Fix miserable coding in pg_stat_get_activity().

Commit dd1a3bccc replaced a test on whether a subroutine returned a
null pointer with a test on whether &pointer->backendStatus was null.
This accidentally failed to fail, at least on common compilers, because
backendStatus is the first field in the struct; but it was surely trouble
waiting to happen.  Commit f91feba87 then messed things up further,
changing the logic to

	local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
	if (!local_beentry)
		continue;
	beentry = &local_beentry->backendStatus;
	if (!beentry)
	{

where the second "if" is now dead code, so that the intended behavior of
printing a row with "" cannot occur.

I suspect this is all moot because pgstat_fetch_stat_local_beentry
will never actually return null in this function's usage, but it's still
very poor coding.  Repair back to 9.4 where the original problem was
introduced.

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 44ccd37e99895b0295927ede0a85bd8e8d7a5a0f..688eea12a93e431e03ae45a1644c37449baed7d5 100644 (file)
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -633,15 +633,13 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
        {
            /* Get specific pid slot */
            local_beentry = pgstat_fetch_stat_local_beentry(*(int *) (funcctx->user_fctx));
-           beentry = &local_beentry->backendStatus;
        }
        else
        {
            /* Get the next one in the list */
            local_beentry = pgstat_fetch_stat_local_beentry(funcctx->call_cntr + 1);    /* 1-based index */
-           beentry = &local_beentry->backendStatus;
        }
-       if (!beentry)
+       if (!local_beentry)
        {
            int         i;
 
@@ -655,6 +653,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
            SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
        }
 
+       beentry = &local_beentry->backendStatus;
+
        /* Values available to all callers */
        values[0] = ObjectIdGetDatum(beentry->st_databaseid);
        values[1] = Int32GetDatum(beentry->st_procpid);