On Wed, Apr 5, 2017 at 4:13 PM, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote: >>> >>> The comment says that the counters are allowed to overflow, i.e. after a >>> long uptime you might get these values >>> >>> parallel_register_count = UINT_MAX + 1 = 1 >>> parallel_terminate_count = UINT_MAX >>> >>> which is fine, because the C handles the overflow during subtraction and >>> so >>> >>> parallel_register_count - parallel_terminate_count = 1 >>> >>> But the assert is not doing subtraction, it's comparing the values >>> directly: >>> >>> Assert(parallel_register_count >= parallel_terminate_count); >>> >>> and the (perfectly valid) values trivially violate this comparison. >>> >> Thanks for the explanation. So, we can't use the above assert >> statement. Even the following assert statement will not be helpful: >> Assert(parallel_register_count - parallel_terminate_count >= 0); >> Because, it'll fail to track the scenario when parallel_register_count >> is not overflowed, still less than parallel_terminate_count. :( >> > > Actually, that assert would work, because C does handle overflows on uint > values during subtraction just fine. That is, > > (UINT_MAX+x) - UINT_MAX = x > > Also, the comment about overflows before BackgroundWorkerArray claims this > is the case. > Agreed on the overflowed case. But, my concern is when an overflow has not yet happened:
Suppose, uint parallel_register_count = 1; /* Didn't overflow* / uint parallel_terminate_count = 2; /* Didn't overflow */ Assert(parallel_register_count - parallel_terminate_count >= 0); We want the assert statement to fail here, but I think it won't since -1 has a valid representation in unsigned int and it is greater than 0, no? -- Thanks & Regards, Kuntal Ghosh EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
