From 41242606a03aace906e307a38fc67c5cefcaec20 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Mon, 11 Oct 2021 16:15:06 -0400 Subject: [PATCH v14 2/4] 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 the counter. inc_counter() is a helper function which can be used to increment these values safely but without unnecessary overhead. Author: Thomas Munro --- src/include/port/atomics.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h index 856338f161..09a2575d6a 100644 --- a/src/include/port/atomics.h +++ b/src/include/port/atomics.h @@ -519,6 +519,16 @@ 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 inability to read and write 64 bit values + * atomically. + */ +static inline void inc_counter(pg_atomic_uint64 *counter) +{ + pg_atomic_write_u64(counter, pg_atomic_read_u64(counter) + 1); +} + #undef INSIDE_ATOMICS_H #endif /* ATOMICS_H */ -- 2.30.2