From ca05447f41270d6b3ac3b6fcf816f86aba86d08f Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Fri, 29 Jan 2021 22:34:23 -0300
Subject: [PATCH 1/2] add pg_atomic_monotonic_advance_u64

---
 src/include/port/atomics.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
index 856338f161..a1c4764d18 100644
--- a/src/include/port/atomics.h
+++ b/src/include/port/atomics.h
@@ -519,6 +519,27 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
 	return pg_atomic_sub_fetch_u64_impl(ptr, sub_);
 }
 
+/*
+ * Monotonically advance the given variable using only atomic operations until
+ * it's at least the target value.
+ */
+static inline void
+pg_atomic_monotonic_advance_u64(volatile pg_atomic_uint64 *ptr, uint64 target_)
+{
+	uint64		currval;
+
+#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
+	AssertPointerAlignment(ptr, 8);
+#endif
+
+	currval = pg_atomic_read_u64(ptr);
+	while (currval < target_)
+	{
+		if (pg_atomic_compare_exchange_u64(ptr, &currval, target_))
+			break;
+	}
+}
+
 #undef INSIDE_ATOMICS_H
 
 #endif							/* ATOMICS_H */
-- 
2.20.1