localbuf: Introduce StartLocalBufferIO()

To initiate IO on a shared buffer we have StartBufferIO(). For temporary table
buffers no similar function exists - likely because the code for that
currently is very simple due to the lack of concurrency.

However, the upcoming AIO support will make it possible to re-encounter a
local buffer, while the buffer already is the target of IO. In that case we
need to wait for already in-progress IO to complete. This commit makes it
easier to add the necessary code, by introducing StartLocalBufferIO().

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/CAAKRu_b9anbWzEs5AAF9WCvcEVmgz-1AkHSQ-CLLy-p7WHzvFw@mail.gmail.com

1 files changed, 2 insertions, 6 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index f3c27d7e77a..79ca9d18d07 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1038,7 +1038,7 @@ ZeroAndLockBuffer(Buffer buffer, ReadBufferMode mode, bool already_valid)
 	{
 		/* Simple case for non-shared buffers. */
 		bufHdr = GetLocalBufferDescriptor(-buffer - 1);
-		need_to_zero = (pg_atomic_read_u32(&bufHdr->state) & BM_VALID) == 0;
+		need_to_zero = StartLocalBufferIO(bufHdr, true);
 	}
 	else
 	{
@@ -1388,11 +1388,7 @@ static inline bool
 WaitReadBuffersCanStartIO(Buffer buffer, bool nowait)
 {
 	if (BufferIsLocal(buffer))
-	{
-		BufferDesc *bufHdr = GetLocalBufferDescriptor(-buffer - 1);
-
-		return (pg_atomic_read_u32(&bufHdr->state) & BM_VALID) == 0;
-	}
+		return StartLocalBufferIO(GetLocalBufferDescriptor(-buffer - 1), true);
 	else
 		return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait);
 }