Replace memcpy() calls in xlog.c critical sections with struct assignments.

This gets rid of a dangerous-looking use of the not-volatile XLogCtl
pointer in a couple of spinlock-protected sections, where the normal
coding rule is that you should only access shared memory through a
pointer-to-volatile.  I think the risk is only hypothetical not actual,
since for there to be a bug the compiler would have to move the spinlock
acquire or release across the memcpy() call, which one sincerely hopes
it will not.  Still, it looks cleaner this way.

Per comment from Daniel Farina and subsequent discussion.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index a7762eafcd0af2a6069a52d763e8fdbe6f65dafe..70b2e1cbeb8272b836f5b451f3c00568f4d8de16 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8158,8 +8158,8 @@ RecoveryRestartPoint(const CheckPoint *checkPoint)
         * work out the next time it wants to perform a restartpoint.
         */
        SpinLockAcquire(&xlogctl->info_lck);
-       XLogCtl->lastCheckPointRecPtr = ReadRecPtr;
-       memcpy(&XLogCtl->lastCheckPoint, checkPoint, sizeof(CheckPoint));
+       xlogctl->lastCheckPointRecPtr = ReadRecPtr;
+       xlogctl->lastCheckPoint = *checkPoint;
        SpinLockRelease(&xlogctl->info_lck);
 }
 
@@ -8194,7 +8194,7 @@ CreateRestartPoint(int flags)
        /* Get a local copy of the last safe checkpoint record. */
        SpinLockAcquire(&xlogctl->info_lck);
        lastCheckPointRecPtr = xlogctl->lastCheckPointRecPtr;
-       memcpy(&lastCheckPoint, &XLogCtl->lastCheckPoint, sizeof(CheckPoint));
+       lastCheckPoint = xlogctl->lastCheckPoint;
        SpinLockRelease(&xlogctl->info_lck);
 
        /*