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-rw-r--r--src/include/port/atomics.h25
-rw-r--r--src/include/port/atomics/fallback.h3
-rw-r--r--src/include/port/atomics/generic.h9
-rw-r--r--src/include/storage/buf_internals.h3
4 files changed, 37 insertions, 3 deletions
diff --git a/src/include/port/atomics.h b/src/include/port/atomics.h
index f7884d72c6e..4e15ff8764d 100644
--- a/src/include/port/atomics.h
+++ b/src/include/port/atomics.h
@@ -255,10 +255,12 @@ pg_atomic_read_u32(volatile pg_atomic_uint32 *ptr)
}
/*
- * pg_atomic_write_u32 - unlocked write to atomic variable.
+ * pg_atomic_write_u32 - write to atomic variable.
*
* The write is guaranteed to succeed as a whole, i.e. it's not possible to
- * observe a partial write for any reader.
+ * observe a partial write for any reader. Note that this correctly interacts
+ * with pg_atomic_compare_exchange_u32, in contrast to
+ * pg_atomic_unlocked_write_u32().
*
* No barrier semantics.
*/
@@ -271,6 +273,25 @@ pg_atomic_write_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
}
/*
+ * pg_atomic_unlocked_write_u32 - unlocked write to atomic variable.
+ *
+ * The write is guaranteed to succeed as a whole, i.e. it's not possible to
+ * observe a partial write for any reader. But note that writing this way is
+ * not guaranteed to correctly interact with read-modify-write operations like
+ * pg_atomic_compare_exchange_u32. This should only be used in cases where
+ * minor performance regressions due to atomics emulation are unacceptable.
+ *
+ * No barrier semantics.
+ */
+static inline void
+pg_atomic_unlocked_write_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
+{
+ AssertPointerAlignment(ptr, 4);
+
+ pg_atomic_unlocked_write_u32_impl(ptr, val);
+}
+
+/*
* pg_atomic_exchange_u32 - exchange newval with current value
*
* Returns the old value of 'ptr' before the swap.
diff --git a/src/include/port/atomics/fallback.h b/src/include/port/atomics/fallback.h
index bdaa795abe0..2290fff196f 100644
--- a/src/include/port/atomics/fallback.h
+++ b/src/include/port/atomics/fallback.h
@@ -133,6 +133,9 @@ pg_atomic_unlocked_test_flag_impl(volatile pg_atomic_flag *ptr)
#define PG_HAVE_ATOMIC_INIT_U32
extern void pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_);
+#define PG_HAVE_ATOMIC_WRITE_U32
+extern void pg_atomic_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val);
+
#define PG_HAVE_ATOMIC_COMPARE_EXCHANGE_U32
extern bool pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
uint32 *expected, uint32 newval);
diff --git a/src/include/port/atomics/generic.h b/src/include/port/atomics/generic.h
index 32a01136e61..1acd19242b2 100644
--- a/src/include/port/atomics/generic.h
+++ b/src/include/port/atomics/generic.h
@@ -58,6 +58,15 @@ pg_atomic_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val)
}
#endif
+#ifndef PG_HAVE_ATOMIC_UNLOCKED_WRITE_U32
+#define PG_HAVE_ATOMIC_UNLOCKED_WRITE_U32
+static inline void
+pg_atomic_unlocked_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val)
+{
+ ptr->value = val;
+}
+#endif
+
/*
* provide fallback for test_and_set using atomic_exchange if available
*/
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index e0dfb2f5b03..c7da9f6ac2f 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -168,7 +168,8 @@ typedef struct buftag
* We use this same struct for local buffer headers, but the locks are not
* used and not all of the flag bits are useful either. To avoid unnecessary
* overhead, manipulations of the state field should be done without actual
- * atomic operations (i.e. only pg_atomic_read/write).
+ * atomic operations (i.e. only pg_atomic_read_u32() and
+ * pg_atomic_unlocked_write_u32()).
*
* Be careful to avoid increasing the size of the struct when adding or
* reordering members. Keeping it below 64 bytes (the most common CPU