v15-0001-Add-pg_atomic_unlocked_add_fetch_XXX.patch

From 85187ee6a1dd4c68ba70cfbce002a8fa66c99925 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Sat, 28 Mar 2020 11:42:59 +1300
Subject: [PATCH v15 1/6] Add pg_atomic_unlocked_add_fetch_XXX().

Add a variant of pg_atomic_add_fetch_XXX with no barrier semantics, for
cases where you only want to avoid the possibility that a concurrent
pg_atomic_read_XXX() sees a torn/partial value.  On modern
architectures, this is simply value++, but there is a fallback to
spinlock emulation.

Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com
---
 src/include/port/atomics.h         | 24 ++++++++++++++++++++++
 src/include/port/atomics/generic.h | 33 ++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
index 4956ec55cb..2abb852893 100644
--- a/src/include/port/atomics.h
+++ b/src/include/port/atomics.h
@@ -389,6 +389,21 @@ pg_atomic_add_fetch_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
 	return pg_atomic_add_fetch_u32_impl(ptr, add_);
 }
 
+/*
+ * pg_atomic_unlocked_add_fetch_u32 - atomically add to variable
+ *
+ * Like pg_atomic_unlocked_write_u32, guarantees only that partial values
+ * cannot be observed.
+ *
+ * No barrier semantics.
+ */
+static inline uint32
+pg_atomic_unlocked_add_fetch_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
+{
+	AssertPointerAlignment(ptr, 4);
+	return pg_atomic_unlocked_add_fetch_u32_impl(ptr, add_);
+}
+
 /*
  * pg_atomic_sub_fetch_u32 - atomically subtract from variable
  *
@@ -519,6 +534,15 @@ pg_atomic_sub_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 sub_)
 	return pg_atomic_sub_fetch_u64_impl(ptr, sub_);
 }
 
+static inline uint64
+pg_atomic_unlocked_add_fetch_u64(volatile pg_atomic_uint64 *ptr, int64 add_)
+{
+#ifndef PG_HAVE_ATOMIC_U64_SIMULATION
+	AssertPointerAlignment(ptr, 8);
+#endif
+	return pg_atomic_unlocked_add_fetch_u64_impl(ptr, add_);
+}
+
 #undef INSIDE_ATOMICS_H
 
 #endif							/* ATOMICS_H */
diff --git a/src/include/port/atomics/generic.h b/src/include/port/atomics/generic.h
index d60a0d9e7f..3e1598d8ff 100644
--- a/src/include/port/atomics/generic.h
+++ b/src/include/port/atomics/generic.h
@@ -234,6 +234,16 @@ pg_atomic_add_fetch_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_)
 }
 #endif
 
+#if !defined(PG_HAVE_ATOMIC_UNLOCKED_ADD_FETCH_U32)
+#define PG_HAVE_ATOMIC_UNLOCKED_ADD_FETCH_U32
+static inline uint32
+pg_atomic_unlocked_add_fetch_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_)
+{
+	ptr->value += add_;
+	return ptr->value;
+}
+#endif
+
 #if !defined(PG_HAVE_ATOMIC_SUB_FETCH_U32) && defined(PG_HAVE_ATOMIC_FETCH_SUB_U32)
 #define PG_HAVE_ATOMIC_SUB_FETCH_U32
 static inline uint32
@@ -399,3 +409,26 @@ pg_atomic_sub_fetch_u64_impl(volatile pg_atomic_uint64 *ptr, int64 sub_)
 	return pg_atomic_fetch_sub_u64_impl(ptr, sub_) - sub_;
 }
 #endif
+
+#if defined(PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY) && \
+	!defined(PG_HAVE_ATOMIC_U64_SIMULATION)
+
+#ifndef PG_HAVE_ATOMIC_UNLOCKED_ADD_FETCH_U64
+#define PG_HAVE_ATOMIC_UNLOCKED_ADD_FETCH_U64
+static inline uint64
+pg_atomic_unlocked_add_fetch_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val)
+{
+	ptr->value += val;
+	return ptr->value;
+}
+#endif
+
+#else
+
+static inline uint64
+pg_atomic_unlocked_add_fetch_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val)
+{
+	return pg_atomic_add_fetch_u64_impl(ptr, val);
+}
+
+#endif
-- 
2.20.1