psql close

From: Anthony LaTorre <tlatorre(at)uchicago(dot)edu>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: psql close
Date: 2016-05-20 19:50:21
Message-ID: CAO49afJWaXVuz8un-w=o1REz+2t7Rhue4wAkkDKuVp92cj_Lyw@mail.gmail.com
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Hi all,

I've been using the libpq asynchronous functions to hook up database
calls into my event loop, and I've noticed a problem and was hoping
someone might know the solution.

The problem is that I have to unregister the file descriptor from the
event loop whenever the postgres connection fails, but often by the
time I notice it has failed in the code, it has already closed its
socket and so I can't guarantee that if I close the previously opened
socket that it hasn't already been opened up by someone else.

Maybe an example will make it clearer:

void send_to_db(PGConn *conn, char *command)
{
PQsendQuery(conn, command);

if (PQstatus(conn) == CONNECTION_BAD) {
Log(WARNING, "database connection disconnected");

/* By this point PQsocket() returns -1. Even if I keep a
reference to the socket number
* it might have already been opened by another socket call. */
PQfinish(conn);

/* Call function to reconnect, but I should have already
deleted the file event callbacks for the postgres connection socket.
*/
}
}

Please let me know what the solution is, or if something isn't clear.

Thanks,

Tony

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