From bc4afef0bf0cb34d90fb6c029ab4c5ff1a6d033d Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Mon, 11 Oct 2021 16:15:06 -0400 Subject: [PATCH 1/8] Read-only atomic backend write function For counters in shared memory which can be read by any backend but only written to by one backend, an atomic is still needed to protect against torn values; however, pg_atomic_fetch_add_u64() is overkill for incrementing such counters. pg_atomic_unlocked_inc_counter() is a helper function which can be used to increment these values safely without unnecessary overhead. Author: Thomas Munro Reviewed-by: Melanie Plageman Discussion: https://www.postgresql.org/message-id/CA%2BhUKGJ06d3h5JeOtAv4h52n0vG1jOPZxqMCn5FySJQUVZA32w%40mail.gmail.com Discussion: https://www.postgresql.org/message-id/flat/20200124195226.lth52iydq2n2uilq%40alap3.anarazel.de --- src/include/port/atomics.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h index 9550e04aaa5..3d1fdc64752 100644 --- a/src/include/port/atomics.h +++ b/src/include/port/atomics.h @@ -519,6 +519,17 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_) return pg_atomic_sub_fetch_u64_impl(ptr, sub_); } +/* + * On modern systems this is really just *counter++. On some older systems + * there might be more to it (due to an inability to read and write 64-bit + * values atomically). + */ +static inline void +pg_atomic_unlocked_inc_counter(pg_atomic_uint64 *counter) +{ + pg_atomic_write_u64(counter, pg_atomic_read_u64(counter) + 1); +} + #undef INSIDE_ATOMICS_H #endif /* ATOMICS_H */ -- 2.17.1