Marko Mäkelä 040c16ab8b MDEV-25404: Optimize srw_mutex on Linux, OpenBSD, Windows ... On Linux, OpenBSD and Microsoft Windows, srw_mutex was an alias for a rw-lock while we only need mutex functionality. Let us implement a futex-based mutex with one bit for HOLDER and 31 bits for counting waiting requests. srw_lock::wr_unlock() can avoid waking up a waiter when no waiting requests exist. (Previously, we only had 1-bit rw_lock::WRITER_WAITING flag that could be wrongly cleared if multiple waiting wr_lock() exist. Now we have no problem with up to 2,147,483,648 conflicting threads.) On 64-bit Microsoft Windows, the advantage is that sizeof(srw_mutex) is 4, while sizeof(SRWLOCK) would be 8. Reviewed by: Vladislav Vaintroub		2021-04-19 18:03:17 +03:00
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srw_lock.cc	MDEV-25404: Optimize srw_mutex on Linux, OpenBSD, Windows	2021-04-19 18:03:17 +03:00