/*
* Async_Notify
*
* This is executed by the SQL notify command.
*
* Adds the relation to the list of pending notifies.
* Actual notification happens during transaction commit.
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
*/
void
Async_Notify(const char *relname)
{
if (Trace_notify)
elog(DEBUG1, "Async_Notify(%s)", relname);
/* no point in making duplicate entries in the list ... */
if (!AsyncExistsPendingNotify(relname))
{
/*
* The name list needs to live until end of transaction, so store it
* in the transaction context.
*/
MemoryContext oldcontext;
oldcontext = MemoryContextSwitchTo(CurTransactionContext);
/*
* Ordering of the list isn't important. We choose to put new entries
* on the front, as this might make duplicate-elimination a tad faster
* when the same condition is signaled many times in a row.
*/
pendingNotifies = lcons(pstrdup(relname), pendingNotifies);
MemoryContextSwitchTo(oldcontext);
}
}
/*
*--------------------------------------------------------------
* Async_Notify
*
* This is executed by the SQL notify command.
*
* Adds the relation to the list of pending notifies.
* Actual notification happens during transaction commit.
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
*
*--------------------------------------------------------------
*/
void
Async_Notify(const char *relname)
{
if (Trace_notify)
elog(DEBUG1, "Async_Notify(%s)", relname);
/* no point in making duplicate entries in the list ... */
if (!AsyncExistsPendingNotify(relname))
{
/*
* The name list needs to live until end of transaction, so store it
* in the transaction context.
*/
MemoryContext oldcontext;
oldcontext = MemoryContextSwitchTo(CurTransactionContext);
pendingNotifies = lcons(pstrdup(relname), pendingNotifies);
MemoryContextSwitchTo(oldcontext);
}
}
/*
*--------------------------------------------------------------
* AtCommit_Notify
*
* This is called at transaction commit.
*
* If there are outbound notify requests in the pendingNotifies list,
* scan pg_listener for matching tuples, and either signal the other
* backend or send a message to our own frontend.
*
* NOTE: we are still inside the current transaction, therefore can
* piggyback on its committing of changes.
*
* Results:
* XXX
*
* Side effects:
* Tuples in pg_listener that have matching relnames and other peoples'
* listenerPIDs are updated with a nonzero notification field.
*
*--------------------------------------------------------------
*/
void
AtCommit_Notify(void)
{
Relation lRel;
TupleDesc tdesc;
HeapScanDesc scan;
HeapTuple lTuple,
rTuple;
Datum value[Natts_pg_listener];
char repl[Natts_pg_listener],
nulls[Natts_pg_listener];
if (pendingNotifies == NIL)
return; /* no NOTIFY statements in this transaction */
/*
* NOTIFY is disabled if not normal processing mode. This test used to be
* in xact.c, but it seems cleaner to do it here.
*/
if (!IsNormalProcessingMode())
{
ClearPendingNotifies();
return;
}
if (Trace_notify)
elog(DEBUG1, "AtCommit_Notify");
/* preset data to update notify column to MyProcPid */
nulls[0] = nulls[1] = nulls[2] = ' ';
repl[0] = repl[1] = repl[2] = ' ';
repl[Anum_pg_listener_notify - 1] = 'r';
value[0] = value[1] = value[2] = (Datum) 0;
value[Anum_pg_listener_notify - 1] = Int32GetDatum(MyProcPid);
lRel = heap_open(ListenerRelationId, ExclusiveLock);
tdesc = RelationGetDescr(lRel);
scan = heap_beginscan(lRel, SnapshotNow, 0, NULL);
while ((lTuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
{
Form_pg_listener listener = (Form_pg_listener) GETSTRUCT(lTuple);
char *relname = NameStr(listener->relname);
int32 listenerPID = listener->listenerpid;
if (!AsyncExistsPendingNotify(relname))
continue;
if (listenerPID == MyProcPid)
{
/*
* Self-notify: no need to bother with table update. Indeed, we
* *must not* clear the notification field in this path, or we
* could lose an outside notify, which'd be bad for applications
* that ignore self-notify messages.
*/
if (Trace_notify)
elog(DEBUG1, "AtCommit_Notify: notifying self");
NotifyMyFrontEnd(relname, listenerPID);
}
else
{
if (Trace_notify)
elog(DEBUG1, "AtCommit_Notify: notifying pid %d",
listenerPID);
/*
* If someone has already notified this listener, we don't bother
* modifying the table, but we do still send a SIGUSR2 signal,
* just in case that backend missed the earlier signal for some
* reason. It's OK to send the signal first, because the other
* guy can't read pg_listener until we unlock it.
*/
if (kill(listenerPID, SIGUSR2) < 0)
{
/*
* Get rid of pg_listener entry if it refers to a PID that no
* longer exists. Presumably, that backend crashed without
* deleting its pg_listener entries. This code used to only
* delete the entry if errno==ESRCH, but as far as I can see
* we should just do it for any failure (certainly at least
* for EPERM too...)
*/
simple_heap_delete(lRel, &lTuple->t_self);
}
else if (listener->notification == 0)
{
HTSU_Result result;
ItemPointerData update_ctid;
TransactionId update_xmax;
rTuple = heap_modifytuple(lTuple, tdesc,
value, nulls, repl);
/*
* We cannot use simple_heap_update here because the tuple
* could have been modified by an uncommitted transaction;
* specifically, since UNLISTEN releases exclusive lock on the
* table before commit, the other guy could already have tried
* to unlisten. There are no other cases where we should be
* able to see an uncommitted update or delete. Therefore, our
* response to a HeapTupleBeingUpdated result is just to
* ignore it. We do *not* wait for the other guy to commit
* --- that would risk deadlock, and we don't want to block
* while holding the table lock anyway for performance
* reasons. We also ignore HeapTupleUpdated, which could occur
* if the other guy commits between our heap_getnext and
* heap_update calls.
*/
result = heap_update(lRel, &lTuple->t_self, rTuple,
&update_ctid, &update_xmax,
GetCurrentCommandId(), InvalidSnapshot,
false /* no wait for commit */ );
switch (result)
{
case HeapTupleSelfUpdated:
/* Tuple was already updated in current command? */
elog(ERROR, "tuple already updated by self");
break;
case HeapTupleMayBeUpdated:
/* done successfully */
#ifdef NOT_USED /* currently there are no indexes */
CatalogUpdateIndexes(lRel, rTuple);
#endif
break;
case HeapTupleBeingUpdated:
/* ignore uncommitted tuples */
break;
case HeapTupleUpdated:
/* ignore just-committed tuples */
break;
default:
elog(ERROR, "unrecognized heap_update status: %u",
result);
break;
}
}
}
}
heap_endscan(scan);
/*
* We do NOT release the lock on pg_listener here; we need to hold it
* until end of transaction (which is about to happen, anyway) to ensure
* that notified backends see our tuple updates when they look. Else they
* might disregard the signal, which would make the application programmer
* very unhappy.
*/
heap_close(lRel, NoLock);
ClearPendingNotifies();
if (Trace_notify)
elog(DEBUG1, "AtCommit_Notify: done");
}
