Some thoughts:
The v1-0003 patch introduced smgropen_cond() to avoid the problem of
IssuePendingWritebacks(), which does desynchronised smgropen() calls
and could open files after the barrier but just before they are
unlinked. Makes sense, but...
1. For that to actually work, we'd better call smgrcloseall() when
PROCSIGNAL_BARRIER_SMGRRELEASE is handled; currently it only calls
closeAllVds(). Here's a patch for that. But...
2. The reason I used closeAllVds() in 4eb21763 is because I didn't
want random CHECK_FOR_INTERRUPTS() calls to break code like this, from
RelationCopyStorage():
for (blkno = 0; blkno < nblocks; blkno++)
{
/* If we got a cancel signal during the copy of the data, quit */
CHECK_FOR_INTERRUPTS();
smgrread(src, forkNum, blkno, buf.data);
Perhaps we could change RelationCopyStorage() to take Relation, and
use CreateFakeRelCacheEntry() in various places to satisfy that, and
also extend that mechanism to work with temporary tables. Here's an
initial sketch of that idea, to see what problems it crashes into...
Fake Relations are rather unpleasant though; I wonder if there is an
SMgrRelationHandle concept that could make this all nicer. There is
possibly also some cleanup missing to avoid an SMgrRelation that
points to a defunct fake Relation on non-local exit (?).
