on other operating systems where MariaDB Server might be able to run?

• AIX
• HP-UX
• Solaris or its derivatives, such as Illumos or OpenIndiana