From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Victor Spirin <v.spirin@postgrespro.ru>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Sometimes the output to the stdout in Windows disappears
Date: Fri, 16 Oct 2020 12:18:32 -0400
Message-ID: <4156857.1602865112@sss.pgh.pa.us> (raw)
In-Reply-To: <ee02eaa2-03f7-74ea-bbdf-3196e506bae3@gmail.com>
References: <ac976d8c-03df-d6b8-025c-15a2de8d9af1@postgrespro.ru>
<4124040.1598898684@sss.pgh.pa.us>
<b92a7e09-9a60-d76b-e226-7e191fdc6f34@postgrespro.ru>
<855416.1600022228@sss.pgh.pa.us>
<ee02eaa2-03f7-74ea-bbdf-3196e506bae3@gmail.com>
Alexander Lakhin <exclusion@gmail.com> writes:
> I've managed to make a simple reproducer. Please look at the patch attached.
> There are two things crucial for reproducing the bug:
> ioctlsocket(sock, FIONBIO, &ioctlsocket_ret); // from pgwin32_socket()
> and
> WSACleanup();
Oh, very interesting.
Now that you have it somewhat in captivity, maybe you could determine
some things:
1. Is it only stdout that's affected? What of other stdio streams?
(Note that testing stderr might be tricky because it's probably
line-buffered.)
2. Does an fflush() just before, or just after, WSACleanup() fix it?
> I see no solution for this on the postgres side for now, but this
> information about Windows quirks could be useful in case someone
> stumbled upon it too.
Depending on your answers to the above, maybe some hack like this
would be acceptable:
free(conn);
#ifdef WIN32
+ fflush(NULL);
WSACleanup();
#endif
}
It's not very nice for a library to be doing global things like that,
but if the alternative is loss of output, maybe we should.
But wait a minute: I just looked at Microsoft's docs [1] and found
In a multithreaded environment, WSACleanup terminates Windows Sockets
operations for all threads.
This makes me (a) wonder if that explains the side-effects on stdio,
and (b) question why libpq is calling WSACleanup at all.
What if we arranged to call WSAStartup just once, during the first
libpq connection-open in a process, and then never did WSACleanup?
Surely the OS can cope with that, and it eliminates any risk that
WSACleanup breaks something.
regards, tom lane
[1] https://docs.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsacleanup
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, exclusion@gmail.com, v.spirin@postgrespro.ru, pgsql-hackers@lists.postgresql.org
Subject: Re: Sometimes the output to the stdout in Windows disappears
In-Reply-To: <4156857.1602865112@sss.pgh.pa.us>
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